Publications by authors named "P Mark Lokman"

53 Publications

An in vitro ovarian explant culture system to examine sex change in a hermaphroditic fish.

PeerJ 2020 11;8:e10323. Epub 2020 Nov 11.

Department of Zoology, University of Otago, Dunedin, New Zealand.

Many teleost fishes undergo natural sex change, and elucidating the physiological and molecular controls of this process offers unique opportunities not only to develop methods of controlling sex in aquaculture settings, but to better understand vertebrate sexual development more broadly. Induction of sex change in some sequentially hermaphroditic or gonochoristic fish can be achieved in vivo through social manipulation, inhibition of aromatase activity, or steroid treatment. However, the induction of sex change in vitro has been largely unexplored. In this study, we established an in vitro culture system for ovarian explants in serum-free medium for a model sequential hermaphrodite, the New Zealand spotty wrasse (). This culture technique enabled evaluating the effect of various treatments with 17-estradiol (E), 11-ketotestosterone (11KT) or cortisol (CORT) on spotty wrasse ovarian architecture for 21 days. A quantitative approach to measuring the degree of ovarian atresia within histological images was also developed, using pixel-based machine learning software. Ovarian atresia likely due to culture was observed across all treatments including no-hormone controls, but was minimised with treatment of at least 10 ng/mL E. Neither 11KT nor CORT administration induced proliferation of spermatogonia (i.e., sex change) in the cultured ovaries indicating culture beyond 21 days may be needed to induce sex change in vitro. The in vitro gonadal culture and analysis systems established here enable future studies investigating the paracrine role of sex steroids, glucocorticoids and a variety of other factors during gonadal sex change in fish.
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http://dx.doi.org/10.7717/peerj.10323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7666549PMC
November 2020

Evaluating the impact of hydropower on downstream migrating anguillid eels: Catchment-wide and fine-scale approaches to identify cost-effective solutions.

Sci Total Environ 2020 Dec 25;748:141111. Epub 2020 Jul 25.

Hull International Fisheries Institute, University of Hull, East Riding of Yorkshire HU6 7RX, United Kingdom. Electronic address:

Hydropower is an increasingly popular source of renewable and 'green' (in terms of emissions) energy, but reduced longitudinal connectivity and diverting flow through turbines can have negative impacts on catadromous anguillid eel species that have declined globally. There is an urgent need for environmental managers to perform remediation actions, such as protecting flows for migratory fish and providing passage solutions at infrastructure, under increasing legislative pressure. To deliver this, a more comprehensive understanding of eel migration in catchments with hydropower is required. Here, we illustrate the importance of catchment-wide and fine-scale acoustic telemetry, coupled with the influence of eel maturation (i.e. sex steroid levels), to determine the impact of Wairua run-of-river Power Station (WPS) on downstream migrating shortfin eels (Anguilla australis; n = 25) in Wairua River, New Zealand. Migration speed through the unregulated reach upstream of WPS was positively correlated with flow, but not eel length or sex steroids. Three eels passed a diversion weir (DW) to follow the natural watercourse and eight entered the WPS canal. Eels predominantly entered (95.2%) and were last detected (85.7%) in WPS forebay during hours of darkness. Eleven (52%) of the 21 eels that entered WPS forebay were impinged or entrained, all when three or four turbines were in operation (power generation >3.04 MW). Ten (48%) passed WPS spillway during significantly higher spill than impinged or entrained eels, with four passing during no turbine operation, after experiencing high flows near the intake (multiple receivers in WPS forebay used to quantify fine-scale behaviour). On average, eels were impinged or entrained at WPS significantly quicker (6.40 ± 11.13 days) than eels that entered the spillway (25.17 ± 15.12 days), but eel length and sex steroids did not significantly influence fate. Of the eels that migrated through the entire 55 km study reach, passage time at DW and WPS equated to 0.01-0.02% and 47.62-92.17% of their migration, respectively. Mitigation for WPS (and similar power schemes) should focus on operational or physical changes at DW to minimise eels entering power station forebay(s). Turbine shutdowns, ensuring WPS spillway is available and the provision of a bypass channel in WPS forebay are also discussed as ways to conserve the species with the potential to save costs for water resource managers.
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http://dx.doi.org/10.1016/j.scitotenv.2020.141111DOI Listing
December 2020

Spatiotemporal expression of activin receptor-like kinase-5 and bone morphogenetic protein receptor type II in the ovary of shortfinned eel, Anguilla australis.

Comp Biochem Physiol B Biochem Mol Biol 2021 Jan 28;251:110509. Epub 2020 Sep 28.

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.

In the eel ovary, the expression of growth differentiation factor-9 (Gdf9) appears to be largely confined to the germ cell in early stages of oogenesis. However, both the target tissue and the function of Gdf9 in fish remain unknown. This study aimed to describe the abundance and localization of activin receptor-like kinase-5 (Alk5) and bone morphogenetic protein receptor type II (Bmpr2), which together mediate the Gdf9 signal, in the ovary of a basal teleost, the shortfinned eel, Anguilla australis, during early folliculogenesis. The cDNA encoding eel alk5 and bmpr2 genes were cloned, characterized and the transcript abundances of these receptors quantified by quantitative real-time PCR. Ovarian transcript abundance for both receptors, along with that of gdf9 and of its paralogue bmp15, increased from the previtellogenic to early vitellogenic stage. Localization of receptor mRNAs by in situ hybridization revealed that these receptors are located in the somatic cells surrounding the oocyte. Furthermore, tissue distribution analysis showed that the expression of alk5 and bmpr2 were highest in ovary and thyroid, respectively. Unexpectedly, however, bmpr2 mRNA levels were lower in the ovary than in any of the other 17 tissues examined, and indeed, lower than ovarian gdf9 transcript abundance. These findings, together with the ovarian expression pattern of Gdf9, suggest that Gdf9, and conceivably, Bmp15, from the oocyte can signal through receptors that are located on the somatic cells surrounding the oocyte; this, in turn, facilitates elucidation of the function of these growth factors during oogenesis in teleost fish.
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http://dx.doi.org/10.1016/j.cbpb.2020.110509DOI Listing
January 2021

Changes in lipid biology during ovarian development in farmed beluga sturgeon, L.

Am J Physiol Regul Integr Comp Physiol 2020 09 5;319(3):R376-R386. Epub 2020 Aug 5.

Department of Zoology, University of Otago, Dunedin, New Zealand.

The present study was conducted to understand key biochemical, physiological, and molecular changes associated with ovarian growth and with lipid transfer and/or accumulation into the ovary during oogenesis in captive beluga sturgeon. Plasma levels of triacylglycerides, cholesterol, phospholipid, and sex steroid hormones were determined and all were found to increase notably throughout development from the perinucleolar to the tertiary yolk stage. Using fast protein liquid chromatography, we recognized three major lipoprotein peaks in chromatograms from all samples. These peaks were characterized as containing very low-density lipoprotein (Vldl), low-density lipoprotein/high-density lipoprotein (Ldl/Hdl), and plasma proteins. While Ldl/Hdl represented the most abundant lipoprotein fraction, the relative abundance of different lipoprotein classes did not change with the stage of oogenesis. Eluted lipoproteins were separated using sodium dodecyl-sulfate polyacrylamide gel electrophoresis and sequenced. The peptide sequence spectra for 66-kDa, 205-kDa, 29-kDa, and 70-kDa bands matched with albumin, vitellogenin (Vtg) AB2b, immunoglobulin light-chain precursor, and immunoglobulin heavy-chain, respectively. The large amount of albumin in the plasma protein peak and the confined presence of Vtg AB2b to within Ldl/Hdl reinforce the lipoprotein classification. Lastly, transcript levels of genes encoding ovarian lipoprotein lipase (), apolipoprotein E (), very low-density lipoprotein receptors (), and low-density lipoprotein receptor-related protein 8-like () were estimated using quantitative RT-PCR. The high mRNA levels of , , and lipoprotein receptors and in previtellogenic females suggest that sturgeon oocytes need to be prepared to accept and traffic Vtg and lipids internally, before the start of vitellogenesis.
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http://dx.doi.org/10.1152/ajpregu.00364.2019DOI Listing
September 2020

The effects of 11-ketotestosterone implants on transcript levels of gonadotropin receptors, and foxl2 and dmrt1 genes in the Previtellogenic ovary of cultured beluga (Huso huso).

J Fish Biol 2020 Aug 11;97(2):374-382. Epub 2020 Jun 11.

Fisheries Department, Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran.

The in vivo effect of 11-ketotestosterone (11KT) on transcript levels of the gonadotropin receptors (fshr and lhr) and sex differentiation-related genes (dmrt1 and foxl2) was examined in the ovaries of immature female beluga. For this purpose, six fish were treated with implants containing 2.5 mg 11KT and a placebo group of six females of the same age and gametogenic stage were given a blank implant. The implants were intraperitoneally inserted into 4-year-old females at the previtellogenic stage (mean body weight 5580 ± 165 g) and maintained under culture conditions for 8 weeks. Ovary samples for gene expression analysis of lhr, fshr, dmrt1 and foxl2 were collected by biopsy at 3 and 8 weeks post implantation. Diameters of oocytes increased in response to 11KT treatment, both at 3 and at 8 weeks post implantation, but no obvious changes were evident in cytology. Three weeks of 11KT treatment did not affect target gene expression, but a tendency for a time-dependent decrease of lhr and dmrt1 mRNA levels was observed in both treatment and placebo groups. By 8 weeks of treatment, however, 11KT implants provoked the upregulation of fshr and foxl2 transcript levels. Furthermore, lhr and dmrt1 transcript abundances recovered by 8 weeks of exposure in both blank- and 11KT-implanted beluga. These results suggest that 11KT, either directly or indirectly, may affect gametogenesis and regulate some key components of the reproductive axis in female beluga.
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http://dx.doi.org/10.1111/jfb.14366DOI Listing
August 2020

Effects of estradiol and 11-ketotestosterone pre-treatment on artificial induction of maturation in silver female shortfinned eels (Anguilla australis).

PLoS One 2020 24;15(2):e0229391. Epub 2020 Feb 24.

Department of Zoology, University of Otago, Dunedin, New Zealand.

Our previous work documented significant advancements in steroid-induced progression of oogenesis, demonstrating that co-treatment of female eels with 11-ketotestosterone (11KT) and estradiol-17β (E2) successfully induced uptake of vitellogenin by oocytes. Here we evaluate the effects of this steroid co-treatment on subsequent time to ovulation and egg quality in shortfinned eels artificially matured by hypophysation. Co-treatment with 11KT (1 mg) and E2 (0.2 or 2 mg) significantly reduced time to ovulation and therefore, the amount of pituitary homogenate required, without any detrimental effects on gonadosomatic index, oocyte diameter or the total weight of stripped eggs. E2 treatment resulted in promising increases in fertilization rates. These indicators suggest that co-treatment with 11KT and E2 holds promise for future artificial maturation practices in terms of minimising fish handling and stress, and of reducing the need for expensive pituitary preparations.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0229391PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7039463PMC
May 2020

First Observation of a Spontaneously Matured Female European Eel (Anguilla anguilla).

Sci Rep 2020 02 11;10(1):2339. Epub 2020 Feb 11.

Kotka Maretarium OY, Sapokankatu 2, 48100, Kotka, Finland.

This study reports on the first observation of a spontaneously matured female European eel. The 43-year-old eel, together with eleven other females, resided at an aquarium house since their capture in 2002 and stocking as glass eels in 1978. In June 2019, the girth of the belly of the female increased as a sign of oocyte maturation. The specimen had an estimated gonadosomatic index (GSI) of 47, only half of the oocytes were hydrated and matured, indicating that European eels are polycyclic batch spawners. The live eels of the cohort were still in the previtellogenic phase but their eye sizes were close to that of the matured eel. We hypothesize that substances released by other maturing and spawning fishes may have triggered puberty of the eel. This first observation, and the possibility of more eels maturing in the near future, provides a natural reference for the sexual maturation of the European eel.
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http://dx.doi.org/10.1038/s41598-020-59331-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7012921PMC
February 2020

Maternal transcripts in good and poor quality eggs from Japanese eel, Anguilla japonica-their identification by large-scale quantitative analysis.

Mol Reprod Dev 2019 12 23;86(12):1846-1864. Epub 2019 Sep 23.

Division of Marine Life Science, Hokkaido University, Hokkaido, Japan.

Our understanding of maternal control of development in vertebrates remains incomplete. In this study, we investigated levels of maternal transcripts in good and poor quality eggs from artificially matured Japanese eel, using RNA-Seq and quantitative polymerase chain reaction (qPCR), to identify candidate maternal transcripts related to development. De novo assembly or mapping of reads to the eel draft genome yielded 619,029 contigs and 85,906 transcripts, respectively; normalized read counts to these assemblies were calculated using reads (RPKM) or fragments (FPKM) per kilobase of transcript per million mapped reads. In silico screening identified 1,594 contigs and 150 transcripts with lower RPKM or FPKM in poor than in good quality eggs, 245 contigs, and 85 transcripts of which could be annotated by BLASTx, respectively. From selected contigs or transcripts, six genes (dnajb4, gnpat, card14, pdp1, fcgbp, ttn) had significantly lower messenger RNA levels in poor than in good quality eggs by qPCR. Multiple regression analysis showed that five genes (gnpat, b4galnt1, acsl6, rtkn, trim24) significantly correlated with hatchability. Taken together, 10 genes were identified as candidate maternal transcripts, regulating development in Japanese eel. Our results contribute to understanding the molecular basis for maternal control of development in vertebrates.
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http://dx.doi.org/10.1002/mrd.23273DOI Listing
December 2019

Conservation and diversity in expression of candidate genes regulating socially-induced female-male sex change in wrasses.

PeerJ 2019 11;7:e7032. Epub 2019 Jun 11.

Department of Anatomy, University of Otago, Dunedin, Otago, New Zealand.

Fishes exhibit remarkably diverse, and plastic, patterns of sexual development, most striking of which is sequential hermaphroditism, where individuals readily reverse sex in adulthood. How this stunning example of phenotypic plasticity is controlled at a genetic level remains poorly understood. Several genes have been implicated in regulating sex change, yet the degree to which a conserved genetic machinery orchestrates this process has not yet been addressed. Using captive and in-the-field social manipulations to initiate sex change, combined with a comparative qPCR approach, we compared expression patterns of four candidate regulatory genes among three species of wrasses (Labridae)-a large and diverse teleost family where female-to-male sex change is pervasive, socially-cued, and likely ancestral. Expression in brain and gonadal tissues were compared among the iconic tropical bluehead wrasse () and the temperate spotty () and kyusen () wrasses. In all three species, gonadal sex change was preceded by downregulation of (encoding gonadal aromatase that converts androgens to oestrogens) and accompanied by upregulation of (encoding anti-müllerian hormone that primarily regulates male germ cell development), and these genes may act concurrently to orchestrate ovary-testis transformation. In the brain, our data argue against a role for brain aromatase () in initiating behavioural sex change, as its expression trailed behavioural changes. However, we find that isotocin (, that regulates teleost socio-sexual behaviours) expression correlated with dominant male-specific behaviours in the bluehead wrasse, suggesting upregulation mediates the rapid behavioural sex change characteristic of blueheads and other tropical wrasses. However, expression was not sex-biased in temperate spotty and kyusen wrasses, where sex change is more protracted and social groups may be less tightly-structured. Together, these findings suggest that while key components of the molecular machinery controlling gonadal sex change are phylogenetically conserved among wrasses, neural pathways governing behavioural sex change may be more variable.
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http://dx.doi.org/10.7717/peerj.7032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6568253PMC
June 2019

Expressional regulation of gonadotropin receptor genes and androgen receptor genes in the eel testis.

Gen Comp Endocrinol 2019 09 19;280:123-133. Epub 2019 Apr 19.

Department of Zoology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.

Receptors for follicle-stimulating hormone (Fshr), luteinizing hormone (Lhcgr1 and Lhcgr2) and androgens (Ara and Arb) transduce the hormonal signals that coordinate spermatogenesis, but the factors that regulate the abundance of these transducers in fish testes remain little-understood. To mend this paucity of information, we first determined changes in transcript abundance for these receptors (fshr, lhcgr1, ara and arb) during spermatogenesis induced by human chorionic gonadotropin (hCG) injection in the eel, Anguilla australis. We related our findings to testicular production of the fish androgen, 11-ketotestosterone (11-KT), and to the levels of the transcripts encoding steroidogenic acute regulatory protein (star) and 11β-hydroxylase (cyp11b), and subsequently evaluated the effects of hCG or 11-KT on mRNA levels of these target genes in vitro. Testicular 11-KT production was greatly increased by hCG treatment, both in vivo and in vitro, and associated with up-regulation of star and cyp11b transcripts. In situ hybridization indicated that testicular fshr mRNA levels were higher in the early stages of hCG-induced spermatogenesis, while lhcgr1 transcripts were most abundant later, once spermatids were observed. In vitro experiments further showed that hCG and its steroidal mediator 11-KT significantly increased fshr transcript abundance. These data provide new angles on the interactions between gonadotropin and androgen signaling during early spermatogenesis. Increases in levels of 11-KT following hCG injection elevated testicular fshr mRNA levels augmenting Fsh sensitivity in the testis. This evidence is suggestive of a positive feedback loop between gonadotropins and 11-KT that may be key to regulating early spermatogenesis in fish.
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http://dx.doi.org/10.1016/j.ygcen.2019.04.020DOI Listing
September 2019

11-Ketotestosterone induces oocyte growth, but does not affect oocyte cytology in pre-vitellogenic captive beluga, Huso huso L.

Comp Biochem Physiol B Biochem Mol Biol 2019 Jun 1;232:51-59. Epub 2019 Mar 1.

Department of Zoology, University of Otago, Dunedin, New Zealand.

An effect of 11-ketotestosterone (11-KT) on growth of previtellogenic (PV) ovaries of eel, salmon and Atlantic cod has been demonstrated. The purpose of this study was to investigate the effects of 11-KT treatment (in vivo) on ovarian growth, on hormonal and biochemical changes in blood, and on ovarian mRNA levels of lipidation-related genes in captive beluga with PV oocytes. In addition, the potential involvement of lipoprotein lipase (Lpl), an important enzyme for extracellular hydrolysis of lipoprotein-associated lipids, was evaluated. Twelve beluga (4-year olds) were treated with an intraperitoneal slow-release implant of either 11-KT (2.5 mg) or a compressed matrix (control). Ovarian biopsy was done to obtain pre- (day 0: T0) and post-treatment (day 21: T21) data on histology and target gene expression. Three weeks of exposure resulted in an increase in serum 11-KT levels from 2.2 ng/mL to 83 ng/mL but did not yield significant changes in serum levels of triacylglycerides and cholesterol. Furthermore, 11-KT implantation increased oocyte diameters from 259 μm (T0) to 309 μm by T21. Regardless of the increase in oocyte size, ovaries remained in the PV stage, mostly as late perinucleolar oocytes. Meanwhile, at the molecular level, the expression of lipidation-related transcripts [lpl, apolipoprotein E (apoe), very low density lipoprotein receptors (vldlr), low-density lipoprotein receptor-related protein 8-like (lrp8)] was significantly up-regulated after three weeks. Immunostaining for Lpl by Western blotting indicated three immunoreactive bands (70, 58 and 37 kDa) in ovarian homogenates from beluga, but signal intensity was not affected by treatment. Altogether, the administration of 11-KT increased 11-KT serum levels, oocyte size, and the expression of genes associated with lipid uptake. However, this treatment did not advance ovarian development beyond the PV stage.
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http://dx.doi.org/10.1016/j.cbpb.2019.02.009DOI Listing
June 2019

A mechanistic model for studying the initiation of anguillid vitellogenesis by comparing the European eel (Anguilla anguilla) and the shortfinned eel (A. australis).

Gen Comp Endocrinol 2019 08 20;279:129-138. Epub 2019 Feb 20.

Wageningen University & Research Animal Breeding and Genomics, Wageningen Livestock Research, PO Box 338, 6700 AH Wageningen, The Netherlands. Electronic address:

An inverse relation exists between the maturation stage at the start of the oceanic reproductive migration and the migration distance to the spawning grounds for the various eel species. The European eel Anguilla anguilla migrates up to 5-6000 km and leaves in a previtellogenic state. The shortfinned eel A. australis migrates 2-4000 km and leaves in an early vitellogenic state. In this study, we compared the early pubertal events in European silver eels with those in silver shortfinned eels to gain insights into the initiation of vitellogenesis. Immediately after being caught, yellow and silver eels of both species were measured and sampled for blood and tissues. Eye index (EI), gonadosomatic index (GSI) and hepatosomatic index (HSI) were calculated. Plasma 11-ketotestosterone (11-KT) and 17β-estradiol (E2) levels were measured by radioimmunoassay. Pituitary, liver and ovaries were dissected for quantitative real-time PCR analyses (pituitary dopamine 2b receptor d2br, gonadotropin-releasing hormone receptors 1 and 2 gnrhr1 and gnrhr2, growth hormone gh and follicle-stimulating hormone-β fshb; liver estrogen receptor 1 esr1; gonad follicle-stimulating hormone receptor fshr, androgen receptors α and β ara and arb, vitellogenin receptor vtgr and P450 aromatase cyp19). Silver eels of both species showed a drop in pituitary gh expression, progressing gonadal development (GSI of ∼1.5 in European eels and ∼3.0 in shortfinned eels) and steroid level increases. In shortfinned eels, but not European eels, expression of fshb, gnrhr1 and gnrhr2, and d2br in the pituitary was up-regulated in the silver-stage as compared to yellow-stage females, as was expression of fshr, ara and arb in the ovaries. Expression of esr1 in European eels remained low while esr1 expression was up-regulated over 100-fold in silver shortfinned eels. The mechanistic model for anguillid vitellogenesis that we present suggests a first step that involves a drop in Gh and a second step that involves Fsh increase when switching in the life history trade-off from growth to reproduction. The drop in Gh is associated with gonadal development and plasma steroid increase but precedes brain-pituitary-gonad axis (BPG) activation. The Fsh increase marks BPG activation and increased sensitivity of the liver to estrogenic stimulation, but also an increase in D2br-mediated dopaminergic signaling to the pituitary.
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http://dx.doi.org/10.1016/j.ygcen.2019.02.018DOI Listing
August 2019

Synergistic effects of estradiol and 11-ketotestosterone on vitellogenin physiology in the shortfinned eel (Anguilla australis).

Biol Reprod 2019 05;100(5):1319-1332

Department of Zoology, University of Otago, Dunedin, New Zealand.

Estradiol-17β (E2) and 11-ketotestosterone (11KT) have been implicated in vitellogenesis and in regulating expression of the follicle-stimulating hormone receptor (fshr), respectively. To override the captivity-induced reproductive block in shortfinned eel, Anguilla australis, we hypothesized that in combination, 11KT and E2 would stimulate ovarian uptake of vitellogenin (Vtg). Early pubertal eels received hormone implants containing varying concentrations of E2 (0, 0.2, 2, 5 mg) with or without 11KT (1 mg). Vtg levels were determined in plasma, liver, and ovarian tissues by histological examination, qPCR, immunoblotting, or single radial immunodiffusion. The expression of gonadotropin-beta subunits and gonadotropin receptors in the pituitary and ovary, respectively, were analyzed to determine mechanisms by which steroid effects may be exerted. When administered alone, E2 increased hepatic production and plasma levels of Vtg. In contrast, 11KT decreased plasma levels of Vtg, seemingly reducing its production. Neither 11KT nor E2 could induce uptake of Vtg into oocytes, although E2 treatment appeared necessary for uptake to occur. This was the case despite 11KT dramatically increasing both oocyte size and fshr mRNA levels. Astonishingly, the uptake of Vtg was successfully induced by co-treatment with 11KT and E2, suggesting that 11KT might facilitate the incorporation of Vtg into the developing oocyte. These results highlight the potential of sex steroid co-treatment, an approach aimed at mimicking oogenesis in wild eels, to induce vitellogenesis, specifically ovarian yolk deposition, even in the absence of exogenous gonadotropin treatment.
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http://dx.doi.org/10.1093/biolre/ioz007DOI Listing
May 2019

Expression of gonadotropin subunit and gonadotropin receptor genes in wild female New Zealand shortfinned eel (Anguilla australis) during yellow and silver stages.

Gen Comp Endocrinol 2019 02 6;272:83-92. Epub 2018 Dec 6.

Department of Zoology, University of Otago, 340 Great King Street, PO Box 56, Dunedin 9054, New Zealand.

Despite tremendous importance of follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) as primary controllers of reproductive development, information on the expression profiles of the genes encoding gonadotropin subunits and gonadotropin receptors (Fshr and Lhr) in wild eels are essentially non-existent. This study investigated pituitary fshb and lhb mRNA levels and ovarian fshr and lhr mRNA levels of wild shortfinned eels, Anguilla australis at different stages of oogenesis. Protein expression of Fsh in the pituitary was also quantified and visualized using slot blot and immunohistochemistry. Pituitary fshb and lhb mRNA levels showed a differential expression pattern, fshb mRNA levels increasing significantly from the perinucleolus (PN) to the oil droplet stage (OD) before slightly decreasing (not significantly) in the early vitellogenic stage (EV). A similar trend was observed in relative Fsh protein levels analyzed by slot blot and immunohistochemistry, but this trend was not reflected in the plasma levels of sex steroids. In contrast, pituitary lhb mRNA levels increased significantly from the PN to EV stage. A higher expression of Fsh at both mRNA and protein levels in the pituitary of eels at the OD stage compared to other investigated stages suggests that synthesis of Fsh production in the pituitary may reach a peak at the OD stage. In the ovary, transcript abundances of fshr and lhr gradually increased during previtellogenic follicle growth, but markedly and significantly increased thereafter. Taken together, our data suggest i) that Fsh release may be very limited, or absent, prior to onset of puberty in shortfinned eels and ii) that Lh is not functionally important in this fish during the EV stage.
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http://dx.doi.org/10.1016/j.ygcen.2018.12.001DOI Listing
February 2019

The evolution of apolipoprotein B and its mRNA editing complex. Does the lack of editing contribute to hypertriglyceridemia?

Gene 2018 Jan 12;641:46-54. Epub 2017 Oct 12.

Department of Zoology, University of Otago, 340 Great King Street, PO Box 56, Dunedin 9054, New Zealand.

The evolution of apolipoprotein B (Apob) has been intensely researched due to its importance during lipid transport. Mammalian full-length apob100 can be post-transcriptionally edited by the enzyme apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like complex-one (Apobec1) resulting in a truncated Apob, known as Apob48. Whilst both full-length and truncated forms of Apob are important for normal lipid homeostasis in mammals, there is no evidence for the presence of apob mRNA editing prior to the divergence of the mammals, yet, non-mammalian vertebrates appear to function normally with only Apob100. To date, the majority of the research carried out in non-mammalian vertebrates has focused on chickens with only a very limited number examining apob mRNA editing in fish. This study focused on the molecular evolution of Apobec1 and Apob in order to ascertain if apob mRNA editing occurs in eels, a basal teleost which represents an evolutionarily important animal group. No evidence for the presence of Apobec1 or the ability for eel apob to be edited was found. However, an important link between mutant mice and the evident hypertriglyceridemia in the plasma of non-mammalian vertebrates was made. This study has provided imperative evidence to help bridge the evolutionary gap between fish and mammals and provides further support for the lack of apob mRNA editing in non-mammalian vertebrates.
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http://dx.doi.org/10.1016/j.gene.2017.10.024DOI Listing
January 2018

Ovarian development of captive F1 wreckfish (hāpuku) Polyprion oxygeneios under constant and varying temperature regimes - Implications for broodstock management.

Gen Comp Endocrinol 2018 02 26;257:86-96. Epub 2017 Aug 26.

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.

In order to better understand how photo-thermal conditions affect oogenesis in captive-bred F1 hāpuku, a wreckfish considered for aquaculture in New Zealand, juvenile (pre-pubertal) fish were assigned to one of two regimes: exposed to a constant temperature of 17°C (CT group) or to seasonally varying temperatures (VT group range: 10-17°C), both under simulated ambient photoperiod, for nearly 2years. Development in females was monitored through repeated gonadal biopsies (histology; target gene mRNA levels) and blood sampling (plasma levels of estradiol-17β; E2). Very little evidence of advancing oogenesis was found in the first year of study, when fish were in their 4th year. In the subsequent year, a proportion of fish reached the pre-spawning stage (fully-grown ovarian follicles); the proportion of females reaching this stage was notably higher in the VT (62%) than the CT (28%) group. Of the few females that did reach maturity in the CT group, significantly lower levels of plasma E2 were observed relative to those in fish from the VT group possibly indicating a temperature-induced endocrine impairment during oogenesis. Interestingly, females that did not reach the pre-spawning stage presented with a small transient, but significant increase in oocyte diameters and plasma E2, suggestive of a dummy run. Clear seasonality was observed for fish under both photo-thermal regimes, and this was reflected in plasma E2 levels and transcript abundances of aromatase, fshr and luteinizing hormone receptor in the ovary; these end points all peaked in maturing females during the late or post-vitellogenic stage. We conclude that captive female F1 hāpuku first mature as five-year-olds and that exposure to a decreased temperature is important for appropriate progression of oogenesis.
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http://dx.doi.org/10.1016/j.ygcen.2017.08.022DOI Listing
February 2018

Effects of neuropeptides and sex steroids on the pituitary-gonadal axis of pre-pubertal F1 wreckfish (hāpuku) Polyprion oxygeneios in vivo: Evidence of inhibitory effects of androgens.

Gen Comp Endocrinol 2018 02 16;257:113-121. Epub 2017 Aug 16.

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.

The ability to advance puberty in broodstock that have a long generation interval and mature at large size is a highly valuable tool in contemporary aquaculture enterprise. Juvenile male and female wreckfish 'hāpuku' (Polyprion oxygeneios), a candidate for commercialization in aquaculture, were subjected to treatment for 8weeks with two implants, one containing steroid (blank; estradiol-17β, E2; 11-ketotestosterone, KT; 17 α-methyltestosterone, MT), the other peptide (blank; gonadotropin-releasing hormone analog, GnRHa; kisspeptin, Kiss2-12). The expression of target genes (glycoprotein homone α-subunit, gpa; follicle stimulating-hormone β-subunit, fshb; luteinizing hormone β-subunit, lhb; GnRH receptor, gnrhr) in the pituitary was assayed by quantitative PCR. KT and MT decreased mRNA levels of all target genes in both male and female hāpuku, suggestive of a strong inhibitory tone by these steroid hormones. E2, GnRHa and Kiss2-12 were largely ineffective, regardless of whether they were administered alone or in combination with steroid implants. Clear differences in release and/or clearance rates between E2 and KT from implants were evident, in part explaining our observations. Advancement of puberty was not achieved, and we pose that different hormone doses and/or administration during more advanced stages of gonadogenesis need to be considered to move this field forward.
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http://dx.doi.org/10.1016/j.ygcen.2017.08.018DOI Listing
February 2018

The effects of migratory stage and 11-ketotestosterone on the expression of rod opsin genes in the shortfinned eel (Anguilla australis).

Gen Comp Endocrinol 2018 02 28;257:211-219. Epub 2017 Jun 28.

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.

The androgen 11-ketotestosterone (11KT) can induce many of the changes associated with silvering, i.e., the transformation of a non-migrating 'yellow' eel into a migrating 'silver' eel. We posited that plasticity in spectral sensitivity of the eye, accompanied by expression of different opsins in the retina during silvering, is controlled by 11KT. To test this hypothesis, mRNA levels of freshwater (fwo) and seawater (swo) opsins and of the two androgen receptors (ara and arb) in retinas of wild-caught female shortfinned eels, Anguilla australis were compared. Swo expression was much higher (3-4 orders of magnitude) and fwo expression substantially lower in silver than in yellow eels, whereas mRNA levels of both ars did not differ between stages. Yellow eel retinas exposed to 11KT in vitro exhibited a robust dose-dependent increase in swo, but weak decreasing effects on fwo transcript abundance were inconsistent. Similarly, increased retinal swo expression was seen after in vivo treatment of yellow eels with 11KT implants, whereas expression of fwo remained unaffected. Lastly, co-treatment with 11KT and the androgen receptor blocker flutamide was undertaken to determine whether 11KT exerts its effects through nuclear androgen receptors. Flutamide did not block 11KT-affected expression of any target gene, neither in vivo nor in vitro. We conclude that 11KT greatly increases the abundance of swo, identifying the androgen as an important regulator of the opsin switch during silvering in freshwater eels.
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http://dx.doi.org/10.1016/j.ygcen.2017.06.025DOI Listing
February 2018

Sexual plasticity: A fishy tale.

Mol Reprod Dev 2017 02 9;84(2):171-194. Epub 2016 Sep 9.

Department of Anatomy, University of Otago, Dunedin, New Zealand.

Teleost fish exhibit remarkably diverse and plastic patterns of sexual development. One of the most fascinating modes of plasticity is functional sex change, which is widespread in marine fish including species of commercial importance; however, the regulatory mechanisms remain elusive. In this review, we explore such sexual plasticity in fish, using the bluehead wrasse (Thalassoma bifasciatum) as the primary model. Synthesizing current knowledge, we propose that cortisol and key neurochemicals modulate gonadotropin releasing hormone and luteinizing hormone signaling to promote socially controlled sex change in protogynous fish. Future large-scale genomic analyses and systematic comparisons among species, combined with manipulation studies, will likely uncover the common and unique pathways governing this astonishing transformation. Revealing the molecular and neuroendocrine mechanisms underlying sex change in fish will greatly enhance our understanding of vertebrate sex determination and differentiation as well as phenotypic plasticity in response to environmental influences. Mol. Reprod. Dev. 84: 171-194, 2017. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/mrd.22691DOI Listing
February 2017

Storage by lyophilization - Resulting RNA quality is tissue dependent.

Anal Biochem 2016 10 8;511:92-6. Epub 2016 Aug 8.

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.

In today's highly collaborative scientific community there is a growing need to transport biological samples across the globe. Lyophilization is a cost-effective preservation method which avoids the use of hazardous chemicals, creating an appealing, yet essentially unexplored, prospect for the long-range transport of animal tissue samples. This study examined the integrity of RNA following its extraction from eel tissue (liver, spleen and ovary) that had been subjected to i) freezing only; ii) freezing and lyophilization, and iii) freezing, lyophilization and subsequent storage at ambient temperature for one week. Only small reductions in RNA integrity were identified in lyophilized, stored sample compared to that of flash-frozen or lyophilized sample not subjected to storage. Reductions in RNA integrity were most profound in ovary tissue, which has a notably higher lipid content (∼35% of dry weight) than liver (∼17%) or spleen (∼15%). However, lowered RNA integrity numbers did not affect qPCR-estimated relative or absolute transcript copy numbers of two arbitrary target genes. These findings confirm that this method is a viable option for shipping animal tissue samples world-wide and could open up numerous benefits for the biological sciences as a whole.
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http://dx.doi.org/10.1016/j.ab.2016.08.005DOI Listing
October 2016

A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star.

Comp Biochem Physiol A Mol Integr Physiol 2016 08 13;198:72-86. Epub 2016 Apr 13.

Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand.

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.
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http://dx.doi.org/10.1016/j.cbpa.2016.04.013DOI Listing
August 2016

Triacylglyceride physiology in the short-finned eel, Anguilla australis--the effects of androgen.

Am J Physiol Regul Integr Comp Physiol 2016 Mar 13;310(5):R422-31. Epub 2016 Jan 13.

Department of Zoology, University of Otago, Dunedin, New Zealand; and.

The importance of androgens (especially 11-ketotestosterone) during previtellogenesis in eels is well established. In wild pubertal migrants, circulating 11-ketotestosterone levels correlate with a number of morphological and molecular changes. Here, we test the prediction that this correlation represents a causal relationship by artificially raising the levels of circulating 11-ketotestosterone in prepubertal nonmigratory female and pubertal, migratory male short-finned eels (Anguilla australis) using sustained-release hormone implants. In females, increases in hepatosomatic index and transcript copy numbers of hepatic apolipoprotein B and microsomal triacylglyceride transfer protein indicated increased repackaging of endogenously sourced triacylglycerides. These changes in liver measures were reflected in increased concentrations of serum triacylglycerides. However, despite a small increase in gonadosomatic index, ovarian lipoprotein receptor transcript abundances were not affected by 11-ketotestosterone. Interestingly, no such changes in hepatic gene expression were detected in a dose-response experiment using males. We propose that the androgens are inducing the observed changes in previtellogenic females, although it remains unclear to what extent these effects are direct or indirect.
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http://dx.doi.org/10.1152/ajpregu.00149.2015DOI Listing
March 2016

ECOLOGICAL AND EVOLUTIONARY APPLICATIONS FOR ENVIRONMENTAL SEX REVERSAL OF FISH.

Q Rev Biol 2015 Mar;90(1):23-44

Environmental sex reversal (ESR), which results in a mismatch between genotypic and phenotypic sex, is well documented in numerous fish species and may be induced by chemical exposure. Historically, research involving piscine ESR has been carried out with a view to improving profitability in aquaculture or to elucidate the processes governing sex determination and sexual differentiation. However, recent studies in evolution and ecology suggest research on ESR now has much wider applications and ramifications. We begin with an overview of ESR in fish and a brief review of the traditional applications thereof. We then discuss ESR and its potential demographic consequences in wild populations. Theory even suggests sex-reversed fish may be purposefully released to manipulate population dynamics. We suggest new research directions that may prove fruitful in understanding how ESR at the individual level translates to population-level processes. In the latter portion of the review we focus on evolutionary applications of ESR. Sex-reversal studies from the aquaculture literature provide insight in to the evolvability of determinants of sexual phenotype. Additionally, induced sex reversal can provide information about the evolution of sex chromosomes and sex-linked traits. Recently, naturally occurring ESR has been implicated as a mechanism contributing to the evolution of sex chromosomes.
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http://dx.doi.org/10.1086/679762DOI Listing
March 2015

Proteomic analysis of early-stage embryos: implications for egg quality in hapuku (Polyprion oxygeneios).

Fish Physiol Biochem 2015 Dec 18;41(6):1403-17. Epub 2015 Jul 18.

Department of Zoology, University of Otago, PO Box 56, 340 Great King St., Dunedin, 9016, New Zealand.

In order to develop biomarkers that may help predict the egg quality of captive hapuku (Polyprion oxygeneios) and provide potential avenues for its manipulation, the present study (1) sequenced the proteome of early-stage embryos using isobaric tag for relative and absolute quantification analysis, and (2) aimed to establish the predictive value of the abundance of identified proteins with regard to egg quality through regression analysis. Egg quality was determined for eight different egg batches by blastomere symmetry scores. In total, 121 proteins were identified and assigned to one of nine major groups according to their function/pathway. A mixed-effects model analysis revealed a decrease in relative protein abundance that correlated with (decreasing) egg quality in one major group (heat-shock proteins). No differences were found in the other protein groups. Linear regression analysis, performed for each identified protein separately, revealed seven proteins that showed a significant decrease in relative abundance with reduced blastomere symmetry: two correlates that have been named in other studies (vitellogenin, heat-shock protein-70) and a further five new candidate proteins (78 kDa glucose-regulated protein, elongation factor-2, GTP-binding nuclear protein Ran, iduronate 2-sulfatase and 6-phosphogluconate dehydrogenase). Notwithstanding issues associated with multiple statistical testing, we conclude that these proteins, and especially iduronate 2-sulfatase and the generic heat-shock protein group, could serve as biomarkers of egg quality in hapuku.
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http://dx.doi.org/10.1007/s10695-015-0095-0DOI Listing
December 2015

Effects of 11-ketotestosterone and temperature on inhibin subunit mRNA levels in the ovary of the shortfinned eel, Anguilla australis.

Comp Biochem Physiol B Biochem Mol Biol 2015 Sep 7;187:14-21. Epub 2015 May 7.

Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand. Electronic address:

Members of the transforming growth factor-b (TGFb) superfamily are important during early oogenesis in mammals. In this study, we tested whether documented effects of 11-ketotestosterone (11KT) on previtellogenic eel ovaries are mediated through affecting the expression of key ovarian TGFb genes. Furthermore, we investigated whether 11KT effects interacted with temperature. Accordingly, three thermal regimes were compared and their interaction with 11KT-mediated actions on expression of TGFb superfamily genes (chiefly inhibin subunits) evaluated in the eel (Anguilla australis). Inhibin subunit mRNA levels were also measured in ovarian explants cultured in vitro with 11KT and in ovaries from eels collected from the wild. In wild eels, inhibin-bA mRNA levels were higher in early than in previtellogenic eels; inhibin-a expression did not differ between stages, whereas that of inhibin-bB first decreased, then recovered with advanced developmental stage. Temperature was ineffective in modulating any of the end points, at least as long as a Q10 adjustment was made to correct for 'metabolic dose'. However, 11KT affected the expression of inhibin-a compared to control fish, while those of inhibin-b subunit genes remained unaffected. In contrast, 11KT dramatically reduced mRNA levels of inhibin-b subunits in vitro, but had inconsistent effects on inhibin-a transcript abundance. We conclude that 11KT affects ovarian inhibin subunit gene expression, but effects are not in keeping with the changes seen during early oogenesis in eels from the wild. We further contend that in vivo temperature experiments are easily biased and that Q10 corrections may be required to identify 'true' temperature effects.
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http://dx.doi.org/10.1016/j.cbpb.2015.04.012DOI Listing
September 2015

Triacylglyceride physiology in the short-finned eel, Anguilla australis—changes throughout early oogenesis.

Am J Physiol Regul Integr Comp Physiol 2015 Jun 25;308(11):R935-44. Epub 2015 Mar 25.

Department of Zoology, University of Otago, Dunedin, New Zealand; and.

During certain stages in an animal's life cycle, energy requirements may exceed energy intake from the diet. The spawning migration of temperate eels is a textbook example of negative energy balance, forcing these fish to rely on stored fats (triacylglycerides) to provide their muscles with energy for swimming and their growing oocytes with the nutrients needed to develop and support healthy offspring. We predicted broad implications of this great need for endogenous triacylglycerides in terms of their packaging, transport, and ovarian uptake. To test this, serum lipid concentrations and transcript abundances of intestinal and hepatic triacylglyceride packagers and ovarian triacylglyceride modifiers and receivers were investigated throughout previtellogenesis (feeding phase) and into early vitellogenesis (fasting phase) in short-finned eels. A switch from exogenous to endogenous triacylglyceride packaging was seen as the liver upregulated transcript levels of apolipoprotein B and microsomal triacylglyceride transport protein and downregulated those of apolipoprotein E and lipoprotein lipase. In the intestine, the reverse response was observed. Furthermore, ovarian transcript abundances of triacylglyceride modifiers and receivers increased (apolipoprotein E, lipoprotein lipase, and vitellogenin receptor), indicative of increased triacylglyceride uptake during previtellogenesis. We propose that increased hepatic apolipoprotein B production is a conserved vertebrate response to prolonged periods of negative energy balance.
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http://dx.doi.org/10.1152/ajpregu.00436.2014DOI Listing
June 2015

Effects of estradiol-17β implantation on ovarian growth, sex steroid levels and vitellogenin proxies in previtellogenic sturgeon Huso huso.

Anim Reprod Sci 2015 Jun 24;157:1-10. Epub 2014 Dec 24.

Department of Zoology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.

Sexual development in female great sturgeon (Huso huso) is arrested at the previtellogenic stage for many years. The present study investigated the effects of different levels of estradiol-17β (E2) on gonadal development, levels of sex steroids and proxies of vitellogenin in 3-year-old cultured previtellogenic great sturgeon. Fish were intraperitoneally implanted every 1.5 months over a 6-month period from January to July with capsules filled with 0, 3, 6 or 12 mg E2/kg body mass as control, low, mid and high experimental groups, respectively. Blood sampling was performed at the start of experimentation and 3 weeks after each implantation for quantification of sex steroid levels and of vitellogenin-associated variables (triacylglycerol, cholesterol, calcium, phosphorus). Gonad biopsy samples were taken at the beginning and the end of the experiment in order to determine the gonad stage and oocyte morphometrical measures were taken to evaluate treatment effects. E2 implants produced a significant elevation in serum concentrations of E2, calcium, triacylglycerol, cholesterol and phosphorus. A rapid significant decrease was observed in serum testosterone levels in a dose-independent manner, so that the highest testosterone concentrations were observed in control fish throughout the experiment. There were no significant differences in oocyte stage or morphometric end points among the treated fish. We conclude that E2 implants do not stimulate ovarian growth, and hence, E2 implants alone are insufficient to reducing the time until onset of sexual maturation in previtellogenic great sturgeon.
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http://dx.doi.org/10.1016/j.anireprosci.2014.12.010DOI Listing
June 2015

Erratum to: Does social status within a dominance hierarchy mediate individual growth, residency and relocation?

Oecologia 2015 Apr;177(4):1231

Department of Zoology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand,

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http://dx.doi.org/10.1007/s00442-015-3272-zDOI Listing
April 2015

How do eggs get fat? Insights into ovarian fatty acid accumulation in the shortfinned eel, Anguilla australis.

Gen Comp Endocrinol 2015 Sep 7;221:94-100. Epub 2015 Feb 7.

Department of Zoology, University of Otago, 340 Great King Street, PO Box 56, Dunedin 9054, New Zealand.

Previous research using eels has shown that 11-ketotestosterone can induce ovarian triacylglyceride accumulation both in vivo and in vitro. Further, accumulation is dramatically enhanced in the presence of very-low density lipoprotein. This study examined the involvement of the low density lipoprotein receptor and vitellogenin receptor in oocyte lipid accumulation. Specific antisera were used in an attempt to block the vitellogenin receptor and/or the low density lipoprotein receptor. Accordingly, incubation with the low density lipoprotein receptor antiserum clearly reduced the oocyte diameter and the amount of oil present within the oocyte. In contrast, blocking the vitellogenin receptor had little effect on either oocyte surface area or the abundance of oil droplets in the cytosol. In keeping with birds, we conclude that the low density lipoprotein receptor is a major player involved in mediating ovarian fatty acid accumulation in the eel. However, lipoprotein lipase-mediated fatty acid accumulation also remains conceivable, for example through interactions between this enzyme and the low density lipoprotein receptor.
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http://dx.doi.org/10.1016/j.ygcen.2014.12.019DOI Listing
September 2015

Does social status within a dominance hierarchy mediate individual growth, residency and relocation?

Oecologia 2014 Nov 27;176(3):771-9. Epub 2014 Aug 27.

Department of Zoology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand,

The availability of food, and hence energy, is known to influence the abundance, habitat choice and growth of individuals. In contrast, there is a paucity of knowledge on how the interaction of energy supply and social status determines patterns of residency and movement. This study tests whether the presence of conspecifics and an individual's social status in relation to food supply influence the fitness and movement of a drift-feeding fish (Galaxias fasciatus). Using an information-theoretic approach (AIC), our analysis indicated that the most parsimonious model of fish movement among pools was one that included food supply, social rank and fish relative growth rate. Our results indicated that subordinate fish relocated more frequently compared to dominant fish, most likely as a consequence of intra-specific competition that limited the access of these smaller fish to resources and constrained their growth. Our results suggest that energy constraints may force individuals to explore new habitats in an effort to find more energetically profitable patches. We conclude that intra-specific competition mediated through the social hierarchy amongst closely interacting individuals plays a key role in determining individual growth, residency and relocation.
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http://dx.doi.org/10.1007/s00442-014-3038-zDOI Listing
November 2014