Publications by authors named "Jonas Jourdan"

15 Publications

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Recovery from air pollution and subsequent acidification masks the effects of climate change on a freshwater macroinvertebrate community.

Sci Total Environ 2021 Mar 24;758:143685. Epub 2020 Nov 24.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany; Faculty of Biology, University of Duisburg-Essen, Essen, Germany.

Freshwater ecosystems are dynamic, complex systems with a multitude of physical and ecological processes and stressors which drive fluctuations on the community-level. Disentangling the effects of different processes and stressors is challenging due to their interconnected nature. However, as protected areas (i.e. national parks) are less anthropogenically impacted, they are ideal for investigating single stressors. We focus on the Bavarian Forest National Park, a Long-Term Ecological Research (LTER) site in Germany, where the major stressors are climate warming, air pollution (i.e. acidification) and bark beetle infestations. We investigated the effects of these stressors on freshwater macroinvertebrates using comprehensive long-term (1983-2014) datasets comprising high-resolution macroinvertebrate and physico-chemical data from a near-natural stream. Macroinvertebrate communities have undergone substantial changes over the past 32 years, highlighted by increases in overall community abundance (+173%) and richness (+51.6%) as well as taxonomic restructuring driven by a disproportional increase of dipterans. Prior to the year 2000, regression analyses revealed a decline in sulphate deposition and subsequent recovery from historical acidification as potential drivers of the increases in abundance and richness rather than to increases in water temperature (1.5 °C overall increase). Post 2000, however, alterations to nutrient cycling caused by bark beetle infestations coupled with warming temperatures were correlated to taxonomic restructuring and disproportional increases of dipterans at the expense of sensitive taxa such as plecopterans and trichopterans. Our results highlight the challenges when investigating the effects of climate change within a multi-stressor context. Even in conservation areas, recovery from previous disturbance might mask the effects of ongoing disturbances like climate change. Overall, we observed strong community restructuring, demonstrating that stenothermal headwater communities face additional stress due to emerging competition with tolerant taxa. Conservation efforts should consider the temporal variability of communities and their recovery from disturbances to adequately identify species vulnerable to local or widespread extinction.
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http://dx.doi.org/10.1016/j.scitotenv.2020.143685DOI Listing
March 2021

A century later: Adaptive plasticity and rapid evolution contribute to geographic variation in invasive mosquitofish.

Sci Total Environ 2020 Jul 18;726:137908. Epub 2020 Mar 18.

Department of Aquatic Ecotoxicology, Johann Wolfgang Goethe University Frankfurt am Main, Frankfurt am Main, Germany. Electronic address:

One century after their introduction to Europe, eastern mosquitofish (Gambusia holbrooki) represent a natural experiment to determine the relative contributions of adaptive plasticity and rapid evolutionary change in creating large-scale geographic variation in phenotypes. We evaluated the population-genetic structure and invasion history based on allele length polymorphisms of 15 nuclear microsatellites, which we quantified for N = 660 individuals from 23 populations sampled in 2013 across the invasive range of G. holbrooki in Europe. We analysed body-shape and life-history variation in N = 1331 individuals from 36 populations, sampled in 2013 and 2017, and tested heritability of phenotypic differences in a subset of four populations using a common-garden experiment. The genetic structure of wild-caught individuals suggested a single introduction for all European mosquitofish, which were genetically impoverished compared to their native counterparts. We found some convergent patterns of phenotypic divergence across native and invasive climatic gradients (e.g., increased body size in colder/more northern populations); however, several phenotypic responses were not consistent between sampling years, pointing towards plastic phenotypes. Our analysis of common-garden reared individuals uncovered moderate heritability estimates only for two measures of male body size (intraclass correlation coefficient, ICC = 0.628 and 0.556) and offspring fat content (ICC = 0.734), while suggesting high levels of plasticity in most other phenotypic traits (ICC ≤ 0.407). Our results highlight the importance of phenotypic plasticity in invasive species during range expansions and demonstrate that strong selective pressures-in this case towards increased body size in colder environments-simultaneously promote rapid evolutionary divergence.
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http://dx.doi.org/10.1016/j.scitotenv.2020.137908DOI Listing
July 2020

Complex and nonlinear climate-driven changes in freshwater insect communities over 42 years.

Conserv Biol 2020 10 6;34(5):1241-1251. Epub 2020 May 6.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, 63571, Germany.

The ongoing biodiversity crisis becomes evident in the widely observed decline in abundance and diversity of species, profound changes in community structure, and shifts in species' phenology. Insects are among the most affected groups, with documented decreases in abundance up to 76% in the last 25-30 years in some terrestrial ecosystems. Identifying the underlying drivers is a major obstacle as most ecosystems are affected by multiple stressors simultaneously and in situ measurements of environmental variables are often missing. In our study, we investigated a headwater stream belonging to the most common stream type in Germany located in a nature reserve with no major anthropogenic impacts except climate change. We used the most comprehensive quantitative long-term data set on aquatic insects available, which includes weekly measurements of species-level insect abundance, daily water temperature and stream discharge as well as measurements of additional physicochemical variables for a 42-year period (1969-2010). Overall, water temperature increased by 1.88 °C and discharge patterns changed significantly. These changes were accompanied by an 81.6% decline in insect abundance, but an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%), and interannual turnover (+34%). Moreover, the community's trophic structure and phenology changed: the duration of emergence increased by 15.2 days, whereas the peak of emergence moved 13.4 days earlier. Additionally, we observed short-term fluctuations (<5 years) in almost all metrics as well as complex and nonlinear responses of the community toward climate change that would have been missed by simply using snapshot data or shorter time series. Our results indicate that climate change has already altered biotic communities severely even in protected areas, where no other interacting stressors (pollution, habitat fragmentation, etc.) are present. This is a striking example of the scientific value of comprehensive long-term data in capturing the complex responses of communities toward climate change.
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http://dx.doi.org/10.1111/cobi.13477DOI Listing
October 2020

Small-scale phenotypic differentiation along complex stream gradients in a non-native amphipod.

Front Zool 2019 11;16:29. Epub 2019 Jul 11.

4College of Animal Science and Technology, Northwest A&F University, Yangling, People's Republic of China.

Background: Selective landscapes in rivers are made up by an array of selective forces that vary from source to downstream regions or between seasons, and local/temporal variation in fitness maxima can result in gradual spatio-temporal variation of phenotypic traits. This study aimed at establishing freshwater amphipods as future model organisms to study adaptive phenotypic diversification (evolutionary divergence and/or adaptive plasticity) along stream gradients.

Methods: We collected from 16 sampling sites in the Rhine catchment during two consecutive seasons (summer and winter). Altogether, we dissected  = 1648 individuals and quantified key parameters related to morphological and life-history diversification, including naturally selected (e.g., gill surface areas) as well as primarily sexually selected traits (e.g., male antennae). Acknowledging the complexity of selective regimes in streams and the interrelated nature of selection factors, we assessed several abiotic (e.g., temperature, flow velocity) and biotic ecological parameters (e.g., conspecific densities, sex ratios) and condensed them into four principal components (PCs).

Results: Generalized least squares models revealed pronounced phenotypic differentiation in most of the traits investigated herein, and components of the stream gradient (PCs) explained parts of the observed differences. Depending on the trait under investigation, phenotypic differentiation could be ascribed to variation in abiotic conditions, anthropogenic disturbance (influx of thermally polluted water), or population parameters. For example, female fecundity showed altitudinal variation and decreased with increasing conspecific densities, while sexual dimorphism in the length of male antennae-used for mate finding and assessment-increased with increasing population densities and towards female-biased sex ratios.

Conclusions: We provide a comprehensive protocol for comparative analyses of intraspecific variation in life history traits in amphipods. Whether the observed phenotypic differentiation over small geographical distances reflects evolutionary divergence or plasticity (or both) remains to be investigated in future studies. Independent of the mechanisms involved, variation in several traits is likely to have consequences for ecosystem functions. For example, leaf-shredding in strongly depends on body size, which varied in dependence of several ecological parameters.
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http://dx.doi.org/10.1186/s12983-019-0327-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6624920PMC
July 2019

Elevated temperatures translate into reduced dispersal abilities in a natural population of an aquatic insect.

J Anim Ecol 2019 10 23;88(10):1498-1509. Epub 2019 Jul 23.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany.

Rising global temperatures force many species to shift their distribution ranges. However, whether or not (and how fast) such range shifts occur depends on species' dispersal capacities. In most ecological studies, dispersal-related traits (such as the wing size or wing loading in insects) are treated as fixed, species-specific characteristics, ignoring the important role of phenotypic plasticity during insect development. We tested the hypothesis that dispersal-related traits themselves vary in dependence of ambient environmental conditions (temperature regimes, discharge patterns and biotic interactions during individual development). We collected data over 8 years from a natural population of the crane fly Tipula maxima in central Germany. Using linear mixed-effect models, we analysed how phenotypic traits, phenological characteristics and population densities are affected by environmental conditions during the preceding 3, 6 and 12 months. We found a moderate (5.6%) increase in wing length per 1°C increase in mean annual temperatures during the previous year. At the same time, body weight increased by as much as 17.8% in females and 26.9% in males per 1°C, likely driven by increased habitat productivity, which resulted in a 16.4% (female) and 19.3% (male) increased wing loading. We further found a shorter, more synchronized emergence period (i.e. a narrower time frame for dispersal) with increasing temperatures. Altogether, our results suggest that dispersal abilities of T. maxima were negatively affected by elevated temperatures, and we discuss how similar patterns might affect the persistence of populations of other aquatic insects, especially stenoecious taxa with narrow distribution ranges. Our study calls for integration of information on temperature-induced phenotypic plasticity of dispersal-related traits into models forecasting range shifts in the face of climate change. Furthermore, the patterns reported here are likely to affect metapopulation dynamics of aquatic insects under climate change conditions and may contribute to the ongoing decline of insect biomass and diversity.
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http://dx.doi.org/10.1111/1365-2656.13054DOI Listing
October 2019

Reintroduction of freshwater macroinvertebrates: challenges and opportunities.

Biol Rev Camb Philos Soc 2019 04 22;94(2):368-387. Epub 2018 Aug 22.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Clamecystr. 12, 63571, Gelnhausen, Germany.

Species reintroductions - the translocation of individuals to areas in which a species has been extirpated with the aim of re-establishing a self-sustaining population - have become a widespread practice in conservation biology. Reintroduction projects have tended to focus on terrestrial vertebrates and, to a lesser extent, fishes. Much less effort has been devoted to the reintroduction of invertebrates into restored freshwater habitats. Yet, reintroductions may improve restoration outcomes in regions where impoverished regional species pools limit the self-recolonisation of restored freshwaters. We review the available literature on macroinvertebrate reintroductions, focusing on identifying the intrinsic and extrinsic factors that determine their success or failure. Our study reveals that freshwater macroinvertebrate reintroductions remain rare, are often published in the grey literature and, of the attempts made, approximately one-third fail. We identify life-cycle complexity and remaining stressors as the two factors most likely to affect reintroduction success, illustrating the unique challenges of freshwater macroinvertebrate reintroductions. Consideration of these factors by managers during the planning process and proper documentation - even if a project fails - may increase the likelihood of successful outcomes in future reintroduction attempts of freshwater macroinvertebrates.
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http://dx.doi.org/10.1111/brv.12458DOI Listing
April 2019

Natural and sexual selection drive multivariate phenotypic divergence along climatic gradients in an invasive fish.

Sci Rep 2018 07 24;8(1):11164. Epub 2018 Jul 24.

College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, 712100, P.R. China.

Invasive species that rapidly spread throughout novel distribution ranges are prime models to investigate climate-driven phenotypic diversification on a contemporary scale. Previous studies on adaptive diversification along latitudinal gradients in fish have mainly considered body size and reported either increased or decreased body size towards higher latitudes (i.e. Bergmann's rule). Our study is the first to investigate phenotypic divergence in multiple traits, including sexually selected traits (size and shape of the male copulatory organ, the gonopodium) of invasive Gambusia affinis in China. We studied body size, life history traits and morphological variation across populations spanning 17 degrees of latitude and 16 degrees of longitude. Even though we found phenotypic variation along climatic gradients to be strongest in naturally selected traits, some sexually selected traits also showed systematic gradual divergence. For example, males from southern populations possessed wider gonopodia with increased armament. Generally, males and females diverged in response to different components of climatic gradients (latitudinal or longitudinal variation) and in different trait suites. We discuss that not only temperature regimes, but also indirect effects of increased resource and mate competition (as a function of different extrinsic overwinter mortality rates) alter the selective landscape along climatic gradients.
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http://dx.doi.org/10.1038/s41598-018-29254-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6057953PMC
July 2018

Diverging response patterns of terrestrial and aquatic species to hydromorphological restoration.

Conserv Biol 2019 02 13;33(1):132-141. Epub 2018 Sep 13.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Clamecystrasse 12, 63571 Gelnhausen, Germany.

Although experiences with ecological restoration continue to accumulate, the effectiveness of restoration for biota remains debated. We complemented a traditional taxonomic analysis approach with information on 56 species traits to uncover the responses of 3 aquatic (fish, macroinvertebrates, macrophytes) and 2 terrestrial (carabid beetles, floodplain vegetation) biotic groups to 43 hydromorphological river restoration projects in Germany. All taxonomic groups responded positively to restoration, as shown by increased taxonomic richness (10-164%) and trait diversity (habitat, dispersal and mobility, size, form, life history, and feeding groups) (15-120%). Responses, however, were stronger for terrestrial than aquatic biota, and, contrary to our expectation, taxonomic responses were stronger than those of traits. Nevertheless, trait analysis provided mechanistic insights into the drivers of community change following restoration. Trait analysis for terrestrial biota indicated restoration success was likely enhanced by lateral connectivity and reestablishment of dynamic processes in the floodplain. The weaker response of aquatic biota suggests recovery was hindered by the persistence of stressors in the aquatic environment, such as degraded water quality, dispersal constraints, and insufficient hydromorphological change. Therefore, river restoration requires combined local- and regional-scale approaches to maximize the response of both aquatic and terrestrial organisms. Due to the contrasting responses of aquatic and terrestrial biota, the planning and assessment of river restoration outcomes should consider effects on both components of riverine landscapes.
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http://dx.doi.org/10.1111/cobi.13176DOI Listing
February 2019

Female Choice Undermines the Emergence of Strong Sexual Isolation between Locally Adapted Populations of Atlantic Mollies ().

Genes (Basel) 2018 May 2;9(5). Epub 2018 May 2.

College of Animal Science & Technology, Northwest A&F University, Yangling 712100, China.

Divergent selection between ecologically dissimilar habitats promotes local adaptation, which can lead to reproductive isolation (RI). Populations in the species complex have independently adapted to toxic hydrogen sulfide and show varying degrees of RI. Here, we examined the variation in the mate choice component of prezygotic RI. Mate choice tests across drainages (with stimulus males from another drainage) suggest that specific features of the males coupled with a general female preference for yellow color patterns explain the observed variation. Analyses of male body coloration identified the intensity of yellow fin coloration as a strong candidate to explain this pattern, and common-garden rearing suggested heritable population differences. Male sexual ornamentation apparently evolved differently across sulfide-adapted populations, for example because of differences in natural counterselection via predation. The ubiquitous preference for yellow color ornaments in poeciliid females likely undermines the emergence of strong RI, as female discrimination in favor of own males becomes weaker when yellow fin coloration in the respective sulfide ecotype increases. Our study illustrates the complexity of the (partly non-parallel) pathways to divergence among replicated ecological gradients. We suggest that future work should identify the genomic loci involved in the pattern reported here, making use of the increasing genomic and transcriptomic datasets available for our study system.
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http://dx.doi.org/10.3390/genes9050232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5977172PMC
May 2018

Effects of changing climate on European stream invertebrate communities: A long-term data analysis.

Sci Total Environ 2018 Apr 29;621:588-599. Epub 2017 Nov 29.

Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany; Faculty of Biology, University of Duisburg-Essen, Essen, Germany.

Long-term observations on riverine benthic invertebrate communities enable assessments of the potential impacts of global change on stream ecosystems. Besides increasing average temperatures, many studies predict greater temperature extremes and intense precipitation events as a consequence of climate change. In this study we examined long-term observation data (10-32years) of 26 streams and rivers from four ecoregions in the European Long-Term Ecological Research (LTER) network, to investigate invertebrate community responses to changing climatic conditions. We used functional trait and multi-taxonomic analyses and combined examinations of general long-term changes in communities with detailed analyses of the impact of different climatic drivers (i.e., various temperature and precipitation variables) by focusing on the response of communities to climatic conditions of the previous year. Taxa and ecoregions differed substantially in their response to climate change conditions. We did not observe any trend of changes in total taxonomic richness or overall abundance over time or with increasing temperatures, which reflects a compensatory turnover in the composition of communities; sensitive Plecoptera decreased in response to warmer years and Ephemeroptera increased in northern regions. Invasive species increased with an increasing number of extreme days which also caused an apparent upstream community movement. The observed changes in functional feeding group diversity indicate that climate change may be associated with changes in trophic interactions within aquatic food webs. These findings highlight the vulnerability of riverine ecosystems to climate change and emphasize the need to further explore the interactive effects of climate change variables with other local stressors to develop appropriate conservation measures.
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http://dx.doi.org/10.1016/j.scitotenv.2017.11.242DOI Listing
April 2018

On the occurrence of three non-native cichlid species including the first record of a feral population of () (Boulenger, 1899) in Europe.

R Soc Open Sci 2017 Jun 21;4(6):170160. Epub 2017 Jun 21.

Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Mueggelseedamm 310, 12587 Berlin, Germany.

Thermally influenced freshwater systems provide suitable conditions for non-native species of tropical and subtropical origin to survive and form proliferating populations beyond their native ranges. In Germany, non-native convict cichlids () and tilapia ( sp.) have established populations in the Gillbach, a small stream that receives warm water discharge from a local power plant. Here, we report on the discovery of spotted tilapia () in the Gillbach, the first record of a reproducing population of this species in Europe. It has been hypothesized that sp. in the Gillbach are descendants of aquaculture escapees and our mtDNA analysis found both and maternal lineages, which are commonly used for hybrids in aquaculture. Convict cichlids and spotted tilapia were most probably introduced into the Gillbach by aquarium hobbyists. Despite their high invasiveness worldwide, we argue that all three cichlid species are unlikely to spread and persist permanently beyond the thermally influenced range of the Gillbach river system. However, convict cichlids from the Gillbach are known to host both native and non-native fish parasites and thus, non-native cichlids may constitute threats to the native fish fauna. We therefore strongly recommend continuous monitoring of the Gillbach and similar systems.
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http://dx.doi.org/10.1098/rsos.170160DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5493913PMC
June 2017

Shared and unique patterns of phenotypic diversification along a stream gradient in two congeneric species.

Sci Rep 2016 12 16;6:38971. Epub 2016 Dec 16.

College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, P.R. China.

Stream ecosystems show gradual variation of various selection factors, which can result in a zonation of species distributions and gradient evolution of morphological and life-history traits within species. Identifying the selective agents underlying such phenotypic evolution is challenging as different species could show shared and/or unique (species-specific) responses to components of the river gradient. We studied a stream gradient inhabited by two mosquitofishes (genus Gambusia) in the Río Grijalva basin in southern Mexico and found a patchy distribution pattern of both congeners along a stretch of 100 km, whereby one species was usually dominant at a given site. We uncovered both shared and unique patterns of diversification: some components of the stream gradient, including differences in piscine predation pressure, drove shared patterns of phenotypic divergence, especially in females. Other components of the gradient, particularly abiotic factors (max. annual temperature and temperature range) resulted in unique patterns of divergence, especially in males. Our study highlights the complexity of selective regimes in stream ecosystems. It exemplifies that even closely related, congeneric species can respond in unique ways to the same components of the river gradient and shows how both sexes can exhibit quite different patterns of divergence in multivariate phenotypic character suites.
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http://dx.doi.org/10.1038/srep38971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5159898PMC
December 2016

Does personality affect premating isolation between locally-adapted populations?

BMC Evol Biol 2016 06 23;16:138. Epub 2016 Jun 23.

College of Animal Science and Technology, Northwest A&F University, Yangling, 712100, People's Republic of China.

Background: One aspect of premating isolation between diverging, locally-adapted population pairs is female mate choice for resident over alien male phenotypes. Mating preferences often show considerable individual variation, and whether or not certain individuals are more likely to contribute to population interbreeding remains to be studied. In the Poecilia mexicana-species complex different ecotypes have adapted to hydrogen sulfide (H2S)-toxic springs, and females from adjacent non-sulfidic habitats prefer resident over sulfide-adapted males. We asked if consistent individual differences in behavioral tendencies (animal personality) predict the strength and direction of the mate choice component of premating isolation in this system.

Results: We characterized focal females for their personality and found behavioral measures of 'novel object exploration', 'boldness' and 'activity in an unknown area' to be highly repeatable. Furthermore, the interaction term between our measures of exploration and boldness affected focal females' strength of preference (SOP) for the resident male phenotype in dichotomous association preference tests. High exploration tendencies were coupled with stronger SOPs for resident over alien mating partners in bold, but not shy, females. Shy and/or little explorative females had an increased likelihood of preferring the non-resident phenotype and thus, are more likely to contribute to rare population hybridization. When we offered large vs. small conspecific stimulus males instead, less explorative females showed stronger preferences for large male body size. However, this effect disappeared when the size difference between the stimulus males was small.

Conclusions: Our results suggest that personality affects female mate choice in a very nuanced fashion. Hence, population differences in the distribution of personality types could be facilitating or impeding reproductive isolation between diverging populations depending on the study system and the male trait(s) upon which females base their mating decisions, respectively.
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http://dx.doi.org/10.1186/s12862-016-0712-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918032PMC
June 2016

Extremophile Poeciliidae: multivariate insights into the complexity of speciation along replicated ecological gradients.

BMC Evol Biol 2016 Jun 22;16:136. Epub 2016 Jun 22.

College of Animal Science and Technology, Northwest A&F University, Xinong Road 22, Yangling, 712100, People's Republic of China.

Background: Replicate population pairs that diverge in response to similar selective regimes allow for an investigation of (a) whether phenotypic traits diverge in a similar and predictable fashion, (b) whether there is gradual variation in phenotypic divergence reflecting variation in the strength of natural selection among populations, (c) whether the extent of this divergence is correlated between multiple character suites (i.e., concerted evolution), and (d) whether gradual variation in phenotypic divergence predicts the degree of reproductive isolation, pointing towards a role for adaptation as a driver of (ecological) speciation. Here, we use poeciliid fishes of the genera Gambusia and Poecilia that have repeatedly evolved extremophile lineages able to tolerate high and sustained levels of toxic hydrogen sulfide (H2S) to answer these questions.

Results: We investigated evolutionary divergence in response to H2S in Gambusia spp. (and to a lesser extent Poecilia spp.) using a multivariate approach considering the interplay of life history, body shape, and population genetics (nuclear miscrosatellites to infer population genetic differentiation as a proxy for reproductive isolation). We uncovered both shared and unique patterns of evolution: most extremophile Gambusia predictably evolved larger heads and offspring size, matching a priori predictions for adaptation to sulfidic waters, while variation in adult life histories was idiosyncratic. When investigating patterns for both genera (Gambusia and Poecilia), we found that divergence in offspring-related life histories and body shape were positively correlated across populations, but evidence for individual-level associations between the two character suites was limited, suggesting that genetic linkage, developmental interdependencies, or pleiotropic effects do not explain patterns of concerted evolution. We further found that phenotypic divergence was positively correlated with both environmental H2S-concentration and neutral genetic differentiation (a proxy for gene flow).

Conclusions: Our results suggest that higher toxicity exerts stronger selection, and that divergent selection appears to constrain gene flow, supporting a scenario of ecological speciation. Nonetheless, progress toward ecological speciation was variable, partially reflecting variation in the strength of divergent selection, highlighting the complexity of selective regimes even in natural systems that are seemingly governed by a single, strong selective agent.
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http://dx.doi.org/10.1186/s12862-016-0705-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918007PMC
June 2016

Microhabitat use, population densities, and size distributions of sulfur cave-dwelling Poecilia mexicana.

PeerJ 2014 15;2:e490. Epub 2014 Jul 15.

Evolutionary Ecology Group, Goethe University of Frankfurt , Frankfurt am Main , Germany.

The Cueva del Azufre in Tabasco, Mexico, is a nutrient-rich cave and its inhabitants need to cope with high levels of dissolved hydrogen sulfide and extreme hypoxia. One of the successful colonizers of this cave is the poeciliid fish Poecilia mexicana, which has received considerable attention as a model organism to examine evolutionary adaptations to extreme environmental conditions. Nonetheless, basic ecological data on the endemic cave molly population are still missing; here we aim to provide data on population densities, size class compositions and use of different microhabitats. We found high overall densities in the cave and highest densities at the middle part of the cave with more than 200 individuals per square meter. These sites have lower H2S concentrations compared to the inner parts where most large sulfide sources are located, but they are annually exposed to a religious harvesting ceremony of local Zoque people called La Pesca. We found a marked shift in size/age compositions towards an overabundance of smaller, juvenile fish at those sites. We discuss these findings in relation to several environmental gradients within the cave (i.e., differences in toxicity and lighting conditions), but we also tentatively argue that the annual fish harvest during a religious ceremony (La Pesca) locally diminishes competition (and possibly, cannibalism by large adults), which is followed by a phase of overcompensation of fish densities.
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http://dx.doi.org/10.7717/peerj.490DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4106196PMC
August 2014
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