Publications by authors named "Kathy Darragh"

8 Publications

  • Page 1 of 1

The Birth-and-Death Evolution of Cytochrome P450 Genes in Bees.

Genome Biol Evol 2021 Dec;13(12)

Department of Evolution and Ecology, University of California, Davis, California, USA.

The birth-and-death model of multigene family evolution describes how gene families evolve and diversify through duplication and deletion. The cytochrome P450s are one of the most diverse and well-studied multigene families, involved in both physiological and xenobiotic functions. Extensive studies of insect P450 genes have demonstrated their role in insecticide resistance. Bees are thought to experience toxin exposure through their diet of nectar and pollen, as well as the resin-collecting behavior exhibited by some species. Here, we describe the repertoire of P450 genes in the orchid bee Euglossa dilemma. Male orchid bees form perfume bouquets used in courtship displays by collecting volatile compounds, resulting in exposure to compounds known to be toxic. In addition, we conducted phylogenetic and selection analyses across ten bee species encompassing three bee families. We find that social behavior and resin collection are not correlated with the repertoire of P450 present in a bee species. However, our analyses revealed that P450 clades can be classified as stable and unstable, and that genes involved in xenobiotic metabolism are more likely to belong to unstable clades. Furthermore, we find that unstable clades are under more dynamic evolutionary pressures and exhibit signals of adaptive evolution. This work highlights the complexity of multigene family evolution, revealing that multiple factors contribute to the diversification, stability, and dynamics of this gene family. Furthermore, we provide a resource for future detailed studies investigating the function of different P450s in economically important bee species.
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http://dx.doi.org/10.1093/gbe/evab261DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8670302PMC
December 2021

Identification and Composition of Clasper Scent Gland Components of the Butterfly Heliconius erato and Its Relation to Mimicry.

Chembiochem 2021 Dec 8;22(23):3300-3313. Epub 2021 Oct 8.

Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.

The butterfly Heliconius erato occurs in various mimetic morphs. The male clasper scent gland releases an anti-aphrodisiac pheromone and additionally contains a complex mixture of up to 350 components, varying between individuals. In 114 samples of five different mimicry groups and their hybrids 750 different compounds were detected by gas chromatography/mass spectrometry (GC/MS). Many unknown components occurred, which were identified using their mass spectra, gas chromatography/infrared spectroscopy (GC/IR)-analyses, derivatization, and synthesis. Key compounds proved to be various esters of 3-oxohexan-1-ol and (Z)-3-hexen-1-ol with (S)-2,3-dihydrofarnesoic acid, accompanied by a large variety of other esters with longer terpene acids, fatty acids, and various alcohols. In addition, linear terpenes with up to seven uniformly connected isoprene units occur, e. g. farnesylfarnesol. A large number of the compounds have not been reported before from nature. Discriminant analyses of principal components of the gland contents showed that the iridescent mimicry group differs strongly from the other, mostly also separated, mimicry groups. Comparison with data from other species indicated that Heliconius recruits different biosynthetic pathways in a species-specific manner for semiochemical formation.
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http://dx.doi.org/10.1002/cbic.202100372DOI Listing
December 2021

A novel terpene synthase controls differences in anti-aphrodisiac pheromone production between closely related Heliconius butterflies.

PLoS Biol 2021 01 19;19(1):e3001022. Epub 2021 Jan 19.

Department of Zoology, University of Cambridge, Cambridge, United Kingdom.

Plants and insects often use the same compounds for chemical communication, but not much is known about the genetics of convergent evolution of chemical signals. The terpene (E)-β-ocimene is a common component of floral scent and is also used by the butterfly Heliconius melpomene as an anti-aphrodisiac pheromone. While the biosynthesis of terpenes has been described in plants and microorganisms, few terpene synthases (TPSs) have been identified in insects. Here, we study the recent divergence of 2 species, H. melpomene and Heliconius cydno, which differ in the presence of (E)-β-ocimene; combining linkage mapping, gene expression, and functional analyses, we identify 2 novel TPSs. Furthermore, we demonstrate that one, HmelOS, is able to synthesise (E)-β-ocimene in vitro. We find no evidence for TPS activity in HcydOS (HmelOS ortholog of H. cydno), suggesting that the loss of (E)-β-ocimene in this species is the result of coding, not regulatory, differences. The TPS enzymes we discovered are unrelated to previously described plant and insect TPSs, demonstrating that chemical convergence has independent evolutionary origins.
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http://dx.doi.org/10.1371/journal.pbio.3001022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7815096PMC
January 2021

Clustering of loci controlling species differences in male chemical bouquets of sympatric butterflies.

Ecol Evol 2021 Jan 16;11(1):89-107. Epub 2020 Dec 16.

Department of Zoology University of Cambridge Cambridge UK.

The degree to which loci promoting reproductive isolation cluster in the genome-that is, the genetic architecture of reproductive isolation-can influence the tempo and mode of speciation. Tight linkage between these loci can facilitate speciation in the face of gene flow. Pheromones play a role in reproductive isolation in many Lepidoptera species, and the role of endogenously produced compounds as secondary metabolites decreases the likelihood of pleiotropy associated with many barrier loci. butterflies use male sex pheromones to both court females (aphrodisiac wing pheromones) and ward off male courtship (male-transferred antiaphrodisiac genital pheromones), and it is likely that these compounds play a role in reproductive isolation between species. Using a set of backcross hybrids between and , we investigated the genetic architecture of putative male pheromone compound production. We found a set of 40 significant quantitative trait loci (QTL) representing 33 potential pheromone compounds. QTL clustered significantly on two chromosomes, chromosome 8 for genital compounds and chromosome 20 for wing compounds, and chromosome 20 was enriched for potential pheromone biosynthesis genes. There was minimal overlap between pheromone QTL and known QTL for mate choice and color pattern. Nonetheless, we did detect linkage between a QTL for wing androconial area and , a color pattern locus known to play a role in reproductive isolation in these species. This tight clustering of putative pheromone loci might contribute to coincident reproductive isolating barriers, facilitating speciation despite ongoing gene flow.
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http://dx.doi.org/10.1002/ece3.6947DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7790645PMC
January 2021

Species specificity and intraspecific variation in the chemical profiles of butterflies across a large geographic range.

Ecol Evol 2020 May 3;10(9):3895-3918. Epub 2020 Apr 3.

Department of Zoology University of Cambridge Cambridge UK.

In many animals, mate choice is important for the maintenance of reproductive isolation between species. Traits important for mate choice and behavioral isolation are predicted to be under strong stabilizing selection within species; however, such traits can also exhibit variation at the population level driven by neutral and adaptive evolutionary processes. Here, we describe patterns of divergence among androconial and genital chemical profiles at inter- and intraspecific levels in mimetic butterflies. Most variation in chemical bouquets was found between species, but there were also quantitative differences at the population level. We found a strong correlation between interspecific chemical and genetic divergence, but this correlation varied in intraspecific comparisons. We identified "indicator" compounds characteristic of particular species that included compounds already known to elicit a behavioral response, suggesting an approach for identification of candidate compounds for future behavioral studies in novel systems. Overall, the strong signal of species identity suggests a role for these compounds in species recognition, but with additional potentially neutral variation at the population level
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http://dx.doi.org/10.1002/ece3.6079DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7244815PMC
May 2020

A major locus controls a biologically active pheromone component in Heliconius melpomene.

Evolution 2020 02 20;74(2):349-364. Epub 2020 Jan 20.

Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, United Kingdom.

Understanding the production, response, and genetics of signals used in mate choice can inform our understanding of the evolution of both intraspecific mate choice and reproductive isolation. Sex pheromones are important for courtship and mate choice in many insects, but we know relatively little of their role in butterflies. The butterfly Heliconius melpomene uses a complex blend of wing androconial compounds during courtship. Electroantennography in H. melpomene and its close relative Heliconius cydno showed that responses to androconial extracts were not species specific. Females of both species responded equally strongly to extracts of both species, suggesting conservation of peripheral nervous system elements across the two species. Individual blend components provoked little to no response, with the exception of octadecanal, a major component of the H. melpomene blend. Supplementing octadecanal on the wings of octadecanal-rich H. melpomene males led to an increase in the time until mating, demonstrating the bioactivity of octadecanal in Heliconius. Using quantitative trait locus (QTL) mapping, we identified a single locus on chromosome 20 responsible for 41% of the parental species' difference in octadecanal production. This QTL does not overlap with any of the major wing color or mate choice loci, nor does it overlap with known regions of elevated or reduced F . A set of 16 candidate fatty acid biosynthesis genes lies underneath the QTL. Pheromones in Heliconius carry information relevant for mate choice and are under simple genetic control, suggesting they could be important during speciation.
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http://dx.doi.org/10.1111/evo.13922DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7027519PMC
February 2020

Male pheromone composition depends on larval but not adult diet in .

Ecol Entomol 2019 Jun 16;44(3):397-405. Epub 2019 Jan 16.

Department of Zoology University of Cambridge Cambridge U.K.

1. Condition-dependent traits can act as honest signals of mate quality, with fitter individuals being able to display preferred phenotypes. Nutrition is known to be an important determinant of individual condition, with diet known to affect many secondary sexual traits. 2. In butterflies, male chemical signalling plays an important role in female mate choice. Potential male sex pheromone components have been identified previously, although it is unclear what information they convey to the female. 3. In the present study, the effect of diet on androconial and genital compound production is tested in male . To manipulate larval diet, larvae are reared on three different host plants: , the preferred host plant, Passiflora vitifolia and Passiflora platyloba. To manipulate adult diet, adult butterflies are reared with and without access to pollen, a key component of their diet. 4. No evidence is found to suggest that adult pollen consumption affects compound production in the first 10 days after eclosion. There is also a strong overlap in the chemical profiles of individuals reared on different larval host plants. The most abundant compounds produced by the butterflies do not differ between host plant groups. However, some compounds found in small amounts differ both qualitatively and quantitatively. Some of these compounds are predicted to be of plant origin and the others synthesised by the butterfly. Further electrophysiological and behavioural experiments will be needed to determine the biological significance of these differences.
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http://dx.doi.org/10.1111/een.12716DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6563479PMC
June 2019

Male sex pheromone components in butterflies released by the androconia affect female choice.

PeerJ 2017 7;5:e3953. Epub 2017 Nov 7.

Department of Zoology, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom.

Sex-specific pheromones are known to play an important role in butterfly courtship, and may influence both individual reproductive success and reproductive isolation between species. Extensive ecological, behavioural and genetic studies of butterflies have made a substantial contribution to our understanding of speciation. Male pheromones, although long suspected to play an important role, have received relatively little attention in this genus. Here, we combine morphological, chemical and behavioural analyses of male pheromones in the Neotropical butterfly First, we identify putative androconia that are specialized brush-like scales that lie within the shiny grey region of the male hindwing. We then describe putative male sex pheromone compounds, which are largely confined to the androconial region of the hindwing of mature males, but are absent in immature males and females. Finally, behavioural choice experiments reveal that females of , and strongly discriminate against conspecific males which have their androconial region experimentally blocked. As well as demonstrating the importance of chemical signalling for female mate choice in butterflies, the results describe structures involved in release of the pheromone and a list of potential male sex pheromone compounds.
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http://dx.doi.org/10.7717/peerj.3953DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5680698PMC
November 2017
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