Genomic and behavioural mechanisms driving the evolution of a novel visual signal in smoky rubyspot damselflies

Sexually selected animal visual signals have long fascinated biologists and lay-people alike, and the processes by which novel signals evolve has long been an important area of research among biologists interested in sexual selection [1]. Yet, many important questions remain unanswered. One potential way forward is to leverage geographic variation in signal traits to examine the mechanisms that generate and maintain such variation. Smoky rubyspot damselflies (Hetaerina titia) vary both geographically and seasonally in the extent of wing pigmentation [2-3] (Fig. 1) and are therefore well suited to such an approach. Previous field research has investigated the adaptive value of dark wing pigmentation: darkly pigmented (‘melanic’) individuals experience relatively low rates of behavioural interference with other sympatric Hetaerina damselfly species [2-5]. Nevertheless, the evolutionary origins of this signal remain unknown.

In this studentship project, the candidate will carry out several studies on smoky rubyspot damselflies to elucidate the factors responsible for the evolution of this polyphenism including:

(1) How does phenotypic variation in wing pigmentation map on to patterns of gene expression? Given the continuous variation observed in the wing colouration of smoky rubyspots (Fig. 1), we can deduce that the variation in melanisation results from phenotypic plasticity. However, the genetic regions that mediate this plasticity are unknown, and may hold further clues to the environmental factors that impact developing wings.

(2) Have pre-existing sensory biases shaped the evolutionary trajectory of wing colour evolution? Although we have experimental evidence suggesting that the dark wing pigmentation did not initially evolve as a response to behavioural interference (i.e., through character displacement) [5], we know very little about the evolutionary origin of the polyphenism. One common pathway for the evolution of novel signals is that the receivers of such signals are already pre-disposed to respond to specific aspects of these signals [1,6]; yet, while this pathway has been well-studied in the context of female mate choice, few studies examine whether signals that impact male mate choice or intrasexual aggression might evolve via similar mechanisms.

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Image Captions

Fig. 1. Seasonal and geographic variation in the proportion of the hindwing with pigment in male H. titia, in representative photos (left), and based on photos submitted to iNaturalist.org (right).


To address these questions, the candidate will combine fieldwork at established field sites in Costa Rica and/or Mexico with genomic laboratory work in Durham, and subsequent bioinformatic analyses. In the field, they will collect and preserve specimens for subsequent RNA-seq analyses and conduct behavioural experiments to measure the impact of extensive wing melanisation on mate and competitor recognition (using established techniques [2,4-5]) in Pacific coast populations with low levels of wing pigmentation. In Durham, they will prepare libraries for RNA-seq, further annotate the existing genomic resources for smoky rubyspot damselflies, and conduct subsequent bioinformatic analyses.

Project Timeline

Year 1

Carry out fieldwork in Costa Rica to collect specimens for RNA-seq and begin behavioural experiments; train in methods for library prep and data analyses of RNA-seq data; attend NEOF workshop on RNA-seq analyses; visit co-supervisor in Glasgow

Year 2

Carry out second year of fieldwork in Costa Rica or Mexico (Oaxaca and/or Chiapas); prepare RNA-seq library and submit for sequencing; improve assembly and further annotation of smoky rubyspot genome. Attend UK-based scientific meeting.

Year 3

Submit first manuscript. Using whole-transcriptome dataset generated in year 2, conduct empirical analyses to identify loci associated with the magnitude of the seasonal polyphenism. Attend scientific meeting to present results.

Year 3.5

Complete and submit thesis, begin submitting remaining manuscripts for publication.

& Skills

The candidate will receive training in (1) field techniques for performing behavioural experiments with free-living damselflies, (2) wet lab protocols for preparation of RNA-seq libraries, (3) computational techniques for analysis of genomic and transcriptomic data, and (4) data management

References & further reading

[1] Broder, E.D., Elias, D.O., Rodríguez, R.L., Rosenthal, G.G., Seymoure, B.M. and Tinghitella, R.M., 2021. Evolutionary novelty in communication between the sexes. Biology Letters, 17(2), p.20200733.

[2] Drury, J.P., Anderson, C.N. and Grether, G.F., 2015. Seasonal polyphenism in wing coloration affects species recognition in rubyspot damselflies (Hetaerina spp.). Journal of Evolutionary Biology, 28(8), pp.1439-1452.

[3] Drury, J.P., Barnes, M., Finneran, A.E., Harris, M. and Grether, G.F., 2019. Continent‐scale phenotype mapping using citizen scientists’ photographs. Ecography, 42(8), pp.1436-1445.

[4] Drury, J.P., Okamoto, K.W., Anderson, C.N. and Grether, G.F., 2015. Reproductive interference explains persistence of aggression between species. Proceedings of the Royal Society B: Biological Sciences, 282(1804), p.20142256.

[5] Drury, J.P., Anderson, C.N., Cabezas Castillo, M.B., Fisher, J., McEachin, S. and Grether, G.F., 2019. A general explanation for the persistence of reproductive interference. The American Naturalist, 194(2), pp.268-275.

[6] Ryan, M.J., 2018. A Taste for the Beautiful. In A Taste for the Beautiful. Princeton University Press.

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