IAP-24-076
The evolution of reproductive isolation in rubyspot damselflies
For speciation to occur, reproductive isolation must evolve between diverging lineages. Consequently, the evolutionary dynamics of traits involved in reproductive isolation are the focus of much research in the field of speciation. In this project, the student will study rubyspot damselflies in the field and lab to test hypotheses about the behavioural and genomic mechanisms leading to reproductive isolation in this lineage, including:
(1) How have mate recognition behaviours coevolved with sexual signals?
Several different mechanisms have been proposed linking divergence in reproductive traits to isolation. For instance, geographical differences in selection pressures may lead to divergence in reproductive traits driven by local adaptation. In contrast, some theory predicts that differences between populations arise simply because of the random order in which beneficial mutations occur [1,2,3].
One way to test these hypotheses is to study geographic variation in reproductive traits. Smoky rubyspot damselflies (Hetaerina titia) vary both geographically and seasonally in the extent of their sexual signal, wing pigmentation [4,5] (Fig. 1) and are therefore well suited to such an approach. Recent work from our lab has revealed that Pacific and Atlantic forms of H. titia split ~3.5Ma and exhibit reproductive isolation at a newly discovered site where they both coexist, suggesting that this lineage is at an advanced stage of the speciation continuum.
Through fieldwork across a network of sites in Costa Rica, Mexico, and/or the United States, the student will conduct behavioural experiments to quantify the role of wing colour in mate recognition and competitor recognition of territorial males. The student will also use an archive of observational data on naturally occurring matings to characterise female mate recognition.
(2) How does competition between species influence the dynamics of reproductive isolation?
A widely accepted model of speciation in damselflies posits that the evolution of reproductive isolation predates secondary contact [6,7]—in other words, sexual or competitive exclusion prevents species from coexisting before sufficient reproductive isolation has evolved. An alternative hypothesis is that selection on traits that mediate interactions between species in sympatry after they meet again in secondary contact (i.e., character displacement) enables coexistence.
A key trait influencing isolation in damselflies is genital morphology, such as the highly variable claspers that males use to grasp females during mating (Fig. 2). To test for character displacement, the student will characterise clasper morphology of males across a network of sites and compare patterns in sympatry vs. allopatry.
Genome-wide data provide powerful insights into the processes leading to reproductive isolation. To determine whether the genomic architectures that mediate speciation and the selective processes that generate reproductive isolation in Hetaerina evolve in response to interactions with other species, the student will scan resequenced genomes from individuals of each lineage in both sympatric and allopatric populations and use advanced scans for outlier loci to identify candidate genes and genetic architecture associated with character displacement [8]. This will enable tests of the role of regulatory vs. coding variation, and involvement of structural variants such as inversions, in the origins of reproductive isolation and character displacement.
Click on an image to expand
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).,Fig 2. Male clasper variation in two lineages of H. titia, (left: Atlantic lineage, right: Pacific lineage, middle panel: dorsal view of claspers, side panel: lateral view of claspers)
Methodology
In this project, the student will conduct phenotype manipulation experiments [9] to quantify how male mate recognition and competitor recognition are influenced by wing pigmentation across a network of populations of at established study sites in Costa Rica, Mexico, and the United States. In addition, the student will visit the drainage where Pacific and Atlantic forms of smoky rubyspot damselflies have recently been found in sympatry to collect further specimens for analyses. In Durham, the student will use microscopy techniques [10] to quantify variation in male clasper shape, conduct lab work to prepare samples for whole genome sequencing, and bioinformatics to identify genetic variants and perform association and functional assessments of loci implicated in reproductive isolation.
Project Timeline
Year 1
Carry out fieldwork in Mexico to collect specimens in sympatric drainage (in Oaxaca) and conduct first round of phenotype manipulation experiments; train in methods for library prep and data analyses of genome data; train in microscopy and morphometric analyses methods
Year 2
Carry out phenotype manipulation experiments in Costa Rica and/or the United States; conduct analyses of field experiments and begin analyses of archival data to characterise female mate recognition. Begin analyses clasper shape data; visit to co-supervisor in St Andrews to begin building approach for analysing genomic data; Attend UK-based scientific meeting
Year 3
Submit first manuscript based on field experiments. Conduct empirical analyses on whole-genome data to identify putative targets of character displacement. Attend international conference (e.g., The Evolution Meeting in San Juan, Puerto Rico) to present results.
Year 3.5
Complete and submit thesis, begin submitting remaining manuscripts for publications.
Training
& Skills
The candidate will receive training in (1) behavioural fieldwork on aquatic insects, (2) morphometric analyses, (3) wet lab protocols for genome libraries, (4) computational techniques for analysis of genomic and transcriptomic data, and (5) data management
This project will build a strong and diverse toolset that can readily be employed by the future evolutionary ecologist. The IAPETUS2 program itself has been developed to build a strong foundation of transferable skills and involves an individual postgraduate certification and several cohort training opportunities. The student will also gain a strong foundation in bioinformatics and statistical analyses using sophisticated computational resources, including working at the command line (e.g. computer programming) in R and other programs. Through writing scientific publications and the thesis, as well as attendance at national and international meetings, the student will develop excellent communication and networking skills.
The student will be primarily based in the Biosciences Department at Durham University under the supervision of Dr Drury. The department has a strong track record in the fields of ecology and evolution, and a friendly and collegial environment. We also host an Ecology Evolution and Environment seminar series with talks from local and international speakers, providing many opportunities for networking. The University offers workshops on transferable skills, such as time management, team working, and leadership skills. Liaison with the co-supervisor at St Andrews will facilitate further networking and training opportunities.
References & further reading
1. Ryan, M. J. & Cummings, M. E. Perceptual biases and mate choice. Annu Rev Ecol Evol Syst 44, 437–459 (2013).
2. Rundle, H. D. & Rowe, L. The contribution of sexual selection to ecological and mutation-order speciation. Evolution 72, 2571–2575 (2018).
3. Mendelson, T. C., Martin, M. D. & Flaxman, S. M. Mutation-order divergence by sexual selection: diversification of sexual signals in similar environments as a first step in speciation. Ecol. Lett. 17, 1053–1066 (2014).
4. Drury, J. P., Anderson, C. N. & Grether, G. F. Seasonal polyphenism in wing coloration affects species recognition in rubyspot damselflies (Hetaerina spp.). J Evol Biol 28, 1439–1452 (2015).
5. Drury, J. P., Barnes, M., Finneran, A. E., Harris, M. & Grether, G. F. Continent-scale phenotype mapping using citizen scientists’ photographs. Ecography 42, 1436–1445 (2019).
6. Paulson, D. R. Reproductive isolation in damselflies. Syst Biol 23, 40–49 (1974).
7. Wellenreuther, M. & Sánchez-Guillén, R. A. Nonadaptive radiation in damselflies. Evol Appl 9, 103–118 (2016).
8. Yusuf, L. H., Pascoal, S., Moran, P. A. & Bailey, N. W. Testing the genomic overlap between intraspecific mating traits and interspecific mating barriers. Evol Lett (2024) doi:10.1093/evlett/qrae042.
9. Drury, J. P., Okamoto, K. W. K. W., Anderson, C. N. C. N. & Grether, G. F. G. F. Reproductive interference explains persistence of aggression between species. Proceedings of the Royal Society B 282, 20142256 (2015).
10. Vega-Sánchez, Y. M., Mendoza-Cuenca, L. & González-Rodríguez, A. Morphological variation and reproductive isolation in the Hetaerina americana species complex. Sci Rep 12, 1–10 (2022).
