Evolution 2018: assortative mating, combinatorial speciation and genome dynamics

The Evolution conference in Montpellier is over, and as the sun, wine and great science become a memory, here is my recap of some conference highlights following on from a great first day:

A sea of scientists waiting for a plenary lecture. Photo: Alex Twyford.

Sharon Strauss (University of California Davis) gave the ASN Presidential Address entitled “Diversity and coexistence in close relatives, and reflections on 150 years of the ASN”. In her talk, she discussed the coexistence of closely related plant species, and whether phylogenetic similarity predicts ecological similarity. Her work centres on herbaceous plant communities at the UC Bodega Marine Reserve in California and combines reciprocal transplant experiments with phylogenetic analysis. One of her main results was a curvilinear relationship in species performance and genetic divergence, i.e. that species perform best in sites of conspecific taxa that share similar ecological preferences, and in sites of distant relatives where there is less competition. She also showed rare species advantage, reproductive character displacement, and fine-scale exclusion within the plant community. The second part of her talk discussed the history of the American Society of Naturalist, a topic covered by the Molecular Ecologist earlier this year.

Tim Birkhead (University of Sheffield) gave the SSE Stephen Jay Gould Prize lecture, entitled “The most perfect thing: the inside (and outside) of a bird’s egg”. This was a fascinating general natural history talk full of wonderful facts about eggs. I had no idea that an hour before most birds lay an egg it rotates 180 degrees and is then laid point first, or that wrynecks are indeterminate egg layers and if you remove eggs as they are produced they will go on to lay 70 eggs. However, Tim’s talk did attract feedback on Twitter for using his lecture to vocally criticise other scientist’s research.

Luke Harmon (University of Idaho) gave the SSB Presidential Address on “Scaling the tree of life”. The talk addressed the broad biological issue of why some parts of the tree of life are so species rich. He also introduced the technical issue of why phylogenetic studies often find high speciation in young clades (Rosenblum et al. 2012). Luke suggested we are in the golden age of time-calibrated phylogenies, where we can now address these types of questions in replicate systems. I’ll save the details here as it’s hard to summarise briefly macroevolutionary pulses and hierarchical models, but it seems clear we need to take a critical view of how we measure speciation rates across trees.

Hopi Hoekstra (Harvard University) gave the SSE Presidential Address entitled “The genetic basis of Behavioural Ecology”. This brilliant talk described the genetic basis of parental behaviour in Peromyscus mice. She showed that differential expression of vasopressin underlies differences in nest-building behaviour (Bendesky et al. 2017), with genetic transformation of key genes changing this behaviour. This talk was one of the best examples of how merging ecological observations, population genomics, and functional genetics can improve our understanding of the evolution of key traits.

Highlights from presentations given in the parallel sessions include:

  • David Marques (University of Bern) used genomic sequencing to trace the origin of Lake Constance sticklebacks. He revealed this population has a complex mosaic genome, and proposed the new term combinatorial speciation to explain the growing number of cases where admixture is involved in the establishment of new taxa.
  • Axel Myer (Universität Konstanz) presented the genetic basis of large-lips in a lake radiation of cichlid fish. Large lips are advantageous as they aid crevice feeding. He showed that a single major QTL underlies this phenotype, and suggested experimental manipulation of lip size (using gelatine!) could be used to test the fitness benefit of this extraordinary phenotype.
  • Lesley Lancaster (University of Aberdeen) showed that the damselfly Ischnura elegans is expanding into colder climates beyond the range predicted by climate change.
  • David Baum (University of Wisconsin–Madison) described how species definitions are ‘artistic’ and there is no single correct species taxonomy. He also introduced exclusivity factors (which build on concordance factors) as a new approach to improve objective species delimitation.
  • Andrew Leitch (Queen Mary University of London) presented ecological evidence that nitrogen and phosphorus are limiting in the wild and that N + P rich environments have species with larger genomes (Guignard et al. 2016). He included a back-of-the-envelope calculation that polyploid genomes must lose around 367bp per generation to explain extant genome sizes, and asked what selective pressures explain this process of diploidization.
  • Greg Owens (The University of British Columbia) showed the importance of knowing the parents in studies of hybrid speciation. A long-term study of artificial hybrids intending to recreate the hybrid sunflower species Helianthus annuus subspecies texanus (with proposed parents H. annuus and H. debilis) revealed selection on particular haplotypes. But sequencing of natural populations revealed other species are more likely to be contributing to the hybrid species than H. debilis.

Common themes from the talks I saw were assortative mating, chromosomal structure and recombination, and balancing selection. I’m expecting these topics to continue to feature heavily as genomic data from more study systems become available.

The conference finished with a wonderful evening at Abbaye de Valmagne, a 13th century abbey surrounded by vineyards.

The stunning Abbaye de Valmagne, Montpellier. Photos: Alex Twyford.

Looking forward to the next Evolution meeting in Providence Rhode Island!

References

Bendesky A, Kwon Y-M, Lassance J-M, et al. (2017) The genetic basis of parental care evolution in monogamous mice. Nature 544, 434.

Guignard MS, Nichols RA, Knell RJ, et al. (2016) Genome size and ploidy influence angiosperm species’ biomass under nitrogen and phosphorus limitation. New phytologist 210, 1195-1206.

Rosenblum EB, Sarver BA, Brown JW, et al. (2012) Goldilocks meets Santa Rosalia: an ephemeral speciation model explains patterns of diversification across time scales. Evolutionary Biology 39, 255-261.

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About Alex Twyford

Alex Twyford is a Research Fellow at the University of Edinburgh, and a Research Associate at the Royal Botanic Garden Edinburgh. He studies the ecology and evolution of plants. Twitter @alex_twyford.
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