Presentation Detail

SSB Symposium: Ernst Mayr Symposium

Martin, Christopher [1].

Novel trophic niches drive variable progress toward speciation within a pupfish adaptive radiation: integrating genomic-scale RAD sequencing with field measurements of a complex adaptive landscape.

Adaptive radiation is recognized by a rapid burst of phenotypic, ecological, and species diversification. However, it is unknown whether different species within an adaptive radiation evolve reproductive isolation at different rates. For my dissertation, I developed a case study of adaptive radiation in Cyprinodon pupfishes, integrating phylogenetic comparative methods,population genomics, field measurements of natural selection, functional morphology, and behavioral ecology. Cyprinodon exhibit a remarkable pattern of adaptation: despite their wide distribution from Massachusetts to Venezuela, adaptive radiation has occurred in only two places: the tiny Bahamian island of San Salvador and an isolated Yucatan lake. In each of these locations, multiple coexisting pupfish species with specialized feeding strategies have evolved from a generalist common ancestor within the past 10,000 years, such as a specialized scale-eater and a hard-shelled prey specialist with a novel nasal appendage on San Salvador Island. By constructing a phylogeny for Cyprinodontidae and comparing one and two-rate models of Brownian motion, I found that ecological novelty in these two adaptive radiations is driving exceptional rates of morphological diversification in trophic traits, up to 130 times faster than background rates in allopatric species.I next asked what mechanisms drive such extreme rates of morphological diversification? I measured a large portion of the adaptive landscape from the growth and survival of 1,865 F2 hybrids placed in field enclosures on San Salvador Island. I found that hybrid phenotypes corresponding to the abundant generalist species sit atop an isolated fitness peak separated by a valley from a higher fitness peak corresponding to the hard-shelled prey specialist species. These neighboring fitness peaks were separated by a large valley from hybrids resembling the scale-eater, indicating strong post-zygotic selection against scale-eater hybrids. Rates of gene flow among these species are consistent with this emerging estimate of the adaptive landscape. Based on 13,912 single-nucleotide polymorphisms (SNPs) genotyped across multiple lakes on San Salvador containing all three species, I found that the scale-eating specialist showed the lowest rate of gene flow and was monophyletic across lakes, whereas the durophage specialist repeatedly showed elevated rates of gene flow with the sympatric generalist population and clustered by lake. I conclude that the scale-eater is further along the speciation-with-gene-flow continuum than the durophage, perhaps because the scale-eating fitness peak is more distant on the adaptive landscape. Thus, the niche itself may also drive variable evolution of reproductive isolation within a sympatric adaptive radiation.

1 - University of California, Davis, Evolution & Ecology, One Shields Ave., Davis, CA, 95616, United States

Keywords:
ecological speciation
adaptive radiation
next-generation sequencing
genotyping-by-sequencing
reproductive isolation
evolutionary ecology
adaptive landscape
admixture
fitness landscapes
Natural selection
introgression.

Presentation Type: Symposium Presentation
Session: 210
Location: Ballroom 2/Cliff Lodge
Date: Sunday, June 23rd, 2013
Time: 9:00 AM
Number: 210003
Abstract ID:476
Candidate for Awards:Ernst Mayr Award