ROMAN YUKILEVICH

Ph.D., Stony Brook University, 2008.
Department of Ecology and Evolution: Advisor John R. True.

General Research

Publications

Funding

Collaborations

General Research:

My major research interests are broadly focused on the topic of speciation. In particular, I see two fundamental questions in the field of speciation as of central importance and yet still relatively unresolved.

First, the evolution of premating isolation is arguably the most important aspect of speciation in nature. Not only do we find that during the early stages of speciation premating mechanisms such as sexual isolation are almost always the first to evolve and are the strongest in sympatric taxa (see Coyne and Orr 1989), but from the point of view of theory, speciation with only postzygotic isolation and no prezygotic isolation is an evolutionary unstable situation in sympatry. Such a scenario would lead to eventual genetic swamping/extinction of one of the incipient species (e.g. see Yukilevich and True 2006). Thus I have very strong interests in studying sexual isolation at all stages of the evolutionary process ranging from incipient divergence in mating preferences and mating cues to reinforcement speciation after secondary contact. My primary interest in this field is to study natural populations that can serve as specific models for testing broader conceptual problems. The strength of my research program stems from understanding the complete picture from ecological and biogeographical patterns of divergence to laboratory study of genetics and phenotypic variation of sexual isolation. I am presently working on two rapidly-evolving Drosophila systems that address different aspects of this research program: The Caribbean D. melanogaster system and the D. athabasca system (see below).

Second, while virtually all speciation is inherently epistatic (i.e. sexual or developmental incompetabilities between species arise from negative interactions between alleles at different loci governing these traits), I am particularly interested in the broader role of epistasis in speciation. Much of my interest is to develop and improve on ideas of earlier thinkers such as Sewall Wright and others as to how epistatic interactions within local populations, gene flow between populations and selection lead to speciation and other evolutionary outcomes. In the light of what we are beginning to learn about genomic evolution, genetic networks underlying phenotypes and the ubiquity of population structure in space and time, it is becoming increasingly difficult to ignore these global interactions in evolutionary biology. At present, most of my research in this field is theoretical, but my aim is to make explicit predictions that one can test with natural and laboratory populations (see below).

The Caribbean Drosophila melanogaster System

My recent work has revealed that the Caribbean populations of D. melanogaster are in the process of divergence in morphology, pheromones and courtship behaviors from mainland US populations. Most interestingly, these populations are also showing evidence of early stages of incipient sexual isolation. Because this system is geographically distinct from the well-known case of sexual isolation between Zimbabwe and cosmopolitan D. melanogaster populations, it is of particular interest to understand its origins and its genetic basis. As a result, the Caribbean system is a model of how multiple geographical cases of sexual isolation evolve in a single, widespread or closely-related species, akin to similar “parallel cases of speciation” in sticklebacks (e.g. Dolph Schlutter) and phytophogous insects (e.g. Daniel Funk, Patrik Nosil).

Desat-2 locus allele frequency cline across US-Caribbean.

Relationships between sexual isolation and other distances across the US-Caribbean system.

Present work is focusing on the population genomics and genetics of the Caribbean populations in the context of North American-African ancestral divergence. This includes using a combination of traditional genetic markers and recent whole-genome sequencing technologies, such as SOLEXA and tiling arrays, to reveal the history and potential selective SNPs that differentiate Caribbean from US populations. To directly address whether the genetic basis of these parallel phenotypic cases of divergence are the same or different, I am mapping the relevant traits using high-throughput genotyping and mutagenesis. I am explicitly comparing the genetic architecture of mating preferences and cues between cosmopolitan-Zimbabwe and US- Caribbean systems in order to achieve this objective.

The Drosophila athabasca System

I am also investigating incipient sexual isolation and geographic divergence in the species complex D. athabasca, which is composed of three behavioral sub-species in northeast US and Canada that have likely diverged between 5,000-20,000 years ago. These races are nearly completely sexually isolated from one another and exhibit overlapping geographical ranges. I am presently performing behavioral, genetic and ecological studies in areas of allopatry versus sympatry to understand how these sub-species have diverged. The D. athabasca system is an excellent model system of a very general phenomenon among Drosophila species that shows strong and rapid sexual isolation in sympatry in the absence of any apparent intrinsic postzygotic isolation (Coyne and Orr 1989). Using this ecologically-informed system, I am testing alternative hypotheses for this pattern in order to resolve the relative role of reinforcement speciation versus other possible explanations.

Geographical range of D. athabasca. Map from Yoon and Aquadro 1994.

Affinis subroup flies (including athabasca) on slime fluxes of deciduous trees (Chicago), likely to be their natural breeding sites.

Spatially Explicit Computer Simulations of Speciation

Example of a simulation run in a panmictic population of long-term adaptation toward a fitness peak. Novel genotypes (and their mutations) are seen sweeping through the population, with their corresponding fitness effects, waiting times and frequencies in the population. Genetic and fitness variance is also shown.

Example of a simulation run using a multi-locus epistatic genetic network in a metapopulation system of 20 demes with gene flow. Several adaptive genotypes are seen spreading and competing across the landscape and eventually lead to incipient speciation in this simulated world.

Publications:

True, J. R. and R. Yukilevich.* Submitted. Mechanisms of incipient speciation between geographically isolated body color morphs of Drosophila elegans. *Authors contributed equally to the work. J. Evolutionary Biology.

Yukilevich, R., T. Turner, F. Aoki, S. Nuzhdin, and J. R. True. 2010. Patterns and processes of genome-wide divergence between North American and African Drosophila melanogaster. Genetics.186(1):219-239.

Yukilevich, R., and J. R. True. 2008b. African morphology, behavior and pheromones underlie incipient sexual isolation between US and Caribbean Drosophila melanogaster. Evolution. 62(11):2807-2828. PDF REPRINT

Yukilevich, R., and J. R. True. 2008a. Incipient sexual isolation among cosmopolitan Drosophila melanogaster populations. Evolution. 62(8):2112-2121. PDF REPRINT

Yukilevich, R., J. Lachance, F. Aoki, and J. R. True. 2008. Long-term adaptation of epistatic genetic networks. Evolution. 62(9):2215-2235. PDF REPRINT

Nosil, P. and R. Yukilevich. 2008. Mechanisms of reinforcement in natural and simulated polymorphic populations. Biol. J. Linn. Soc. 95:305-319. PDF REPRINT

Yukilevich, R., and J. R. True. 2006. Divergent outcomes of reinforcement speciation: the relative importance of assortative mating and migration modification. American Naturalist. 167(55):638-654. PDF REPRINT

Yukilevich, R. 2005. Dispersal evolution in fragmented habitats: the interplay between the tendency and ability to disperse. Evolutionary Ecology Research. 7(7):973-992. PDF REPRINT

Funding:

Postdoctoral Fellowship from University of Chicago (2008)

National Science Foundation: Dissertation Improvement Grant (2006)

Collaborations:

Sergey Nuzhdin Lab

Thomas Turner Lab

Patrick Nosil Lab

Norman Johnson

John True Lab

Fumio Aoki

Joe Lachance