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The focus of my research is the study of fish in the genus Phoxinus distributed within Canada. I am especially interested in a hybrid species between P. eos and P. neogaeus. Hybrid Phoxinus and its parental species are widely distributed and abundant throughout Canada. The hybrid is, however, a rarity among vertebrates because it reproduces without sex. It is the only asexual vertebrate in North America with a wide (almost pan-continental) distribution. Like many asexual vertebrates, hybrid Phoxinus reproduce gynogenetically, requiring sperm from a male of either parental species to stimulate egg development but not for its genetic constitution.

Origin of hybrid Phoxinus

Discovering the age and origin of asexual vertebrate species will contribute valuable insight towards both understanding how sex is advantageous and appreciating the ways in which hybridization contributes to diversification. If all hybrid Phoxinus have a shared ancestry that can be traced back to a single ancient hybridization event, one must conclude that the persistence of asexual species does not depend on recurring origins, and that asexually reproducing species can, over a long time period, maintain fitness levels equivalent to analogous sexually reproducing species. If different hybrid Phoxinus lineages or populations have originated in different locations at different times, then the possibility remains that these asexual lineages persist at least partly due to ongoing (although potentially rare) hybridization events.

Coexistence of Asexual and Sexual Phoxinus

In several asexual taxa, reproduction requires mating with related sexual species to stimulate egg development, even though genetic material is not incorporated from the sexuals (gynogenesis). In cases where gynogens do not invest in male function, they can potentially have a two-fold competitive advantage over sexuals because the asexuals avoid the cost of producing males. If unmitigated, however, the competitive success of the asexuals would ultimately lead to their own demise, following the extinction of the sexual species that stimulate egg development. In collaboration with Sally Otto, I have studied a model to determine how gynogenetic and sexual individuals can coexist over the long-term within a community. Our model shows that coexistence can only occur if males prefer to mate with sexual females, and is facilitated if there is variation in how picky the males are. Also, our model predicts that coexistence should be facilitated if the gynogens are less fecund, have lower survival, or are generally less fit than the sexuals./p>

I have compared the fitness of asexual and sexual Phoxinus in a number of contexts. In collaboration with Colin Brauner, I used a test of repeat swimming performance as a fitness proxy to compare asexual Phoxinus to its sexually reproducing host species, P. eos and P. neogaeus. This test suggested that asexual Phoxinus are, at best, no worse at recovering from exhaustive swimming than the sexuals. I have also compared the fecundity and growth rate of asexual and sexual Phoxinus, showing that differences both fitness measures reflect differences in body size in a predictable manner. Finally, by counting Gyrodactylus parasites on the fins of these fish in the wild, I have shown that asexual Phoxinus harbour higher parasite loads than sexuals.