title: Repeat swimming performance and its implications for inferring the relative fitness of asexual hybrid dace (Pisces: Phoxinus) and their sexually reproducing parental species.
abstract: While theories explaining the evolution and maintenance of sex are abundant, empirical data on the costs and benefits of asexual relative to sexual reproduction are less common. Asexually reproducing vertebrates, while few, provide a rare opportunity to measure differences in fitness between asexual and sexual species. All known asexually reproducing vertebrates are of hybrid origin, and hybrid disadvantage (i.e., reduced hybrid fitness) is thought to facilitate long-term coexistence between asexual and sexual species. We used repeat swimming performance as a proxy for fitness to compare the fitness of asexual hybrid dace (Pisces: Phoxinus) and their sexually reproducing parental species, finescale dace (Phoxinus neogaeus) and northern redbelly dace (Phoxinus eos). We tested the prediction that, given the widespread coexistence of these hybrid and parental dace, the parental species should show equivalent and perhaps superior repeat performance relative to hybrids. A repeat constant acceleration test (U(max)) was conducted at both acclimation temperature (16 °C) and at an elevated temperature (25 °C) to simulate the combined influence of a repeat swim and acute temperature change that fish might experience in the wild. The asexual hybrids performed more poorly than at least one of the parental species. There was a negative effect of temperature on repeat swimming performance in all fish, and the repeat performance of hybrids was more severely affected by temperature than that of finescale dace. No difference in the effect of temperature on repeat performance was detected between hybrids and northern redbelly dace. These results suggest that hybrids suffer physiological costs relative to the parentals or at least that the hybrids do not gain advantage from hybrid vigor, which probably contributes to the coexistence of asexual and sexual species in this system.
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T1Z4, Canada. mee@zoology.ubc.ca
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Mee
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Brauner
authors.forename: Eric B
authors.initials: EB
authors.lastname: Taylor
mesh_terms: D000416:Alberta; D000818:Animals; D003530:Cyprinidae / Q000502:physiology*; D005260:Female; D056084:Genetic Fitness; D006823:Hybrid Vigor; D006824:Hybridization, Genetic; D009864:Ontario; D012100:Reproduction, Asexual; D013550:Swimming; D013696:Temperature