The effect of hybridization on Killifish (Fundulus spp.) metabolic rate

Abstract

Interspecific hybridization occurs when two species successfully mate to produce offspring. This phenomenon is relatively common in nature and can produce hybrids with advantaged, disadvantaged, or intermediate physiology compared to parental species. To better understand the outcomes of hybridization, I studied two species of fish, the Banded Killifish (<i>Fundulus diaphanus</i>) and the Common Killifish (<i>F. heteroclitus</i>), and their inter-specific hybrids. In the wild, female <i>F. diaphanus</i> and male <i>F. heteroclitus</i> can naturally hybridize to produce all-female asexual clones. To compare the physiology of these Killifish hybrids to their parental species, I measured the resting metabolic rates (RMR) and maximal metabolic rates (MMR) of the three species to determine their aerobic scope (difference between RMR and MMR). I predicted that the hybrids would have an aerobic scope above that of <i>F. diaphanus</i> but below that of <i>F. heteroclitus</i>, as they display intermediate values in other physiological traits. The resting and maximal aerobic metabolic rates of Killifish caught from Porters Lake, Nova Scotia were measured using intermittent-flow respirometry. RMR was measured while fish were resting, after a short acclimation period, whereas MMR was measured after fish were swam to exhaustion using the chase method. It can be difficult to distinguish between <i>F. heteroclitus</i> and hybrids visually, so I also measured distinctive morphological traits and genotyped the mitochondrial DNA to confirm species identities. Unfortunately, I was unable to collect sufficient data for inter-specific MMR comparisons, but RMR data suggests that these Killifish hybrids have similar RMR to both parental species. To assess aerobic scope, additional MMR data is required.