Abstract for presentation at Biodiversity Extinction Crisis Conference - A Pacific Response

Management practices often aim to increase the level of gene flow by either: introducing animals from captive breeding programs, translocating of animals from abundant areas, or by increasing the chance of animals dispersing between populations by creating habitat corridors. These practices provide opportunity for the hybrid offspring of introduced and resident animals to experience either increased fitness via positive heterosis (hybrid vigour) or decreased relative fitness via negative heterosis (hybrid break down). There is very little quantitative data available to adequately assess whether heterosis is likely to be beneficial or detrimental to populations managed in these ways. Using Drosophila melanogaster populations, we conducted two experiments that simulate common management practices: firstly reintroduction/ translocation and secondly wildlife habitat corridors. We monitored the frequency, direction and magnitude of heterosis over a biologically relevant time scale (0-32 generations) to assess the relative risks and benefits of heterosis. We also monitored population reproductive success (number adults produced from controlled crosses) to assess whether the populations were stable or in decline. Significant heterosis occurred in 18% of the reintroduction/translocation experiments. Positive and negative heterosis occurred at the equal frequencies. In the habitat corridor experiments, populations with moderate to high dispersal (1- 4% per generation) did not develop significant heterosis. However, 12.5% of the populations experiencing low dispersal (0.25% per generation) displayed significant heterosis. Again, positive heterosis occurred at an equal frequency to negative heterosis, confirming the results of the first experiment. We suggest that our ability to utilise positive heterosis as a tool to increase the viability of small, endangered populations is limited because there is an equal likelihood of encountering negative heterosis that may drive the population into further decline. However, population reproductive success is positively correlated with dispersal rate, suggesting that induced dispersal generally has a positive effect on populations.