Partitioning the Effects of Selection and Immigration in Small Populations

William Marsh Rice University, Houston TX

Investigators

Abstract

The role of immigration in rescuing a population from the threat of extinction remains to be tested in a comprehensive experiment. By exploiting the amenability of the housefly for large-scale long-term experiments, the effects of immigration and selection on the survival of persistently small populations will be examined. Replicate metapopulations (i.e., interacting sets of small subpopulations) will be constructed. Over the course of 20 generations, each metapopulation will be managed under one of six specific treatments for immigration and selection effects. For the selection treatments, only the adults with the highest reproductive activity will be allowed to contribute offspring to the next generation. For the immigration treatments, members from one subpopulation will be allowed to breed in another subpopulation. Measures will be made on reproductive activity and on the genetic variation for molecular and complex traits to assess the threat of extinction. The central hypothesis is that a low level of immigration will bolster the selection response for higher mating activity and rescue subpopulations from inbreeding depression. In agricultural programs to select for economically important traits and in efforts to save endangered species, immigration is commonly used to relieve the detrimental effects of inbreeding. Recent studies in laboratories and in nature, however, have identified gaps in our understanding of the genetic complexities of near-extinction events. This large-scale long-term experiment is uniquely designed to explain how populations in nature, agriculture, laboratories, and conservation projects escape the threat of extinction.