Grantee Research Project Results
Genetic Differentiation in Metapopulations: Effects of Demographic Characteristics, Extinction, Recolonization Mode, and Number of ColonistsEPA Grant Number: U915027
Title: Genetic Differentiation in Metapopulations: Effects of Demographic Characteristics, Extinction, Recolonization Mode, and Number of Colonists
Investigators: McMillan, Amy M.
Institution: University of Kansas
EPA Project Officer: Edwards, Jason
Project Period: January 1, 1996 through July 26, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996)
Research Category: Fellowship - Molecular Biology/Genetics , Academic Fellowships , Biology/Life Sciences
As habitat destruction increases, more populations will become subdivided into smaller units connected by migration. The genetic structure resulting from demographic and evolutionary processes in these metapopulations is of great interest. This study used two different model systems to explore the genetic and evolutionary consequences of population fragmentation.Approach:
First, the population genetic structure of an apiculture pest, the greater wax moth, was quantified with Wright's F-statistics. Wax moths naturally occur in discrete populations because they are dependent on beehives. Some populations probably experience extinction as hive resources are expended, and the commercial movement of beehives in the United States may enhance wax moth dispersal and colonization. Populations from Kansas, Alabama, and Louisiana were surveyed for allozymic variability. Data from three polymorphic allozymes indicated significant differentiation of all populations sampled (average FST = 0.118 ± 0.004) and Kansas populations (average FST = 0.164 ± 0.013). This study suggests dispersal of greater wax moths is limited in the scale studied, and new colonies are probably derived from few local sources.
Second, replicated laboratory metapopulations of Drosophila melanogaster were used to examine the effects of extinction and recolonization on metapopulation genetic structure. Genetic structure was quantified over 21 generations for a continuous population and five metapopulations; persistent (no extinction) and high or low extinction followed by propagule pool colonization (colonists derived from a single demes). A priori expectations were that continuous populations would be least differentiated followed by high- and low-extinction migrant pool, persistent, and low- and high-extinction propagule pool the most differentiated. Colonist number was varied in another small experiment with the prediction that metapopulations with fewer colonists would become more differentiated. The data fit colonist number predictions more closely than extinction/recolonization predictions. Three phenotypic markers exhibited different patterns of differentiation, and selection may have played a role in these patterns. Fluctuating variables (i.e., migrant number, population size) also may have influenced these results. Metapopulation replicates were variable, suggesting that conclusions about natural metapopulation differentiation should carefully be considered. More replicated studies are necessary to understand the process of differentiation in metapopulations.Supplemental Keywords:
fellowship, metapopulations, genetics differentiation, habitat, habitat destruction, populations, Drosophila melanogaster, genetic structure.