9322655 Hedrick In this research, the PI's will examine inbreeding depression over two generations for several components of fitness in different populations of the endangered species, the Gila topminnow. In a series of experiments, the PI's will compare fitness values between progeny of sib matings and the progeny of random matings between individuals within the same population. Next, the PI's will measure the effect of crossing individuals from different populations on the same fitness components. Populations of topminnows were thought to undergo periodic oscillations with population bottlenecks, local extinctions, recolonizations, and even crossing between populations. As a result, it is important in determining the pattern of genetic variation over populations whether crosses between individuals from different populations are no different than within population crosses, are heterotic, or show outbreeding depression. These crosses should give information on whether the different populations are fixed for detrimental alleles that can be covered up by outcrossing or are so different that F1 and F2 progeny have reduced fitness. The major histocompatibility complex may be the most important adaptive genetic region in mammals, conferring resistance to various pathogens. Recent work in fish has demonstrated that there is extensive variation for MHC in several species and that the pattern of variation is consistent with that in mammals. The PI's will document the extent and pattern of MHC in the four metapopulations of the Gila topminnow to determine if this species, which is fixed for allozymic variation in all populations except one, has variation in this important adaptive region. %%% The primary principles of conservation genetics are related to inbreeding depression and the retention of potentially adaptive genetic variation. It is therefore of fundamental importance to characterize both the extent of inbreeding depression and adaptive genetic variation in particular endangered species. In this study, the PI's have a unique opportunity to measure these values in the endangered Gila topminnow which exists in only four natural populations in sub-basins of springs and headwater streams in Arizona. In addition, this research will add further information on variability in the major histocompatibility complex which has received only limited attention in fish. ***
