MHC VARIATION IN THE ENDANGERED GILA TOPMINNOW.

Area of Science:

• Genetics
• Evolutionary Biology
• Conservation Biology

Background:

• The Major Histocompatibility Complex (MHC) plays a crucial role in immune responses to pathogens.
• Understanding MHC variation is vital for assessing the adaptive potential of endangered species.
• The Gila topminnow (Poeciliopis o. occidentalis) is an endangered species with limited remaining populations.

Purpose of the Study:

• To estimate the sequence variation of MHC genes in the remaining U.S. populations of the endangered Gila topminnow.
• To assess the genetic differentiation at MHC loci among these geographically isolated populations.
• To inform conservation and management strategies for this endangered species.

Main Methods:

• Analysis of MHC gene sequence variation in four distinct Gila topminnow watersheds.
• Use of single-stranded conformational polymorphism (SSCP) to genotype MHC alleles.
• Segregation analysis in families to confirm Mendelian inheritance of MHC alleles.

Main Results:

• One historically bottlenecked population was monomorphic for MHC variation.
• Another population exhibited five MHC alleles, with four unique to that group.
• Nine distinct MHC alleles were identified across the four populations, with high divergence and lack of shared alleles between some pairs.
• Amino acid level differentiation varied significantly between populations that did not share alleles.

Conclusions:

• Significant genetic differentiation at MHC loci exists among Gila topminnow populations.
• The unique MHC profiles suggest independent evolutionary trajectories and adaptive potentials.
• Separate conservation and management plans for each watershed are recommended due to high genetic divergence at this potentially adaptive gene.