NO BILATERAL ASYMMETRY IN WILD-CAUGHT, ENDANGERED POECILIOPSIS-OCCIDENTALIS-OCCIDENTALIS (GILA TOPMINNOWS)

A well-known example of a positive association between the level of ge netic variation and fitness in endangered species is the studies in Gi la topminnow. The work of Vrijenhoek and his colleagues showed lower v alues for four fitness correlates in laboratory-raised fish from a pop ulation that was monomorphic for all 25 allozyme loci examined (Monkey Spring) than for fish from a population that was heterozygous for two of the allozyme loci (Sharp Spring). Here, bilateral asymmetry in wil d-caught fish from these sites is examined to determine if the same en vironmental stressor (or one with similar effects) was present in natu ral populations of Gila topminnows. There were no differences for all three traits, lateral-line scales, pectoral-fin rays and pelvic-fin ra ys, previously found to be significantly different between Monkey Spri ng and Sharp Spring. This, coupled with our earlier finding that fish raised in our laboratory (where there is low mortality) had low bilate ral asymmetry, supports the hypothesis that some unknown, and perhaps unnatural, environmental factor in the Vrijenhoek laboratory was respo nsible for the differences observed in bilateral asymmetry between Mon key Spring and Sharp Spring.