Conservation Genetics of Six Species of GenusDionda(Cyprinidae) in the Southwestern United States

Abstract

We examined allelic variation at nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA in 10 geographic samples representing 6 nominal species of the cyprinid genus Dionda. Species of Dionda are found in springs and spring-fed headwaters in the southwestern United States and Mexico and are of particular interest to conservation and management, in part because of their limited distribution and habitat specificity, and in part as indicator species of habitat quality. All 10 samples examined appear to be discrete, demographically independent populations, with greater observed FST values between or among samples within species (0.123–0.280) than threshold values above which demographic independence is indicated. All 10 exhibited microsatellite and mtDNA variation comparable to or lower than that found in other cyprinids considered to be threatened or endangered; across microsatellites, average number of alleles across populations ranged from of 2.09 to 9.76, allelic richness from 2.24 to 8.45, and gene diversity from 0.0211 to 0.606; for mtDNA, the number of haplotypes across populations ranged from 1 to 14. Estimates of historical and present-day genetic demography indicated that all 10 populations have experienced order-of-magnitude declines in effective population size, with lower bounds of time intervals for the declines in 9 of the populations ranging from 6 to 65 years. Estimates of average long-term effective population size (536 in Dionda argentosa from San Felipe Creek to 2335 in D. texensis) and effective number of breeders (22 in D. flavipinnis from Fessenden Spring to 555 in D. diaboli from Devils River) also indicated recent declines in effective size, and at least 5 of the populations appear to have undergone recent, severe bottlenecks (mean Mc range 0.806–0.848, P value range 0.000–0.0350). The observation that all 10 populations are demographically independent indicates that local extirpations likely would not be replaced by new migrants and that loss of any of the populations would represent loss of a unique genetic entity. Conservation recommendations for each of the populations are briefly discussed.