Technical Report

Genetic Consequences of Supportive Breeding in the Endangered Rio Grande Silvery Minnow (Hybognathus amarus): Genetic Evaluation of Wild and Captively Reared and Propagated Stocks, 1999-2004

URL: https://webapps.usgs.gov/mrgescp/documents/Turner%20and%20Osborne_Genetic%20Consequences%20of%20Supportive%20Breeding%20in%20the%20Endangered%20RGSM%20%28Hybognathus%20amarus%29%20Genetic%20Evaluation%20of%20Wild%20and%20Captively%20Reared%20and%20Propagated%20Stocks%2C%201999-2004.pdf

Date: 2004/01/01

Author(s): Turner T.F., Osborne M.J.

Publication: Report prepared for U.S. Bureau of Reclamation, 33 p.

Abstract:

The genetic effects of artificial propagation and captive-rearing of wild-caught Rio Grande silvery minnow eggs were evaluated. The primary aim of this study was to determine whether these two methods of supportive breeding captured the genetic variation and levels of heterozygosity that were present in the remaining ‘wild’ Rio Grande silvery minnow population. This aim was addressed by examining variation at ten microsatellite loci and a mitochondrial DNA locus for seven generations of wild Rio Grande silvery minnow, five stocks of captively spawned and reared fish and five stocks of adults reared from wild-caught eggs. The principle findings of this study were:

i) Two dramatic losses of allelic diversity have occurred in the ‘wild’ (i.e., sampled in the Rio Grande proper) Rio Grande silvery minnow population. These losses followed major declines in abundance of Rio Grande silvery minnow in the wild.

ii) A supportive breeding program that uses wild caught-eggs better reflects the levels of genetic diversity than one that relies on captive spawning. Supplementation of the wild population with adults reared from salvaged eggs appears to have slowed the loss of allelic diversity in the wild population. However, heterozygosity has declined in stocks reared from wild-caught eggs.

iii) The genetic effects of captive spawning are determined primarily by the breeding strategy that is used. The combination of communal spawning (where there is the potential for unequal parental contributions), small broodstocks and unequal sex ratios has resulted in loss of allelic diversity in these stocks compared to wild fish or fish reared from wild-caught eggs. There has also been a slight decline in observed heterozygosity when compared to the wild population. Collaborative work with ABQ Biopark in FY 2004 will compare genetic diversity of progeny from one to one paired matings and communal spawns to identify the optimal strategy from a genetic perspective.