“Wild at Heart”: maintaining genetic diversity in an endangered species using alternative breeding and rearing strategies

Authors: Megan J. Osborne, Thomas F. Turner

Year: 2012 (xliv)

Abstract

Wild at heart’ : The endangered Rio Grande silvery minnow persists as a remnant population in a highly fragmented and regulated arid-land river system. The species is subject to dramatic fluctuations in density hence, captive breeding, rearing and refugial populations have become central elements for conservation of this species. The captive propagation and augmentation plan for silvery minnow seeks to maintain a strong connection between the wild and captive/refugial populations. For example, eggs are collected from natural spawning events and reared in protective custody and then released to the wild at a less vulnerable life stage. These fish are also used as a broodstock. Unlike ‘zoo-based’ breeding programs, which may select individuals for mating based on measures such as those that reduce average relatedness (as a way to maximize genetic diversity), the breeding program for Rio Grande silvery minnow incorporates group spawning with randomly selected individuals. In this study, genetic outcomes in addition to measures of productivity (number of eggs and viability) were compared between three mating designs currently in use for this species. Measures of genetic diversity did not differ significantly across mating designs nor did the number of eggs produced. The percentage of viable eggs was significantly greater in the environmentally-induced communal spawn compared to the alternative strategies. We also present results of 15 years of genetic monitoring for the species which shows that augmentation of the wild population with captive reared and/or bred individuals has buffered the population against catastrophic losses of genetic diversity that are predicted to coincide with periods of extremely low population density.