Genetic monitoring and complex population dynamics: insights from a 12‐year study of the Rio Grande silvery minnow

Abstract

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 annual fluctuations in density. Since 2003, the wild population has been supplemented by hatchery-reared fish. We report on a 12-year (1999–2010) monitoring study of genetic diversity and effective population size (Ne) of wild and hatchery stocks. Our goals were to evaluate how genetic metrics responded to changes in wild fish density and whether they corresponded to the number and levels of diversity of hatchery-reared repatriates. Genetic diversity and all measures of Ne in the wild population did not correlate with wild fish density until hatchery supplementation began in earnest. Estimates of variance and inbreeding effective size were not correlated. Our results suggest source–sink dynamics where captive stocks form a genetically diverse source and the wild population behaves as a sink. Nevertheless, overall genetic diversity of silvery minnow has been maintained over the last decade, and we attribute this to a well-designed and executed propagation management plan. When multiple factors like environmental fluctuation and hatchery supplementation act simultaneously on a population, interpretation of genetic monitoring data may be equally complex and require considerable ecological data.

The emblematic minnows of the North American Great Plains: A synthesis of threats and conservation opportunities

“…This section is fragmented by three diversion dams (maximum fragment length 90 rkm) that are impassable in the upstream direction. In most years since 2003, the wild populations of Rio Grande silvery minnow have been augmented, primarily with fish reared from captive broodstock or from wild‐caught eggs hatched and reared in captivity before transfer to the wild (Osborne, Carson & Turner, ). Genetic monitoring of wild and captive stocks occurred in 1987 and annually since 1999.…”

“… Estimates of N e are small relative to abundances of the adult population (Aló & Turner, ; Osborne et al., ). Normally, N e is smaller than N c , the census population size (Palstra & Ruzzante, ), but this is exaggerated in Rio Grande silvery minnow in which some estimates of variance effective population size ( N eV < N e estimated from temporal variation in N c ) are <100 at times when N c is 10,000s.…”

Spatio‐temporal variation in parasite communities maintains diversity at the major histocompatibility complex class IIβ in the endangered Rio Grande silvery minnow

“…Data from neutral loci have also shown that over the species' current range, there is no population structure due to the drifting nature of Rio Grande silvery minnow eggs (Osborne et al . ). However, these studies do not allow for specific predictions about whether species harbour genetic diversity needed to respond to immunological stressors.…”

“…Since 2002, the Rio Grande silvery minnow population has been supported to varying degrees by augmentation (Osborne et al . ) to prevent extinction. We have tracked neutral genetic diversity in Rio Grande silvery minnow (Alò & Turner ; Turner et al .…”

“…; Osborne et al . ) for 17 consecutive years; providing crucial information about demography, genetic effective size and the effects of population augmentation. Data from neutral loci have also shown that over the species' current range, there is no population structure due to the drifting nature of Rio Grande silvery minnow eggs (Osborne et al .…”