Genetic heterogeneity among pelagic egg samples and variance in reproductive success in an endangered freshwater fish, H
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Springer 2005
Genetic heterogeneity among pelagic egg samples and variance in reproductive success in an endangered freshwater fish, Hybognathus amarus (Cyprinidae) Megan J. Osborne, Melissa A. Benavides & Thomas F. Turner Department of Biology and Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM 87131, U.S.A. (e-mail: [email protected]) Received 26 July 2004
Accepted 8 February 2005
Key words: sweepstakes–mismatch hypothesis, differential mortality, temporal genetic variation, range fragmentation, species restoration, genetic conservation Synopsis A sweepstakes–mismatch process whereby reproduction is poorly coordinated with appropriate resources for larval development and recruitment can result in large variance in reproductive success among individuals and spawning aggregations. This process has been proposed to explain low ratio of genetic effective population size (Ne) to adult census size (N) ratios in marine species with high fecundity, pelagic spawning, and extensive mortality in early life stages. This process is also hypothesized to also account for very low Ne/N ([ 0.001) observed in the federally endangered Rio Grande silvery minnow, Hybognathus amarus. This species is a freshwater fish that shares life-history features with marine pelagic spawners. We tested two key predictions of the sweepstakes–mismatch hypothesis using molecular data: (i) that temporally distinct samples of eggs differ in genetic composition and, (ii) that egg samples do not comprise a random subset of potential adult breeders. We present genetic data that supports both predictions and that are consistent with the hypothesis that high variance in reproductive success among adult breeders is an important factor that lowers Ne/N in H. amarus. This study highlights the importance of understanding the interaction of early life history and fragmentation in devising conservation plans for endangered aquatic organisms.
Introduction Although remarkably tolerant of severe environmental conditions, freshwater fishes of the southwestern United States have suffered declines in abundance, local extirpation and extinction as human demand for water has increased in this arid region (Minckley & Deacon 1991, Minckley et al. 2003). River fragmentation by impoundments and large-scale diversion of water are implicated as major factors driving species decline and extinction (Minckley & Deacon 1968, Moyle & Williams 1990, Winston et al. 1991). The federally endangered (United States Department of the Interior 1994) Rio Grande silvery minnow,
Hybognathus amarus (Cyprinidae), is a case in point. Historically, this species was abundant and widely distributed throughout the Rio Grande basin in New Mexico and Texas (USA) and in northern Mexico (Trevino-Robinson 1959). Now however, H. amarus occupies only 5% of its historical range and is restricted to a 280-km river reach in New Mexico where the river is fragmented by three water diversion dams (Angostura, Isleta, San Acacia) and two major storage dams (Cochiti, Elephant Butte) (Figure
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