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Temporal genetic variability in pelagic eggs in the endangered Rio Grande silvery minnow.
Benavides, Melissa*,1, Osborne, Megan1, Alo, Dominique1, Turner, Thomas1, 1 Department of Biology, Albuquerque, NM, USA
ABSTRACT- The Rio Grande silvery minnow (Hybognathus amarus) exhibits a rare life history feature for a freshwater fish in that it spawns pelagic eggs and larvae. Consequently, much of the annual production of offspring is moved downstream with river currents after spawning. This life history may suggest that juveniles and adults historically migrated upstream in attempt to return to their natal sites. The Rio Grande is now highly fragmented by dams and other diversion structures that impede upstream movement of fish. We have undertaken a long term study of temporal and spatial genetic variation in silvery minnow, and have shown that genetic effective size Ne is three orders of magnitude smaller than census size. The cause of low Ne/N appears to be associated with high variance in reproductive success among individuals, exacerbated by annual loss of reproductive output to entrainment through diversion dams. Loss of production would exert maximal effect on variance in reproductive success if genetic diversity of eggs is structured spatiotemporally, such that groups of genetically related eggs are subject to mortality that varies in space and time. We tested whether genetic diversity of eggs collected at a single location from natural spawning varied among temporally-spaced samples. Preliminary genetic screening of eggs using mtDNA gene markers, SSCP, and nucleotide sequencing suggests strong temporal variability among egg samples, implicating high variance in reproductive success as an important factor for lowering genetic diversity in wild populations of silvery minnow.
Key words: genetics, Hybognathus amarus, eggs