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A Natural Experiment in Life-History Evolution: Field Data on the Introduction of Mosquitofish (Gambusia affinis) to Hawaii

Stephen C. Stearns
Evolution
Vol. 37, No. 3 (May, 1983), pp. 601-617
DOI: 10.2307/2408273
Stable URL: http://www.jstor.org/stable/2408273
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Natural Experiment in Life-History Evolution: Field Data on the Introduction of Mosquitofish (Gambusia affinis) to Hawaii
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Abstract

About 150 mosquitofish were introduced from Texas to Hawaii in 1905. I analyzed 1,367 pregnant females collected in 1974 from four stable and 20 fluctuating reservoirs and the time-series of water levels in the fluctuating reservoirs. Fish from stable reservoirs had fewer offspring, lower reproductive allocations, were thinner, shorter, and weighed less, than fish from fluctuating reservoirs. Stocks differed for those traits and in weight of yolked and yolking eggs. Length and condition explain 21-53% of variation of reproductive traits among stocks. Effects of samples within stocks were only significant for one of the eight reservoirs with adequate sample sizes, and accounted for only 3-5% of variation in reproductive traits. In this case the stable-fluctuating dichotomy misled; the fluctuating reservoirs differ significantly in their fluctuation patterns, and these differences are reflected in the life-history traits of the fish living in them. Much of the variation among stocks was caused by plastic responses to short-term environmental change. The pattern of variation in water levels in the more distant past (3-6 months) had strong effects on weight-adjusted fecundity than did the more recent past (1-3 months). The environment can induce significant lag effects in less than a generation via physiological plasticity. Water level fluctuations affect the expression of life-history traits in these stocks, but they cannot account for variation among the stocks from stable reservoirs. Founder effects may contribute to divergence among all stocks, and drift may contribute to divergence among fluctuating stocks.

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