Variation in the Degree of Viviparity in the Sailfin Molly, Poecilia latipinna

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Abstract
Female poeciliids retain developing embryos internally and give birth to live young. Within the family, the degree of true viviparity is highly variable. This paper reports evidence consistent with facultative viviparity in Poecilia latipinna. The embyros of three of four populations studied showed no signs of weight loss during development. In a fourth population, females produced large ova that lost about 40% of their weight before parturition. In the following year the embryos of females from this population did not lose weight during development. Such temporal and spatial variation in the level of viviparity indicates that interdemic differences may be environmentally induced.