The offspring size/fecundity trade-off and female fitness in the Atlantic molly (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, Poeciliidae) |
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Authors: | Rüdiger Riesch Martin Plath Ingo Schlupp |
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Institution: | 1.Department of Zoology,University of Oklahoma,Norman,USA;2.Department of Biology & W. M. Keck Center for Behavioral Biology,North Carolina State University,Raleigh,USA;3.Abteilung für ?kologie & Evolution,J. W. Goethe Universit?t Frankfurt am Main,Frankfurt a. M.,Germany |
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Abstract: | Across a variety of taxa, large offspring have been demonstrated to have a fitness advantage over smaller offspring of the
same species. However, producing large offspring often comes at the cost of having to produce fewer young, and the payoff
(and thus, evolutionary outcome) of this trade-off is expected to vary between environments. Atlantic mollies (Poecilia mexicana: Poeciliidae, Teleostei), inhabiting a sulfidic cave and various non-sulfidic surface habitats in Tabasco (Mexico), are reproductively
isolated and evolved divergent female life-history traits: females of the cave ecotype produce considerably fewer, but larger
offspring. Stressful (sulfidic) environments may favor the production of larger offspring, as they are better able to cope
with chemical stressors. It remains to be determined though if increased offspring survival outweighs the fitness cost of
producing fewer but larger offspring even under benign laboratory conditions. We tested 30-day newborn survival of offspring
from wild-caught P. mexicana females from diverging populations in a low-density, no predation, no cannibalism, and ad-libitum-food, benign laboratory
environment. Survival rates were highly skewed towards larger cave molly offspring; however, surface molly females still had
a higher fitness than cave molly females in terms of higher total numbers of surviving offspring. Our study provides evidence
for an innate fitness advantage of larger cave molly offspring. Furthermore, the observed differences in life-history strategies
could promote further divergence and reproductive isolation among these ecotypes of P. mexicana, because cave molly females immigrating into the adjacent surface habitats would most likely be selected against. |
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