Researchers have proposed an explanation for how three species of tiny fish manage to coexist despite having seemingly incompatible modes of reproduction, according to a study published in __Oikos__ last week. The Amazon molly (__Poecilia formosa__) is an asexually reproducing species in which females produce only female clones via parthenogenesis. To initiate embryogenesis, however, Amazon mollies require sperm from the males of one of two closely related, but sexually reproducing, species sharing their habitats in southern Texas and northern Mexico -- the sailfin molly (__Poecilia latipinna__) or the shortfin molly (__Poecilia mexicana__).
Ecological theory predicts that such species living as a complex in nature are doomed because population growth in the asexual species should overwhelm the metapopulation with females. That in turn would lead to a shortage of sperm and a collapse of the entire system. The ecological model proposed in the study suggests...
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