Coercive mating and gonopodium length in two populations of a livebearering toothcarp (Poecilia mexicana): do cave molly males have shorter gonopodia?

Martin Plath & Michael Tobler
2006

Male livebearering toothcarps (Poeciliidae) ue their gonopodium, a modified anal fin, to transfer sperm bundles (spermatozeugmata) into the female's gonoduct.  There is a wide range of variation in the patterns of male behavior proceeding and accompanying copulations in poeciliid fishes.  Males of some species, such as the guppy (Poecilia reticulata) may court females before they attempt to insert their gonopodium (HOUDE 1997), whereas males of other species never court, and the latter completely rely on coercive mating attempts ("sneak copulations", BISAZZA 1993, Poecilia Mexicana: Plath et al. 2003).