Species and Mate-Quality Recognition in Poecillia Latipinna
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Examination of the species recognition process may shed light on an evolutionary paradox: the persistence of Amazon mollies (Poecilia formosa) that are unisexual gynogens. Amazon mollies require sperm from the closely related sailfin molly, P. latipinna, to initiate embryogenesis, however, inheritance is strictly maternal. In the following chapters, I address both proximate and ultimate questions pertaining to species recognition by male sailfin mollies in this unisexual-bisexual species complex.
In Chapter II, I examine a mechanism for the persistence of Amazon mollies via conflict between species and mate-quality recognition cues. Previous work has found that male sailfin mollies in sympatry exhibit a significantly greater mating preference for female sailfin mollies over Amazon mollies compared with males in allopatry. In addition, male sailfin mollies prefer to mate with larger conspecific females and these females are more fecund and represent higher quality mates. Therefore, when choosing mates, male sailfin mollies from populations sympatric with Amazon mollies may rely on traits indicating species identity (genetic compatibility) rather than those indicating mate-quality (increased fitness benefits). Conversely, allopatric males may rely more on traits indicating mate-quality. I hypothesized that Amazon mollies may be taking advantage of body size as a mate-quality cue. To test this, I paired males with a larger Amazon molly and a smaller female sailfin molly to determine whether there is a conflict in species and mate-quality recognition. I tested males from three allopatric and five sympatric populations. In each trial I scored the number of mating attempts that males directed to conspecific and heterospecific females. I found that males in most sympatric and allopatric populations no longer demonstrate the preference for conspecifics found in previous work when females were matched for standard length. In addition, I found a significant difference in mating preference between allopatric and sympatric populations with males from allopatry showing a greater heterospecific mate preference. These results indicate a conflict between species and mate-quality cues in sympatry, which may contribute to the persistence of gynogenetic Amazon mollies.
Chapter III examined morphological cues that may be used for species recognition. Understanding the cues used for species recognition is important in closely related sympatric species where there is a high risk of mating with heterospecifics. Multiple cues may be used or there may be more emphasis on specific individual traits. Herein, I examine possible cues used by male sailfin mollies (Poecilia latipinna) to distinguish between conspecific females and sympatric Amazon mollies (P. formosa). Digital photos were used to create models to test male P. latipinna preference for model female P. latipinna and P. formosa with a full suite of traits and altered P. latipinna and P. formosa models. I found that P. latipinna males significantly preferred models of either species over no stimulus, demonstrating that models elicit a male response. Second, I found that males significantly preferred model P. latipinna females over P. formosa. Third, I tested male preference for altered models in the following combinations; (1) P. formosa vs. P. formosa with a female P. latipinna fin (2) P. formosa vs. P. formosa with a female P. latipinna lateral spot pattern (3) P. formosa vs. P. latipinna with a P. formosa fin and their spotless lateral pattern. Males did not significantly prefer models with any isolated traits over the unaltered P. formosa models. Thus, males may be using traits other than the ones isolated for species recognition or males may be using a suite of multiple traits to recognize conspecific females.
CitationGumm, J. M. (2004). Species and mate-quality recognition in Poecillia latipinna (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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