Hormonal Basis to Mate Choice Behavior in a Unisexual-bisexual Mating System
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Steroid hormones play an important role in reproductive behavior. Steroid hormone levels might explain individual differences within species in the frequency of sexual behavior and species recognition. One system where hormones may affect species recognition is in the unisexual-bisexual species complex of mollies. Amazon mollies, Poecilia formosa, are a gynogenetic (all female) species that must mate with male sailfin mollies, P. latipinna, to initiate embryogenesis, but inheritance is maternal (male sailfin mollies are sexually parasitized by Amazon mollies). We examined if variation in male sailfin molly mate preference is affected by variation in steroid hormones. We tested individual male mating behavior and hormone levels with: (1) a female conspecific and (2) an Amazon molly. We measured levels of 11-Ketotestosterone (11-Kt) and Testosterone (T) in males and females before and after each 10-minute mating trial, and calculated the relat! ive increase of each hormone (post-mating sample/pre-mating sample). We found a significant interaction between male 11-Kt hormone ratio and female species on thrusting: males that mated more with conspecifics had higher 11-Kt ratios. We also found a significant interaction between female T ratios and female species on male thrusting: males thrusted more towards conspecific females that had higher T ratios. Thus male and female sailfin molly hormone levels are important factors affecting male species recognition in this complex unisexual-bisexual mating system. When we tested this with the Atlantic mollies, the other parental species, did not show this KT response suggesting that Amazon mollies inherited this lack of ability to increase KT.