Female preference variation has implications for the maintenance of an alternative mating strategy in a swordtail fish

Female preference variation over space and time could be an alternative to frequency-dependent selection as a mechanism maintaining alternative male reproductive strategies. In the swordtail fish, Xiphophorus nigrensis, males have alternative strategies where large courting males (courters) and smaller males (sneakers) have equal fitnesses due to a mating advantage for the courters and a higher probability of reaching sexual maturity for the sneakers. Variation in one of these advantages over space or time may be the mechanism that maintains these two strategies. We examined female preference variation for the courting strategy in Xiphophorus multilineatus, a species with the same strategies. Females had an overall significant preference for courters. The strength of this preference was positively related to female size, with smaller females having a weak preference for courters. If the relationship between female size and strength of preference is consistent over space and time, more smaller females would result in an weaker preference for courters, which would increase the relative mating advantage of sneakers. We assessed female size distribution and the frequency of each strategy across space and time and detected significant differences in mean female size across subpopulations and across time, as well as a relationship between mean female size and the relative frequencies of the two male strategies: courters were significantly more common in those samples with the largest females. These results suggest that variation across subpopulations of X. multilineatus in female preferences over space and/or time could shift the balance in fitness between the two strategies.