Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.

Recent advances in the development and availability of genetically modified animals enable researchers to examine the effects of phenotypic characters on social behavior. In fish, shoaling behavior is known to be influenced by characteristics such as body coloration, striping pattern, body shape, and size. GloFishTM are genetically engineered zebrafish (Danio rerio) that express red fluorescent protein (RFP), resulting in on overall red coloration under the dark longitudinal stripes. The GloFish pattern is distinct from the light body coloration underlying the dark longitudinal stripes seen in wildtype zebrafish. We presented wildtype and transgenic RFP zebrafish with same‐sex shoals of both strains of fish in dichotomous choice tests. No preference for either of the shoals was shown, however, both strains showed significant preferences for swimming near shoals vs. swimming near an empty tank compartment. When presented with opposite‐sex individuals of both strains, no preference was shown by either sex of either strain. Thus, the red body coloration of transgenic zebrafish does not appear to affect choice of social partner, in either a shoaling or a potentially reproductive context.

Mainland species of the camaenid genus Rhagada, endemic to northern Western Australia, have relatively large, non-overlapping geographic ranges. In contrast, over much smaller distances in the Dampier Archipelago, several locally endemic, morphologically distinctive species occur with intermingled ranges. To test alternative origins of the unusual local diversity, we compared allozymes at 21 loci in 12 archipelago populations and 14 mainland populations, representing 14 species. Genetic distances were consistently low, averaging 0.019 (range 0.000–0.051) within species, and only 0.043 (range 0.001–0.133) between species. In the Dampier Archipelago, the average genetic distance between species was even smaller (0.023). This result was indistinguishable from the within-species comparisons, highlighting the disconnection between morphological diversification and levels of molecular genetic divergence. A pattern of isolation by distance among all comparisons within the archipelago also suggests a historic cohesiveness of the species in the Dampier Archipelago. Although providing no resolution of relationships among mainland populations, a neighbour-joining tree provided further support for an in situ morphological radiation in the Dampier Archipelago, transcending variation seen over much larger distances on the mainland.