Why does size matter? A test of the benefits of female mate choice in a teleost fish based on morphological and physiological indicators of male quality.

In female mate choice, a female chooses a reproductive partner based on direct or indirect benefits to the female. While sexual selection theory regarding female mate choice is well developed, there are few mechanistic studies of the process by which females evaluate reproductive partners. Using paternal-care-providing smallmouth bass (Micropterus dolomieu) as a model, the purpose of this study was to determine the relationship between female mate choice and the morphological and physiological status of chosen males. This was accomplished by locating nests within 1 d of spawning and categorizing brood size (indicator of female mate choice). This was followed by capture of parental males, which were blood sampled (for nutritional analyses), digitally photographed (for morphometric analyses), and released. Principal components analysis (PCA) of morphometric measurements described 72.7% of the variance associated with body morphology and generated three principal components (PCs) indicative of fusiform body shape, increased posterior size, and body stoutness. PCA of nutritional indicators described 75.4% of the variance associated with physiological metrics and generated two PCs indicative of plasma mineral content (Ca(++) and Mg(+)) and energetic condition (total protein, triglyceride, and cholesterol). Male total length and body stoutness were the only significant predictors of female mate choice. Interestingly, no nutritional indicators were predictive of female mate choice, and there were no direct relationships between morphological variables and nutritional physiology indicators. Further research is needed to elucidate the mechanistic relationships between morphology and nutritional physiology (especially in relation to the parental-care period) of individual fish to determine the basis of female mate preference.