Tarsal asymmetry, nutritional condition, and survival in water boatmen (Callicorixa Vulnerata)

Fluctuating asymmetry (FA) has been used as a measure of developmental stability and may indicate individual phenotypic or genotypic quality. Using water boatmen (Callicorixa vulnerata) from a natural population, we examined the relationship between tarsal FA (tarsal spine number, tarsal length) and indices of body condition in two habitats. We used body weight and residual body weight (controlling for body length) as indices of condition because experimental food deprivation in water boatmen led to a reduction in each. We detected a negative relationship between FA and both indices of condition in two ecologically distinct pond habitats. We predicted this association was due to a negative relationship between FA and competitive feeding ability. Consequently, we examined associations between survival time and tarsal FA in C. vulnerata under resource-limited laboratory conditions. Univariate analyses revealed a negative correlation between survival and tarsal FA in each trait. Inclusion of survival time, body length, gender, tarsal spine number, tarsal length, and measures of FA into multivariate analyses revealed a negative correlation between survival and FA. Individuals with the greatest survival had higher nutritional condition than individuals that succumbed early in the experiment. Asymmetric individuals may suffer a foraging handicap as a result of the use of tarsi in feeding or they may be of poor genetic quality. Our results suggest elevated FA may limit resource acquisition and are consistent with the use of FA as a measure of fitness.