Terminal Investment Strategies and Male Mate choice: Extreme Tests of Bateman

Bateman's principle predicts the intensity of sexual selectiondepends on rates of increase of fecundity with mating successfor each sex (Bateman slopes). The sex with the steeper increase(usually males) is under more intense sexual selection and isexpected to compete for access to the sex under less intensesexual selection (usually females). Under Bateman and modernrefinements of his ideas, differences in parental investmentare key to defining Bateman slopes and thus sex roles. Othertheories predict sex differences in mating investment, or anyexpenditures that reduce male potential reproductive rate, canalso control sex roles. We focus on sexual behaviour in systemswhere males have low paternal investment but frequently mateonly once in their lifetimes, after which they are often killedby the female. Mating effort (=terminal investment) is highfor these males, and many forms of investment theory might predictsex role reversal. We find no qualitative evidence for sex rolereversal in a sample of spiders that show this extreme maleinvestment pattern. We also present new data for terminally-investingredback spiders (Latrodectus hasselti). Bateman slopes are relativelysteep for male redbacks, and, as predicted by Bateman, thereis little evidence for role reversal. Instead, males are competitiveand show limited choosiness despite wide variation in femalereproductive value. This study supports the proposal that highmale mating investment coupled with low parental investmentmay predispose males to choosiness but will not lead to rolereversal. We support the utility of using Bateman slopes topredict sex roles, even in systems with extreme male matinginvestment.