ANDRADE, MCB; University of Toronto at Scarborough: Terminal Investment Strategies and Male Mate Choice: Extreme Tests of Bateman

Bateman’s principle predicts the intensity of sexual selection is controlled by rates of increase of fecundity with mating success for each sex (Bateman’s slopes). The sex with a steeper increase (usually males) is under more intense sexual selection and is expected to mate indiscriminately relative to the sex under less intense sexual selection (usually females) which should be choosy about their mating partners. Other theories predict sex differences in mating investment control the direction of sexual selection. Testing the relative importance of Bateman slopes vs mating investment in shaping mating strategies is difficult because in many systems variation in mating investment drives differences in potential reproductive output. An opportunity for such a test arises in systems where predictions of these theories diverge. I outline the value of studying male mate choice in systems where males invest little in offspring but mate with few females and die shortly thereafter or become sterile. In such systems, male total investment per mating is high (terminal investment), and many forms of investment theory would predict male mate choice. But Bateman slopes for terminally investing males are often steep, so sexual selection on males is expected to be strong, and male mate choice is not predicted. I report empirical tests of male mate preferences in redback spiders (Latrodectus hasselti), a species with terminally investing, sacrificial males and significant variation in female reproductive value but in which many males never mate and male Bateman slopes are steep. I discuss results from field and lab trials in light of other systems with terminally investing males and argue that the Bateman’s slope approach leads to more accurate predictions regarding male mate choice and sex roles than do alternative approaches.