Age-specific reproductive success: evidence for the selection hypothesis.

Age-specific reproductive success has been demonstrated in many species. Three hypotheses have been raised to explain this general phenomenon: the experience hypothesis based on age-specific reproductive experience, the effort hypothesis based on age-specific reproductive effort, and the selection hypothesis based on progressive disappearance of phenotypes due to variation in individual productivity and survival. We used data from a long-term study of Leach's storm-petrels (Oceanodroma leucorhoa) to present a single test of mutually exclusive predictions about the relationship between early breeding success and longevity. There should be no correlation between early breeding success and longevity under the experience hypothesis, a negative correlation under the effort hypothesis, and a positive correlation under the selection hypothesis. We found a significant (P < 0.0001) positive relationship between success in the first two breeding attempts and longevity in this population of long-lived seabirds, strongly suggesting that low-productivity parents were also less likely to survive early breeding. These data provide some of the strongest support to date for the selection hypothesis.

Adult Survival and Imperfect Assessment of Parentage: Effects on Male Parenting Decisions.

Applications of molecular methods to assess parentage have revealed that the distribution of reproductive success among individuals often differs, sometimes dramatically, from expectation based on observation of behavioral association. Much theory exists on whether and when males should reduce parental care in response to level of paternity. Life-history theory predicts that trade-offs in reproductive effort should be influenced by adult survival. We used a dynamic programming approach to address how level of paternity, ability to assess paternity, and adult survival rate interact to affect male tolerance of reduced parentage in a given brood. Adult survival has the greatest influence on male decisions such that, for any given cost of reproduction and value of male care, tolerance of extrapair fertilizations (EPFs) decreases as adult survival increases. An unexpected result of these models is that an optimal response also depends on a male's ability to predict probability of parentage (i.e., uncertainty). These models better characterize the nature of paternity uncertainty and its effect on EPF tolerance than have previous models and add to our understanding of the complex relationship between uncertainty, mating strategies, and adult survival.