Central tenets of life history theory hinge on hypothesized tradeoffs between current and future reproduction and how effort within a reproductive bout is divided among offspring. I have studied how these tradeoffs affect the evolution of reproductive tactics in the treehole dwelling mosquito, Aedes triseriatus, and in the side-blotched lizard Uta stansburiana. In both systems, I used direct manipulation of reproductive investment to reveal patterns in reproductive allocation or costs among types (geographic populations, sexes, morphotypes) that would not have been apparent if only naturally-occurring levels of reproductive investment had been investigated.
A. triseriatus is well suited to studies of reproductive investment because host blood is a quantifiable, easily manipulated resource used exclusively for egg production. As a M.S. student under Steve Juliano, I studied how reproductive investment, division of reproductive resources among offspring, and costs of reproduction varies across the geographic range of A. triseriatus. In particular, we were interested to test predictions relating reproductive investment to expected larval mortality rates caused by a voracious predator, Toxorhynchites rutilus. Although we found no relationship between expected larval mortality levels and reproductive tactics, we did find interesting geographic patterns in some fitness components. Moreover, our results suggested that the devotion of host blood to reproduction may reduce the predicted costs of reproduction that are rooted in resource allocation tradeoffs among growth, maintenance, and reproduction.
U. stansburiana are well suited to studies of life history evolution because they can be studied in large numbers in the wild, have naturally occurring morphotypes, lend themselves to a variety of ecological performance studies, and are amenable to a variety of physiological manipulations that affect behavior, locomotor performance, and reproduction. In collaboration with Barry Sinervo and Don Miles, I used such manipulations to experimentally alter reproductive investment directly in females and males and then measured the effects of naturally occurring and experimentally-induced reproductive variation on locomotor performance and survival in the wild. We found that individual female’s reproductive investment was negatively related to endurance and survival; experimental reduction of reproductive investment increased post-oviposition endurances relative to that of unmanipulated females, indicating that some performance cost is due to the physiological toll of reproduction. Manipulation of males revealed that experimentally elevated testosterone levels raise the locomotor capacity of two morphotype classes to that of a third, territory holding/high-endurance/high-visibility morphotype, with a concomitant increase in access to females and mortality. These studies reveal the mechanistic basis of tradeoffs that influence the evolution of reproductive investment in these lizards.
Frankino, W. A., and S. A. Juliano. 1999. Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus. Oecologia 120:59-68.
Miles, D. B., B. Sinervo, and W. A. Frankino. 2000. Reproductive burden, locomotor performance, and the cost of reproduction in free ranging lizards. Evolution 54:1386-1395.
Sinervo, B., D. B. Miles, D. DeNardo, W. A. Frankino, and M. Klukowski. 2000. Testosterone, endurance, and Darwinian fitness: Natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards. Hormones and Behavior 38:222-233.