Research
What shapes sexually-selected traits?
Sexual selection has resulted in the evolution of some of the most extravagant and exaggerated behavioral and morphological traits in nature, ranging from flashy sexual ornaments to elaborate courtship rituals. We focus on the processes that have shaped those traits - the selective forces that lead to their exaggeration, and those that limit it.
In the waxmoth Achroia grisella, the male makes ultrasonic calls to attract females. Females have preferences for certain song traits. Male calls attract not only females, but also predators - bats!
In the bean beetle Callosobruchus maculatus, wing size depends on population density. Individuals with larger wings grow smaller testes, and vice-versa: a life-history trade-off.
In the katydid Ephippiger diurnus, males produce a nuptial gift - a gelatinous mass that the female (pictured with attached nuptial gift) eats after copulation. Males also sing to attract females.
In the soldier fly Merosargus cingulatus, males wave their black-and-white hind legs and rub the female during copulation. Females select against males that do not stimulate them while mating.
Proximate and ultimate causes of trade-offs in bean beetles
Trade-offs are a central concept to life-history theory, arising due to differential trait investment within an organism and resulting in negative covariances between traits. A full understanding of why trade-offs occur requires the integration of their proximate mechanisms and fitness consequences. In the bean beetle Callosobruchus maculatus, larval density induces differential resource allocation: High density results in the development of dispersal morphs with large, functional wings, as opposed to the short-winged flightless morphs that develop under low densities. We have found that high-density individuals develop larger wings and smaller gonads, and larval density also affected a suite of mating behaviors in both sexes. This project will investigate the role of Juvenile Hormones in the developmental mechanisms involved in these trade-offs, as well as how sex differences and resource allocation to immunity affect overall resource allocation. The ultimate explanations will also be investigated by measuring fitness effects of differential allocation to gonads and mating behaviors such as courtship and oviposition strategies.
Nutrition, energy and sexual traits
Waxmoths feed as larvae, but adults do not eat and only live for a few days. Differences in nutrition during development result in dramatic size differences in adults. How do small and large individuals differ in their pattern of energy allocation? Do energy limitations have different effects in the two sexes?
Social environment effects on mating behavior
The expression of traits such as mating calls and preferences, as well as other forms of reproductive investment, can be greatly affected by an individual’s social environment, as the individual garner information about the quantity and quality of competitors and potential mates through interactions with conspecifics. I am studying the effects of social environment during development in several mating behaviors and traits of males and females of bean beetles and waxmoths.
The function of nuptial gifts
Nuptial gifts - anything a male donates to a female during copulation beyond his sperm - are a common feature of insect mating systems. Many crickets and katydids produce a spermatophore nuptial gift: a sperm-filled sac that may be surrounded by an edible mass to be consumed by the female. There are different ways in which nuptial gifts may benefit males: they may function as nutrition for the female and indirectly benefit males by increasing their mate’s fecundity or their offspring’s fitness. They may also increase male fertilization success by prolonging sperm transfer (which will last as long as it takes for females to consume the spermatophore) or decreasing female receptivity to future mates by containing anti-aphrodisiac compounds. I am interested in how the different functions of nuptial gift may have different evolutionary consequences for males and females.