Dr. Scott K. Sakaluk
Dr. Scott K. Sakaluk
Office - FSA 138, Labs – FSA 137, 141 and 143
Phone – 309-438-2161, Email - sksakal@ilstu.edu
Reproductive Behavior
My laboratory investigates behavioral adaptations related to sex, specifically, the evolution of mating preferences and traits arising through sexually antagonistic coevolution. In many insect species, females are well positioned to determine the fate of their mates’ gametes through various means, including control of copulation duration, premature removal of spermatophores, and internal manipulation of ejaculates. Because it is in the interests of males to have all of their sperm utilized in fertilizations, female control of sperm transfer and usage is often at odds with the reproductive interests of their sexual partners. Theoretically at least, such control represents a potent selective force: a wide array of male secondary traits in the insects have been attributed to selection on males to circumvent post-copulatory female preferences.
Crickets offer an ideal model with which to examine the evolution of post-copulatory female choice: the ejaculate of a male typically remains attached outside the female’s genital opening after mating in the form of an externally attached spermatophore, and females are thus well positioned to determine the fate of their mates’ gametes through the judicious removal of spermatophores. In studies supported by the National Science Foundation, we tested the hypothesis that post-copulatory manipulation of ejaculates by female decorated crickets constitutes a potent form of female choice, imposing significant sexual selection on males. By experimentally altering sperm transfer of rival males and using genetic markers to assess the paternity of offspring, we were able confirm that female ejaculate manipulation, manifest in the removal of the externally attached spermatophore, directly affects male fitness. This work helped establish that nuptial food gifts function to entice females into relinquishing at least some of their control of the insemination process, and thereby aid males’ own selfish reproductive interests.
More recent studies have been directed at the chase-away model of sexual selection as it applies to the coevolution of nuptial food gifts and post-copulatory female choice in insects. Specifically, we have been testing the hypothesis that the spermatophylax, a gelatinous mass forming part of the spermatophore of male decorated crickets and consumed by the female after mating, contains substances that function to reduce female sexual receptivity, but that females have evolved resistance to these substances. Our results support a recent suggestion that food ‘gifts’ are in fact ‘Medea’ gifts, male-derived refractory-inducing substances dressed up as nutritional offerings.
Evolution of Polyandry in Birds
Charles Thompson, Laura Vogel and I have recently been awarded an NSF collaborative grant to conduct studies designed to test the hypothesis that females in socially monogamous species engage in extra-pair matings to secure paternal genes for their offspring that enhance offspring immunocompetence and viability. Specifically, we will are testing the critical prediction that all else being equal, the immunocompetence of extra-pair young should be higher than that of within-pair young residing in the same nest . A particularly critical and novel aspect of the proposed research is that it will be the first to determine if differences in the immunocompetence of within- and extra-pair young are the result of the extra-pair male's genetic contribution, or arise instead from the differential investment by females in the eggs or nestlings sired by different males in their brood.