Dr. Charles F. Thompson
Dr. Charles F. Thompson
Office - FSA 135, Labs – FSA 137 and 139
Phone – 309-438-2656, Email - wrens@ilstu.edu
Fitness-related Advantages of Extra-pair Mating in Birds
My students, collaborators, and I investigate the question of why female passerine birds engage in extra-pair matings with males other than their social mates. In socially monogamous species of birds, the male and female of a pair typically cooperate in rearing the offspring, but the application of DNA ‘fingerprinting’ techniques has revealed that the progeny of females in socially monogamous species often are sired not only by their social mate, but by other males as well. This results in broods of mixed paternity. Why females mate with more than one male remains obscure, because females seldom derive direct material benefits from their extra-pair partners. A widely accepted explanation for extra-pair mating is that females derive indirect genetic benefits through the enhancement of the genetic quality of their offspring.
The focus of our current research is 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 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. Predicted differences between within-pair and extra-pair young could also come about as a result of maternal effects and not just paternally derived genes. Potential maternal effects could arise from the preferential provisioning by females of extra-pair young, or the differential allocation of resources to eggs fertilized by extra-pair partners. Thus, we are also determining 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.
Maternal Behavioral Control of Hatching Synchrony in Birds
Another project is investigating how the incubation behavior of female songbirds can influence the degree of hatching synchrony of their eggs. Female songbirds can manipulate investment in their offspring prior to the nestling/fledgling-provisioning stage by differentially allocating resources among their eggs and by manipulating the timing of hatching of their eggs. By manipulating the time of hatching of the eggs in their clutch, hatching can occur over a period of one (i.e., synchronous hatching) to three or more days (i.e., asynchronous hatching). When eggs hatch asynchronously, nestlings of different sizes occur within the brood because the older chicks have been fed by their parents for one or more days before their younger siblings have hatched. Often one or more of the youngest chicks dies from starvation in asynchronously hatched broods. It has been proposed that asynchronous hatching is a form of parental manipulation that maximizes parental fitness at the cost of the survival of some individual offspring.
Many hypotheses have been proposed to explain the evolution and maintenance of asynchronous hatching, with most assuming that the degree of hatching synchrony is controlled by the parents through variation in the time of onset of incubation behavior. However, little is known about the relationship between incubation behavior and degree of hatching synchrony, despite the widely held assumption that variation in incubation behavior is the underlying mechanism that brings about variation in hatching synchrony. The main focus of this project is to determine how female behavior influences the degree of hatching synchrony in birds.
The Study System: The House Wren (Troglodytes aedon)
The house wren (Troglodytes aedon) provides an excellent study system for testing behavior-based hypotheses. The house wren is a migratory songbird that arrives to breed in central Illinois in late April. Egg-laying begins in early May and continues until August each year. House wrens are secondary cavity nesters, so they readily accept nestboxes as nesting sites. We maintain two adjacent study areas on which there are 813 identical nestboxes. Each year approximately 500 adult house wrens produce 500-600 nests on the study areas, thereby providing a large sample of birds for behavioral studies.