Mad River Sculpins: Just Another Fish Story?

Abstract

Jerry Downhower is associate professor in the Department of Zoology, Ohio State University, Columbus 43210. He has also been a visiting associate professor at the University of Wyoming and program director for Population Biology and Physiological Ecology at the National Science Foundation. Downhower received his B.A. degree from Occidental College, and his M.A. and Ph.D. degrees from the University of Kansas. He was a postdoctoral fellow in neurobiology and behavior at Cornell University. He has published extensively on the subject of behavioral ecology and sociobiology with special emphasis on mating systems, sexual selection, sex determination, and sexual dimorphism in body size. Luther Brown is associate professor of biology at George Mason University, Fairfax, VA 22030. He holds a B.A. degree from Elmhurst College and M.S. and Ph.D. degrees from The Ohio State University. Brown is a former graduate student of Downhower and has focused his research efforts on the patterns, mechanisms, and consequences of mate selection by females. Female animal mating preferences have played an important role in the evolution and maintenance of mating systems because females generally make greater investments in reproduction than do males (Darwin 1871; Fisher 1958; Orians 1969; Emlen and Oring 1977; Wittenberger 1981). Females are thus thought to be the more prudent sex, and a large body of theory has developed to account for the factors that alter or influence the kinds of choices that females make. If female mate choice is important evolutionarily, then we may be able to understand why a particular species breeds in the way it does by identifying the factors that influence female preferences. For the past several years, we have been attempting to unravel the factors that influence the mating preferences of female mottled sculpins, a small North American fish. Our findings suggest that female mate preferences are influenced by at least four major factors, and that the relative importance of these factors changes through time. The type of choice that a female makes thus depends on the time of breeding. Mottled sculpins are polygynous: in each year, a male may spawn with more than one female whereas females only spawn once. The breeding biology of this species is not complicated. Generally, a male takes up residence under a rock, or in some other naturally occurring crevice on the stream bed. Gravid females approach a male and are courted. During courtship the male will spread and fan his anterior or pectoral fins, which are greatly enlarged in this species (Plate 1). The male may also spread his opercular plates (the large flat bony structure that cover the gills). He may gape at the female, and in certain instances he may take the female's entire head into his mouth. Should the female spawn with the male, she will turn over and deposit her eggs on the ceiling of the grotto occupied by the