EVOLUTIONARY CHANGES IN EGG-EATING BEHAVIOR OF FLOUR BEETLES IN MIXED-SPECIES POPULATIONS.

Theoretical studies in many areas of evolutionary biology have far outpaced experimental work designed to test the assumptions and/or even the models themselves. One of these areas is that of foraging strategies of predators. There is a vast literature on optimal strategies for searching, pursuing and capturing food (e.g., MacArthur and Pianka, 1966; Emlen, 1966, 1968; Royama, 1970; Rapport, 1971; Schoener, 1971; Katz, 1974; Pulliam, 1974; Estabrook and Dunham, 1976). Natural selection is viewed as a "black box" (somewhat as a computer is viewed by many workers)-predators, prey and environments (inputs) are fed into the box and adaptations (outputs) come out. Natural selection is supposed to assimilate the information contained in the inputs and generate optimal solutions to the problem of obtaining food. Experimental studies to support the theory are meager by comparison (but see Charnov, 1976; Zach and Falls, 1976; Cowie, 1977). To my knowledge there are no studies that involve the black box component. What one would like is an experimental system where there is sufficient knowledge to enable one to make predictions about changes in the output from planned alterations in the input. Even though natural selection would still be treated as a black box, the predictions would be based on some notion of optimal solutions to the changes in input. Such a system is available in the form of "the Tribolium model," long used by population ecologists and more recently by geneticists and by population biologists (King and Dawson, 1972). Two species of flour beetles, Tribolium castaneum and T. confusum, are ecologically similar but reproductively isolated, thus permitting the maintenance of mixed-species cultures. The two species form a mutual predatorprey system; cannibalism is one of the primary regulators of population size and along with predation serves as an important determinant of the outcome of interspecific competition (Park et al., 1964, 1965; King and Dawson, 1972). Both larval and adult stages prey on eggs and pupae. I have suggested that cannibalistic behavior in flour beetles evolved through individual selection (Dawson, 1968a). Others prefer arguments based on group selection (e.g., Brereton, 1962). It has even been argued that cannibalism is a laboratory artifact (Colinvaux, 1973). That is, through the combination of artificially high densities and prevention of dispersal, the aberrant behavior of cannibalism is elicited. Several years ago I established a series of cultures designed to permit changes in competitive ability and foraging behavior through time. The rationale for starting these cultures was as follows: In a mixedspecies culture, both species act as predators, prey, cannibals and victims. Predatory behavior is not random; both adults and larvae of the two species have different rates and patterns of eating (Park et al.,-1965, 1968, 1970, 1974). Therefore, if this behavior is subject to natural selection, we should be able to observe changes in rates and patterns of eating in cultures where we artificially maintain different amounts of intraspecific and interspecific association. In our cultures there are populations of both species, in varying proportions, along with an alternative food (the flour-yeast medium) that is perfectly adequate to sustain populations. This paper is one of several on evolu-