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AN EXPERIMENTAL STUDY OF EVOLUTION IN HETEROGENEOUS ENVIRONMENTS: PHENOLOGICAL ADAPTATION BY A BRUCHID BEETLE

Heterogeneity is a fundamental feature of any habitat. Organisms live in physical settings that change from place to place and from time to time; and the biological environment, being made of objects that grow, reproduce, and die, is also constantly changing. These straightforward observations raise two obvious questions. Do organisms adapt to environmental flux? If they do, how do they do it? The work discussed below was prompted by these questions. This paper documents behavioral changes by which a bruchid beetle adapted phenologically to spatial and temporal variations in laboratory habitats. Beetles in most of the experimental environments evolved particular rates of oviposition that damped out different phenological effects of different environments. The beetle's ability to adapt depended on the environment's temporal predictability. In serially uncorrelated habitats, phenological adaptation did not occur. Other components of oviposition behavior also evolved differently in different environments; these other changes, which affected host discrimination, will be discussed elsewhere (Mark, unpubl.). Most of the previous studies of the evolutionary effects of environmental heterogeneity were motivated by the question, "How does environmental heterogeneity affect gene frequencies?" A rather large literature, reviewed by Felsenstein (1976) and Hedrick et al. (1976), has built up around this question, but it is peripheral to the work to be described here.