Reproductive Allocation in Tropical Drosophilidae: Further Evidence on the Role of Breeding-Site Choice

Abstract

Observations on reproductive allocation in 23 spp. of tropical African Drosophilidae revealed a wide array of reproductive patterns associated with their degree of specialization in the field. The reproductive performances tested experimentally under laboratory conditions can provide valuable insight on how life history characteristics have evolved. The data presented clearly suggest an inverse relationship between reproduction and age at maturity. Regression analyses further demonstrate that growth and longevity are positively correlated with age at maturity. Shorter-lived species concentrate the production of many offspring in early age classes; longer-lived species delay maturity in later age classes and then produce fewer offspring. The former are those generalists exploiting the environmental mosaic in a fine-grained manner; the latter are those specialists with coarse-grained behavioral response. The capacity to delay maturity and to produce limited offspring is assumed to be associated with the nature of the breeding sites used. Colonizing species, i.e., those living in the largest range of habitats and breeding in the widest array of host plants, are placed at a medial position on the continuum of reproductive patterns. The hypothesis is then made that their colonizing ability results from their capacity to reevaluate rapidly their allocative options from one generation to the next. Comments are made on the relative merits of different alternative explanations for specific patterns of life history variation. The data could not be correctly interpreted as arising only from frequency-dependent selection. The adequacy of various alternative hypothetical causes was analyzed including effects of spatial population structure of host plants, phenologies of fruit production and chemical yields of host plants.