Reproductive behavior of the cactus fly, Odontoloxozus longicornis, male territoriality and female guarding as adaptive strategies

Abstract

1. Mating behavior in the cactus fly, Odontoloxozus longicornis Bigot, is investigated using a model modified from Parker (1974). Male territoriality at oviposition sites, repeated matings, and postcopulatory guarding behaviors are described for a population utilizing giant saguaro cacti (Carnega gigantea) in Pima County, Arizona. Observations of flies under varying physical conditions indicate that the males follow two general copulatory patterns. Under optimum conditions described in the report, when large areas of the cactus surface can be utilized, a territorial defense strategy is adapted by the larger males while males unable to hold territories search for females. When conditions restrict the movements of flies on the cactus surface, all males search for females in the refuges. 2. To attempt to explain the maintenance of mixed strategies in the populations, data were collected and analyzed by applying a modification of Parker's (1974) optimization model. This model assesses the success of a mating strategy in terms of a gain (G) to investment (I) ratio. Data in Table 1 include those factors identical for males employing either territorial or searching strategy. Table 2 includes factors that differ for the males employing either of the two strategies, and Tables 3 and 4 summarize the data and calculations applied to the optimization (G/I) model. 3. Avoidance of sperm displacement by intervening matings and increased fertility of females encountered are shown to be major advantages of territorial strategies. Higher investments in territorial defense and longer waiting times between females are hypothesized to be the factors that select against this strategy. Male territoriality in this species is hypothesized to have evolved as a more efficient means of postcopulatory guarding, a strategy described for several other dipteran species by Parker (1974). The harsh desert environment and lack of sympatric closely related species are discussed as factors that allow sexual selection to maintain a variable reproductive strategy in males of this species. © 1979 Springer-Verlag.