Sexual signaling and speciation, a microevolutionary perspective

Despite the growing evidence that sexual selection can drive speciation, the evolution of sexual signals in natural populations is far from being well-understood. Sexual signals evolve in response to a variety of factors. Some of the most important selective factors are conspecifics, transmission efficiency in a particular environment, detection by predators, and phylogenetic constraints. These factors have been addressed quite successfully in studies of single types of signals in both vertebrates and invertebrates. However, it is less clear how multimodal signals evolve because the factors listed above will act on every component of the signaling system, and the relative weights of each type of signal must be taken into account. Species of Drosophila are excellent for such analyses because they are amenable to both phenotypic experimentation and genetic manipulation. This paper presents an approach that involves two analyses: studies of which signals are sexually selected within a species, and parallel studies of the signals that are involved in behavioral isolation between closely related species. If the same signal characteristics are involved in both processes, they would provide support for the hypothesis that sexual selection can drive speciation. This approach is illustrated with studies of Hawaiian Drosophila and a review of signals that could be sexually selected in Drosophila melanogaster.