On the scent of speciation: the chemosensory system and its role in premating isolation

Abstract

Chemosensory speciation is characterized by the evolution of barriers to genetic exchange that involve chemosensory systems and chemical signals. Here, we review some representative studies documenting chemosensory speciation in an attempt to evaluate the importance and the different aspects of the process in nature and to gain insights into the genetic basis and the evolutionary mechanisms of chemosensory trait divergence. Although most studies of chemosensory speciation concern sexual isolation mediated by pheromone divergence, especially in Drosophila and moth species, other chemically based behaviours (habitat choice, pollinator attraction) can also play an important role in speciation and are likely to do so in a wide range of invertebrate and vertebrate species. Adaptive divergence of chemosensory traits in response to factors such as pollinators, hosts and conspecifics commonly drives the evolution of chemical prezygotic barriers. Although the genetic basis of chemosensory speciation remains largely unknown, genomic approaches to chemosensory gene families and to enzymes involved in biosynthetic pathways of signal compounds now provide new opportunities to dissect the genetic basis of these complex traits and of their divergence among taxa.

The origin and dynamic evolution of chemical information transfer

“…For example, the chemical class of emitted terpenoids comprises over 40 000 substances, many of which have various protective, defensive and attractive functions [9]. If chemicals are involved in species/mate recognition, speciation and character displacement may play a predominant role in their diversification [10,11]. However, speciation mechanisms cannot alone account for the ubiquity and high abundance of chemical signals.…”

Identification of quantitative trait loci function through analysis of multiple cuticular hydrocarbons differing between Drosophila simulans and Drosophila sechellia females

“…Mating signals in multiple modalities may influence sexual isolation. Chemosensory reception, which includes olfaction and gustation, may have a large role so that differences in pheromones functioning as mating signals can influence sexual isolation (Smadja and Butlin, 2009).…”

Sexual isolation of male moths explained by a single pheromone response QTL containing four receptor genes

“…However, no pleiotropy has been found between signal production and response in moths (e.g., 5, 10). Because female and male moths with divergent signals and responses appear to be selected against (11, 12), we have no simple explanation for the great diversity of moths (∼180,000 species) and moth pheromones (5,13,14).Beyond capturing the attention of evolutionary biologists, the diversity of long distance, pheromone-based sexual communication traits in moths has become a focus of some molecular biologists, biochemists, neurophysiologists, and communications specialists because of the surprisingly high specificity of signals and responses within a species and the clear differentiation in signaling systems among species (15, 16). In the past 20 years, a great deal has been learned about the biosynthetic pathways that result in precise ratios of specific compounds in pheromone blends (17), and major breakthroughs have recently been made in our understanding of the mechanisms that enable a male to detect incredibly low concentrations of pheromone molecules (18,19).…”

“…However, no pleiotropy has been found between signal production and response in moths (e.g., 5, 10). Because female and male moths with divergent signals and responses appear to be selected against (11, 12), we have no simple explanation for the great diversity of moths (∼180,000 species) and moth pheromones (5,13,14).…”