Levels of Mate Recognition Within and Between Two Drosophila Species and Their Hybrids

Abstract

If sexual selection is to result in speciation, traits involved in mate choice within species need to be capable of producing sexual isolation between species. We investigated the association between mate choice and sexual isolation using interspecific hybrids between two sibling species, Drosophila serrata and Drosophila birchii. A perfuming experiment demonstrated that olfaction was involved in the sexual isolation between the two species. A quantitative genetic analysis using 30 populations of hybrids between the two species indicated that mating success in hybrid individuals was predominately determined by cuticular hydrocarbons; the average genetic correlation between mating success and cuticular hydrocarbon profile was 0.84, and in some instances exceeded 0.95. Multivariate analysis of the cuticular hydrocarbons of the two species revealed that there were three independent blends of cuticular hydrocarbons that separated three levels of organization: species, sex, and sex within species. The hydrocarbons used by hybrids in mate choice included those that separated the two species, demonstrating that species-specific characters may be used in mate choice within populations. The interspecific reciprocal cross had major effect on which cuticular hydrocarbons were associated with mating success, indicating that the expression of the cuticular hydrocarbons was strongly sex linked.

Genetic Constraints and the Evolution of Display Trait Sexual Dimorphism by Natural and Sexual Selection

“…Nine homologous CHCs were analyzed using 4-day-old virgin flies (male and female) and employing standard gas chromatography methods: Z,Z-5,9-C 24:2 , Z,Z-5,9-C 25:2 , Z-9-C 25:1 , Z-9-C 26:1 , 2-Me-C 26 , Z,Z-5,9-C 27:2 , 2-Me-C 28 , Z,Z-5,9-C 29:2 , and 2-Me-C 30 (Blows and Allan 1998;Howard et al 2003). In some instances, the two dienes-Z,Z-5,9-C 24:2 and Z,Z-5,9-C 25:2 -could not be resolved on gas chromatographs, and so these individuals were omitted from further analysis.…”

“…Drosophila serrata has a well-characterized mate and species recognition system (Blows and Allan 1998;Higgie et al 2000), in which both males and females discriminate among potential mates via display traits consisting of a suite of homologous, but sexually dimorphic, nonvolatile contact pheromones composed of cuticular hydrocarbons (CHCs; Chenoweth and Blows 2003). These CHCs have previously been shown to experience sexually antagonistic sexual selection under laboratory conditions (Chenoweth and Blows 2005), and sexual dimorphism has evolved during adaptation to novel laboratory environments (Rundle et al 2005).…”

Comparing Complex Fitness Surfaces: Among‐Population Variation in Mutual Sexual Selection inDrosophila serrata

“…Vials were observed, and once intromission had been achieved, all flies were anesthetized using CO 2 , and the choosing fly was discarded. The remaining individuals, one chosen and one rejected by the discarded choosing individual, then had their CHCs extracted for gas chromatography analysis using a standard protocol (Blows and Allan 1998). Individual flies were treated as independent replicates in subsequent analyses because past work indicates that this has no discernible effect on the magnitude or significance of the resulting selection gradients .…”

“…We studied variation in sexual selection among geographic populations of the fruit fly Drosophila serrata, a species that uses a suite of contact pheromones composed of cuticular hydrocarbons (CHCs) in both mate choice within populations (Blows and Allan 1998;Blows 2003, 2005;Blows et al 2004;Hine et al 2004) and species recognition (Blows and Allan 1998). Mate choice in this species, which has been well characterized via a series of evolutionary and genetic experiments, is mutual: both males and females discriminate among potential mates based on CHCs Blows 2003, 2005).…”

Positive genetic correlation between female preference and offspring fitness

“…First, the mechanism of mate recognition in the D. serrata complex is well understood. Species within the D. serrata complex use cuticular hydrocarbons (CHCs) for mate recognition (Blows & Allan 1998), and CHCs have been shown to be important for mate recognition under field conditions, and to respond to selection under laboratory conditions (Higgie et al 2000). Second, females may use male CHCs to indicate male genetic quality in this species complex.…”