Premating isolation is determined by larval rearing substrates in cactophilicDrosophila mojavensis. VIII. Mating success mediated by epicuticular hydrocarbons within and between isolated populations

Abstract

We tested the hypothesis that intrademic sexual selection has caused sexual isolation between populations of geographically isolated populations of cactophilic Drosophila mojavensis, and was mediated by epicuticular hydrocarbons (EHCs), contact pheromones in this system. Sexual selection and sexual isolation were estimated using a Baja California and mainland population by comparing the number of mated and unmated males and females in each of four pairwise population mating trials. EHC profiles were significantly different in mated and unmated males in the interdemic (Baja♀ × Mainland♂ and Mainland♀ × Baja♂), but not the intrademic mating trials. A small number of EHCs was identified that best discriminated among mated and unmated males, mostly alkadienes with 34 and 37 carbons. Females showed population‐specific preferences for male EHC profiles. However, EHC profiles between mated and unmated males in the intrademic mating trials were not significantly different, consistent with undetectable sexual selection estimated directly from numbers of copulating pairs vs. unmated adults. Thus, sexual isolation among populations was much stronger than sexual selection within these populations of D. mojavensis.

Male-Specific Transfer and Fine Scale Spatial Differences of Newly Identified Cuticular Hydrocarbons and Triacylglycerides in a Drosophila Species Pair

“…A few pheromonal components, e.g. C 34 alkadienes [41] were not reliably measured in this study because they overlapped with isotopic signals from other compounds. Since alkanes are currently not detected with this method, variation in the major CHC components 2-methyloctacosane and 2-methyltricontane could not be assessed.…”

“…Studies of rearing substrate effects on cuticular hydrocarbon profiles of D. arizonae and D. mojavensis [19], [20] demonstrated significant differences between cactus and lab food reared flies, so subsequent studies have employed cactus-reared flies only [9], [26], [29], [41]. Host rearing effects on agria vs. organ pipe cactus influenced a small number of hydrocarbon components in Baja California and mainland populations, but these differences due to cactus species were far smaller than those for cactus vs. lab food.…”

Natural Variation in the Strength and Direction of Male Mating Preferences for Female Pheromones in Drosophila melanogaster

“…The quantity of CHCs transferred to our perfumed flies appears lower than those naturally found on oe + females (Figure S1). If male preferences for female CHCs are dose-dependent, as has been found in D. mojavensis [39], then CHCs may be more attractive to D. melanogaster males at lower concentrations compared to higher concentrations. Similarly, the CHC profile of the white females used for perfuming differs somewhat from that of the oe + females (Figure S1), which might explain our inconsistent results using the two methods.…”

Mating success depends on rearing substrate in cactophilic Drosophila

“…Cuticular hydrocarbons are known to play a major role (Markow and Toolson 1990;Billeter et al 2009). For example, the larval rearing substrate is known to affect the relative amounts of epicuticular hydrocarbons that function as sex pheromones in the cactophilic D. mojavensis and D. arizonae (Markow and Toolson 1990;Etges and Tripodi 2008). Alternatively, nutritional condition of larvae could imprint adult mating behavior affecting, for instance, the number of courtship attempts, courtship songs or female receptivity.…”

“…For instance, a series of experiments in D. melanogaster showed that larvae reared in an enriched environment are twice as successful in acquiring mates as are males reared in standard medium (Dukas and Mooers 2003). In addition, it has been shown that mate choice, courtship success and song variation are influenced by the rearing substrate in the cactophilic D. mojavensis (Brazner and Etges 1993;Etges and Tripodi 2008). In this species, the host cactus where larvae develop affects adult epicuticular hydrocarbon profiles, which have been implicated as determinants of mate choice and mating success (Stennett and Etges 1997;Etges et al 2007).…”