Abstract
Analysis of sexual selection and sexual isolation in Drosophila mojavensis and its relatives has revealed a pervasive role of rearing substrates on adult courtship behavior when flies were reared on fermenting cactus in preadult stages. Here, we assessed expression of contact pheromones comprised of epicuticular hydrocarbons (CHCs) from eclosion to 28 days of age in adults from two populations reared on fermenting tissues of two host cacti over the entire life cycle. Flies were never exposed to laboratory food and showed significant reductions in average CHC amounts consistent with CHCs of wild-caught flies. Overall, total hydrocarbon amounts increased from eclosion to 14–18 days, well past age at sexual maturity, and then declined in older flies. Most flies did not survive past 4 weeks. Baja California and mainland populations showed significantly different age-specific CHC profiles where Baja adults showed far less age-specific changes in CHC expression. Adults from populations reared on the host cactus typically used in nature expressed more CHCs than on the alternate host. MANCOVA with age as the covariate for the first six CHC principal components showed extensive differences in CHC composition due to age, population, cactus, sex, and age × population, age × sex, and age × cactus interactions. Thus, understanding variation in CHC composition as adult D. mojavensis age requires information about population and host plant differences, with potential influences on patterns of mate choice, sexual selection, and sexual isolation, and ultimately how these pheromones are expressed in natural populations. Studies of drosophilid aging in the wild are badly needed.
Highlights
Estimates of egg-to-adult viability and development time (DEVT) of each population reared on either agria or organ pipe revealed greater viability (F = 10.26, P = 0.002, df = 1/56) of Punta Prieta, Baja California flies than Las Bocas, Sonora flies, X Æ 1 SE, 78.8 Æ 0.02 vs. 71.1 Æ 0.02, respectively, and longer DEVT (F = 77.20, P < 0.0001, df = 1/112) of Las Bocas flies than Punta Prieta flies, X Æ 1 SE, 16.45 Æ 0.09 da vs. 15.38 Æ 0.09 da, respectively
Punta Prieta adults produced more total comprised of epicuticular hydrocarbons (CHCs) when reared on their host plant, agria cactus, while Las Bocas adults expressed more CHCs when reared on their native host, organ pipe cactus (Fig. 1)
We found extensive variation in the expression of these molecules in D. mojavensis throughout adult life, documenting both increases and decreases in different combinations of CHCs from eclosion to age at first reproduction (AAFR) and to age at death that was significantly influenced by population and host plant differences
Summary
Studies of cuticular hydrocarbons (CHCs) serving as contact pheromones in insects have revealed a wealth of information concerning their biosynthesis (Schal et al 1998; Howard and Blomquist 2005), regulation by a handful of genes (Dallerac et al 2000; Gleason et al 2005), diversity in closely related species (Page et al 1997; Oliveira et al 2011; Schwander et al 2013), roles in waterproofing and transcuticular water loss (Gibbs and Pomonis 1995; Gibbs and Rajpurohit 2010), and sensitivity to biotic and abiotic factors.
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