Hydrocarbon divergence and reproductive isolation in Timema stick insects

The genitalia of internally fertilizing taxa represent a striking example of rapid morphological evolution. Although sexual selection can shape variation in genital morphology, it has been difficult to test whether multiple sexual selection pressures combine to drive the rapid evolution of individual genital structures. Here, we test the hypothesis that both pre‐ and postcopulatory sexual selection can act in concert to shape complex structural variation in secondary genital morphology. We genetically modified the size and shape of the posterior lobes of Drosophila melanogaster males and tested the consequences of morphological variation on several reproductive measures. We found that the posterior lobes are necessary for genital coupling and that they are also the targets of multiple postcopulatory processes that shape quantitative variation in morphology, even though these structures make no direct contact with the external female genitalia or internal reproductive organs during mating. We also found that males with smaller and less structurally complex posterior lobes suffer substantial fitness costs in competitive fertilization experiments. Our results show that sexual selection mechanisms can combine to shape the morphology of a single genital structure and that the posterior lobes of D. melanogaster are the targets of multiple postcopulatory selection pressures.

Section: Discussionsupporting

confidence: 86%

Multiple sexual selection pressures drive the rapid evolution of complex morphology in a male secondary genital structure

Frazee

Masly

2015

“…; Schwander et al. ), roles in waterproofing and transcuticular water loss (Gibbs and Pomonis ; Gibbs and Rajpurohit ), and sensitivity to biotic and abiotic factors. As pheromones, these molecules are involved in species and sex‐specific recognition (Singer ) and mating status (Everaerts et al.…”

Section: Introductionmentioning

confidence: 99%

“…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. As pheromones, these molecules are involved in species and sex-specific recognition (Singer 1998) and mating status (Everaerts et al 2010) during courtship and have been shown to mediate female preference by sexual selection Havens and Etges 2013) and sexual isolation (Coyne and Charlesworth 1997;Etges and Ahrens 2001;Ishii et al 2001;Dopman et al 2004;Peterson et al 2007) between populations and species.…”

Section: Introductionmentioning

confidence: 99%

Premating isolation is determined by larval rearing substrates in cactophilic Drosophila mojavensis. X. Age‐specific dynamics of adult epicuticular hydrocarbon expression in response to different host plants

Etges

Oliveira

2014

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.

“…The Timema host phylogeny is very robust (Schwander et al. , ). For the parasite phylogeny, although several nodes are weakly supported, topology errors for the weakly supported nodes would not influence the main result.…”

Section: Discussionmentioning

confidence: 99%

“…Both TreeMap 3.0b and Jane 4.0 use the phylogenies of hosts and their parasites as input. To perform the cophylogenetic analyses implemented in TreeMap 3.0b, we used a robust, previously published Timema phylogeny (Schwander et al 2011(Schwander et al , 2013, which includes host species for which we did not find any parasites during 9 years of sampling. Because hosts without associated parasites cannot be used in Jane 4.0, we pruned the host phylogeny to comprise only the nine Timema species for which we found parasites in analyses with Jane 4.0.…”

Section: Host-parasite Cophylogenetic Analysesmentioning

confidence: 99%

Nematode endoparasites do not codiversify with their stick insect hosts

Larose

Schwander

2016

Self Cite

Host–parasite coevolution stems from reciprocal selection on host resistance and parasite infectivity, and can generate some of the strongest selective pressures known in nature. It is widely seen as a major driver of diversification, the most extreme case being parallel speciation in hosts and their associated parasites. Here, we report on endoparasitic nematodes, most likely members of the mermithid family, infecting different Timema stick insect species throughout California. The nematodes develop in the hemolymph of their insect host and kill it upon emergence, completely impeding host reproduction. Given the direct exposure of the endoparasites to the host's immune system in the hemolymph, and the consequences of infection on host fitness, we predicted that divergence among hosts may drive parallel divergence in the endoparasites. Our phylogenetic analyses suggested the presence of two differentiated endoparasite lineages. However, independently of whether the two lineages were considered separately or jointly, we found a complete lack of codivergence between the endoparasitic nematodes and their hosts in spite of extensive genetic variation among hosts and among parasites. Instead, there was strong isolation by distance among the endoparasitic nematodes, indicating that geography plays a more important role than host‐related adaptations in driving parasite diversification in this system. The accumulating evidence for lack of codiversification between parasites and their hosts at macroevolutionary scales contrasts with the overwhelming evidence for coevolution within populations, and calls for studies linking micro‐ versus macroevolutionary dynamics in host–parasite interactions.