Journal - Science (New York, N.Y.) (United States )

Journal - Proceedings. Biological sciences / The Royal Society (ENGLAND )

Abstract :

Mate recognition systems (MRSs) play a major role in sexual selection and speciation, yet few studies have analysed both male and female components in detail. Here, female preference functions have been characterized for the tettigoniid bushcricket Ephippiger ephippiger, and the inheritance of male song and female preference functions followed in crosses between subspecies. Songs are disproportionately determined by sex-linked genes. However, there is no evidence for a role of maternally derived sex-linked genes in female preference or of maternal effects. At the genetic level, there is a mismatch between peak preferences and male song, consistent with an evolutionary history of persistent directional preferences. Such a pattern of inheritance could contribute to the process of speciation via the evolution of new MRSs.

Journal - BMC Evolutionary Biology

Abstract :

BackgroundIn acoustic species, traits such as male calling song are likely to diverge quickly between allopatric populations due to sexual selection, and divergence in parameters such as carrier frequency, chirp structure, and other important song characters can influence sexual isolation. Here we make use of two forms of Mormon crickets to examine differences in a broad suite of traits that have the potential to influence speciation via sexual isolation. Mormon crickets in "gregarious" populations aggregate into dense migratory bands, and females are the sexually competitive sex (sex-role reversal). There is also a non-outbreak "solitary" form. These two forms are largely but not perfectly correlated with a significant mtDNA subdivision within the species that is thought to have arisen in allopatry. Combined information about multiple, independently evolving traits, such as morphology and structural and behavioural differences in calling song, provides greater resolution of the overall differences between these allopatric populations, and allows us to assess their stage of divergence. We test two predictions, first that the forms differ in song and second that gregarious males are more reluctant to sing than solitary males due to sex role reversal. We also tested for a difference in the relationship between the size of the forewing resonator, the mirror, and carrier frequency, as most models of sound production in crickets indicate that mirror size should predict carrier frequency.ResultsMultivariate analyses showed that solitary and gregarious individuals from different populations representing the two mtDNA clades had almost non-overlapping distributions based on multiple song and morphological measurements. Carrier frequency differed between the two, and gregarious males were more reluctant to sing overall. Mirror size predicted carrier frequency; however, the relationship between mirror size and surface area varied between solitary and gregarious forms, suggesting that factors above and beyond mirror size contribute to carrier frequency.ConclusionThe two clades of Mormon crickets differ in a broad suite of independent traits that probably justify subspecies status (the two can successfully mate so may not be reproductively isolated). However, our results emphasize the importance of carefully distinguishing the ultimate causation of differences between traits used to delineate species or subspecies boundaries.

Journal - Biology Letters

Abstract :

Drosophila olfactory (ORs) and gustatory (GRs) receptors areevolutionarily unrelated to vertebrate ORs or nematode chemosensoryreceptors. Insect ORs display a reverse membrane topology comparedwith conventional G-protein-coupled receptors, suggesting thatthe mammalian scheme of chemosensory signal transduction cannotdirectly apply to insects. Experimental studies of GR membranetopology are lacking. We analysed the distribution of aminoacid sites in GRs and ORs that show evidence for divergenceunder either positive selection or relaxed purifying constraints,in the genomes of 12 Drosophila species and found significantdifferences between these two receptor types. This suggeststhat insect ORs and GRs have distinct molecular properties andmechanisms of ligand recognition and/or signal transduction.

Journal - Proceedings of the Royal Society B: Biological Sciences

Abstract :

Mate recognition systems (MRSs) play a major role in sexualselection and speciation, yet few studies have analysed bothmale and female components in detail. Here, female preferencefunctions have been characterized for the tettigoniid bushcricketEphippiger ephippiger, and the inheritance of male song andfemale preference functions followed in crosses between subspecies.Songs are disproportionately determined by sex–linkedgenes. However, there is no evidence for a role of maternallyderived sex–linked genes in female preference or of maternaleffects. At the genetic level, there is a mismatch between peakpreferences and male song, consistent with an evolutionary historyof persistent directional preferences. Such a pattern of inheritancecould contribute to the process of speciation via the evolutionof new MRSs.