Divergent host plant adaptation drives the evolution of sexual isolation in the grasshopper Hesperotettix viridis (Orthoptera: Acrididae) in the absence of reinforcement

Abstract

Early stages of lineage divergence in insect herbivores are often related to shifts in host plant use and divergence in mating capabilities, which may lead to sexual isolation of populations of herbivorous insects. We examined host preferences, degree of differentiation in mate choice, and divergence in cuticular morphology using near-infrared spectroscopy in the grasshopper Hesperotettix viridis aiming to understand lineage divergence. In Kansas (USA), H. viridis is an oligophagous species feeding on Gutierrezia and Solidago host species. To identify incipient mechanisms of lineage divergence and isolation, we compared host choice, mate choice, and phenotypic divergence among natural grasshopper populations in zones of contact with populations encountering only one of the host species. A significant host-based preference from the two host groups was detected in host-paired feeding preference studies. No-choice mate selection experiments revealed a preference for individuals collected from the same host species independent of geographic location, and little mating was observed between individuals collected from different host species. Female mate choice tests between males from the two host species resulted in 100% fidelity with respect to host use. Significant differentiation in colour and cuticular composition of individuals from different host plants was observed, which correlated positively with host choice and mate choice. No evidence for reinforcement in the zone of contact was detected, suggesting that divergent selection for host plant use promotes sexual isolation in this species.

Hydrocarbon divergence and reproductive isolation in Timema stick insects

“…Among other insects, cuticular hydrocarbon variation has been implicated in a range of developmental, ecological and behavioral contexts, including ecological adaptation to the local abiotic or biotic environment [40], effects from temperature and nutrition during juvenile stages [41,42], interactions with host plants [43,44], and mate choice and sexual selection within species [45,46]. Evidence for cuticular hydrocarbons mediating the evolution of reproductive isolation has thus far centered mainly on associations between variation in hydrocarbon profiles and variation in propensities to mate [47].…”

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

“…Grace et al. ). Here, we report the first attempt at characterizing CHC variation in adult D. mojavensis from eclosion to 28 days of age in flies exposed only to natural conditions, that is, fermenting cactus tissues like those used in nature.…”

“…However, a full understanding of environmentally sensitive mating behaviors requires knowledge of conditions experienced by adults under natural conditions that contribute to differences in courtship success (see e.g. Grace et al 2010). Here, we report the first attempt at characterizing CHC variation in adult D. mojavensis from eclosion to 28 days of age in flies exposed only to natural conditions, that is, fermenting cactus tissues like those used in nature.…”

Divergent Egg Physiologies in Two Closely Related Grasshopper Species:Taeniopoda equesversus Romalea microptera (Orthoptera: Romaleidae)

“…Under the right conditions, populations and species quickly adjust to local conditions via genetic change (Loxdale 2010) or phenotypic plasticity (Whitman and Ananthakrishnan 2009), or both (Grace et al 2010). Such evolution can be surprisingly rapid (Carroll et al, 2003, Carroll 2008, Bradshaw and Holzapfel 2010, Huang et al 2010, Loxdale 2010).…”

“…Comparisons among closely related populations and species living in divergent habitats provide some of the best evidence in support of adaptive evolution and incipient speciation (Ghalambor et al 2003, Willmer et al 2005, Grace et al 2010). Because closely related taxa only recently diverged from a common ancestor, we would normally expect them to possess similar characteristics (i.e., phylogenetic conservatism; Prinzing et al 2001, Willis et al 2008).…”