The neural basis for host shifts in Rhagoletis pomonella

Abstract

Host shifts are considered a key generator of insect biodiversity. For insects, adaptation to new host plants often requires changes in larval/pupal development and adult behavioural preference toward new hosts (Rajus et al., 2021). I am studying the neural mechanism for ecological speciation in Rhagoletis sp. (Diptera: Tephritidae). This speciation is being observed over the past 300 years in North America. Introduction of domesticated apples (Malus pumila) by European colonists around 1800-1850 caused a shift in host preference by these flies from their native host downy hawthorn (Crataegus mollis). However, the question of how such a rapid and specific change in host preference could occur in such a short period of evolutionary time remains unanswered. newlineI, along with my colleagues, have identified a neuronal switch at the first synapse in the chemosensory system in the brain associated with differential host choice behaviour (Tait et al., 2021). This suggests that any changes in host preference must occur via network-level changes in the brain. In addition to behavioural preference, these races exhibit differences in pupal diapause timing with respect to their hosts. The dual role of neuromodulators in regulating both insect development and host-seeking behaviour provides a potential source for linking network level changes in the brain to changes in life history timing. Thus, I also correlated life-history timing, brain development and corresponding levels of 14 neurochemicals in Rhagoletis pomonella (Kharva et al., 2022). I found that apple race pupae exhibited adult brain morphogenesis three weeks faster after an identical simulated winter than the hawthorn race, which correlated with significantly lower titres of several neurochemicals. In some cases, particularly biogenic amines, differences in titres were reflected in the mature adult stage, when host preference is exhibited. newline