Rapid and repeatable shifts in life‐history timing of Rhagoletis pomonella (Diptera: Tephritidae) following colonization of novel host plants in the Pacific Northwestern United States

Abstract

Host shifts of phytophagous insect specialists to novel plants can result in divergent ecological adaptation, generating reproductive isolation and potentially new species. Rhagoletis pomonella fruit flies in eastern North America underwent a host shift ~160 ya from native downy hawthorn (Crataegus mollis) to introduced, domesticated apple (Malus domestica). Divergent selection on diapause phenology related to the earlier fruiting time of apples versus downy hawthorns resulted in partial allochronic reproductive isolation between the fly races. Here, we test for how rapid and repeatable shifts in life‐history timing are driving ecological divergence of R. pomonella in the Pacific Northwestern USA. The fly was introduced into the region via larval‐infested apples 40–65 ya and now attacks native black hawthorn (Crataegus douglasii) and introduced ornamental hawthorn (Crataegus monogyna), in addition to early‐ and late‐maturing apple varieties in the region. To investigate the life‐history timing hypothesis, we used a field‐based experiment to characterize the host‐associated eclosion and flight activity patterns of adults, and the feeding times of larvae at a field site in Vancouver, Washington. We also assessed the degree to which differences in host‐fruiting time generate allochronic isolation among apple‐, black hawthorn‐, and ornamental hawthorn‐associated fly populations. We conclude that host‐associated fly populations are temporally offset 24.4% to 92.6% in their seasonal distributions. Our results imply that R. pomonella possesses the capacity for rapid and repeatable shifts in diapause life history to match host‐fruiting phenology, which can generate ecologically based reproductive isolation, and potentially biodiversity in the process.

Cascading reproductive isolation: Plant phenology drives temporal isolation among populations of a host‐specific herbivore

“…; Mattsson et al. ). Thus, we use this approach to quantify temporal RI between host‐associated populations.…”

“…If populations emerge at different times on alternative host plants, but earlier emerging individuals survive long enough to partially/completely overlap with the later emerging population during reproduction, RI will be reduced/eliminated. To date, few studies have combined these phenotypes to estimate temporal RI between insect populations residing on different hosts (Feder et al 1993;Forbes et al 2009;Hood et al 2015;Mattsson et al 2015). Thus, we use this approach to quantify temporal RI between host-associated populations.…”

The damage risk evaluation of Aphis gossypii on wheat by host shift and fitness comparison in wheat and cotton

“…This allows insects to escape from natural enemies or competition and seek better nutrition (Blair et al 2010;Zvereva et al 2010). In addition, host plant shifts of herbivorous insects may cause sympatric speciation and can create new pests for agricultural crops (Bass et al 2013;Mattsson et al 2015). Life table analysis is able to provide some useful biological and demographic parameters for studying insect populations under specific conditions, and these parameters can be used as indicators for assessing the potential of the growth of a pest population under new conditions (Maia et al 2000;Diaz and Fereres 2005;Obopile and Ositile 2009).…”

Reproductive ecology of a parasitic plant differs by host species: vector interactions and the maintenance of host races

“…Pollinators determine which individuals exchange genetic material, and seed dispersers determine where offspring have the opportunity to establish. For many better studied, directly transmitted parasites, divergence is facilitated by mate choice, phenology, or sensitivity to host cues (Linn et al 2003;Ferrari et al 2006;Mattsson et al 2015). However, for vector transmitted parasites, vector feeding preferences can be the dominant factor influencing host infections (Altizer et al 1998;Simpson et al 2012).…”