Cryptic Speciation and Host-Race Formation in a Purportedly Generalist Tumbling Flower Beetle

Abstract

Host-race formation remains controversial as a source of herbivorous insect diversity, and examples of host races are still fairly scarce. In this study, analysis of five enzyme loci in the ostensibly generalist tumbling flower beetle Mordellistena convicta (Coleoptera: Mordellidae) revealed hidden host-plant and plant-organ related genetic differentiation. Mordellistena convicta turned out to be a complex of cryptomorphic species, each with fewer hosts than the nominal species. These cryptic species, in turn, were divided into taxa that showed host-race characteristics: samples from different host plants and organs exhibited (1) genetic indications of partial reproductive isolation, (2) differences in size and emergence timing that suggested divergent host-related selection, and (3) among-host selective differences in mortality from parasitoids. Host-race formation in M. convicta, which has a somewhat different life history from the well-studied host races, enlarges the group of insects considered likely to undergo this process. The widespread sympatry of the M. convicta species complex, along with its spectrum of host-correlated genetic differentiation, suggests that these host specialist taxa developed in sympatry.

Host‐associated genetic differentiation in pecan leaf phylloxera

“…Gall-making insects should be even more subject to plant-specific selective pressures than other types of endophages because they must directly manipulate their host plants to produce novel structures to survive (Dreger-Jauffret & Shorthouse, 1992;Tooker & De Moraes, 2009). In the goldenrod system, HAD was found in four of seven endophagous herbivores and zero of two exophagous herbivores (Waring et al, 1990;Abrahamson & Weis, 1997;Blair et al, 2005;Stireman et al, 2005). In the goldenrod system, HAD was found in four of seven endophagous herbivores and zero of two exophagous herbivores (Waring et al, 1990;Abrahamson & Weis, 1997;Blair et al, 2005;Stireman et al, 2005).…”

The role of olfactory cues in the sequential radiation of a gall‐boring beetle, Mordellistena convicta

“…Beetles from a sympatric area were used because beetles from these populations must be actively segregating themselves, otherwise genetic differences between the two populations would be swamped out as a result of hybridisation (Blair et al, 2005). Beetles from a sympatric area were used because beetles from these populations must be actively segregating themselves, otherwise genetic differences between the two populations would be swamped out as a result of hybridisation (Blair et al, 2005).…”

“…The volatiles emitted from the galls and ungalled stems must be different, especially if the gall beetles are cuing in on a wound response emitted by the plants in response to gall formation (Stelinski et al, 2006;Takabayashi et al, 2006). This suggests that differentiation of the gall-boring beetle from its stem-boring ancestors (Blair et al, 2005) may have been as a result of an attraction to these volatiles. There is evidence that the volatiles emitted by galled and ungalled S. altissima plants have different concentrations of salicylic acid (Tooker et al, 2008), a hormone frequently emitted by plants that have been wounded (Bennett & Wallsgrove, 1994;Rani, 2006;Jahangir et al, 2009).…”

Nutrition as a facilitator of host‐race formation: the shift of a stem‐boring beetle to a gall host

“…The species and host races are distinguished by allozyme differences. Altogether, three host races of species 2 have been identified: a single stem-boring host race which attacks three species of Solidago and an Aster, and two gall host races which attack only E. solidaginis galls, one race on Solidago gigantea and the other on S. altissima (Eubanks et al, 2003;Blair et al, 2005). Altogether, three host races of species 2 have been identified: a single stem-boring host race which attacks three species of Solidago and an Aster, and two gall host races which attack only E. solidaginis galls, one race on Solidago gigantea and the other on S. altissima (Eubanks et al, 2003;Blair et al, 2005).…”

“…Because hosts differ in elemental chemistry, another possible benefit is superior nutrition on the new host which could promote the establishment of a population and its subsequent adaptation, leading to the formation of a new host race. Furthermore, the beetles of the gall host race regularly consume the gall-inducing fly, which could have been an added nutritional benefit during the shift (Uhler, 1961;Abrahamson et al, 1989;Blair et al, 2005;Dixon et al, 2009). As a model system for studying this role for nutrition, we examined the formation of a host race of the tumbling flower beetle Mordellistena convicta LeConte (Coleoptera: Mordellidae) which shifted from boring stems in several Asteraceae to boring fly-induced galls on the goldenrods Solidago gigantea Ait (Asteraceae) and S. altissima L. Like shifting to a new host plant, shifting to a new host organ presents ecological challenges (Cook et al, 2002;Joy & Crespi, 2007).…”