Recent Speciation in Three Closely Related Sympatric Specialists: Inferences Using Multi-Locus Sequence, Post-Mating Isolation and Endosymbiont Data

Abstract

Shifting between unrelated host plants is relatively rare for phytophagous insects, and distinct host specificity may play crucial roles in reproductive isolation. However, the isolation status and the relationship between parental divergence and post-mating isolation among closely related sympatric specialists are still poorly understood. Here, multi-locus sequence were used to estimate the relationship among three host plant–specific closely related flea beetles, Altica cirsicola, A. fragariae and A. viridicyanea (abbreviated as AC, AF and AV respectively). The tree topologies were inconsistent using different gene or different combinations of gene fragments. The relationship of AF+(AC+AV) was supported, however, by both gene tree and species tree based on concatenated data. Post-mating reproductive data on the results of crossing these three species are best interpreted in the light of a well established phylogeny. Nuclear-induced but not Wolbachia-induced unidirectional cytoplasmic incompatibility, which was detected in AC-AF and AF-AV but not in AC-AV, may also suggest more close genetic affinity between AC and AV. Prevalence of Wolbachia in these three beetles, and the endosymbiont in most individuals of AV and AC sharing a same wsp haplotype may give another evidence of AF+(AC+AV). Our study also suggested that these three flea beetles diverged in a relative short time (0.94 My), which may be the result of shifting between unrelated host plants and distinct host specificity. Incomplete post-mating isolation while almost complete lineage sorting indicated that effective pre-mating isolation among these three species should have evolved.

Assortative mating between two sympatric closely-related specialists: inferred from molecular phylogenetic analysis and behavioral data

“…Considering the incomplete post-mating reproductive isolation181920, we suggest near perfect assortative mating has evolved. Differing from many studies in which allochronic factors play an important role in reproductive isolation and speciation41, allochronic isolation contribute little in the present system.…”

“…The insects were fed their respective host plants ( D. indica fed to AF and G. nepalens fed to AV) in growth chambers at 16:8 LD and 25°C181920. To eliminate the possible effects due to different physiology, virgin captive-bred offspring were used for no-choice tests.…”

Manipulating two olfactory cues causes a biological control beetle to shift to non‐target plant species

“…Most phytophagous beetles feed on a limited range of taxonomically related plant species, and some are highly specialized on one or a few host plant species (Winkler & Mitter 2008;Chapman 2009;Xue et al 2011). Studies on host specialization and adaptation have revealed that plant chemistry plays an important role in the evolution of plant-beetle associations (Feeny 1975;St€ adler 1992;Landolt & Phillips 1997;Rasmann & Agrawal 2011).…”

The draft genome of the specialist flea beetle Altica viridicyanea (Coleoptera: Chrysomelidae) provides insight into host plant specialization

“…The high rate of diversi cation among host-speci c herbivorous insects is thought to result from their shift and specialization to distinct host-plant species, creating conditions that promote reproductive isolation and contribute to the process of speciation [1][2][3]. A model herbivore that has been used to address questions about host plant specialization, reproductive isolation, and ecological speciation is the leaf beetle genus Altica (Coleoptera: Chrysomelidae) [4][5][6][7][8][9][10]. This group has undergone rapid divergence that is largely associated with host plant use.…”