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

Abstract

Host plant shifting of phytophagous insects can lead to the formation of host associated differentiation and ultimately speciation. In some cases, host plant specificity alone acts as a nearly complete pre-mating isolating barrier among insect populations. We here test whether effective pre-mating isolation and host-independent behavioral isolation have evolved under the condition of extreme host specilization using two sympatric flea beetles with incomplete post-mating isolation under laboratory conditions. Phylogenetic analysis and coalescent simulation results showed that there is a limited interspecific gene flow, indicating effctive isolation between these species. Three types of mating tests in the absence of host plant cues showed that strong host-independent behavioral isolation has evolved between them. We conclude that almost perfect assortative mating between these two extreme host specialists results from a combination of reduced encounter rates due to differential host preference and strong sexual isolation.

Difference in diel mating time contributes to assortative mating between host plant-associated populations of Chilo suppressalis

“…female vs male choice) give different I PSI values and similar variation has been reported in previous studies233739. This is consistent with the hypothesis that the degree of reproductive isolation varies under different mating systems, and therefore, experimental designs3745.…”

“…The mating patterns and degree of sexual isolation between the W and R populations in different choice tests were estimated by the pair total index (PTI) and joint isolation index (I PSI )3739. The PTI estimates whether the mating pattern of each pairing is different from random mating.…”

“…Although the contribution of differences in diel mating time is confounded by mate preference, I PSI was also calculated for male-choice and female-choice tests to compare the degrees of sexual isolation estimated by different choice tests. A similar method of data analysis was used in previous studies3739. The PTI and I PSI were calculated using the JMATING software package40.…”

Phylogenetic test of speciation by host shift in leaf cone moths (Caloptilia) feeding on maples (Acer)

“…; Ohshima ; Xue et al. ), providing a mechanistic explanation of how host shifts may promote speciation. Understanding the role of host plant shifts in generating diversity is thus a current focus in the study of herbivorous insect diversification (Marvaldi et al.…”

“…For example, a classical study by Farrell (1998) showed that herbivorous insects using angiosperms as hosts are more species rich than those using gymnosperms among the Phytophaga beetles, suggesting that the diversity of angiosperms has facilitated speciation by host shift in the beetles that feed on them. Studies of host races in herbivorous insects showed that specialization to a novel host plant sometimes results in reproductive isolation between insects using different hosts (Feder et al 1988;Groman and Pellmyr 2000;Hawthorne and Via 2001;Nosil et al 2002;Thomas et al 2003;Malausa et al 2005;Ohshima 2012;Xue et al 2014), providing a mechanistic explanation of how host shifts may promote speciation. Understanding the role of host plant shifts in generating diversity is thus a current focus in the study of herbivorous insect diversification (Marvaldi et al 2002;Stireman et al 2005;Wheat et al 2007;Winkler et al 2009;Fordyce 2010;Funk 2010;Matsubayashi et al 2010;Nyman 2010;Soria-Carrasco et al 2014).…”