Abstract
The development of host races, genetically distinct populations of the same species with different hosts, is considered to be the initial stage of ecological speciation. Ecological and biological differences consistent with host race formation have been reported between water‐oat and rice‐associated populations of Chilo suppressalis. In order to confirm whether these differences have a genetic basis, we conducted experiments to determine the extent to which various life‐history traits and the time of peak mating activity of these populations were influenced by the species of host plant larvae were raised on. Individuals from each population were reared for three consecutive generations on either water‐oat fruit pulp or rice seedlings. Descendants of both populations had higher larval survival rates, shorter larval developmental periods, higher pupal weight, and longer adult forewings, when reared on water‐oats than when reared on rice. The time of peak of mating activity differed between the descendants of each population, irrespective of whether they were raised on water‐oats or rice. These results indicate that although some life‐history traits of host‐associated populations of C. suppressalis are influenced by the host plant larvae are raised on, time of peak mating activity is not. Because it is a stable, objective, phenotypic trait, further research on difference in the time of peak mating activity between host‐associated populations of C. suppressalis should be conducted to clarify the mechanism responsible for host race formation in this species.
Highlights
Host race formation is thought to be the first step in the process of ecological speciation responsible for much of the diversity of phytophagous, parasitic invertebrates, and even some vertebrates (Via 2001)
Previous studies of herbivorous insects suggest that adaptation to different host plants can lead to sufficient differences in life-history traits to cause the reproductive isolation of sympatric host races (Feder and Filchak 1999; Dres and Mallet 2002; Funk et al 2002)
The results of this study indicate that the larval survival rate, larval developmental period, and body size of C. suppressalis differ significantly between putative rice and water-oat host races, variation in these traits is affected by the host plant larvae are reared on
Summary
Host race formation is thought to be the first step in the process of ecological speciation responsible for much of the diversity of phytophagous, parasitic invertebrates, and even some vertebrates (Via 2001). The genetic divergence of host races through their adaptation to different host plants is considered to have contributed to insects becoming the most diverse multicellular animal taxon on Earth (Dres and Mallet 2002; Funk et al 2002). Host races are defined as sympatric parasite populations that have different hosts, appreciable gene flow, and a degree of genetic divergence (Dres and Mallet 2002). Host races generally differ in life-history traits such as survival rate, developmental period, body size and mating behavior
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