野村 昌史

Evolutionary theory predicts that the spread of cytoplasmic sex ratio distorters leads to the evolution of host nuclear suppressors, although there are extremely few empirical observations of this phenomenon. Here, we demonstrate that a nuclear suppressor of a cytoplasmic male killer has spread rapidly in a population of the green lacewing <italic>Mallada desjardinsi</italic> . An <italic>M. desjardinsi</italic> population, which was strongly female-biased in 2011 because of a high prevalence of the male-killing <italic>Spiroplasma</italic> endosymbiont, had a sex ratio near parity in 2016, despite a consistent <italic>Spiroplasma</italic> prevalence. Most of the offspring derived from individuals collected in 2016 had 1 : 1 sex ratios in subsequent generations. Contrastingly, all-female or female-biased broods appeared frequently from crossings of these female offspring with males derived from a laboratory line founded by individuals collected in 2011. These results suggest near-fixation of a nuclear suppressor against male killing in 2016 and reject the notion that a non-male-killing <italic>Spiroplasma</italic> variant has spread in the population. Consistently, no significant difference was detected in mitochondrial haplotype variation between 2011 and 2016. These findings, and earlier findings in the butterfly <italic>Hypolimnas bolina</italic> in Samoa, suggest that these quick events of male recovery occur more commonly than is generally appreciated.

Three plusiine species, Autographa nigrisigna, Macdunnoughia confusa, and Thysanoplusia intermixta (Lepidoptera: Noctuidae), are commonly found together in lettuce, Lactuca sativa L., fields in Japan. Given the marked morphological similarities between these species and the difficulty associated with discriminating between them using only visual cues, we used multiplex polymerase chain reaction (PCR) assay to distinguish between the three target species. Multiplex PCR uses four primers to simultaneously amplify a specific region of the mitochondrial DNA and produce species-specific banding patterns. The stringency of the method was tested using specimens of different sex, location, and developmental stage, and consistent results were obtained for all samples. Indeed, our method has the potential to clarify the species structure of plusiine species in lettuce fields. © 2011 Entomological Society of America.

It was recently recognized that in Japan, the common yellow butterfly, Eurema hecabe, consists of two sibling species, which have been unnamed yet and tentatively called yellow (Y) type and brown (B) type. We investigated the diversity of nuclear and mitochondrial genes in Japanese populations of Y type and B type of E. hecabe. The phylogeny based on nuclear genes agreed with the distinction between Y type and B type, which had been also supported by a wide array of biological data. However, the phylogeny based on mitochondrial genes did not reflect the distinction. PCR survey of Wolbachia revealed that B-type populations were all infected while Y-type populations contained both infected and uninfected individuals. A single genotype of Wolbachia, which was inferred to be a CI-inducing strain from their wsp gene sequence, was prevalent in these populations. Notably, the mitochondrial phylogeny was in perfect agreement with the pattern of Wolbachia infection, suggesting that the Wolbachia infection had affected the mitochondrial genetic structure of the host insects. Probably, the Wolbachia strain and the associated mitochondrial genomes have been occasionally introduced from B-type populations to Y-type populations through migration and subsequent interspecific hybridization, and CI-driven population sweep has been spreading the Wolbachia strain and the particular mitochondrial haplotypes, which originated from B-type populations, into Y-type populations. On the basis of these results together with the geological and biogeographical knowledge of the Japanese Archipelago, we proposed an evolutionary hypothesis on the invasion and spread of Wolbachia infection in B-type and Y-type of E. hecabe.

The green lacewing, Chrysoperla carnea (Stephens), is an important natural enemy of various crop pests, especially aphids. In the Japanese fauna. there are two types of larval forms, A and B, characterized by different head capsule markings. The Type A form is distributed throughout Japan, but the Type B form has a more limited distribution. Adults use abdominal vibration as a communication signal (courtship song) during mating. We analyzed oscillograms of these songs among several Japanese populations of C carnea. The courtship songs of types A and B are distinctly different from one another. We then performed crossing tests between the two types. Copulation between same-type pairings was much more likely than between different-type pairings. We also analyzed courtship songs of European C carnea sensu stricti, introduced to Japan as a natural enemy of crop pests. The song of these introduced green lacewings appeared to differ from either type of Japanese C carnea. The two types of C carnea are likely to be different species, and also distinct from C carnea sensu stricti of Europe.

Reproductive isolation was studied in four syntopic species of Petunia sensu Jussieu (Solanaceae) at a site in Rio Grande do Sul State, Brazil. Reciprocal artificial crossing experiments confirmed that a genetic barrier exists between Petunia (P. axillaris and P. integrifolia) and Calibrachoa (C. parviflora and C. heterophylla), and also between C. parviflora and C. heterophylla. Petunia axillaris (white, nocturnally scented flower) is genetically compatible with the syntopic and allotopic P. integrifolia (coloured, unscented flower). Reproductive isolation appears to be maintained by the two species having different pollinators: nocturnally active hawkmoths (Manduca contracta and M. diffissa subsp. petuniae) pollinate P. axillaris while a diurnally active bee (Hexantheda sp.) pollinates P. integrifolia. Flowers of P. integrifolia exhibit diurnal opening and closing movements synchronous with the activity period of the bee. Other than a probable nectar robber (a carpenter bee, Xylocopa augusti), no insect visited flowers of P. axillaris in the day. Amounts of floral nectar in P. axillaris and P. integrifolia were within the range of hawkmoth- and bee-pollinated flowers, respectively. Reproductive isolating mechanisms in the genus Petunia sensu Jussieu are discussed. © 2001 Annals of Botany Company.