村上 正志

Abstract Polyphagous insect herbivores feed on multiple host‐plant species and face a highly variable chemical landscape. Comparative studies of polyphagous herbivore metabolism across a range of plants is an ideal approach for exploring how intra‐ and interspecific chemical variation shapes species interactions. We used polyphagous caterpillars of Lymantria mathura (Erebidae, Lepidoptera) to explore mechanisms that may contribute to its ability to feed on various hosts. We focused on intraspecific variation in polyphenol metabolism, the fates of individual polyphenols, and the role of previous feeding experience on polyphenol metabolism and leaf consumption. We collected the caterpillars from Acer amoenum (Sapindaceae), Carpinus cordata (Betulaceae), and Quercus crispula (Fagaceae). We first fed the larvae with the leaves of their original host and characterized the polyphenol profiles in leaves and frass. We then transferred a subset of larvae to a different host species and quantified how host shifting affected their leaf consumption and polyphenol metabolism. There was high intraspecific variation in frass composition, even among caterpillars fed with one host. While polyphenols had various fates when ingested by the caterpillars, most of them were passively excreted. When we transferred the caterpillars to a new host, their previous experience influenced how they metabolized polyphenols. The one‐host larvae metabolized a larger quantity of ingested polyphenols than two‐host caterpillars. Some of these metabolites could have been sequestered, others were probably activated in the gut. One‐host caterpillars retained more of the ingested leaf biomass than transferred caterpillars. The pronounced intraspecific variation in polyphenol metabolism, an ability to excrete ingested metabolites and potential dietary habituation are factors that may contribute to the ability of L. mathura to feed across multiple hosts. Further comparative studies can help identify if these mechanisms are related to differential host‐choice and response to host‐plant traits in specialist and generalist insect herbivores.

Understanding the process underlying the spatial gradients in biodiversity is a fundamental issue in ecology. Altitudinal gradients are ideal systems for examining the community assembly process because they represent rapid changes in environmental conditions over relatively short distances. The functional and phylogenetic approaches allow a deeper mechanistic understanding of the underlying assembly process. However, whether community assembly from montane to alpine zones is driven more by ecological constraints or human settlement patterns is not fully resolved and may vary by system. Here, we examined the phylogenetic and trait-based functional structures from the montane to alpine zones and clarified the effects of natural environmental factors and human-induced landscape transformation on the breeding bird assemblage on Mount Norikura, central Japan. Breeding birds from 700 to 3026 m a.s.l. were surveyed in 2016–2017. Bird community structures were examined based on species richness, functional and phylogenetic structures. A null modelling approach was performed to examine functional and phylogenetic cluster/overdispersion structures; clustering and overdispersion imply species elimination by environmental filters and limiting similarity as a corollary of competitive exclusion of species, respectively. Furthermore, we examined the relative effect of natural environments and human disturbance. Bird species richness was high in the mountain base to mid-elevation, then decreased with elevation. We found a contrasting pattern in the phylogenetic and functional structures in the alpine zone: phylogenetic overdispersion and functional clustering. In contrast, the functional and phylogenetic structures were clustered in the upper parts of the subalpine zone. The functional and phylogenetic clusterings in the lower parts of the subalpine and montane zones were negligible with the weak effects of the environmental filtering. Single-trait analysis showed that the high abiotic tolerance and foraging or nesting capabilities in treeless environments were clustered in the alpine zone, and mobility was clustered in the subalpine zones. Natural environments strongly affected bird community structures, but human disturbance added species to assemblages in the mountain base to mid-elevation and changed the functional and phylogenetic structures. Our findings highlight that filtering by severe natural environments is a fundamental community assembly process in high mountain regions, whereas filtering effects can be weaker at lower elevations. Furthermore, the filtering effect should differ between the alpine and the upper parts of the subalpine zones because of different combinations of clustered traits. Climate change and landscape transformation pressures may strongly impact biodiversity in the alpine and subalpine zones, respectively.

We collected seven fixed pairs of Rhyacophila lezeyi during mating copulation and observed four different states of copulation. We investigated the underlying mechanism for the variations in the morphology of each copulating device, based on the copulation state. Notably, the male anal sclerites underwent considerable changes from the early stages of copulation. Initially, the female segment VIII approached the male anal sclerites, which were pushed downwards by the female VIII and IX segments, extending from IX. With the progression of mating stage, the distended end of the female’s segment VIII covered the anal sclerites, pushing them further down. The male parameres were initially folded in bellows-like shapes under the aedeagus before copulation initiation. However, as the copulation stage advanced, they extended to about 3.2 times of their original length. Distended ends of both parameres adhered to the position of the spiracles at the anterior margin of the lateral part of the female’s VII abdominal sternite. The attachment site was the external surface of the hair bulb of the male parameres. During the middle stage of copulation, movements involving the opening and closing of the male gonopods started. The gonoslylus made strong contact with the female’s abdominal segment VIII, resulting in the deformation of segment VIII due to the contact pressure.