Akira Shinkai

The effects of forest fragmentation on web spider communities in urban areas

Spiders are generalist arthropod predators living in all kinds of forests. Since food limitation appears to be widespread, this group may be influenced by forest fragmentation in various ways. We examined web spider communities in one continuous forest and 17 forest fragments surrounded by built-up areas in Yokohama and Tokyo, Japan. Smaller fragments had fewer species and lower density of individuals. For a given size fragment, those in Yokohama harbored more species than those in Tokyo, probably due to the lower degree of isolation from surrounding fragments in Yokohama. Large araneids were most sensitive to fragmentation in the sense of species loss, small araneids intermediate, and theridiids least sensitive. The body size of Nephila clavata, a common species in fragments, was smaller in smaller fragments. We propose that one important mechanism of species loss in web spiders is the lower abundance of large prey in small fragments.

Molecular Phylogeny of Moth-Specialized Spider Sub-Family Cyrtarachninae, which Includes Bolas Spiders

The evolutionary process of the unique web architectures of spiders of the sub-family Cyrtarachninae, which includes the triangular web weaver, bolas spider, and webless spider, is thought to be derived from reduction of orbicular ‘spanning-thread webs’ resembling ordinal orb webs. A molecular phylogenetic analysis was conducted to explore this hypothesis using orbicular web spiders Cyrtarachne, Paraplectana, Poecilopachys, triangular web spider Pasilobus, bolas spiders Ordgarius and Mastophora, and webless spider Celaenia. The phylogeny inferred from partial sequences of mt-COI, nuclear 18S-rRNA and 28S-rRNA showed that the common ancestor of these spiders diverged into two clades: a spanning-thread web clade and a bolas or webless clade. This finding suggests that the triangular web evolved by reduction of an orbicular spanning web, but that bolas spiders evolved in the early stage, which does not support the gradual web reduction hypothesis.

Highly diversified population structure of the spider Lycosa ishikariana inhabiting sandy beach habitats

Sandy beach ecosystems are decreasing worldwide and organisms living there are becoming threatened. The burrowing wolf spider Lycosa ishikariana is one such example. To establish effective conservation strategies under habitat fragmentation, we examined population genetic structure of L. ishikariana from mitochondrial cytochrome oxidase I gene and 6 microsatellite loci. Mitochondrial sequence data revealed 6 population subgroups with very high fixation indices, indicating that L. ishikariana has a clear phylogeographic structure and that the level of differentiation among regions is considerable. In particular, one subgroup in the western Honshu mainland (clade G) has a highly distinct genetic structure, despite having no clear geographic barriers from its parapatric population. Moreover, the distribution ranges of the other two subgroups (clades D and E) were highly restricted, suggesting their vulnerability to local human impacts and highlighting their high conservation priorities. Microsatellite data revealed 10 subgroups that were compatible with the clades identified from the mitochondrial data. Fixation indices among these groups were very high, indicating a limited gene flow induced by male spiders. Based on these results, we proposed six conservation units of L. ishikariana and effective conservation/restoration strategies in the face of ongoing coastal armoring.