Hiroshi Abé

A search for collision orbits in the free-fall three-body problem I. Numerical procedure

A numerical procedure is devised to find binary collision orbits in the free-fall three-body problem. Applying this procedure, families of binary collision orbits are found and a sequence of triple collision orbits are positioned. A property of sets of binary collision orbits which is convenient to search triple collision orbits is found. Important numerical results are formulated and summarized in the final section.

Water mites (Acari: Hydrachnidiae) parasitic on aquatic hemipterans in Japan, with reference to host preferences and selection sites

Water mites are known to temporarily live on the surface of aquatic insects in their life cycle. Investigations of the host–parasite relationship between water mites and aquatic insects are quite limited in Japan. Therefore, we examined several aquatic hemipterans to clarify the parasitic nature of water mites on aquatic insects. During the survey, the following seven hemipteran species were collected from farm ponds and rice fields in Kanagawa, Yamanashi, and Hyogo prefectures in 2011 and 2012: Appasus japonicus, Appasus major, Laccotrephes japonensis, Aquarius paludum, Ranatra chinensis, Kirkaldyia deyrolli, and Notonecta triguttata. Among these species, water mites were found only on Ap. japonicus and R. chinensis. The water mites were all in a post-larval resting stage and identified as Hydrachna spp. The mites attached to R. chinensis were clearly larger than those on Ap. japonicus. Although mites do not select by host sex and their abundance was not affected by the host body size, their abundance per female host was greater than per male host. Further, the mite parasitism on nymphs was greater than that on adults in Ap. japonicus. Concerning site selection on a host body of R. chinensis for attachment, mites significantly prefer the leg and meso- and metathoraxes to the abdomen, respiratory siphon, and head of a host insect. The results mentioned above accorded well with several studies in Europe.

Phylogeny and character evolution of the marine mite genus Isobactrus (Acari: Halacaridae)

A morphology-based phylogenetic analysis of the 24 species of Isobactrus (Acari: Halacaridae) demonstrated three major monophyletic groups supported by synapomorphies. Each group is geographically distinct being tropical Pacific, North Atlantic and Holarctic. Character optimization indicates some evolutionary tendencies of character transformation. Reduction of idiosomal lateral setation, loss of setae on the genu and the addition of female subgenital setae are postulated synapomorphies congruent throughout the tropical lineage. Similarly, setal addition on the telofemur occurred in the North Atlantic lineage, while reduction of genital area sclerotization is recognized in a northern phyletic group.

Nesting habits of the Japanese foliage spider, Cheiracanthium japonicum (Araneae: Miturgidae): host plant preference based on the physical traits of plant leaves

A Japanese foliage spider, Cheiracanthium japonicum, builds nests with plant leaves. The nests are classified into seven types in relation to the seasons and purposes of nesting. We investigated whether the spider selects a plant species according to the nest type and how the physical traits of leaves influence the spiders plant selection. The difference between the composition of the host plant species used for nesting and that of the seasonal vegetation cover was confirmed. This suggests that the spider chooses the host plant species regardless of its abundance in their habitat. Early juveniles use small living or large dead leaves of various plant species to build moulting nests. Females prefer long and large leaves found in Miscanthus sinensis and Phragmites japonica over other plant leaves to build breeding nests.

New data on the water mite fauna (Acari, Hydrachnidia, Halacaroidea) of the Sakha Republic (Yakutia)

Examination of the water mite collection made by the authors in the territory of the Sakha Republic (Yakutia) in 2006 has revealed 43 mite species of the phalanx Hydrachnidia, belonging to 19 genera and 12 families, 1 species of the phalanx Trombidia, and 2 freshwater species of the superfamily Halacaroidea, belonging to 2 genera and 1 family. All the species registered, except for two species of the phalanx Hydrachnidia (Mixobates processifer and Lebertia porosa), were recorded in the Sakha Republic for the first time. The species Aturus miyashitai Uchida, 1934 and A. parapilosus Kim et Chung, 1993 (Hydrachnidia) and the family Johnstonianidae Thor, 1935 (Trombidia) are new for the Russian fauna. The female of A. parapilosus is described for the first time.

Offspring discrimination by female parents of the matriphagous spider Cheiracanthium japonicum (Araneae: Eutichuridae)

ABSTRACT The ability of females of the matriphagous spider Cheiracanthium japonicum to discern their own offspring was examined based on a comparison of her maternal care for her own eggs and spiderlings with other conspecific females as well as those of other congeneric species. Cheiracanthium japonicum females did not discern their own nest from those of conspecific and congeneric individuals. In addition, the female did not distinguish her own egg sac from those of other conspecific or congeneric individuals. On the other hand, the female clearly discriminated between her own spiderlings and those of other congeneric species only if the congeneric spiderlings were introduced into the breeding nest. Consequently, the female will allow conspecific spiderlings to predate her (i.e. cannibalism). However, it is hardly expected that spiderlings of a certain female would eat another female in the field, as the reproductive period is quite short and synchronised in a population. Considering that the female can only recognise spiderlings of other species, the recognition ability of C. japonicum females will be evolved only to work as a protection against intruders of other species into the breeding nest.

A new species of Rhombognathus (Acari: Halacaridae) from the coast of Accra, Ghana

This paper describes a new species of the genus Rhombognathus in the family Halacaridae (Acari: Prostigmata) under the name of Rhombognathus accrue sp. n. The material examined in the present study was collected at Labadi Beach on the coast of Accra in Ghana. Mites were recovered from small algae of the order Gigartinales in the phylum Rhodophyta on several rocks on the shore less than 0.5 m depth. Rhombognathus accrae is characterized by 1) dorsal plates ornamented with areolae, 2) anterior epimeral region with two adjunctive setae and posterior epimeral region with one adjunctive seta, 3) five perigenital and four subgenital setae in the female, 4) nine or 10 perigenital setae on each side of the genital foramen and four subgenital setae in the male, 5) telofemora I-IV with 4/3, 4/3, 3/0, 3/0 dorsal/ventral setae, genua I-IV with 5, 5, 3, 3 setae, 6) narrow palmate accessory process with about seven teeth. This is the first record of the genus from West Africa. A key to the African species of Rhombognathus is provided.

Phylogenetic taxonomy of the marine mite genus Rhombognathides (Acari: Halacaridae: Rhombognathinae)

Taxonomic revision of the marine mite genus Rhombognathides is executed in the phylogenetic and phenetic contexts. Relationships among all the species in the genus are analyzed by two different procedures, i.e. parsimony and distance, on the basis of morphological data. The parsimony analysis reveals several monophyletic lineages within the genus. Phylogenetic relationships among R. exoplus, R. nigrescens and R. seahami cannot be clarified due to the absence of informative apomorphies in these species The distance analysis shows a lack of phenetic distance between R. nigrescens and R. seahami. According to the characters used, these two species are not morphologically distinguishable from each other. These results suggest that R. nigrescens should be synonymous with R. seahami. Consequently, eight distinct species, Rhombognathides brevipes, R. exoplus , R. merrimani, R. mucronatus, R. pascens , R. seahami, R. spinipes and R. trionyx, can be recognized in the current taxonomy of the genus Rhombognathides.

Structural comparisons of isomorphic breeding nests between closely allied spiders Cheiracanthium japonicum and Cheiracanthium lascivum (Araneae: Eutichuridae)

ABSTRACT Closely allied spider species Cheiracanthium japonicum and Cheiracanthium lascivum make a closed breeding nest for egg laying and parental care. The nest provides the internal climatic stability required for suitable development of eggs and the physical durability required for protection against intruders. Although the breeding nests of these two spiders are quite similar in structure and appearance, their climatic stability and physical durability seem to be empirically different. Such physical features of the nests of these two spiders were compared based on a balance between the inner and outer air temperature and humidity of the nest as well as on the amount and size of spider silks lining the nest. In addition, the female’s relative energy allocation to egg production versus nest construction was examined based on the number or weight of eggs versus the climatic stability and physical durability of the nest. According to the results, the stability of temperature and humidity was maintained better in the breeding nest of C. japonicum than in that of C. lascivum. Furthermore, the nest of C. japonicum was more strongly constructed, with a greater volume and size of silks, than that of C. lascivum. On the other hand, the number or weight of eggs in relation to the female’s body weight in C. japonicum was smaller than that in C. lascivum. These results suggested that the reproductive effort towards nest construction for the purpose of egg and juvenile care in C. japonicum was larger than that in C. lascivum. In contrast, the effort towards egg production in C. japonicum was smaller than that in C. lascivum. Consequently, it is likely that the structural differences in breeding nests between these two spiders are responsible for the discrepancies in the female’s relative energy allocation to nest construction.

Evolutionary Trends of External Morphology in the Marine Mite Genus Rhombognathides (Acari: Halacaridae: Rhombognathinae)

A morphology-based phylogenetic analysis of the eight species of Rhombognathides (Acari: Halacaridae) demonstrated some evolutionary tendencies of character transformation. In the course of the evolution of Rhombognathides, idiosomal plates increased in size or fused. Simple filiform setae transformed into spiniform or bipectinate setae. The number of tarsal claws, the length of median claw and leg chaetotaxy of telofemora and tibiae were reduced. The fusion or expansion of dorsal plates, transformation from filiform to other setal forms, and reduction of leg setae would have recurrently occurred in halacarid evolution. The claw structure most likely reflects adaptation to specific habitat.