BEHAVIOR OF SECONDARY SPERMATOGONIA OF THE NEWT, CYNOPS PYRRHOGASTER, IN IN VITRO CULTURE

Several cell types migrated cut from small pieces of newt testes cultivated in vitro. Flat fibroblastic cells migrated out within a few days. Then, secondary spermatogonia, identified by the presence of germ cell-specific substances and by the shape and appearance of their nucleus and subcellular organelles, migrated out over the sheet of fibroblastic cells. Sertoli cells co-migrated with secondary spermatogonia, maintaining a similar cellular arrangement to that of testicular cells in vivo. Mitosis of secondary spermatogonia both in clusters and as single cells was frequent from the third day until about 2 weeks after inoculation. During mitosis, active and periodic rotation of chromosomes was observed. Identification of the cell types and studies on their behavior were performed by electron microscopy and phase contrast microscopy.     

CHANGES IN THE LEVEL OF ARGININE PHOSPHATE FOLLOWING FERTILIZATION OF ECHINODERM EGGS*

The content of arginine phosphate was measured following fertilization of sea-urchin eggs and starfish oocytes. In sea-urchin eggs, a rise in the level of arginine phosphate occurred within 2 min after insemination: this was not accompanied by any detectable alteration in the level of ATP. On the other hand, the level of arginine phosphate in starfish oocytes did not change on fertilization.     

FIRST RECORD OF THE CIRRIPEDE GENUS STRAMENTUM (THORACICA, SCALPELLIFORMES) FROM THE UPPER CRETACEOUS OF JAPAN

Abstract:  The scalpelliform genus Stramentum is described from upper Turonian–Coniacian (Upper Cretaceous) strata in the Mikasa area, Hokkaido (Japan), documenting the first record of the genus from the north-west Pacific Realm. The single articulated skeleton, which is horizontally embedded in a dark grey laminated mudstone, is specifically indeterminate because capitular plates are missing. However, peduncular morphology resembles that of S. ( S .) pulchellum (Sowerby Jr), which has been described from the Cenomanian–Turonian of Europe. The present record from Japan demonstrates that this cirripede genus had a wider geographic distribution than previously assumed during the youngest phase of its radiation.     

Drastic changes in host preference in a gall‐parasitic flea weevil,Orchestes hustachei,during the last decade

1. Factors affecting host preference in herbivorous insects are actively discussed. Larval performance, competition and predation on each host, and host abundance are reportedly factors affecting the host preference of ovipositing females. In the present study, chronological changes in female host preference were examined by employing a flea weevil species that uses the original host and a newly introduced host simultaneously. 2. Orchestes hustachei Klima (Coleoptera: Curclionidae) is an aphidophagous flea weevil that oviposits on aphid galls, and the larvae feed on aphids inside. The weevil's native hosts are galls of the Tetraneura species on Ulmus davidiana, while the novel hosts are galls of an introduced species, Paracolopha morrisoni on Zelkova serrata, an introduced hardwood. Choice experiments were conducted using Tetraneura galls and Paracolopha galls and the results were compared with experiments conducted 10 years ago. 3. More than 90% of ovipositing females selected Paracolopha galls. This result is in marked contrast with the result of the 2002 experiment, in which 66.3% of females selected Paracolopha galls. To explore driving forces of the preference change, mortality factors, pupal mass on the two hosts, and temporal changes in the abundance of the host galls were examined. 4. Abundance of Tetraneura galls decreased gradually throughout the last 26 years. By contrast, weevil survival and performance did not vary significantly between the two hosts. Therefore, it is concluded that temporal changes in the relative abundance of two hosts are main factors of the change in host preference.     

Host range and host preference of a flea weevil, Orchestes hustachei, parasitizing aphid galls

Although larvae of flea weevils (Curculioninae: Rhamphini) have been known to be leaf miners, larvae of the rhamphine weevil Orchestes hustachei have been found in aphid galls of four Tetraneura species on Ulmus davidiana and in galls of Paracolopha morissoni on Zelkova serrata. This study clarified the feeding habits of O. hustachei larvae and evaluated gall selection by ovipositing females to test the hypothesis of host race formation on their hosts, Tetraneura and Paracolopha galls. When weevil larvae were placed in half‐cut galls, they always fed on aphids rather than on gall tissue. When given gall tissue only, all larvae failed to reach adulthood. The number of aphids surviving in a parasitized gall decreased significantly with the development of the weevil larvae. These results suggest that O. hustachei larvae use aphids as their major food source. In the field, ovipositing females did not discern between four Tetraneura species on U. davidiana, in spite of a large difference in suitability as food. Paracolopha morrisoni was introduced into Hokkaido approximately 100 years ago, together with the host plant Z. serrata. It is probable that P. morrisoni has recently come to be used as a host by O. hustachei in Hokkaido. Host choice experiments using Tetraneura sp. O and P. morrisoni galls indicated that female weevils from Z. serrata preferred P. morrisoni to Tetraneura sp. O galls, while females from U. davidiana selected the two types of gall randomly. On Z. serrata, female weevils selected larger P. morrisoni galls, while on U. davidiana, females did not show a preference for gall size. These results suggest that a host shift to P. morrisoni galls may have led to an initial stage of host race formation between the weevil population using Tetraneura galls on U. davidiana, and that using P. morrisoni galls on Z. serrata.     

Isolation of six microsatellite markers from the pea aphid,Acyrthosiphon pisum (Homoptera,Aphididae)

Using the magnetic particles method, we isolated six polymorphic microsatellite loci from the pea aphid, Acyrthosiphon pisum (Harris), which feeds on a wide range of legume species. The isolated loci were polymorphic, with three to six alleles in 40 aphids. Expected heterozygosities ranged from 0.12 to 0.65. These loci can be used to quantify clonal diversity and compare genetic population structure between sexual and asexual populations.     

Distinctive developmental variability of genital parts in the sexually dimorphic beetle, Prosopocoilus inclinatus (Coleoptera: Lucanidae)

Recent comparative studies have revealed that the rapid diversity of genitalia is closely related to sexual selection and that genital development interacts with the development of different body parts. Hypotheses about developmental stability due to selection to genital parts were tested by estimating allometric relations in a sexually dimorphic stag beetle Prosopocoilus inclinatus . All genital parts of males scaled to body size with a slope of less than 1 and all but the median lobe (male intromittent organ) showed smaller variability than other body parts. This supported the 'one-size-fits-all' hypothesis, which suggests broad copulation opportunity by males of any size with females within a population. Nevertheless, we found large variation among different genital parts in coefficients of variation and in values of the switch point where the allometric relations varied significantly. These results strongly support the view that developmental trajectories of genital traits are not necessarily integrated. Among the genitalic traits, male intromittent organ and female genitalia exhibited large variability, suggesting a high responsiveness to the selective regimes and physical interaction during copulation. This may account for rapid diversification of genital morphology, even in closely-related populations in beetle species.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 573–581.     

Relationship between size and shape in the sexually dimorphic beetle Prosopocoilus inclinatus (Coleoptera: Lucanidae)

Male characters that are used for male−male combat are often developed and exaggerated, whereas female equivalent characters are vestigial or vanished. In order to assess whether the characters common to both sexes share the same phenotypic variability due to common genetic architecture, we compared males and females of the stag beetle Prosopocoilus inclinatus using recently developed geometric morphometric methods. Elliptic Fourier analysis was used to compare shape variation between male characters (including exaggerated mandibles) and developmentally homologous female characters. A significant positive correlation was found between the size or between the weight of different body parts in both sexes, but a conspicuous difference was detected in the frequency distribution of the weight of all the body parts. Elliptic Fourier analysis demonstrated that there was marked discontinuous variation in mandibles in males, whereas such a discontinuity was not clear in females. The shape of a character in males exhibited some similarity with that of other characters, but this was not found in females. In a character, growth trajectory of shape was significantly affected by both size and weight in males, whereas size and shape tended to vary independently in female characters. These results support the hypothesis that a large sexual dimorphism in variation in shape is due to alleles accumulating in tight linkage with a sex-determining gene.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 219–233     

Mating frequency and genetic relatedness of workers in the hornet Vespa analis (Hymenoptera: Vespidae)

Mating frequency of Vespa analis queens and the genetic relatedness of their workers was analyzed by DNA microsatellite genotyping. Of 20 colonies studied, 18 had a queen inseminated by a single male and two had queens each inseminated by two males. The estimated effective number of matings was 1.05 ± 0.037 (mean ± SE), with 75–85% of the offspring of the two multiply mated queens sired by a single male. The pedigree relatedness between nestmate workers averaged over the 20 colonies was estimated to be 0.74 ± 0.008, almost identical to the predicted value of 0.75 for colonies headed by a singly mated queen. Multiple matrilines; that is, the presence of workers not related to the current queens, were detected in six colonies, suggesting that queen replacement occurred via usurpation of the founding queens in these six colonies. These results demonstrate that the kin structure of V. analis is similar to that reported in other vespid species.