Takahiro Nanri

Occurrence of abnormal sexual dimorphic structures in the gonochoristic crustacean, Upogebia major (Thalassinidea: Decapoda), inhabiting mud tidal flats in Japan

Normal females of the mud shrimp, Upogebia major, have a pair of pleopods on the first abdominal segment, while normal males do not. We have investigated nine populations in the Seto-Inland Sea, Japan, and found morphological disorders on the first abdominal segments of both males and females. In males, the first pleopods occurred. Morphology and arrangement of these additional pleopods were classified into four types. The pleopods of Types M-1 and M-2 were similar in structure to those of normal females. These males could be considered as de-masculinized individuals, and the occurrence of males with these morphological disorders showed local variation: while their frequency was high in two specific sites in Kasaoka Inlet ( 11 . 5 % in Site 6 and 5 . 5 % in Site 7 ), it was less than 3.5% in other sites. Other types had abnormal additional appendages similar to the walking legs (pereiopods) (Type M- 3 ) or biramous leaf-like pleopods (Type M-4), but their frequency was extremely low (only 3 out of 155 8 males inspected). Morphological disorders in males (Types M-1 and M-2) occurred independently of gonadal development, and did not affect the sexual characteristics as revealed by analyses of allometric growth and gonadal index. In females, morphological disorders were classified into five types: incomplete first pleopods (Type F-1); lack of the first pleopods (Type F-2 and F- 3 ); transformation into the pereiopod-like pleopods (Type F-4); and biramous leaf-like pleopods (Type F- 5 ). The frequency of Types 1-3 was especially high in Site 6 in Kasaoka Inlet ( 24 . 4 %), but was less than 9 . 4 % in other sites. A feature was that cuticular lesions often co-occurred with the morphological disorders. Possible causal factors of these abnormalities are discussed.

Prevalence and patterns of infection by the epicaridean parasite, Gyge ovalis and the emergence of intersex in the estuarine mud shrimp, Upogebia major

A population of the mud shrimp, Upogebia major , inhabiting Kasaoka Inlet had a higher frequency of intersex males compared to other populations in the Seto Inland Sea, Japan. This population also featured a high prevalence of the branchial epicaridean parasite, Gyge ovalis , and inhabited a tidal flat characterized by increasingly softer sediments going into the lower tidal areas. We examined the rates at which infection co-occurred with intersex features and checked whether infection patterns varied with intersex occurrence according to host size and tidal level position. Fewer specimens were both intersex and infected than those having only one of either condition; infection was not a significant predictor of intersex. However, infection in young hosts that recovered from the parasite could be associated with the intersex morphologies and account for the majority of cases that were intersex but parasite-free. Deletions of the cuticular ridge (CRD) between the first and second abdominal segment and tidal level position were correlated with intersex. Lower tidal zone mud shrimp were, respectively, three and four times more likely to be intersex and exhibit CRD than those in the upper tidal zone. Potentially inclusive factors that may influence these trends are higher rates of early infection and increased exposure to sediment-bound pollutants in mud shrimp inhabiting the lower tidal areas.

Chela asymmetry in a durophagous crab: predominance of right-handedness and handedness reversal is linked to chela size and closing force.

ABSTRACT The swimming crab Portunus trituberculatus is a durophagous brachyuran. Right-handed crabs are predominant, but left-handed crabs are also found in nature. Left-handedness may arise from loss of the right crusher. We examined whether heterochely (morphology) was correlated with differences in closing force (physical property) and handedness (behaviour). The closing force was stronger in larger chela with greater apodeme height and handedness resided in the chela with stronger closing force. With loss of the right chela (autotomy), handedness transitioned from the right to left chela, and all crabs were left-handed thereafter. Reversed handedness was accompanied with a reduction of size and closing force in the regenerated right chela, and growth of the original left chela. After handedness reversal, dentition on the left dactylus of the newly-converted crusher was close to that of the original right crusher, but did not attain the same shape, even after 10 moults. Left-handed crabs were significantly worse than right-handed crabs at crushing hard-shelled prey. Chela formation was symmetrical in the zoea, and heterochely and right-handedness started in the megalopa, regardless of maternal handedness. Since the left chela is capable of being the crusher, heterochely may be caused by differences in morphogenetic velocity between the right and left chelae, under a signal discriminating right from left. Right-handedness is an attribute of P. trituberculatus, that would be inheritable across generations. It is probable that right-handedness was used in the earliest durophagous crabs, and this trend has been succeeded to extant species. Summary: Handedness in the swimming crab resides in the claw that is larger with greater apodeme height and has the stronger closing force.

Classification of the Intertidal and Estuarine Upogebiid Shrimps (Crustacea: Thalassinidea), and Their Settlement in the Ryukyu Islands, Japan

Classification of the Intertidal and Estuarine Upogebiid Shrimps (Crustacea: Thalassinidea), and Their Settlement in the Ryukyu Islands, Japan Upogebiid shrimps (Crustacea: Thalassinidea) inhabit sandstones exposed on the intertidal zone of two of the islands of the Ryukyu Arc, Japan (islands located between 24°N, 123°E and 28°N, 129°E). The upogebiids here are morphologically similar; so, their classification is open to debate. In addition, when the upogebiids settled on the Ryukyu Arc has not been studied till date. Based on morphological features, we suspect that six stone upogebiid species are distributed in the Ryukyu Arc. This hypothesis was tested by molecular phylogenetic analysis of mitochondrial DNA markers. Furthermore, Bayesian evolutionary analysis, which was used to estimate TMRCA (time to most recent common ancestor) of each upogebiid, showed that stone upogebiids diverged 5-15 Ma (second half of the Miocene). Stone upogebiids may have occurred in the islands near the equator 5-15 Ma. On the contrary, Bayesian analysis indicated that the time of ‘intraspecific’ divergence varied from 1.15 Ma to 0 Ma, suggesting that stone upogebiids may have settled in the Ryukyu Arc from the Pleistocene to the present. In Iriomote Island, sedimentary layers suitable for burrowing occurred on the shores from the west to the northern half of the island, but not on the east. The Ryukyu Arc was a passive continental margin until the beginning of the Pleistocene, but the warm Kuroshio current completely separated the Ryukyu Arc from the Eurasian continent about 1.55 Ma. With subduction of the Ryukyu Arc northwestward, sedimentary layers for burrowing may have appeared on the ‘front’ of the island (i.e. on the shores from the west to the north), thereby providing suitable habitats for the stone upogebiids to settle, since 1.15 Ma.

Anhydrobiosis Affects Thermal Habituation in the Bdelloid Rotifer, Adineta sp.

The bdelloid rotifer of the genus Adineta is a freshwater metazoan characterized by anhydrobiosis, a highly stable state of suspended animation induced by desiccation. This study investigated the influence of anhydrobiosis on the thermal habituation by use of an index, Activity Ratio (AR = the number of active rotifers at each experimental temperature/ number of active rotifers at the 25°C stage). In the first experiment, rotifers were divided into two groups: one group was cultivated at 25°C throughout experiment, and another group was transferred to 15°C for two days. AR was estimated during heating up to 40°C, or during cooling down to 5°C in each group. The largest difference in AR occurred at 35°C and 10°C, indicating that AR was changed depending on the pretreated medium temperature. In the next experiment, rotifers were maintained at 15°C, and were desiccated (anhydrobiosis). AR was estimated in the high temperature range (25°C to 40°C), using rotifers that had recovered from anhydrobiosis. AR was significantly different between the groups with and without desiccation, suggesting that thermal habituation at 15°C was completely cancelled by anhydrobiosis. Possible mechanisms on the influence of anhydrobiosis on the thermal habituation have been discussed in terms of neural changes and proteins.

Effect of Nestbox Provisioning on Breeding Density of Dollarbirds ( Eurystomus orientalis )

Abstract: The Dollarbird (Eurystomus orientalis) is a secondary cavity-nesting bird that is distributed quite locally in Japan. We carried out extensive surveys across Okayama Prefecture to estimate the number of pairs and found that the major breeding site was holes excavated by woodpeckers in wooden electricity and telegraph poles. Wooden poles were abundant until the 1970s, but most were replaced by concrete poles in the 1980s. Removal of wooden poles containing cavities seriously threatened the breeding population over the first half of the 1990s. In an effort to preserve the Dollarbird population in Japan, beginning in 1991 we provided nestboxes in the village of Kibi (Okayama Prefecture). This resulted in only a small increase in population size over the following 5 yr, but between 1996 and 2001 there was a large annual increase in the breeding population. Increase then leveled off after 2002. Population increase showed a time lag following increase in number of available boxes. Finding new nestboxes may take some time, initially resulting in a low occupation rate for some years after start of box provisioning. Finding of nestboxes by pairs that had bred near Kibi and their subsequent reproduction may have led to a sharp population increase between 1995 and 2002. On the other hand, leveling off of increase in Dollarbird breeding pairs after 2003 may have been directly derived from leveling off of increase in available nestboxes. This suggests a maximum nestbox occupancy rate of 70%–80% in Kibi.