Journal: Zoological science
Anemonefish, Amphiprion spp., are socially controlled, protandrous sex changers with a monogamous mating system. Under certain conditions, sexually immature anemonefish with ambisexual gonads differentiate directly into males or females. Formation and maintenance of social rank in a group are considered key requirements for the induction of sex change or differentiation. Generally, each animal living in a social group experiences a different level of social stress in accordance with its social rank, and we hypothesize that the stress situation of individual anemonefish influences its sex determination. Groups of three sexually immature anemonefish were placed into each of five experimental tanks and kept for 10 days to allow for social rank formation and behavioral observation. The fish were then euthanized, and blood and brain samples were collected from each fish. The social rank of each individual was distinguishable from day 1 of the experiment. Aggressive behaviors were most frequent and blood Cortisol values were higher in dominant individuals. The transcription of mRNA for stress-related genes, i.e., those encoding for glucocorticoid and arginine vasotocin receptors, was higher in the brains of dominant individuals than in other social ranks. Furthermore, we detected higher transcription levels of gonad and brain aromatase genes, which encode the enzyme that converts androgens into estrogens, in the brains of dominant individuals. These results suggest that social rank reflects the blood Cortisol value, which in turn leads to sex differentiation by manipulating transcription of genes, including aromatase genes, in the brain.
A new species of genus Hydra (Cnidaria: Hydrozoa: Hydridae), Hydra shenzhensis sp. nov. from Guangdong Province, China, is described and illustrated. Most polyps have five tentacles. Column length reaches 11 mm when relaxed. Buds do not acquire tentacles synchronously. Stenotele is broad and pyriform in shape, 1.2 times as long as its width. Holotrichous isorhiza is asymmetrical and slender (more than 2.7 times as long as its width), with transverse and slanting coils. Atrichous isorhiza is long, resembling a melon-seed in shape. Desmoneme is asymmetrically pyriform in shape. The new species, belonging to the vulgaris group, is dioecious; sexual reproduction was found to occur mostly during November and December under conditions of dense culture or food shortage. Two to thirteen testes, cone-like shape with papilla, formed beneath the tentacles. One to three ovaries, with an egg cup, milky white in color, formed on body column. Ninety percent of individuals developed only one ovum. On a mother polyp, a fertilized ovum developed an embryonic theca covering its surface. The embryotheca is brown, with a spine-like structure, covering a layer of transparent, membrane-like material. For phylogenetic analysis, the mitochondrial cytochrome oxidase subunit I gene (COI) of six hydra species collected from China was amplified by polymerase chain reaction (PCR) and sequenced. Morphological characters in combination with molecular evidence support the hydra described here as a new species.
The Japanese pine sawyer, Monochamus alternatus Hope, 1842, an important forest pest, mainly occurs in Far East. It is the main vector of pine wood nematode Bursaphelenchus xylophilus, which causes pine wilt disease. We determined the complete mitochondrial genome coding region of M. alternatus using long PCR and conserved primer walking. Our results show that the entire mitogenome coding region is 14,649 bp long, with 78.22% A+T content [deposited in GenBank (JX987292)]. Positions and arrangement of the 37 genes encoded by the coding region are identical to those of two other longhorn beetles (Psacothea hilaris and Anoplophora glabripennis) for which the complete gene content and arrangement are known. All protein-coding genes start with a typical initiation codon ATN in insects. All tRNAs show standard clover-leaf structure, except the tRNA(Ser) (AGN), which lacks dihydrouridine (DHU) arm. The most unusual feature found is the use of TCT as tRNA(Ser) (AGN) anticodon instead of GCT, which is used in most other arthropods. This provides further insights into the diversity and evolution of the Cerambycidae family of long-horned beetles.
The circannual pupation rhythm of Anthrenus verbasci is entrained to an environmental cycle by changes in photoperiod. Exposure of larvae reared under short-day conditions to long days induced a clear phase delay of the circannual rhythm. There was no notable difference in the initial phase or period of the circannual rhythm among four geographically distinct populations of A. verbasci in Japan: Takanabe (32.1°N), Osaka (34.7°N), Sendai (38.3°N), and Sapporo (43.1°N) populations. The range of photoperiodic changes effective for phase delay in the circannual pupation rhythm was compared among the four populations. Although larvae did not show a typical threshold response, but responded quantitatively to the photophase duration in intermediate conditions, the critical daylengths were calculated as those under which the pupation was delayed by 50%: 12.8 h in the Takanabe population, 13.2 h in the Osaka population, and 13.6 h in the Sendai and Sapporo populations. Thus, the critical daylength for entrainment of the circannual rhythm in A. verbasci was correlated to the habitat latitude, but the differences among the populations were much smaller than those reported in photoperiodism for induction of diapause in various insects. Consequently, the difference in the pupation time among the four geographic populations was very small under the natural photoperiod in Osaka at 20°C, and absent under the natural photoperiod and temperature in Osaka. These results suggest that A. verbasci survives and successfully produces the next generation in different geographic regions without changing the parameters of the circannual rhythm.
It has been reported that endocrine disrupter compounds (EDCs) interfere with the endocrine system, mimicking the action of sex steroid hormones in different species of mollusks. Prosobranchs are frequently used as a reliable bioindicator to evaluate EDC exposure. In this article, we evaluate the effects of the xenoestrogen 4-n-nonylphenol (NP) in the prosobranch gastropod Patella caerulea, which exhibits protandrous hermaphroditism as its reproductive strategy. We isolated a partial sequence of a GnRH-like molecule from the gonads of Patella caerulea. The deduced amino acid sequence is highly homologous to that reported for the Lottia gigantea GnRH. Patella caerulea GnRH (pGnRH) mRNA expression is widespread in both male and female germ lines during gametogenesis. We suggest pGnRH as a novel biomarker for the early assessment of presence of EDCs and monitoring short and long-term impacts on Patella caerulea community structure.
The inertial power and inertial force of wings are important factors in evaluating the flight performance of native bats. Based on measurement data of wing size and motions of Eptesicus fuscus, we present a new computational bat wing model with divided fragments of skeletons and membrane. The motions of the model were verified by comparing the joint and tip trajectories with native bats. The influences of flap, sweep, elbow, wrist and digits motions, the effects of different bones and membrane of bat wing, the components on vertical, spanwise and fore-aft directions of the inertial power and force were analyzed. Our results indicate that the flap, sweep, and elbow motions contribute the main inertial power and force; the membrane occupies an important proportion of the inertial power and force; inertial power on flap direction was larger, while variations of inertial forces on different directions were not evident. These methods and results offer insights into flight dynamics in other flying animals and may contribute to the design of future robotic bats.
There have been only a few reports on the directional reflection of light by butterfly wings. Here, we systematically investigated this phenomenon in a lycaenid butterfly, Chrysozephyrus smaragdinus,in which males have bright green wings based on structural coloration. We used a device that measures intensities of light in hemispherical space by vertical shifting of a sensor and horizontal rotation of the stage carrying the wing, which is illuminated from the top, to determine the direction of light reflected by the fore- and hindwings. The orientation and curvature of wing scales were also examined microscopically. The forewing of this species reflected light shone from the top largely forward, whereas the hindwing reflected it slightly forward. This difference was attributed to the tilt angles of the wing scales. Light reflection by the forewing was relatively weak, and widely scattered, whereas that by the hindwing was rather concentrated, resulting in higher reflectance. This difference was attributed to difference in the curvature of the wing scales on the two wings.
To evaluate the colonization histories of the Japanese house mice (Mus musculus), phenotypic and genotypic admixtures of the subspecific traits were studied by evaluation of external body characteristics and mitochondrial gene elements. We analyzed mitochondrial Cytb gene and coat colorations and body dimensions as subspecific characteristics in mice from four areas of the Japanese Islands, the Sorachi, Ishikari and Iburi areas of Hokkaido, the Hidaka area of Hokkaido, and northeastern and central Honshu. Three occurrence patterns of the subspecific haplotypes of Cytb-the castaneus type only, the musculus type only, and the castaneus, musculus, and domesticus types together-were observed in the study areas. In central Honshu, the properties of haplotypes were in accord with the external characteristics as reported in previous findings. In contrast, complicated external characteristics were observed in the Hidaka area, where mice showed multiple haplotype properties. In addition, in northeastern Honshu, coat colorations were not in accord with haplotype properties and such discordance was also observed in most mice in the Sorachi, Ishikari and Iburi areas of Hokkaido. These complexities and discordances suggest that the genetic and phenotypic properties have been caused by different processes, not only through founder effects by migrations and subsequent subspecific hybridizations but also through differentiation in each study area.
It has long been hypothesized that the flower-like appearance of the juvenile orchid mantis is used as visual camouflage to capture flower-visiting insects, although it is doubtful whether such morphological resemblance alone could increase their success in hunting. We confirmed that juvenile female orchid mantes often succeed in capturing oriental honeybees, while adult females often fail. Since most of the honeybees approached the juveniles from the front, we hypothesized that juvenile orchid mantes might attract honeybees by emitting some volatile chemical cues. Gas chromatography-mass spectrometry analyses revealed that the mantes' mandibular adducts contained 3-hydroxyoctanoic acid (3HOA) and 10-hydroxy-(E)-2-decenoic acid (10HDA), both of which are also features of the pheromone communication of the oriental honeybee. We also successfully detected 3HOA emitted in the head space air only at the time when the juvenile mantes were attempting to capture their prey. Field bioassay showed that the Oriental Honeybee predominantly preferred to visit dummies impregnated with a mixture of the appropriate amounts and ratios of 3HOA and 10HDA. We therefore conclude that the juvenile mantes utilize these as allelochemicals to trick and attract oriental honeybees.
The Japanese bush warbler has a very distinctive song, shows marked sexual size dimorphism, and has a polygynous mating system. However, the physical traits of males and seasonal variation in such traits have remained unknown. Twenty-five anatomical measurements representing physical traits of males in the breeding (summer, n = 5) and non-breeding (winter, n = 5) seasons were examined morphologically and compared statistically. Differences were evident between summer and winter (P < 0.05, t test) in the following seven items: body mass (19.8 ± 0.7 g vs. 15.6 ± 1.2 g [mean ± SD]), mass of male reproductive organs (184.0 ± 25.7 mg vs. 6.0 ± 1.4 mg), hind limb (3789.2 ± 346.2 mg vs. 3003.4 ± 226.8 mg), leg muscles (883.0 ± 63.5 mg vs. 581.4 ± 33.2 mg in either side), skin around the neck/throat (1280 ± 34.9 mg vs. 287.2 ± 84.7 mg), and syrinx (35.8 ± 2.39 mg vs. 25.0 ± 3.24 mg), and circumference of the neck/throat (52.1 ± 2.3 mm vs. 38.3 ± 2.6 mm). In contrast to winter males, summer males had thickened flabby skin prominently in the neck/throat area and an inflatable esophagus, perhaps a morphological basis for the throat sac as a vocal resonator. Also, the remarkable development of the flexor muscles of the legs of summer males suggests that perching and movement using the legs increases during the breeding season. These distinct characteristics of summer males may be related to the polygynous mating system of this species.