Zoological Science最新文献

The mechanisms underlying sexual differentiation in viviparous chondrichthyans remain poorly understood, particularly regarding the impact of the maternal environment on early gonadal differentiation. In this study, we examined gonadal and reproductive duct differentiation in red stingray (Hemitrygon akajei) embryos before and after clasper formation through detailed histological analyses. Histological observations revealed that early embryos (stage 3, before clasper formation) exhibited undifferentiated gonads with scattered primordial germ cells, whereas later embryos (stage 4, during clasper development) exhibited clear sexual dimorphism. Female gonads contained numerous germ cells localized in the dorsal region, whereas male gonads contained fewer scattered germ cells. Both the Müllerian and Wolffian ducts were present in both sexes, with the Wolffian ducts emerging from the Müllerian ducts in a segmental pattern. Stage 4 female embryos exhibited a selective enlargement of the right Müllerian duct, establishing reproductive tract asymmetry. The sex ratio of red stingray embryos was 1:1. These findings provide the first detailed histological characterization of gonadal differentiation and reproductive duct development in a viviparous chondrichthyan and establish an essential foundation for future studies on sexual development in these evolutionarily significant vertebrates.

The acanthocephalan genus Longicollum Yamaguti, 1935 currently comprises 12 fish-parasitic species. Except for L. pagrosomi Yamaguti, 1935, the remaining 11 congeners have not been the subject of molecular phylogenetic studies. Longicollum alemniscus (Harada, 1935) has been found in brackish and marine fish in Taiwan and Japan, but its morphology remains inadequately understood. In this paper, we provide a morphological redescription and infer the phylogenetic position of L. alemniscus within the Pomphorhynchidae. Furthermore, we summarize the morphological characteristics of Longicollum to distinguish it from the morphologically similar genus Paralongicollum Amin, Bauer, and Sidorov, 1991.

Many animals build shelters to avoid predation, but some predators cope with these shelters to prey on them. To explore the behavioral interactions between shelter-building prey and their predators, we investigated the shelter defenses of two caterpillar species (Lepidoptera: Crambidae) and the hunting behavior of each predator species (Hymenoptera: Vespidae: Eumeninae) under laboratory conditions. Female wasps of Anterhynchium flavomarginatum and A. gibbifrons were observed attacking the larvae of Haritalodes derogata and Demobotys pervulgalis (Lepidoptera: Crambidae), which construct open and closed leaf shelters, respectively. The attack behaviors differed between the two wasp species. Anterhynchium flavomarginatum employed two attack strategies: (I) boring holes in shelters and driving caterpillars out, and (II) invading shelters and searching for prey inside. In contrast, A. gibbifrons utilized a single strategy: cutting the silk threads binding the leaves with their mandibles to open the shelters and search for prey inside. Approximately half of the prey caterpillars could avoid predation; the shelter morphology and behavior of each caterpillar species likely contributed to evading the wasps. Each caterpillar species may have adapted a specific anti-wasp defense, while each wasp species may have acquired offensive traits to overcome the defense of each prey.

During a faunal survey in Baños del Inca hot spring (40-50°C), Cajamarca, Peru, we collected a cyprinotine ostracod species, the sixth example of a thermophilic ostracod inhabiting freshwater in temperatures above 40°C. Because this could not be assigned to any of nine genera in Cyprinotinae, we established the new genus Thermocypris for it and described it as Thermocypris isabella gen. et sp. nov., defined by the following combination of characters: (1) no dorsal hump on carapace, (2) no tubercles on either valve, (3) left valve slightly overlapping right valve along all margins, (4) no selvage on anterior part of right valve, (5) only seta d1 on first podomere of 6th limb, (6) only two shields (medial and lateral) on hemipenis, and (7) medial shield unilobed and lateral shield tooth-shaped. We determined partial sequences for the mitochondrial cytochrome c oxidase subunit I (COI) and nuclear 18S and 28S rRNA genes from a specimen of the new species. In a maximum likelihood tree based on 18S + 28S, T. isabella was the sister taxon to Heterocypris chetumalensis (Yoo, Cohuo, Macario-Gonzalez, and Karanovic, 2017), with high branchial support. A clade including Cyprinotinae (Cyprinotus Brady, 1868 + Heterocypris Claus, 1892 + Thermocypris) and Eucypridinae (Eucypris Vavra, 1891) was fully supported; our phylogeny showed Heterocypris not to be monophyletic.

Photoperiod and melatonin regulate reproduction in mammals. The rice rat (Oryzomys palustris) is reproductively photoperiodic and on a long photoperiod responds to melatonin administration with inhibited reproduction. I examined whether photoperiod, melatonin, and the removal of gonadal steroids via castration affected growth, reproduction, pelage, and swimming ability. Juvenile males were housed on 14L:10D or 11L:13D and at 68 days of age rice rats were weighed, allowed to swim for 10 minutes while being videotaped to quantify swimming and floating times, and then reweighed. One day later, these rice rats were euthanized and the testes, seminal vesicles (SV), Harderian glands (HG), and spleen were weighed. The shorter photoperiod significantly decreased body, testes, SV, and HG masses only. The pelage of rice rats absorbed more water on 14L:10D than on 11L:13D, despite no difference in pelage lengths. Melatonin implants decreased body mass, the masses of the testes, SV, and HG, and pelage water absorption, but increased pelage length. Lastly, castration decreased SV and HG masses, but increased body and spleen masses. Swimming and floating times were not affected by any treatment. Taken together, these results show that all treatments affected growth and reproduction in rice rats, but did not affect swimming ability. Thus, the physiological changes characteristic of winter are not sufficient to alter aspects of swimming ability as swimming ability appears to be independent of reproductive condition.

The selection of settlement sites by larvae is a crucial event in the life cycle of sessile animals, as they are usually unable to migrate after settlement and metamorphosis into sessile forms. For example, some species prefer hydrophilic substrates, whereas others prefer hydrophobic substrates. Understanding larval preferences for substrates will provide an essential basis for controlling biofouling. In this study, we focused on the water wettability of substrates for settlement and investigated larval substrate preference in three ascidian species, Phallusia philipinennsis, Ascidia sydneiensis, and Ciona robusta (= C. intestinalis type A), using a four-choice assay with substrates of different water wettability (contact angle of a water droplet): silicone rubber (115°), polyvinyl chloride (80°), glass (31°), and hydrophilic film SH2CLHF (14°). In some regions of the world, A. sydneiensis and C. robusta are often noted as invasive species and are serious biofoulants. In all three species, larvae showed a significant preference for more hydrophobic substrates, and none settled on the most hydrophilic substrate, that is, SH2CLHF. It is difficult to explain why ascidian larvae prefer a more hydrophobic substrate, since hydrophobic materials, such as silicon, are often used as antifouling measures. This inconsistent substrate preference can be applied to mitigate biofouling.

We describe a new species of loach, Oreonectes daguishanensis sp. nov. from Guangxi Daguishan Crocodile Lizard National Reserve in Hezhou City, Guangxi Zhuang Autonomous Region, China. Morphologically, the new species can be distinguished from congeneric species by the following combination of characters: dorsal-fin origin posterior to pelvic-fin origin; pectoral fins short, not reaching pelvic-fin base; pelvic-fin tip does not exceed anus; body width 10.2%-13.6% of standard length; eye diameter 15.5%-19.3% of head length; posterior chamber of swim bladder degenerated. Phylogenetic analysis of the mitochondrial cytochrome c oxidase subunit I and cytochrome b gene markers supports its species-level distinctiveness, with uncorrected p-distances ranging from 7.4% to 9.7% from closest relatives.

In species belonging to the phylum Ctenophore, comb plates consisting of bundles of multiple cilia are a characteristic synapomorphy and are essential for active swimming. However, in most species of the order Platyctenida, even though pelagic larvae have comb plates, adults completely lose comb plates and exhibit a sessile lifestyle. To understand the evolution of platynectids' unique lifestyles, it is necessary to reveal how comb plates are lost during the larval stages. Therefore, in this study, to reveal the process of comb plate degeneration, histological observations on larvae of different post-hatching ages were carried out in the harp comb jelly, Lyrocteis imperatoris (Platyctenida: Lyroctenidae). The observations showed that the number of comb plates decreased along with the larval growth, and they completely disappeared before the larvae settled down. Also, it was shown that the sizes of the ribs (rows of comb plates) in larvae increased until around 30 days after hatching, while relative sizes of ribs with respect to larval body sizes continued to get smaller after hatching. This suggested that, in L. imperatoris, although the ability to disperse away from their parents would be maintained after hatching as long as ribs develop, this ability would significantly decrease after the cessation of rib development. Therefore, in contrast to pelagic comb jellies in which ribs continue to develop throughout their lives, L. imperatoris acquired mechanisms to cease rib development and promote rib degeneration during their post-hatching growth, which are involved in the evolution of novel sessile lifestyles.

The Siberian weasel (Mustela sibirica) is a mustelid widely distributed in Asia. Previous mitochondrial DNA (mtDNA) phylogenetic analyses showed that this species consists of two clades (the northern and southern lineages) in native populations, and that introduced populations currently expanding in western Japan could have originated from Korea. To elucidate the origin and history of expansion, genome-wide single nucleotide polymorphisms (SNPs) were obtained through double-digestion restriction site-associated DNA sequencing (ddRAD-seq) of biparentally inherited nuclear DNA in addition to the maternally inherited mtDNA. The SNPs were used to study the population genetics of Siberian weasels across the Asian continent, the Korean Peninsula, Taiwan, and the Japanese archipelago, including Tsushima and three of the four main islands: western part of Honshu, Shikoku, and Kyushu. Our results showed genetic differentiation among native populations between the continent and Taiwan. The Taiwan population differed markedly from other populations. Our phylogenetic analyses indicated that introduced founders from the continent and their offspring expanded their range from west to east in Japan, which is consistent with a previously reported mtDNA phylogeny. Our study detected no evidence of hybridization between the Siberian weasel and the related Japanese weasel (M. itatsi), which have overlapping habitat ranges.

Scientific names, especially epithets (specific names in the zoological nomenclature), are derived from various factors, not only species characteristics but also cultural backgrounds, such as the names of people. They reflect how species were perceived at the time. However, several ethical issues have been raised, such as naming species after criminals and gender imbalance in eponyms (epithets named after people). Previous research has been conducted through thorough literature reviews with random sampling, which requires significant time and effort. In this study, the accuracy of the automated labeling using a large language model (LLM) was assessed, and the temporal etymological trends of 2705 species of phytophagous arthropods were investigated. LLM-based classification achieved F1 scores above 75% and accuracy above 90% in Morphology, Host, Geography, and People. However, Ecology & Behavior and Other exhibited accuracy issues. Analyses using the generalized additive model (GAM) revealed shifting naming trends, with a decrease in Morphology and an increase in Geography and People, consistent with previous research on spiders. This study demonstrates the effectiveness of LLM-based classification for epithets and provides a new perspective on the social and scientific debates surrounding scientific names based on etymological trends.