Water temperature is a key environmental factor shaping sex determination in many gonochoristic fishes, with direct consequences for population responses to climate warming. This study is the first examination of temperature effects on sex determination in an atherionid fish, a family belonging to a taxonomic group (Atheriniformes) with abundant examples of temperature-dependent sex determination (TSD). It integrates field observations with controlled rearing experiments to analyze the possibility of TSD in the bearded silverside Atherion elymus population of Tokyo Bay, near the northern limit of distribution of this species. Histological analysis of the gonads and daily age estimation using otolith increment analyses indicated that sex determination in wild fish was completed in both males and females at about 14 days after hatching and 10 mm standard length. Reconstruction of the thermal experience of individual fish during this period did not support the assumption of thermal effects on sex determination in wild individuals. Laboratory rearing experiments conducted with five families in environmentally-relevant temperatures also consistently failed to produce sex ratio biases. These results demonstrate that sex determination in the bearded silverside population of Tokyo Bay is largely insensitive to temperature and highlight the importance of integrative field- and experiment-based approaches for assessing temperature effects on sex determination under climate warming. Although the current findings negate the presence of TSD in the bearded silverside, examination of more southern populations is warranted to rule out the possibility of a latitudinal cline in thermal sensitiveness in this species.
The Australian marine atherinid fish, Hypoatherina tropicalis (Whitley 1948), having long been the subject of taxonomic confusion because of its wide intraspecific variation, is redescribed as a valid species based on the holotype and 19 non-type specimens collected from the east coast of Australia. In this process, we describe three new atherinid species, Hypoatherina gracilis sp. nov., Hypoatherina platysoma sp. nov. and Hypoatherina polylepis sp. nov., which were previously confused with H. tropicalis and Hypoatherina temminckii (Bleeker 1854). Hypoatherina gracilis sp. nov. and H. polylepis sp. nov. are distinguishable from all congeners except H. tropicalis in having a short and blunt ascending process of the premaxilla, its height 2.4–2.8 and 2.3–2.8 times the maximum width, respectively, and shorter than half of the premaxillary horizontal length. Hypoatherina gracilis sp. nov. can be distinguished from H. tropicalis by having a narrower interorbital width, 31–33
Understanding how genetic differentiation is maintained between closely related species with overlapping habitats is a central question in evolutionary biology. The sticklebacks Gasterosteus aculeatus and Gasterosteus nipponicus occur in sympatry with reproductive isolation on the Pacific coast of Hokkaido Island. However, their distributions and hybridization patterns in more northern regions remain largely elusive. Here, we analyzed species distributions and hybrid occurrences in Sakhalin, the Northern Territories, the Kuril Islands, the Pacific and Okhotsk coasts of Kamchatka, Chukotka, and the open Bering Sea using genome-wide nucleotide variant data. We found that G. nipponicus is largely restricted to Sakhalin, while G. aculeatus predominates in other regions, with only rare hybrids detected. These findings indicate largely allopatric distributions around the Sea of Okhotsk and the Bering Sea. These allopatric populations provide valuable opportunities for comparing patterns of genetic differentiation and phenotypic divergence between allopatric and sympatric species pairs.
The global antimicrobial resistance (AMR) crisis, fueled by the cross-border dissemination of antibiotic resistance genes (ARGs), poses a critical and escalating threat to public health. Migratory birds, with their extensive mobility and broad ecological connectivity, effectively bridge human-influenced and natural ecosystems, thereby playing a key role in the worldwide circulation of ARGs. While significant advances have been made in detecting ARGs in birds and tracing their links to anthropogenic sources, research remains fragmented: birds are often regarded merely as passive samplers, without due consideration of the mechanistic processes through which ARGs are acquired via avian traits, evolve within gut microbiomes, and are disseminated across continents through migratory networks. This review synthesizes current evidence to position migratory birds not only as global vectors but also as evolutionary incubators of ARGs. Integrating ecological, microbiological, and One Health perspectives, we delineate the pathways of bird-mediated ARG transmission across multiple scales—from molecular events within the avian gut and individual-level traits, to population-level migratory networks, and up to global flyways. A particular focus is placed on the gut microbiome, where mobile genetic elements (MGEs) serve as crucial drivers of ARG reassortment, stabilization, and horizontal transfer, thereby bridging micro-scale genetic mechanisms with macro-scale ecological spread. Looking forward, we recommend future studies to quantify ARG fluxes at key stopover sites, clarify the role of under-represented migratory taxa, and develop predictive frameworks that integrate avian movement ecology with resistome surveillance. We advocate for integrated One Health strategies and propose the Flyway-Node-Resistome (FNR) Framework as a basis for future research and transnational governance, aimed at mitigating AMR spread while conserving migratory bird populations.
The South Basin of Lake Biwa, Japan, has undergone significant changes in fish fauna due to the introduction of invasive species and habitat alterations. This study assessed the current status of native fish species recovery through environmental DNA (eDNA) metabarcoding and capture surveys conducted in 2008 and 2021. The eDNA survey detected 40 fish taxa, including 31 native and nine non-native taxa, while capture surveys identified 18 taxa. Notably, ten native taxa absent from the 2008 survey were detected in both the 2021 capture and eDNA surveys, indicating their potential recolonization. Among these, eight taxa not subject to fisheries stocking suggest natural population recovery. The decline in invasive largemouth bass (Micropterus nigricans) and bluegill (Lepomis macrochirus) populations may have contributed to this resurgence. Additionally, eDNA surveys detected several benthic and elusive species, highlighting their effectiveness over traditional capture methods. A novel detection of Gobio gobio, a Eurasian cyprinid with no prior records in Japan, suggests possible human-mediated introduction. Conversely, nine native species previously recorded in the South Basin were not detected, warranting conservation attention. The study underscores the utility of eDNA metabarcoding for biodiversity monitoring and conservation, providing a non-invasive and comprehensive approach to assessing fish community dynamics in high-diversity lake ecosystems.
A new ophidiid fish, Sirembo quinquefasciatus, is described based on the holotype and 13 paratypes, 125–172 mm in standard length, collected from the southern South China Sea (Gulf of Thailand, off the east coast of Peninsular Malaysia and off the west coast of Borneo). The new species can be distinguished from all other congeners by having two dark longitudinal bands on the anal fin, one along its base, the other submarginal. Furthermore, S. quinquefasciatus sp. nov. differs from Sirembo amaculata (Cohen and Nielsen 1982) and Sirembo wami Nielsen, Schwarzhans and Uiblein 2014 in having several blotches on the dorsal fin (vs. a single dark longitudinal band in S. amaculata and only two blotches in S. wami). The present new species can be distinguished from Sirembo metachroma Cohen and Robins 1986 by having dark bands along the dorsal-fin base and the lateral line (vs. no band along dorsal-fin base and a distinctive black streak along lateral line in the latter). The new species resembles Sirembo imberbis (Temminck and Schlegel 1846) and Sirembo jerdoni (Day 1888) in sharing many dark blotches on the dorsal fin and several dark longitudinal bands on the body and the anal fin. The former is distinguishable from S. imberbis by having 6–8 scale rows between the dorsal-fin origin and the lateral line (vs. 9–11), and from S. jerdoni by the position of the dorsal-fin origin (above fourth or fifth vertebra vs. first to third).
Size-dependent survival is a well-known phenomenon in fishes, typically positive but with exceptions. I investigated survival of chum salmon, Oncorhynchus keta, smolts in coastal waters of the Shiretoko Peninsula, northern Japan, using tethering experiments. Of 111 smolts, only 11 survived. Survival was explained solely by body size and was negatively correlated with it. These results suggest that predator foraging strategy and hatchery-wild differences may underlie the observed pattern, with implications for salmon management strategies.
Ocosia fasciata Matsubara 1943 (Synanceiidae: Tetraroginae) is redescribed on the basis of the lectotype, 37 available paralectotypes and 39 non-type specimens from Japan and Taiwan. A reassessment of diagnostic characters within the genus is made, with emphasis on comparisons with the morphologically similar congener Ocosia zaspilota Poss and Eschmeyer 1975, and two other Japanese congeners, Ocosia spinosa Chen 1981 and Ocosia vespa Jordan and Starks 1904. Ocosia fasciata is distinguished from O. zaspilota by a relatively narrower body and longer head, in addition to previously recognized differences in the lengths of the anterior dorsal-fin spines. Ocosia fasciata also tends to have slightly fewer lateral-line tubes and gill rakers that O. zaspilota. Ocosia spinosa and O. vespa share a combination of characters, including usually 16 dorsal-fin spines (almost always 15 in O. fasciata), the presence of lateral lacrimal and suborbital spines (almost always absent), moderately incised or weakly concave interspinous dorsal-fin membranes (strongly incised), and a relatively broad membrane between the last pelvic-fin soft ray and abdomen (narrow). Compared with O. spinosa, O. vespa has broader dorsal-fin membranes, apparently lacking incisions in life, although slightly concave in preserved specimens, and densely distributed papillae on both jaws. Molecular analyses based on mitochondrial COI sequences (443 bp) showed no clear interspecific divergence among the four species, despite clear morphological differentiation, suggesting that COI-based DNA barcoding does not consistently match morphological species definitions in Ocosia.
Eavesdropping on heterospecific alarm signals provides critical predator information, yet whether recognition is driven by innate phylogenetic biases or learning and ecology remains unclear. We hypothesize that decoding strategies arise from interactions between evolutionarily inherited perceptual biases and current ecological adaptations. To test this, we chose Asian Tits (Parus cinereus minor) as an “information hub species”, along with the Green-backed Tits (P. monticolus) and the Coal Tits (Periparus ater), forming a phylogenetic gradient. Playbacks used three call types: territorial song, ground alarm calls (hereafter “alarms”), and aerial alarms. Results demonstrated that Asian Tits exhibited a strong conspecific bias exclusively for ground alarms: fleeing probability in response to conspecific ground alarms (79.3%) was significantly higher than to heterospecific ground alarms, with no difference between the two heterospecific sources. Coal Tits were 2.89 times more likely to flee than Green-backed Tits in response to Asian Tit calls. These results support a binary conspecific-heterospecific distinction for ground threats, not a phylogenetic gradient. Decoding is call-type-specific: ground alarms elicit accuracy-driven responses, whereas aerial alarms permit more permissive decoding. Thus, heterospecific alarm decoding is shaped by signal function, a clear conspecific dichotomy and ecological niche, not by fine-scale phylogenetic distance.
Recognition and rejection of parasitic eggs are crucial host defenses against brood parasitism. Template-based recognition and recognition by discordancy are two main mechanisms of egg recognition used by bird hosts. However, even in hosts that utilize template-based recognition, a decrease or absence of templates in the nest may affect parental judgment when the disparity between foreign and host eggs is small. This study examined two sympatrically breeding bunting species, the Godlewski’s Bunting (Emberiza godlewskii) and Yellow-throated Bunting (E. elegans), both of which are potential hosts of the Common Cuckoo (Cuculus canorus). To examine the egg recognition mechanisms, we introduced red model eggs, Budgerigar (Melopsittacus undulatus) eggs, inter-specific eggs, and conspecific eggs at different ratios of host to foreign eggs and observed the rejection behaviors by two bunting species. The results showed that both bunting hosts mainly employed template-based recognition to reject foreign eggs. However, when the disparity between the foreign and host eggs was minimal, both species exhibited a decrease in rejection rates as the number and ratio of host eggs decreased. Our findings support the perspective that repeated egg-laying by cuckoos may contribute to enhancing the success rate of parasitism. However, constrained by the density of cuckoo populations and the trade-off between reproductive investment and returns for cuckoos, the two bunting species with strong egg recognition abilities and template-based recognition are rarely parasitized.
Sex changes in fish are commonly driven by social or reproductive advantages associated with body size, and protogyny is particularly prevalent in species exhibiting male territoriality or haremic mating systems. Within the family Serranidae, several species exhibit sexual dimorphism and protogyny; however, in the genus Selenanthias, only Selenanthias analis Tanaka 1918 has been reported to exhibit sexual dimorphism. The present study investigated sexual dimorphism and the occurrence of protogynous hermaphroditism in two serranid species, S. analis and Selenanthias sp. sensu Ikeda and Nakabo 2015, based on external morphology, gonadal histology, and mitochondrial DNA sequences (partial COI region). Morphological and histological analyses revealed consistent sex-specific coloration and differences in the fin filament lengths in both species. Six individuals of S. analis possessed gonads containing both ovarian and testicular tissues. Among these, two individuals morphologically identified as males and four individuals represented both female and male characteristics. In addition to these six individuals, two individuals exhibited both female and male morphological characteristics but possessed only ovarian tissue. Genetic analyses supported the recognition of two distinct species (S. analis and Selenanthias sp.) and confirmed that the color morphs within each species represent intraspecific sexual dimorphism. These findings provide the first evidence of sex change in the genus Selenanthias, establishing S. analis as a protogynous species and suggesting a similar potential for sex change in Selenanthias sp.
Although a ninespine stickleback (Pungitius d'Annone 1760) inhabiting the Kanto region of Honshu Island, Japan, was reported as an undescribed species in the early 1960’s, it has at no time been formally described. Morphologically similar to Pungitius sinensis (Guichenot 1869), the former is now described as Pungitius nakamurai sp. nov., being usually differentiated from all other congeners by the following combination of characters: dorsal-fin rays IX + 11; anal-fin rays I + 9; pectoral-fin rays 10; pelvic-fin rays I + 1; procurrent caudal-fin rays 5 + 5 = 10; lateral plates in an incomplete row, forming a distinct lateral keel on caudal peduncle; 6 plates on ventral surface of caudal peduncle; vertebrae 33 (14 abdominal and 19 caudal vertebrae); dorsal-fin spines inclining alternately to sides of mid-line; first dorsal-fin spine antero- or postero-dorsal to upper end of pectoral-fin base; ascending process of pelvis well-developed, upper end of pelvis reaching to level of fifth pectoral-fin ray base; antero-ventral process of ectocoracoid present, right and left ectocoracoids articulating anteriorly with each other; no distinct ridge on cleithrum and ectocoracoid; body dark yellow or dark green; membranes of dorsal-fin spines hyaline or with a few minute black spots; membrane of pelvic-fin spine of adult males white, becoming blue during courtship behavior; membrane of anal-fin spine of adult males whitish with a distinct white blotch (turning blue during courtship).
Persistent organic pollutants (POPs), primarily from industrial and agricultural sources, pose significant risks to birds due to their environmental pervasiveness, bioaccumulation, and toxicological impacts. Bird's trophic position and ecological traits make them vulnerable to POP exposure while also serving as bioindicators of environmental contamination. This review aims to systematically evaluate the global occurrence and bioaccumulation of POPs in birds, focusing on exposure pathways, non-invasive and tissue-based monitoring, species-specific sensitivity, and long-term toxicological impacts on avian physiology, behaviour, reproduction, and neural development. A systematic literature review was conducted following PRISMA guidelines, using peer-reviewed articles and international reports. Key themes and trends were analyzed using VOSviewer for keyword clustering and network visualization, allowing assessment of POP exposure in avian populations. POPs were widespread with higher bioaccumulation in seabirds and passerines than freshwater and terrestrial species, reflecting biomagnification through the food web. Notably, terrestrial birds accumulate hydrophobic POPs more readily than aquatic birds due to reduced elimination efficiency and dietary differences. Bioaccumulation was most pronounced in tissues such as liver, blood, preen gland oil, feathers, and eggs, reflecting species-specific, ecological, and migratory variations. Non-invasive matrices provide valuable tools for long term monitoring. POPs exposure in birds leads to multiple behavioral and physiological disruptions, primarily affecting endocrine and immune systems, influencing growth, survival, and reproductive success. POPs activate aryl hydrocarbon receptor (AHR) and disrupt the hypothalamus-pituitary-thyroid axis, causing prenatal hypothyroidism, delayed hatching, impaired ovarian steroidogenesis, reproductive failure, and reduced eggshell thickness through altered calcium transport and bioavailability. POPs can cross the blood-brain barrier, leading to neural effects including spinal cord dysmyelination, cerebral asymmetry, oxidative stress, disrupting dopaminergic, cholinergic, and serotonergic neuronal pathways, ultimately disrupting navigation, spatial behaviour, and cognitive function. Temporal trends indicate a decline in some legacy POPs following regulatory measures, though contamination persists in high trophic species, reflecting complex global contamination patterns. These findings emphasize the importance of monitoring POPs in birds and underscore the need for stringent restrictions and regulations to mitigate ecological risks and protect wildlife.
Penguins are usually framed as marine predators, yet freshwater can strongly alter the environments in which they forage, breed and survive. This narrative mini review synthesises evidence for how river outflows, glacial meltwater, snowmelt and rainfall shape penguin ecology across estuarine, fjord, colony and climatic settings. In southern Australia, river plumes reorganise penguin foraging habitat, and prolonged drought linked to reduced coastal freshwater delivery has coincided with major demographic decline. In Antarctic and subantarctic fjords, glacial meltwater can enhance stratification, alter prey depth and influence penguin foraging conditions, but its effects are not uniformly beneficial because increased turbidity, contaminant transport and physical disturbance may also degrade habitat. At breeding colonies, snow can provide a local freshwater source that helps reduce osmoregulatory costs, whereas excessive meltwater and rainfall can flood nests, collapse burrows, chill chicks and reduce breeding success. Physiological and isotopic evidence further suggests that freshwater influences penguins not only through habitat and reproduction, but also through hydration, salt balance and longer-term environmental archives. Across systems, freshwater acts both as a resource and a hazard, and its effects depend on timing, magnitude and local context. This freshwater-centred perspective highlights penguins as indicators of linked land–sea and ice–sea change, clarifies key thresholds and uncertainties, and points to more targeted priorities for future interdisciplinary research.
The Qinghai-Tibet Plateau serves as a critical hub along the Central Asian Flyway (CAF) and a recognized hotspot for the emergence of highly pathogenic avian influenza (HPAI) viruses. Despite recurrent outbreaks, the migratory dynamics of key reservoir species, such as the Brown-headed Gull (Chroicocephalus brunnicephalus) and their potential contributions to viral dissemination remain poorly understood. Here, we integrated highresolution GPS telemetry with Bayesian discrete phylogeographic analyses to investigate the potential association between migration and HPAI H5Nx dissemination. Based on tracking data from 11 individuals, we identified 5 major life-history stages and 12 important stopover sites used during migration, including 6 in autumn and 6 in spring, and characterized their spatiotemporal distribution patterns. Phylogenetic reconstruction showed that three independent introductions of HPAI H5Nx viruses occurred on the Qinghai-Tibet Plateau between 2021 and 2024, all involving strains associated with Brown-headed Gulls and classified into the 2021-H5N8 I, 2021-H5N8 II, and 2022-H5N1 clusters. These viral clusters were distributed primarily along the CAF and the East Asian-Australasian Flyway (EAAF), with diffusion patterns broadly consistent with the spatiotemporal dynamics of migratory birds. Notably, the spread of the 2022-H5N1 cluster along the CAF was highly concordant with the migratory route and phenology of Brown-headed Gulls, while host transition analysis suggested that gulls may serve as bridging hosts in interspecies transmission. Together, these findings suggest that Brown-headed Gulls may contribute to the cross-regional dissemination and interspecies transmission of HPAI H5Nx viruses, and highlight the value of combining tracking data with viral genomics for cross-border surveillance.
While it is well established that climate change is driving species toward higher latitudes, the spatiotemporal dynamics of dispersal-particularly from subtropical to warm-temperate zones-remain poorly understood. Here, we combined ecological niche differentiation, functional landscape connectivity, and species distribution models (SDMs) to investigate the northward expansion of the Collared Finchbill (Spizixos semitorques) from southern China (subtropical zone) to northern China (warm temperate zone) over the past decade (2015-2024). The species was first recorded in Beijing in 2015, providing a clear temporal marker for the onset of rapid colonization at the expansion front. Our analyses revealed that compared to native-range populations, those in the expansion region show a partial shift in their ecological niche, occupying new environmental and geographic spaces. Functional landscape connectivity analysis further identified two main dispersal routes from the native range toward the expansion front region: a dominant "mountain corridor" along the Qinling, Taihang, and Yanshan ranges, and a secondary "plain corridor" across the eastern plains, with Mount Tai serving as a key dispersal hub. Moreover, SDM-based projections for 2060 and 2100 suggest that this northward expansion might continue and reach Liaoning Province, which could become a potential suitable habitat. Overall, our findings highlight the critical interplay between climatic niche shifts and landscape connectivity in facilitating rapid range expansion, providing a mechanistic framework for understanding how subtropical species colonize warmtemperate zones.
Behavioral innovation, defined as the ability to exhibit novel behaviors that may contribute to problem-solving and adaptability, has been increasingly recognized as a key factor in species’ resilience to environmental shifts. Here we investigate the association between behavioral innovation and climatic niche breadths (the range of climatic conditions a species can tolerate) across 9338 bird species, representing the majority of extant birds, exploring its potential role in coping with climatic variability. We quantified climatic niches using high-resolution spatial and bioclimatic data to capture both species-overall extremes and among-locality variations. By using Bayesian Phylogenetic Generalized Linear Mixed Models, we analyzed correlations between these realized climatic niche breadths and two metrics of behavioral innovation—innovativeness (the propensity to exhibit novel behaviors) and innovation rate (the frequency of such behaviors)—while incorporating ecological and life-history traits as covariates. Innovativeness significantly correlates with broader climatic niche breadths for both temperature and precipitation. In contrast, innovation rate shows only a positive association with precipitation niche breadth and no significant correlation with any temperature niche metrics. Our findings reveal that while innovativeness significantly correlates with broader climatic niche breadths in birds, further variation in climatic niche breadth among innovative species is minimally associated with their innovation rates. This relationship is linked to a distinct spatial pattern: for temperature, innovative species exhibit broader niches alongside both wider within-locality tolerance and greater variation among localities; for precipitation, broader niches are associated primarily with greater variation among localities, despite having narrower within-locality niches. These results highlight that integrating innovativeness into climate vulnerability assessments could better capture resilience, complementing established predictors.
Cognitive traits such as brain size are hypothesized to influence avian reproductive strategies, yet the ecological mechanisms linking neural investment to fitness under natural conditions remain underexplored. According to the cognitive buffer hypothesis, larger brains should facilitate adaptive decision-making, potentially translating into indirect fitness benefits. In this study, we investigated the relationships among head size (a validated proxy for brain size), structural body size, nest-site selection, and reproductive success in Barn Swallows (Hirundo rustica) breeding in southern China. We found that head size was independent of structural body size metrics (e.g., tarsus length), confirming that it represents a distinct trait related to neural investment rather than allometric scaling. Although males possessed slightly larger heads than females, head size in both sexes was a significant predictor of fine-scale nest-site selection. Larger-headed individuals consistently selected nest sites located closer to overhead structures and opposing shelters. These specific architectural choices were, in turn, strong predictors of reproductive output: nests with greater enclosure produced significantly more fledglings, likely due to reduced predation risk and improved microclimatic buffering against extreme weather. Crucially, head size itself did not directly predict fledging success, suggesting that the fitness advantages of larger brains are realized indirectly through superior habitat selection decisions. Our findings provide empirical support for an indirect pathway between cognitive capacity and fitness, suggesting that individuals with larger cognitive proxies achieve higher reproductive success not by increasing fecundity per se, but by securing safer, buffered microhabitats for their offspring.
