An incomplete mussel (Mytilus complex) distribution map makes it difficult to distinguish between morphologically and genetically similar species. Correspondingly, mussel DNA samples from 15 sites across eastern Canada and Europe were genotyped using a specialized panel of 69 single nucleotide polymorphisms (SNPs). These findings helped delineate Mytilus edulis (Linnaeus, 1758), Mytilus trossulus (Gould, 1850), Mytilus galloprovincialis (Lamarck, 1819), and hybrid zones across the North Atlantic. Notably, all mussels sampled within the Northumberland Strait and the southern half of the Gulf of St. Lawrence were Mytilus edulis, with no signs of M. trossulus introgression. In contrast, there were varying levels of M. edulis, M. trossulus, and hybrids identified along the northern coast of the Gaspé Peninsula, Nova Scotia, and eastern Newfoundland. In Europe, pure populations of M. galloprovincialis and M. edulis were found in Spain and the Netherlands, respectively. Mussels in southern Norway were a mixture of M. edulis and hybrids with M. galloprovincialis and M. trossulus. Altogether, these results are valuable in understanding the population dynamics within current and potential future farming sites. Ecologically, this information also serves as a reliable baseline for future assessments of mussel species distributions that may be altered by climate change or other human activities.
Subtle morphological asymmetries, common in most species, typically originate from developmental noise rather than being adaptive responses. However, diverse taxa exhibit left versus right biases in behavioural traits due to hemispheric specialization, raising the possibility that subtle morphological asymmetries have functionality. Here we provide a rare test of this hypothesis by investigating the extent to which subtle left and right departures from bilateral symmetry in the defensive apparatus of threespine stickleback (Gasterosteus aculeatus Linnaeus, 1758) influence: (1) susceptibility to predator capture and (2) fitness of asymmetric relative to symmetric fish. Using large samples (N = 10 126), we found that left-biased asymmetrics had lower frequencies of predator-induced injuries than did symmetrics, while the latter had lower frequencies than did right-biased asymmetrics. This pattern occurred in four of five years and in each sex. Relative fitness based on ontogenetic shifts in frequencies within six cohorts showed both left and right-biased asymmetrics often had a fitness advantage over symmetrics, but this varied among years in conjunction with shifts in bird versus trout predation. The results suggest that subtle departures from symmetry can comprise an axis of functional phenotypic space maintained by fluctuating ecological and selective processes.
Diet composition analyses such as stable isotope analyses are widely used to infer food sources in wild animals, reflecting assimilated dietary inputs in body tissues. Collecting tissue samples is often invasive and costly, making opportunistic sampling of animals captured for other purposes (hunting, fishing, and trapping) particularly attractive. We thus aimed to assess whether the post-mortem handling commonly associated with fur-trapped mammals (freezing, thawing, and early decomposition) alters stable isotopic values of muscle tissue, thereby affecting their suitability for ecological studies. We used muscle tissue samples from coyotes (Canis latrans Say, 1823) harvested by trappers to investigate the effect of muscle decomposition on carbon (C) and nitrogen (N) stable isotopes ratios, and on C:N ratios. We sampled muscle tissue from four frozen carcasses that were kept outdoors at ambient temperature for a 10-day period. We found no effect of accumulated degree-days or time since start of trial on stable isotopic values. Our results suggest that samples from frozen trapped carcasses are suitable for isotopic analyses for up to 10 days or 82 accumulated degree-days post-mortem, especially under boreal climates where cool seasonal temperatures preserve tissue integrity. This underused and easily accessible source of samples represents a valuable opportunity for researchers.
Vertebrates affect aquatic nutrient cycling by storing, excreting, and egesting important nutrients. The elemental phenotype, which defines (1) elemental acquisition (diet), (2) intestinal elemental absorption and elemental incorporation into tissues, (3) elemental allocation to processes and structures, (4) body elemental composition, and (5) elemental release in wastes, can summarize and evaluate these effects. Trait investment may influence the elemental phenotype, as some traits exert or relieve nutritional demands. We test whether variation in bone, a phosphorus (P)-rich vertebrate trait, affects the P-specific elemental phenotype of a species with substantial bone variation: the threespine stickleback (Gasterosteus aculeatus Linnaeus, 1758). Given bone's unique impact on nutrient demand, we predicted that increased bone would (1) increase whole-body %P, (2) decrease dietary P intake or intestinal P absorption, and (3) increase P excretion and egestion. Ultimately, increased bone increased whole-body %P and P excretion but did not affect diet, intestinal absorption, or fecal %P. Nonetheless, threespine stickleback absorbed relatively less P in their guts than carbon or nitrogen, suggesting that their P demand is low overall and masking relationships between bone and demand. Our results suggest that bone content may both increase P storage in threespine stickleback bodies and increase P release in wastes.
The miniature fish Placopleurus (Neopterygii) is commonly reported from Middle Triassic marine deposits of the Western Tethys but has remained poorly understood due to the incompleteness of the original material. We present a comprehensive redescription of this genus based on new specimens from Middle Triassic Southern Alpine localities. Five new species are established: Placopleurus taibonensis sp. nov. from the upper Ladinian Pelsa/Vazzoler Lagerstätte (Dolomites), Placopleurus verbanensis sp. nov. from the mid-Ladinian of Castelveccana (western Lombardy), Placopleurus seidli sp. nov. and Placopleurus zmelkooworum sp. nov. from Anisian sites in the Kamnik-Savinja Alps (Slovenia), and Placopleurus evelynae sp. nov. from the Anisian Prà della Vacca (Dolomites). The new material provides clearer insights into the skull and tail anatomy of the genus. Placopleurus species-specific characters chiefly involve ornamentation of bones and scales, bone shape (e.g., cleithrum, dermopterotic), presence/absence of particular features (teeth, hook-like element), and overall size. These are combined with meristic characters such as number of deep flank scales, number of horizontal scale rows, and insertion of the pelvic, dorsal, and anal fins. Notably, a juvenile from the Dolomites permits ontogenetic inferences of the taxon. Moreover, some Slovenian specimens exhibit the oldest known near-homocercal tail, resembling that of teleosts. These findings support placing Placopleurus closer to more advanced neopterygians, in the new order Placopleuriformes.
In small mammal population cycles, after explosive reproduction during the phase of increasing population density the animals slow their reproductive rate during the high-mortality decline phase. Existing theory about reproductive restraint involves delayed compensating benefits, but those are of little value during the decline phase when survival is very unlikely. Changing prevalence of differing genotypes has been ruled out for small mammal populations, so now the reproductive slowdown is attributed to stress, which is known to suppress reproduction and have trans-generation effects. However, why are there no stress-immune animals that keep reproducing at a high rate regardless of circumstances? This analysis shows why there is an immediate benefit of reproductive restraint: it both slows the rate of decline and diminishes the probability of local extinction. With a simple model I calculate how reproduction should vary to maximize the probability of persistence under differing mortality rates, and then simulate the evolution of a reaction norm of reproductive effort under cycling mortality rates. I find that animals should restrain reproduction when mortality rates are high or very low. These results link the death rates produced by extrinsic factors with the intrinsic change in reproductive output and show why the effects of stress on reproductive output seem appropriate.
Marine-derived subsidies link coastal and terrestrial food webs, yet their use by large terrestrial mammals remains poorly documented. We investigated wrack-associated foraging by brown bears ( Ursus arctos Linnaeus, 1758) along the White Sea coast of the Onega Peninsula (Russia) using records of foraging instances from standardized coastal surveys (2015–2025) and invertebrate sampling (2025) of decomposing wrack deposits. We analyzed seasonal and spatial patterns using generalized linear models. We recorded 66 wrack-foraging instances during standardized coastal surveys. Foraging occurred across seasons, with peak activity in early spring (mean 10.0 instances per survey) and lower levels in autumn (3.39). Wrack-foraging activity varied among coastal sectors and was concentrated in the semi-enclosed Eastern Solovetsky Salma Strait, where model-based counts were higher than in Onega Bay (incidence rate ratio (IRR) = 9.98, 95% CI 2.97–33.5). Decomposing wrack contained abundant detritivorous invertebrates dominated by dipteran larvae of the kelp fly Coelopa frigida (Fabricius, 1805) and enchytraeid oligochaetes. Bears excavated moist wrack deposits and consumed invertebrate-rich material rather than macroalgal tissue. These findings indicate that wrack-associated invertebrates represent a predictable marine-derived food resource and reveal an underrecognized pathway linking coastal detrital systems to large terrestrial consumers.
Artificial light at night (ALAN) is a rapidly expanding environmental threat. The ongoing shift from warm yellow light to cool white LEDs is expected to increase its detrimental effects on wildlife. Currently, light pollution is rapidly increasing in densely populated coastal areas, which are important breeding habitats for many animals, especially fishes. Yet, the effects of ALAN on fish reproduction remain poorly known. We investigated if ALAN influences the development of nuptial colouration in three-spined stickleback ( Gasterosteus aculeatus Linnaeus, 1758) males at the start of the breeding season, and if any such effect depends on the light spectrum. We found that males developed nuptial colouration faster in the presence of ALAN. This effect was especially pronounced under longer peak wavelength, yellow light, whereas it was weaker under shorter peak wavelength, cool white light. Our results demonstrate that ALAN has the potential to alter the reproductive physiology of stickleback and influence the timing of spawning, and that the strength of this effect depends on the light spectrum. Earlier spawning readiness under ALAN could desynchronise spawning from optimal ecological conditions, potentially affecting individual reproductive success and population dynamics.
Mate choice and courtship preferences of hybrids between incipient species can directly influence patterns of gene flow and speciation. Here, we study mate choice in hybrids between two sympatric threespine stickleback species (i.e., the benthic and limnetic species of Gasterosteus aculeatus Linnaeus, 1758) using experimental no-choice mating trials to record the preference of hybrid females (F1 hybrids and backcrosses) toward males of the parental species. Our results indicate that hybrid females preferred males with an ancestry proportion similar to their own, and that the pattern of preference toward alternate male species was additive and nearly symmetric, suggesting that mate choice shows intermediate inheritance rather than dominance. Size-based assortative mating—previously reported to direct species mate choice in this system—did not appear to shape hybrid female mate choice among hybrids. Finally, males of the parental species based mating behavior toward hybrid females on size and shape similarity rather than ancestry proportion. This suggests that body size and body shape play significant role in interspecific interactions between males and females. Our results can elucidate the role of hybrid behaviour and preference in shaping barriers to gene flow between young sympatric species.
Late Cretaceous acanthomorph fishes are well represented in freshwater vertebrate microfossil localities in the Western Interior of North America but are not well known from articulated specimens. Microfossils—isolated disarticulated elements—provide data on diversity and distribution but can be difficult to assign to known lineages. Articulated specimens are needed to evaluate the evolutionary relationships of early acanthomorphs, but these are rarely preserved in fluvial beds, limiting our understanding of the taxa present in these environments. An exceptional freshwater locality that preserves a diverse assemblage of small articulated specimens is Pisces Point sampling the Scollard Formation of Alberta, Canada. Known taxa in the locality include two osteoglossomorphs, an esocid, the percopsiform (Acanthomorpha) Lindoeichthys albertensis Murray et al., 2019, and the otophysan Acronichthys maccagnoi Liu et al., 2025. Here we describe two additional acanthomorph fishes: a polymixiiform tentatively in family Boreiohydriidae, and a percomorph of uncertain relationships. These specimens, along with the previously named Pisces Point percopsiform, indicate that at least three distantly related acanthomorph lineages were present in fresh waters of North America by the late Maastrichtian, and increase our understanding of the acanthomorph evolutionary and geographic diversity prior to the end of the Cretaceous.
Sexual selection promotes exaggerated weapons and alternative reproductive tactics, but the ecological factors maintaining male dimorphism remain poorly resolved. In the European rhinoceros beetle, Oryctes nasicornis (Linnaeus, 1758), males occur as alpha morphs with combat horns or beta morphs with reduced horns that adopt sneaker tactics. We combined opportunistic records collected from 2005 to 2021 with standardized transect surveys conducted from 2022 to 2025 across seven landscapes in central Italy to test how anthropogenic matrix affects sex ratios, morph frequencies, and activity. Habitat composition and heterogeneity were quantified using land use data and diversity indices. Sex ratios differed among landscapes. Morph frequencies also varied with habitat structure and anthropogenic matrix intensity. Across landscapes, beta male frequency increased with anthropogenic matrix and decreased with habitat evenness, whereas alpha males were associated with semi natural, tree rich environments. Generalized Linear Models showed dataset dependent responses along the anthropogenic gradient and indicated that alpha male abundance reflected population size and morph specific processes. Generalized Linear Mixed Models using 1 km buffers confirmed increasing beta male frequency and declining alpha male abundance in landscapes. Seasonal activity followed sinusoidal patterns without interannual trends, supporting the allocation hypothesis.
Road salt runoff entering aquatic habitats is an important issue in climates that experience winter, threatening the health of these ecosystems. Using outdoor mesocosms, this study examined how two different road salts, NaCl and CaCl2, at a concentration of 1 g Cl−/L affect (1) decomposition of leaf litter by amphipods (Malacostraca: Amphipoda), (2) survival of amphipods, and (3) colonization of aquatic ecosystems by macroinvertebrates. We hypothesized that NaCl and CaCl2 would differ in the extent of decomposition and amphipod survival, predicting higher survival in CaCl2 treatments due to added calcium. Additionally, we hypothesized that salinization would affect the colonization of aquatic ecosystems by other flight-capable macroinvertebrates, predicting higher colonization of control treatments. We found (1) higher decomposition of leaves in the CaCl2 treatment than the NaCl treatment or the control, (2) a significant effect of salinity on amphipod survival, with more individuals surviving in CaCl2 than NaCl or control treatments, and (3) salinity did not have a significant effect on colonization of mesocosms by macroinvertebrates. Amphipod size did not differ between treatments at the end of the experiment. We found that NaCl and CaCl2 road salts at a concentration of 1 g/L may influence amphipod survival and decomposition of leaf litter, but have little effect on colonizing macroinvertebrates. The knowledge gained from this study will be important for guiding road salt use in cold climates.
The resistance of the snow surface to penetration, or snow hardness, is an important factor affecting wildlife movement. Snow hardness can change dramatically over the course of the day, but it is unknown how animals respond to temporal changes in snow hardness. Using 260 hourly sinking depth measurements as indices of surface hardness along a latitudinal gradient in Norway, we quantified diel cycles of snow hardness in relation to environmental variables. Time relative to sunrise and sunset, temperature, canopy cover, and snow density were the best predictors of surface hardness (R2 = 0.57). We matched diel cycles of the predicted surface hardness index to diel activity in roe deer (Capreolus capreolus (Linneaus, 1758)) and mountain hares (Lepus timidus Linneaus, 1758), using data from the large-scale Scandcam camera-trap network in Norway from 2017 to 2023 (n = 698 cameras). Roe deer increased morning activity when the snow was harder and deeper, and hares did not show diel shifts in relation to the snow hardness index and preferred softer snow at higher snow depths. As snow conditions and wintertime temperatures continue to change, this study highlights the importance of diel activity adaptations to environmental conditions.
Disentangling the relative roles of environmental filtering, biotic interactions, and stochasticity in community assembly is a fundamental goal of ecology, which we investigate using reptiles as a model system across wetland habitats (28 study sites) in Uganda. We analyzed 142 species from 65 genera and 20 families using standardized visual encounter surveys, supported by pitfall traps and opportunistic observations. Lizards dominated assemblages in abundance and site occupancy, whereas snakes were less abundant but exhibited the highest taxonomic diversity. Species richness showed strong spatial structuring, with northern and western wetlands supporting the highest richness. Vegetation type influenced richness, as savannahs and woodlands hosted fewer species than gallery forests. Rank–abundance curves indicated low evenness in lizards, dominated by a few taxa, versus more equitable abundances in snakes, reflecting differences in niche occupation. Beta diversity was turnover-dominated, suggesting environmental filtering as a primary driver of composition. Null-model analyses revealed taxon-specific co-occurrence patterns: lizard segregation was weak and sensitive to null-model assumptions, whereas snake assemblages exhibited consistently strong segregation, indicating stronger exclusionary processes. Together, these results highlight multiscale structuring in tropical wetland reptiles, where broad-scale environmental gradients shape species composition, and local biotic interactions further influence community assembly.
Arctic marine ecosystems are undergoing rapid environmental shifts, creating a need to understand how key species respond to changing sea-ice and habitat conditions. The Atlantic walrus (Odobenus rosmarus rosmarus (Linnaeus, 1758); aiviq in Inuktitut) is a culturally and nutritionally important species for Inuit communities in Nunavik, northern Québec. Because walrus distribution and behavior are closely linked to sea-ice and benthic habitats, we expected Inuit Knowledge to reveal recent ecological changes in Hudson Strait. We conducted 30 semi-structured interviews with experienced hunters in five Inuit communities (Akulivik, Ivujivik, Salluit, Kangiqsujuaq, and Quaqtaq) to document observations related to walrus abundance, migration, haul-out sites, behavior, and changes linked to climate and sea-ice conditions. Participants reported a perceived increase in walrus presence around communities, associated with reduced sea-ice cover and shifts in migration routes. A decline in the number of walruses hunted annually was also noted, attributed to changing lifestyles and decreased reliance on subsistence harvesting. Respondents described changes in haul-out sites, feeding behavior, and walrus interactions with other species. Many linked these changes to earlier sea-ice breakup, warmer waters, and altered marine conditions. This study provides novel insights into Atlantic walrus ecology and offers a community-based perspective on environmental change in Hudson Strait.
Understanding how consumers exploit transient resource pulses requires studying the localized responses they trigger. To explore how brown bears ( Ursus arctos (Linnaeus, 1758)) exploit Pacific salmon pulses outside of migration bottlenecks, we used 9 years of genetic detections along six small streams—grouped into trios along the northern and southern shores of Lake Aleknagik, Alaska where distinct bear populations prey on sockeye salmon ( Oncorhynchus nerka (Walbaum 1792))—to test hypotheses about stream use in relation to salmon abundance and stream morphology. Bear detections in the northern trio were inversely proportional to water depth, whereas in the southern trio greater salmon abundance boosted detection rates and repeat detections were more common for females. Thus, bear behavior comported with optimal foraging theory, as stream use increased with salmon abundance and accessibility, and with the idea that females are less sensitive to anthropogenic disturbance, as these streams are visited by humans. Our findings reveal that factors affecting bear presence along small streams can vary, even among streams separated by a few kilometers, underscoring the complexity of the bear–salmon relationship. Finally, some bears consistently visited streams but most were detected once, implying that impacts and reliance on salmon differ among individuals in bear populations.
Wildlife are often expected to avoid human activity, but responses to anthropogenic development can be complex. We used 9 years of remote camera data to investigate the effects of human disturbance on a population of mountain goats ( Oreamnos americanus Blainville 1816) at the Sunwapta Canyon Viewpoint in Jasper National Park, Alberta, Canada, where the Glacier Skywalk tourist attraction was constructed and operated. We monitored goat presence and activity patterns before, during, and after construction of the Skywalk. Our study assessed changes in goat photograph rates, as well as shifts in seasonal and diel site use across construction phases. Because mountain goats are often considered sensitive to human disturbance, we hypothesized that goats might abandon the site or change their behaviour to avoid humans. Our results show that although goats shifted their daily activity patterns to avoid times of peak human disturbance, goat activity increased during and after construction of the Glacier Skywalk. Mountain goat continued use of a disturbed site may have been influenced by local resource availability. These results provide insight into mountain goat responses to prolonged human activity and infrastructure development, informing future management and conservation strategies.
We describe a new jianghanichthyid species, Jianghanichthys huachongensis sp. nov., from the middle–late Eocene Huachong (also known as Huayong) Formation in the Sanshui Basin, Guangdong, China. This species differs from the previously described Jianghanichthys hub eiensis (Lei, 1977) and Jianghanichthys sanshuiensis (Li et Wang, 1979) in opercular morphology, the pattern of sensory canals in the opercular region, as well as in meristic and morphometric characteristics. Although specimens of J. huachongensis sp. nov. are typically preserved as partially disarticulated and fragile slabs because of the shallow lacustrine or swamp-like paleoenvironment, J. huachongensis sp. nov. exhibits exceptional preservation of the delicate cephalic sensory canal system. This preservation provides new diagnostic features for the family and sheds light on sensory system diversity in early-derived clades of Cypriniformes.
Wound healing is a complex multi-system process that enables organs and tissues to re-establish their form and function post-injury. Exposure to stress and nutritional restrictions results in energetic trade-offs at a physiological level, usually at the expense of immunity and tissue repair. Relatively few studies have focused on how stress and nutrition mediate immune function and healing capacity in fishes. We subjected wild-caught pumpkinseed (Lepomis gibbosus (Linnaeus, 1758)) to a subcutaneous incision (a standardized wound) while experimentally manipulating plasma cortisol levels (via a slow-release cortisol implant) and nutrition (via restricting food intake) to evaluate how these affected wound healing over time (2, 7, and 14 days). Wound healing was poorest for cortisol-treated fed fish at 7 days post-implant. While cortisol implants resulted in lymphocyte apoptosis and neutropenia, which are well-described immunological responses to increased cortisol concentrations, fasting had little effect. Reproductively active males had different leukocyte counts than non-reproductive males, though the direction varied with leukocyte type, suggesting a trade-off in immune response during reproduction. The negative influence of cortisol on tissue repair and inflammation aligns with the wound healing literature across taxa. However, the ability of fasting to reduce these negative effects was unexpected and deserves further study.
Oftentimes, laboratory conditions standardized for the maintenance of a model species serve as an idealisation of the environmental conditions that natural populations experience. As such, a primary challenge of compiling results of studies from different laboratories and extrapolating those results to wild populations is that laboratory conditions and practices, such as temperature and feeding, are often unique and idealistic. One model species for which this may be the case is the freshwater mollusc, Lymnaea stagnalis (O.F. Linnaeus, 1758), formerly Helix stagnalis Linnaeus, 1758, which is increasingly utilized in neurophysiology and toxicology assessments. This study explores how laboratory conditions and culturing practices may influence L. stagnalis growth, breathing modality, and behaviour; the latter two specifically in response to hypoxia. We cultured L. stagnalis in a full factorial design spanning five food types, two feeding regimens, and two temperature regimens. We observed significant interactions among all culturing conditions tested for each of our endpoints. These interactions were strongest for breathing modality. Our study suggests that assessing bimodal breathing as a hypoxic response may be a rapid way to compare the physiological condition between populations of L. stagnalis. Our findings highlight the importance of considering culturing conditions when utilizing L. stagnalis in research.
