Abstract Animal coloration has diverse functions such as camouflage, communication, thermoregulation, protection from UV damage and more, and can be shaped by environmental selective pressures. Some climatic selective pressures are strong enough to produce consistent patterns in many species across large-scale geographic gradients, leading to the creation of macrophysiological rules such as Gloger’s rule, which predicts that endothermic populations in hot, humid areas will be visibly darker than those in cool, dry areas, and the thermal melanism hypothesis, which predicts that ectothermic animals will be visibly darker in cooler areas. While these rules often capture trends in animal absorptance in the visible spectrum, wavelengths of visible light are not the only relevant wavelengths to an animal’s energy budget: solar radiation extends beyond the visible spectrum [0.4–0.7 μm] into the near-infrared; thus, thermal pressures may result in changes in surface reflectance characteristics beyond the visible [e.g., 0.7–2.5 μm] in birds. Further, heat exchange with the environment extends into the mid-infrared (MIR), including heat loss through the atmospheric transparency window [8–14 μm]. It is unknown whether animal absorptance in the NIR or emittance in MIR might also follow macrophysiological rules, as seen in the visible spectrum, such as more absorptance of NIR and less emittance of MIR in cooler areas for ectotherms under the thermal melanism hypothesis. Here, we examine both UV-NIR absorptance and MIR emittance in five species of birds: the Great Horned Owl, Northern Bobwhite, Steller’s Jay, Song Sparrow, and Common Raven. We show that NIR absorptance varies by species and population, corresponding to their habitat and thermoregulatory strategies. MIR emittance, by contrast, was stable across species and populations but differed slightly across populations of Northern Bobwhites. We conclude by highlighting the importance of considering the full spectrum from UV to MIR in research on animal adaptation. Further consideration of infrared radiation is necessary for a complete view of animals’ phenotypic diversity and possible responses to thermal challenge.

Abstract The helmeted hornbill (Rhinoplax vigil), a critically endangered bird prized for the distinctive helmet-like “casque” capping its beak, faces threats from poaching and habitat loss. This study applies biomaterials/imaging techniques to wildlife forensics, using micro-computed tomography to forensically analyse bullet-induced damage in a unique collection of helmeted hornbill skull specimens, confiscated by the Agriculture, Fisheries and Conservation Department (AFCD) of Hong Kong. The findings reveal diverse healing responses, bullet characteristics and indications of the poaching strategies used. For example, specimen scans—showing various bullets embedded in skull tissue—suggest that poachers may use the conspicuous casque as a target when shooting upward from the ground. Additionally, our observations of casque anatomy exhibit two different types of tissue repair, arguing that several of the individuals lived long after being shot. The study highlights the value of confiscated specimens for understanding life history factors and poaching impacts in rare species, vital for developing tailored conservation strategies and advancing knowledge of the biology of elusive wildlife.

SynopsisCourse-based undergraduate research experiences (CUREs) provide a scalable model for engaging students in authentic scientific inquiry, bridging core biological concepts with real-world environmental applications. We introduce a new CURE lab tailored for introductory biology students at the undergraduate level, utilizing duckweed as a model organism to investigate ecological interactions and environmental management. Our paper presents a curriculum that engages students in hands-on research with a focus on duckweed’s role in ecosystem dynamics, pollutant remediation, and its potential as a bioresource, along with scientific results from student projects that serve as tangible examples of the curriculum’s outcomes. Through experimentation, students explore how duckweed can be applied to address real-world environmental challenges, utilizing advanced laboratory techniques and data analysis tools. Successfully implemented with 192 students across three semesters at our institutions, this CURE lab has produced reliable duckweed growth data with high reproducibility. This curriculum addresses the gap between traditional laboratory exercises and authentic research experiences through introducing opportunities to conduct reproducible experiments, analyze real data, and communicate scientific findings in meaningful contexts.

SynopsisGlucocorticoids facilitate the integration of environmental information and coordination of organismal responses to perturbations. Circulating glucocorticoids are hypothesized to depend on an individual’s environment and condition (i.e., state) to facilitate surviving challenges while minimizing fitness costs. Studies specifically focused on sources of individual variation in circulating glucocorticoids are critical to understanding state-dependent modulation of glucocorticoids and integrated phenotypes more broadly. Such studies can also provide insight into the evolution and adaptive significance of circulating glucocorticoids. Here, we repeatedly sample individuals before and during food restriction to identify how and when food availability and intrinsic differences (i.e., body condition and telomere length), including those of social partners, covary with glucocorticoids in captive Red Crossbills (Loxia curvirostra), a nomadic songbird that specializes on foraging for conifer seeds. Conifer seeds are ephemeral resources produced during unpredictable, but locally synchronous, masting events. Fluctuating food availability and social cues, change the behavior and glucocorticoid physiology of Red Crossbills. Pairs consisting of an adult and juvenile were food restricted using an environmental manipulation known to induce socially mediated changes in glucocorticoid signaling. Baseline and stress-induced glucocorticoids were measured before and during food restriction. Amongst adults, stress-induced glucocorticoids declined following food restriction and positively covaried with telomere length, independent of food availability. These results support the hypothesis that the acute glucocorticoid response is adaptively modulated based on environmental conditions and individual differences in state as measured by telomere length. Under food restriction, juvenile baseline glucocorticoids negatively covaried with body condition and the telomere lengths of adult social partners. The covariation between adult telomere lengths and juvenile baseline glucocorticoids suggests that telomere lengths of adults may relate to adult phenotypes, a hypothesis supported by the covariation between adult telomeres and stress-induced glucocorticoids. Further, as patterns were absent before food restriction, our results demonstrate how environmental challenges can reveal the importance of intrinsic differences to organismal responses and social cues. This study leverages a non-model organism experiencing an ecologically relevant environmental challenge to exemplify how intrinsic differences, including those of social partners, can modulate an endocrine mediator of organismal responses to environmental perturbations.

SynopsisUnderstanding a species’ physiological state is important for advancing animal ecology and conservation. Endocrine responses to reproduction, stress, and nutritional status are commonly assessed through gonadal, adrenal, and thyroid hormones, respectively. Using nonconventional samples for endocrinological evaluation is an increasingly utilized method but remains uncommon for snakes. In this study, we assessed whether feces, urine, or shed skin from two Neotropical pit vipers (Bothrops jararaca and B. jararacussu) contain detectable testosterone (T), progesterone (P4), 17β-estradiol (E2), corticosterone (CORT), and triiodothyronine (T3) using enzyme immunoassay (EIA). We collected samples from 23 individuals, 10 B. jararaca and 13 B. jararacussu, and assessed detectability of hormones and/or immunoreactive hormone metabolites (IHM). We used tests of parallelism and accuracy to validate assays. Triiodothyronine was not detected in urine of either species; all other hormones were detected in all matrices. Testosterone and T3 showed good parallelism for all matrices tested. Parallelism tests for E2 (urine, both species), CORT (urine, B. jararaca, and shed skin, B. jararacussu), and P4 (urine, B. jararaca) showed marginally acceptable results. All accuracy validations were successful, except for T3 in shed skin extract (B. jararacussu) and P4 in urine extract (B. jararaca). This study demonstrates the applicability of nonconventional samples for hormone and IHM detection and quantification, offering valuable tools to monitor the endocrinological status of both free-ranging and confined snakes.

SynopsisUnderstanding physiological responses to short-term changes in temperature is of growing interest considering the rising frequency and severity of transient temperatures such as heat waves. During the embryonic development of egg-laying vertebrates, inducible physiological responses to transient heat are likely critical to short-term survival but may also be energetically costly or disruptive to development. Inducible heat-shock proteins (HSPs) are conserved molecular chaperones which act to safeguard cellular protein homeostasis during transient stress. However, experiments in ectotherms have shown that overexpression of HSPs can increase embryonic mortality and reduce later thermotolerance. Yet, few studies have explored natural developmental patterns of HSP expression and heat inducibility in embryos of egg-laying ectothermic vertebrates. Using the red-eared slider turtle (Trachemys scripta), we characterized the response of five HSP genes in embryonic trunks following repeated 3-d transient heat wave exposures. Interestingly, we found that the expression of most HSPs naturally declined during early development and that warm temperatures amplified this decline, while also accelerating developmental rate. Only in a few instances did we observe induction of certain HSP genes during heat wave exposures, though this depended on the thermal history of the embryo. Specifically, induction of these genes during a particular heat wave was reduced in embryos that had already experienced two recent prior exposures relative to those experiencing it for the first or second time, suggesting repeated heat exposures can attenuate subsequent responses. The observed changes in HSP expression and inducibility may relate to an individual’s need to balance thermotolerance alongside extensive cellular differentiation and proliferation during early development. The effects of incubation temperature on these changes could also have important implications for how turtle embryos deal with subsequent heat stress and may be similarly present in other ectothermic vertebrates. Our study demonstrates the importance of considering ontogenetic changes in physiological responses to temperature even across embryonic development.

SynopsisThe evolutionary origins of the avian air sac pulmonary system are enigmatic due to the rarity of soft-tissue preservation in fossils. Here, we test whether fine anchoring fibers on the endosteal bone of bird and non-avian dinosaur vertebrae—termed “pneumosteum”—are absent in taxa lacking pneumatic openings. We studied thin sections from the caudalmost cervical and cranial dorsal vertebrae of 21 extant amniotes to infer the presence or absence of invading diverticula through vertebral foramina. We also provide a differential diagnosis of the structural features of pneumosteum. We found that the secondarily aquatic Western grebe (Aechmophorus occidentalis) and Magellanic penguin (Spheniscus magellanicus) lack external pneumaticity and pneumosteum. In addition, the small passerine bird examined (Estrildidae spp.) exhibits invading diverticula but no pneumosteum. This suggests that ventilatory air sacs and associated diverticula can be present despite the absence of osteological and histologic correlates and that these features are lost when transitioning to an aquatic lifestyle or in small-bodied birds. In volant pneumatized birds, diverticula and pneumosteum are associated with pneumatic foramina. This suggests that, in fossil birds, pneumatic foramina are good indicators of the presence of pulmonary diverticula. Furthermore, the loss of invading respiratory diverticula and pneumatic osteological characters in the postcranial skeleton of pursuit diving birds serves as a reminder that adaptation to specific ecologies, such as an aquatic environment, may obscure our ability to reconstruct soft tissue systems accurately in fossil taxa when relying on osteological correlates.

SynopsisSpecies of filter-feeding invertebrates are exposed to natural oil droplets or petroleum oil droplets in water, and many species feed on these droplets. Here, we investigate oil droplet capture by benthic tunicates. We used videography, dissections, and tetramethylrhodamine isothiocyanate (TRITC) fluorescence microscopy to study the capture of oil droplets by 10 different species of tunicate. Eight of nine species fed on waste motor oil demonstrating that it is a general phenomenon. The exception was Clavelina huntsmani. Corella willmeriana fed on light crude oil based on evidence of droplets in the branchial basket, gut, and feces. These results demonstrate that tunicates can provide an entry for oils into marine food webs. A further experiment found that Styela gibbsii fed on emulsions of fish, canola, marine 10W-30, semi-synthetic 2-cycle, and waste 5W-20 oil in filtered seawater and unfiltered seawater. It showed no selectivity despite differences in chemistry, density, viscosity, and interfacial tensions. Finally, the size distribution of oil droplets captured by S. gibbsii and Ciona intestinalis were compared to the feeding trial emulsions and found to be significantly narrower, and on the smaller end of the range. This study provides some general insights into oil droplet capture by tunicates, the mechanics of droplet capture, the absence of selection based on the type of oil, and oil droplet size capture. Tunicates are some of the most ubiquitous and abundant animals in the world’s oceans and the pelagic species significantly alter global carbon cycles. Here, we show that benthic species, common on docks and wharves, ingest natural occurring and engine oils, offering a new puzzle piece in our knowledge on the bioaccumulation and trophic transfer of oils in marine food networks.

SynopsisA general tenet in stress physiology is that the hypothalamic-pituitary-adrenal axis predominantly produces one glucocorticoid (GC) in response to stressors. However, most vertebrates produce both cortisol and corticosterone, these steroids show variation across species in absolute levels, relative proportions, and stress responsivity, and they regulate much more than just stress physiology. In the present commentary, we argue that focusing on a single GC may not capture the whole story, presenting an overview of previous studies and an example from our own work on poisons frogs—a group relatively new to endocrinological studies. We originally set out to validate non-invasive waterborne hormone measurements in our focal species, the dyeing poison frog Dendrobates tinctorius. In pursuing this goal, we uncovered unexpected patterns of GC abundance within and across species. Dendrobates tinctorius had higher amounts of corticosterone than cortisol in both plasma and waterborne samples, and corticosterone was responsive to adrenocorticotropic hormone as canonically assumed. However, corticosterone and cortisol levels were surprisingly similar in D. tinctorius, and cortisol was more abundant than corticosterone in water samples from four additional poison frog species. Alongside those of other studies, these results challenge the broadly accepted assumption that corticosterone is always more abundant in amphibians and add to the growing literature highlighting the importance of measuring both GCs to understand (stress) physiology.

SynopsisThe taxonomic composition of the suborder Tylopoda is an ongoing debate. Recently, the internal otic region (petrosal and bony labyrinth) has been intensively studied as a source of additional morphological data, but the morphology of this region in extinct tylopods is not well documented. To remedy this, we used µCT scanning to image and describe the petrosal and bony labyrinth of two oromerycids (Protylopus, Eotylopus), four early camelids (Poebrotherium wilsoni, Poebrotherium eximium, Paratylopus primaevus, Stevenscamelus franki), and the living vicuña (Vicugna vicugna). Several early camelid specimens also preserved the ear ossicles (malleus, incus, stapes), enabling us to describe their morphology for the first time. Our sample allows us to not only compare among taxa, but to also examine variation within taxa and during ontogeny. We found that the morphology of the petrosal is far more variable than that of the bony labyrinth, both within and across taxa. There is no notable ontogenetic variation between the juveniles and adults in our sample. Protylopus has an unusual petrosal morphology, and its bony labyrinth is somewhat reminiscent of early dichobunoid artiodactyls. Conversely, Eotylopus has a transitional morphology that seemingly links it to camelids. Poebrotherium wilsoni and Po. eximium do not noticeably differ in their morphology, but there are identifiable differences in Pa. primaevus and S. franki, suggesting that the petrosal of camelids is diagnostic at a genus level. The early camelids were distinct from the vicuña in petrosal, bony labyrinth, and ossicular chain morphology, highlighting the importance of examining basally branching members to resolve evolutionary relationships.