Integrative and Comparative Biology最新文献

Stress exerts negative effects on fish health through stimulation of the hypothalamic-pituitary-interrenal axis and autonomic nervous system, resulting in heightened neural and neuroendocrine responses. Energetic investment and physiological adaptation are then required to re-establish homeostatic stability or reach a new allostatic state. The cost of the energetic investment is referred to as allostatic load (AL). While determining the sources of stress and assessing their consequences have resulted in estimates of AL, most of this work has been conducted in adult mammals and humans; no ALs exist for developing fish. From a series of experiments on a model species, zebrafish (Danio rerio), whose yolk-sac larvae were exposed to two chronic stressors (high-temperature and hypoxia), ALs were quantified based on biomarkers of ontogenetic changes in growth, morphometrics, and metabolic activities. Results showed that for zebrafish yolk-sac larvae, chronic stress imposed high AL and, thus, high total allostatic energetic costs, (Rt (AL)), because of prolonged energy demand in the face of limited resources (e.g., yolk). Under severe chronic stress, energetic costs were sufficiently large that energy-limited developing fish may not be able to fully compensate, resulting in maladaptive responses from allostatic overload, leading either to death or to novel allostatic states, possibly more resilient to environmental change.

Many plant species are known to take up metals from the soil and accumulate them to potentially toxic levels. This may provide tolerance to soils with high metal content or a defensive mechanism against herbivores and pathogens. Accumulators, plants that uptake and store elevated concentrations of metals, can be used in phytoremediation as a means to remove metals from contaminated soils. In this study, the native weed Conyza canadensis was grown in soils contaminated with elevated levels of lead (Pb), barium (Ba), zinc (Zn), copper (Cu), or chromium (Cr). All metals, except for Cr, were accumulated by the plants. Zinc and Cu, both essential elements, accumulated to the highest levels, while Pb and Ba were present at lower levels. All treatments except Cr showed accelerating rates of accumulation over the eight-week experiment. Barium, Cu, and Cr reduced aboveground biomass of the plants, indicating toxicity or a cost to metal accumulation. Lead and Zn promoted early flowering, while plants accumulating Ba, Cr, and Cu flowered in lower numbers. Overall, C. canadensis has promise in the phytoremediation of Pb, Cu, and Zn.

Musculoskeletal simulations can provide insights into the underlying mechanisms that govern animal locomotion. In this study, we describe the development of a new musculoskeletal model of the horse, and to our knowledge present the first fully muscle-driven, predictive simulations of equine locomotion. Our goal was to simulate a model that captures only the gross musculoskeletal structure of a horse, without specialized morphological features. We mostly present simulations acquired using feedforward control, without state feedback ("top-down control"). Without using kinematics or motion capture data as an input, we have simulated a variety of gaits that are commonly used by horses (walk, pace, trot, tölt, and collected gallop). We also found a selection of gaits that are not normally seen in horses (half bound, extended gallop, ambling). Due to the clinical relevance of the trot, we performed a tracking simulation that included empirical joint angle deviations in the cost function. To further demonstrate the flexibility of our model, we also present a simulation acquired using spinal feedback control, where muscle control signals are wholly determined by gait kinematics. Despite simplifications to the musculature, simulated footfalls and ground reaction forces followed empirical patterns. In the tracking simulation, kinematics improved with respect to the fully predictive simulations, and muscle activations showed a reasonable correspondence to electromyographic signals, although we did not predict any anticipatory firing of muscles. When sequentially increasing the target speed, our simulations spontaneously predicted walk-to-run transitions at the empirically determined speed. However, predicted stride lengths were too short over nearly the entire speed range unless explicitly prescribed in the controller, and we also did not recover spontaneous transitions to asymmetric gaits such as galloping. Taken together, our model performed adequately when simulating individual gaits, but our simulation workflow was not able to capture all aspects of gait selection. We point out certain aspects of our workflow that may have caused this, including anatomical simplifications and the use of massless Hill-type actuators. Our model is an extensible, generalized horse model, with considerable scope for adding anatomical complexity. This project is intended as a starting point for continual development of the model and code that we make available in extensible open-source formats.

The air-water interface of the planet's water bodies, such as ponds, lakes, and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia americana move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on M. americana's ability to walk on water. Removal of both hind tarsi causes M. americana to rock their bodies (yaw) while running across the water surface at $pm 19^{circ }$, compared to $pm 7^{circ }$ in nonablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that M. americana use their hind legs as "rudders" to regulate yaw, originating from the contralateral middle legs' strokes on the water's surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making M. americana turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, M. americana lose their ability to use the alternating tripod gait to walk on water on the day of contralateral ablation. Remarkably, by the next day, M. americana adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of M. americana, and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.

Functional novelties play important roles in creating new ways for organisms to access resources. In fishes, jaw protrusion has been attributed to the massive diversity of suction-based feeding systems, facilitating the dominant mode of prey capture in this group. Nearly all fishes that feed by suction use upper jaw protrusion, achieved by rotation of the mandible at its base, which then transmits forward motion to independently mobile upper jaw bones. In this study, by contrast, we explore an unusual form of lower jaw protrusion in the freshwater invertivore, Nannocharax fasciatus, enabled by a novel intramandibular joint (IMJ). We combine morphological, kinematic, and biomechanical data to show that the added mobility created by the IMJ influences the pattern of suction-based prey capture movements and contributes to lower jaw protrusion (increasing it by 25%, based on biomechanical modeling). Interestingly, the upper jaw bones are fused in N. fasciatus and rotate about a single fixed joint, like the lower jaws of most other suction feeding fishes. We suggest that this vertical inversion of the jaw protrusion mechanism for ventrally directed suction-feeding on benthic prey is a likely exaptation, as the IMJ is used for biting in related taxa. This work highlights the ability of novelties to facilitate ecological specialization by enabling new functional capabilities.

Intraspecific variation can be as great as variation across species, but the role of intraspecific variation in driving local and large-scale patterns is often overlooked, particularly in the field of thermal biology. In amphibians, which depend on environmental conditions and behavior to regulate body temperature, recognizing intraspecific thermal trait variation is essential to comprehensively understanding how global change impacts populations. Here, we examine the drivers of micro- and macrogeographical intraspecific thermal trait variation in amphibians. At the local scale, intraspecific variation can arise via changes in ontogeny, body size, and between the sexes, and developmental plasticity, acclimation, and maternal effects may modulate predictions of amphibian performance under future climate scenarios. At the macrogeographic scale, local adaptation in thermal traits may occur along latitudinal and elevational gradients, with seasonality and range-edge dynamics likely playing important roles in patterns that may impact future persistence. We also discuss the importance of considering disease as a factor affecting intraspecific variation in thermal traits and population resilience to climate change, given the impact of pathogens on thermal preferences and critical thermal limits of hosts. Finally, we make recommendations for future work in this area. Ultimately, our goal is to demonstrate why it is important for researchers to consider intraspecific variation to determine the resilience of amphibians to global change.

Antimicrobial peptides (AMPs) play a fundamental role in the innate defense against microbial pathogens, as well as other immune and non-immune functions. Their role in amphibian skin defense against the pathogenic fungus Batrachochytrium dendrobatidis (Bd) is exemplified by experiments in which depletion of host's stored AMPs increases mortality from infection. Yet, the question remains whether there are generalizable patterns of negative or positive correlations between stored AMP defenses and the probability of infection or infection intensity across populations and species. This study aims to expand on prior field studies of AMP quantities and compositions by correlating stored defenses with an estimated risk of Bd exposure (prevalence and mean infection intensity in each survey) in five locations across the United States and a total of three species. In all locations, known AMPs correlated with the ability of recovered secretions to inhibit Bd in vitro. We found that stored AMP defenses were generally unrelated to Bd infection except in one location where the relative intensity of known AMPs was lower in secretions from infected frogs. In all other locations, known AMP relative intensities were higher in infected frogs. Stored peptide quantity was either positively or negatively correlated with Bd exposure risk. Thus, future experiments coupled with organismal modeling can elucidate whether Bd infection affects secretion/synthesis and will provide insight into how to interpret amphibian ecoimmunology studies of AMPs. We also demonstrate that future AMP isolating and sequencing studies can focus efforts by correlating mass spectrometry peaks to inhibitory capacity using linear decomposition modeling.

Foundational habitats such as seagrasses and coral reefs are at severe risk globally from climate warming. Infectious disease associated with warming events is both a cause of decline and an indicator of stress in both habitats. Since new approaches are needed to detect refugia and design climate-smart networks of marine protected areas, we test the hypothesis that the health of eelgrass (Zostera marina) in temperate ecosystems can serve as a proxy indicative of higher resilience and help pinpoint refugia. Eelgrass meadows worldwide are at risk from environmental stressors, including climate warming and disease. Disease outbreaks of Labyrinthula zosterae are associated with recent, widespread declines in eelgrass meadows throughout the San Juan Islands, Washington, USA. Machine language learning, drone surveys, and molecular diagnostics reveal climate impacts on seagrass wasting disease prevalence (proportion of infected individuals) and severity (proportion of infected leaf area) from San Diego, California, to Alaska. Given that warmer temperatures favor many pathogens such as L. zosterae, we hypothesize that absent or low disease severity in meadows could indicate eelgrass resilience to climate and pathogenic stressors. Regional surveys showed the San Juan Islands as a hotspot for both high disease prevalence and severity, and surveys throughout the Northeast Pacific indicated higher prevalence and severity in intertidal, rather than subtidal, meadows. Further, among sites with eelgrass declines, losses were more pronounced at sites with shallower eelgrass meadows. We suggest that deeper meadows with the lowest disease severity will be refuges from future warming and pathogenic stressors in the Northeast Pacific. Disease monitoring may be a useful conservation approach for marine foundation species, as low or absent disease severity can pinpoint resilient refugia that should be prioritized for future conservation efforts. Even in declining or at-risk habitats, disease surveys can help identify meadows that may contain especially resilient individuals for future restoration efforts. Our approach of using disease as a pulse point for eelgrass resilience to multiple stressors could be applied to other habitats such as coral reefs to inform conservation and management decisions.

Science is becoming increasingly interdisciplinary; the widespread emergence of dedicated interdisciplinary journals, conferences, and graduate programs reflects this trend. Interdisciplinary scientific events are extremely valuable in that they offer opportunities for career advancement, especially among early career researchers, for collaboration beyond traditional disciplinary echo chambers, and for the creative generation of innovative solutions to longstanding scientific problems. However, organizing such events can pose unique challenges due to the intentionality required to meaningfully break down the barriers that separate long-independent disciplines. In this paper, we propose five key strategies for organizing and hosting interdisciplinary scientific events. The recommendations offered here apply both to small symposia aiming to contribute an interdisciplinary component to a larger event and to broad interdisciplinary conferences hosting hundreds or thousands of attendees.

Marine organisms have complex life histories. For broadcast spawners, successful continuation of the population requires their small gametes to make contact in the water column for sufficiently long periods for fertilization to occur. Anthropogenic climate change has been shown to impact fertilization success in various marine invertebrates, including sea urchins, which are key grazers in their habitats. Gamete performance of both sexes declined when exposed to elevated temperatures and/or pCO2 levels. Examples of reduced performance included slower sperm swimming speed and thinning egg jelly coat. However, such responses to climate change stress were not uniform between individuals. Such variations could serve as the basis for selection. Fertilization kinetics have long been modeled as a particle collision process. Here, we present a modified fertilization kinetics model that incorporates individual variations in performance in a more environmentally relevant regime, and which the performance of groups with different traits can be separately tracked in a mixture. Numerical simulations highlight that fertilization outcomes are influenced by changes in gamete traits as they age in sea water and the presence of competition groups (multiple dams or sires). These results highlight the importance of considering multiple individuals and at multiple time points during in vivo assays. We also applied our model to show that interspecific variation in climate stress vulnerabilities elevates the risk of hybridization. By making a numerical model open-source, we aim to help us better understand the fate of organisms in the face of climate change by enabling the community to consider the mean and variance of the response to capture adaptive potential.