Integrative and Comparative Biology最新文献

Dimensionless numbers have long been used in comparative biomechanics to quantify competing scaling relationships and connect morphology to animal performance. While common in aerodynamics, few relate the biomechanics of the organism to the forces produced on the environment during flight. We discuss the Weis-Fogh number, N, as a dimensionless number specific to flapping flight, which describes the resonant properties of an insect and resulting tradeoffs between energetics and control. Originally defined by Torkel Weis-Fogh in his seminal 1973 paper, N measures the ratio of peak inertial to aerodynamic torque generated by an insect over a wingbeat. In this perspectives piece, we define N for comparative biologists and describe its interpretations as a ratio of torques and as the width of an insect's resonance curve. We then discuss the range of N realized by insects and explain the fundamental tradeoffs between an insect's aerodynamic efficiency, stability, and responsiveness that arise as a consequence of variation in N, both across and within species. N is therefore an especially useful quantity for comparative approaches to the role of mechanics and aerodynamics in insect flight.

The mussel Mytilus californianus is an ecosystem engineer forming beds along the coastlines of Northeastern Pacific shores. As sessile organisms, they modulate their energy balance through valve movements, feeding, and digestive functionality. A recent study observed that activity of the digestive enzyme cellulase was higher than predicted in mussels high on the shore, where temperatures are characteristically high and food availability is limited compared to low-shore habitats. In the current study, we predicted that this scavenging behavior is induced to mitigate energy losses related to heat-shock responses-that cellulase and amylase will display hyperactivity for limited recourses in the face of aerial heating. In the laboratory, we acclimated mussels to three complex diets that differed in starch and cellulose composition, followed by two acute heat shocks (+8°C) in the laboratory. Results showed no hyperactivity of amylase and cellulase in heated mussels. These results differ from previous studies that showed lowered amylase activity following heat acclimation. This difference in amylase activity across heat-stress exposure time is important when analyzing mussel bed disturbances following heat waves that compromise energy balance or cause death within adult populations.

Peak metabolic rate reflects maximal performance and may have direct fitness consequences, whereas resting metabolic rate (RMR) represents the maintenance cost of the whole animal. These traits may be linked, which has significant implications for the evolution of both traits. In vertebrates, a positive correlation between RMR and aerobic capacity has been proposed to explain the origin of endothermy. However, as studies on the relationship between RMR and aerobic capacity have focused on vertebrates, we know much less about these traits in ectothermic insects. I measured RMR in the Glanville fritillary butterfly (Melitaea cinxia) using two configurations: one optimized for measuring flight metabolic rate and the other optimized for RMR. The relationship between RMR and body mass was similar for the two configurations. Body mass explained 82% of the variation in RMR when it was measured using the "flight" configuration at 32°C, and 91% when using the "rest" configuration at 23°C. The Q10 coefficient calculated based on the two RMR measurements was 2.8. Mass-independent RMR was positively correlated between measurements obtained using the two instrument configurations. However, neither measure of RMR was correlated with peak metabolic rate, which indicates that RMR cannot be used as a surrogate measure for aerobic capacity in the Glanville fritillary. Ectothermic insects may be able to combine high metabolic capacity with no apparent increase in maintenance cost. Even though RMR is among the most frequently measured physiological variables, it may have limited predictive power when it comes to questions related to activity or aerobic capacity, or in the case of butterflies, flight performance.

Climate change will increase the frequency and intensity of extreme climatic events (e.g., storms) that result in repeated pulses of hyposalinity in nearshore ecosystems. Sea urchins inhabit these ecosystems and are stenohaline (restricted to salinity levels ∼32‰), thus are particularly susceptible to hyposalinity events. As key benthic omnivores, sea urchins use hydrostatic adhesive tube feet for numerous functions, including attachment to and locomotion on the substratum as they graze for food. Hyposalinity severely impacts sea urchin locomotor and adhesive performance but several ecologically relevant and climate change-related questions remain. First, do sea urchin locomotion and adhesion acclimate to repeated pulses of hyposalinity? Second, how do tube feet respond to tensile forces during single and repeated hyposalinity events? Third, do the negative effects of hyposalinity exposure persist following a return to normal salinity levels? To answer these questions, we repeatedly exposed green sea urchins (Strongylocentrotus droebachiensis) to pulses of three different salinities (control: 32‰, moderate hyposalinity: 22‰, severe hyposalinity: 16‰) over the course of two months and measured locomotor performance, adhesive performance, and tube foot tensile behavior. We also measured these parameters 20 h after sea urchins returned to normal salinity levels. We found no evidence that tube feet performance and properties acclimate to repeated pulses of hyposalinity, at least over the timescale examined in this study. In contrast, hyposalinity has severe consequences on locomotion, adhesion, and tube foot tensile behavior, and these impacts are not limited to the hyposalinity exposure. Our results suggest both moderate and severe hyposalinity events have the potential to increase sea urchin dislodgment and reduce movement, which may impact sea urchin distribution and their role in marine communities.

Climate change will disrupt biological processes at every scale. Ecosystem functions and services vital to ecological resilience are set to shift, with consequences for how we manage land, natural resources, and food systems. Increasing temperatures cause morphological shifts, with concomitant implications for biomechanical performance metrics crucial to trophic interactions. Biomechanical performance, such as maximum bite force or running speed, determines the breadth of resources accessible to consumers, the outcome of interspecific interactions, and thus the structure of ecological networks. Climate change-induced impacts to ecosystem services and resilience are therefore on the horizon, mediated by disruptions of biomechanical performance and, consequently, trophic interactions across whole ecosystems. Here, we argue that there is an urgent need to investigate the complex interactions between climate change, biomechanical traits, and foraging ecology to help predict changes to ecological networks and ecosystem functioning. We discuss how these seemingly disparate disciplines can be connected through network science. Using an ant-plant network as an example, we illustrate how different data types could be integrated to investigate the interaction between warming, bite force, and trophic interactions, and discuss what such an integration will achieve. It is our hope that this integrative framework will help to identify a viable means to elucidate previously intractable impacts of climate change, with effective predictive potential to guide management and mitigation.

To smell, fish rely on passive water flow into their olfactory chambers and through their olfactory rosettes to detect chemical signals in their aquatic environment. The olfactory rosette is made up of secondarily folded tissues called olfactory lamellae. The olfactory morphology of cartilaginous fishes varies widely in both rosette gross morphology and lamellar microstructure. Previous research has shown differences in lamellar sensory morphology depending on the position along the rosette in hammerheads (family Sphyrnidae). Here, we investigate if this pattern continues in members of two other chondrichthyan families: Squalidae and Chimaeridae. Using contrast-enhanced microCT and scanning electron microscopy, we investigated patterns in lamellar morphology based on lamellar position along the olfactory rosette in Pacific spiny dogfish (Squalus suckleyi) and spotted ratfish (Hydrolagus colliei). We describe the gross olfactory rosette anatomy and lamellar microstructure of both species. We also put forth a new method, combining 3D morphological microCT data with 2D SEM microstructure data to better approximate lamellar sensory surface area. We found that in both species, lamellae in the center of the rosette were larger with more secondary folds. However, we found no significant differences in lamellar sensory surface area among lamellar positions. Previously, differences in lamellar sensory morphology have been tied to the internal fluid dynamics of the olfactory chamber. It is possible that the internal flow dynamics of these species are like other chondrichthyan models, where water flow patterns differ in the lateral vs the medial part of the organ, and the consistent distribution of sensory tissue does not correspond to this flow. Alternatively, the olfactory morphology of these species may result in uniform flow patterns throughout the olfactory chamber, correlating with the consistent distribution of sensory tissue throughout the organ. This study emphasizes that further investigations into chondrichthyan fluid dynamics is paramount to any future studies on the correlations between distribution of sensory tissues and water flow.

Pandalid shrimp use morphological and behavioral defenses against their numerous fish and invertebrate predators. Their rapid tail-flip escape and rigid exoskeleton armor may be sensitive to changes in ocean temperature and carbon chemistry in ways that alter their efficacy and impact mortality. Here we tested the hypothesis that ocean warming and acidification conditions affect the antipredator defenses of Pandalus gurneyi. To test this hypothesis, we exposed shrimp to a combination of pH (8.0, 7.7, 7.5) and temperature (13°C, 17°C) treatments and assessed their tail-flip escape and exoskeleton armor after short-term (2 weeks) and medium-term (3 months) exposure. Results revealed complex effects on escape kinematics, with changes in different variables explained by either pH, temperature, and/or their interaction; decreased pH, for instance, primarily explains reduced acceleration while cold temperature explains increased flexion duration. Carapace mineral content (Ca and Mg) was unaffected, but warmer temperatures primarily drove enhanced mechanical properties (increased hardness and stiffness). No effects were observed in the stiffness and strength of the rostrum. Furthermore, most of the observed effects were temporary, as they occurred after short-term exposure (2 weeks), but disappeared after longer exposure (3 months). This demonstrates that P. gurneyi defenses are affected by short-term exposure to temperature and pH variations; however, they can acclimate to these conditions over time. Nonetheless, changes in the tail-flip escape kinematics may be disadvantageous when trying to flee predators and the enhanced exoskeleton armor could make them more resistant to predation during short periods of environmental change.

Flight muscle histolysis is a widespread strategy used by insects to break down functional flight muscle and modulate the energetic costs associated with flight muscle use and maintenance. The variable field cricket, Gryllus lineaticeps, undergoes histolysis during their transition between dispersal flight and reproduction. Despite the importance of histolysis on insect reproduction and fitness, the molecular mechanisms driving this flight muscle breakdown are not well understood. Here, we show that beclin-mediated autophagy, a conserved lysosomal-dependent degradation process, drives breakdown of dorsal longitudinal flight muscle in female flight-capable G. lineaticeps. We found that female G. lineaticeps activate autophagy in their dorsal longitudinal flight muscle (DLM), but to a greater extent than the neighboring dorsoventral flight muscle (DVM) during histolysis. RNA interference knockdown of beclin, a gene that encodes a critical autophagy initiation protein, delayed DLM histolysis, but did not affect DVM histolysis. This suggests that crickets selectively activate autophagy to break down the DLMs, while maintaining DVM function for other fitness-relevant activities such as walking. Overall, we confirmed that autophagy is a critical pathway used to remodel flight muscle cells during flight muscle histolysis, providing novel insights into the mechanisms underlying a major life history transition between dispersal and reproduction.