In recent years, record heat events have been shown to impose thermal barriers on the migration of temperate salmonids, often resulting in mass mortality events. High water temperatures are also known to limit the survival of juvenile salmonids, impeding conservation efforts during freshwater life stages. This temperature-induced mortality is thought to be caused, in part, by a collapse in cardiac scope. Previous studies in salmon have demonstrated that cardiorespiratory thresholds for thermal performance are locally adapted to historic river temperatures. Local adaptations in heart morphology and function have also been observed, such that fish from populations with more aerobically demanding migrations display higher peak heart rates, larger ventricles, and improved coronary blood supply. However, as climate warming threatens to outpace adaptation, it is important to understand how the cardiorespiratory system of fishes can respond to heightened demands over developmental time. Here, we assessed cardiorespiratory thresholds for thermal performance in juvenile Atlantic salmon reared in present day (+0°C) or projected future temperature conditions (+4°C). At the parr stage, maximum heart rate was measured in response to acute warming. Fish reared in the +4°C treatment displayed a 4.5°C increase in the Arrhenius breakpoint temperature (TAB) for maximum heart rate (where cardiac scope is maximized), and a 2.5°C increase in the temperature at which heat-induced cardiac arrythmias occurred (TArr). However, we observed no difference in mean peak heart rate between developmental treatments. To investigate potential morphological differences underlying the observed plasticity in thermal performance, we performed histological analysis of the heart. While relative ventricle size did not differ between treatments, the proportion of compact myocardium in the ventricular wall was significantly greater in fish raised in the +4°C treatment. Given that the compact myocardium is the portion of the ventricle which receives a coronary blood supply, this could represent a compensatory response to oxygen limitation within the heart, preventing a collapse in cardiac scope at high temperatures. This research contributes to our understanding of how thermal conditions experienced during development can affect performance later in life and identifies a morphological strategy which may allow fishes to cope with increased water temperatures, as climate change increases the frequency of record heat events.

Thirteen-lined ground squirrels (TLGS, Ictidomys tridecemlineatus) hibernate during winter months. Hibernation consists of two distinct steady states: torpor (low metabolic rate (MR)) and interbout euthermia (IBE, high MR), with transition states of entrance and arousal between. Previous findings in the lab suggest that changes to the electron transport system (ETS) contribute to suppressing metabolism during hibernation. Each ETS complex consists of 4-45 individual protein subunits. These complexes can also combine to form different supercomplexes (SCs) within the inner mitochondrial membrane (IMM). SCs are thought to improve ETS efficiency by limiting diffusion of intermediates and decrease the escape of electrons which may form reactive oxygen species (ROS). I hypothesize that SCs decrease with mitochondrial metabolic suppression. My research question is as follows: If the abundance of SCs increases to fulfill a higher metabolic demand2, do SCs decrease to facilitate metabolic suppression seen during hibernation? We isolated mitochondria from liver, brown adipose tissue, and heart of hibernating and torpid TLGS, and performed high-resolution respirometry. State 3 (phosphorylating) respiration is significantly lower in torpor compared to IBE in all tissues. I then separated mitochondrial proteins by molecular mass using blue-native gels following solubilization with a gentle detergent. This allowed me to quantify SC abundance by staining intensity. I then cut each lane from the native gel and further separated proteins using SDS gels. This will separate SC bands into subunit components of the ETS complexes which I identified using western blotting. Preliminary results from brown adipose tissue demonstrate higher abundance of CIII in a CI/CIII2/CIV SC during IBE but higher abundance in a CIII2/CIV1-2 SC in torpor. These findings suggest a dynamic transition of the location of CIII within the ETS during the transition from torpor to IBE, perhaps contributing to changes in mitochondrial respiration and ROS production among phases of torpor bouts.

Vibrations are crucial for a spider to obtain information about its surroundings. Information such as prey location in a web, presence of predators and mate communication are transmitted through the web as vibrations. As vibrations transmit from the web into the legs towards the abdomen, they are sensed mainly at the leg joints in spiders by mechanosensory organs called lyriform organs. Interestingly, spiders come in a range of weights, sizes and leg morphologies, all traits that are expected to affect the mechanics of vibration transmission, and hence perception. Yet, the theoretical framework to predict exactly how morphology impacts vibration transmission is largely based on inexact verbal models and intuitions. One method to generate a more exact framework is by creating physics-based models of different morphologies. This study aims to investigate such biomechanical models where we mainly consider spiders with varying leg lengths to analyze how leg length influences vibration transmission to the lyriform organs. Three species were selected in order of decreasing leg length: Pholcus phalangioides, Latrodectus hesperus and Araneus diadematus. Our intuitive expectation was that longer legs would accommodate more vibrational patterns (modes) than shorter legs, and we used quantitative biomechanical models to test this expectation. In fact, detailed biomechanical models predicted the opposite; all else being equal, longer legs did not actually accommodate more modal shapes. However, leg length has subtler effects on vibration transmission, affecting joint tuning and altering the optimal position for the placement of a vibration sensor. Thus, our biomechanical models suggest that morphology has the potential to subtly affect how a spider senses the world, emphasizing the link between brain and body as posited by the idea that perception, and more generally cognition is deeply ‘embodied’.