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    AES Physiology II & AES Genetics & AES Biogeography

    2021-07-23   13:45 - 15:45

    Moderator: Andrew Fields

    1.  13:45  IN-PERSON    High resolution acoustic telemetry reveals swim speeds and inferred field metabolic rates in juvenile white sharks (Carcharodon carcharias). James Anderson*, California State University; Christopher Lowe, California State University

    White sharks (Carcharodon carcharias) are the largest shark species to display regionalendothermy. This capability facilitates exploitation of resources beyond thermaltolerance thresholds of potential sympatriccompetitors as well as sustained elevatedswim speeds, but comes atthe cost of increased metabolic requirements, which hasbeen documented in different studies. However, little is known of the metabolicrequirements in free-swimming juveniles ofthe species. We derived swim speeds fromspeed-over-ground calculations, and associated mass-specific oxygen consumptionrates as a proxy for field metabolic rates, from high resolution VPS positioning data foreighteen individual juvenilewhite sharks. Our resultingestimates of mass-specificroutine metabolic rates (361.79 ± 39.19 mg O2kg?1h?1[mean ± s.d]) scaled negativelywith body size, and approach those of similar sized non-endotherm shark species. Thus, median cruising speeds (0.60m s-1[mean ± S.E = 0.59 ±0.001]) are likely afeature of behavioral strategies designed to optimize bioenergetic efficiency, whichmore closely resemble those exhibited inectotherm sharks than mature conspecifics.

    2.  14:00  IN-PERSON    Sex-related metabolic outcomes in wild stingrays with differential exposure to polychlorinated biphenyl exposure from southern California. Kady Lyons*, Georgia Aquarium; Katherine Wynne-Edwards, University of Calgary

    Organisms have constrained energy budgets and any additional cost, such as that added by contaminant exposure, represents energy taken away from growth or reproduction. Little is known about the sublethal effects of contaminant exposure on elasmobranch energy budgets. We compared tissue quality and metabolic capacity in male and female Round Stingrays (Urobatis halleri), as well as embryos, from two populations experiencing different levels of environmental PCB exposure. With histotrophic matrotrophy, pregnancy is energetically costly in this species. Pregnant females from the exposed population experienced larger decreases in tissue quality and mass than reference females. In addition, higher PCB burden resulted in decreases in relative hepatic energy reserves, supporting the hypothesis that contaminant exposure compounds energy demands during pregnancy. Despite the large energetic strain on pregnant females, contaminant-exposed males had the highest metabolic capacities accompanied with the lowest tissue quality metrics. We support the accumulating evident that in utero exposure to contaminants via maternal offloading results in negative embryo outcomes. Embryos from the reference site had higher tissue quality measures, with similar metabolic capacities as contaminant-exposed embryos, suggesting contaminant exposure reduced resource utilization efficiencies. These sex and age class-related impacts of contaminants are likely to have broad, negative, population-level consequences for elasmobranchs.

    3.  14:15  VIRTUAL    Associations Between Total Mercury Levels, Trace Minerals, and Blood Health Markers in North Atlantic White Sharks. Lisa Crawford*, Stony Brook University; Alisa Newton, Disney’s Animals, Science and Environment; Lisa Hoopes, Georgia Aquarium; James Gelsleichter, University of North Florida; Nicholas Fisher, Stony Brook University; Cheng-Schiuan Lee, Stony Brook University; Douglas Adams, Cape Canaveral Scientific; Maeva Giraudo, Environment & Climate Change Canada; Anne McElroy, Stony Brook University

    The feeding ecology and related life-history characteristics of white sharks (Carcharodon carcharias) make this species susceptible to bioaccumulation of contaminants like mercury;however, the potential effects of mercury exposure on shark health are understudied, particularly in wild-caught animals.We measured muscle and plasma total mercury (THg)and blood health markers and trace minerals in plasma collected from white sharks (n=36)sampled during 2018-2021 OCEARCH expeditions ranging from Nova Scotia, Canada to Jacksonville, Florida. THg in muscle tissue averaged 10.7 mg/kg d.w. (range 4.30-25.3 mg/kg d.w), while THg in blood plasma averaged 587 ug/L (range 69-1245 ug/L). There were significant positive correlations between THg levels in muscle tissue and shark precaudal length (163-419 cm) as well as blood plasma THg, indicating larger individuals bioaccumulate THg over time and muscle and plasma THg are accumulated proportionally.No relationships between plasma THg and select blood health markers (white blood cell counts, granulocyte:lymphocyte ratios, and acute phase protein response) were identified.The mean selenium:mercury molar ratio (n=14) in blood plasma was 0.597, potentially indicating free selenium in the blood was depleted and protective effects of the trace mineral were diminished.This study is the first to report THg bioaccumulation and associated trace element and health biomarker relationships in North Atlantic white sharks across their entire migratory range sampled at multiple seasonal time points. Our results will enhance the understanding of physiological responses of white sharks to mercury bioaccumulation.

    4.  14:30  VIRTUAL    Methods for Applying MHC Immune Genes into Shark Population Studies. Eloise Cave*, Florida Institute of Technology; Michael Criscitiello, Texas A&M University; Toby Daly-Engel, Florida Institute of Technology

    Elasmobranch fishes have a variety of physiological, morphological, and behavioral innovations that have helped them persist over evolutionary time. One such innovation is the Major Histocompatibility Complex (MHC), the part of the vertebrate adaptive immune system that codes for proteins that process and present antigens to T-cells and B-cells. Because diversity at MHC is important for disease resistance, MHC are the most diverse genes known. This diversity and the fact that MHC genes are targets for selection in other taxa makes them ideal candidates for studying functional adaptation in elasmobranchs, but developing such loci for use in conservation studies on non-model organisms is challenging. We address the lack of methodology for incorporating functional genes into elasmobranch population assessments by identifying, amplifying, and sequencing the polymorphic peptide binding region (PBR) of two shark MHC subunit genes (Class II ? and ?). We aligned sequences from reference genomes and published data from nurse sharks to identify conserved regions for which primers could be designed, which we then tested on other species to determine allele diversity. We recovered 150-200 bp products that we used to characterize diversity in four shark species. This study demonstrates the feasibility of using MHC genes as biomarkers in elasmobranch conservation, where they can provide a contrast to estimates of neutral diversity and improve our understanding of environmental adaptation and evolutionary persistence.

    5.  14:45  IN-PERSON    Once Bitten Thrice Swabbed: Identifying Species From Transfer DNA In Shark Bite Incidents. Derek Kraft*, Hawai'i Institute of Marine Biology; Lauren Meyer, Southern Shark Ecology Group; Maryann Webb, Hawai'i Institute of Marine Biology; Kaylee Scidmore-Rossing, Hawai'i Institute of Marine Biology; Charlie Huveneers, Southern Shark Ecology Group; Eric Clua, EPHE, PSL Research University

    Identifying the species involved in shark bite incidents is an ongoing challenge but is important to mitigate risk. We developed a sampling protocol to identify shark species from DNA transferred to inanimate objects during bite incidents. To develop and refine the technique, we swabbed shark bite impressions on surfboards and wetsuit neoprene collected under semi-controlled conditions. Methods were tested experimentally and then successfully used to identify the species involved in a real-world shark bite incident. Thirty-two of 33 bite impressions yielded sufficient DNA sequences for species identification, producing barcodes from five test species, including dusky, Galapagos, bull, tiger, and white shark. The latter three species collectively account for a majority of shark bites worldwide. Our method successfully identified the species (Galeocerdo cuvier) responsible for a fatal shark bite on December 8th, 2020 on the island of Maui, from swab samples collected from the victim’s surfboard 49 hours after the bite incident. Our experimental results demonstrate that shark species can be accurately identified from transfer DNA recovered from bite impressions on surfboards and wetsuit neoprene. The successful use of our method in the real-world incident shows great potential for the practicality of this tool. We recommend DNA swabbing as a routine part of the forensic analysis of shark bites to help identify the species involved in human-shark interactions.

    6.  15:00  VIRTUAL    Cryptic speciation and genetic diversity in the genus Squalus. Carly McCall*, Florida Institute of Technology; Toby Daly-Engel, Florida Institute of Technology

    Deep-sea dogfish sharks (genus Squalus) have long (24 month) reproductive intervals, slow growth rates, and low standing genetic diversity. Often caught as bycatch in trawl fisheries, some dogfishes have undergone catastrophic declines as a result of overfishing and are slow to recover, leading to conservation concern for this group. Similarities in morphology among Squalusspecies has historically led to widespread taxonomic confusion. In recent years, genetic tools have led to the discovery of several cryptic shark species (genetically distinct species that are nearly impossible to distinguish from other, more common species), including dogfishes. To investigate the occurrence of cryptic diversity among Squalus species, we tested for evolutionary divergence among 20 putative Squalus species using four genes, two mitochondrial and two nuclear (2,654 bp total). Bayesian phylogenetic analysis indicated the presence of at least five genetically and ecologically distinct groups, all previously identified as Squalus mitsukurii or S. megalops. We hypothesize that evolutionary divergence events within the genus are more common around periods of geological warming and paleoceanographic changes, and that temperature plays a prominent role in driving dispersal of deep-water sharks. The genus Squalus is currently considered Data Deficient by the IUCN, and taxonomic evaluation is an important first step in being able to properly classify and eventually manage cryptic species.

    7.  15:15  VIRTUAL    Genetic evidence of cryptic speciation in deep-water sixgill sharks. Shannon Barry*, Florida Institute of Technology; Dean Grubbs, Florida State University; Shawn Larson, Seattle Aquarium; Toby Daly-Engel, Florida Institute of Technology

    The sixgill sharks (Hexanchiformes, Hexanchidae) are among the largest of the deep-sea sharks, but remain poorly understood. Recent genetic work identified cryptic speciation within the genus Hexanchus, resulting in the resurrection of the Atlantic sixgill shark, Hexanchus vitulus. The emergence of these cryptic species in different ocean basins raises the question of how biogeographic barriers to dispersal, especially sea surface temperature (SST) barriers, can influence dispersal in vagile, deep-water sharks. We used three mitochondrial genes and one nuclear gene (6.3 kb total) in a coalescent molecular clock approach to examine the timing of evolutionary divergences within the genus Hexanchusin an ecological context. We found significant within-species divergence between the Atlantic and Pacific Oceans in H. griseus, and even deeper divergence in the bigeye sixgill that indicate a second cryptic species, with Pacific H. nakamurai more closely related to H. vitulus than putative congeners in the Indian Ocean. We found that divergence timings coincided with geological and climatic warming events, and that physical land barriers coupled with SST change is the most likely mechanism of speciation in this group. This indicates that shark range and diversity is largely shaped by changes in SST even in the deep sea, and that habitat shifts in response to global climate change are possible for sixgill sharks.

    8.  15:30  IN-PERSON    Population structure of angel sharks in the western North Atlantic Ocean. Andrew Fields*, Texas A&M University Corpus Christi; William Driggers III, National Marine Fisheries Service; Christian Jones, National Marine Fisheries Service; David Portnoy, Texas A&M University Corpus Christi

    Harvest of sharks has led to population declines across the globe, with some of the most imperiled species being the “ray-like” angel sharks. Even in countries with well-established regulations, limitations on the knowledge of a given species and population boundaries can limit the ability to properly manage these fishes. The distribution of angel sharks (family Squatinidae) in the U.S. waters of the western North Atlantic Ocean, including off the east coast of the U.S. (hereafter Atlantic) and in the Gulf of Mexico (hereafter Gulf), has recently been reassessed. Based on catch records, two distinct breaks were found, as well as apparent differences in depth preference between the Gulf and Atlantic. Using reduced representation genomics, we investigated population structure and found three distinct genetic units in this region, one in the Atlantic and two in the Gulf, which have significant FST values between them (FST = 0.004-0.024). By contrast, only two groups could be distinguished using mitochondrial DNA sequence data, with one group encompassing the eastern Gulf and Atlantic and the other group consisting of mainly western Gulf samples. Taken as a whole, the data are consistent with three distinct genetic units, with recent contact between the Atlantic and eastern Gulf. There is also evidence consistent with local adaptation among the angel shark populations.

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