Session 42: AES GeneticsRoom: Conference Theater2022-07-31 08:00 - 09:30 |
| Moderator: Marcus Drymon |
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1. 08:00 Long Live the Queens: Patterns of Kinship and Relatedness Indicate the Presence of Shark BOFFFFs. Toby Daly-Engel*, Florida Institute of Technology tdalyengel@fit.edu
The term BOFFFF (big old fat fertile female fish) was coined by Hixon and colleagues to describe the relatively few individual bony fish that survive to reach a size that is exponentially more fecund than smaller animals, and which are thought to sustain some fisheries through sheer productivity. The idea of shark BOFFFFs has been largely discounted because their size-fecundity relationship is weaker, but shark fecundity does increase with size, and as with bony fishes, most mortality occurs in the juvenile phase. It is therefore possible for a few high-value reproducers to be particularly valuable to maintaining numbers, especially in small populations. We examined patterns of kinship and relatedness alongside inbreeding coefficients derived from molecular diversity data in several shark species, and found an unexpectedly high number of first order related individuals (kin pairs sharing 50% of their DNA) comprising 9-34% of various sample sets. Among these, several high pairwise relatedness values (80-98%) were detected, but maximum average relatedness did not exceed 2.6%, and levels of inbreeding among individuals ranged from 0.08-0.09. This high number of kin points to the existence of shark BOFFFFs, highly successful females with indeterminate growth and low mortality that continue to reproduce over long lifetimes, making a disproportionately large contribution to the next generation compared with conspecifics. Though this effect is likely minimal compared with bony fishes and not an appropriate basis for management, increased variation in reproductive success can drastically reduce effective population size, threatening the health and viability of shark populations. |
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2. 08:15 Is Blood Thicker than Water? Relatedness and kinship in Bull Sharks (Carcharhinus leucas). Tessa Morgan*, Florida Institute of Technology; Shannon Barry, Florida Institute of Technology; Simon Gulak, Riverside Technologies, Inc; Marcus Drymon, Coastal Research and Extension Center; Emily Seubert, Coastal Research and Extension Center; Toby Daly-Engel tmorgan2017@my.fit.edu
The Bull Shark (Carcharhinus leucas) is a widely-distributed coastal species with the unique ability to fully occupy both marine and freshwater environments. Female Bull Sharks are known to exhibit philopatry, returning to the same shallow nearshore estuarine and freshwater “nursery” habitats to give birth biennially, with offspring residing in these areas year-round until they approach adulthood. Proximity to coastlines leaves juveniles particularly vulnerable to anthropogenic pressures, which along with commercial and recreational exploitation has resulted in Bull Sharks being listed as “Near Threatened” by the International Union for Conservation of Nature (IUCN). Despite being a relatively well-studied, charismatic species, little is known about the dynamics that drive Bull Shark reproductive behavior and distribution, especially among juveniles within nursery habitats. Here we use 26 highly polymorphic microsatellite DNA markers to describe patterns of genetic relatedness and paternity among 124 individual Bull Sharks taken from sites around the southeastern US. This includes four full litters (mothers and pups) used to derive within-brood relatedness, which we compare to kinship and relatedness values among 13 putatively-unrelated juvenile Bull Sharks that were recovered from a ghost net, and another 103 similar-sized juveniles sampled from Manatee River, Florida, and elsewhere. We found an unexpectedly-high degree of relatedness among Bull Sharks, indicating low effective population size and low genetic diversity, which acts as a buffer against extinction. Understanding population dynamics in and around Bull Shark nursery sites, including behavioral associations among kin, is crucial to improving the management and conservation of the species as a whole. |
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3. 08:30 Polyandry and Inheritance of Adaptive Immune Genes in Sandbar Sharks (Carcharhinus plumbeus). Manav Agarwal, Florida Institute of Technology; Jasmine Hall*, Florida Institute of Technology; Eloise Cave, Florida Institute of Technology; Dean Grubbs, Florida State University; Toby Daly-Engel, Florida Institute of Technology hallj2018@my.fit.edu
Elasmobranchs (sharks, skates, and rays) are a subclass of Chondrichthyes, cartilaginous fishes, which were the first vertebrates to evolve an adaptive immune system (AIS). A crucial part of the AIS is the major histocompatibility complex (MHC), a suite of genes that code for molecules that recognize pathogens and trigger an immune response to rid the body of infection. It is speculated that the AIS first evolved in response to sharks’ reproductive strategies, which include live birth and polyandry (females mating with multiple males). Previously, we estimated allele inheritance in female Sandbar Sharks (Carcharhinus plumbeus) in Hawaii to document polyandry, and found that only ~40% of females use this behavior compared with 80% in other populations. But because neutral genes do not respond to selection pressure and have low diversity, we hypothesize that coding genes may show a higher frequency of polyandry. This study aims to amplify three MHC genes (Class I, Class II?, and Class IIß) in DNA from Sandbar Sharks litters (mothers and pups) to compare patterns of inheritance and diversity with neutral loci. We amplified MHC I, MHC II?, and MHC IIß sequences using polymerase chain reaction (PCR), then aligned the sequences for each brood and used Bayesian phylogenetic tree-building to identify different alleles within broods. Findings from this study will give us unique insight into the evolution of the “prototype” MHC complex, and provide a novel tool for investigating genetic mating systems in sharks. |
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4. 08:45 Allelic Richness of the MHC Gene Complex in Four Species of Sharks. Eloise Cave*, Florida Institute of Technology; Michael Criscitiello, Texas A&M University; Toby Daly-Engel, Florida Institute of Technology ecave2018@my.fit.edu
High levels of genetic diversity can help populations respond and adapt to pathogens, predators, and environmental change. Functional genes like the Major Histocompatability Complex (MHC), a highly polymorphic multigene complex that is part of the adaptive immune system, can be a target for evaluating population health and local adaptation, but our knowledge of shark MHC is limited to a handful of species. Here we investigate gene copy number and allele diversity of the MHC in four shark species: the tiger shark, Atlantic sharpnose shark, Cuban dogfish shark, and Genie’s dogfish shark, whose overlapping depths span a range of shark ecological niches. Specifically, the exon 2 of the MHC II alpha and beta genes were amplified via polymerase chain reaction, and each sequence was visually analyzed for variable sites and assembled on a Bayesian phylogenetic tree to determine number of alleles. We found that allele number at MHC class IIb varies widely, with the tiger shark showing the lowest number of alleles (five) and the Cuban dogfish shark with the highest number of alleles (18). With high variability and selection potential, MHC loci represent a formidable tool to study the specific genetic mechanisms underlying evolutionary response to environmental shifts in sharks, pinpoint which species/populations/habitats are most vulnerable to climate change, and to predictively model future shifts in habitat use and dispersal patterns. |
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5. 09:00 Assessing Climate Impacts on the Connectivity of the Bull Shark (Carcharhinus leucas) between Nursery Habitats in the northwestern Atlantic. Shannon Barry*, Florida Institute of Technology; Douglas Adams, Florida Fish and Wildlife Conservation Commision; Charles Bangley, Dalhousie University; Matthew Ajemian, Florida Atlantic University; James Gelsleichter, University of North Florida; Neil Hammerschlag, University of Miami; Toby Daly-Engel, Florida Institute of Technology barrys2018@my.fit.edu
Bull sharks (Carcharhinus leucas) are highly mobile, with the potential to link disparate ecosystems and adapt to new habitats in response to environmental change. Research has shown that females are philopatric to shallow coastal nursery habitats, where juveniles remain for several years. The Indian River Lagoon (IRL) on the eastern coast of Florida was formerly the northernmost bull shark nursery in the northwestern Atlantic, but a recent study indicated that female bull sharks are moving up the Atlantic Coast and establishing new stable nurseries in response to increasing water temperature. We aim to understand how climate change is driving habitat shifts in bull sharks by using 17 microsatellite genes on hundreds of juvenile bull sharks, including historical samples from the IRL, to assess dispersal and relatedness patterns within and between northwest Atlantic nursery habitats. We found limited connectivity between the Gulf of Mexico and northwestern Atlantic, with higher-than-expected levels of kinship within nurseries that carries implications for effective population size. Given the effects of modern climate change, understanding the genetic connectivity between novel and established nursery habitats is crucial for understanding how range shifts affect the viability of bull shark populations. |
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6. 09:15 Historical Demography of the World’s White Shark Populations. Gavin Naylor*, U. Florida; Shannon Corrigan, Minderoo Foundation; Lei Yang, U. Florida; Romuald Laso-jadart, Paris Museum; Elise Gay, Paris Museum; Stefano Mona*, Paris Museum gjpnaylor@gmail.com
Sequential Markov Coalescent (SMC++) analyses were used to infer the change in population size and population structure over time using whole genome comparisons. Results were contrasted with those obtained from nuclear exon capture and whole mitochondrial genomes sequences for ~ 150 samples collected throughout the range of the species. The biogeographical sequence of events that led to the current population structure will be presented, |