More Like this

1. Is MHC diversity a better marker for conservation than neutral genetic diversity? A case study of two contrasting dolphin populations

   https://doi.org/10.1002/ece3.5265  

   Manlik, Oliver ; Krützen, Michael ; Kopps, Anna M. ; Mann, Janet ; Bejder, Lars ; Allen, Simon J. ; Frère, Celine ; Connor, Richard C. ; Sherwin, William B. ( May 2019 , Ecology and Evolution)

   Genetic diversity is essential for populations to adapt to changing environments. Measures of genetic diversity are often based on selectively neutral markers, such as microsatellites. Genetic diversity to guide conservation management, however, is better reflected by adaptive markers, including genes of the major histocompatibility complex (MHC). Our aim was to assess MHC and neutral genetic diversity in two contrasting bottlenose dolphin (Tursiops aduncus) populations in Western Australia—one apparently viable population with high reproductive output (Shark Bay) and one with lower reproductive output that was forecast to decline (Bunbury). We assessed genetic variation in the two populations by sequencing the MHC class II DQB, which encompasses the functionally important peptide binding regions (PBR). Neutral genetic diversity was assessed by genotyping twenty‐three microsatellite loci.

   We confirmed that MHC is an adaptive marker in both populations. Overall, the Shark Bay population exhibited greater MHC diversity than the Bunbury population—for example, it displayed greater MHC nucleotide diversity. In contrast, the difference in microsatellite diversity between the two populations was comparatively low.

   Our findings are consistent with the hypothesis that viable populations typically display greater genetic diversity than less viable populations. The results also suggest that MHC variation is more closely associated with population viability than neutral genetic variation. Although the inferences from our findings are limited, because we only compared two populations, our results add to a growing number of studies that highlight the usefulness of MHC as a potentially suitable genetic marker for animal conservation. The Shark Bay population, which carries greater adaptive genetic diversity than the Bunbury population, is thus likely more robust to natural or human‐induced changes to the coastal ecosystem it inhabits.

    

   more » « less
2. Elevated Calf Mortality and Long-Term Responses of Wild Bottlenose Dolphins to Extreme Climate Events: Impacts of Foraging Specialization and Provisioning

   https://doi.org/10.3389/fmars.2021.617550  

   Mann, Janet ; Foroughirad, Vivienne ; McEntee, Molly H. ; Miketa, Madison L. ; Evans, Taylor C. ; Karniski, Caitlin ; Krzyszczyk, Ewa ; Patterson, Eric M. ; Strohman, John C. ; Wallen, Megan M. ( March 2021 , Frontiers in Marine Science)

   null (Ed.)

   As demands for wildlife tourism increase, provisioning has become a popular means of providing up-close viewing to the public. At Monkey Mia, Shark Bay, Australia, up to five adult female Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) visit a 100 m stretch of beach daily to receive fish handouts. In 2011, a severe marine heatwave (MHW) devastated seagrass and fish populations in Shark Bay. Offspring survival declined precipitously among seagrass specialists (dolphins that forage disproportionately in seagrass habitat). As all provisioned dolphins at the site are seagrass specialists, we examined how provisioned and non-provisioned seagrass specialists responded to the MHW. Using 27 years of data we compare habitat use, home range size, calf mortality, and predation risk between provisioned and non-provisioned females and their offspring before and after the MHW. Our results show that provisioned females have extremely small home ranges compared to non-provisioned females, a pattern attributable to their efforts to remain near the site of fish handouts. However, weaned offspring (juveniles) born to provisioned females who are not provisioned themselves also had much smaller home ranges, suggesting a persistent maternal effect on their behavior. After the MHW, adult females increased their use of seagrass habitats, but not their home range size. Provisioned females had significantly lower calf mortality than non-provisioned females, a pattern most evident pre-MHW, and, in the first 5 years after the MHW (peri-MHW, 2011–2015), calf mortality did not significantly increase for either group. However, the ecosystem did not recover, and post-MHW (2016–2020), calf mortality was substantially higher, regardless of provisioning status. With few survivors, the impact of the MHW on juvenile mortality post-weaning is not known. However, over three decades, juvenile mortality among offspring of provisioned vs. non-provisioned females did not statistically differ. Thus, the survival benefits accrued to calves in the provisioned group likely cease after weaning. Finally, although shark attack rates on seagrass specialists did not change over time, elevated predation on calves cannot be ruled out as a cause of death post-MHW. We discuss our results as they relate to anthropogenic influences on dolphin behavioral plasticity and responses to extreme climate events. 

   more » « less
3. Whole‐genome resequencing reveals persistence of forest‐associated mammals in Late Pleistocene refugia along North America’s North Pacific Coast

   https://doi.org/10.1111/jbi.14068  

   Colella, Jocelyn P. ; Lan, Tianying ; Talbot, Sandra L. ; Lindqvist, Charlotte ; Cook, Joseph A. ( March 2021 , Journal of Biogeography)

   Numerous glacial refugia have been hypothesized along North America's North Pacific Coast that may have increased divergence of refugial taxa, leading to elevated endemism and subsequently clustered hybrid zones following deglaciation. The locations and community composition of these ice‐free areas remains controversial, but whole‐genome sequences now enable detailed analysis of the demographic and evolutionary histories of refugial taxa. Here, we use genomic data to test spatial and temporal processes of diversification among martens with respect to the Coastal Refugium Hypothesis, to understand the role of climate cycling in shaping diversity across complex landscapes.

   North America and North Pacific Coast archipelagos.

   North American martens (Martes).

   Short‐read whole‐genome resequencing data were generated for 11 martens: fourM. americana, fourM. caurina, two hybrids, and one outgroup (Martes zibellina). Sampling was representative of known genetic clades within New World martens, including sampling within insular and continental hybrid zones and along the North Pacific Coast (five island populations).ADMIXTURE, F‐statistics, andD‐statistics (ABBA‐BABA) were used to identify introgression and infer directionality. Heterozygosity densities, estimated via PSMC, were used to characterize historical demography at and below the species level to infer refugial and colonization processes.

   Forest‐associated Pacific martens (M. caurina) are divided into distinct insular and continental clades consistent with the Coastal Refugium Hypothesis. There was no evidence of introgression on islands that received historical translocations of American pine martens (M. americana), but introgression was detected in two active zones of secondary contact: one insular and one continental. Only early‐generational hybrids were identified across multiple hybrid zones, a pattern consistent with potential genetic swamping ofM. caurinabyM. americana.

   Despite an incomplete fossil record, genomic evidence supports the persistence of forest‐associated martens, likely the insular Pacific marten lineage, along the western edges of the Alexander Archipelago during the Last Glacial Maximum. This discovery informs our understanding of refugial paleoenvironments, critical to interpreting refugial timing, duration, and community composition. Genomic reevaluations of other taxa along North America's North Pacific Coast may yield new and deeper perspectives on the history of refugial forest communities and the role of dynamic climate shifts in shaping high‐latitude diversity across complex insular landscapes.

    

   more » « less
4. Ocean current patterns drive the worldwide colonization of eelgrass (Zostera marina)

   https://doi.org/10.1038/s41477-023-01464-3  

   Yu, Lei ; Khachaturyan, Marina ; Matschiner, Michael ; Healey, Adam ; Bauer, Diane ; Cameron, Brenda ; Cusson, Mathieu ; Emmett Duffy, J. ; Joel Fodrie, F. ; Gill, Diana ; et al ( August 2023 , Nature Plants)

   Currents are unique drivers of oceanic phylogeography and thus determine the distribution of marine coastal species, along with past glaciations and sea-level changes. Here we reconstruct the worldwide colonization history of eelgrass (Zostera marinaL.), the most widely distributed marine flowering plant or seagrass from its origin in the Northwest Pacific, based on nuclear and chloroplast genomes. We identified two divergent Pacific clades with evidence for admixture along the East Pacific coast. Two west-to-east (trans-Pacific) colonization events support the key role of the North Pacific Current. Time-calibrated nuclear and chloroplast phylogenies yielded concordant estimates of the arrival ofZ. marinain the Atlantic through the Canadian Arctic, suggesting that eelgrass-based ecosystems, hotspots of biodiversity and carbon sequestration, have only been present there for ~243 ky (thousand years). Mediterranean populations were founded ~44 kya, while extant distributions along western and eastern Atlantic shores were founded at the end of the Last Glacial Maximum (~19 kya), with at least one major refuge being the North Carolina region. The recent colonization and five- to sevenfold lower genomic diversity of the Atlantic compared to the Pacific populations raises concern and opportunity about how Atlantic eelgrass might respond to rapidly warming coastal oceans.

    

   more » « less
5. The hidden landscape: Evidence that sea‐level change shaped the present population genomic patterns of marginal marine species

   https://doi.org/10.1111/mec.15826  

   Dolby, Greer A. ( March 2021 , Molecular Ecology)

   Oftentimes, to understand the genetic relatedness and diversity of today's populations requires considering the ancient landscape on which those populations evolved. Nowhere is this clearer than along Earth's coastline, which has been in its present‐day configuration for only about 6.5% of the past 800,000 years (Dolby et al., 2020; Miller et al., 2005). During ice ages when glaciers expanded in the Northern Hemisphere, they stored enough of the planet's water to drop global sea level by ~120 m below present levels (“lowstand”, Figure 1a), and there have been at least eight of these 100,000‐year cycles preceding today. When glaciers melted, ocean water reflooded shorelines, shifting and re‐forming marginal marine habitats globally and shaping the relatedness of populations (Dolby et al., 2016). In a From the Cover article in this issue ofMolecular Ecology, Stiller et al. (2020) integrate population genomic analysis of leafy seadragons in southern Australia with estimates of available seabed area to reveal that the expansion of habitat that accompanied this reflooding led to strong demographic expansions. With statistical models, they also show that western populations were eliminated and then recolonized because the continental shelf there is narrow, leaving little available habitat when sea level was low (Figure 1b). Their results document the dynamic and interrelated nature of a hidden, changing landscape and the evolution of species inhabiting it.

    

   more » « less