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1. Probing the Ecology and Climate of the Eocene Southern Ocean With Sand Tiger Sharks Striatolamia macrota

   https://doi.org/10.1029/2020PA003997  

   Kim, Sora L.; Zeichner, Sarah S.; Colman, Albert S.; Scher, Howie D.; Kriwet, Jürgen; Mörs, Thomas; Huber, Matthew (December 2020, Paleoceanography and Paleoclimatology)

   Abstract Many explanations for Eocene climate change focus on the Southern Ocean—where tectonics influenced oceanic gateways, ocean circulation reduced heat transport, and greenhouse gas declines prompted glaciation. To date, few studies focus on marine vertebrates at high latitudes to discern paleoecological and paleoenvironmental impacts of this climate transition. The Tertiary Eocene La Meseta (TELM) Formation has a rich fossil assemblage to characterize these impacts;Striatolamia macrota, an extinct (†) sand tiger shark, is abundant throughout the La Meseta Formation. Body size is often tracked to characterize and integrate across multiple ecological dimensions. †S. macrotabody size distributions indicate limited changes during TELMs 2–5 based on anterior tooth crown height (n = 450, mean = 19.6 ± 6.4 mm). Similarly, environmental conditions remained stable through this period based on δ¹⁸O_PO4values from tooth enameloid (n = 42; 21.5 ± 1.6‰), which corresponds to a mean temperature of 22.0 ± 4.0°C. Our preliminaryε_Nd(n = 4) results indicate an early Drake Passage opening with Pacific inputs during TELM 2–3 (45–43 Ma) based on single unit variation with an overall radiogenic trend. Two possible hypotheses to explain these observations are (1) †S. macrotamodified its migration behavior to ameliorate environmental changes related to the Drake Passage opening, or (2) the local climate change was small and gateway opening had little impact. While we cannot rule out an ecological explanation, a comparison with climate model results suggests that increased CO₂produces warm conditions that also parsimoniously explain the observations. 

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2. Dental morphology and community structure of Plio-Pleistocene cercopithecid primates from East and South Africa

   https://doi.org/10.1002/ajpa.24262  

   Smail, Irene E. (March 2021, American Journal of Physical Anthropology)

   null (Ed.)

   Fossil cercopithecid primates of the African Plio-Pleistocene are often found together in fossil deposits across East and South Africa. These species may have co-occurred in life and exploited similar types of resources in shared environments, as extant monkeys in Africa and Asia are known to do. Some of these fossil species are represented today by congeneric or descendant species with similar adaptations while others have no modern analogue. This project uses dental morphology to compare community structure across potentially co-occurring fossil and modern cercopithecid populations (the cercopithecid taxocene). Relative enamel thickness, shearing potential, and dental shape ratios from the P4 – M3 toothrow were measured from extant (n > 700) and fossil cercopithecid specimens (n > 1000). The latter primarily targeted the Hadar, Shungura, and Koobi Fora Formations of East Africa and the sites of Makapansgat, Sterkfontein, and Swartkrans in South Africa. Principal component analyses were performed separately on the maxillary and mandibular dentitions and resulting component scores were used to reconstruct the taxocene dental morphology at each site. In general, the African cercopithecid taxocene is similar across the main fossil sites analyzed. Patterns of overlap between fossil and modern sites may reflect environmental similarities or the adaptability of generalist cercopithecids. An apparent niche shift from the Plio-Pleistocene to today reflects both taphonomic and ecological factors: a lack of smaller-bodied fossil cercopithecin and colobine species combined with an expanded dental ecomorphological niche of larger-bodied fossil species. 

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3. Genetic and phenotypic variation exhibit both predictable and stochastic patterns across an intertidal fish metapopulation

   https://doi.org/10.1111/mec.15829  

   Thia, Joshua A.; McGuigan, Katrina; Liggins, Libby; Figueira, Will F.; Bird, Christopher E.; Mather, Andrew; Evans, Jennifer L.; Riginos, Cynthia (January 2021, Molecular Ecology)

   null (Ed.)

   Interactions among selection, gene flow, and drift affect the trajectory of adaptive evolution. In natural populations, the direction and magnitude of these processes can be variable across different spatial, temporal, or ontogenetic scales. Consequently, variability in evolutionary processes affects the predictability or stochasticity of microevolutionary outcomes. We studied an intertidal fish, Bathygobius cocosensis (Bleeker, 1854), to understand how space, time, and life stage structure genetic and phenotypic variation in a species with potentially extensive dispersal and a complex life cycle (larval dispersal preceding benthic recruitment). We sampled juvenile and adult life stages, at three sites, over three years. Genome-wide SNPs uncovered a pattern of chaotic genetic patchiness, that is, weak-but-significant patchy spatial genetic structure that was variable through time and between life stages. Outlier locus analyses suggested that targets of spatially divergent selection were mostly temporally variable, though a significant number of spatial outlier loci were shared between life stages. Head shape, a putatively ecologically responsive (adaptive) phenotype in B. cocosensis also exhibited high temporal variability within sites. However, consistent spatial relationships between sites indicated that environmental similarities among sites may generate predictable phenotype distributions across space. Our study highlights the complex microevolutionary dynamics of marine systems, where consideration of multiple ecological dimensions can reveal both predictable and stochastic patterns in the distributions of genetic and phenotypic variation. Such considerations probably apply to species that possess short, complex life cycles, have large dispersal potential and fecundities, and that inhabit heterogeneous environments. 

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4. Species' attributes predict the relative magnitude of ecological and genetic recovery following mass mortality

   https://doi.org/10.1111/mec.16707  

   Schiebelhut, Lauren M.; Gaylord, Brian; Grosberg, Richard K.; Jurgens, Laura J.; Dawson, Michael N (September 2022, Molecular Ecology)

   Theoretically, species' characteristics should allow estimation of dispersal potential and, in turn, explain levels of population genetic differentiation. However, a mismatch between traits and genetic patterns is often reported for marine species, and interpreted as evidence that life-history traits do not influence dispersal. Here, we couple ecological and genomic methods to test the hypothesis that species with attributes favouring greater dispersal potential—e.g., longer pelagic duration, higher fecundity and larger population size—have greater realized dispersal overall. We used a natural experiment created by a large-scale and multispecies mortality event which created a “clean slate” on which to study recruitment dynamics, thus simplifying a usually complex problem. We surveyed four species of differing dispersal potential to quantify the abundance and distribution of recruits and to genetically assign these recruits to probable parental sources. Species with higher dispersal potential recolonized a broader extent of the impacted range, did so more quickly and recovered more genetic diversity than species with lower dispersal potential. Moreover, populations of taxa with higher dispersal potential exhibited more immigration (71%–92% of recruits) than taxa with lower dispersal potential (17%–44% of recruits). By linking ecological with genomic perspectives, we demonstrate that a suite of interacting life-history and demographic attributes do influence species' realized dispersal and genetic neighbourhoods. To better understand species' resilience and recovery in this time of global change, integrative eco-evolutionary approaches are needed to more rigorously evaluate the effect of dispersal-linked attributes on realized dispersal and population genetic differentiation. 

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5. Whole genome analyses reveal weak signatures of population structure and environmentally associated local adaptation in an important North American pollinator, the bumble bee Bombus vosnesenskii

   https://doi.org/10.1111/mec.17125  

   Heraghty, Sam D.; Jackson, Jason M.; Lozier, Jeffrey D. (September 2023, Molecular Ecology)

   Abstract Studies of species that experience environmental heterogeneity across their distributions have become an important tool for understanding mechanisms of adaptation and predicting responses to climate change. We examine population structure, demographic history and environmentally associated genomic variation inBombus vosnesenskii, a common bumble bee in the western USA, using whole genome resequencing of populations distributed across a broad range of latitudes and elevations. We find thatB. vosnesenskiiexhibits minimal population structure and weak isolation by distance, confirming results from previous studies using other molecular marker types. Similarly, demographic analyses with Sequentially Markovian Coalescent models suggest that minimal population structure may have persisted since the last interglacial period, with genomes from different parts of the species range showing similar historical effective population size trajectories and relatively small fluctuations through time. Redundancy analysis revealed a small amount of genomic variation explained by bioclimatic variables. Environmental association analysis with latent factor mixed modelling (LFMM2) identified few outlier loci that were sparsely distributed throughout the genome and although a few putative signatures of selective sweeps were identified, none encompassed particularly large numbers of loci. Some outlier loci were in genes with known regulatory relationships, suggesting the possibility of weak selection, although compared with other species examined with similar approaches, evidence for extensive local adaptation signatures in the genome was relatively weak. Overall, results indicateB. vosnesenskiiis an example of a generalist with a high degree of flexibility in its environmental requirements that may ultimately benefit the species under periods of climate change. 

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