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1. Migratory strategy explains differences in timing of female reproductive development in seasonally sympatric songbirds

   https://doi.org/10.1111/1365-2435.13386  

   Kimmitt, Abigail A. ; Hardman, Jack W. ; Stricker, Craig A. ; Ketterson, Ellen D. ; Sockman, ed., Keith ( July 2019 , Functional Ecology)

   Divergent migratory strategies among populations can result in population‐level differences in timing of reproduction (allochrony) and local adaptation. However, the mechanisms underlying among‐population variation in timing are insufficiently understood, particularly in females.

   We studied differences in reproductive development and its related mechanisms along the hypothalamic–pituitary–gonadal axis (HPG) in closely related migratory and sedentary (i.e. resident) female dark‐eyed juncos (Junco hyemalis) living together in sympatry during early spring. Despite exposure to the same environmental cues in early spring, residents initiate breeding prior to the departure of migrants for their breeding grounds. We investigated whether residents would be more reproductively developed than migrants based on their behavioural differences. Alternatively, females could exhibit similar reproductive development in response to the same environmental cues despite differences in migratory behaviour. To compare their degree of reproductive development during seasonal sympatry and the underlying mechanisms of these differences, we collected ovarian and liver tissue in early spring prior to migration and compared transcript abundance of genes associated with reproduction using quantitative PCR. We also used stable hydrogen isotopes to infer relative breeding and wintering latitude of migrants.

   We found higher transcript abundance of luteinizing hormone receptor and aromatase in the ovary in addition to significantly heavier ovaries in residents than in migrants. Together, these results suggest greater sensitivity and response to upstream endocrine stimulation in resident females. Transcript abundance for other receptors in the ovary and liver associated with reproduction, however, did not differ between populations. When comparing ovarian development within migrants, females with lower hydrogen isotopes (indicating higher breeding latitudes) had smaller ovaries, suggesting that longer‐distance migrations may further delay reproductive development.

   Based on differences in ovary mass and transcript abundance, we conclude that females that differ in migratory strategy also differ in timing of reproductive development. These results support that divergent migratory behaviour drives allochrony and could enable reproductive isolation between populations; mechanistic differences at the level of gonadal stimulation can explain these differences in timing of reproductive development.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Integrative population genetics and metagenomics reveals urbanization increases pathogen loads and decreases connectivity in a wild bee

   https://doi.org/10.1111/gcb.16757  

   Chau, Katherine D. ; Samad‐zada, Farida ; Kelemen, Evan P. ; Rehan, Sandra M. ( May 2023 , Global Change Biology)

   As urbanization continues to increase, it is expected that two‐thirds of the human population will reside in cities by 2050. Urbanization fragments and degrades natural landscapes, threatening wildlife including economically important species such as bees. In this study, we employ whole genome sequencing to characterize the population genetics, metagenome and microbiome, and environmental stressors of a common wild bee,Ceratina calcarata. Population genomic analyses revealed the presence of low genetic diversity and elevated levels of inbreeding. Through analyses of isolation by distance, resistance, and environment across urban landscapes, we found that green spaces including shrubs and scrub were the most optimal pathways for bee dispersal, and conservation efforts should focus on preserving these land traits to maintain high connectivity across sites for wild bees. Metagenomic analyses revealed landscape sites exhibiting urban heat island effects, such as high temperatures and development but low precipitation and green space, had the highest taxa alpha diversity across all domains even when isolating for potential pathogens. Notably, the integration of population and metagenomic data showed that reduced connectivity in urban areas is not only correlated with lower relatedness among individuals but is also associated with increased pathogen diversity, exposing vulnerable urban bees to more pathogens. Overall, our combined population and metagenomic approach found significant environmental variation in bee microbiomes and nutritional resources even in the absence of genetic differentiation, as well as enabled the potential early detection of stressors to bee health.

    

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3. Local prey community composition and genetic distance predict venom divergence among populations of the northern Pacific rattlesnake (Crotalus oreganus)

   Holding, M.L. ( October 2018 , Journal of evolutionary biology)

   Identifying the environmental correlates of divergence in functional traits between populations can provide insights into the evolutionary mechanisms that generate local adaptation. Here, we assess patterns of population differentiation in expressed venom proteins in Northern Pacific rattlesnakes (Crotalus oreganus) from 13 locations across California. We evaluate the relative importance of major biotic (prey species community composition), abiotic (temperature, precipitation, and elevation) and genetic factors (genetic distance based on RADseq loci) as correlates of population divergence in venom phenotypes. We found that over half of the variation in venom composition is associated with among-population differentiation for genetic and environmental variables, and that this variation occurred along axes defining previously observed functional trade-offs between venom proteins that have neurotoxic, myotoxic and hemorrhagic effects. Surprisingly, genetic differentiation among populations was the best predictor of venom divergence, accounting for 46% of overall variation, whereas differences in prey community composition and abiotic factors explained smaller amounts of variation (23% and 19%, respectively). The association between genetic differentiation and venom composition could be due to an isolation-by-distance effect or, more likely, an isolation-by-environment effect where selection against recent migrants is strong, producing a correlation between neutral genetic differentiation and venom differentiation. Our findings suggest that even coarse estimates of prey community composition can be useful in understanding the selection pressures acting on patterns of venom protein expression. Additionally, our results suggest that factors other than adaptation to spatial variation in prey need to be considered when explaining population divergence in venom. 

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4. Investigation of the geographic origin of burrowing owl fleas with implications for the ecology of plague

   https://doi.org/10.1093/auk/uky011  

   Navock, Kara A ; Johnson, David H ; Evans, Samantha ; Kohn, Matthew J ; Belthoff, James R ( January 2019 , The Auk)

   ABSTRACT Host-parasite relationships between Western Burrowing Owls (Athene cunicularia hypugaea) and the fleas (Pulex irritans, Siphonaptera:Pulicidae) they harbor were studied to understand the extent to which migratory Burrowing Owls translocated fleas from wintering grounds to breeding grounds. This has implications for host-parasite relationships in Burrowing Owls and also potentially for the dynamics of plague, as Burrowing Owl distributions overlap plague foci, owls inhabit fossorial mammal colonies where epizootic outbreaks of plague occur, and owls may harbor species of flea that are competent plague vectors. We used hydrogen stable isotope analysis to help elucidate geographic origins of fleas collected from adults and nestlings in 2 migratory populations of Burrowing Owls in Idaho and Oregon, USA. For adults, we posited that bird-mediated dispersal would impart flea isotopic compositions representative of southern latitudes and be similar to owl toenail tissue recently grown on wintering grounds, but they would differ from contour feathers presumably grown on breeding grounds the previous year. We assumed nestling feathers and toenails would have isotopic compositions representative of the breeding grounds. We analyzed contour feathers and toenails from adults collected shortly after they arrived in breeding grounds following spring migration and from nestlings later in the breeding season, to which we compared isotopic compositions in fleas collected from individuals of both age classes. Fleas on nestlings in both populations had isotopic compositions that did not differ from nestling feathers and toenails, suggesting that nestling fleas had breeding ground origins. Fleas on adults in one population (Oregon) had breeding ground isotopic signatures, as flea compositions did not differ from nestling feathers or toenails. Adult owls in Idaho had fleas that similarly did not express a wintering ground signature, but they were enriched in the heavy isotope (deuterium) relative to nestling feathers and toenails. Therefore, we discuss the possibility that adult owls in Idaho acquired fleas at migratory stopover sites. While the latter indicates that Burrowing Owls have the potential to disperse fleas, there was no evidence of continent-wide movement of fleas by owls from wintering grounds to breeding grounds. 

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5. The roles of ecology, behaviour and effective population size in the evolution of a community

   https://doi.org/10.1111/mec.14152  

   Hung, Chih‐Ming ; Drovetski, Sergei V. ; Zink, Robert M. ( June 2017 , Molecular Ecology)

   Organismal traits such as ecological specialization and migratory behaviour may affect colonization potential, population persistence and degree of isolation, factors that determine the composition and genetic structure of communities. However, studies focusing on community assembly rarely consider these factors jointly. We sequenced 16 nuclear genes and one mitochondrial gene from Caucasian and European populations of 30 forest‐dwelling avian species that represent diverse ecological (specialist–generalist) and behavioural (migratory‐resident) backgrounds. We tested the effects of organismal traits on population divergence and community assembly in the Caucasus forest, a continental mountain island setting. We found that (i) there is no concordance in divergence times between the Caucasus forest bird populations and their European counterparts, (ii) habitat specialists tend to be more divergent than generalists and (iii) residents tend to be more divergent than migrants. Thus, specialists and residents contribute to the high level of endemism of Caucasus forest avifauna more than do generalists and migrants. Patterns of genetic differentiation are better explained by differences in effective population sizes, an often overlooked factor in comparative studies of phylogeography and speciation, than by divergence times or levels of gene flow. Our results suggest that the Caucasus forest avifauna was assembled through time via dispersal and/or multiple vicariant events, rather than originating simultaneously via a single isolation event. Our study is one of the first multilocus, multispecies analyses revealing how ecological and migratory traits impact the evolutionary history of community formation on a continental island.

    

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