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Abstract Understanding the processes that shape genetic diversity by either promoting or preventing population divergence can help identify geographic areas that either facilitate or limit gene flow. Furthermore, broadly distributed species allow us to understand how biogeographic and ecogeographic transitions affect gene flow. We investigated these processes using genomic data in the Northern Alligator Lizard (Elgaria coerulea), which is widely distributed in Western North America across diverse ecoregions (California Floristic Province and Pacific Northwest) and mountain ranges (Sierra Nevada, Coastal Ranges, and Cascades). We collected single-nucleotide polymorphism data from 120 samples of E. coerulea. Biogeographic analyses of squamate reptiles with similar distributions have identified several shared diversification patterns that provide testable predictions for E. coerulea, including deep genetic divisions in the Sierra Nevada, demographic stability of southern populations, and recent post-Pleistocene expansion into the Pacific Northwest. We use genomic data to test these predictions by estimating the structure, connectivity, and phylogenetic history of populations. At least 10 distinct populations are supported, with mixed-ancestry individuals situated at most population boundaries. A species tree analysis provides strong support for the early divergence of populations in the Sierra Nevada Mountains and recent diversification into the Pacific Northwest. Admixture and migration analyses detect gene flow among populations in the Lower Cascades and Northern California, and a spatial analysis of gene flow identified significant barriers to gene flow across both the Sierra Nevada and Coast Ranges. The distribution of genetic diversity in E. coerulea is uneven, patchy, and interconnected at population boundaries. The biogeographic patterns seen in E. coerulea are consistent with predictions from co-distributed species. 

Abstract Natural history collections are repositories of biodiversity specimens that provide critical infrastructure for studies of mammals. Over the past 3 decades, digitization of collections has opened up the temporal and spatial properties of specimens, stimulating new data sharing, use, and training across the biodiversity sciences. These digital records are the cornerstones of an “extended specimen network,” in which the diverse data derived from specimens become digital, linked, and openly accessible for science and policy. However, still missing from most digital occurrences of mammals are their morphological, reproductive, and life-history traits. Unlocking this information will advance mammalogy, establish richer faunal baselines in an era of rapid environmental change, and contextualize other types of specimen-derived information toward new knowledge and discovery. Here, we present the Ranges Digitization Network (Ranges), a community effort to digitize specimen-level traits from all terrestrial mammals of western North America, append them to digital records, publish them openly in community repositories, and make them interoperable with complimentary data streams. Ranges is a consortium of 23 institutions with an initial focus on non-marine mammal species (both native and introduced) occurring in western Canada, the western United States, and Mexico. The project will establish trait data standards and informatics workflows that can be extended to other regions, taxa, and traits. Reconnecting mammalogists, museum professionals, and researchers for a new era of collections digitization will catalyze advances in mammalogy and create a community-curated trait resource for training and engagement with global conservation initiatives. 

Research on plant-pollinator interactions requires a diversity of perspectives and approaches, and documenting changing pollinator-plant interactions due to declining insect diversity and climate change is especially challenging. Natural history collections are increasingly important for such research and can provide ecological information across broad spatial and temporal scales. Here, we describe novel approaches that integrate museum specimens from insect and plant collections with field observations to quantify pollen networks over large spatial and temporal gradients. We present methodological strategies for evaluating insect-pollen network parameters based on pollen collected from museum insect specimens. These methods provide insight into spatial and temporal variation in pollen-insect interactions and complement other approaches to studying pollination, such as pollinator observation networks and flower enclosure experiments. We present example data from butterfly pollen networks over the past century in the Great Basin Desert and Sierra Nevada Mountains, United States. Complementary to these approaches, we describe rapid pollen identification methods that can increase speed and accuracy of taxonomic determinations, using pollen grains collected from herbarium specimens. As an example, we describe a convolutional neural network (CNN) to automate identification of pollen. We extracted images of pollen grains from 21 common species from herbarium specimens at the University of Nevada Reno (RENO). The CNN model achieved exceptional accuracy of identification, with a correct classification rate of 98.8%. These and similar approaches can transform the way we estimate pollination network parameters and greatly change inferences from existing networks, which have exploded over the past few decades. These techniques also allow us to address critical ecological questions related to mutualistic networks, community ecology, and conservation biology. Museum collections remain a bountiful source of data for biodiversity science and understanding global change. 

Abstract Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co-occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of “trait remixing” in the geographic mosaic theory, the process by which non-adaptive forces dictate spatial variation in the interactions among species. 

Abstract Antagonistic coevolution between natural enemies can produce highly exaggerated traits, such as prey toxins and predator resistance. This reciprocal process of adaptation and counter‐adaptation may also open doors to other evolutionary novelties not directly involved in the phenotypic interface of coevolution. We tested the hypothesis that predator–prey coevolution coincided with the evolution of conspicuous coloration on resistant predators that retain prey toxins. In western North America, common garter snakes (Thamnophis sirtalis) have evolved extreme resistance to tetrodotoxin (TTX) in the coevolutionary arms race with their deadly prey, Pacific newts (Tarichaspp.). TTX‐resistant snakes can retain large amounts of ingested TTX, which could serve as a deterrent against the snakes' own predators if TTX toxicity and resistance are coupled with a conspicuous warning signal. We evaluated whether arms race escalation covaries with bright red coloration in snake populations across the geographic mosaic of coevolution. Snake colour variation departs from the neutral expectations of population genetic structure and covaries with escalating clines of newt TTX and snake resistance at two coevolutionary hotspots. In the Pacific Northwest, bright red coloration fits an expected pattern of an aposematic warning to avian predators: TTX‐resistant snakes that consume highly toxic newts also have relatively large, reddish‐orange dorsal blotches. Snake coloration also seems to have evolved with the arms race in California, but overall patterns are less intuitively consistent with aposematism. These results suggest that interactions with additional trophic levels can generate novel traits as a cascading consequence of arms race coevolution across the geographic mosaic. 

Abstract Classical theory suggests that parasites will exhibit higher fitness in sympatric relative to allopatric host populations (local adaptation). However, evidence for local adaptation in natural host–parasite systems is often equivocal, emphasizing the need for infection experiments conducted over realistic geographic scales and comparisons among species with varied life history traits. Here, we used infection experiments to test how two trematode (flatworm) species (Paralechriorchis syntomenteraandRibeiroia ondatrae) with differing dispersal abilities varied in the strength of local adaptation to their amphibian hosts. Both parasites have complex life cycles involving sequential transmission among aquatic snails, larval amphibians and vertebrate definitive hosts that control dispersal across the landscape. By experimentally pairing 26 host‐by‐parasite population infection combinations from across the western USA with analyses of host and parasite spatial genetic structure, we found that increasing geographic distance—and corresponding increases in host population genetic distance—reduced infection success forP. syntomentera, which is dispersed by snake definitive hosts. For the avian‐dispersedR. ondatrae, in contrast, the geographic distance between the parasite and host populations had no influence on infection success. Differences in local adaptation corresponded to parasite genetic structure; although populations ofP. syntomenteraexhibited ~10% mtDNA sequence divergence, those ofR. ondatraewere nearly identical (<0.5%), even across a 900 km range. Taken together, these results offer empirical evidence that high levels of dispersal can limit opportunities for parasites to adapt to local host populations. 

Abstract The Geographic Mosaic Theory of Coevolution predicts that coevolutionary arms races will vary over time and space because of the diverse ecological settings and population histories of interacting species across the landscape. Thus, understanding coevolution may require investigating broad sets of populations sampled across the range of the interaction. In addition, comparing coevolutionary dynamics between similar systems may reveal the importance of specific factors that structure coevolution.Here, we examine geographic patterns of prey traits and predator traits in the relatively unstudied interaction between the Sierra garter snake (Thamnophis couchii) and sympatric prey, the rough‐skinned newt (Taricha granulosa), Sierra newt (Ta. sierrae) and California newt (Ta. torosa). This system parallels, in space and phenotypes, a classic example of coevolution between predatory common garter snakes (Th. sirtalis) and their toxic newt prey exhibiting hotspots of newt tetrodotoxin (TTX) levels and matching snake TTX resistance.We quantified prey and predator traits from hundreds of individuals across their distributions, and functional trait matching at sympatric sites.We show strong regional patterns of trait covariation across the shared ranges ofTh. couchiiand newt prey. Traits differ significantly among localities, with lower newt TTX levels and snake TTX resistance at the northern latitudes, and higher TTX levels and snake resistance at southern latitudes. Newts and snakes in northern populations show the highest degree of functional trait matching despite possessing the least extreme traits. Conversely, newts and snakes in southern populations show the greatest mismatch despite possessing exaggerated traits, with some snakes so resistant to TTX they would be unaffected by any sympatric newt. Nevertheless, individual variation was substantial, and appears to offer the opportunity for continued reciprocal selection in most populations.Overall, the three species of newts appear to be engaged in a TTX‐mediated arms race withTh. couchii. These patterns are congruent with those seen between newts andTh. sirtalis, including the same latitudinal gradient in trait covariation, and the potential ‘escape’ from the arms race by snake predators. Such concordance in broad scale patterns across two distinct systems suggests common phenomena might structure geographic mosaics in similar ways.