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Species with extensive geographical ranges pose special challenges to assessing drivers of wildlife disease, necessitating collaborative and large-scale analyses. The imperilled foothill yellow-legged frog ( Rana boylii ) inhabits a wide geographical range and variable conditions in rivers of California and Oregon (USA), and is considered threatened by the pathogen Batrachochytrium dendrobatidis (Bd). To assess drivers of Bd infections over time and space, we compiled over 2000 datapoints from R. boylii museum specimens (collected 1897-2005) and field samples (2005-2021) spanning 9° of latitude. We observed a south-to-north spread of Bd detections beginning in the 1940s and increase in prevalence from the 1940s to 1970s, coinciding with extirpation from southern latitudes. We detected eight high-prevalence geographical clusters through time that span the species' geographical range. Field-sampled male R. boylii exhibited the highest prevalence, and juveniles sampled in autumn exhibited the highest loads. Bd infection risk was highest in lower elevation rain-dominated watersheds, and with cool temperatures and low stream-flow conditions at the end of the dry season. Through a holistic assessment of relationships between infection risk, geographical context and time, we identify the locations and time periods where Bd mitigation and monitoring will be critical for conservation of this imperilled species., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

Stream temperature science and management is rapidly shifting from single-metric driven approaches to multi-metric, thermal regime characterizations of streamscapes. Given considerable investments in recovery of cold-water fisheries (e.g., Pacific salmon and other declining native species), understanding where cold water is likely to persist, and how cold-water thermal regimes vary, is critical for conservation. California's unique position at the southern end of cold-water ecosystems in the northern hemisphere, variable geography and hydrology, and extensive flow regulation requires a systematic approach to thermal regime classification. We used publicly available, long-term (> 8 years) stream temperature data from 77 sites across California to model their thermal regimes, calculate three temperature metrics, and use the metrics to classify each regime with an agglomerative nesting algorithm. Then, we assessed the variation in each class and considered underlying physical or anthropogenic factors that could explain differences between classes. Finally, we considered how different classes might fit existing criteria for cool- or cold-water thermal regimes, and how those differences complicate efforts to manage stream temperature through regulation. Our results demonstrate that cool- and cold-water thermal regimes vary spatially across California. Several salient findings emerge from this study. Groundwater-dominated streams are a ubiquitous, but as yet, poorly explored class of thermal regimes. Further, flow regulation below dams imposes serial discontinuities, including artificial thermal regimes on downstream ecosystems. Finally, and contrary to what is often assumed, California reservoirs do not contain sufficient cold-water storage to replicate desirable, reach-scale thermal regimes. While barriers to cold-water conservation are considerable and the trajectory of cold-water species towards extinction is dire, protecting reaches that demonstrate resilience to climate warming remains worthwhile., Competing Interests: The authors have declared that no competing interests exist.

Contact zones between species provide a unique opportunity to test whether taxa can hybridize or not. Cross-breeding or hybridization between closely related taxa can promote gene flow (introgression) between species, adaptation, or even speciation. Though hybridization events may be short-lived and difficult to detect in the field, genetic data can provide information about the level of introgression between closely related taxa. Hybridization can promote introgression between species, which may be an important evolutionary mechanism for either homogenization (reversing initial divergence between species) or reproductive isolation (potentially leading to speciation). Here, we used thousands of genetic markers from nuclear DNA to detect hybridization between two parapatric frog species (Rana boylii and Rana sierrae) in the Sierra Nevada of California. Based on principal components analysis, admixture, and analysis of heterozygosity at species diagnostic SNPs, we detected two F1 hybrid individuals in the Feather River basin, as well as a weak signal of introgression and gene flow between the frog species compared with frog populations from two other adjacent watersheds. This study provides the first documentation of hybridization and introgression between these two species, which are of conservation concern., (© 2019 John Wiley & Sons Ltd.)

For Helicobacter pylori, the hsp60 heat shock protein encoded by hspB is being considered as a potential candidate for subunit vaccines. We investigated the humoral and cellular responses to H. pylori hsp60 and its cross-reactivity with the homologous Mycobacterium bovis p65 protein and autologous human hsp60 protein. H. pylori-infected persons had significantly higher levels than uninfected persons of serum immunoglobulin G antibodies recognizing H. pylori hsp60, but not M. bovis p65 or human hsp60, as determined by enzyme-linked immunosorbent assay. In contrast, immunoblotting demonstrated cross-reactivity of H. pylori hsp60 with human hsp60. T-cell recognition of H. pylori hsp60 was found in both infected and uninfected subjects, and there was no recognition of human hsp60. T cells from infected and uninfected subjects that had been activated in response to H. pylori hsp60 or M. bovis p65 were phenotypically similar but appeared to secrete different levels of gamma interferon and interleukin-10. These results demonstrate an apparent difference in the epitopes recognized by the T and B cells responding to H. pylori hsp60 in H. pylori-infected persons. In contrast to the T-cell responses, which were highly variable in all subjects and showed no recognition of autologous proteins, a specific B-cell response that may have cross-reactivity to human hsp60 is evident in some infected subjects.