Phylogeography and Genetic Structure in the California Giant Salamander (Dicamptodon ensatus): Impacts of current and historic landscape features

The California Floristic Province contains numerous ecological regions and a complex geological and geographical history that make it one of the worlds biodiversity hotspots. A number of wide-ranging taxa span across these regions and show complex patterns of dispersal, vicariance and lineage diversification, making localized small ranged species with lower levels of vagility essential to understanding the overall region. Here, we investigate the biogeography and population structure of the California Giant Salamander (Dicamptodon ensatus) (Eschscholtz 1833), an endemic species localized to a narrow coastal region between two areas of biological significance in the California Floristic Province, the North Coast Divide and Monterey Bay. We sequenced one mtDNA fragment (control region) for 133 individuals and a subset of 38 individuals for the anonymous nuclear locus E16C7. We analyzed these sequences with phylogenetic, coalescent, Bayesian clustering, and population genetic approaches in order to infer population structure, phylogenetic structure, and biogeographic history. Additionally, we examined occurrence data with species distribution modeling to generate a habitat suitability map to aid our interpretation of geographic structure. Our analyses recovered 4 major mtDNA lineages, two of which are combined into 3 major lineages when nuDNA is examined. These 3 major lineages are bounded by 4 major current or past geological features; the North Coast Divide, the former Wilson Grove Embayment/current Petaluma Gap, San Francisco Bay, and Monterey Bay. Other low-vagility species linked to moist microclimates and forest habitat do share similarities with the genetic patterns of D. ensatus hinting at a larger role for the past Wilson Grove embayment and modern Petaluma Gap in California biogeography.

Ancient introgression between distantly related white oaks (Quercus sect Quercus) shows evidence of climate-associated asymmetric gene exchange

Ancient introgression can be an important source of genetic variation that shapes the evolution and diversification of many taxa. Here, we estimate the timing, direction and extent of gene flow between two distantly related oak species in the same section (Quercus sect. Quercus). We estimated these demographic events using genotyping by sequencing data (GBS), which generated 25,702 single nucleotide polymorphisms (SNPs) for 24 individuals of California scrub oak (Quercus berberidifolia) and 23 individuals of Engelmann oak (Q. engelmannii). We tested several scenarios involving gene flow between these species using the diffusion approximation-based population genetic inference framework and model-testing approach of the Python package DaDi. We found that the most likely demographic scenario includes a bottleneck in Q. engelmannii that coincides with asymmetric gene flow from Q. berberidifolia into Q. engelmannii. Given that the timing of this gene flow coincides with the advent of a Mediterranean-type climate in the California Floristic Province, we propose that changing precipitation patterns and seasonality may have favored the introgression of climate-associated genes from the endemic into the non-endemic California oak.

Thirteen new weeds on Cedros Island, Baja California, Mexico

Background and Aims: Cedros Island is the southernmost outpost of the California Floristic Province, the largest island in the Californian archipelago, and home to a suite of endemic plants and animals. As such, it is an important resource within the Pacific Islands Biosphere Reserve, with many management concerns. The goal of this study was to document newly arrived plant species on Cedros Island, Baja California, Mexico.Methods: From the 8th to the 11th February 2019 we visited Cedros Island and made observations of plants around Cedros Village using the platform NaturaLista (iNaturalist).Key results: Thirteen new plant taxa were detected around Cedros village, all were non-native. These discoveries follow a very recently published checklist on the flora and suggest that new non-native plants are arriving rapidly. Conclusions: Recommended management implications include monitoring and eradication of new species, particularly at inhabited areas, and with priority given to highly invasive species such as Cenchrus setaceus and C. ciliaris.