Defining evolutionary boundaries across parapatric ecomorphs of Black Salamanders (Aneides flavipunctatus) with conservation implications

Genome Evolution and the Future of Phylogenomics of Non-Avian Reptiles

Non-avian reptiles comprise a large proportion of amniote vertebrate diversity, with squamate reptiles-lizards and snakes-recently overtaking birds as the most species-rich tetrapod radiation. Despite displaying an extraordinary diversity of phenotypic and genomic traits, genomic resources in non-avian reptiles have accumulated more slowly than they have in mammals and birds, the remaining amniotes. Here we review the remarkable natural history of non-avian reptiles, with a focus on the physical traits, genomic characteristics, and sequence compositional patterns that comprise key axes of variation across amniotes. We argue that the high evolutionary diversity of non-avian reptiles can fuel a new generation of whole-genome phylogenomic analyses. A survey of phylogenetic investigations in non-avian reptiles shows that sequence capture-based approaches are the most commonly used, with studies of markers known as ultraconserved elements (UCEs) especially well represented. However, many other types of markers exist and are increasingly being mined from genome assemblies in silico, including some with greater information potential than UCEs for certain investigations. We discuss the importance of high-quality genomic resources and methods for bioinformatically extracting a range of marker sets from genome assemblies. Finally, we encourage herpetologists working in genomics, genetics, evolutionary biology, and other fields to work collectively towards building genomic resources for non-avian reptiles, especially squamates, that rival those already in place for mammals and birds. Overall, the development of this cross-amniote phylogenomic tree of life will contribute to illuminate interesting dimensions of biodiversity across non-avian reptiles and broader amniotes.

Taxonomic revision of black salamanders of theAneides flavipunctatuscomplex (Caudata: Plethodontidae)

We present a taxonomic revision of the black salamander (Aneides flavipunctatus) complex of northwestern California and extreme southeastern Oregon. The revision is based on a number of published works as well as new molecular and morphological data presented herein. The subspecies Aneides flavipunctatus niger Myers & Maslin 1948 is raised in rank to a full species. It is isolated far to the south of the main range on the San Francisco Peninsula, south and west of San Francisco Bay. Another geographically isolated set of populations occurs well inland in Shasta County, northern CA, mainly in the vicinity of Shasta Lake. It is raised from synonymy and recognized as Aneides iecanus (Cope 1883). The remaining taxa occur mainly along and inland from the coast from the vicinity of the Russian River and Lake Berryessa/Putah Creek, north to the vicinity of the Smith River near the Oregon border and more inland along the Klamath and Trinity Rivers and tributaries into Oregon. The northern segment of this nearly continuous range is named Aneides klamathensis Reilly and Wake 2019. We use molecular data to provide a detailed examination of a narrow contact zone between the northern A. klamathensis and the more southern A. flavipunctatus in southern Humboldt County in the vicinity of the Van Duzen and main fork of the Eel rivers. To the south is the remnant of the former species and it takes the name Aneides flavipunctatus (Strauch 1870). It is highly diversified morphologically and genetically and requires additional study.

In silico phylogenomics using complete genomes: a case study on the evolution of hominoids

The increasing availability of complete genome data is facilitating the acquisition of phylogenomic data sets, but the process of obtaining orthologous sequences from other genomes and assembling multiple sequence alignments remains piecemeal and arduous. We designed software that performs these tasks and outputs anonymous loci (AL) or anchored enrichment/ultraconserved element loci (AE/UCE) data sets in ready-to-analyze formats. We demonstrate our program by applying it to the hominoids. Starting with human, chimpanzee, gorilla, and orangutan genomes, our software generated an exhaustive data set of 292 ALs (∼1 kb each) in ∼3 h. Not only did analyses of our AL data set validate the program by yielding a portrait of hominoid evolution in agreement with previous studies, but the accuracy and precision of our estimated ancestral effective population sizes and speciation times represent improvements. We also used our program with a published set of 512 vertebrate-wide AE "probe" sequences to generate data sets consisting of 171 and 242 independent loci (∼1 kb each) in 11 and 13 min, respectively. The former data set consisted of flanking sequences 500 bp from adjacent AEs, while the latter contained sequences bordering AEs. Although our AE data sets produced the expected hominoid species tree, coalescent-based estimates of ancestral population sizes and speciation times based on these data were considerably lower than estimates from our AL data set and previous studies. Accordingly, we suggest that loci subjected to direct or indirect selection may not be appropriate for coalescent-based methods. Complete in silico approaches, combined with the burgeoning genome databases, will accelerate the pace of phylogenomics.

Long-term demographic decline and late glacial divergence in a Californian paleoendemic: Sequoiadendron giganteum (giant sequoia)

Mediterranean ecosystems comprise a high proportion of endemic taxa whose response to climate change will depend on their evolutionary origins. In the California flora, relatively little attention has been given to the evolutionary history of paleoendemics from a molecular perspective, yet they number among some of the world's most iconic plant species. Here, we address questions of demographic change in Sequoiadendron giganteum (giant sequoia) that is restricted to a narrow belt of groves in the Sierra Nevada Mountains. We ask whether the current distribution is a result of northward colonization since the last glacial maximum (LGM), restriction of a broader range in the recent past (LGM) or independent colonizations in the deeper past. Genetic diversity at eleven microsatellite loci decreased with increasing latitude, but partial regressions suggested this was a function of smaller population sizes in the north. Disjunct populations north of the Kings River were divergent from those south of the Kings River that formed a single cluster in Bayesian assignment tests. Demographic inferences supported a demographic contraction just prior to the LGM as the most likely scenario for the current disjunct range of the species. This contraction appeared to be superimposed upon a long‐term decline in giant sequoia over the last 2 million years, associated with increasing aridity due to the Mediterranean climate. Overall, low genetic diversity, together with competition in an environment to which giant sequoia is likely already poorly adapted, will pose major constraints on its success in the face of increasing aridity.

DNA barcoding reveals species level divergence between populations of the microhylid frog genus Arcovomer (Anura: Microhylidae) in the Atlantic Rainforest of southeastern Brazil

The microhylid frogs belonging to the genus Arcovomer have been reported from lowland Atlantic Rainforest in the Brazilian states of Espírito Santo, Rio de Janeiro, and São Paulo. Here, we use DNA barcoding to assess levels of genetic divergence between apparently isolated populations in Espírito Santo and Rio de Janeiro. Our mtDNA data consisting of cytochrome oxidase subunit I (COI) nucleotide sequences reveals 13.2% uncorrected and 30.4% TIM2 + I + Γ corrected genetic divergences between these two populations. This level of divergence exceeds the suggested 10% uncorrected divergence threshold for elevating amphibian populations to candidate species using this marker, which implies that the Espírito Santo population is a species distinct from Arcovomer passarellii. Calibration of our model-corrected sequence divergence estimates suggests that the time of population divergence falls between 12 and 29 million years ago.

Speciation, population structure, and demographic history of the Mojave Fringe-toed Lizard (Uma scoparia), a species of conservation concern

The North American deserts were impacted by both Neogene plate tectonics and Quaternary climatic fluctuations, yet it remains unclear how these events influenced speciation in this region. We tested published hypotheses regarding the timing and mode of speciation, population structure, and demographic history of the Mojave Fringe-toed Lizard (Uma scoparia), a sand dune specialist endemic to the Mojave Desert of California and Arizona. We sampled 109 individual lizards representing 22 insular dune localities, obtained DNA sequences for 14 nuclear loci, and found that U. scoparia has low genetic diversity relative to the U. notata species complex, comparable to that of chimpanzees and southern elephant seals. Analyses of genotypes using Bayesian clustering algorithms did not identify discrete populations within U. scoparia. Using isolation-with-migration (IM) models and a novel coalescent-based hypothesis testing approach, we estimated that U. scoparia diverged from U. notata in the Pleistocene epoch. The likelihood ratio test and the Akaike Information Criterion consistently rejected nested speciation models that included parameters for migration and population growth of U. scoparia. We reject the Neogene vicariance hypothesis for the speciation of U. scoparia and define this species as a single evolutionarily significant unit for conservation purposes.

Fuzzy boundaries: color and gene flow patterns among parapatric lineages of the western shovel-nosed snake and taxonomic implication

Accurate delineation of lineage diversity is increasingly important, as species distributions are becoming more reduced and threatened. During the last century, the subspecies category was often used to denote phenotypic variation within a species range and to provide a framework for understanding lineage differentiation, often considered incipient speciation. While this category has largely fallen into disuse, previously recognized subspecies often serve as important units for conservation policy and management when other information is lacking. In this study, we evaluated phenotypic subspecies hypotheses within shovel-nosed snakes on the basis of genetic data and considered how evolutionary processes such as gene flow influenced possible incongruence between phenotypic and genetic patterns. We used both traditional phylogenetic and Bayesian clustering analyses to infer range-wide genetic structure and spatially explicit analyses to detect possible boundary locations of lineage contact. Multilocus analyses supported three historically isolated groups with low to moderate levels of contemporary gene exchange. Genetic data did not support phenotypic subspecies as exclusive groups, and we detected patterns of discordance in areas where three subspecies are presumed to be in contact. Based on genetic and phenotypic evidence, we suggested that species-level diversity is underestimated in this group and we proposed that two species be recognized, Chionactis occipitalis and C. annulata. In addition, we recommend retention of two subspecific designations within C. annulata (C. a. annulata and C. a. klauberi) that reflect regional shifts in both genetic and phenotypic variation within the species. Our results highlight the difficultly in validating taxonomic boundaries within lineages that are evolving under a time-dependent, continuous process.

Conservation phylogeography: does historical diversity contribute to regional vulnerability in European tree frogs (Hyla arborea)?

Documenting and preserving the genetic diversity of populations, which conditions their long-term survival, have become a major issue in conservation biology. The loss of diversity often documented in declining populations is usually assumed to result from human disturbances; however, historical biogeographic events, otherwise known to strongly impact diversity, are rarely considered in this context. We apply a multilocus phylogeographic study to investigate the late-Quaternary history of a tree frog (Hyla arborea) with declining populations in the northern and western part of its distribution range. Mitochondrial and nuclear polymorphisms reveal high genetic diversity in the Balkan Peninsula, with a spatial structure moulded by the last glaciations. While two of the main refugial lineages remained limited to the Balkans (Adriatic coast, southern Balkans), a third one expanded to recolonize Northern and Western Europe, loosing much of its diversity in the process. Our findings show that mobile and a priori homogeneous taxa may also display substructure within glacial refugia ('refugia within refugia') and emphasize the importance of the Balkans as a major European biodiversity centre. Moreover, the distribution of diversity roughly coincides with regional conservation situations, consistent with the idea that historically impoverished genetic diversity may interact with anthropogenic disturbances, and increase the vulnerability of populations. Phylogeographic models seem important to fully appreciate the risks of local declines and inform conservation strategies.

How to fail at species delimitation

Species delimitation is the act of identifying species-level biological diversity. In recent years, the field has witnessed a dramatic increase in the number of methods available for delimiting species. However, most recent investigations only utilize a handful (i.e. 2-3) of the available methods, often for unstated reasons. Because the parameter space that is potentially relevant to species delimitation far exceeds the parameterization of any existing method, a given method necessarily makes a number of simplifying assumptions, any one of which could be violated in a particular system. We suggest that researchers should apply a wide range of species delimitation analyses to their data and place their trust in delimitations that are congruent across methods. Incongruence across the results from different methods is evidence of either a difference in the power to detect cryptic lineages across one or more of the approaches used to delimit species and could indicate that assumptions of one or more of the methods have been violated. In either case, the inferences drawn from species delimitation studies should be conservative, for in most contexts it is better to fail to delimit species than it is to falsely delimit entities that do not represent actual evolutionary lineages.