Genetic, bioacoustic and morphological analyses reveal cryptic speciation in the warbling vireo complex (Vireo gilvus: Vireonidae: Passeriformes)

Cryptic species are closely related taxa that are difficult to separate morphologically, but are reproductively isolated. Here we examine the warbling vireo complex (Vireo gilvus), a widespread songbird speculated to be comprised of more than one cryptic species. We included three taxa within the complex: two of the western (Vireo gilvus swainsonii and Vireo gilvus brewsteri) subspecies and the single eastern (Vireo gilvus gilvus) subspecies. We used mtDNA and microsatellite loci to assess the congruence of genetic data to the current subspecies boundaries. We then incorporated bioacoustic, morphometric and ecological niche modelling analyses to further examine differences. We found two genetic groups with mtDNA analysis, splitting eastern and western warbling vireos. Microsatellite analyses revealed four genetic groups: an eastern group, a Black Hills group and two western groups that do not agree with current western subspecies boundaries based on phenotypic data. Our results suggest that eastern and western warbling vireos have been reproductively isolated for a long period of time and therefore may be best treated as separate species. However, more research into areas of contact to examine the presence of hybridization is advised before making a taxonomic revision. Differences between the two western genetic groups appear less clear, requiring additional research.

Characterization of the gut microbiome in wild rocky mountainsnails (Oreohelix strigosa)

Background

The Rocky Mountainsnail (Oreohelix strigosa) is a terrestrial gastropod of ecological importance in the Rocky Mountains of western United States and Canada. Across the animal kingdom, including in gastropods, gut microbiomes have profound effects on the health of the host. Current knowledge regarding snail gut microbiomes, particularly throughout various life history stages, is limited. Understanding snail gut microbiome composition and dynamics can provide an initial step toward better conservation and management of this species.

Results

In this study, we employed 16S rRNA gene amplicon sequencing to examine gut bacteria communities in wild-caught O. strigosa populations from the Front Range of Colorado. These included three treatment groups: (1) adult and (2) fetal snails, as well as (3) sub-populations of adult snails that were starved prior to ethanol fixation. Overall, O. strigosa harbors a high diversity of bacteria. We sequenced the V4 region of the 16S rRNA gene on an Illumina MiSeq and obtained 2,714,330 total reads. We identified a total of 7056 unique operational taxonomic units (OTUs) belonging to 36 phyla. The core gut microbiome of four unique OTUs accounts for roughly half of all sequencing reads returned and may aid the snails’ digestive processes. Significant differences in microbial composition, as well as richness, evenness, and Shannon Indices were found across the three treatment groups.

Conclusions

Comparisons of gut microbiomes in O. strigosa adult, fetal, and starved samples provide evidence that the host internal environments influence bacterial community compositions, and that bacteria may be transmitted vertically from parent to offspring. This work provides the first comprehensive report on the structure and membership of bacterial populations in the gastropod family Oreohelicidae and reveals similarities and differences across varying life history metrics. Strong differentiation between these life history metrics demonstrates the need for wider sampling for studies of dynamics of the snail gut microbiome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00111-6.

Comparative phylogeography of two Northern Rocky Mountain endemics: the widespread Anguispira kochi occidentalis and the narrow-range Anguispira nimapuna (Gastropoda: Discidae)

The Northern Rocky Mountain ecosystem supports rich biological diversity with many endemic and rare species. Extant endemics display two biogeographic patterns: widespread species with fragmented populations, and narrow-range endemics. These distributions are shown by the congeneric snails Anguispira kochi occidentalis and Anguispira nimapuna. These two taxa are disjunct from the remaining species of the genus, which achieves its greatest diversity in eastern North America. Given the disjunct nature of A. k. occidentalis and A. nimapuna, we here present a mtDNA phylogeny of the genus that includes both eastern and western species to assess the phylogenetic position of A. k. occidentalis and A. nimapuna. We then reconstruct the demographic history of A. k. occidentalis and A. nimapuna by analysing current patterns of genetic variation and interpreting the results considering the historical biogeography of the region. Both A. k. occidentalis and A. nimapuna represent unique taxa that are genetically and geographically distinct from their congeners. The current distribution and genetic structure of A. k. occidentalis has been shaped by both historical isolation in refugia and more recent northward shifts, whereas A. nimapuna is represented by two populations with shallow divergence in an area of long-term habitat stability.

Living on the edge: comparative phylogeography and phylogenetics of Oreohelix land snails at their range edge in Western Canada

BACKGROUND

The biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range.

RESULTS

We found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three genetic clusters, of which one was O. cooperi. Cluster 1 contained most individuals in COI clade X and some from clade B and cluster 2 was predominantly made up of individuals from COI clades B and B' and a few from clade X. ITS2 alleles were shared in a narrow contact zone between two COI clades, suggestive of hybridization between the two.

CONCLUSIONS

A sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.