Benjamin W. Stone, Alexander Ward, Max Farenwald, Andrew W. Lutz, Andrea D. Wolfe. Conserv. Genet. 2019. https://doi.org/10.1007/s10592-019-01204-1

Penstemon caryi is a narrow-range endemic angiosperm found primarily on sparsely vegetated limestone outcrops in the Bighorn and Pryor Mountains of north-central Wyoming and south-central Montana. A former candidate for listing under the Endangered Species Act, and currently a species of concern in these states, P. caryi is potentially threatened by habitat loss due to encroaching anthropogenic activities, such as limestone quarrying and road construction. In an effort to assess the capacity of P. caryi to withstand habitat loss and degradation, we used simple sequence repeats (SSRs) and amplified fragment length polymorphism (AFLP) markers to examine genetic diversity and differentiation of P. caryi populations from the Pryor Mountains of Montana and the southern Bighorn Mountains of Wyoming. Our analyses revealed overall moderate to high levels of genetic diversity in P. caryi, but with relatively lower levels of diversity in populations from the Pryor Mountains. There are fewer known individuals of Penstemon caryi in Montana, and because the examined populations from Montana exhibited less genetic diversity than those from Wyoming, populations from Montana may face an increased risk of population decline and extirpation. Both the AFLP and SSR data sets found population structure between different regions (Montana vs. Wyoming), while AFLP markers identified further subdivision between Wyoming populations. Despite moderate to high levels of genetic diversity, P. caryi is still a species at risk due to impending environmental stresses such as global climate change and human encroachment, which may be especially troublesome given its narrow distribution and the specificity of its habitat preferences.

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Genomic signatures of sympatric speciation with historical and contemporary gene flow in a tropical anthozoan (Hexacorallia: Actiniaria)

Benjamin M. Titus, Paul D. Blischak, Marymegan Daly. 2019. Molecular Ecology. https://doi.org/10.1111/mec.15157

Sympatric diversification is recognized to have played an important role in the evolution of biodiversity. However, an in situ sympatric origin for co‐distributed taxa is difficult to demonstrate because different evolutionary processes can lead to similar biogeographic outcomes, especially in ecosystems that can readily facilitate secondary contact due to a lack of hard barriers to dispersal. Here we use a genomic (ddRADseq), model‐based approach to delimit a species complex of tropical sea anemones that are co‐distributed on coral reefs throughout the Tropical Western Atlantic. We use coalescent simulations in fastsimcoal2 and ordinary differential equations in Moments to test competing diversification scenarios that span the allopatric‐sympatric continuum. Our results suggest that the corkscrew sea anemone Bartholomea annulata (Le Sueur, 1817) is a cryptic species complex whose members are co‐distributed throughout their range. Simulation and model selection analyses from both approaches suggest these lineages experienced historical and contemporary gene flow, supporting a sympatric origin, but an alternative secondary contact model receives appreciable model support in fastsimcoal2. Leveraging the genome of the closely related Exaiptasia diaphana, we identify five loci under divergent selection between cryptic B. annulata lineages that fall within mRNA transcripts or CDS regions. Our study provides a rare empirical, genomic example of sympatric speciation in a tropical anthozoan and the first range‐wide molecular study of a tropical sea anemone, underscoring that anemone diversity is under‐described in the tropics, and highlighting the need for additional systematic studies into these ecologically and economically important species.

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Contributions of autochthonous, allochthonous, and aged carbon and organic matter to macroinvertebrate nutrition in the Susquehanna River basin

Amber R. Bellamy, James E. Bauer, and Andrea G. Grottoli. 2019. Freshwater Science
Volume 38, Number 3

Abstract

Previous research suggests that rivers transport large amounts of aged allochthonous material, but it is unclear how much of this material contributes nutritionally to macroinvertebrate biomass. Furthermore, little research has investigated allochthonous vs autochthonous nutritional resource use by macroinvertebrates in the tributaries and low-order streams of major river systems. The primary goal of this study was to quantify both the sources and ages of organic matter (OM) that contributes to the nutrition of stream macroinvertebrates in different functional feeding groups (FFGs). We used natural abundance stable (δ13C, δ15N, and δ2H) and radiogenic (Δ14C) isotopes to assess resource use in a network of 7 subwatershed streams in the Susquehanna River basin. Isotope mixing models revealed that autochthonous OM contributed as much as 80% of macroinvertebrate biomass for scraper, filtering collector, and collector–gatherer FFGs, whereas allochthonous sources contributed much less (6–44%) to macroinvertebrate biomass of these FFGs. However, allochthonous OM contributed up to 73% of shredder FFG biomass. Contributions of aged (ranging from 75–11,700 y B.P.) OM to macroinvertebrate biomass varied by macroinvertebrate group. Chironomids assimilated the most aged OM (43%) of any macroinvertebrate group, most of which was from soil and sediment sources. We also found that macroinvertebrates in a stream with active methane seepage had the oldest C in their tissues of the streams in this study (5600–4200 y B.P.), which was probably a result of the macroinvertebrates consuming C derived from this methane seep. Our findings show that the sources and ages of OM assimilated by macroinvertebrates largely varied as a function of FFG and that these differences probably resulted from FFG habitats and diet preferences, as well as the presence or absence of ancient forms of C in streams.

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Divergence of tropical pitvipers promoted by independent colonization events of dry montane Andean habitats

David Salazar‐Valenzuela, Ulrich Kuch, Omar Torres‐Carvajal, Jorge H. Valencia, H. Lisle Gibbs. 2019. Journal of Biogeography. https://doi.org/10.1111/jbi.13661

Abstract

A poorly explored feature of the origin and maintenance of Neotropical biodiversity is how the evolutionary dynamics of colonization and differentiation in relation to lowland and highland habitats has impacted lineage formation. Most speciation models for this region have focused on vicariant events, whereas the need to assess the influence of demographic processes has been recognized only recently. We evaluate if the origin of Andean montane lineages of terciopelo pitvipers is explained by either of two historical processes that represent distinct phylogeographic mechanisms: differentiation by isolation within the highlands or different dispersal events from the lowlands. We use genomic data and genetic clustering analyses, evaluation of historical migration between genetic clusters and demographic model selection to investigate recent diversification events in South America using a vertebrate group rarely explored in phylogeographic studies: tropical Andean snakes. Specifically, the origin of two Ecuadorian montane lineages of terciopelo pitvipers was evaluated given ambiguous phylogenetic relationships with the presumably ancestral Pacific lowland lineage.