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The passerine superfamily Certhioidea lacks a complete phylogeny despite decades of recognition as a clade and extensive systematic work within all its constituent families. Here, we inferred a near-complete species-level phylogeny of Certhioidea from a molecular supermatrix, including the first comprehensive sampling of the wrens (Troglodytidae), and used this phylogeny to infer its biogeographic and diversification histories. We also inferred an expanded phylogeny including nearly 100 putative phylospecies previously documented in the literature, and we found that including this diversity had notable impacts on the inferred evolutionary history of Certhioidea. This phylospecies-level tree documented a few instances of species paraphyly, some previously described in the literature and some novel. We found that Certhioidea originated largely in Eurasia and dispersed into North America five times in the last 20 million years, including at the origin of the "New World certhioids," wrens and gnatcatchers, a clade herein named Orthourae. After this initial dispersal event, both wrens and gnatcatchers diversified extensively across the hemisphere, with both lineages repeatedly crossing between continents. However, we detected no notable impact of the formation of the Isthmus of Panama on the frequency of dispersal events between North and South America. The inclusion of phylospecies altered this biogeographic inference in some portions of the tree but overall was largely consistent. With species-level sampling, we found that diversification rates within Certhioidea were largely constant through time with a detectable deceleration toward the present. By contrast, phylospecies-level sampling recovered a different diversification history with a significant rate increase at the crown node of Orthourae after dispersing into the Americas and increased speciation rates particularly within the genera Polioptila and Henicorhina. This largely resolved phylogeny for Certhioidea has yielded important insights into the evolutionary history of this group and provides a framework for future comparative work on this fascinating clade. [ABSTRACT FROM AUTHOR]

Island biotas have become paradigms for illustrating many evolutionary processes. The fauna of the Galapagos Islands includes several taxa that have been focal points for evolutionary studies. Perhaps their most famous inhabitants, Darwin's finches, represent a go-to icon when thinking about how species originate and adapt to the environment. However, unlike other adaptive radiations, past morphological and molecular studies of Darwin's finches have yielded inconsistent hypotheses of species limits and phylogenetic relationships. Expecting that idiosyncrasies of prior data and analytic methods explained different proposed classifications, we were surprised to observe that three new phylogenetic hypotheses derived mostly from the same genomics data were topologically inconsistent. We found that the differences between some of these genomics trees were as great as one would expect between two random trees with the same number of taxa. Thus, the phylogeny of Darwin's finches remains unresolved, as it has for more than a century. A component of phylogenetic uncertainty comes from unclear species limits, under any species concept, in the ground finches (Geospiza) and tree finches (Camarhynchus). We suggest that past authors should have tested the species limits of Lack, rather than uncritically accepting them. In fact, the impressive amount of genomics data do not provide unambiguous hypotheses of the number of species of Geospiza or Camarhynchus, although they imply greater species diversity than Lack's taxonomy. We suggest that insufficient sampling of species populations across islands (35.6% for morphometrics and 20.4% for genomics) prevents accurate diagnoses of species limits. However, it is unknown whether samples from a greater number of islands might result in bridging differences between species, or reveal many new ones. We conclude that attempts to interpret patterns of variation among the finches under standard evolutionary paradigms have obscured some major messages, most specifically the ongoing reciprocal interactions between geographic isolation and lineage divergence, and dispersal and gene flow caused by the volatile ecological conditions in the islands. Although the finches provide textbook examples of natural selection, better understanding of species limits and a robust phylogenetic hypothesis are required to corroborate past hypotheses of speciation and adaptive radiation in the finches of the Galapagos. [ABSTRACT FROM AUTHOR]

High-quality RNA is an important precursor for high-throughput RNA sequencing (RNAseq) and subsequent analyses. However, the primary metric used to assess RNA quality, the RNA Integrity Number (RIN), was developed based on model bacterial and vertebrate organisms. Though the phenomenon is not widely recognized, invertebrate 28S ribosomal RNA (rRNA) is highly prone to a form of denaturation known as gap deletion, in which the subunit collapses into two smaller fragments. In many nonmodel invertebrates, this collapse of the 28S subunit appears as a single band similar in size to the 18S rRNA subunit. This phenomenon is hypothesized to be commonplace among arthropods and is often misinterpreted as a “degraded" rRNA profile. The limited characterization of gap deletion in arthropods, a highly diverse group, as well as other nonmodel invertebrates, often biases RNA quality assessments. To test whether the collapse of 28S is a general pattern or a methodological artifact, we sampled more than half of the major lineages within Arthropoda. We found that the 28S collapse is present in ~90% of the species sampled. Nevertheless, RNA profiles exhibit considerable diversity with a range of banding patterns. High-throughput RNAseq and subsequent assembly of high-quality transcriptomes from select arthropod species exhibiting collapsed 28S subunits further illustrates the limitations of current RIN proxies in accurately characterizing RNA quality in nonmodel organisms. Furthermore, we show that this form of 28S denaturation, which is often mistaken for true “degradation," can occur at relatively low temperatures. [ABSTRACT FROM AUTHOR]