Faster evolution of a premating reproductive barrier is not associated with faster speciation rates in New World passerine birds

Why are speciation rates so variable across the tree of life? One hypothesis is that this variation is explained by how rapidly reproductive barriers evolve. We tested this hypothesis by conducting a comparative study of the evolution of bird song, a premating barrier to reproduction. Speciation in birds is typically initiated when geographically isolated (allopatric) populations evolve reproductive barriers. We measured the strength of song as a premating barrier between closely related allopatric populations by conducting 2339 field experiments to measure song discrimination for 175 taxon pairs of allopatric or parapatric New World passerine birds, and estimated recent speciation rates from molecular phylogenies. We found evidence that song discrimination is indeed an important reproductive barrier: taxon pairs with high song discrimination in allopatry did not regularly interbreed in parapatry. However, evolutionary rates of song discrimination were not associated with recent speciation rates. Evolutionary rates of song discrimination were also unrelated to latitude or elevation, but species with innate song (suboscines) evolved song discrimination much faster than species with learned song (oscines). We conclude that song is a key premating reproductive barrier in birds, but faster evolution of this reproductive barrier between populations does not consistently result in faster diversification between species.

Phylogeographic analysis reveals an ancient East African origin of the human herpes simplexvirus 2 dispersal out-of-Africa.

Human herpes simplex virus 2 (HSV-2) is a globally ubiquitous, slow evolving DNA virus. HSV-2 genomic diversity can be divided into two main groups: an African lineage and worldwide lineage. Competing hypotheses have been put forth to explain the history of HSV-2. HSV-2 may have originated in Africa and then followed the first wave of human migration out of Africa between 50-100 kya. Alternatively, HSV-2 may have migrated out of Africa via the trans-Atlantic slave trade within the last 150-500 years. The lack of HSV-2 genomes from West and Central Africa, combined with a lack of molecular clock signal in HSV-2 has precluded robust testing of these competing hypotheses. Here, we expand the geographic sampling of HSV-2 genomes in order to resolve the geography and timing of divergence events within HSV-2. We analyze 65 newly sequenced HSV-2 genomes collected from primarily West and Central Africa along with 330 previously published genomes sampled over a 47-year period. Evolutionary simulations confirm that the molecular clock in HSV-2 is too slow to be detected using available data. However, phylogeographic analysis indicates that all biologically plausible evolutionary rates would place the ancestor of the worldwide lineage in East Africa, arguing against the trans-Atlantic slave trade as the source of worldwide diversity. The best supported evolutionary rates between 4.2x10-8 and 5.6x10-8 substitutions/site/year suggest a most recent common ancestor for HSV-2 around 90-120 kya and initial dispersal around 21.9-29.3 kya. These dates suggest HSV-2 left Africa during subsequent waves of human migration out of East Africa.

The evolution of sexual dichromatism in a large radiation of landfowls: re-examining the female-biased selection in Wallace's model

Sexual dichromatism, the colour difference between males and females, has been particularly important for studying the interplay between sexual and natural selection. However, previous studies on the evolutionary forces of sexual dichromatism examing the Darwin's and Wallace's model have produced mixed results. Phasianidae is a species-rich family with worldwide distribution, occupancy in nearly all terrestrial habitats, and a wide diversity of plumage patterns and colourations. Here, we use phylogenetic comparative methods to test the relationship between sexual dichromatism and colour complexity of males and females on both evolutionary direction and tempo including all species in Phasianidae. We show that the evolutionary direction of sexual dichromatism is negatively correlated with colour complexity in females but not males, and the evolutionary rates of sexual dichromatism are positively correlated with the evolutionary rates of colour complexity in both sexes. These results highlight the important role of female colour evolution in shaping sexual dichromatism in the pheasant family, and provide strong empirical supports for Wallace's hypothesis via a mosaic of sexual and natural selection in both sexes.

INTRAHOST EVOLUTION OF THE HIV-2 CAPSID CORRELATES WITH PROGRESSION TO AIDS

Background: HIV-2 infection will progress to AIDS in most patients without treatment, albeit at approximately half the rate of HIV-1 infection. HIV-2 p26 amino acid variations are associated with lower viral loads and enhanced processing of T cell epitopes, which may lead to protective Gag-specific CTL responses common in slower disease progressors. Lower virus evolutionary rates, and positive selection on conserved residues in HIV-2 env have been associated with slower progression to AIDS. We therefore aimed to determine if intrahost evolution of HIV-2 p26 is associated with disease progression. Methods: Twelve treatment-naive, HIV-2 mono-infected participants from the Guinea-Bissau Police cohort with longitudinal CD4+ T cell data and clinical follow-up were included in the analysis. CD4% change over time was analysed via linear regression models to stratify participants into relative faster and slower disease progressor groups. Gag amplicons of 735 nucleotides which spanned the p26 region were amplified by PCR and sequenced. We analysed p26 sequence diversity evolution, measured site-specific selection pressures and evolutionary rates, and determined if these evolutionary parameters were associated with progression status. Amino acid polymorphisms were mapped to existing p26 protein structures. Results: In total, 369 heterochronous HIV-2 p26 sequences from 12 male patients with a median age of 30 (IQR: 28-37) years at enrolment were analysed. Faster progressors had lower CD4% and faster CD4% decline rates. Median pairwise sequence diversity was higher in faster progressors (5.7x10-3 versus 1.4x10-3 base substitutions per site, P<0.001). p26 evolved under negative selection in both groups (dN/dS=0.12). Virus evolutionary rates were higher in faster than slower progressors - synonymous rates: 4.6x10-3 vs. 2.3x10-3; and nonsynonymous rates: 6.9x10-4 vs. 2.7x10-4 substitutions/site/year, respectively. Virus evolutionary rates correlated negatively with CD4% change rates (rho = -0.8, P=0.02), but not CD4% level. However, Bayes factor (BF) testing indicated that the association between evolutionary rates and CD4% kinetics was supported by weak evidence (BF=0.5). The signature amino acid at p26 positions 6, 12 and 119 differed between faster (6A, 12I, 119A) and slower (6G, 12V, 119P) progressors. These amino acid positions clustered near to the TRIM5 alpha/p26 hexamer interface surface. Conclusions: Faster p26 evolutionary rates were associated with faster progression to AIDS and were mostly driven by synonymous substitutions. Nonsynonymous evolutionary rates were an order of magnitude lower than synonymous rates, with limited amino acid sequence evolution over time within hosts. These results indicate the HIV-2 p26 may be an attractive vaccine or therapeutic target.

Macroevolutionary dynamics of climatic niche space

How and why lineages evolve along niche space as they diversify and adapt to different environments is fundamental to evolution. Progress has been hampered by the difficulties of linking a comprehensive empirical characterization of species niches with flexible evolutionary models that describe their evolution. Consequently, the relative influence of external episodic and biotic factors remains poorly understood. Here we characterize species' two-dimensional temperature and precipitation niche space occupied (i.e., species niche envelope) as complex geometries and assess their evolution across a large vertebrate radiation (all Aves) using a model that captures heterogeneous evolutionary rates on time-calibrated phylogenies. We find that extant birds coevolved from warm, mesic climatic niches into colder and drier environments and responded to the K-Pg boundary with a dramatic increase in disparity. Contrary to expectations of subsiding rates of niche evolution as lineages diversify, our results show that overall rates have increased steadily, with some lineages experiencing exceptionally high evolutionary rates, associated with colonization of novel niche spaces, and others showing niche stasis. Both competition- and environmental change-driven niche evolution transpire and result in highly heterogeneous rates near the present. Our findings share the limitations of all work based purely on extant taxa but highlight the growing ecological and conservation insights arising from the model-based integration of increasingly comprehensive and robust environmental and phylogenetic information.

De novo assembly of 20 chickens reveals the undetectable phenomenon for thousands of core genes on sub-telomeric regions

The gene numbers and evolutionary rates of birds were assumed to be much lower than that of mammals, which in sharp contrast to the huge species number and morphological diversity of birds. It is very necessary to construct a complete avian genome and analyze its evolution.We constructed a chicken pan-genome from 20 de novo genome assemblies with high sequencing depth, newly identified 1,335 protein-coding genes and 3,011 long noncoding RNAs. The majority of these novel genes were detected across most individuals of the examined transcriptomes but were accidentally measured in each of the DNA sequencing data regardless of Illumina or PacBio technology. Furthermore, different from previous pan-genome models, most of these novel genes were overrepresented on chromosomal sub-telomeric regions, surrounded with extremely high proportions of tandem repeats, and strongly blocked DNA sequencing. These hidden genes were proved to be shared by all chicken genomes, included many housekeeping genes, and enriched in immune pathways. Comparative genomics revealed the novel genes had three-fold elevated substitution rates than known ones, updating the evolutionary rates of birds. Our study provides a framework for constructing a better chicken genome, which will contribute towards the understanding of avian evolution and improvement of poultry breeding.

Organization and composition of apicomplexan kinetochores reveals plasticity in chromosome segregation across parasite modes of division

Kinetochores are multiprotein assemblies directing mitotic spindle attachment and chromosome segregation. In apicomplexan parasites, most known kinetochore components and associated regulators are apparently missing, suggesting a minimal structure with limited control over chromosome segregation. In this study, we use interactomics combined with deep homology searches to identify six divergent eukaryotic kinetochore proteins in apicomplexan parasites, in addition to a set of eight apicomplexan components (AKiTs) that bear no detectable sequence similarity to known proteins. The nanoscale organization of the apicomplexan kinetochore includes four subdomains, each displaying different evolutionary rates across the phylum. Functional analyses confirm AKiTs are essential for mitosis and reveal architectures parallel to biorientation at metaphase. Furthermore, we identify a homolog of MAD1 at the apicomplexan kinetochore, suggesting conserved spindle assembly checkpoint signaling. Finally, we show unexpected plasticity in kinetochore composition and segregation throughout the parasite lifecycle, indicating diverse requirements to maintain fidelity of chromosome segregation across apicomplexan modes of division.