Congruence between nuclear and mitochondrial DNA: Combination of multiple nuclear introns resolves a well-supported phylogeny of New World orioles (Icterus)

Demographic responses of forest-utilizing bats to past climate change in South Africa

Historical forest contractions may have restricted the distributions of forest-utilizing fauna while providing opportunities for range expansions for open-habitat species. We aimed to test if habitat associations have played an important role in determining population genetic structure and demographic responses of six bats to oscillations in forest extent since the Last Glacial Maximum (LGM). We hypothesized that forest-associated species would display high levels of population structure and past population contractions as their distribution is dependent on fragmented forests. By contrast, habitat generalists would demonstrate low geographical structuring and historical population stability as suitable habitats are widely available. We used mitochondrial DNA to generate genetic diversity and population structure metrics of three forest-associated species and three habitat generalists in South Africa. Neutrality tests and Bayesian skyline plots were used to investigate demographic histories. A forest habitat association did not inform the population genetics of the study species. Rather, species-specific traits of roosting requirements, philopatry to the natal range and dispersal ability informed the observed structure. All species demonstrated population expansions during the Pleistocene, with no apparent decline during the LGM. It appears that the lower climate change footprint and refuge-status of eastern South Africa prevented population declines of insectivorous bats during the LGM.

Phylogeny, evolution and mitochondrial gene order rearrangement in scale worms (Aphroditiformia, Annelida)

Next-generation sequencing (NGS) has become a powerful tool in phylogenetic and evolutionary studies. Here we applied NGS to recover two ribosomal RNA genes (18S and 28S) from 16 species and 15 mitochondrial genomes from 16 species of scale worms representing six families in the suborder Aphroditiformia (Phyllodocida, Annelida), a complex group of polychaetes characterized by the presence of dorsal elytra or scales. The phylogenetic relationship of the several groups of scale worms remains unresolved due to insufficient taxon sampling and low resolution of individual gene markers. Phylogenetic tree topology based on mitochondrial genomes is comparable with that based on concatenated sequences from two mitochondrial genes (cox1 and 16S) and two ribosomal genes (18S and 28S) genes, but has higher statistical support for several clades. Our analyses show that Aphroditiformia is monophyletic, indicating the presence of elytra is an apomorphic trait. Eulepethidae and Aphroditidae together form the sister group to all other families in this suborder, whereas Acoetidae is sister to Iphionidae. Polynoidae is monophyletic, but within this family the deep-sea subfamilies Branchinotogluminae and Macellicephalinae are paraphyletic. Mitochondrial genomes in most scale-worm families have a conserved gene order, but within Polynoidae there are two novel arrangement patterns in the deep-sea clade. Mitochondrial protein-coding genes in polynoids as a whole have evolved under strong purifying selection, but substitution rates in deep-sea species are much higher than those in shallow-water species, indicating that purifying selection is relaxed in deep-sea polynoids. There are positive selected amino acids for some mitochondrial genes of the deep-sea clade, indicating they may involve in the adaption of deep-sea polynoids. Overall, our study (1) provided more evidence for reconstruction of the phylogeny of Aphroditiformia, (2) provided evidence to refute the assumption that mitochondrial gene order in Errantia is conserved, and (3) indicated that the deep-sea extreme environment may have affected the mitochondrial genome evolution rate and gene order arrangement in Polynoidae.

Matching loci surveyed to questions asked in phylogeography

Although mitochondrial DNA (mtDNA) has long been used for assessing genetic variation within and between populations, its workhorse role in phylogeography has been criticized owing to its single-locus nature. The only choice for testing mtDNA results is to survey nuclear loci, which brings into contrast the difference in locus effective size and coalescence times. Thus, it remains unclear how erroneous mtDNA-based estimates of species history might be, especially for evolutionary events in the recent past. To test the robustness of mtDNA and nuclear sequences in phylogeography, we provide one of the largest paired comparisons of summary statistics and demographic parameters estimated from mitochondrial, five Z-linked and 10 autosomal genes of 30 avian species co-distributed in the Caucasus and Europe. The results suggest that mtDNA is robust in estimating inter-population divergence but not in intra-population diversity, which is sensitive to population size change. Here, we provide empirical evidence showing that mtDNA was more likely to detect population divergence than any other single locus owing to its smaller Ne and thus faster coalescent time. Therefore, at least in birds, numerous studies that have based their inferences of phylogeographic patterns solely on mtDNA should not be readily dismissed.

Molecular systematics of the new world screech-owls (Megascops: Aves, Strigidae): biogeographic and taxonomic implications

Megascops screech-owls are endemic to the New World and range from southern Canada to the southern cone of South America. The 22 currently recognized Megascops species occupy a wide range of habitats and elevations, from desert to humid montane forest, and from sea level to the Andean tree line. Species and subspecies diagnoses of Megascops are notoriously difficult due to subtle plumage differences among taxa with frequent plumage polymorphism. Using three mitochondrial and three nuclear genes we estimated a phylogeny for all but one Megascops species. Phylogenies were estimated with Maximum Likelihood and Bayesian Inference, and a Bayesian chronogram was reconstructed to assess the spatio-temporal context of Megascops diversification. Megascops was paraphyletic in the recovered tree topologies if the Puerto Rican endemic M. nudipes is included in the genus. However, the remaining taxa are monophyletic and form three major clades: (1) M. choliba, M. koepckeae, M. albogularis, M. clarkii, and M. trichopsis; (2) M. petersoni, M. marshalli, M. hoyi, M. ingens, and M. colombianus; and (3) M. asio, M. kennicottii, M. cooperi, M. barbarus, M. sanctaecatarinae, M. roboratus, M. watsonii, M. atricapilla, M. guatemalae, and M. vermiculatus. Megascops watsonii is paraphyletic with some individuals more closely related to M. atricapilla than to other members in that polytypic species. Also, allopatric populations of some other Megascops species were highly divergent, with levels of genetic differentiation greater than between some recognized species-pairs. Diversification within the genus is hypothesized to have taken place during the last 8 million years, with a likely origin in Central America. The genus later expanded over much of the Americas and then diversified via multiple dispersal events from the Andes into the Neotropical lowlands.

Differential introgression and effective size of marker type influence phylogenetic inference of a recently divergent avian group (Phasianidae: Tympanuchus)

Life history strategies can influence the effective population size (Ne) of loci differently based on their mode of inheritance. Recognizing how this may affect the rate of lineage sorting among marker types is important for studies focused on resolving phylogenetic relationships among recently divergent taxa. In this study, we use gene tree, coalescent-based species tree, and isolation-with-migration analyses to explore the differences between marker types (autosomal, Z-linked, and mitochondrial) in resolving phylogenetic relationships among North American prairie grouse (Tympanuchus). We found that Z-linked loci were more likely to identify monophyletic relationships among prairie grouse species compared to autosomal and mtDNA loci in both species and gene tree analyses, with species tree analyses outperforming gene trees. These results were further supported with isolation-with-migration analyses, where Z-linked loci largely followed a strict isolation model while autosomal loci were more likely to fit a model with gene flow between species following population divergence. While accounting for differences in inheritance pattern (or Ne) for marker type, results suggest that additional factors, such as strong sexual selection and sex-biased introgression (i.e., male-biased postzygotic hybrid behavioral isolation or "unsexy son"), may further explain the decreased diversity levels and increased rate of lineage sorting observed with the Z-linked loci relative to autosomal and mtDNA loci. In fact, to our knowledge no hybrid male prairie grouse have been observed breeding in the wild, yet hybrid females along with backcross females are known to produce viable offspring. Overall, this study highlights that more work is needed to determine how complex models of gene flow (i.e., sex biased introgression) and differences in the effective size among marker types based on differing life history strategies influence divergence date estimation and species delimitation.

Coalescent analyses show isolation without migration in two closely related tropical orioles: the case of Icterus graduacauda and Icterus chrysater

The Isthmus of Tehuantepec has played an important role in shaping the avian diversity of Mexico, as well as the rest of the Western Hemisphere. It has been both a barrier and a land connector between North and South America for many groups of birds. Furthermore, climatic change over the Pleistocene has resulted in ecological fluctuations that led to periods of connection and isolation of the highlands in this area. Here we studied the divergence of two species of orioles whose distribution in the highlands is separated by the lowlands of the Isthmus of Tehuantepec: Icterus graduacauda (west of the Isthmus) and Icterus chrysater (east of the Isthmus). We sequenced multiple loci (one mitochondrial gene and six nuclear introns) and performed coalescent analyses (Isolation with Migration) to test whether their divergence resulted from prior occupancy of the ancestral area followed by a vicariant event or recent dispersal from one side or the other of this Isthmus. Results strongly indicate a vicariant event roughly 300,000 years ago in the Pleistocene followed by little or no gene flow. Both mitochondrial and nuclear genes show that the Isthmus of Tehuantepec is a strong barrier to gene flow. Thus, these two species appear to not exchange genes despite their recent divergence and the close geographic proximity of their ranges.

Molecular phylogeny and new classification of the genera Eulophias and Zoarchias (PISCES, Zoarcoidei)

Morphological and osteological studies of the Zoarcoidei group have previously been undertaken, but the group (especially the genera Eulophias and Zoarchias) still remains enigmatic. Therefore, we conducted molecular phylogenetic studies on the two genera Eulophias and Zoarchias using two mitochondrial (16S rRNA and COI) and two nuclear genes (RAG2 and RNF213). Our phylogenetic analysis supported the monophyly of the suborder level of the Zoarcoidei, but rejected the previous morphology- and osteology-based classification hypotheses regarding the two genera. Conflict between mtDNA and nDNA phylogenies within the genus Eulophias implies that the genus shows a complicated relationship such as hybridization in the process of the evolutionary history. The genetic distances between the Eulophias (or Zoarchias) and other Zoarcoidei spp. were the greatest, showing different family-level affiliations. In addition, the mtDNA topology showed the two genera were clearly separated from each other as well as from the families Stichaeidae and Zoarcidae. Considering the new molecular phylogeny, we suggest a new classification for the two genera: (1) Eulophias belongs to a new family named as the Eulophiidae; (2) Zoarchias belongs to the family Neozoarcidae (sensu Radchenko et al., 2012b) rather than to Stichaeidae and Zoarcidae.

Extensive introgressive hybridization within the northern oriole group (Genus Icterus) revealed by three-species isolation with migration analysis

Until recently, studies of divergence and gene flow among closely-related taxa were generally limited to pairs of sister taxa. However, organisms frequently exchange genes with other non-sister taxa. The “northern oriole” group within genus Icterus exemplifies this problem. This group involves the extensively studied hybrid zone between Baltimore oriole (Icterus galbula) and Bullock's oriole (I. bullockii), an alleged hybrid zone between I. bullockii and black-backed oriole (I. abeillei), and likely mtDNA introgression between I. galbula and I. abeillei. Here, we examine the divergence population genetics of the entire northern oriole group using a multipopulation Isolation-with-Migration (IM) model. In accordance with Haldane's rule, nuclear loci introgress extensively beyond the I. galbula–I. bullockii hybrid zone, while mtDNA does not. We found no evidence of introgression between I. bullockii and I. abeillei or between I. galbula and I. abeillei when all three species were analyzed together in a three-population model. However, traditional pairwise analysis suggested some nuclear introgression from I. abeillei into I. galbula, probably reflecting genetic contributions from I. bullockii unaccounted for in a two-population model. Thus, only by including all members of this group in the analysis was it possible to rigorously estimate the level of gene flow among these three closely related species.