Evolutionary history of alpine and subalpine Daphnia in western North America

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Recent and rapid diversification of the small carpenter bees in eastern North America

Bees fulfil a critical ecological role as pollinators, significantly contributing to the reproductive success of myriad angiosperm species. Although increasingly appreciated for their agricultural contributions, relatively little is yet known about the natural history of the vast majority of the more than 20 000 wild bee species worldwide. The small carpenter bee genus Ceratina occurs globally, and is represented in North America by its most recently diverged subgenera, Ceratinula and Zadontomerus. Recent genetic analysis of eastern Ceratina (Zadontomerus) supports the existence of five closely related, yet genetically distinct species living in sympatry. This phylogeographical study employs molecular barcoding of the most comprehensive specimen collection yet assembled to confirm the identities of these recently diverged eastern North American Ceratina (Zadontomerus) species. Delineation of extant population structure, evolutionary history and known range of this emerging model native pollinator are greatly improved by this study. We consider ecological and behavioural factors potentially contributing to the maintenance of genetic identity among these sympatric species.     

Hybridization in natural sympatric populations of Dermacentor ticks in northwestern North America

Hybridization in ticks has been described in a handful of species and mostly as a result of laboratory experiments. We used 148 AFLP loci to describe putative hybridization events between D. andersoni and D. variabilis in sympatric populations from northwestern North America. Recently, D. variabilis has expanded its range westward into the natural range of D. andersoni. Using a sample of 235 D. andersoni and 62 D. variabilis, we identified 31 individuals as putative hybrids: four F₂ individuals and 27 backcrosses to D. andersoni (as defined by NewHybrids ). We found no evidence of hybrids backcrossing into D. variabilis. Furthermore, all hybrids presented 16S mtDNA signatures characteristic of D. andersoni, which indicates the directionality of the hybrid crosses: female D. andersoni × male D. variabilis. We also discovered 13 species‐specific AFLP fragments for D. andersoni. These loci were found to have a decreased occurrence in the putative hybrids and were absent altogether in D. variabilis samples. AFLP profiles were also used to determine the levels of genetic population structure and gene flow among nine populations of D. andersoni and three of D. variabilis. Genetic structure exists in both species (D. andersoni, Φ_ST = 0.110; D. variabilis, Φ_ST = 0.304) as well as significant estimates of isolation by distance (D. andersoni, ρ = 0.066, P = 0.001; D. variabilis, ρ = 0.729, P = 0.001).     

Glass in the water: Molecular phylogenetics and evolution of Indian glassy perchlets (Teleostei: Ambassidae)

Glassfishes of the family Ambassidae, comprising around 50 species, are distributed in the Indo‐West Pacific where they inhabit marine, estuarine, and freshwater ecosystems. We investigated for the first time the molecular phylogenetic and evolutionary relationships of this group using a combined dataset of mitochondrial and nuclear genes, particularly focusing on the taxa occurring in the Indian subcontinent. Results revealed that marine and freshwater genera of Ambassidae diverged during the Paleocene (~62 mya). The enigmatic monotypic genus Chanda is nested within the larger clade currently recognized as Parambassis, indicating its paraphyly. Based on cleared and stained osteological preparations and phylogenetic placement of Chanda nama, we hypothesize that the elongated and protruding lower jaw is an autapomorphic character that might have evolved for the lepidophagous habit of the species. The southern Indian species of Parambassis, Parambassis dayi, and Parambassis thomassi, which formed a monophyletic group, probably diverged from other species of Parambassis and Chanda nama around the Eocene (~42 mya) and can potentially be recognized as a distinct genus in view of the apomorphic characters such as the presence of serration on the ventral fringe of interopercle, densely serrated palatine and ectopterygoid, and the presence of more than 30 serrations along the lower preopercle and the posterior edge. Our analysis provides new insights into the evolution and phylogenetic relationships of glassy perchlets, including detailed relationships among the Indian species within this family.     

Age composition of winter irruptive Snowy Owls in North America

Patterns of winter irruptions in several owl species apparently follow the ‘lack of food’ hypothesis, which predicts that individuals leave their breeding grounds in search of food when prey populations do not allow breeding and are too small to ensure survival. Recent analyses, however, suggest an alternative mechanism dubbed the ‘breeding success’ hypothesis, which predicts that winter irruptions might instead be the result of a very successful breeding season, with a large pool of young birds subsequently migrating south from the breeding grounds. Here we assessed age‐class (juvenile vs. non‐juvenile) composition of winter irruptive Snowy Owls Bubo scandiacus over a 25‐year period (winter 1991–1992 to 2015–2016) between regular (North American Prairies and Great Plains) and irregular wintering areas (northeastern North America) using live‐trapped individuals and high‐resolution images of individual owls. Our results show that the proportion of juveniles (birds less than 1 year of age) varies considerably annually but is positively correlated with irruption intensity in both regions. In irregular wintering areas, it can constitute the majority (up to more than 90%) of winter irruptive Snowy Owls over a large geographical area. These results are consistent with the idea that large winter irruptions at temperate latitudes are not the result of adults massively leaving the Arctic in search of food after a breeding failure but are more likely to be a consequence of good reproductive conditions in the Arctic that create a large pool of winter migrants.     

Explicit tests of palaeodrainage connections of southeastern North America and the historical biogeography of Orangethroat Darters (Percidae: Etheostoma: Ceasia)

The alteration in palaeodrainage river connections has shaped patterns of speciation, genetic diversity and the geographical distribution of the species‐rich freshwater fauna of North America. The integration of ancestral range reconstruction methods and divergence time estimates provides an opportunity to infer palaeodrainage connectivity and test alternative palaeodrainage hypotheses. Members of the Orangethroat Darter clade, Ceasia, are endemic to southeastern North America and occur north and south of the Pleistocene glacial front, a distributional pattern that makes this clade of closely related species an ideal system to investigate the number and location of glacial refugia and compare alternative hypotheses regarding the proposed evolution of the Teays‐Mahomet palaeodrainage. This study utilized time‐calibrated mitochondrial and nuclear gene phylogenies and present‐day geographical distributions to investigate hypothesized Teays‐Mahomet River connections through time using a dispersal–extinction–cladogenesis (DEC) framework. Results of DEC ancestral area reconstructions indicate that the Teays‐Mahomet River was a key dispersal route between disjunct highland regions connecting the Mississippi River tributaries to the Old‐Ohio Drainage minimally at two separate occasions during the Pleistocene. There was a dynamic interplay between palaeodrainage connections through time and postglacial range expansion from three glacial refugia that shaped the current genetic structure and geographical distributions of the species that comprise Ceasia.     

Phylogenetics,delimitation and historical biogeography of the pantropical tree genus Thespesia (Malvaceae,Gossypieae)

Thespesia consists of 16 species of trees and shrubs from Southeast Asia–Oceania, Africa and America, the most well known being T. populnea, a small tree of tropical coastal areas around the world. Phylogenetic relationships in the genus and among its allies in tribe Gossypieae were inferred using three plastid and two nuclear regions to ascertain its generic delimitation and explore its biogeographical history. Maximum‐likelihood and Bayesian analyses confirmed that Thespesia is not monophyletic and, based on these results, Azanza is reinstated to accommodate the two species previously placed in Thespesia section Lampas. Dating analyses and ancestral range estimation indicated that Thespesia s.s. most likely originated in Southeast Asia–Oceania c. 30 Mya, but extant species did not begin to differentiate until the late Miocene. Two dispersal events, one into Africa c. 11 Mya and another into America (Antilles) c. 9 Mya, gave rise to the African and the Greater Antillean endemics, respectively. The two most widespread hydrochorous species, T. populnea and T. populneoides, originated in Southeast Asia–Oceania from where they spread to other parts of the world. Our analysis also indicated a much earlier origin than previously reported for the eumalvoid clade and its tribes Gossypieae, Malveae and Hibisceae suggesting that vicariance might have had an important role early in the history of these groups.     

Comparative phylogeography of unglaciated eastern North America

Regional phylogeographical studies involving co-distributed animal and plant species have been conducted for several areas, most notably for Europe and the Pacific Northwest of North America. Until recently, phylogeographical studies in unglaciated eastern North America have been largely limited to animals. As more studies emerge for diverse lineages (including plants), it seems timely to assess the phylogeography across this region: (i) comparing and contrasting the patterns seen in plants and animals; (ii) assessing the extent of pseudocongruence; and (iii) discussing the potential applications of regional phylogeography to issues in ecology, such as response to climatic change. Unglaciated eastern North America is a large, geologically and topographically complex area with the species examined having diverse distributions. Nonetheless, some recurrent patterns emerge: (i) maritime - Atlantic vs. Gulf Coast; (ii) Apalachicola River discontinuity; (iii) Tombigbee River discontinuity; (iv) the Appalachian Mountain discontinuity; (v) the Mississippi River discontinuity; and (vi) the Apalachicola River and Mississippi River discontinuities. Although initially documented in animals, most of these patterns are also apparent in plants, providing support for phylogeographical generalizations. These patterns may generally be attributable to isolation and differentiation during Pleistocene glaciation, but in some cases may be older (Pliocene). Molecular studies sometimes agree with longstanding hypotheses of glacial refugia, but also suggest additional possible refugia, such as the southern Appalachian Mountains and areas close to the Laurentide Ice Sheet. Many species exhibit distinct patterns that reflect the unique, rather than the shared, aspects of species' phylogeographical histories. Furthermore, similar modern phylogeographical patterns can result from different underlying causal factors operating at different times (i.e. pseudocongruence). One underemphasized component of pseudocongruence may result from the efforts of researchers to categorize patterns visually - similar patterns may, in fact, not fully coincide, and inferring agreement may obscure the actual patterns and lead to erroneous conclusions. Our modelling analyses indicate no clear spatial patterning and support the hypothesis that phylogeographical structure in diverse temperate taxa is complex and was not shaped by just a few barriers.     

Testing biogeographical hypotheses in space and time: faunal relationships of the putative ancient Lake Egˇirdir in Asia Minor

Aim The aims of this study are to establish a multi‐locus phylogeny‐based hypothesis for the biogeographical relationship of gastropods from the putative ancient Lake Egˇirdir, to test the respective null hypothesis, to estimate the timing of biogeographical events based on independent molecular clock approaches, and to interpret the data with respect to the putative ancient character of Lake Egˇirdir. Location Lake Egˇirdir, western Taurus Lake District, Turkey. Methods DNA sequences from the putatively only extant endemic taxon of Lake Egˇirdir, Falsipyrgula pfeiferi, as well as representatives of other pyrgulinid genera from Europe and western Asia are used for phylogenetic analyses based on Bayesian inference. The respective null hypothesis is tested utilizing parametric bootstrapping. The timing of evolutionary events is estimated based on two independent molecular clock approaches, which involve the modelling of judicious errors associated with branch‐length calculations and calibration points. Results Bayesian inference indicates a very close relationship between the Lake Egˇirdir and Ponto‐Caspian taxa. Parametric bootstrapping rejects the null hypothesis that these taxa are not monophyletic (P ≤ 0.01). The alternative hypothesis, namely monophyly of the Ponto‐Caspian and Egˇirdir taxa, can therefore be accepted. The two independent molecular clock approaches show diversion times for the Ponto‐Caspian/Egˇirdir taxa of 0.42 ± 0.18 and 0.43 ± 0.63 Ma. Main conclusions The present study shows that there is no close biogeographical affiliation between the probably only remaining endemic taxon of Lake Egˇirdir and taxa from central Europe or the Balkan region. Instead, there is a very close and relatively young (i.e. late Pleistocene) biogeographical relationship with the Ponto‐Caspian pyrgulinids. However, fossil and comparative data from other invertebrates indicate that biogeographical connections between Lake Egˇirdir and the Ponto‐Caspian region existed during various time periods, i.e. the Miocene/Pliocene, early Pleistocene, and late Pleistocene. Acknowledging the still‐restricted knowledge of the evolutionary history of the lake, the data presented here do not reject the putative ancient status of Lake Egˇirdir. Future studies utilizing endemic taxa of other lakes in the region need to show whether the western Taurus Lake District represents a melting pot of Pleistocene refuge biodiversity from different regions, and whether the admixture of divergent lineages has created a genetically distinct set of taxa that would warrant the designation of the area as a unique biogeographical subregion.