Coastal Clade Research Articles

Fast satellite DNA evolution in Nothobranchius annual killifishes

Satellite DNA (satDNA) is a rapidly evolving class of tandem repeats, with some monomers being involved in centromere organization and function. To identify repeats associated with (peri)centromeric regions, we investigated satDNA across Southern and Coastal clades of African annual killifishes of the genus Nothobranchius. Molecular cytogenetic and bioinformatic analyses revealed that two previously identified satellites, designated here as NkadSat01-77 and NfurSat01-348, are associated with (peri)centromeres only in one lineage of the Southern clade. NfurSat01-348 was, however, additionally detected outside centromeres in three members of the Coastal clade. We also identified a novel satDNA, NrubSat01-48, associated with (peri)centromeres in N. foerschi, N. guentheri, and N. rubripinnis. Our findings revealed fast turnover of satDNA associated with (peri)centromeres and different trends in their evolution in two clades of the genus Nothobranchius.

Geographic restriction, genetic divergence, and morphological disparity in the Brazilian Atlantic Forests: Insights from Leposoma lizards (Gymnophthalmidae, Squamata)

Lineage differentiation, long-term persistence, and range limitation promote high levels of phylogenetic and phylogeographic endemisms and likely underlie the abundant morphologically cryptic diversity observed in the Brazilian Atlantic Forests (AF). We explore lineage differentiation and range restriction in the AF and ask if genetic divergence and morphological disparity are correlated by integrating coalescent-based species delimitation, molecular phylogenetic, and morphological analyses in the lizard genus Leposoma. We present the first species tree for Leposoma and of their tribe, the Ecpleopodini. The analyses are based on the largest dataset ever assembled for Leposoma in terms of number of species (all represented), genetic markers (12 loci), and geographic coverage (~2,500 km). The exercise allows us to robustly delimit species within the genus and phylogeographic lineages within all species. We find support for the monophyly of the genus and for the recognition of a yet undescribed species around the Baía de Todos-os-Santos, in the state of Bahia; this form is distinct from all other congeners, both genetically and morphologically. We find that L. baturitensis, from the northeastern state of Ceará, is basal to the genus – and sister to a clade of six species restricted to the AF across the eastern coast of Brazil. Relationships within this coastal clade are ((((L. annectans, Leposoma sp.), L. scincoides), L. puk) (L. nanodactylus, L. sinepollex)). Phylogenetic and phylogeographic analyses, together with precise distribution data, allowed us to update the ranges of species and phylogeographic lineages. We reveal pervasive geographic restriction of divergent lineages in Leposoma at and below species level and discuss how forest refuges and rivers might have contributed to it. We find that morphological disparity lags behind genetic divergence in the genus because although they are correlated, the first accumulates at a much slower rate than the latter. We hope to encourage new studies in the area of AF north of the Doce river; phylogeographic sampling in that region has been much less common relative to southern sites, yet it may hold the key to several important processes defining biodiversity patterns in eastern Brazil. This appears to specially apply to processes underlying geographic restriction of morphologically cryptic, yet genetic divergent lineages, as the case of Leposoma.

Reappraisal of the systematics of Microglanis cottoides (Siluriformes, Pseudopimelodidae), a catfish from southern Brazil.

The southern region of Brazil is characterized by high species diversity and endemism of freshwater fishes distributed across geographically isolated river basins. Microglanis cottoides has a widespread range across these river basins and occurs in sympatry with other endemic species of the genus (e.g. M. cibelae, M. eurystoma, and M. malabarbai). Herein we tested the monophyly of M. cottoides and presented for the first time information about the molecular phylogeny of species in the genus. The results suggest that M. cottoides currently forms a non-monophyletic group which includes populations endemic to the Uruguay River basin that are more closely related to M. malabarbai, and excludes M. cibelae, found to be nested within M. cottoides. Based on an integrative approach using morphological and molecular data, we propose M. cibelae as a junior synonym of M. cottoides, and the populations of the Uruguay River basin previously assigned to M. cottoides in fact belong to M. malabarbai. Our molecular phylogeny shows that M. cottoides is sister to M. parahybae, which is also a coastal species, and M. malabarbai is sister of M. garavelloi, both endemic to inland river basins. The time-calibrated phylogeny indicates that the separation between inland and the coastal clades occurred in the Tertiary period, and that the species within the coastal basins diverged in the Pliocene, which overlaps with the diversification times estimated for the two inland species as well. This pattern of diversification corroborates some previous studies with other fishes from the same region.

Seasonal patterns in Arctic prasinophytes and inferred ecology of Bathycoccus unveiled in an Arctic winter metagenome

Prasinophytes occur in all oceans but rarely dominate phytoplankton populations. In contrast, a single ecotype of the prasinophyte Micromonas is frequently the most abundant photosynthetic taxon reported in the Arctic from summer through autumn. However, seasonal dynamics of prasinophytes outside of this period are little known. To address this, we analyzed high-throughput V4 18S rRNA amplicon data collected from November to July in the Amundsen Gulf Region, Beaufort Sea, Arctic. Surprisingly during polar sunset in November and December, we found a high proportion of reads from both DNA and RNA belonging to another prasinophyte, Bathycoccus. We then analyzed a metagenome from a December sample and the resulting Bathycoccus metagenome assembled genome (MAG) covered ~90% of the Bathycoccus Ban7 reference genome. In contrast, only ~20% of a reference Micromonas genome was found in the metagenome. Our phylogenetic analysis of marker genes placed the Arctic Bathycoccus in the B1 coastal clade. In addition, substitution rates of 129 coding DNA sequences were ~1.6% divergent between the Arctic MAG and coastal Chilean upwelling MAGs and 17.3% between it and a South East Atlantic open ocean MAG in the B2 Clade. The metagenomic analysis also revealed a winter viral community highly skewed toward viruses targeting Micromonas, with a much lower diversity of viruses targeting Bathycoccus. Overall a combination of Micromonas being relatively less able to maintain activity under dark winter conditions and viral suppression of Micromonas may have contributed to the success of Bathycoccus in the Amundsen Gulf during winter.

New species in the Sitalcina sura species group (Opiliones, Laniatores, Phalangodidae), with evidence for a biogeographic link between California desert canyons and Arizona sky islands

The western United States is home to numerous narrowly endemic harvestman taxa (Arachnida, Opiliones), including members of the genus Sitalcina Banks, 1911. Sitalcina is comprised of three species groups, including the monospecific Sitalcina californica and Sitalcina lobata groups, and the Sitalcina sura group with eight described species. All species in the Sitalcina sura group have very small geographic distributions, with group members distributed like disjunct “beads on a string” from Monterey south to southern California and southeast to the sky-island mountain ranges of southern Arizona. Here, molecular phylogenetic and species delimitation analyses were conducted for all described species in the Sitalcina sura group, plus several newly discovered populations. Species trees were reconstructed using multispecies coalescent methods implemented in *BEAST, and species delimitation was accomplished using Bayes Factor Delimitation (BFD). Based on quantitative species delimitation results supported by consideration of morphological characters, two new species (Sitalcina oasiensis sp. n., Sitalcina ubicki sp. n.) are described. We also provide a description of the previously unknown male of Sitalcina borregoensis Briggs, 1968. Molecular phylogenetic evidence strongly supports distinctive desert versus coastal clades, with desert canyon taxa from southern California more closely related to Arizona taxa than to geographically proximate California coastal taxa. We hypothesize that southern ancestry and plate tectonics have played a role in the diversification history of this animal lineage, similar to sclerophyllous plant taxa of the Madro-Tertiary Geoflora. Molecular clock analyses for the Sitalcina sura group are generally consistent with these hypotheses. We also propose that additional Sitalcina species await discovery in the desert canyons of southern California and northern Baja, and the mountains of northwestern mainland Mexico.

Distribution and genetic differentiation of Macrobrachium jelskii (Miers, 1877) (Natantia: Palaemonidae) in Brazil reveal evidence of non-natural introduction and cryptic allopatric speciation

Macrobrachium jelskii (Miers, 1877) occurs in all major Brazilian drainage basins. Considering its wide distribution and the supposed isolation of certain populations, we evaluated phylogenetic relationships among populations from several river basins. Analyses of molecular data using the mitochondrial COI and 16S genes suggest the division of the species into two clades, “Amazonian” and “coastal.” The genetic divergence between these two groups is greater than the genetic divergence within the respective groups. Based on the time of divergence and the probable natural distribution of the species, we suggest two evolutionary scenarios to explain the origin of the coastal clade. The first scenario considers the capacity of M. jelskii to tolerate saline environments. The second is based on Pliocene climate changes that would have caused river confluence from sea level regression. The two clades occur sympatrically but this is a recent condition. The wide geographic distribution and low genetic divergence of the Amazonian clade allows us to propose that the current distribution of M. jelskii is partly due to human activity. Pending future analysis, the absence of a consistent morphological synapomorphy precludes the description of a new cryptic taxonomic entity for M. jelskii .

New genetic data on Genista anglica L. versus Genista ancistrocarpa Spach (Fabaceae, Fabales) in the Iberian Peninsula and Morocco. Phylogeographic clues. Novos dados genéticos sobre a Genista anglica L. versus Genista ancistrocarpa Spach (Fabaceae, Fabales) na Península Ibérica e Marrocos. Indícios filogeográficos

English. The genetic analysis through the nuclear ribosomal DNA of some Iberian and NW Morocco populations of Genista ancistrocarpa Spach and G. anglica L. has validated the separation of these two sister taxa as two distinct genetic entities, strengthening the already described morphological differentiation. The studied populations neatly show the G. ancistrocarpa as a coastal taxon with occidental Iberian and NW Morocco distribution, contrary to the G. anglica. The distribution areas of the two species appear to be distinct and with an important biogeographical significance. The coastal clade is determined by populations of G. ancistrocarpa, and outlines a biogeographic region that seems to depart genetically from the remaining peninsular populations, also in several molecular analyses of other plants and animals by many authors, supporting the idea of a distinct evolution from the Miocene onwards, when the installation of dry and hot conditions has pushed the moisture-dependent populations of G. ancistracarpa toward the westernmost sectors of Iberia and Morocco with an atlantic influence.Portugués. A análise genética de ADN nuclear ribossomal, levada a cabo em algumas populações peninsulares e do NW de Marrocos de Genista ancistrocarpa e de G. anglica, permitiu validar estes dois taxa irmãos como entidades genéticas distintas, reforçando, desta forma, a sua diferenciação morfológica. As análises permitem definir a G. ancistrocarpa como um taxon litoral com distribuição oeste ibérica e NW de África, por oposição à G. anglica. As áreas de distribuição das duas espécies parecem ser distintas e com importante significado biogeográfico. O clado litoral definido pelas populações de G. ancistrocarpa define um território biogeográfico, que parece destacarse geneticamente das restantes populações peninsulares, em diversas plantas e animais analisados geneticamente por vários autores, reforçando a ideia de uma evolução distinta a partir do Mioceno médio, quando a instalação de um clima seco e quente empurrou e isolou uma parte da população da higrófila G. ancistrocarpa para ocidente, onde podiam receber uma influência atlântica.

Early Pliocene range expansion of a clade of subterranean Pyrenean beetles

Aim To investigate the possibility of range expansion and diversification within the subterranean environment in a genus of troglobiont beetles of the family Leiodidae (Troglocharinus), which have a disjunct distribution between the Pyrenees and the Catalonian coast. Location North-eastern Iberian Peninsula. Methods We sequenced 4 kb of five mitochondrial and two nuclear genes of 50 specimens of 12 of the 18 species of Troglocharinus, plus several outgroups. We reconstructed a phylogeny using Bayesian inference and maximum likelihood, estimated divergence times using Bayesian probabilities and an a priori evolutionary rate, compared the diversification of the main clades within the genus, and reconstructed their ancestral distribution using maximum likelihood. Results We found strong support for the monophyly of Troglocharinus and the clades in each of the geographical areas, which diverged in the early Pliocene. The coastal clade was further divided into geographically well-defined lineages, separated by Quaternary deposits. The origin of the coastal clade was a single colonization in the early Pliocene from the central Pyrenees. The diversification of the Pyrenean clade followed a constant rate, while the diversification rate of the coastal clade significantly decreased through the Plio-Pleistocene transition. Main conclusions Troglocharinus expanded its range from its ancestral area in the central Pyrenees to the coast of Catalonia and subsequently diversified, probably within the subterranean environment. Our favoured scenario is a stepping-stone migration, with possibly short-distance dispersals through the surface, along the eastern margin of the north-eastern Ebro basin. The range expansion took place in a narrow temporal window with favourable conditions between the early Pliocene and the onset of the Mediterranean climate by the mid-Pliocene. Surface dispersal was probably severely limited afterwards, as shown by the fragmentation of the coastal lineage.

Genetic diversity in natural and introduced island populations of koalas in Queensland

Island populations of animals are expected to show reduced genetic variation and increased incidence of inbreeding because of founder effects and the susceptibility of small populations to the effects of genetic drift. Koalas (Phascolarctos cinereus) occur naturally in a patchy distribution across much of the eastern Australian mainland and on a small number of islands near the Australian coast. We compared the genetic diversity of the naturally occurring population of koalas on North Stradbroke Island in south-east Queensland with other island populations including the introduced group on St Bees Island in central Queensland. The population on St Bees Island shows higher diversity (allelic richness 4.1, He = 0.67) than the North Stradbroke Island population (allelic richness 3.2, He = 0.55). Koalas on Brampton, Newry and Rabbit Islands possessed microsatellite alleles that were not identified from St Bees Island koalas, indicating that it is most unlikely that these populations were established by a sole secondary introduction from St Bees Island. Mitochondrial haplotypes on the central Queensland islands were more similar to a haplotype found at Springsure in central Queensland and the inland clades in south-east Queensland, rather than the coastal clade in south-east Queensland.

Cytochrome-bSequence Variation in Water Shrews (Sorex palustris) from Eastern and Western North America

Mitochondrial DNA sequence data for the cytochrome-b gene was used to assess genetic divergence among samples of Sorex palustris (Water Shrew) from eastern and western North America. Phylogenetic analysis revealed the presence of three previously observed clades—Cordilleran (S. p. navigator and S. p. brooksi), Coastal (S. bendirii), Boreal (S. p. palustris)—along with a novel Eastern clade (S. p. gloveralleni and/or S. p. albibarbis). Intraspecific divergence between the Boreal and Eastern clades was 3.42%, exceeding interspecific divergence between the Cordilleran and Coastal clades (3.35%). Application of the genetic species concept to the results of this study suggests that the Boreal and Eastern clades of Water Shrews warrant further investigation for recognition as two distinct sister species (i.e., S. palustris and S. albibarbis, respectively). Additional samples and analysis of nuclear markers will be required to substantiate this proposed taxonomic revision.

Global distribution patterns of distinct clades of the photosynthetic picoeukaryote Ostreococcus

Ostreococcus is a marine picophytoeukaryote for which culture studies indicate there are 'high-light' and 'low-light' adapted ecotypes. Representatives of these ecotypes fall within two to three 18S ribosomal DNA (rDNA) clades for the former and one for the latter. However, clade distributions and relationships to this form of niche partitioning are unknown in nature. We developed two quantitative PCR primer-probe sets and enumerated the proposed ecotypes in the Pacific Ocean as well as the subtropical and tropical North Atlantic. Statistical differences in factors such as salinity, temperature and NO(3) indicated the ecophysiological parameters behind clade distributions are more complex than irradiance alone. Clade OII, containing the putatively low-light adapted strains, was detected at warm oligotrophic sites. In contrast, Clade OI, containing high-light adapted strains, was present in cooler mesotrophic and coastal waters. Maximal OI abundance (19 555±37 18S rDNA copies per ml) was detected in mesotrophic waters at 40 m depth, approaching the nutricline. OII was often more abundant at the deep chlorophyll maximum, when nutrient concentrations were significantly higher than at the surface (stratified euphotic zone waters). However, in mixed euphotic-zone water columns, relatively high numbers (for example, 891±107 18S rDNA copies per ml, Sargasso Sea, springtime) were detected at the surface. Both Clades OI and OII were found at multiple euphotic zone depths, but co-occurrence at the same geographical location appeared rare and was detected only in continental slope waters. In situ growth rate estimates using these primer-probes and better comprehension of physiology will enhance ecological understanding of Ostreococcus Clades OII and OI which appear to be oceanic and coastal clades, respectively.

Further disintegration and redefinition of Clerodendrum (Lamiaceae): Implications for the understanding of the evolution of an intriguing breeding strategy

AbstractThe genus Clerodendrum s.l. is polyphyletic. Although recent studies have resulted in C. subg. Cyclonema and C. sect. Konocalyx being removed to the resurrected genus Rotheca, and the unispecific genus Huxleya being sunk into Clerodendrum, it has been unclear whether Clerodendrum as currently circumscribed is monophyletic, particularly in relation to the American genera Aegiphila, Amasonia, and Tetraclea. This phylogenetic study employs four relatively fast‐evolving chloroplast DNA regions, trnT‐L, trnL‐F, trnD‐T, and trnS‐fM, to clarify the generic boundaries of Clerodendrum and its relationship to allied genera. The results corroborate previous studies that there are three well‐supported clades in the currently recognized Clerodendrum: an Asian clade, an African clade, and a Pantropical Coastal clade. The Asian clade and African clade are sister groups and together form a monophyletic group. However, the Pantropical Coastal clade is more closely related to the three American genera than it is to the other two Clerodendrum clades. In addition, a Caribbean species, C. spinosum, is found to be more closely related to the American genera than it is to any of the three major Clerodendrum groups. These results indicate that Clerodendrum as currently circumscribed is not monophyletic. We propose to separate the Pantropical Coastal clade and C. spinosum by reviving the genera Volkameria (including Huxleya) and Ovieda, respectively for these, and to restrict Clerodendrum to the Asian and African clades. Brief descriptions of the genera to be recognized are provided. All Neotropical 'Clerodendrum' taxa are referred to other genera, necessitating six new combinations, which are also provided, where required, for two other well‐studied Old World Volkameria species; all names ever used in Ovieda are given their modern placings (two placed newly in synonymy). The study also sheds light on the evolution of an intriguing breeding strategy that avoids self‐pollination or/and sexual interference. This strategy involves presentation of pollen and stigma in the centre of the flower in a sequential fashion by moving the filaments and style. It appears to have evolved in the common ancestor of Clerodendrum, Volkameria, Ovieda, Amasonia, Tetraclea, Aegiphila and Kalaharia, and still occurs in all of these taxa except Aegiphila, where it has been succeeded by a heterostylous system.

Phylogeography of the longnose dace (Rhinichthys cataractae) species group in northwestern North America — the origin and evolution of the Umpqua and Millicoma dace

The Umpqua and Millicoma dace are small cyprinid fishes endemic, respectively, to the Umpqua and Coos rivers on the central coast of Oregon. The origins and relationships of these dace are unclear; however, two hypotheses have been postulated that assume these dace had evolved from a longnose dace ( Rhinichthys cataractae (Valenciennes, 1842)) like ancestor, but from different modes of origin. The direct origin hypothesis postulates that each of these dace originated directly, but independently, from a common ancestor. In contrast, the indirect origin hypothesis postulates that the Umpqua dace originated from a R. cataractae like ancestor and that the Millicoma dace evolved from the Umpqua dace. We used mitochondrial (cytochrome b and control region) sequences to test the two hypotheses. Our maximum likelihood analysis supports the indirect origin hypothesis and argues that together the Umpqua and Millicoma dace form a distinctive Oregon coastal clade within the R. cataractae species group. We also attempt to reconcile this result with the observation that the geographic distribution of the morphologically divergent Umpqua dace is sandwiched between the geographic ranges of the morphologically similar Millicoma dace and longnose dace.

Cryptic lineages of little free-tailed bats, Chaerephon pumilus (Chiroptera: Molossidae) from southern Africa and the western Indian Ocean islands

We investigate mitochondrial DNA and craniometric variation in southern African and Malagasy populations of the small and morphologically variable, house-roosting molossid bat, Chaerephon pumilus in relation to Malagasy populations of the related, smaller-sized species, C. leucogaster. Both cytochrome b and D-loop sequences show C. leucogaster to be nested within C. pumilus sensu lato, with Malagasy C. pumilus forming a sister group to African C. pumilus and Malagasy C. leucogaster. Four distinct D-loop clades are found in southern African populations, all of which occur sympatrically in the greater Durban area of KwaZulu-Natal Province, whilst two of the Durban clades also characterize 1) northern KwaZulu-Natal and low-lying (<600 m) areas of Swaziland, and 2) ‘inland’ populations comprising the Kruger National Park and higher-lying (>600 m) areas of Swaziland. Clades from low-lying areas show evidence of historical demographic expansion around 3300–13 000 years ago (KwaZulu-Natal coastal clade, Clade A1) to 14 700–60 000 years ago (Durban clade, Clade B1), whilst the inland clade (Clade B2a) was demographically more stable. The origin of these clades can be explained by sea level and vegetation changes hypothesized to follow the Last Glacial Maximum (LGM) after 18 000 years ago. Sympatric clades are shown to differ significantly in the proportional width of the braincase, and ongoing work will test evidence for acoustic and other morphological differences between them.

Cryptic Lineages of Little Free-Tailed Bats,Chaerephon pumilus(Chiroptera: Molossidae) from Southern Africa and the Western Indian Ocean Islands

We investigate mitochondrial DNA and craniometric variation in southern African and Malagasy populations of the small and morphologically variable, house-roosting molossid bat, Chaerephon pumilus in relation to Malagasy populations of the related, smaller-sized species, C. leucogaster. Both cytochrome b and D-loop sequences show C. leucogaster to be nested within C. pumilus sensu lato, with Malagasy C. pumilus forming a sister group to African C. pumilus and Malagasy C. leucogaster. Four distinct D-loop clades are found in southern African populations, all of which occur sympatrically in the greater Durban area of KwaZulu-Natal Province, whilst two of the Durban clades also characterize 1) northern KwaZulu-Natal and low-lying ( 600 m) areas of Swaziland. Clades from low-lying areas show evidence of historical demographic expansion around 3300–13 000 years ago (KwaZulu-Natal coastal clade, Clade A1...

A Likelihood Framework for Estimating Phylogeographic History on a Continuous Landscape

Due to lack of an adequate statistical framework, biologists studying phylogeography are abandoning traditional methods of estimating phylogeographic history in favor of statistical methods designed to test a priori hypotheses. These new methods may, however, have limited descriptive utility. Here, we develop a new statistical framework that can be used to both test a priori hypotheses and estimate phylogeographic history of a gene (and the statistical confidence in that history) in the absence of such hypotheses. The statistical approach concentrates on estimation of geographic locations of the ancestors of a set of sampled organisms. Now we use (2) to derive the likelihood of the ancestral geographic coordinates and the value of the scaled dispersal parameter, given the observed geographic coordinates (assuming known topology and branch lengths). Using a maximum likelihood approach, which is implemented in the new program PhyloMapper, we apply this statistical framework to a 246-taxon mitochondrial genealogy of North American chorus frogs, focusing in detail on one of these species. We demonstrate three lines of evidence for recent northward expansion of the mitochondrion of the coastal clade of Pseudacris feriarum: higher per-generation dispersal distance in the recently colonized region, a noncentral ancestral location, and directional migration. After illustrating one method of accommodating phylogenetic uncertainty, we conclude by discussing how extensions of this framework could function to incorporate a priori ecological and geological information into phylogeographic analyses.

The SAR92 Clade: an Abundant Coastal Clade of Culturable Marine Bacteria Possessing Proteorhodopsin

Proteorhodopsin (PR) is a protein that is abundant in marine bacterioplankton. PR is hypothesized to be a light-dependent proton pump, thus creating a proton gradient that can be used for energy production without electron transport. Currently, the only culture that has been reported to possesses PR is the highly abundant alphaproteobacterium "Candidatus Pelagibacter ubique" (SAR11 clade), but surprisingly, its growth in batch culture was not enhanced by light. Here, we present the first cultured gammaproteobacterium that possesses a PR gene. Genome sequencing and analysis of HTCC2207 showed that the PR gene is present as a lone transcriptional unit directly followed by an operon containing genes that are presumably involved in the synthesis of retinal, the chromophore of PR. Half-time decay times of different PR intermediates in native HTCC2207 cells ranged between 2 and 15 ms, and the absorbance maximum of PR was determined to be 528 nm. Proteorhodopsin was identified in three additional strains, using a specific PCR assay on other cultured members of the SAR92 clade. Phylogenetic analyses of the PR genes determined that they form a deeply rooting cluster not closely related to any PR genes recovered so far. Fluorescence in situ hybridization and RNA blots showed that the SAR92 clade reaches up to 10% of the total bacterial population in surface waters close to the Oregon coast and decreases over depth and distance from the shore. Although the growth of HTCC2207 is limited by the amount of available carbon that is present in the medium applied, these cultures do not grow at higher rates nor do they have higher growth yields when incubated under light.

Phylogeography of the dusky shrew, Sorex monticolus (Insectivora, Soricidae): insight into deep and shallow history in northwestern North America

Phylogenetic relationships among the dusky shrew (Sorexmonticolus) and eight related species (S. bairdi, S. bendirii, S. neomexicanus, S.ornatus, S. pacificus, S. palustris, S. sonomae and S.vagrans) were assessed using sequences from the mitochondrial cytochrome b gene (801 bp). Analyses using parsimony and maximum likelihood revealed significant molecular variation not reflected in previous morphological studies of these species. Conversely, three morphologically defined species (S.bairdi, S.neomexicanus and S.pacificus) were poorly differentiated. Sorexornatus and S.vagrans represented basal taxa for a more inclusive group that included: (i) a widespread Continental clade containing S.monticolus (Arizona to Alaska, including S. neomexicanus); (ii) a Coastal clade containing S.monticolus (Oregon to south-east Alaska, including S. bairdi and S. pacificus); (iii) the semiaquatic species (S. bendirii and S. palustris); and (iv) S.sonomae. Additional subdivision was observed within the Continental clade corresponding to populations from the northern and southern Rocky Mountains. Average uncorrected sequence divergence between the Coastal and Continental clades was 5.3% (range 4.5-6.2%), which exceeds many interspecific comparisons within this species complex and within the genus Sorex. Lack of resolution of internal nodes within topologies suggests a deep history of rapid diversification within this group. Late Pleistocene/Holocene glacial perturbations are reflected in the shallow phylogeographic structure within these clades in western North America. Our results suggest also that S. monticolus is not monophyletic under current taxonomic nomenclature. This perspective on phylogeographic history was developed within a growing comparative framework for other organisms in western North America.