Deep genealogies and the mid-peninsular seaway of Baja California

Geological forces and long-term climate changes can have profound effects on species. Such effects may be manifested in the pattern and magnitude of genealogical diversity, as revealed by mitochondrial DNA (mtDNA) lineages. The relative importance of the different forces on a regional biota must be evaluated along with a good understanding of geological and climatological history. The peninsula of Baja California of north-western Mexico is one area where both geology and climate have affected the historical biogeography of the regional biota. Molecular studies based on the genealogical relationships among mtDNA lineages have contributed greatly towards elucidating the historical biogeography of Baja California. Perhaps most noticeably, numerous concordant breaks in mtDNA genealogies half-way along the peninsula suggest a vicariant history in which the mid-peninsula was temporarily submerged. This vicariant explanation has recently been criticized, as no conclusive geological evidence exists for a continuous submergence of the mid-peninsula. As an alternative, a scenario based on climatological factors has been suggested. Here we discuss the validity of the hypothesized mid-peninsular vicariance event and the climate-based alternative in explaining the concordant genealogical breaks. We argue that, despite the significant changes in climate brought about by the glacial cycles throughout the Quaternary, a vicariant history involving a mid-peninsular seaway remains the most parsimonious explanation of the observed patterns in mtDNA genealogies.     

A peninsula as an island: multiple forms of evidence for overwater colonization of Baja California by the gartersnake Thamnophis validus

The recent shift toward dispersal rather than vicariant explanations of disjunct distributions has been driven by the use of molecular data to estimate divergence dates between lineages. However, other kinds of evidence can also be critical in evaluating such biogeographic hypotheses. In the present study, we used a multifaceted approach employing diverse analyses of mitochondrial DNA sequences to assess explanations for the disjunct distribution of the gartersnake Thamnophis validus. The occurrence of this species in the Cape Region of the Baja California peninsula, isolated from mainland populations that occur along the west coast of Mexico, might be explained by: (1) separation of the peninsula from mainland Mexico through rifting 4–8 Mya (tectonic vicariance); (2) fragmentation of the range of this semi‐aquatic species because of post‐Pleistocene aridification (vicariance by aridification); (3) natural overwater dispersal across the Gulf of California; or (4) human introduction. Divergence dating indicates that peninsular and mainland T. validus separated from each other within the last 0.5 Myr, thus rejecting tectonic vicariance. In addition, the estimated closest mainland relatives of peninsular snakes are found farther north than expected under this hypothesis. Three findings argue against vicariance by aridification: (1) peninsular snakes and their closest mainland relatives are more genetically similar than predicted; (2) the location of closest mainland relatives is farther south than predicted; and (3) the species is absent from areas where one might expect to find relict populations. Taken together, refutation of the vicariance hypotheses and the fact that the estimated closest mainland relatives are found almost directly across the Gulf from the Cape Region supports some form of overwater colonization. Various additional arguments suggest that natural dispersal is more likely than human introduction. The present study emphasizes the need for multiple kinds of evidence, beyond divergence dates, to discriminate among hypotheses and to provide independent sources of corroboration or refutation in historical biogeography. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 409–424.     

Historical biogeography and the evolution of the latitudinal gradient of species richness in the Papionini (Primata: Cercopithecidae)

We apply historical biogeography techniques to the macaques, baboons and their relatives (Primata: Papionini) and relate the inferred history of range shifts, and associated evolutionary events, to the latitudinal distribution of extant species, which is strongly tropical. The results of reversible parsimony, weighted ancestral area and dispersal-vicariance analyses all agree that Central Africa was part of the range of the ancestor of the tribe. Tropical regions with high current species richness (Central Africa, South-east Asia, Indonesia) have: (1) had a relatively long history of occupation, (2) experienced both a greater number and a greater average rate of speciation events and (3) given rise to more dispersal events to other regions. However, nested sister-taxon comparisons across the tribe show no overall association between differences in latitude and differences in rates of cladogenesis. Our historical reconstructions are largely consistent with previous hypotheses and fossil data, and suggest that both the passage of time since colonization and rates of cladogenesis have enhanced tropical species richness. Historical biogeography may thus considerably aid understanding of this and other spatial problems in macroecology.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 235–246.     

Phylogenetic relationships and biogeographical history of the genus Rhinoclemmys Fitzinger, 1835 and the monophyly of the turtle family Geoemydidae (Testudines: Testudinoidea)

Rhinoclemmys is an interesting genus of turtles biogeographically and ecologically, being the only genus of the family Geoemydidae that occurs in the New World and inhabiting a wide range of habitats from aquatic to highly terrestrial. Here we present a molecular phylogeny of Rhinoclemmys using both mitochondrial and nuclear genes. Our results strongly support the monophyletic and subfamilial status of Rhinoclemmys within the monophyletic family Geoemydidae. Within Rhinoclemmys , two clades are strongly supported, i.e. R. annulata  +  R. pulcherrima and R. areolata  +  R. punctularia  +  R. diademata  +  R. funerea  +  R. melanosterna , but the positions of R. nasuta and R. rubida are still weakly supported. In terms of the biogeographical history, the results of this study, coupled with palaeontological evidence, corroborate the hypothesis that this group migrated from Asia to the Americas across the Bering Strait during the early Eocene. The radiation of Rhinoclemmys in Central and South America corresponds well with vicariance events, including the emergence of the Sierra Madres of Mexico and the Nuclear Highland, and dispersals across the Panama land bridge. Interestingly, our resulting phylogeny suggests this group invaded South America at least four times and that dispersal of R. nasuta to South America probably took place in the early Miocene before the emergence of the Isthmus of Panama. We finally discuss our phylogenetic results with regard to the monophyly of the family Geoemydidae and in the context of previous morphological analyses. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 153 , 751–767.     

Deep genealogical history without population differentiation: discordance between mtDNA and allozyme divergence in the zebra-tailed lizard (Callisaurus draconoides)

The peninsula of Baja California has a complex geological history that has strongly affected the regional biota. Genealogical histories of many species have revealed congruent patterns, which suggest that the peninsula was temporarily submerged at two locations. We sequenced a total of 1953 base pairs (bp) of the mitochondrial genome for 42 specimens of the zebra-tailed lizard (Callisaurus draconoides). The resulting maternal genealogy supports the former existence of a mid-peninsular seaway and a Plio-Quaternary seaway across the Isthmus of La Paz. In addition, a genealogical break is revealed in the vicinity of Loreto. This genealogical break may have resulted from prolonged submergence of the Loreto Basin during Pliocene. The mid-peninsular seaway may have occurred as early as late Miocene, at a time significantly earlier than previously hypothesized. Comparison with other genealogies and geological evidence suggests that current models on the evolution of Baja California's fauna are temporally shallow. The deep genealogical patterns of C. draconoides also disagree with the very limited population differentiation previously reported for allozyme markers, suggesting that maternal history may not be an appropriate approximation for population differentiation.     

Application of parsimony analysis of endemicity to Mexican gymnosperm distributions: grid-cells, biogeographical provinces and track analysis

Parsimony analysis of endemicity (PAE) was used to analyse the distributional patterns of 124 species of Mexican gymnosperms, using two different sample units: grid-cells and biogeographical provinces. PAE analyses were based on distributional data from herbarium specimens and specialized literature. Two data matrices were constructed for 60 grid-cells of 2° and 14 biogeographical provinces. The analysis of the 2° grid-cell matrix led to 7084 cladograms. The strict consensus cladogram showed several clades equivalent to the results obtained with the biogeographical provinces. Three clades agree with some principal regions of distribution of Mexican pines, previously identified by several authors, located at the northern portion of the Baja California peninsula, the Sierra Madre Occidental, and the Sierra Madre Oriental. These areas represent important centres of species diversity and endemism for Mexican gymnosperms. The analysis of the province matrix led to two most parsimonious cladograms, which only differed in the position of the Sierra Madre Occidental province. The iterative procedure PAE with progressive character elimination was applied to identify generalized tracks, where clades of provinces were considered equivalent to generalized tracks, and each time a cladogram was obtained, species defining its clades were deleted and a new run was undertaken. We found five generalized tracks, mainly located in montane provinces. The distribution patterns of gymnosperms agree with the existence of several Mexican biogeographical provinces, and a different historical biogeography of the Mexican peninsulas from the rest of the country is evident.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 405–417.     

Phylogeographic diversification of antelope squirrels (Ammospermophilus) across North American deserts

We investigated the biogeographic history of antelope squirrels, genus Ammospermophilus, which are widely distributed across the deserts and other arid lands of western North America. We combined range‐wide sampling of all currently recognized species of Ammospermophilus with a multilocus data set to infer phylogenetic relationships. We then estimated divergence times within identified clades of Ammospermophilus using fossil‐calibrated and rate‐calibrated molecular clocks. Lastly, we explored generalized distributional changes of Ammospermophilus since the last glacial maximum using species distribution models, and assessed responses to Quaternary climate change by generating demographic parameter estimates for the three wide‐ranging clades of A. leucurus. From our phylogenetic estimates we inferred strong phylogeographic structure within Ammospermophilus and the presence of three well‐supported major clades. Initial patterns of historical divergence were coincident with dynamic alterations in the landscape of western North America, and the formation of regional deserts during the Late Miocene and Pliocene. Species distribution models and demographic parameter estimates revealed patterns of recent population expansion in response to glacial retreat. When combined with evidence from co‐distributed taxa, the historical biogeography of Ammospermophilus provides additional insight into the mechanisms that impacted diversification of arid‐adapted taxa across the arid lands of western North America. We propose species recognition of populations of the southern Baja California peninsula to best represent our current understanding of evolutionary relationships among genetic units of Ammospermophilus. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 949–967.     

Lineage diversification on an evolving landscape: phylogeography of the California newt, Taricha torosa (Caudata: Salamandridae)

We used mitochondrial cytochrome  b sequences (up to 778 bp) and starch gel electrophoresis (45 loci) to examine the phylogeographical history of 39 populations of the California newt, Taricha torosa . Phylogenetic and population genetic methods were integrated to infer history at deep and shallow time depths. Using a molecular clock, the subspecies T. t. torosa and T. t. sierrae were estimated to have diverged 7–13 Mya. Within T. t. torosa, genetically differentiated groups were identified along coastal California, in southern California, and in the southern Sierra Nevada. The coastal group exhibited isolation by distance, but a lack of genetic variation north of present-day Monterey was indicative of a recent range expansion. In southern California, a disjunct population in central San Diego County was genetically diverged from coastal populations to the north (Nei's genetic distance of 0.113). However, mtDNA and protein data were geographically discordant regarding the boundary between the coastal and southern Californian groups, and a biogeographical scenario was developed to account for this discordance. The southern Sierran clade of T. t. torosa was weakly diverged from coastal populations for mtDNA sequence variation, yet was strongly differentiated for allozyme variation (Nei's genetic distance of 0.17–0.20). Populations of T. t. sierrae exhibited substantial population structure, and showed a steeper pattern of isolation by distance than did coastal populations of T. t. torosa . These results are interpreted in consideration of the known geomorphological history of California.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 213–239.     

Novel patterns of historical isolation, dispersal, and secondary contact across Baja California in the Rosy Boa (Lichanura trivirgata)

Mitochondrial DNA (mtDNA) sequence variation was examined in 131 individuals of the Rosy Boa (Lichanura trivirgata) from across the species range in southwestern North America. Bayesian inference and nested clade phylogeographic analyses (NCPA) were used to estimate relationships and infer evolutionary processes. These patterns were evaluated as they relate to previously hypothesized vicariant events and new insights are provided into the biogeographic and evolutionary processes important in Baja California and surrounding North American deserts. Three major lineages (Lineages A, B, and C) are revealed with very little overlap. Lineage A and B are predominately separated along the Colorado River and are found primarily within California and Arizona (respectively), while Lineage C consists of disjunct groups distributed along the Baja California peninsula as well as south-central Arizona, southward along the coastal regions of Sonora, Mexico. Estimated divergence time points (using a Bayesian relaxed molecular clock) and geographic congruence with postulated vicariant events suggest early extensions of the Gulf of California and subsequent development of the Colorado River during the Late Miocene-Pliocene led to the formation of these mtDNA lineages. Our results also suggest that vicariance hypotheses alone do not fully explain patterns of genetic variation. Therefore, we highlight the importance of dispersal to explain these patterns and current distribution of populations. We also compare the mtDNA lineages with those based on morphological variation and evaluate their implications for taxonomy.     

Molecular phylogeny of the endemic Philippine rodent Apomys (Muridae) and the dynamics of diversification in an oceanic archipelago

We analysed the phylogenetic relationships of ten of the 13 known species of the genus Apomys using DNA sequences from cytochrome b . Apomys, endemic to oceanic portions of the Philippine archipelago, diversified during the Pliocene as these oceanic islands arose de novo . Several of the speciation events probably took place on Luzon or Mindanao, the two largest, oldest, and most topographically complex islands. Only one speciation event is associated with vicariance due to Pleistocene sea-level fluctuation, and a Pleistocene diversification model in which isolation is driven by sea-level changes is inconsistent with the data. Tectonic vicariance is nearly absent from the Philippines, in which tectonic coalescence plays a significant role. Most speciation events (about two-thirds) are associated with dispersal to newly developed oceanic islands. The data imply that the species have persisted for long periods, measured in millions of years after their origins; further implications therefore are that faunal turnover is very slow, and persistence over geological time spans is more prominent than repeated colonization and extinction. Neither the equilibrium nor the vicariance model of biogeography adequately encompasses these results; a model incorporating colonization, extinction, and speciation is necessary and must incorporate long-term persistence to accommodate our observations.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 699–715.     

Late Pleistocene to Holocene distributional stasis in scorpions along the Baja California peninsula

The biota of the Baja California peninsula (BCP) assembled in response to a complex history of Neogene tectonics and Quaternary climates. We constructed species distribution models (SDMs) for 13 scorpion species from the BCP to compare current suitable habitat with that at the latest glacial maximum about 21 000 years ago. Using these SDMs, we modelled climatic suitability in relation to latitude along the BCP. Our SDMs suggested that most BCP scorpion distributions have remained remarkably conserved across the latest glacial to interglacial climatic transformation. Three areas of climatic suitability coincide remarkably well with genetic discontinuities in other co‐distributed taxa along the BCP, indicating that long‐term persistence of zones of abrupt climatic transition offer a viable alternative, or synergistic enhancement, to hypotheses of trans‐peninsular seaways as drivers of peninsular divergences. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 450–461.     

Global historical biogeography of hadrosaurid dinosaurs

Hadrosaurids were the most derived ornithopods and amongst the most diverse herbivore dinosaurs during the Late Cretaceous of Europe, Asia, and the two Americas. Here, their biogeographical history is reconstructed using dispersal‐vicariance analysis (DIVA). The results showed that Hadrosauridae originated in North America and soon after dispersed to Asia no later than the Late Santonian. The most recent common ancestor of Saurolophidae (= Saurolophinae + Lambeosaurinae) is inferred to have been widespread in North America and Asia. The split between saurolophines and lambeosaurines occurred in response to vicariance no later than the Late Santonian: the former clade originated in North America, whereas the latter did so in Asia. Saurolophine biogeographical history included a minimum of five dispersal events followed by vicariance. Four of these dispersals were inferred to have occurred from North America to Asia during the Campanian and Early Maastrichtian, whereas a fifth event represented a southward dispersal from North to South America no later than the Late Campanian. The historical biogeography of lambeosaurines was characterized by an early evolution in Asia, with a Campanian dispersal to the European archipelago followed by vicariance. Reconstruction of the ancestral areas for the deepest nodes uniting the more derived lambeosaurines clades (‘hypacrosaurs’, ‘corythosaurs’, and ‘parasaurolophs’) is ambiguous. The split between North American and Asian clades of ‘hypacrosaurs’ and ‘parasaurolophs’ occurred in response to vicariance during the Campanian. The evolutionary history of North American ‘hypacrosaurs’ and ‘parasaurolophs’ was characterized by duplication events. The latter also characterized the Late Campanian ‘corythosaurs’, which remained restricted to North America. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 503–525.     

The phylogeographical and management implications of genetic population structure in the imperiled snuffbox mussel, Epioblasma triquetra (Bivalvia: Unionidae)

Seven populations of the imperiled snuffbox mussel, Epioblasma triquetra , were sampled from across the central basin of North America. Samples were genotyped using 15 microsatellite DNA loci, and maternal history was inferred using mitochondrial DNA (mtDNA) cytochrome  c oxidase subunit-I (COI) sequences. Populations in the Clinch and St Francis rivers were quite distinct in their mtDNA. The population in the St Francis River had a unique, fixed haplotype. Among a suite of haplotypes, the population in the Clinch River had two unique haplotypes of common ancestry. The other populations were dominated by a common haplotype, which also occurred in the Clinch River population. Analysis of DNA microsatellites revealed much greater divergences and showed significant genetic structure between populations in the formerly glaciated regions. Divergence has occurred between the populations, as evidenced by moderate to high fixation indices ( F _ST and R _ST values) and nearly perfect assignment tests. These results indicate the occurrence of three glacial refugia for E. triquetra : the Tennessee River, rivers south of the Ozark Crest, and the lower Ohio River drainage near the confluence with the Mississippi. Populations in the lower Ohio River were likely to be responsible for the postglacial reinvasion into formerly glaciated regions, and into the upper Tennessee River drainage. The population of the St Francis River may constitute a distinct taxonomic entity. Conservation efforts, if necessary for this imperiled species, should not mix populations.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 371–384.     

Historical vicariance and postglacial colonization effects on the evolution of genetic structure in Lophocereus,a Sonoran Desert columnar cactus

Distinguishing the historical effects of gene migration and vicariance on contemporary genetic structure is problematic without testable biogeographic hypotheses based on preexisting geological and environmental evidence. The availability of such hypotheses for North America's Sonoran Desert has contributed to our understanding of the effect of historical vicariance and dispersal events on the diversification of this region's vertebrate biota but have not yet been applied to its flora. In this paper we describe a detailed allozyme analysis of the population genetic structure and phylogeography of the Sonoran Desert columnar cactus, Lophocereus schottii (senita). Inferred phylogroup distributions reflect two historical vicariance events: (1) a middle Pliocene northward transgression of the Sea of Cortéz that is reflected in well-supported Baja California peninsular and continental phylogroups but not in current taxonomic treatments of the species; and (2) a late Pliocene transpeninsular seaway across southern Baja that is reflected in tentative support for peninsular and southern Cape Region phylogroups corresponding to taxonomic varieties L. schottii var. schottii and L. schottii var. australis, respectively. A middle Pleistocene midpeninsular seaway hypothesized to explain congruent phylogroup distributions in several vertebrate taxa is not reflected in L. s. var. schottii, nor is the distinction of a third variety, L. s. var. tenuis, from continental populations of L. s. var. schottii. Linear regression of pairwise estimates of interpopulation differentiation (M and F(ST)/[1 - F(ST)]) on interpopulation geographic distance revealed significant evidence of isolation by distance within peninsular and continental phylogroups but not between them, consistent with historical vicariance between but not within these regions. We also found significant evidence of isolation by distance between putative L. s. var. schottii and L. s. var. australis phylogroups, suggesting that reproductive isolation between peninsular and Cape Region forms is incomplete. Within peninsular, but not continental, phylogroups, northward range expansion from southern Pleistocene refugia is reflected in significant declines in genetic variation with increasing latitude and in an area phenogram in which populations are progressively nested from south (ancestral) to north (descendant) along the Baja peninsula. Although the geographic concordance of phylogenetic topologies suggests that ancient vicariance events, and not dispersal, have primarily influenced the biogeographic distributions of Baja's vertebrate biota, the phylogeographic structure of L. schottii suggests that Sonoran Desert plant species may exhibit genetic signatures of postglacial range expansion and gene flow as well as vicariance.     

Phylogeny, divergence times and species limits of spiny lizards (Sceloporus magister species group) in western North American deserts and Baja California

The broad distribution of the Sceloporus magister species group (squamata: phrynosomatidae) throughout western North America provides an appropriate model for testing biogeographical hypotheses explaining the timing and origins of diversity across mainland deserts and the Baja California Peninsula. We inferred concordant phylogenetic trees describing the higher-level relationships within the magister group using 1.6 kb of mitochondrial DNA (mtDNA) and 1.7 kb of nuclear DNA data. These data provide strong support for the parallel divergence of lineages endemic to the Baja California Peninsula (S. zosteromus and the orcutti complex) in the form of two sequential divergence events at the base of the magister group phylogeny. A relaxed phylogenetic analysis of the mtDNA data using one fossil and one biogeographical constraint provides a chronology of these divergence events and evidence that further diversification within the Baja California clades occurred simultaneously, although patterns of geographical variation and speciation between clades differ. We resolved four major phylogeographical clades within S. magister that (i) provide a novel phylogenetic placement of the Chihuahuan Desert populations sister to the Mojave Desert; (ii) illustrate a mixed history for the Colorado Plateau that includes Mojave and Sonoran Desert components; and (iii) identify an area of overlap between the Mojave and Sonoran Desert clades near Yuma, Arizona. Estimates of bidirectional migration rates among populations of S. magister using four nuclear loci support strong asymmetries in gene flow among the major mtDNA clades. Based on the nonexclusivity of mtDNA haplotypes, nuclear gene flow among populations and wide zones of phenotypic intergradation, S. magister appears to represent a single geographically variable and widespread species.     

Cryptic vicariance in Gulf of California fishes parallels vicariant patterns found in Baja California mammals and reptiles

Comparisons across multiple taxa can often clarify the histories of biogeographic regions. In particular, historic barriers to movement should have affected multiple species and, thus, result in a pattern of concordant intraspecific genetic divisions among species. A striking example of such comparative phylogeography is the recent observation that populations of many small mammals and reptiles living on the Baja California peninsula have a large genetic break between northern and southern peninsular populations. In the present study, I demonstrate that five species of near-shore fishes living on the Baja coastline of the Gulf of California share this genetic pattern. The simplest explanation for this concordant genetic division within both terrestrial and marine vertebrates is that the Baja Peninsula was fragmented by a Plio-Pleistocene marine seaway and that this seaway posed a substantial barrier to movement for near-shore fishes. For some fish species, the signal of this vicariance in mtDNA has been eroded by gene flow and is not evident with classic, equilibrium measures of population structure. Yet, significant divisions are apparent in coalescent analyses that jointly estimate divergence with gene flow. The genetic divisions within Gulf of California fishes also coincide with recognized biogeographic regions based on fish community composition and several environmental factors. It is likely that adaptation to regional environments and present-day oceanographic circulation limit gene exchange between biogeographic regions and help maintain evidence of past vicariance.     

Phylogenetic perspective on ecological niche evolution in american blackbirds (Family Icteridae)

Analysis of ecological characters on phylogenetic frameworks has only recently appeared in the literature, with several studies addressing patterns of niche evolution, generally over relatively recent time frames. In the present study, we examined patterns of niche evolution for a broad radiation of American blackbird species (Family Icteridae), exploring more deeply into phylogenetic history. Within each of three major blackbird lineages, overlap of ecological niches in principal components analysis transformed environmental space varied from high to none. Comparative phylogenetic analyses of ecological niche characteristics showed a general pattern of niche conservatism over evolutionary time, with differing degrees of innovation among lineages. Although blackbird niches were evolutionarily plastic over differing periods of time, they diverged within a limited set of ecological possibilities, resulting in examples of niche convergence among extant blackbird species. Hence, an understanding of the patterns of ecological niche evolution on broad phylogenetic scales sets the stage for framing questions of evolutionary causation, historical biogeography, and ancestral ecological characteristics more appropriately.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 869–878.     

Biogeographic distribution of the Phytoseiidae (Acari: Mesostigmata)

More than 1982 species in 90 genera were included in an analysis of the biogeography of the Phytoseiidae, a family of predatory mites. Seven biogeographic regions were taken into account: Nearctic, Neotropical, Ethiopian, West Palaearctic, East Palaearctic, Oriental, and Australasian. The number of species was particularly high in the Neotropical, Oriental, and West Palaearctic regions. These regions also present the highest levels of species endemism. The number of genera was quite similar in all regions except for the Neotropics, which also had a high level of endemism. The possible Gondwanian (Neotropical, Ethiopian, Australasian, and Oriental regions) origin of the Phytoseiidae, most probably in the Neotropics, and their possible radiation to Laurasia (Nearctic, West Palaearctic, and East Palaearctic regions) are discussed. The comparison between genera and species in the different biogeographic regions indicate the importance of both dispersal and vicariance events in the evolution of the group. Dispersal is assumed to have been most important between Neotropical and Nearctic regions and between East Palaearctic and Oriental regions, whereas vicariance could have been the dominating process between Australasian, Ethiopian, and Oriental regions, as well as between West and East Palaearctic regions. A parsimony analysis of endemicity showed the Neotropical and the Nearctic regions to be isolated from the other regions. This is certainly due to a diversification after the continents drifted apart and then a high dispersal between Nearctic and Neotropical regions. Different phylogenetic hypotheses and scenarios are proposed for each subfamily based on the results obtained and further investigations are proposed.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 845–856.     

Not just vicariance: phylogeography of a Sonoran Desert euphorb indicates a major role of range expansion along the Baja peninsula

To examine the generality of population-level impacts of ancient vicariance identified for numerous arid-adapted animal taxa along the Baja peninsula, we tested phylogeographical hypotheses in a similarly distributed desert plant, Euphorbia lomelii (Euphorbiaceae). In light of fossil data indicating marked changes in the distributions of Baja floristic assemblages throughout the Holocene and earlier, we also examined evidence for range expansion over more recent temporal scales. Two classes of complementary analytical approaches — hypothesis-testing and hypothesis-generating — were used to exploit phylogeographical signal from chloroplast DNA sequence data and genotypic data from six codominant nuclear intron markers. Sequence data are consistent with a scenario of mid-peninsular vicariance originating c. 1 million years ago (Ma). Alternative vicariance scenarios representing earlier splitting events inferred for some animals (e.g. Isthmus of La Paz inundation, c. 3 Ma; Sea of Cortez formation, c. 5 Ma) were rejected. Nested clade phylo-geographical analysis corroborated coalescent simulation-based inferences. Nuclear markers broadened the temporal spectrum over which phylogeographical scenarios could be addressed, and provided strong evidence for recent range expansions along the north–south axis of the Baja peninsula. In contrast to previous plant studies in this region, however, the expansions do not appear to have been in a strictly northward direction. These findings contribute to a growing appreciation of the complexity of organismal responses to past climatic and geological changes — even when taxa have evolved in the same landscape context.     

Molecular evidence suggests an ancient radiation for the fairy shrimp genus Streptocephalus (Branchiopoda: Anostraca)

Phylogenetic relationships among assumed Gondwanan aquatic inland invertebrate fauna are generally largely neglected, and biogeographical hypotheses for these organisms are generally inferred from historic (palaeogeographical) and contemporary distribution patterns. The distribution of the monogeneric thermophilic freshwater fairy shrimp family Streptocephalidae ( Streptocephalus ) provides a particularly useful framework to test the three contrasting biogeographical scenarios proposed for the evolution of this group: (1) the genus evolved in Laurasia and subsequently dispersed into Africa and North America; (2) the genus evolved and dispersed out of Africa and (3) the current distribution of the genus is the result of vicariance following the fragmentation of Gondwana. In the present study, the phylogenetic relationships of species in this genus are examined with the use of two mitochondrial genes (12S rRNA and COI mtDNA), while the phylogenetic relationships among the North American species and selected African taxa was investigated using the nuclear fragment (5.8S-ITS-1-18S). Phylogenetic results indicate that Streptocephalus probably evolved in Gondwana and that the current distribution patterns are a consequence of a combination of vicariance and limited dispersal. The implications for the evolution of continental freshwater crustaceans are discussed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 313–327.