DIVERSIFICATION AND PERSISTENCE AT THE ARID–MONSOONAL INTERFACE: AUSTRALIA‐WIDE BIOGEOGRAPHY OF THE BYNOE'S GECKO (HETERONOTIA BINOEI; GEKKONIDAE)

Late Neogene aridification in the Southern Hemisphere caused contractions of mesic biota to refugia, similar to the patterns established by glaciation in the Northern Hemisphere, but these episodes also opened up new adaptive zones that spurred range expansion and diversification in arid‐adapted lineages. To understand these dynamics, we present a multilocus (nine nuclear introns, one mitochondrial gene) phylogeographic analysis of the Bynoe's gecko (Heteronotia binoei), a widely distributed complex spanning the tropical monsoon, coastal woodland, and arid zone biomes in Australia. Bayesian phylogenetic analyses, estimates of divergence times, and demographic inferences revealed episodes of diversification in the Pliocene, especially in the tropical monsoon biome, and range expansions in the Pleistocene. Ancestral habitat reconstructions strongly support recent and independent invasions into the arid zone. Our study demonstrates the varied responses to aridification in Australia, including localized persistence of lineages in the tropical monsoonal biome, and repeated invasion of and expansion through newly available arid‐zone habitats. These patterns are consistent with those found in other arid environments in the Southern Hemisphere, including the South African succulent karoo and the Chilean lowlands, and highlight the diverse modes of diversification and persistence of Earth's biota during the glacial cycles of the Pliocene and Pleistocene.     

Ancient drainages divide cryptic species in Australia's arid zone: morphological and multi-gene evidence for four new species of Beaked Geckos (Rhynchoedura)

Deserts and other arid zones remain among the least studied biomes on Earth. Emerging genetic patterns of arid-distributed biota suggest a strong link between diversification history and both the onset of aridification and more recent cycles of severe aridification. A previous study based on 1 kb of mtDNA of the monotypic gecko genus Rhynchoedura identified five allopatric clades across the vast Australian arid zone. We supplemented this data with 2.2kb from three nuclear loci and additional mtDNA sequences. Phylogenetic relationships estimated from the mtDNA data with ML and Bayesian methods were largely concordant with relationships estimated with the nDNA data only, and mtDNA and nDNA data combined. These analyses, and coalescent-based species-tree inference methods implemented with (?)BEAST, largely resolve the relationships among them. We also carried out an examination of 19 morphological characters for 268 museum specimens from across Australia, including all 197 animals for which we sequenced mtDNA. The mtDNA clades differ subtly in a number of morphological features, and we describe three of them as new species, raise a fourth from synonymy, and redescribe it and the type species, Rhynchoedura ornata. We also describe a morphologically distinctive new species from Queensland based on very few specimens. The distribution of arid zone clades across what is now relatively homogeneous sand deserts seems to be related to a topographic divide between the western uplands and eastern lowlands, with species' distributions correlated with dryland rivers and major drainage divides. The existence of five cryptic species within the formerly monotypic Rhynchoedura points to ancient divergences within the arid zone that likely were driven by wet phases as well as dry ones.     

Birth of a biome: insights into the assembly and maintenance of the Australian arid zone biota

The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth's biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1-4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesic-adapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights the opportunities that development of arid conditions provides for rapid and diverse evolutionary radiations, and re-enforces the emerging view that Pleistocene environmental change can have diverse impacts on genetic structure and diversity in different biomes. There is a clear need for more detailed and targeted phylogeographical studies of Australia's arid biota and we suggest a framework and a set of a priori hypotheses by which to proceed.     

Evolutionary refugia and ecological refuges: key concepts for conserving Australian arid zone freshwater biodiversity under climate change

Refugia have been suggested as priority sites for conservation under climate change because of their ability to facilitate survival of biota under adverse conditions. Here, we review the likely role of refugial habitats in conserving freshwater biota in arid Australian aquatic systems where the major long‐term climatic influence has been aridification. We introduce a conceptual model that characterizes evolutionary refugia and ecological refuges based on our review of the attributes of aquatic habitats and freshwater taxa (fishes and aquatic invertebrates) in arid Australia. We also identify methods of recognizing likely future refugia and approaches to assessing the vulnerability of arid‐adapted freshwater biota to a warming and drying climate. Evolutionary refugia in arid areas are characterized as permanent, groundwater‐dependent habitats (subterranean aquifers and springs) supporting vicariant relicts and short‐range endemics. Ecological refuges can vary across space and time, depending on the dispersal abilities of aquatic taxa and the geographical proximity and hydrological connectivity of aquatic habitats. The most important are the perennial waterbodies (both groundwater and surface water fed) that support obligate aquatic organisms. These species will persist where suitable habitats are available and dispersal pathways are maintained. For very mobile species (invertebrates with an aerial dispersal phase) evolutionary refugia may also act as ecological refuges. Evolutionary refugia are likely future refugia because their water source (groundwater) is decoupled from local precipitation. However, their biota is extremely vulnerable to changes in local conditions because population extinction risks cannot be abated by the dispersal of individuals from other sites. Conservation planning must incorporate a high level of protection for aquifers that support refugial sites. Ecological refuges are vulnerable to changes in regional climate because they have little thermal or hydrological buffering. Accordingly, conservation planning must focus on maintaining meta‐population processes, especially through dynamic connectivity between aquatic habitats at a landscape scale.     

The genetic legacy of aridification: climate cycling fostered lizard diversification in Australian montane refugia and left low-lying deserts genetically depauperate

It is a widely held assumption that populations historically restricted to mountain refugia tend to exhibit high levels of genetic diversity and deep coalescent histories, whereas populations distributed in surrounding low-lying regions tend to be genetically depauperate following recent expansion from refugia. These predicted genetic patterns are based largely on our understanding of glaciation history in Northern Hemisphere systems, yet remain poorly tested in analogous Southern Hemisphere arid systems because few examples in the literature allow the comparison of widespread taxa distributed across mountain and desert biomes. We demonstrate with multiple datasets from Australian geckos that topographically complex mountain regions harbor high nucleotide diversity, up to 18 times higher than that of the surrounding desert lowlands. We further demonstrate that taxa in topographically complex areas have older coalescent histories than those in the geologically younger deserts, and that both ancient and more recent aridification events have contributed to these patterns. Our results show that, despite differences in the details of climate and landscape changes that occurred in the Northern and Southern hemispheres (ice-sheets versus aridification), similar patterns emerge that illustrate the profound influence of the Pleistocene on contemporary genetic structure.     

Out of Africa: biogeographic history of the open‐habitat chats (Aves,Muscicapidae: Saxicolinae) across arid areas of the old world

Arid and semi‐arid areas constitute a prominent feature of the earth today, especially in Asia and Africa. Their formation started in the middle Miocene with increased stepwise aridification since the Pliocene. This aridification had strong ecological and evolutionary consequences and not only led to fragmentation of moist‐adapted biota, but also fostered the evolution of arid‐adapted taxa from mesic ancestors and triggered speciation within arid areas. The open‐habitat chats, a clade within Saxicolinae (Aves, Muscicapidae), constitute one of the most significant arid‐adapted passerine groups of Africa and Eurasia. Here, we present a temporal and spatial framework for the diversification of open‐habitat chats, using probabilistic approaches for the reconstruction of their biogeographic history based on a time‐calibrated multilocus molecular phylogenetic hypothesis. The diversification of open‐habitat chats was initiated in the late Miocene at around 7.4 Ma, most likely in sub‐Saharan Africa. Southern Africa and the Horn of Africa acted as centres of diversification and biogeographic expansion. From the latter area, the Arabo‐Sindic region and subsequently further parts of Eurasia and North Africa were colonized. The colonization history out of sub‐Saharan Africa contrasts with that of several other songbird clades, where a biogeographic expansion from Eurasia or northern Africa to southern Africa was prevalent. Habitat fragmentation through forest expansions during intermittent wetter periods in Africa influenced diversification in several clades. However, phases of increased aridity, with hyperarid regions acting as drivers of vicariance, seem to have also been important in radiations of the Arabo‐Sindic region and the Horn of Africa during the Pleistocene. Different processes such as colonization of new areas followed by vicariance or speciation across ecotones might have played a role throughout the radiation of open‐habitat chats.     

Interglacial genetic diversification of Moussonia deppeana (Gesneriaceae), a hummingbird‐pollinated,cloud forest shrub in northern Mesoamerica

Recent empirical work on cloud forest‐adapted species supports the role of both old divergences across major geographical areas and more recent divergences attributed to Pleistocene climate changes. The shrub Moussonia deppeana is distributed in northern Mesoamerica, with geographically disjunct populations. Based on sampling throughout the species range and employing plastid and nuclear markers, we (i) test whether the fragmented distribution is correlated with main evolutionary lineages, (ii) reconstruct its phylogeographical history to infer the history of cloud forest in northern Mesoamerica and (iii) evaluate a set of refugia/vicariance scenarios for the region and demographic patterns of the populations whose ranges expanded and tracked cloud forest conditions during the Last Glacial Maximum. We found a deep evolutionary split in M. deppeana about 6–3 Ma, which could be consistent with a Pliocene divergence. Comparison of variation in plastid and nuclear markers revealed several lineages mostly congruent with their isolated geographical distribution and restricted gene flow among groups. Results of species distribution modelling and coalescent simulations fit a model of multiple refugia diverging during interglacial cycles. The demographic history of M. deppeana is not consistent with an expanding–contracting cloud forest archipelago model during the Last Glacial Maximum. Instead, our data suggest that populations persisted across the geographical range throughout the glacial cycles, and experienced isolation and divergence during interglacial periods.     

Multiple Pleistocene refugia and Holocene range expansion of an abundant southwestern American desert plant species (Melampodium leucanthum,Asteraceae)

Pleistocene climatic fluctuations had major impacts on desert biota in southwestern North America. During cooler and wetter periods, drought‐adapted species were isolated into refugia, in contrast to expansion of their ranges during the massive aridification in the Holocene. Here, we use Melampodium leucanthum (Asteraceae), a species of the North American desert and semi‐desert regions, to investigate the impact of major aridification in southwestern North America on phylogeography and evolution in a widespread and abundant drought‐adapted plant species. The evidence for three separate Pleistocene refugia at different time levels suggests that this species responded to the Quaternary climatic oscillations in a cyclic manner. In the Holocene, once differentiated lineages came into secondary contact and intermixed, but these range expansions did not follow the eastwardly progressing aridification, but instead occurred independently out of separate Pleistocene refugia. As found in other desert biota, the Continental Divide has acted as a major migration barrier for M. leucanthum since the Pleistocene. Despite being geographically restricted to the eastern part of the species’ distribution, autotetraploids in M. leucanthum originated multiple times and do not form a genetically cohesive group.     

A temporally dynamic approach for cladistic biogeography and the processes underlying the biogeographic patterns of North American deserts

We implemented a temporally dynamic approach to the cladistic biogeographic analysis of 13 areas of North American deserts and several plant and animal taxa. We undertook a parsimony analysis of paralogy‐free subtrees based on 43 phylogenetic hypotheses of arthropod, vertebrate and plant taxa, assigning their nodes to three different time slices based on their estimated minimum ages: Early‐Mid‐Miocene (23?7 Ma), Late Miocene/Pliocene (6.9?2.5 Ma) and Pleistocene (2.4?0.011 Ma). The analyses resulted in three general area cladograms, one for each time slice, showing different area relationships. They allowed us to detect influences of different geological and palaeoclimatological events of the Early‐Mid‐Miocene, Late Miocene/Pliocene and Pleistocene that might have affected the diversification of the desert biota. Several diversification events in the deserts of North America might have been driven by Neogene uplift, marine incursion and the opening of the California Gulf during the Miocene–Pliocene, whereas climatic fluctuations had the highest impact during the Pleistocene.     

Phylogeography of Douglas‐fir based on mitochondrial and chloroplast DNA sequences: testing hypotheses from the fossil record

The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range‐wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas‐fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas‐fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas‐fir varieties diverged about 2.11 Ma (4.37 Ma–755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas‐fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50–165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights.     

The evolution of sexual and parthenogenetic Warramaba: a window onto Plio–Pleistocene diversification processes in an arid biome

Environmental changes over the Plio‐Pleistocene have been key drivers of speciation patterns and genetic diversification in high‐latitude and mesic environments, yet comparatively little is known about the evolutionary history of species in arid environments. We applied phylogenetic and phylogeographic analyses to understand the evolutionary history of Warramaba grasshoppers from the Australian arid zone, a group including sexual and parthenogenetic lineages. Sequence data (mitochondrial COI) showed that the four major sexual lineages within Warramaba most likely diverged in the Pliocene, around 2–7 million years ago. All sexual lineages exhibited considerable phylogenetic structure. Detailed analyses of the hybrid parthenogenetic species W. virgo and its sexual progenitors showed a pattern of high phylogenetic diversity and phylogeographic structure in northern lineages, and low diversity and evidence for recent expansion in southern lineages. Northern sexual lineages persisted in localized refugia over the Pleistocene, with sustained barriers promoting divergence over this period. Southern parts of the present range became periodically unsuitable during the Pleistocene, and it is into this region that parthenogenetic lineages have expanded. Our results strongly parallel those for sexual and parthenogenetic lineages of the gecko Heteronotia from the same region, indicating a highly general effect of Plio‐Pleistocene environmental change on diversification processes in arid Australia.     

Evolution of Asian Interior Arid-Zone Biota: Evidence from the Diversification of Asian Zygophyllum (Zygophyllaceae)

The Asian interior arid zone is the largest desert landform system in the Northern Hemisphere, and has high biodiversity. Little is currently known about the evolutionary history of its biota. In this study, we used Zygophyllum, an important and characteristic component of the Asian interior arid zone, to provide new insights into the evolution of this biota. By greatly enlarged taxon sampling, we present the phylogenetic analysis of Asian Zygophyllum based on two plastid and one nuclear markers. Our phylogenetic analyses indicate that Asian Zygophyllum and Sarcozygium form a clade and Sarcozygium is further embedded within the shrub subclade. An integration of phylogenetic, biogeographic, and molecular dating methods indicates that Zygophyllum successfully colonized the Asian interior from Africa in the early Oligocene, and Asian Zygophyllum became differentiated in the early Miocene and underwent a burst of diversification in the late Miocene associated with the expansion of Asian interior arid lands due to orogenetic and climatic changes. Combining diversification patterns of other important components of the Asian interior arid zone, we propose a multi-stage evolution model for this biota: the late Eocene–early Oligocene origin, the early Miocene expansion, and the middle-late Miocene rapid expansion to the whole Asian interior arid zone. This study also demonstrates that, for Zygophyllum and perhaps other arid-adapted organisms, arid biomes are evolutionary cradles of diversity.     

Of glaciers and refugia: a decade of study sheds new light on the phylogeography of northwestern North America

Glacial cycles have played a dominant role in shaping the genetic structure and distribution of biota in northwestern North America. The two major ice age refugia of Beringia and the Pacific Northwest were connected by major mountain chains and bordered by the Pacific Ocean. As a result, numerous refugial options were available for the regions taxa during glacial advances. We reviewed the importance of glaciations and refugia in shaping northwestern North America’s phylogeographic history. We also tested whether ecological variables were associated with refugial history. The recurrent phylogeographic patterns that emerged were the following: (i) additional complexity, i.e. refugia within refugia, in both Beringia and the Pacific Northwest; and (ii) strong evidence for cryptic refugia in the Alexander Archipelago and Haida Gwaii, the Canadian Arctic and within the ice‐sheets. Species with contemporary ranges that covered multiple refugia, or those with high dispersal ability, were significantly more likely to have resided in multiple refugia. Most of the shared phylogeographic patterns can be attributed to multiple refugial locales during the last glacial maximum or major physiographic barriers like rivers and glaciers. However, some of the observed patterns are much older and appear connected to the orogeny of the Cascade‐Sierra chain or allopatric differentiation during historic glacial advances. The emergent patterns from this review suggest we should refine the classic Beringian‐southern refugial paradigm for northwestern North American biota and highlight the ecological and evolutionary consequences of colonization from multiple refugia.     

Quaternary range dynamics and polyploid evolution in an arid brushland plant species (Melampodium cinereum,Asteraceae)

Pleistocene climatic fluctuations played a principal role for range formation and population history of many biota, including regions not directly affected by glaciations, such as the arid habitats of the southwestern United States and adjacent Mexico. Specifically, drought-adapted species are expected to have persisted during cooler and wetter periods in one or more refugia, resulting in lineage differentiation, from where they reached their current distribution after range expansion in the course of Holocene aridification. Here, we test this hypothesis using Melampodium cinereum (Asteraceae), a morphologically and cytologically variable species of dry brushlands of Texas and adjacent Mexico. In line with the hypothesized presence of several refugia, AFLP data provide strong evidence for the presence of geographically distinct genetic lineages, which, however, only partly agree with current intraspecific taxonomy. Despite multiple origins, tetraploids form a genetically cohesive group. The exclusive occurrence of tetraploids in a range parapatric to that of the diploids likely results from former geographic isolation of cytotypes, lending further support for the presence of Pleistocene refugia. Whereas plastid sequence data show a clear signal for the expected Holocene range and population expansion, they show little geographic structure and high levels of intrapopulational diversity. This may be due to lineage sorting during periods of population separation and/or substantial gene flow among populations via seeds, which has not been sufficient to erode the overall pattern of genetic divergence resulting from geographic isolation.     

Gondwanan radiation of the Southern Hemisphere crayfishes (Decapoda: Parastacidae): evidence from fossils and molecules

Aim The sequential break‐up of Gondwana is thought to be a dominant process in the establishment of shared biota across landmasses of the Southern Hemisphere. Yet similar distributions are shared by taxa whose radiations clearly post‐date the Gondwanan break‐up. Thus, determining the contribution of vicariance versus dispersal to seemingly Gondwanan biota is complex. The southern freshwater crayfishes (family Parastacidae) are distributed on Australia and New Guinea, South America, Madagascar and New Zealand and are unlikely to have dispersed via oceans, owing to strict freshwater limitations. We test the hypotheses that the break‐up of Gondwana has led to (1) a predominately east–west (((Australia, New Zealand: 80 Ma) Madagascar: 160–121 Ma) South America: 165–140 Ma), or (2) a southern (((Australia, South America: 52–35 Ma) New Zealand: 80 Ma) Madagascar: 160–121 Ma) pattern for parastacid crayfish. Further, we examine the evidence for a complete drowning of New Zealand and subsequent colonization by freshwater crayfish. Location Southern Hemisphere. Methods The evolutionary relationships among the 15 genera of Parastacidae were reconstructed using mitochondrial [16S, cytochrome c oxidase subunit I (COI)] and nuclear (18S, 28S) sequence data and maximum likelihood and Bayesian methods of phylogenetic reconstruction. A Bayesian (multidivtime ) molecular dating method using six fossil calibrations and phylogenetic inference was used to estimate divergence time among crayfish clades on Gondwanan landmasses. Results The South American crayfish are monophyletic and a sister group to all other southern crayfish. Australian crayfish are not monophyletic, with two Tasmanian genera, Spinastacoides and Ombrastacoides, forming a clade with New Zealand and Malagasy crayfish (both monophyletic). Divergence of crayfish among southern landmasses is estimated to have occurred around the Late Jurassic to Early Cretaceous (109–178 Ma). Main conclusions The estimated phylogenetic relationships and time of divergence among the Southern Hemisphere crayfishes were consistent with an east–west pattern of Gondwanan divergence. The divergence between Australia and New Zealand (109–160 Ma) pre‐dated the rifting at around 80 Ma, suggesting that these lineages were established prior to the break‐up. Owing to the age of the New Zealand crayfish, we reject the hypothesis that there was a complete drowning of New Zealand crayfish habitat.     

Postglacial colonization of the Tibetan plateau inferred from the matrilineal genetic structure of the endemic red-necked snow finch, Pyrgilauda ruficollis

Most phylogeographical studies of postglacial colonization focus on high latitude locations in the Northern Hemisphere. Here, we studied the phylogeographical structure of the red-necked snow finch Pyrgilauda ruficollis, an endemic species of the Tibetan plateau. We analysed 879 base pairs (bp) of the mitochondrial cytochrome b gene and 529 bp of the control region in 41 birds from four regional groups separated by mountain ranges. We detected 34 haplotypes, 31 of which occurred in a single individual and only three of which were shared among sampling sites within regional groups or among regional groups. Haplotype diversity was high (h = 0.94); nucleotide diversity was low (eth = 0.00415) and genetic differentiation was virtually non-existent. Analyses of mismatch distributions and geographically nested clades yielded results consistent with contiguous range expansion, and the expansion times were estimated as 0.07-0.19 million years ago (Ma). Our results suggest that P. ruficollis colonized the Tibetan plateau after the extensive glacial period (0.5-0.175 Ma), expanding from the eastern margin towards the inner plateau. Thus, in contrast to many of the post-glacial phylogeographical structures known at high latitudes, this colonization occurred without matrilineal population structuring. This might be due to the short glacial cycles typical of the Tibetan plateau, adaptation of P. ruficollis to cold conditions, or refugia and colonized habitat being semicontinuous and thus promoting population mixing.     

Evolutionary shifts in habitat aridity predict evaporative water loss across squamate reptiles

Aridity is an important determinant of species distributions, shaping both ecological and evolutionary diversity. Lizards and snakes are often abundant in deserts, suggesting a high potential for adaptation or acclimation to arid habitats. However, phylogenetic evidence indicates that squamate diversity in deserts may be more strongly tied to speciation within arid habitats than to convergent evolution following repeated colonization from mesic habitats. To assess the frequency of evolutionary transitions in habitat aridity while simultaneously testing for associated changes in water‐balance physiology, we analyzed estimates of total evaporative water loss (EWL) for 120 squamate species inhabiting arid, semiarid, or mesic habitats. Phylogenetic reconstructions revealed that evolutionary transitions to and from semiarid habitats were much more common than those between arid and mesic extremes. Species from mesic habitats exhibited significantly higher EWL than those from arid habitats, while species from semiarid habitats had intermediate EWL. Phylogenetic comparative methods confirmed this association between habitat aridity and EWL despite phylogenetic signal in each. Thus, the historical colonization of arid habitats by squamates is repeatedly associated with adaptive changes in EWL. This physiological convergence, which may reflect both phenotypic plasticity and genetic adaptation, has likely contributed to the success of squamates in arid environments.     

Radiation and speciation of pelagic organisms during periods of global warming: the case of the common minke whale, Balaenoptera acutorostrata

How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean‐surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control‐region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re‐establishment of the polar–equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.     

Evolutionary systematics and biogeography of the arid habitat‐adapted rodent genus Gerbillus (Rodentia,Muridae): a mostly Plio‐Pleistocene African history

The systematics of the arid‐adapted Old World Gerbillus rodent genus has always been challenging, with many different taxonomic arrangements proposed. Beyond such taxonomic aspects, the timing and geographical pattern of the evolutionary history of this group remains largely unknown. Based on mitochondrial (cytochrome b) and nuclear (interphotoreceptor retinoid‐binding protein) sequences obtained from the specimens of 21 species, we conducted a phylogenetic analysis of the group, estimated the ages and putative ancestral ranges of its major lineages. Four major clades were clearly retrieved within Gerbillus, for which we propose a subgenus rank. We showed that the emergence of the genus dates back to the end of the Miocene, which corresponds to a period of aridification and C4 vegetation expansion in open habitats, while the four sublineages originated at the end of the Pliocene. Most subsequent diversification events occurred during the Pleistocene, a period characterized by recurrent climatic/environmental shifts with increasing aridification during the last two millions of years. Finally, we suggested that most of the Gerbillus evolutionary history took place in Africa. Only in a few instances did dispersal events from Africa to Asia give birth to extant Asian lineages, a pattern that contrasts with what has been found in many animal groups.     

Parallel adaptive radiations in arid and temperate Australia: molecular phylogeography and systematics of the Egernia whitii (Lacertilia: Scincidae) species group

It has been an enduring belief that increasing aridity combined with Pliocene‐Pleistocene glacial cycles resulted in the formation of distinct arid zone and temperate zone faunas within Australia. We assembled a molecular phylogeny for the Egernia whitii species group, an endemic group of skinks that comprises representatives from arid and temperate Australia, in order to test several biogeographical hypotheses regarding the origin of the Australian arid zone fauna. Sequence data were obtained from ten of the 11 species within the species group, plus three other Egernia species and an outgroup (Eulamprus heatwolei). We targeted portions of the ND4 (696 base pairs) and 16S rRNA (500 bp) mitochondrial genes and the β‐Fibrinogen 7th Intron nuclear gene (648 bp). The edited alignment comprised 1844 characters, of which 551 (30%) were variable and 382 (69%) were parsimony informative. We analysed the data using maximum likelihood and Bayesian techniques and produced a single optimal tree. Our phylogeny strongly supports two major clades within the species group, corresponding to temperate‐adapted rock‐dwelling species and arid‐adapted obligate burrowing species. However, the phylogenetic affinities of E. pulchra were not resolved. Our topology indicates that the New South Wales population of E. margaretae is actually E. whitii and reveals that E. margaretae margaretae and E. m. personata are distinct species. There also appears to be a major phylogeographical break within E. whitii occurring in eastern Victoria. Although our data supported several previously proposed phylogenetic relationships, Shimodaira–Hasegawa tests soundly rejected several suggested affinities between certain species. The arid zone members of the E. whitii species group had been suggested to have originated as a result of multiple periods of colonization during the Pleistocene glaciation cycles. However, our genetic data suggest a single origin (presumably from a semiarid E. multiscutata‐like ancestor) for the arid zone members of the group prior to the Plio‐Pleistocene, probably during the late Miocene to early Pliocene. Our topology displays substantial sequence divergence between species with short internodes and long terminal branches, indicating rapid adaptive radiations within the arid and temperate zones. The presence of temperate‐adapted species within more mesic refugia of the arid zone suggests that the necessary adaptations to aridity for colonizing the dry interior of the continent have not evolved since the initial period of adaptive radiation, despite the long evolutionary history of the species group. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 157–173.