The Effects of Social Experience on Aggressive Behavior in the Green Anole Lizard (Anolis carolinensis)

To understand how context-specific aggression emerges from past experience, we examined how consecutive aggressive encounters influence aggressive behavior and stress responses of male green anole lizards ( Anolis carolinensis ). Animals were shown a video clip featuring an aggressively displaying conspecific male, which provoked aggressive responding, while control animals viewed a neutral video. After 5 d of interaction with the videos, both the subject and control groups were presented with a live conspecific. As a non-invasive assay of stress responses, we measured changes in body color and eyespot darkness, two features known to be strongly correlated with titers of stress hormones. Our results demonstrate that experience increased aggression in male anoles, but that increases in aggression to a repeated stimulus were transient. Tests with a novel conspecific indicate that the experienced animals remained aggressive when presented with novel stimuli. Although there were differences in the morphological indicators of the stress response between experimental and control groups during video presentations, there were no differences when presented with novel conspecifics. These data indicate that experience-dependent differences were not mediated by differences in the 'stressfulness' of aggressive interaction, as thought to be the case for animals in chronic subordinate/dominant dyads. We suggest that habituation and reinforcement interact to promote aggressive responding and to restrict it to novel individuals. Such context specificity is a hallmark of natural patterns of aggression in territorial species.     

Genetic variation in the green anole lizard (Anolis carolinensis) reveals island refugia and a fragmented Florida during the quaternary

The green anole lizard (Anolis carolinensis) is a model organism for behavior and genomics that is native to the southeastern United States. It is currently thought that the ancestors of modern green anoles dispersed to peninsular Florida from Cuba. However, the climatic changes and geological features responsible for the early diversification of A. carolinensis in North America have remained largely unexplored. This is because previous studies (1) differ in their estimates of the divergence times of populations, (2) are based on a single genetic locus or (3) did not test specific hypotheses regarding the geologic and topographic history of Florida. Here we provide a multi-locus study of green anole genetic diversity and find that the Florida peninsula contains a larger number of genetically distinct populations that are more diverse than those on the continental mainland. As a test of the island refugia hypothesis in Pleistocene Florida, we use a coalescent approach to estimate the divergence times of modern green anole lineages. We find that all demographic events occurred during or after the Upper Pliocene and suggest that green anole diversification was driven by population divergence on interglacial island refugia in Florida during the Lower Pleistocene, while the region was often separated from continental North America. When Florida reconnected to the mainland, two separate dispersal events led to the expansion of green anole populations across the Atlantic Seaboard and Gulf Coastal Plain.     

An Analysis of Inter-Population Divergence in Visual Display Behavior of the Green Anole Lizard (Anolis carolinensis)

Variation in habitat structure can profoundly affect the evolution of visual displays in animals. We compared the field display behavior of two populations of the green anole lizard (Anolis carolinensis) in Southern Louisiana. These two populations occupy habitats varying markedly in structure (clumped vs. continuous), ecological setting (urban vs. natural) and the degree of male competition and predation. We filmed 56 large adult male lizards during the active spring reproductive period and detected substantial divergence in display behavior between populations. We found that (1) relative dewlap areas did not differ significantly between populations, (2) Tulane anoles spent about twice as much time displaying compared with Good Hope field anoles, although the average display duration did not differ significantly between populations, and (3) the two populations differed significantly in the relative frequency of display types: lizards from the Tulane population used a higher proportion of A and B display types, whereas Good Hope Field anoles used C displays more often. Finally, we detected differences in other aspects of display behavior (use of display modifiers, volley length distributions). We suggest that these display differences may result from differences in green anole male density (three times higher at Tulane), combined with habitat differences (clumped vs. continuous).     

Assessment Strategies and the Effects of Fighting Experience on Future Contest Performance in the Green Anole (Anolis carolinensis)

Social experiences can be useful sources of information for animals charged with making fitness‐related decisions. Fighting experience can alter an animal's perception of its fighting ability possibly leading to changes in future contest decisions, which may increase/decrease their probability of winning future contests. Winner and loser effects have been revealed in a wide array of animals, but studies using reptilian models are rare. This study investigated the impact of fighting experience on future contest performance and outcome in the green anole lizard and investigated the assessment strategies used by anoles during contests of different intensities. To determine whether the green anole expresses winner or loser effects, focal animals engaged in a primary contest with a smaller (larger) opponent to gain a winning (losing) experience; opponent size asymmetries were a significant predictor of contest outcome. Focal individuals were isolated for 2 d before being given a secondary contest with a size‐matched, naïve opponent. We found no evidence of winner or loser effects 2 d following a previous contest. Although previous contest outcome did not dictate future contest success, dynamics of the previous contest did. Highly aggressive primary contest losers won a significant proportion of the secondary contests, while less aggressive losers were more apt to lose the secondary contest. Secondary contest success of prior winners was not influenced by earlier contest performance. Further analyses of contest dynamics reveal that individuals may use different assessment strategies depending on the intensity of the contest. Our results demonstrate that future contest success may be driven more by individual performance in a prior contest and less by prior contest outcome.     

A phylogeographic analysis of populations of the wood turtle (Glyptemys insculpta) throughout its range

We investigated the phylogeography of wood turtles, Glyptemys insculpta, in North America using 750 bp of the mitochondrial control region from 117 individuals sampled at 29 localities across the species' range. A total of 21 haplotypes were identified and little genetic variation was found. The highest pairwise difference was 2%. From nested clade analysis (NCA), one main postglacial dispersal route was inferred along the east coast, with subsequent westward dispersal. NCA further revealed some patterns of restricted gene flow/dispersal. We propose that wood turtles experienced a combined effect of bottleneck during the Pleistocene as well as of selective sweep, which produced the low level of variation observed. Following the Pleistocene, wood turtles would have undergone a rapid northward expansion from a common southern refugium as glaciers retreated. These findings shed light on where to direct conservation priorities, on conservation strategies needed, and on the potential effects of interpopulation transfers for this vulnerable species.     

Phylogeography of Plathymenia reticulata (Leguminosae) reveals patterns of recent range expansion towards northeastern Brazil and southern Cerrados in Eastern Tropical South America

Little is known about past vegetation dynamics in Eastern Tropical South America (ETSA). Here we describe patterns of chloroplast (cp) DNA variation in Plathymenia reticulata, a widespread tree in the ETSA Atlantic Forest and Cerrado biomes, but not found in the xeromorphic Caatinga. Forty one populations, comprising 220 individuals, were analysed by sequencing the trnS‐trnG and trnL‐trnL‐trnF cpDNA regions. Combined, they resulted in 18 geographically structured haplotypes. The central region of the sampling area, comprising Minas Gerais and Goiás Brazilian states, is a centre of genetic diversity and probably the most longstanding area of the distribution range of the species. In contrast, populations from northeastern Brazil and the southern Cerrados showed very low diversity levels, almost exclusively with common haplotypes which are also found in the central region. Coupled with a long‐branched star‐like network, these patterns suggest a recent range expansion of P. reticulata to those regions from central region sources. The recent origin of the species (in the early Pleistocene) or the extinction of some populations due to drier and cooler climate during the last glacial maximum could have been responsible for that phylogeographic pattern. The populations from northeastern Brazil originated from two colonization routes, one eastern (Atlantic) and one western (inland). Due to its high diversity and complex landscape, the central region, especially central‐north Minas Gerais (between 15°–18° S and 42°–46° W), should be given the highest priority for conservation.     

Phylogeography of the bigeye chub Hybopsis amblops (Teleostei: Cypriniformes): early Pleistocene diversification and post‐glacial range expansion

The bigeye chub, Hybopsis amblops, is a member of the Central Highlands ichthyofauna of eastern North America. Phylogenetic analyses of the H. amblops species group based on a 1059 bp fragment of the mitochondrial DNA cytochrome b gene did not recover a monophyletic group. The inclusion of Hybopsis hypsinotus in the species complex is questionable. Within H. amblops, five strongly supported clades were identified; two clades containing haplotypes from the Ozark Highlands and three clades containing haplotypes from the Eastern Highlands and previously glaciated regions of the Ohio and Wabash River drainages. Estimates of the timing of divergence indicated that prior to the onset of glaciation, vicariant events separated populations east and west of the Mississippi River. East of the Mississippi River glacial cycles associated with the blocking and rerouting of the Teays River system caused populations to be pushed southward into refugia of the upper Ohio River. Following the most recent Wisconsinan glaciation, populations expanded northward into previously glaciated regions and southward into the Cumberland River drainage. In the Ozarks, west of the Mississippi River, isolation of clades appears to be maintained by the lack of stream capture events between the upper Arkansas and the White River systems and a barrier formed by the Arkansas River.     

Phylogeography of the Western Lyresnake (Trimorphodon biscutatus): testing aridland biogeographical hypotheses across the Nearctic-Neotropical transition

The Western Lyresnake (Trimorphodon biscutatus) is a widespread, polytypic taxon inhabiting arid regions from the warm deserts of the southwestern United States southward along the Pacific versant of Mexico to the tropical deciduous forests of Mesoamerica. This broadly distributed species provides a unique opportunity to evaluate a priori biogeographical hypotheses spanning two major distinct biogeographical realms (the Nearctic and Neotropical) that are usually treated separately in phylogeographical analyses. I investigated the phylogeography of T. biscutatus using maximum likelihood and Bayesian phylogenetic analysis of mitochondrial DNA (mtDNA) from across this species' range. Phylogenetic analyses recovered five well-supported clades whose boundaries are concordant with existing geographical barriers, a pattern consistent with a model of vicariant allopatric divergence. Assuming a vicariance model, divergence times between mitochondrial lineages were estimated using Bayesian relaxed molecular clock methods calibrated using geological information from putative vicariant events. Divergence time point estimates were bounded by broad confidence intervals, and thus these highly conservative estimates should be considered tentative hypotheses at best. Comparison of mtDNA lineages and taxa traditionally recognized as subspecies based on morphology suggest this taxon is comprised of multiple independent lineages at various stages of divergence, ranging from putative secondary contact and hybridization to sympatry of 'subspecies'.     

Phylogeography of the olive sea snake, Aipysurus laevis (Hydrophiinae) indicates Pleistocene range expansion around northern Australia but low contemporary gene flow

Pleistocene sea-level fluctuations profoundly changed landmass configurations around northern Australia. The cyclic emergence of the Torres Strait land bridge and concomitant shifts in the distribution of shallow-water marine habitats repeatedly sundered east and west coast populations. These biogeographical perturbations invoke three possible scenarios regarding the directions of interglacial range expansion: west to east, east to west, or bidirectional. We evaluated these scenarios for the olive sea snake, Aipysurus laevis, by exploring its genetic structure around northern Australia based on 354 individuals from 14 locations in three regions (Western Australia, WA; Gulf of Carpentaria, GoC; Great Barrier Reef, GBR). A 726-bp fragment of the mitochondrial DNA ND4 region revealed 41 variable sites and 38 haplotypes, with no shared haplotypes among the three regions. Population genetic structure was strong overall, phiST=0.78, P<0.001, and coalescent analyses revealed no migration between regions. Genetic diversity was low in the GBR and GoC and the genetic signatures of these regions indicated range or population expansions consistent with their recent marine transgressions around 7000 years ago. By contrast, genetic diversity on most WA reefs was higher and there were no signals of recent expansion events on these reefs. Phylogenetic analyses indicated that GBR and GoC haplotypes were derived from WA haplotypes; however, statistical parsimony suggested that recent range expansion in the GBR-GoC probably occurred from east coast populations, possibly in the Coral Sea. Levels of contemporary female-mediated gene flow varied within regions and reflected potential connectivity among populations afforded by the different regional habitat types.     

Genotyping‐by‐sequencing and ecological niche modeling illuminate phylogeography,admixture, and Pleistocene range dynamics in quaking aspen (Populus tremuloides)

Populus tremuloides is the widest‐ranging tree species in North America and an ecologically important component of mesic forest ecosystems displaced by the Pleistocene glaciations. Using phylogeographic analyses of genome‐wide SNPs (34,796 SNPs, 183 individuals) and ecological niche modeling, we inferred population structure, ploidy levels, admixture, and Pleistocene range dynamics of P. tremuloides, and tested several historical biogeographical hypotheses. We found three genetic lineages located mainly in coastal–Cascades (cluster 1), east‐slope Cascades–Sierra Nevadas–Northern Rockies (cluster 2), and U.S. Rocky Mountains through southern Canadian (cluster 3) regions of the P. tremuloides range, with tree graph relationships of the form ((cluster 1, cluster 2), cluster 3). Populations consisted mainly of diploids (86%) but also small numbers of triploids (12%) and tetraploids (1%), and ploidy did not adversely affect our genetic inferences. The main vector of admixture was from cluster 3 into cluster 2, with the admixture zone trending northwest through the Rocky Mountains along a recognized phenotypic cline (Utah to Idaho). Clusters 1 and 2 provided strong support for the “stable‐edge hypothesis” that unglaciated southwestern populations persisted in situ since the last glaciation. By contrast, despite a lack of clinal genetic variation, cluster 3 exhibited “trailing‐edge” dynamics from niche suitability predictions signifying complete northward postglacial expansion. Results were also consistent with the “inland dispersal hypothesis” predicting postglacial assembly of Pacific Northwestern forest ecosystems, but rejected the hypothesis that Pacific‐coastal populations were colonized during outburst flooding from glacial Lake Missoula. Overall, congruent patterns between our phylogeographic and ecological niche modeling results and fossil pollen data demonstrate complex mixtures of stable‐edge, refugial locations, and postglacial expansion within P. tremuloides. These findings confirm and refine previous genetic studies, while strongly supporting a distinct Pacific‐coastal genetic lineage of quaking aspen.     

Climate change and evolution of the New World pitviper genus Agkistrodon (Viperidae)

Aim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacépède, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa. Location Midwestern and eastern North America. Methods We reconstructed maximum parsimony (MP) and maximum likelihood (ML) relationships based on 846 base pairs of mitochondrial DNA (mtDNA) ATPase 8 and ATPase 6 genes sequenced over 178 individuals. We quantified range expansions, demographic histories, divergence dates and potential size differences among clades since their last period of rapid expansion. We used the Shimodaira–Hasegawa (SH) test to compare our ML tree against three biogeographical hypotheses. Results A significant SH test supported diversification of A. contortrix from northeastern Mexico into midwestern–eastern North America, where its trajectory was sundered by two vicariant events. The first (c. 5.1 Ma) segregated clades at 3.1% sequence divergence (SD) along a continental east–west moisture gradient. The second (c. 1.4 Ma) segregated clades at 2.4% SD along the Mississippi River, coincident with the formation of the modern Ohio River as a major meltwater tributary. A single glacial refugium was detected within the Apalachicola region of southeastern North America. Significant support was also found for a hypothesis of trans‐Gulf rafting by the common ancestor of A. piscivorus from eastern Mexico (possibly the Yucatan Peninsula) to northern Florida. There, a Mid–Late Pliocene marine transgression separated it at 4.8% SD from mainland North America. Significant range expansions followed compressive glacial effects in three (of four) A. contortrix clades and in two (of three) A. piscivorus clades, with the Florida A. piscivorus clade exhibiting significant distributional stasis. Main conclusions Pliocene glaciations, rapidly developing western aridity, and Pleistocene glacial meltwaters seemingly led to the diversification of A. contortrix and A. piscivorus in North America. Both species were pushed southwards by Pleistocene climate change, with subsequent northward expansions uninhibited topographically. The subspecific taxonomy used for A. contortrix and A. piscivorus today, however, appear non‐representative. The monophyletic Florida subspecies of A. piscivorus may be a distinct species (at 4.8% SD), whereas two western subspecies of A. contortrix also appear to constitute a single distinct species, pending additional analyses. We conclude that both species of Agkistrodon can be used as suitable ectothermic models to gauge impacts of future climate change.     

Molecular systematics,phylogeography, and the effects of Pleistocene glaciation in the painted turtle (Chrysemys picta) complex

Abstract.— The painted turtle, Chrysemys picta , is currently recognized as a continentally distributed polytypic species, ranging across North America from southern Canada to extreme northern Mexico. We analyzed variation in the rapidly evolving mitochondrial control region (CR) in 241 turtles from 117 localities across this range to examine whether the painted turtle represents a continentally distributed species based on molecular analysis. We found strong support for the novel hypothesis that C. p. dorsalis is the sister group to all remaining Chrysemys , with the remaining Chrysemys falling into a single, extremely wide-ranging and genetically undifferentiated species. Given our goal of an evolu-tionarily accurate taxonomy, we propose that two evolutionary lineages be recognized as species within Chrysemys : C. dorsalis (Agassiz 1857) in the southern Mississippi drainage region, and C. picta (Schneider 1783) from the rest of the range of the genus. Neither molecular nor recent morphological analyses argue for the hybrid origin of C. p. marginata as previously proposed. Within C. picta , we find evidence of at least two independent range expansions into previously glaciated regions of North America, one into New England and the other into the upper Midwest. We further find evidence of a massive extinction/recolonization event across the Great Plains/Rocky Mountain region encompassing over half the continental United States. The timing and extent of this colonization is consistent with a recently proposed regional aridification as the Laurentide ice sheets receded approximately 14,000 years ago, and we tentatively propose this paleoclimatological event as a major factor shaping genetic variation in Chrysemys .     

The rise and fall of the mountain hare (Lepus timidus) during Pleistocene glaciations: expansion and retreat with hybridization in the Iberian Peninsula

The climatic fluctuations during glaciations have affected differently arctic and temperate species. In the northern hemisphere, cooling periods induced the expansion of many arctic species to the south, while temperate species were forced to retract in southern refugia. Consequently, in some areas the alternation of these species set the conditions for competition and eventually hybridization. Hares in the Iberian Peninsula appear to illustrate this phenomenon. Populations of Iberian hare (Lepus granatensis), brown hare (Lepus europaeus) and broom hare (Lepus castroviejoi) in Northern Iberia harbour mitochondrial haplotypes from the mountain hare (Lepus timidus), a mainly boreal and arctic species presently absent from the peninsula. To understand the history of this past introgression we analysed sequence variation and geographical distribution of mitochondrial control region and cytochrome b haplotypes of L. timidus origin found in 378 specimens of these four species. Among 124 L. timidus from the Northern Palaearctic and the Alps we found substantial nucleotide diversity (2.3%) but little differentiation between populations. Based on the mismatch distribution of the L. timidus sequences, this could result from an expansion at a time of temperature decrease favourable to this arctic species. The nucleotide diversity of L. timidus mtDNA found in Iberian L. granatensis, L. europaeus and L. castroviejoi (183, 70 and 1 specimens, respectively) was of the same order as that in L. timidus over its range (1.9%), suggesting repeated introgression of multiple lineages. The structure of the coalescent of L. granatensis sequences indicates that hybridization with L. timidus was followed by expansion of the introgressed haplotypes, as expected during a replacement with competition, and occurred when temperatures started to rise, favouring the temperate species. Whether a similar scenario explains the introgression into Iberian L. europaeus remains unclear but it is possible that it hybridized with already introgressed L. granatensis.     

Northern and Southern expansions of Atlantic brown trout (Salmo trutta) populations during the Pleistocene

The phylogeography of Atlantic brown trout ( Salmo trutta ) was analysed using mitochondrial DNA control region complete sequences of 774 individuals from 57 locations. Additionally, the available haplotype information from 100 published populations was incorporated in the analysis. Combined information from nested clade analysis, haplotype trees, mismatch distributions, and coalescent simulations was used to characterize population groups in the Atlantic basin. A major clade involved haplotypes assigned to the Atlantic (AT) lineage, but another major clade should be considered as a distinct endemic lineage restricted to the Iberian Peninsula. The phylogeography of the Atlantic populations showed the mixed distribution of several Atlantic clades in glaciated areas of Northern Europe, whereas diverged haplotypes dominated the coastal Iberian rivers. Populations inhabiting the Atlantic rivers of southern France apparently contributed to postglacial colonization of northern basins, but also comprised the source of southern expansions during the Pleistocene.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 904–917.     

Early stages of divergence: phylogeography, climate modeling, and morphological differentiation in the South American lizard Liolaemus petrophilus (Squamata: Liolaemidae)

This study examines the phylogeographic structure within the Patagonian lizard Liolaemus petrophilus and tests for patterns of between-clade morphological divergence and sexual dimorphism, as well as demographic and niche changes associated with Pleistocene climate changes. We inferred intraspecific relationships, tested hypotheses for historical patterns of population expansion, and incorporated ecological niche modeling (ENM) with standard morphological and geometric morphometric analyses to examine between-clade divergence as indirect evidence for adaptation to different niches. The two inferred haploclades diverged during the early Pleistocene with the Southern clade depicting the genetic signature of a recent population increase associated with expanding niche envelope, whereas the Northern clade shows stable populations in a shrinking niche envelope. The combination of molecular evidence for postisolation demographic change and ENM, suggest that the two haploclades have responded differently to Pleistocene climatic events.     

Complex patterns of morphological and mtDNA variation in Lacerta perspicillata (Reptilia; Lacertidae)

Lacerta perspicillata is a north-west African lacertid lizard that shows considerable intraspecific variation, with three subspecies described on the basis of colour pattern and body size. Recent observations of a population containing two morphological forms and more than one deep genetic lineage, as well as an apparent lack of concordance between forms and genetic lineages, suggest that the complexity is greater than previously thought. To analyse and quantify this variation, we studied the variability within this species at two levels: (1) external morphology (multivariate analysis of scalation, body dimensions, and colour pattern) and (2) mtDNA (sequencing and single-strand confirmation polymorphism analysis). Fifty-two individuals were studied at Taza, northern Morocco. Two morphological groupings (ostensibly representing two previously described subspecies) and two deep mtDNA lineages were detected at this site, with complete correspondence between the two. This, together with an apparent lack of hybrids, would normally support respective full species recognition. However, analysis of 98 individuals from other populations demonstrated that the situation is highly complex with the same genetic lineages having reversed morphotypes in other areas, making such a designation difficult. Across the other studied populations, we found no support for any of the currently recognized subspecies. The lack of congruence between mtDNA lineages and morphometric patterns (in some cases) and the morphological similarity among lizards from different lineages suggest ecophenotypic convergence or multiple introgressive hybridization. The study highlights the tremendous complexity that may exist within a taxon and the inadequacy of older alpha-taxonomy based designations in describing it.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 479–490.     

Testing the ‘Pleistocene species pump’ in alpine habitats: lineage diversification of flightless ground beetles (Coleoptera: Carabidae: Nebria) in relation to altitudinal zonation

Alpine species often have similar demographic responses to Pleistocene climate changes, but exhibit different spatial patterns of genetic diversity. Using a comparative phylogeographical approach, we examined the factors influencing lineage formation in three alpine carabid beetles of the genus Nebria Latreille inhabiting the California Sierra Nevada. These flightless beetles differ in altitudinal zonation and habitat preferences, but overlap spatially, have limited dispersal capacities and share life history characteristics. Species distribution modelling predicted decreasing population connectivity in relation to increasing altitudinal preferences. Diversity patterns at the cytochrome oxidase subunit I gene revealed north–south genetic structure and recent population growth in all three species. The high‐elevation‐restricted species, Nebria ingens Horn, exhibited a deep phylogeographical split, morphological divergence and evidence of limited, unidirectional gene flow towards the south. This was supported by additional data from three nuclear genes and isolation with migration analysis. Nebria spatulata Van Dyke, inhabiting an intermediate altitudinal range, exhibited fixed morphological differences between northern and southern populations, but showed limited structure. The broadly distributed Nebria ovipennis LeConte showed less structure and lacked morphological variation. Diversification of these Nebria species supports the role of altitudinal zonation in lineage formation and is consistent with the Pleistocene species pump model. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Multiple introgression events and range shifts in Schizocodon (Diapensiaceae) during the Pleistocene

Range shifts during the Pleistocene shaped the unique phylogeographical structures of numerous species. Accompanying species migration, sister taxa may have experienced multiple introgression events. Here, we report the signature of introgression events in multiple areas in Schizocodon, herbs endemic to Japan, using amplified fragment length polymorphism (AFLP) fingerprinting and plastid DNA haplotyping in 48 populations. Although the present distributions of S. soldanelloides and S. ilicifolius are mainly allopatric, the species share plastid DNA haplotypes in each region (north‐eastern, north‐central, south‐central and south‐western Japan); in contrast, the specific groups were highly supported by AFLP analyses. These results support the occurrence of multiple introgression events in Schizocodon. Notably, the disjunct plastid haplotypes found only in S. ilicifolius var. intercedens suggest complete plastid DNA replacement at local areas from S. soldanelloides into S. ilicifolius var. ilicifolius. Furthermore, we found that S. soldanelloides experienced range contraction and expansion during glacial and interglacial cycles based on mismatch distribution analysis and ecological niche modelling. Based on several pieces of evidence, our study supports the idea that historical range shifts associated with Pleistocene climatic oscillations favoured multiple and regional introgression events in Schizocodon. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 46–63.     

Extensive chloroplast haplotype variation indicates Pleistocene hybridization and radiation of North American Arabis drummondii, A. x divaricarpa, and A. holboellii (Brassicaceae)

Arabis drummondii, A. holboellii and their hybrid A. x divaricarpa are widespread perennials of open habitats in North America. A phylogenetic analysis based on noncoding chloroplast DNA sequences (trnL intron and trnL/F intergenic spacer) resolved A. drummondii as a monophyletic taxon, but found A. holboellii to bear chloroplast haplotypes from highly diverged evolutionary lineages. This raised the question of a possible polyphyletic origin of A. holboellii. Arabis x divaricarpa was found to be of recent and polytopic origin, a result consistent with its presumed hybrid origin. One hundred and three chloroplast haplotypes were detected within 719 Arabis accessions investigated. The majority of chloroplast-types were estimated to have arisen prior to the Wisconsin glaciation. Phylogeographical analysis using nested clade analysis, suggested for A. holboellii (i). past fragmentation events, partitioning genetic variation in several instances between the Sierra Nevada, the Southern Rocky Mountains and the Colorado Plateau on the one hand and the Central to Northern Rockies of the United States and adjacent Cascades on the other; and for both parental species (ii). recolonization of major areas formerly covered by the Wisconsin glaciation by three haplotypes; and (iii). restricted gene flow indicating isolation by distance in areas south of the last glacial maximum. Arabis x divaricarpa is closely codistributed with its parental species and resampled their haplotypes. The highest genetic diversity was found in the Rocky Mountains from Idaho and Montana south to Utah and Colorado. This area was further hypothesized to have played a major role in the origin of both parental species and probably represented an important glacial refugium. However, evidence for glacial refugia was also found in arctic and boreal regions of Alaska and near the Great Lakes. In comparison to nuclear ribosomal internal transcribed spacer data, chloroplast DNA divergence was very high and evidently predated the origin of A. drummondii and possibly A. holboellii. Divergence of major chloroplast lineages dates back to the middle of the Pleistocene at least. Extensive hybridization is the most likely evolutionary factor working on A. holboellii to explain the revealed discrepancy in nuclear DNA and chloroplast DNA diversification.