Biogeographic Break Research Articles

The Vascular Flora and Phytogeographical Analysis of the Tennessee River Gorge, Hamilton and Marion Counties, Tennessee

An inventory of the vascular flora of the Tennessee River Gorge (TRG) was conducted between April 2009 and July 2011. The TRG is a 41-km-long river canyon located on the Cumberland Plateau physiographic province within Hamilton and Marion counties, TN. According to prior ecological surveys, the 4970-ha study area contains 12 natural communities. This survey documented 123 families, 392 genera, and 700 species and sub-specific taxa, including 138 county range extensions. Approximately 13% of the flora (92 species) is considered non-native. Fifteen imperiled species were reported, including 3 that are undescribed and 9 not documented in any previous Cumberland Plateau flora. In addition to the floristic component of this work, a phytogeographical analysis was conducted for the TRG and 12 other Cumberland Plateau floras in Tennessee and Kentucky. An important finding of this research was the identification of a biogeographical transition zone, from a higher northern to a higher southern species richness. This biogeographic break was identified in the vicinity of Fentress, Scott, and Morgan counties, TN.

Identifying biases at different spatial and temporal scales of diversification: a case study in the Neotropical parrotlet genus Forpus

The temporal origins of the extraordinary biodiversity of the Neotropical region are highly debated. Recent empirical work has found support for alternative models on the tempo of speciation in Neotropical species further fuelling the debate. However, relationships within many Neotropical lineages are poorly understood, and it is unclear how this uncertainty impacts inferences on the evolution of taxa in the region. We examined the robustness of diversification patterns in the avian genus Forpus by testing whether the use of different units of biodiversity (i.e. biological species and statistically inferred species) impacted diversification rates and inferences regarding important biogeographic breaks in the genus. We found that the best-fit model of diversification for the biological species data set was a declining rate of diversification; whereas a model of constant diversification was the best-fit model for statistically inferred species or subspecies. Moreover, the relative importance of different landscape features in delimiting genetic structure across the landscape varied across data sets with differing units of biodiversity. Patterns based on divergence times among biological species indicated old speciation events across major geographic and river barriers. In contrast, data sets more inclusive of the diversity in Forpus illustrate the role of both old divergence across major landscape features and more recent divergences that are possibly attributed to Pleistocene climatic changes. Overall, these results indicate that conflicting models on the temporal origins of Neotropical birds may be attributable to sampling biases.

Range‐wide population genetic structure of the Caribbean sea fan coral, Gorgonia ventalina

The population structure of benthic marine organisms is of central relevance to the conservation and management of these often threatened species, as well as to the accurate understanding of their ecological and evolutionary dynamics. A growing body of evidence suggests that marine populations can be structured over short distances despite theoretically high dispersal potential. Yet the proposed mechanisms governing this structure vary, and existing empirical population genetic evidence is of insufficient taxonomic and geographic scope to allow for strong general inferences. Here, we describe the range-wide population genetic structure of an ecologically important Caribbean octocoral, Gorgonia ventalina. Genetic differentiation was positively correlated with geographic distance and negatively correlated with oceanographically modelled dispersal probability throughout the range. Although we observed admixture across hundreds of kilometres, estimated dispersal was low, and populations were differentiated across distances <2 km. These results suggest that populations of G. ventalina may be evolutionarily coupled via gene flow but are largely demographically independent. Observed patterns of differentiation corroborate biogeographic breaks found in other taxa (e.g. an east/west divide near Puerto Rico), and also identify population divides not discussed in previous studies (e.g. the Yucatan Channel). High genotypic diversity and absence of clonemates indicate that sex is the primary reproductive mode for G. ventalina. A comparative analysis of the population structure of G. ventalina and its dinoflagellate symbiont, Symbiodinium, indicates that the dispersal of these symbiotic partners is not coupled, and symbiont transmission occurs horizontally.

Patterns of endemicity and range restriction among southern African coastal marine invertebrates

Southern Africa supports a rich marine biota of 12 734 currently described marine species. Although the distribution and overall species-richness patterns of several component taxa are well documented, studies considering range sizes are absent. This study considers range size frequencies and distribution patterns of seven major marine invertebrate taxa. The most commonly observed pattern of size frequency distributions is bimodal, with a predominance of species with either small or large range sizes, and few taxa with intermediate-sized ranges. This pattern is displayed by prosobranch and opisthobranch molluscs, polychaetes and amphipods, and for all invertebrate taxa examined combined. Peaks in small range sizes are likely a reflection of the numerous poorly sampled and/or endemic species in the region, while the high number of species with large range sizes can be attributed to the large proportion of widespread tropical Indo-Pacific species within the regional fauna. Overall, the largest peaks of range-restricted endemic species occurred around False Bay, Port Elizabeth, Durban, St Lucia and Maputo Bay. These areas are all situated at or adjacent to recognised biogeographic breaks for invertebrate assemblages, but coincidentally also tend to also be areas of enhanced research and shipping activity. The Cape Point region supports the highest number of endemics, with 73 species restricted to ranges of <100 km and 28 species to ranges <200 km.

Fine‐scale quantification of floral and faunal breaks and their geographic correlates, with an example from south‐eastern Australia

AbstractAim We introduce a method to quantify shared breaks in aggregate biotic distributions and their relationships to geographic variables. The method is based on quantification of distributional taxic and abiotic data that can be applied over multiple spatial scales. We aim to show biogeographic breaks and varying transition zones at a fine level of detail (5‐km resolution) and develop an approach to assess existing bioregionalization schemes.Location Global applicability, using an example from New South Wales in south‐eastern Australia.Methods Moving window analyses, rotated in 15° increments through 360°, are used to assess the degree of anisotropic spatial turnover between sets of gridded cells containing georeferenced species observations. Patterns of biotic turnover are compared with equivalent analyses for elevation and lithology. Identified breaks are assessed against an existing bioregionalization scheme (Interim Biogeographic Regionalisation of Australia, IBRA).Results There was fine‐scale concordance between turnover patterns and several IBRA bioregions. Breaks in turnover of flora and fauna corresponded with the boundaries of the Hunter Valley and Sydney Basin regions, particularly the boundary between the Brigalow Belt South and Sydney Basin. Low‐turnover zones were quantified; prominent examples are the Sydney Cataract and Wyong bioregions. Turnover along many boundaries was gradational, confirming that mapped breaks are not abrupt. A previously unidentified break was identified in the South East Corner bioregion. Spatial turnover patterns were similar between biota and were reflected in mean correlation coefficients between turnover in each group: mammals–reptiles (r = 0.70, P &lt;&lt; 0.01); mammals–flora (r = 0.56, P &lt;&lt; 0.01); and reptiles–flora (r = 0.51, P &lt;&lt; 0.01). Generally, patterns of abiotic turnover reflected biotic turnover, although mean turnover correlations were weaker than between biota.Main conclusions Using this method we were able to characterize taxic breaks and overlaps in detail and at a spatially fine resolution. For our study region, we confirm the overall integrity of the IBRA framework, but suggest that it may benefit from revision in some respects.

Species replacement along a linear coastal habitat: phylogeography and speciation in the red alga Mazzaella laminarioidesalong the south east pacific

BackgroundThe Chilean shoreline, a nearly strait line of coast expanding across 35 latitudinal degrees, represents an interesting region to assess historical processes using phylogeographic analyses. Stretching along the temperate section of the East Pacific margin, the region is characterized by intense geologic activity and has experienced drastic geomorphological transformations linked to eustatic and isostatic changes during the Quaternary. In this study, we used two molecular markers to evaluate the existence of phylogeographic discontinuities and detect the genetic footprints of Pleistocene glaciations among Patagonian populations of Mazzaella laminarioides, a low-dispersal benthic intertidal red seaweed that inhabits along ~3,700 km of the Chilean coastal rocky shore.ResultsThree main genetic lineages were found within M. laminarioides. They are distributed along the Chilean coast in strict parapatry. The deep divergence among lineages suggests that they could be considered putative genetic sibling species. Unexpectedly, genetic breaks were not strictly concordant with the biogeographic breaks described in the region. A Northern lineage was restricted to a broad transition zone located between 30°S and 33°S and showed signals of a recent bottleneck. The reduction of population size could be related to warm events linked to El Niño Southern Oscillation, which is known to cause massive seaweed mortality in this region. To the south, we propose that transient habitat discontinuities driven by episodic tectonic uplifting of the shoreline around the Arauco region (37°S-38°S); one of the most active forearc-basins in the South East Pacific; could be at the origin of the Central/South genetic break. The large beaches, located around 38°S, are likely to contribute to the lineages’ integrity by limiting present gene flow. Finally, the Southern lineage, occupies an area affected by ice-cover during the last glaciations. Phylogeny suggested it is a derived clade and demographic analyses showed the lineage has a typical signature of postglacial recolonization from a northern glacial refugium area.ConclusionsEven if environmental adaptation could have strengthened divergence among lineages in M. laminarioides, low dispersal capacity and small population size are sufficient to generate phylogeographic discontinuities determined by genetic drift alone. Interestingly, our results confirm that seaweed population connectivity over large geographic scales does not rely only on dispersal capacity but also seem to depend highly on substratum availability and population density of the receiving locality.

Phylogeography and Biogeography Concordance in the Marine Gastropod Crepipatelladilatata (Calyptraeidae) along the Southeastern Pacific Coast

The biogeography and phylogeography concordance hypothesis suggests that the same factors, for instance physical barriers or environmental gradients, shape both species assemblages and intraspecific genetic structure. In the marine realm, previous studies have however suggested that phylogeographic patterns are also explained by the life-history strategy of the species. However, evidence is contradictory and comes mainly from the northern hemisphere, which is characterized by specific environmental conditions and evolutionary histories of species. In this work, we evaluated the concordance hypothesis in the southern Pacific using the marine gastropod Crepipatella dilatata as a case study. This intertidal species with direct development exhibited a restricted dispersal potential, a feature that contrasts with previous species studied in the same area. Using the gene cytochrome oxidase I, we analyzed 253 individuals sampled at 10 locations covering 543 km of the coast of Chile. The study sites also incorporated 2 biogeographic regions separated by a well-studied biogeographic break (at 30°S). Populations of C. dilatata displayed a high degree of genetic structure and a perfect match between phylogeographic and biogeographic breaks at 30°S. When comparing our data with previous research over the same geographic range, life history traits related to dispersal ability seem to be a good proxy for explaining the concordance between biogeography and phylogeography along the southeastern pacific coast. In addition, in this and other marine invertebrate species, gene flow limitations across both sides of the 30°S break may act as a driver of the speciation process.

Locating faunal breaks in the nearshore fish assemblage of Victoria, Australia

Marine communities are frequently biogeographically structured, despite the potential for dispersal. Previous research on a variety of marine taxa in south-eastern Australia has suggested that a biogeographic break occurs along the coastline of Victoria. However, little of this research has focussed on nearshore ichthyofauna and the location of the break remains debated. Using fish abundance measured by two methods: underwater visual census (UVC); and baited remote underwater video (BRUV) at six locations along the open coast of Victoria, we examined (1) whether there is sufficient concordance among species to indicate the presence of a faunal break; and if present (2) where any such breaks occur. Differences in assemblage composition between locations were tested with analyses of similarity and examination of residuals from regressions of pairwise dissimilarities against coastline distance. Data collected using UVC revealed two large faunal breaks co-located with a habitat discontinuity, the convergence of two currents and a thermal gradient. Data collected by BRUV revealed only a gradation of change across the study region. Greater understanding of the biogeographic structure of these communities will facilitate more effective management, especially in light of anticipated range shifts in response to global climate change.

Phylogeography and reproductive variation of the poecilogonous polychaeteBoccardiaproboscidea(Annelida:Spionidae) along theWestCoast ofNorthAmerica

The ability to produce more than one kind of offspring, or poecilogony, is a striking example of reproductive variability. Traditionally, larval nutrition has been classified as a dichotomy: if offspring obtain nutrition from their mothers (lecithotrophy), there is lower fecundity and greater chance of offspring survival than when they get their nutrition from plankton (planktotrophy). The polychaete Boccardia proboscidea (Spionidae) produces both types of embryos using three different reproductive strategies. In this study, we examined the roles of genetic history and phenotypic plasticity on explaining natural variation in B. proboscidea along the Pacific coast of the United States using two genetic mitochondrial markers, 16S rDNA and Cyt b, and common garden experiments. These data show a single North American West Coast network that is structured, geographically, by the well-documented biogeographic break near Point Conception, California. The southern group within this network covers a smaller range, but has larger haplotype diversity, than the northern group. Some individuals differing in reproductive type had the same haplotype, indicating independence of these features; however, differences between laboratory and field data suggest additional geographic variation within one of the reproductive types. Females from higher latitudes provide offspring with larger supplies of extra embryonic nutrition than females from southern latitudes. Results herein suggest that both genetic history and developmental plasticity are playing a role in the maintenance of this reproductive polymorphism.

Population Genetic Structure of the New Zealand Estuarine Clam Austrovenus stutchburyi (Bivalvia: Veneridae) Reveals Population Subdivision and Partial Congruence with Biogeographic Boundaries

We examined the population genetic structure of the New Zealand endemic clam, Austrovenus stutchburyi, to determine (1) whether populations of this estuarine taxon are genetically subdivided and (2) if the locations of genetic boundaries were congruent with known biogeographic break points. We obtained sequences of the mitochondrial gene cytochrome c oxidase I for 372 A. stutchburyi from 29 New Zealand estuaries and conducted analyses to identify population genetic structure. We detected a pattern of genetic isolation by distance and identified six A. stutchburyi subpopulations, a greater number of subpopulations than reported for much of New Zealand’s open coast benthos. Although these data indicate that long distance dispersal may be less frequent in estuarine than in open coast taxa, partial congruence between genetic and biogeographic boundaries suggests that historical events and natural selection may also contribute to the observed population genetic structure.

Spatial pattern of genetic and morphological diversity in the direct developer Acanthina monodon (Gastropoda: Mollusca)

Three biogeographic areas have been recognized along the Chilean coast, with biogeo- graphic breaks located at 30 and 42° S allowing us to test the concordance between biogeographic patterns and spatial patterns of genetic and morphological diversity in marine species. We examined the marine gastropod Acanthina monodon, whose range spans the 2 major biogeographic breaks detected in the South-Eastern Pacific (SEP) coast. This species exhibits high variability in the mor- phology of its shell and has a direct development cycle. Based on the analysis of mitochondrial sequences of 258 individuals from 9 locations in the 3 biogeographic areas, we found 3 clades with contrasting levels of genetic diversity and with spatial population genetic structure. A perfect match between biogeography and pylogeography was observed only at the 30° S break. In contrast, we did not find a clear genetic break in concordance with the 42° S phylogeographic break, although haplo- type distribution suggested a second phylogeographic boundary located between 45 and 53° S. Only one haplotype was observed in the most southerly location, which may be explained by the historical influence of glaciations. A break in shell morphology was evidenced only at around 40 to 46° S, with a group characterized by thinner shells and longer spires compared to the northern group. Our results supported the concordance hypothesis and indicated that the influence of life cycle strategy, habitat discontinuity and historical processes may determine the phylogeographical and shell mor- phology spatial pattern of A. monodon. In contrast to previous studies, our genetic analysis showed the presence of a single Acanthina species along the SEP coast.

Patterns of genetic diversity in the critically endangered Central American river turtle: human influence since the Mayan age?

We conducted a phylogeographic analysis of the strictly aquatic and critically endangered Central American river turtle, Dermatemys mawii, as part of a conservation management program for the species. We sampled 238 individuals from 15 different localities throughout the species range. Using sequence fragments from the mtDNA Cyt b and ND4 genes, we identified 16 different haplotypes. Overall, our results reveal a signal of phylogeographic structure throughout the range, which appears to have been secondarily blurred by extensive gene flow. Notably, this also applies to genetic structuring across three major hydrological basins that pose biogeographic breaks in other aquatic taxa. Divergence times of mtDNA haplotypes in D. mawii suggest that the main lineages split in the Pliocene–Pleistocene (3.73–0.227 MA) and demographic tests indicate that the species has undergone drastic demographic size fluctuations since this time period. One ancient haplotype (1D) was found to exhibit sequence divergence of up to 2% from other haplogroups. Divergence of this magnitude is indicative of species level differentiation in other turtle genera. Haplotype 1D was found in only two localities, Sarstun and Salinas, but specimens with other haplotypes were also found in those localities. It is not known whether the individuals with the 1D haplotype interbreed with non-1D individuals. Our results suggest that human activity, such as harvesting and long distance transport of animals, may have influenced the current patterns of genetic diversity. For more than 2000 years, D. mawii has been consumed by people from Middle American cultures, and the archeological record contains strong evidence that the Mayans transported animals between villages and far away from their natural distribution range. Therefore, the large-scale pattern of haplotype sharing even across hydrological barriers, the observed low haplotype diversity in some populations and the contemporary absence of a pronounced phylogeographic pattern is likely due to a combination of population expansions, gene flow, extensive human-mediated-movements and recent bottlenecks resulting from over-harvesting.

A Southern Hemisphere Bathyal Fauna Is Distributed in Latitudinal Bands

The large-scale spatial distribution of seafloor fauna is still poorly understood. In particular, the bathyal zone has been identified as the key depth stratum requiring further macroecological research, particularly in the Southern Hemisphere. Here we analyze a large biological data set derived from 295 research expeditions, across an equator-to-pole sector of the Indian, Pacific, and Southern oceans, to show that the bathyal ophiuroid fauna is distributed in three broad latitudinal bands and not primarily differentiated by oceanic basins as previously assumed. Adjacent faunas form transitional ecoclines rather than biogeographical breaks. This pattern is similar to that in shallow water despite the order-of-magnitude reduction in the variability of environmental parameters at bathyal depths. A reliable biogeography is fundamental to establishing a representative network of marine reserves across the world's oceans.

Genetic structure of the giant kelp Macrocystis pyrifera along the southeastern Pacific

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 420:103-112 (2010) - DOI: https://doi.org/10.3354/meps08893 Genetic structure of the giant kelp Macrocystis pyrifera along the southeastern Pacific E. C. Macaya1,2,*, G. C. Zuccarello1 1School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand 2Present address: Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile *Email: erasmomacaya@udec.cl ABSTRACT: We assessed the genetic structure of the giant kelp Macrocystis pyrifera across a broad latitudinal range along the southeastern Pacific coast (SEP). Specifically we analyzed the concordance of putative biogeographic breaks with genetic discontinuities and the effect of historical and contemporary events on the genetic pattern of this important seaweed. Mitochondrial DNA and single-strand DNA conformation polymorphism (SSCP) analysis for a total of 730 samples were carried out. Only 5 haplotypes were found among individuals collected along 4800 km of coastline, with very low haplotype diversity and a shallow genealogy compared with other macroalgal species. Some phylogeographic disjunctions in M. pyrifera were found to correspond roughly to established biogeographic breaks. On the southern coast we found a genetic break at 42°S (Chiloé Island) coincident with a well-known biogeographic boundary, while the genetic break found between samples in central/northern Chile (33°S) does not correspond to any known biogeographic breaks in other brown algae, but does reflect a break associated with other marine taxa. The low genetic diversity in northern Chile may be related to contemporary events (e.g. El Niño Southern Oscillation) while in southern Chile the haplotype distribution may reflect the effect of historical events (Last Glacial Maximum; LGM). Additionally, we compared the SEP data with samples from some of the subantarctic islands and New Zealand. The results showed shared haplotypes among some of the subantarctic islands and southern-central Chile, suggesting a recent colonization of the subantarctic region. The high dispersal potential of kelp rafts may also help to explain the low genetic diversity observed. We conclude that both present and historic events are responsible for the genetic structure of M. pyrifera along the SEP. KEY WORDS: Dispersal · Biogeography · ENSO · Kelp · Macrocystis pyrifera · Mitochondrial DNA Phylogeography · Southeastern Pacific · Subantarctic Full text in pdf format PreviousNextCite this article as: Macaya EC, Zuccarello GC (2010) Genetic structure of the giant kelp Macrocystis pyrifera along the southeastern Pacific. Mar Ecol Prog Ser 420:103-112. https://doi.org/10.3354/meps08893 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 420. Online publication date: December 16, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Ommastrephid squids Sthenoteuthis oualaniensis and Dosidicus gigas in the eastern Pacific show convergent biogeographic breaks but contrasting population structures

Dosidicus gigas and Sthenoteuthis oualaniensis (Teuthoidea: Ommastrephidae: Ommastrephinae) are abundant, ecologically important squid that co-occur in the eastern tropical Pacific. Little is known about the genetic basis of population structure in either species, although the presence of 2 species within S. oualaniensis has been suggested. We report here on a comparative population genetic study of D. gigas and S. oualaniensis using the mitochondrial marker NADH dehydrogenase subunit 2. Despite the high potential for dispersal in these active swimmers, both spe- cies exhibit a distinct biogeographic break at 5 to 6° N. S. oualaniensis contains multiple deeply divergent, geographically segregated clades, whereas D. gigas shows only mild divergence between northern and southern hemisphere populations. We suggest that dispersal and genetic mixing across the eastern tropical Pacific may be impeded by both oceanographic and ecological factors.

Molecular systematics of Selenops spiders (Araneae: Selenopidae) from North and Central America: implications for Caribbean biogeography

The Caribbean region includes a geologically complex mix of islands, which have served as a backdrop for some significant studies of biogeography, mostly with vertebrates. Here, we use the tropical/subtropical spider genus Selenops (Selenopidae) to obtain a finer resolution of the role of geology in shaping patterns of species diversity. We obtained a broad geographic sample from over 200 localities from both the islands and American mainland. DNA sequence data were generated for three mitochondrial genes and one nuclear gene for eleven outgroup taxa and nearly 60 selenopid species. Phylogenetic analysis of the data revealed several biogeographic patterns common to other lineages that have diversified in the region, the most significant being: (1) a distinct biogeographic break between Northern and Southern Lesser Antilles, although with a slight shift in the location of the disjunction; (2) diversification within the islands of Jamaica and Hispaniola; (3) higher diversity of species in the Greater Antilles relative to the Lesser Antilles. However, a strikingly unique pattern in Caribbean Selenops is that Cuban species are not basal in the Caribbean clade. Analyses to test competing hypotheses of vicariance and dispersal support colonization through GAARlandia, an Eocene–Oligocene land span extending from South America to the Greater Antilles, rather than over-water dispersal. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 288–322.

An emergent community ecosystem model applied to the California Current System

An ecosystem model that supports considerable phytoplankton diversity is coupled to a circulation model of the California Current System. The Regional Ocean Modeling System is configured for a realistic simulation at 0.1° resolution for years 2000–2004. The concentration-based ecosystem model includes multiple nutrients, dissolved and particulate organic pools, two grazers, and 78 phytoplankton organism. Primary producers divide into 4 functional groups representing diatoms, large phytoplankton that do not require silicate, Prochlorococcus-like organisms, and small phytoplankton that can use nitrate. Random selection of phytoplankton growth parameters creates an autotrophic community able to fill multiple environmental niches created by the physical circulation and plankton population. In the 5-year average, over 98% of the total biomass at the surface is contained within 8 primary producers, with 30 additional phytoplankton sustained at lower levels. Modeled surface phytoplankton biomass is evaluated on multi-annual and seasonal bases using satellite chlorophyll estimates for the same period. The self-organized communities produced by the model represent various features of the California Current Ecosystem, including the biogeographic break at Pt. Conception. The annual average fields generally reveal high diatom concentrations nearshore, with small phytoplankton more broadly distributed. Prochlorococcus-like organisms are absent or at relatively low concentrations at the coast, increasing across the California Current. Small non- Prochlorococcus-like phytoplankton types are found at highest concentrations nearshore and far offshore. The model exhibits both surface and subsurface features, including a seasonal subsurface chlorophyll maximum along CalCOFI Line 77 between May and October. Time-series of area averaged model fields show seasonal progressions of different phytoplankton groups.

Using regional comparative phylogeographic data from snake lineages to infer historical processes in Middle America

Understanding how historical processes have either similarly, or differentially, shaped the evolution of lineages or biotic assemblages is important for a broad spectrum of fields. Gaining such understanding can be particularly challenging, however, especially for regions that have a complex geologic and biological history. In this study we apply a broad comparative approach to distill such regional biogeographic perspectives, by characterizing sets of divergence times for major biogeographic boundaries estimated from multiple codistributed lineages of snakes. We use a large combined (mitochondrial gene sequence) phylogeographic/phylogenetic dataset containing several clades of snakes that range across Middle America – the tropical region between Mexico and northwestern South America. This region is known for its complex tectonic history, and poorly understood historical biogeography. Based on our results, we highlight how phylogeographic transition zones between Middle and South America and the Nicaragua Depression appear to have undergone multiple episodes of diversification in different lineages. This is in contrast to other examples we find where apparently a single vicariant period is shared across multiple lineages. We specifically evaluate the distributions of divergence time estimates across multiple lineages and estimate the number of temporal periods of lineage diversification per biogeographic break. Overall, our results highlight a great deal of shared temporal divergence, and provide important hypotheses for yet unstudied lineages. These multi‐lineage comparisons across multiple spatial and temporal scales provide excellent predictive power for identifying the roles of geology, climate, ecology and natural history in shaping regional biodiversity.

Life history, ecology and the biogeography of strong genetic breaks among 15 species of Pacific rockfish, Sebastes

Strong genetic change over short spatial scales is surprising among marine species with high dispersal potential. Concordant breaks among several species signals a role for geographic barriers to dispersal. Along the coast of California, such breaks have not been seen across the biogeographic barrier of Point Conception, but other potential geographic boundaries have been surveyed less often. We tested for strong-population structure in 11 species of Sebastes sampled across two regions containing potential dispersal barriers, and conducted a meta-analysis including four additional species. We show two strong breaks north of Monterey Bay, spanning an oceanographic gradient and an upwelling jet. Moderate genetic structure is just as common in the north as it is in the south, across the biogeographic break at Point Conception. Gene flow is generally higher among deep-water species, but these conclusions are confounded by phylogeny. Species in the subgenus Sebastosomus have higher structure than those in the subgenus Pteropodus, despite having larvae with longer pelagic phases. Differences in settlement behavior in the face of ocean currents might help explain these differences. Across similar species across the same coastal environment, we document a wide variety of patterns in gene flow, suggesting that interaction of individual species traits such as settlement behavior with environmental factors such as oceanography can strongly impact population structure.

Variable responses of skinks to a common history of rainforest fluctuation: concordance between phylogeography and palaeo‐distribution models

There is a growing appreciation of impacts of late-Quaternary climate fluctuations on spatial patterns of species and genetic diversity. A major challenge is to understand how and why species respond individualistically to a common history of climate-induced habitat fluctuation. Here, we combine modelling of palaeo-distributions and mitochondrial-DNA phylogeographies to compare spatial patterns of population persistence and isolation across three species of rainforest skinks (Saproscincus spp.) with varying climatic preferences. Using Akaike Information Criterion model-averaged projections, all three species are predicted to have maintained one or more small populations in the northern Wet Tropics, multiple or larger populations in the central region, and few if any in the south. For the high-elevation species, Saproscincus czechurai, the warm-wet climate of the mid Holocene was most restrictive, whereas for the generalist S. basiliscus and lower-elevation S. tetradactyla, the cool-dry last glacial maximum was most restrictive. As expected, S. czechurai was the most genetically structured species, although relative to modelled distributions, S. basiliscus had surprisingly deep phylogeographical structure among southern rainforest isolates, implying long-term isolation and persistence. For both S. basiliscus and S. tetradactyla, there was high genetic diversity and complex phylogeographical patterns in the central Wet Tropics, reflecting persistence of large, structured populations. A previously identified vicariant barrier separating northern and central regions is supported, and results from these species also emphasize a historical persistence of populations south of another biogeographical break, the Tully Gorge. Overall, the results support the contention that in a topographically heterogeneous landscape, species with broader climatic niches may maintain higher and more structured genetic diversity due to persistence through varying climates.