THE EVOLUTION OF LOCAL ENDEMISM IN MADAGASCAR: WATERSHED VERSUS CLIMATIC GRADIENT HYPOTHESES EVALUATED BY NULL BIOGEOGRAPHIC MODELS

Substantial insular speciation has resulted in exceptionally high levels of endemism in Madagascar, creating locally restricted species' ranges that remain poorly understood. The contributions of alternative processes that could influence patterns of local endemism—including speciation by geographic isolation or adaptation to environmental gradients—are widely debated, both for Madagascar and elsewhere. A recently proposed hypothesis (the "watershed hypothesis") suggests that allopatric speciation driven by isolation in watersheds during Quaternary climate shifts provides a general explanation for patterns of local endemism across taxa in Madagascar. Here we tested coincidence between species' distributions and areas of endemism predicted by two contrasting biogeographic hypotheses: (1) the watershed hypothesis, and (2) an alternative hypothesis driven by climatic gradients (the "current climate hypothesis"). Statistical significance of coincidence was assessed by comparing against a null model. Surprisingly, we found that extant distributions of lemurs, geckos, and chameleons reveal species patterns that are significantly coincident with the watershed and current climate hypotheses. These results strongly support local endemism developing from multiple processes, even among closely related species. Our findings thus indicate that pluralistic approaches will offer the best option both for understanding processes that generate local endemism, and for incorporating endemism within conservation priority setting.     

Two decades of interaction between the MacArthur-Wilson model and the complexities of mammalian distributions

More than two decades after its publication, MacArthur and Wilson's equilibrium model of insular biogeography continues to provide the conceptual foundation for investigating the distribution of species on islands and the composition of insular biotas. During this period, studies of the distributions of mammals among insular habitats have tested, modified, and extended MacArthur and Wilson's simple formalism to enhance greatly our understanding of the complexities of biogeographic patterns and processes. The papers in this symposium summarize many of the past contributions of mammalian biogeographers and introduce important new data and ideas. The diversity of biological characteristics and associated distributional patterns exhibited by mammals has facilitated this endeavour. Some insular mammalian faunas appear to represent approximate equilibria between opposing rates of contemporary colonization and extinction. Other faunas are currently decreasing in diversity because of extinctions, owing either to natural habitat fragmentation that has occurred since the Pleistocene or to human activities within the last few centuries. Still other faunas have been increasing in diversity (at least until recent human impacts) because limiting rates of origination, both colonization and speciation, have been extremely low. The questions and analyses of island biogeography can also be applied to continents with comparable overall results: the distributions of continental faunas reflect the consequences of similar processes of colonization, speciation and extinction. Analyses of insular distributions show unequivocally that probabilities of extinction, colonization and speciation are highly deterministic and vary in predictable ways among different taxa and archipelagos. These findings have important implications for applying the theory and data of insular biogeography to the pressing practical problems of designing natural reserves to preserve native species.     

Evolution of abdominal pigmentation differences across species in the Drosophila dunni subgroup

The Drosophila dunni subgroup displays a nearly perfect latitudinal cline in abdominal pigmentation that likely resulted from selective forces acting in the habitat of each species during speciation. Here we characterize the nature of this clinal variation by developing a quantitative measure to assess variation in abdominal pigmentation within and between the D. dunni subgroup species. Using discriminant analysis, we confirm the existence of a cline and find that our quantitative measure of pigmentation distinguishes each of the species with singular efficacy. We then combine our quantitative phenotypic analysis of pigmentation with the phylogeny of the D. dunni subgroup species and map the species relationships into the three-dimensional morphological space defined by our pigmentation measures. In this manner, we can visualize how the species have traversed the morphological pigmentation space during the course of speciation. Our analysis reveals that natural selection has caused overall intensity of pigmentation among the northernmost species of the cline to converge. Along with this convergence in phenotype has been a relaxation in expression of sexual dimorphism in these species, indicating a possible shift in the relative intensity of natural and sexual selection. Our analysis indicates an accelerated rate of change in pigmentation for the darkest species in addition to this species evolving a novel abdominal pigmentation trait.     

Inverting the null-hypothesis of speciation: a marine snail perspective

Speciation is currently an intensely debated topic, much more so than 20–30 years ago when most biologists held the view that new species (at least of animals) were formed through the split of evolutionary lineages by the appearance of physical barriers to gene flow. Recent advances have, however, lent both theoretical and empirical support to speciation in the presence of gene flow. Nevertheless, the allopatric hypothesis of speciation is still the default model. The consequence of this is that to support sympatric and parapatric modes of speciation all allopatric alternatives must be rejected, while an allopatric explanation is usually accepted without rejecting possible non-allopatric alternatives. However, classical cases of allopatric speciation can be challenged by alternative non-allopatric explanations, and this begs for a more respectful view of how to deal with all models of speciation. An appealing approach is studying parallel evolution of reproductive barriers, which allows for comparative approaches to distinguish between allopatric and non-allopatric events, and explicit tests of a suitable null-hypothesis. Parallel evolution of reproductive isolation in a strongly polymorphic marine snail species serves as an illustrative example of such an approach. In conclusion, a more balanced debate on allopatric and non-allopatric speciation is needed and an urgent issue is to treat both allopatric and nonallopatric hypotheses critically, rather than using allopatry as the default model of speciation.     

The geography of mammalian speciation: mixed signals from phylogenies and range maps

The importance of geographic isolation in speciation has been debated since the 19th century. Since the beginning of the 20th century, the consensus has been that most speciation involves divergence in allopatry. This consensus was based largely on decades of observations by naturalists and verbal arguments against speciation without isolation. Recent attempts to quantify the importance of allopatric versus sympatric speciation using comparative methods called "age-range correlation" (ARC) suggest that allopatric speciation is more common than sympatric speciation. However, very few taxa have been studied and there are concerns about the adequacy of the methods. We propose methodological improvements including changes in the way overlap between clades is quantified and Monte Carlo methods to test the null hypothesis of no relationship between phylogenetic relatedness and geographic range overlap. We analyze 14 clades of mammals, chosen because of the availability of data and the consensus among mammalogists that speciation is routinely allopatric. Although data from a few clades clearly indicate allopatric speciation, divergence with gene flow is plausible in others and many results are inconclusive. The relative rarity of significant correlations between phylogenetic distance and range overlap may have three distinct causes: (1) post-speciation range changes, (2) relative rarity of range overlap, and (3) a mixture of geographic modes of speciation. Our results support skepticism about ARC's power for inferring the biogeography of speciation. Yet, even if few clades provide clear signals, meta-analytic approaches such as ARC may set bounds on the prevalence of alternative modes of speciation.     

Reinforcement shapes clines in female mate discrimination in Drosophila subquinaria

Reinforcement of species boundaries may alter mate recognition in a way that also affects patterns of mate preference among conspecific populations. In the fly Drosophila subquinaria, females sympatric with the closely related species D. recens reject mating with heterospecific males as well as with conspecific males from allopatric populations. Here, we assess geographic variation in behavioral isolation within and among populations of D. subquinaria and use cline theory to understand patterns of selection on reinforced discrimination and its consequences for sexual isolation within species. We find that selection has fixed rejection of D. recens males in sympatry, while significant genetic variation in this behavior occurs within allopatric populations. In conspecific matings sexual isolation is also asymmetric and stronger in populations that are sympatric with D. recens. The clines in behavioral discrimination within and between species are similar in shape and are maintained by strong selection in the face of gene flow, and we show that some of their genetic basis may be either shared or linked. Thus, while reinforcement can drive extremely strong phenotypic divergence, the long‐term consequences for incipient speciation depend on gene flow, genetic linkage of discrimination traits, and the cost of these behaviors in allopatry.     

Host–pathogen coevolution,secondary sympatry and species diversification

The build-up of species locally within a region by allopatric speciation depends on geographically separated (allopatric) sister populations becoming reproductively incompatible followed by secondary sympatry. Among birds, this has happened frequently in remote archipelagos, spectacular cases including the Darwin''s finches (Geospizinae) and Hawaiian honeycreepers (Drepanidinae), but similar examples are lacking in archipelagos nearer to continental landmasses. Of the required steps in the speciation cycle, achievement of secondary sympatry appears to be limiting in near archipelagos and, by extension, in continental regions. Here, I suggest that secondary sympatry might be prevented by apparent competition mediated through pathogens that are locally coevolved with one population of host and are pathogenic in sister populations. The absence of numerous pathogens in remote archipelagos might, therefore, allow sister populations to achieve secondary sympatry more readily and thereby accelerate diversification. By similar reasoning, species should accumulate relatively slowly within continental regions. In this essay, I explore the assumptions and some implications of this model for species diversification.     

THE RATE TEST OF SPECIATION: ESTIMATING THE LIKELIHOOD OF NON‐ALLOPATRIC SPECIATION FROM REPRODUCTIVE ISOLATION RATES IN DROSOPHILA

Among the most debated subjects in speciation is the question of its mode. Although allopatric (geographical) speciation is assumed the null model, the importance of parapatric and sympatric speciation is extremely difficult to assess and remains controversial. Here I develop a novel approach to distinguish these modes of speciation by studying the evolution of reproductive isolation (RI) among taxa. I focus on the Drosophila genus, for which measures of RI are known. First, I incorporate RI into age‐range correlations. Plots show that almost all cases of weak RI are between allopatric taxa whereas sympatric taxa have strong RI. This either implies that most reproductive isolation (RI) was initiated in allopatry or that RI evolves too rapidly in sympatry to be captured at incipient stages. To distinguish between these explanations, I develop a new “rate test of speciation” that estimates the likelihood of non‐allopatric speciation given the distribution of RI rates in allopatry versus sympatry. Most sympatric taxa were found to have likely initiated RI in allopatry. However, two putative candidate species pairs for non‐allopatric speciation were identified (5% of known Drosophila). In total, this study shows how using RI measures can greatly inform us about the geographical mode of speciation in nature.     

Rejecting strictly allopatric speciation on a continental island: prolonged postdivergence gene flow between Taiwan (Leucodioptron taewanus,Passeriformes Timaliidae) and Chinese (L. canorum canorum) hwameis

Allopatry is conventionally considered the geographical mode of speciation for continental island organisms. However, strictly allopatric speciation models that assume the lack of postdivergence gene flow seem oversimplified given the recurrence of land bridges during glacial periods since the late Pliocene. Here, to evaluate whether a continental island endemic, the Taiwan hwamei (Leucodioptron taewanus, Passeriformes Timaliidae) speciated in strict allopatry, we used weighted‐regression‐based approximate Bayesian computation (ABC) to analyse the genetic polymorphism of 18 neutral nuclear loci (total length: 8500 bp) in Taiwan hwamei and its continental sister species, the Chinese hwamei (L. canorum canorum). The nonallopatry model was found to fit better with observed genetic polymorphism of the two hwamei species (posterior possibility = 0.82). We also recovered unambiguous signals of nontrivial bidirectional postdivergence gene flow (N_em » 1) between Chinese hwamei and Taiwan hwamei until 0.5 Ma. Divergence time was estimated to be 3.5 to 2 million years earlier than that estimated from mitochondrial cytochrome b sequences. Finally, using the inferred nonallopatry model to simulate genetic variation at 24 nuclear genes examined showed that the adiponectin receptor 1 gene may be under divergent adaptation. Our findings imply that the role of geographical barrier may be less prominent for the speciation of continental island endemics, and suggest a shift in speciation studies from simply correlating geographical barrier and genetic divergence to examining factors that facilitate and maintain divergence, e.g. differential selection and sexual selection, especially in the face of interpopulation gene flow.     

Strong selection against hybrids at a hybrid zone in the Ensatina ring species complex and its evolutionary implications

The analysis of interactions between lineages at varying levels of genetic divergence can provide insights into the process of speciation through the accumulation of incompatible mutations. Ring species, and especially the Ensatina eschscholtzii system exemplify this approach. The plethodontid salamanders E. eschscholtzii xanthoptica and E. eschscholtzii platensis hybridize in the central Sierran foothills of California. We compared the genetic structure across two transects (southern and northern Calaveras Co.), one of which was resampled over 20 years, and examined diagnostic molecular markers (eight allozyme loci and mitochondrial DNA) and a diagnostic quantitative trait (color pattern). Key results across all studies were: (1) cline centers for all markers were coincident and the zones were narrow, with width estimates of 730 m to 2000 m; (2) cline centers at the northern Calaveras transect were coincident between 1981 and 2001, demonstrating repeatability over five generations; (3) there were very few if any putative F1s, but a relatively high number of backcrossed individuals in the central portion of transects; and (4) we found substantial linkage disequilibrium in all three studies and strong heterozygote deficit both in northern Calaveras, in 2001, and southern Calaveras. Both linkage disequilibrium and heterozygote deficit showed maximum values near the center of the zones. Using estimates of cline width and dispersal, we infer strong selection against hybrids. This is sufficient to promote accumulation of differences at loci that are neutral or under divergent selection, but would still allow for introgression of adaptive alleles. The evidence for strong but incomplete isolation across this centrally located contact is consistent with theory suggesting a gradual increase in postzygotic incompatibility between allopatric populations subject to divergent selection and reinforces the value of Ensatina as a system for the study of divergence and speciation at multiple stages.     

Continental faunal exchange and the asymmetrical radiation of carnivores

Lineages arriving on islands may undergo explosive evolutionary radiations owing to the wealth of ecological opportunities. Although studies on insular taxa have improved our understanding of macroevolutionary phenomena, we know little about the macroevolutionary dynamics of continental exchanges. Here we study the evolution of eight Carnivora families that have migrated across the Northern Hemisphere to investigate if continental invasions also result in explosive diversification dynamics. We used a Bayesian approach to estimate speciation and extinction rates from a substantial dataset of fossil occurrences while accounting for the incompleteness of the fossil record. Our analyses revealed a strongly asymmetrical pattern in which North American lineages invading Eurasia underwent explosive radiations, whereas lineages invading North America maintained uniform diversification dynamics. These invasions into Eurasia were characterized by high rates of speciation and extinction. The radiation of the arriving lineages in Eurasia coincide with the decline of established lineages or phases of climate change, suggesting differences in the ecological settings between the continents may be responsible for the disparity in diversification dynamics. These results reveal long-term outcomes of biological invasions and show that the importance of explosive radiations in shaping diversity extends beyond insular systems and have significant impact at continental scales.     

The relative importance of ecology and geographic isolation for speciation in anoles

The biogeographic patterns in sexually reproducing animals in island archipelagos may be interpreted as reflecting the importance of allopatric speciation. However, as the forms are allopatric, their reproductive isolation is largely untestable. A historical perspective integrating geology and molecular phylogeny reveals specific cases where ancient precursor islands coalesce, which allows the application of population genetics to critically test genetic isolation. The Anolis populations on Martinique in the Lesser Antilles are one such case where species-level populations on ancient precursor islands (ca 6-8Myr BP) have met relatively recently. The distribution of the mtDNA lineages is tightly linked to the precursor island, but the population genetic analysis of microsatellite variation in large samples shows no evidence of restricted genetic exchange between these forms in secondary contact. This tests, and rejects, the hypothesis of simple allopatric speciation in these forms. By contrast, Martinique has pronounced environmental zonation, to which anoles are known to adapt. The population genetic analysis shows restricted genetic exchange across the ecotone between xeric coastal habitat and montane rainforest. This does not indicate full ecological speciation in these forms, but it does suggest the relative importance of the role of ecology in speciation in general.     

Ernst Mayr and the integration of geographic and ecological factors in speciation

Mayr's best recognized scientific contributions include the biological species concept and the theory of geographic speciation. In the latter, reproductive isolation evolves as an incidental by‐product of genetic divergence between allopatric populations. Mayr noted that divergent natural selection could accelerate speciation, but also argued that gene flow so strongly retards divergence that, even with selection, non‐allopatric speciation is unlikely. However, current theory and data demonstrate that substantial divergence, and even speciation, in the face of gene flow is possible. Here, I attempt to connect some opposing views about speciation by integrating Mayr's ideas about the roles of ecology and geography in speciation with current data and theory. My central premise is that the speciation process (i.e. divergence) is often continuous, and that the opposing processes of selection and gene flow interact to determine the degree of divergence (i.e. the degree of progress towards the completion of speciation). I first establish that, in the absence of gene flow, divergent selection often promotes speciation. I then discuss how population differentiation in the face of gene flow is common when divergent selection occurs. However, such population differentiation does not always lead to the evolution of discontinuities, strong reproductive isolation, and thus speciation per se. I therefore explore the genetic and ecological circumstances that facilitate speciation in the face of gene flow. For example, particular genetic architectures or ecological niches may tip the balance between selection and gene flow strongly in favour of selection. The circumstances allowing selection to overcome gene flow to the extent that a discontinuity develops, and how often these circumstances occur, are major remaining questions in speciation research. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 26–46.     

Speciation in North American black basses,Micropterus (Actinopterygii: Centrarchidae)

Abstract.— The Pleistocene Epoch has been frequently cited as a period of intense speciation for a significant portion of temperate continental biotas. To critically assess the role of Pleistocene glaciations on the evolution of the freshwater fish clade Micropterus , we use a phylogenetic analysis of complete gene sequences from two mitochondrial genes (cytochrome b and ND2), and a fossil calibration of the molecular clock to estimate ages of speciation events and rates of diversification. The absence of substantial morphological and ecological divergence together with endemism of five of the eight species in North American tributaries of the Gulf of Mexico may be interpreted as the result of a recent Pleistocene origin for these species. Speciation dates in Micropterus range from 1.01 ± 0.32 to 11.17 ± 1.02 million years ago. Only one speciation event is dated to the Pleistocene, and rates of diversification are not significantly variable in Micropterus. The premise that the Pleistocene was an exceptional period of speciation in Micropterus is not supported. Instead, a Gulf Coast allopatric speciation model is proposed, and predicts periods of dynamic speciation driven by sea level fluctuations in the Late Miocene and Pliocene. The Pleistocene, however, was a period of significant intraspecific mitochondrial lineage diversification. The application of the Gulf Coast allopatric speciation model to the remaining aquatic fauna of the Gulf of Mexico coast in North America will rely on robust phylogenetic hypotheses and accurate age estimations of speciation events.     

Quantitative traits and mode of speciation in Martinique anoles

We investigate extensive quantitative trait variation (dewlap hue, colour pattern, dorsum hue, body proportions and scalation) in the Martinique anole across eight transects representing nascent parapatric ecological speciation, nascent allopatric speciation and allopatric divergence without sufficient genetic structure to suggest speciation. Quantitative trait divergence can be extremely large between adjacent sets of populations, but with one exception that this is associated with difference in habitat rather than past allopatry. Nascent ecological speciation shows the greatest level of quantitative trait divergence across all character sets including those implicated in natural, as well as sexual selection. The sole example of nascent allopatric speciation is associated with fairly strong quantitative trait divergence among most character sets, but not the set most implicated in natural (rather than sexual) selection. The role of sexual selection in ecological speciation is discussed, both in terms of female choice with assortative mating and male–male competition with condition‐dependant sexual signals.     

Combining Biogeographic and Phylogenetic Data to Examine Primate Speciation: An Example Using Cercopithecin Monkeys

We combined phylogenetic and biogeographic data to examine the mode of speciation in a group of African monkeys, the Cercopithecini. If allopatric speciation is the major force producing species, then there should be a positive relationship between the relative divergence time of taxa and their degree of geographic range overlap. Alternatively, an opposite relationship between divergence time and geographic range overlap is consistent with sympatric speciation as the main mechanism underlying the cercopithecin radiation. We collected biogeographic and phylogenetic data for 19 guenon species from the literature. We digitized geographic range maps and utilized three different phylogenetic hypotheses based on Y chromosome, X chromosome, and mitochondrial (mtDNA) data. We used regressions with Monte Carlo simulation to examine the relationship between the relative time since divergence of taxa and their degree of geographic range overlap. We found that there was a positive relationship between relative divergence time and the proportion of geographic range overlap between taxa using all three molecular data sets. Our findings provide evidence for allopatric speciation being the common mode of diversification in the cercopithecin clade. Because most of these primates are forest adapted mammals, the cyclical contraction and expansion of African forests from the late Miocene to the present has likely been an important factor driving allopatric speciation. In addition, geographic barriers such as the Congo and Sanaga rivers have probably played a complementary role in producing new species within the clade.     

Local endemism and within‐island diversification of shrews illustrate the importance of speciation in building Sundaland mammal diversity

Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (i) little differentiation of terrestrial organisms among continental shelf islands and (ii) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well‐sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analysed nine unlinked loci from shrews of the genus Crocidura from seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognized Crocidura species from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species of Crocidura in the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra‐island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species‐level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within‐island diversification. Our results suggest that both between‐ and within‐island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the region's fauna is relictual and primarily governed by extinction.     

Combination of geometric morphometric and genetic approaches applied to a debated taxonomical issue: the status of Onthophagus massai (Coleoptera, Scarabaeidae) as an endemic species vicarious to Onthophagus fracticornis in Sicily

The present study deals with the phenomenon of insular speciation and discusses, as a case study, the debated taxonomical issue of the status of Onthophagus massai (Coleoptera, Sarabaeidae) as an endemic species vicarious to Onthophagus fracticornis in Sicily. The authors investigated the differentiation patterns between an insular population belonging to the supposed species O. massai (collected in its locus typicus, Piano Battaglia) and three Italian O. fracticornis populations (collected along a N–S latitudinal gradient). These patterns are described and analysed using multiple approaches: the qualitative inspection of the microsculpture of elytral surfaces, considered a diagnostic character for O. massai identification; the comparison of horn static allometries, known to be a good indicator of divergence processes between closely related species or isolated populations of the same species; the comparison of the patterns of shape and size difference of the head, epipharynx and genitalia attained with a combination of traditional and geometric (landmark and semilandmark) morphometric methods; and, finally, the estimation of the genetic relationships between Sicilian and continental populations obtained by analysing cytochrome oxidase subunit 1 mitochondrial gene sequences. The integration of the results of these approaches indicates that there is not sufficient evidence to vindicate the species status for O. massai, which should more likely be considered a small-sized version of O. fracticornis (a possible case of insular dwarfism). However, the complex pattern of shape, size and genetic variation observed between the populations analysed hinted at the possibility that a diversification process is ongoing, but not only between insular and continental populations; each population showed a tendency to evolve as an evolutionarily independent unit.     

Genetic differentiation among populations of a Hispaniolan trunk anole that exhibit geographical variation in dewlap colour

Long neglected by classic island biogeographical theory, speciation within and among islands is increasingly recognized as a major contributor to insular diversity. Although the factors responsible for island speciation remain poorly understood, this process appears critically dependent on geographical variation and speciation in allopatry or parapatry. Here, we investigate geographical variation and speciation in a complex of Hispaniolan trunk anoles (Anolis distichus), where populations with strikingly distinct dewlap colours and patterns correspond with deeply divergent mtDNA structure. Using a multilocus, population‐level analysis, we investigate whether these phenotypically and mitochondrially distinct populations exhibit the type of nuclear differentiation expected among species or incipient species. Along a transect that extends across a recently recessed marine barrier, our results are consistent with the persistence of an abrupt phenotypic and mitochondrial transition following secondary contact, in spite of little or no evidence for a reduction in nuclear gene flow. Along a second transect extending across a steep environmental gradient, our phenotypic and microsatellite data suggest a sharp genetic break with little or no admixture, whereas mtDNA recovers a signature of extensive unidirectional introgression. Together, these results are consistent with previous studies of Lesser Antillean anoles, suggesting that allopatric divergence alone is insufficient for speciation, whereas reduced gene flow and partial reproductive isolation may accumulate in the presence of ecological gradients.     

The geographical pattern of speciation and floral diversification in the neotropics: the tribe sinningieae (gesneriaceae) as a case study

The geographical pattern of speciation and the relationship between floral variation and species ranges were investigated in the tribe Sinningieae (Gesneriaceae), which is found mainly in the Atlantic forests of Brazil. Geographical distribution data recorded on a grid system of 0.5 x 0.5 degree intervals and a near-complete species-level phylogenetic tree of Sinningieae inferred from a simultaneous analysis of seven DNA regions were used to address the role of geographical isolation in speciation. Geographical range overlaps between sister lineages were measured across all nodes in the phylogenetic tree and analyzed in relation to relative ages estimated from branch lengths. Although there are several cases of species sympatry in Sinningieae, patterns of sympatry between sister taxa support the predominance of allopatric speciation. The pattern of sympatry between sister taxa is consistent with range shifts following allopatric speciation, except in one clade, in which the overlapping distribution of recent sister species indicates speciation within a restricted geographical area and involving changes in pollinators and habitats. The relationship between floral divergence and regional sympatry was also examined by analyzing floral contrasts, phenological overlap, and the degree of sympatry between sister clades. Morphological contrast between flowers is not increased in sympatry and phenological divergence is more apparent between allopatric clades than between sympatric clades. Therefore, our results failed to indicate a tendency for sympatric taxa to minimize morphological and phenological overlap (geographic exclusion and/or character displacement hypotheses). Instead, they point toward adaptation in phenology to local conditions and buildup of sympatries at random with respect to flower morphology. Additional studies at a lower geographical scale are needed to identify truely coexisting species and the components of their reproductive isolation.