Ecogeographic Isolation Research Articles

Floral colour variation across life history and geography in Mimulus ringens (Phrymaceae)

Abstract Floral and life history traits play important roles in plant speciation. The genus Mimulus is a model system for studying speciation. It includes examples of species in which floral colour facilitates isolation through pollinator shifts, as well as life history changes that result in temporal or ecogeographic isolation. We investigate the possibility that both floral colour and life history have shifted together in a recently described, genetically distinct group within the species Mimulus ringens. Using a large, range-wide citizen science dataset, we test for geographic trends in flower colour and flowering time. We combine this with greenhouse studies in populations of known life history to test for differences in flower colour with life history. We show that darker-flowered plants are more common at higher latitudes, that annual-like populations have darker flowers, and that flowering time varies with latitude only in the subset of populations that have lighter flowers. This suggests that annual-like populations (with the earlier flowering time typical of this life history) are restricted to the northern part of the species range and may have distinct trends in flowering date.

Mechanisms of reproductive isolation between annual and perennial plants of Incarvillea sinensis

AbstractQuantifying the relative strength of isolating barriers is a major focus of research on plant speciation. Contrasting life histories and mating systems have the potential to limit gene exchange between closely related populations growing in sympatry. However, few studies have quantified reproductive isolating barriers between conspecific annual and perennial populations and their contributions to total reproductive isolation (RI). Incarvillea sinensis Lam. (Bignoniaceae) is an insect‐pollinated herb with largely allopatric annual and perennial populations that differ in mating systems. The perennial populations are primarily outcrossing whereas annual populations are predominantly selfing. At a rare sympatric site in northern China we estimated prezygotic and postzygotic barriers to gene exchange between annual and perennial plants and found complete RI between the two life histories. Annuals exhibited significantly higher ecogeographic isolation than perennials whereas perennials experienced more isolation through pollen–pistil interactions than annuals. Crosses between annuals and perennials demonstrated that postzygotic barriers influencing fruit and seed formation, F1 germination and survival were negligible for annuals but played a small role for perennials. However, F1 hybrids of crosses between annuals and perennials produced no pollen and their ovules were largely sterile. Our study provides insight into the relative importance of prezygotic and postzygotic isolating barriers between closely related annual and perennial populations of I. sinensis and some of these barriers could have been involved with speciation. Annuals and perennials of I. sinensis represent two biological species and thus deserve to be recognized as distinct taxonomic species.

The past, present, and future of ecogeographic isolation between closely related Aquilegia plants.

Quantifying the strength of the ecogeographic barrier is an important aspect of plant speciation research, and serves as a practical step to understanding the evolutionary trajectory of plants under climate change. Here, we quantified the extent of ecogeographic isolation in four closely related Aquilegia species that radiated in the Mountains of SW China and adjacent regions, often lacking intrinsic barriers. We used environmental niche models to predict past, present, and future species potential distributions and compared them to determine the degree of overlap and ecogeographic isolation. Our investigation found significant ecological differentiation in all studied species pairs except A. kansuensis and A. ecalacarata. The current strengths of ecogeographic isolation are above 0.5 in most cases. Compared with current climates, most species had an expanding range in the Last Glacial Maximum, the Mid Holocene, and under four future climate scenarios. Our results suggested that ecogeographic isolation contributes to the diversification and maintenance of Aquilegia species in the Mountains of northern and SW China and would act as an essential reproductive barrier in the future.

Ecological and Evolutionary Origin of Costus flammulus (Costaceae): A New Species from the Montane Cloud Forests of the Volcanic Cordilleras in Northern Costa Rica

Abstract— Costus flammulus is a new herbaceous species endemic to montane cloud forests of the volcanic cordilleras in northern Costa Rica. Costus flammulus has been mistaken for C. wilsonii, but phylogenetic evidence demonstrates that it is closely related to the widespread lowland species C. pulverulentus. Here, we use an integrated framework of species concepts to evaluate whether C. flammulus and C. pulverulentus are distinct species. First, we re-evaluate prior phylogenetic analyses to assess whether C. flammulus bifurcated from or budded off from within C. pulverulentus and whether C. flammulus is monophyletic. We then compare phenotypic traits to determine which diagnostic vegetative and inflorescence traits can be used to identify species in herbarium specimens and examine whether floral traits may confer floral isolation. We compare pollinator assemblages to examine whether pollinator specificity may contribute to reproductive isolation. Finally, we model species distributions and climatic niche overlap to assess ecogeographic isolation. We found that C. flammulus is a monophyletic species phenotypically, ecologically, and geographically distinct from C. pulverulentus and may have speciated as a peripheral isolate at the high elevation range edge of C. pulverulentus. Several lines of evidence, such as C. pulverulentus paraphyly, range size asymmetry, and C. flammulus’ nested distribution and vegetative traits, suggest that C. flammulus budded off from a C. pulverulentus‐like progenitor species, evolving to tolerate a colder and more seasonal montane environment.

Weak reproductive isolation and extensive gene flow between Mimulus glaucescens and M. guttatus in northern California.

Barriers to reproduction are often how progress in speciation is measured. Nonetheless, an unresolved question concerns the extent to which reproductive barriers diminish gene flow between incipient species. The Sierra Nevada foothill endemic Mimulus glaucescens and the widespread M. guttatus are considered distinct species based on striking differences in vegetative morphology, but barriers to reproduction have not been previously identified, nor has gene flow between species been characterized. Here, we examined 15 potential reproductive barriers within a Northern California area of broad sympatry. Most barriers, with the exception of ecogeographic isolation, were weak or absent, and total isolation for each species was incomplete. Population genomic analyses of range-wide and broadly sympatric accessions revealed extensive gene flow between these taxa, particularly in sympatry. Despite widespread introgression, Mimulus glaucescens, emerged as monophyletic and largely comprised a single ancestry that was found at intermediate frequency within M. guttatus. This result, along with observed ecological and phenotypic differentiation, suggests that natural selection may contribute to the maintenance of distinct phenotypic forms in the earliest stages of speciation. Integrating estimates of barrier strength with direct estimates of gene flow can strengthen a more nuanced interpretation of the process of speciation in natural communities.

Reproductive Isolation Among Three Nocturnal Moth-Pollinated Sympatric Habenaria Species (Orchidaceae).

Comparison and quantification of multiple pre- and post-pollination barriers to interspecific hybridization are important to understand the factors promoting reproductive isolation. Such isolating factors have been studied recently in many flowering plant species which seek after the general roles and relative strengths of different pre- and post-pollination barriers. In this study, we quantified six isolating factors (ecogeographic isolation, phenological isolation, pollinator isolation, pollinia-pistil interactions, fruit production, and seed development) that could possibly be acting as reproductive barriers at different stages among three sympatric Habenaria species (H. limprichtii, H. davidii, and H. delavayi). These three species overlap geographically but occupy different microhabitats varying in soil water content. They were isolated through pollinator interactions both ethologically (pollinator preference) and mechanically (pollinia attachment site), but to a variable degree for different species pairs. Interspecific crosses between H. limprichtii and H. davidii result in high fruit set, and embryo development suggested weak post-pollination barriers, whereas bidirectional crosses of H. delavayi with either of the other two species fail to produce fruits. Our results revealed that pollinators were the most important isolating barrier including both ethological and mechanical mechanisms, to maintain the boundaries among these three sympatric Habenaria species. Our study also highlights the importance of a combination of pre-and post-pollination barriers for species co-existence in Orchidaceae.

A greenhouse experiment partially supports inferences of ecogeographic isolation from niche models of Clarkia sister species.

PremiseEcogeographic isolation, or geographic isolation caused by ecological divergence, is thought to be of primary importance in speciation, yet is difficult to demonstrate and quantify. To determine whether distributions are limited by divergent adaptation or historical contingency, the gold standard is to reciprocally transplant species between their geographic ranges. Alternatively, ecogeographic isolation is inferred from species distribution models and niche divergence tests using widely available environmental and occurrence data.MethodsWe tested for ecogeographic isolation between two sister species of California annual wildflowers, Clarkia concinna and C. breweri, with a hybrid approach. We used niche models to predict water availability as the major axis of ecological divergence and then tested that with a greenhouse experiment. Specifically, we manipulated water availability in field soils for two populations of each species and predicted higher fitness in conditions representing home habitats to those representing the environment of each's sister species.ResultsWater availability and soil representing C. concinna generally increased both species' fitness. Thus, water and soil may indeed limit C. concinna from colonizing the range of C. breweri, but not vice versa. We suggest that the competitive environment and pollinator availability, which are not directly captured with either approach, may be key biotic factors correlated with climate that contribute to unexplained ecogeographic isolation for C. breweri.ConclusionsOurs is a valuable approach to assessing ecogeographic isolation, in that it balances feasibility with model validation, and our results have implications for species distribution modeling efforts geared toward predicting climate change responses.

Assessment of genetic divergence of Sesame seeds based on biochemical parameters

The assessment of genetic divergence plays a significant role to identify promising genotypes to initiate crossing programme for crop improvement. The sesame being a nutritious oil seed crop containing various biochemical constituents used as a good dietary choice. The biochemical analysis was done taking freshly harvested seeds of eight (8) parental genotypes and twenty one (21) advance lines. The studies revealed that all the genotypes differed significantly among themselves for all the biochemical parameters including moisture content, oil content, its iodine number and saponification value, both crude and soluble protein, some mineral matters – Ca, P, Mn, Zn, Cu & Fe and Carbohydrate and ascorbic acid content. Mahalanobis generalized genetic distance using D² statistics for the assessment of genetic divergence amongst 29 genotypes based on biochemical parameters. All the genotypes were grouped into eleven distinct clusters. Maximum intra cluster divergence was noted against cluster IX with advance lines having black coloured seeds as its constituents. With regard to inter-cluster distance values the cluster X was mostly divergent from all other clusters and cluster II as the less divergent one from the rest. Cluster X with parental genotype B-14 was identified as superior cluster for the biochemical parameters on the basis of securing higher position for maximum number of characters. Constitution pattern clustering was independent of eco-geographical isolation. Promising segregants with higher oil yielding potentially may yield from inter se mating of advance line 14 and HT-1 with T-12, R-9 or advance lines 10, 14, 20.

Incipient speciation in Oncocyclus irises: Eco-geographic isolation and genetic divergence with no reproductive isolation?

The establishment of reproductive isolation is considered to be an ultimate result of ecological speciation, but empirical evidence for the latter is limited. We hypothesized that in the absence of inter-specific gene flow and with subtle environmental differences, local adaptation will not require trade-offs in performance across environments and therefore will not result in reproductive isolation. We tested this hypothesis on four iris species, Iris atrofusca, I. atropurpurea, I. petrana and I. mariae, which have non-overlapping geographical distributions, grow naturally in different environmental conditions with respect to amount of rainfall and soil type, and possess suites of diagnostic traits that previously were assumed to result from local selection. We analyzed their genetic (AFLP) and quantitative trait divergence (by means of a common garden experiment), conducted a habitat suitability analysis, examined experimentally the effects of soil type and water availability on plant performance, and tested for postzygotic reproductive isolation using a crossing experiment. Our results supported the hypothesis that eco-geographical isolation does not necessarily lead to local adaptation or to postzygotic reproductive isolation when environmental differences are subtle. Thus, we obtained some evidence that the desert I. atrofusca was reproductively isolated from coastal I. atropurpurea, but not from desert I. mariae, although genetically the first two are more similar to each other than I. atrofusca is to I. mariae.

Implications for evolutionary trends from the pairing frequencies among golden‐winged and blue‐winged warblers and their hybrids

Extensive range loss for the Golden‐winged Warbler (Vermivora chrysoptera) has occurred in areas of intrusion by the Blue‐winged Warbler (V. cyanoptera) potentially related to their close genetic relationship. We compiled data on social pairing from nine studies for 2,679 resident Vermivora to assess evolutionary divergence. Hybridization between pure phenotypes occurred with 1.2% of resident males for sympatric populations. Pairing success rates for Golden‐winged Warblers was 83% and for Blue‐winged Warblers was 77%. Pairing success for the hybrid Brewster's Warbler was significantly lower from both species at 54%, showing sexual selection against hybrids. Backcross frequencies for Golden‐winged Warblers at 4.9% were significantly higher than for Blue‐winged Warblers at 1.7%. More frequent backcrossing by Golden‐winged Warblers, which produces hybrid phenotypes, may contribute to the replacement of Golden‐winged by Blue‐winged Warblers. Reproductive isolation due to behavioral isolation plus sexual selection against hybrids was 0.960. Our analyses suggest that plumage differences are the main driving force for this strong isolation with reduced hybrid fitness contributing to a lesser degree. The major impact of plumage differences to reproductive isolation is compatible with genomic analyses (Current Biology, 2016, 26, 2313), which showed the largest genetic difference between these phenotypes occurred with plumage genes. These phenotypes have maintained morphological, behavioral, and ecological differences during two centuries of hybridization. Our estimate of reproductive isolation supports recognition of these phenotypes as two species. The decline and extirpation of the Golden‐winged Warbler in almost all areas of recent sympatry suggest that continued coexistence of both species will require eco‐geographic isolation.

The contribution of multiple barriers to reproduction between edaphically divergent lineages in the Amazonian tree Protium subserratum (Burseraceae).

Disentangling the strength and importance of barriers to reproduction that arise between diverging lineages is central to our understanding of species origin and maintenance. To date, the vast majority of studies investigating the importance of different barriers to reproduction in plants have focused on short‐lived temperate taxa while studies of reproductive isolation in trees and tropical taxa are rare. Here, we systematically examine multiple barriers to reproduction in an Amazonian tree, Protium subserratum (Burseraceae) with diverging lineages of soil specialist ecotypes. Using observational, molecular, distributional, and experimental data, we aimed to quantify the contributions of individual prezygotic and postzygotic barriers including ecogeographic isolation, flowering phenology, pollinator assemblage, pollen adhesion, pollen germination, pollen tube growth, seed development, and hybrid fitness to total reproductive isolation between the ecotypes. We were able to identify five potential barriers to reproduction including ecogeographic isolation, phenological differences, differences in pollinator assemblages, differential pollen adhesion, and low levels of hybrid seed development. We demonstrate that ecogeographic isolation is a strong and that a combination of intrinsic and extrinsic prezygotic and postzygotic barriers may be acting to maintain near complete reproductive isolation between edaphically divergent populations of the tropical tree, P. subserratum.

Climate change increases ecogeographical isolation between closely related plants

Abstract Ecogeographical isolation is a fundamental prezygotic barrier to reproduction and a step towards diversification in flowering plants. However, whether ecogeographical isolation acts as a reproductive barrier between species and thus as a mechanism for species divergence is unclear and is expected to change as species distributions shift under climate change. Using a Maxent framework, we quantified the extent of ecogeographical isolation of nine closely related species of the European plant genus Pulmonaria, which lack premating barriers and often form hybrids. We investigated ecogeographical isolation under both current conditions and four climate change scenarios; two unrelated future climate models, each with two predictions of the potential trajectories of climate change. Compared with current climates, under these future climate scenarios, there will be an increase in mean annual temperature, but not in mean annual precipitation in the range of Pulmonaria throughout Europe. This will result in a range contraction in three of the nine Pulmonaria species, a range expansion in two species, and no clear effect of climate change on the ranges of four species. Climate change will result in an overall increase in ecogeographical isolation between these species in future. In particular, species that have low ecogeographical isolation under current conditions are predicted to increase the most in their ecogeographical isolation under climate change. Synthesis. These results highlight that climate change can strongly impact on a major premating barrier of closely related species, therefore potentially affect the evolutionary trajectory of plants in the future.

Consequences of multiple mating-system shifts for population and range-wide genetic structure in a coastal dune plant.

Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating-system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (Ne ) caused by selfing, small-flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large-flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on Ne alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage-wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating-system differentiation observed across the range of this species.

Multiple factors contribute to reproductive isolation between two co-existing Habenaria species (Orchidaceae).

Reproductive isolation is a key feature that forms barriers to gene flow between distinct plants. In orchids, prezygotic reproductive isolation has been considered to be strong, because their associations with highly specific pollinators. In this study, the reproductive ecology and reproductive isolation of two sympatric Habenaria species, H. davidii and H. fordii, was investigated by floral phenology and morphology, hand-pollination experiments and visitor observation in southwest China. The two species were dependent on insects for pollination and completely self-compatible. A number of factors have been identified to limit gene flow between the two species and achieved full reproductive isolation. Ecogeographic isolation was a weak barrier. H. fordii and H. davidii had completely overlapped flowering periods, and floral morphology plays an important role in floral isolation. The two species shared the same hawkmoth pollinator, Cechenena lineosa, but the pollinaria of the two orchids were attached on different body parts of pollinators. Prezygotic isolation was not complete, but the interspecific pollination treatments of each species resulted in no seed sets, indicating that unlike many other orchid species, in which the postzygotic reproductive isolation is very weak or complete absence, the post-zygotic isolation strongly acted in the stage of seed production between two species. The results illustrate the reproductive isolation between two species involves multiple plant life-history stages and a variety of reproductive barriers can contribute to overall isolation.

Secondary contact after divergence in allopatry explains current lack of ecogeographical isolation in two hybridizing alpine plant species

AbstractAimAllopatric speciation plays an important role in generating the high diversity of alpine biomes, but in cases of species with largely overlapping distribution, allopatric divergence is usually rather assumed than explicitly tested. The hypothesis of allopatric divergence in currently sympatric and hybridizing species is here tested using phylogeographical tools.LocationEuropean high mountain ranges (Alps, Pyrenees).MethodsWe gathered amplified fragment length polymorphism (AFLP) data and plastid DNA sequences from (1–)2–7 individuals of each of 38 populations of Androsace helvetica and of nine populations of A. pubescens (Primulaceae), spanning their entire distributional areas. AFLP data were analysed with Bayesian clustering approaches, PopGraphs analysis and Bayesian tree estimation methods, the latter permitting ancestral area reconstruction including estimation of Bayes factor support for specific regions. Relationships among plastid haplotypes were inferred using statistical parsimony.ResultsAndrosace helvetica and A. pubescens originated in allopatry and attained their overlapping distributional areas after range expansion. Gene flow between species did occur (evidenced by haplotype sharing in areas of sympatry), but apparently was not sufficient to erode species boundaries (no signature for gene flow from AFLP data even in syntopic populations of the two Androsace species). Distributional patterns of gene pools and of plastid haplotypes suggest that the largely centrifugal pattern in A. helvetica and the unidirectional pattern of range expansion in A. pubescens were modulated by range contractions during Pleistocene climate oscillations into peripheral and interior refugia.Main conclusionsThe hypothesis of allopatric divergence in closely related and ecologically similar species can be readily tested using ancestral area reconstruction at the intraspecific level. Phylogeographical patterns in the two Androsace species emphasize the relevance of both peripheral and interior refugia for Pleistocene range formation.

Quaternary climate change drives allo-peripatric speciation and refugial divergence in the Dysosma versipellis-pleiantha complex from different forest types in China

Subtropical China harbours the world’s most diverse temperate flora, but little is known about the roles of geographical and eco-climatic factors underlying the region’s exceptionally high levels of species diversity and endemism. Here we address this key question by investigating the spatio-temporal and ecological processes of divergence within the Dysosma versipellis-pleiantha species complex, endemic to subtropical China. Our cpDNA phylogeny showed that this monophyletic group of understory herbs is derived from a Late Pliocene ancestor of the Qinghai-Tibetan Plateau (QTP)/Southwest China. Genetic and ENM data in conjunction with niche differentiation analyses support that the early divergence of D. versipellis and D. pleiantha proceeded through allo-peripatric speciation, possibly triggered by Early Pleistocene climate change, while subsequent climate-induced cycles of range contractions/expansions enhanced the eco-geographical isolation of both taxa. Furthermore, modelling of population-genetic data indicated that major lineage divergences within D. versipellis likely resulted from long-term allopatric population isolation in multiple localized refugia over the last glacial/interglacial periods, and which in turn fostered endemic species formation (D. difformis, D. majoensis) from within D. versipellis in Southwest China. These findings point to an overriding role of Quaternary climate change in triggering essentially allopatric (incipient) speciation in this group of forest-restricted plant species in subtropical China.

Both morph- and species-dependent asymmetries affect reproductive barriers between heterostylous species.

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre‐ versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre‐ and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co‐occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species‐dependent asymmetries, morph‐dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short‐styled flowers to stigmas of long‐styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long‐styled flowers to stigmas of short‐styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long‐styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph‐ and species‐dependent asymmetries shape boundaries between heterostylous species.

Hybridization and hybrid speciation under global change.

Contents 1170 I. 1170 II. 1172 III. 1175 IV. 1180 V. 1183 1184 References 1184 SUMMARY: An unintended consequence of global change is an increase in opportunities for hybridization among previously isolated lineages. Here we illustrate how global change can facilitate the breakdown of reproductive barriers and the formation of hybrids, drawing on the flora of the British Isles for insight. Although global change may ameliorate some of the barriers preventing hybrid establishment, for example by providing new ecological niches for hybrids, it will have limited effects on environment-independent post-zygotic barriers. For example, genic incompatibilities and differences in chromosome numbers and structure within hybrid genomes are unlikely to be affected by global change. We thus speculate that global change will have a larger effect on eroding pre-zygotic barriers (eco-geographical isolation and phenology) than post-zygotic barriers, shifting the relative importance of these two classes of reproductive barriers from what is usually seen in naturally produced hybrids where pre-zygotic barriers are the largest contributors to reproductive isolation. Although the long-term fate of neo-hybrids is still to be determined, the massive impact of global change on the dynamics and distribution of biodiversity generates an unprecedented opportunity to study large numbers of unpredicted, and often replicated, hybridization 'experiments', allowing us to peer into the birth and death of evolutionary lineages.

Evidence of incipient speciation in the Neotropical mangrovePelliciera rhizophorae(Tetrameristaceae) as revealed by molecular, morphological, physiological and climatic characteristics

Two variants of the Neotropical mangrove species Pelliciera rhizophorae distributed along both sides of the Isthmus of Panama were detected by different colouration of the floral bracts and the size of the floral and vegetative structures. These findings raised questions concerning a possible speciation event in P. rhizophorae, for which a series of macro- and microscopic morphological traits (reproductive and vegetative structures), molecular markers from plastid DNA and climatic profiles were analyzed. Samples of P. rhizophorae were collected in three localities from the Panamanian Caribbean and Pacific coasts. The data obtained from molecular markers and morphological traits showed significant differences between the variants. The climatic profiles showed contrasting characteristics of rainfall and temperature in their habitats: variant A is found in wetter zones and variant B occupies drier zones. Evidence suggesting that a process of incipient speciation has occurred in P. rhizophorae in response to ecogeographical isolation due to climatic factors is presented. The presence of two geographically separate genetic-morphological groups, adapted to contrasting climatic conditions, will be the basis for suggesting the existence of incipient lineages in Pelliciera. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 499–510.

Ecogeographic isolation and speciation in the genus Mimulus.

Despite a long history of examining the geographic context of speciation, differences in geographic range have rarely been considered a legitimate isolating mechanism. This likely results from the complex relationship between historical and ecological processes in determining the spatial distribution of species. Ecogeographic isolation is the proportion of geographic isolation that results from genetically based ecological differences between taxa and should therefore be measured as an isolating mechanism under the biological species concept. In this study, species distribution modeling was used to evaluate the potential ranges of 12 recently diverged pairs of species in the genus Mimulus. Variation in the distribution models showed that these species differ significantly in the niches they occupy. These differences result in substantial ecogeographic isolation, with an average strength of 0.67, revealing that, on average, Mimulus species exhibit only 33% overlap in the extent of suitable habitat with their closest relatives. Because prezygotic barriers act early in the life cycle of organisms, this strong barrier has the potential to contribute greatly to the total isolation experienced between diverging species. Therefore, ecogeographic isolation appears to play an important role in Mimulus, and estimating the strength of this barrier is essential to our general understanding of speciation.