Ecogeographic Isolation Research Articles

Genetic and Morphometric Variability of Triatoma sordida (Hemiptera: Reduviidae) from the Eastern and Western Regions of Paraguay.

Triatoma sordida is widely distributed throughout the Chaco and the Eastern Region of Paraguay. It is associated to palm trees and artificial ecotopes located in peridomestic environments. The aim of this work was to determine genetic and morphometric variability and feeding behavior among population of T. sordida captured in domicile and peridomicile areas of Paraguay. Feeding contents and levels of genetic and morphometric variation were determined in 124 T. sordida from domicile and peridomicile populations of San Pedro and Paraguarí departments of the Eastern Region and Boquerón and Presidente Hayes departments of the Western region using Double Diffusion Gel, random amplified polymorphic DNA (RAPD), and head and wings morphometry. Morphometric analysis revealed isolation of populations by geographic region and larger size in triatomine populations from the Western Region. RAPD showed no specific patterns for domicile and peridomicile populations. The estimator of diversity (FST; 0.08) and high gene flow obtained (Nm; 5.7) did not allow the establishment of genetic differentiation within the same region. The blood meal source showed that poultry feeding was 38% of host preferences, and human blood was the second feeding preference (24%) in the insects from the Eastern Region while poultry feeding was predominant in those from the Western Region (30%). This work showed homogeneity between T. sordida populations of the same region and between domicile and peridomicile. The genetic diversity was determined among T. sordida populations of both geographical regions suggesting differentiation associated to eco-geographical isolation by distance. It is important to notice that pattern feedings were different between the two regions. Further studies should be focused on how phenetic and genetic variations could be related to the adaptation capacity of these triatomine populations to domicile, increasing their vector potentiality in the transmission of Chagas disease.

Phylogeographic analysis of a temperate-deciduous forest restricted plant (Bupleurum longiradiatum Turcz.) reveals two refuge areas in China with subsequent refugial isolation promoting speciation

This study investigates the influence of climate-induced oscillations and complicated geological conditions on the evolutionary processes responsible for species formation in presently fragmented temperate forest habitats, located in continental East Asia. In addition to this, we also investigate the heavily debated issue of whether temperate forests migrated southwards during such glacial periods or, alternatively, whether there existed refugia within north China, enabling localized survival of temperate forests within this region. In order to achieve these, we surveyed the phylogeography of Bupleurum longiradiatum Turcz. (a herbaceous plant solely confined to temperate forests) constructed from sequence variation in three chloroplast (cp) DNA fragments: trnL–trnF, psbA–trnH and rps16. Our analyses show high genetic diversity within species (hT=0.948) and pronounced genetic differentiation among groups (yellow and purple flowers) with a significant phylogeographical pattern (NST>GST, P<0.05). Forty-three haplotypes were identified and clustered into two lineages (the purple-flowered lineage and the yellow-flowered lineage). Two corresponding refuge areas, one in Qinling and its adjacent regions and one in the Changbai Mountains/eastern China, were revealed across the entire distribution ranges of Bupleurum longiradiatum. These results provide evidence for the hypothesis that independent refugia were maintained across the range of temperate forests in northern China during the last glacial maximum or earlier cold periods. Bupleurum longiradiatum var. porphyranthum formed a single taxon based on molecular data. This specific formation process suggests that the historical vicariance factors, i.e. climate-induced eco-geographic isolation through the biotic displacement of temperate-deciduous forest habitats, enhanced the divergence of the yellow and purple flower lineages at different spatial–temporal scales and over glacial and interglacial periods. Additionally, geological conditions that restricted gene flow might also be responsible for the observed high genetic and geographic differentiation. A nested clade analysis (NCA) revealed that allopatric fragmentation was a major factor responsible for the phylogeographic pattern observed, and also supported a role for historical vicariance factors. Our results therefore support the inference that Quaternary refugial isolation promoted allopatric speciation of temperate plants in East Asia. This may help to explain the existence of high diversity and endemism of plant species in East Asia.

RECONCILING EXTREMELY STRONG BARRIERS WITH HIGH LEVELS OF GENE EXCHANGE IN ANNUAL SUNFLOWERS

In several cases, estimates of gene flow between species appear to be higher than we might predict given the strength of interspecific barriers separating these species pairs. However, as far as we are aware, detailed measurements of reproductive isolation have not previously been compared with a coalescent-based assessment of gene flow. Here, we contrast these two measures in two species of sunflower, Helianthus annuus and H. petiolaris. We quantified the total reproductive barrier strength between these species by compounding the contributions of the following prezygotic and postzygotic barriers: ecogeographic isolation, reproductive asynchrony, niche differentiation, pollen competition, hybrid seed formation, hybrid seed germination, hybrid fertility, and extrinsic postzygotic isolation. From this estimate, we calculated the probability that a reproductively successful hybrid is produced: estimates of P(hyb) range from 10(-4) to 10(-6) depending on the direction of the cross and the degree of independence among reproductive barriers. We then compared this probability with population genetic estimates of the per generation migration rate (m). We showed that the relatively high levels of gene flow estimated between these sunflower species (N(e) m= 0.34-0.76) are mainly due to their large effective population sizes (N(e) > 10(6)). The interspecific migration rate (m) is very small (<10(-7)) and an order of magnitude lower than that expected based on our reproductive barrier strength estimates. Thus, even high levels of reproductive isolation (>0.999) may produce genomic mosaics.

Ecogeographic isolation: a reproductive barrier between species and between cytotypes in Houstonia (Rubiaceae)

‘Ecogeographic isolation’ describes the combined role of ecology and geography as a reproductive barrier, and an important component in speciation. Evidence increasingly shows that this form of isolation is important for maintaining the genetic integrity of populations and species. Further, ecogeographic isolation can be a reproductive barrier between polyploid individuals and their diploid progenitors. New ecoinformatic methods, which includes niche modeling and associated statistical assessments of these models with spatially explicit environmental data, allow us to test if ecogeographic isolation is a contributing isolating barrier between species and between cytotypes within a species. We tested the hypothesis that ecogeographic isolation contributes to isolation of species and cytotypes within species of the plant genus Houstonia. We found that species in this group occupied significantly different niches, which suggests ecogeographic isolation is a contributing reproductive barrier. We also found that diploid and tetraploid forms of H. longifolia show some level of ecogeographic isolation, but H. purpurea diploids and tetraploids did not. Our results suggest that ecogeographic isolation plays a role in reproductive isolation between Houstonia species and between cytotypes of H. longifolia.

The stability of Quaternary speciation: a case study in Primula sect. Auricula

Primula sect. Auricula, a group of 25 species distributed in the European Alpine System, has been hypothesised to have diversified in the Quaternary through speciation in geographically isolated glacial refugia. We here examine whether the integrity of species is endangered through hybridisation upon contact in the Holocene. To do this, we (1) critically screened the literature for reported hybrids and supplemented this with our own knowledge of the group, (2) performed an admixture analysis of AFLP variation of two partly sympatric species pairs, P. hirsuta/P. daonensis and P. latifolia/P. marginata, and (3) analysed long-known hybrid populations of P. lutea × P. hirsuta in Wipptal/Austria to identify possible mechanisms of reproductive isolation. The literature survey revealed that populations of the 32 hybrid combinations known have been observed at 63 localities. In the admixture analysis, two admixed individuals per species were found among 524 individuals of P. latifolia and P. marginata, and 21 admixed individuals were found among 234 individuals of P. hirsuta. The analysis of P. lutea × P. hirsuta hybrids revealed that they show reduced pollen and seed fertility, and are limited to soils with intermediate pH values. We conclude that although species of P. sect. Auricula can readily be hybridised experimentally, hybridisation is rare in nature and species are stable. Mechanisms of reproductive isolation include geographical and ecogeographical isolation, ecological hybrid inviability and reduced hybrid fertility.

Did glacials and/or interglacials promote allopatric incipient speciation in East Asian temperate plants? Phylogeographic and coalescent analyses on refugial isolation and divergence in Dysosmaversipellis

To explore the evolutionary consequences of climate-induced fluctuations in presently fragmented temperate forest habitats in continental East Asia we investigated the phylogeography and demographic history of the temperate-deciduous forest endemic Dysosma versipellis from disjunct montane sites in Central-Southeast China. Based on a survey of chloroplast (cp) DNA sequence variation, our analyses show that this perennial herb consists of morphologically indistinguishable western and central/eastern cpDNA lineages. Coalescent analyses under the ‘isolation with migration’ (IM) model support an ancient (Mid-Pleistocene) divergence between these lineages, with the western lineage having persisted without significant population growth in a long-term refuge just east of the Tibetan (Qinghai-Xizang) Plateau. In contrast, for the central/eastern lineage, we found strong evidence for population expansion from a refuge located south of the middle and lower reaches of the Yangtze River, and likely coinciding with the last or penultimate interglacial, followed by considerable population isolation and divergence in situ over (at least) the latest glacial–interglacial cycle. In line with recent evidence from palaeomodeling of East Asian forest biomes, our results suggest that the same vicariance factor, i.e. climate-induced eco-geographic isolation through (a)biotic displacement of temperate-deciduous forested habitats, promoted the divergence of D. versipellis lineages and populations at different spatial–temporal scales and over glacial and interglacial periods. Thus, there is no evidence that populations of D. versipellis merged at lower elevations during the last glacial(s). As such, D. versipellis accords with the premise that Late Quaternary refugial isolation is likely to have enhanced allopatric (incipient) species formation of temperate plants in East Asia.

Assessment of genetic diversity and genetic relationships among 29 populations of Azadirachta indica A. Juss. using RAPD markers

Randomly amplified polymorphic DNA (RAPD) analysis was employed to assess genetic divergence among 29 neem accessions collected from two agro-ecological regions of India (11 agro-climatic sub-zones), which cover three states, Punjab, Haryana and Rajasthan. Out of 24, 10-mer random primers used for studying genetic divergence, 14 were polymorphic, generating a total of 73 amplification products with an average of 5.21 products per polymorphic primer and estimated gene diversity of 0.49. Genetic relationships among accessions were evaluated by generating a similarity matrix based on Jaccard’s coefficient, ranging from 0.70 to 0.96. The phenetic dendrogram generated by UPGMA analysis grouped accessions into five clusters. RAPD performed within accessions (individual seedlings collected from the same mother plant) showed no variation indicating homogeneous population within accessions. Primers OPA-18, OPC-08 and OPI-03 were found most informative based on their resolving power. The degree of genetic variation detected among the 29 accessions with RAPD analysis suggests that RAPD can be used for studying genetic diversity in neem. The study also demonstrated that neem germplasm collected from northwestern plains of India shows no eco-geographical isolation based on sub-zones because accessions collected from different sub-regions are grouping together in the genetic tree.

Salivary Gland Chromosomes ofCulex Quinquefasciatus

SUMMARYThe salivary gland chromosomes of Culex quinquefasciatus from a wild population of Bhanja Bihar (Berhampur, Orissa) have been mapped with a view to resolving the controversy that exists with regard to its nomenclatural status. A comparison of this banding pattern with that of an NICD (National Institute of Communicable Disease, Delhi) strain of this species, previously described under the name of Culex pipiens fatigans, shows considerable similarities. The minor differences observed are perhaps the result of ecogeographical isolation on the genetic variability of C. pipiens fatigans.

THE ORGANIZATION OF GENETIC VARIABILITY IN PHLOX DRUMMONDII.

thousands of individuals. The species is divisible into six morphologically distinct subspecies which are largely allopatric or parapatric (Erbe and Turner, 1962). Their ranges are depicted in Figure 1. Subspecies glabriflora grows principally on stabilized sandy dune soils in open fields of the Coastal Plain, ssp-. littoralis on coastal beach sands, ssp. tharpii on sandy soils in open prairies of the Rio Grande Plain, ssp. goldsmithii and ssp. drummondii on sandy loams in open or cleared forest areas, and ssp. mcallisteri in open fields on shallow sandy soils of granitic origin on the Edwards Plateau. Reproductive barriers to gene exchange are weak (Erbe and Turner, 1962; Levin, 1976), and the integrity of the subspecies seems due to their ecogeographical isolation. All of the subspecies exhibit gametophytic self-incompatibility, and have the same chromosome number, n = 7. The primary objectives of this study are (1) to characterize each taxon in terms of gene frequencies, genetic diversity and genotype frequencies relative to HardyWeinberg expectation, (2) to apportion genetic diversity within and between subspecies, (3) to describe gene frequency heterogeneity between populations of the same subspecies and the species as a whole, (4) to describe geographical variation patterns for alleles and genetic diversity, and (5) to determine the genetic affinities of the subspecies. In doing this an attempt is made to discern the roles of gene flow restriction within and among populations and stochastic processes in fostering and maintaining the organization of genetic variability in P. drummondii. The concordance between morphological and allozymic variation also is considered. EVOLUTION 31:477-494. September 1977 477