SEARCH · PubMed Health

Results for “ecological speciation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources

PubMed2006

Symbioses of methanotrophs and deep-sea mussels (Mytilidae: Bathymodiolinae).

The symbioses between invertebrates and chemosynthetic bacteria allow both host and symbiont to colonize and thrive in otherwise inhospitable deep-sea habitats. Given the global distribution of the bathymodioline symbioses, this association is an excellent model for evaluating co-speciation and evolution of symbioses. Thus far, the methanotroph and chemoautotroph endosymbionts of mussels are tightly clustered within two independent clades of gamma Proteobacteria, respectively. Further physiological and genomic studies will elucidate the ecological and evolutionary roles that these bacterial clades play in the symbiosis and chemosynthetic community. Due to the overall abundance of the methanotrophic symbioses at hydrothermal vents and hydrocarbon seeps, they likely play a significant, but as of yet unquantified, role in the biogeochemical cycling of methane. With this in mind, the search for methanotrophic symbioses should not be restricted to these known deep-sea habitats, but rather should be expanded to include methane-rich coastal marine and freshwater environments inhabited by methanotrophs and bivalves. Our current understanding of the bathymodioline symbioses provides a strong foundation for future explorations into the origin, ecology, and evolution of methanotroph symbioses, which are now becoming possible through a combination of classical and advanced molecular techniques.

Animals↗

PubMed2000

Evidence from sequence-tagged-site markers of a recent progenitor-derivative species pair in conifers.

Black spruce (Picea mariana [B.S.P.] Mill.) and red spruce (Picea rubens Sarg.) are two conifer species known to hybridize naturally in northeastern North America. We hypothesized that there is a progenitor-derivative relationship between these two taxa and conducted a genetic investigation by using sequence-tagged-site markers of expressed genes. Based on the 26 sequence-tagged-site loci assayed in this study, the unbiased genetic identity between the two taxa was quite high with a value of 0.920. The mean number of polymorphic loci, the mean number of alleles per polymorphic locus, and the average observed heterozygosity were lower in red spruce (P = 35%, A(P) = 2.1, H(o) = 0.069) than in black spruce (P = 54%, A(P) = 2.9, H(o) = 0.103). No unique alleles were found in red spruce, and the observed patterns of allele distribution indicated that the genetic diversity of red spruce was essentially a subset of that found in black spruce. When considered in combination with ecological evidence and simulation results, these observations clearly support the existence of a progenitor-derivative relationship and suggest that the reduced level of genetic diversity in red spruce may result from allopatric speciation through glaciation-induced isolation of a preexisting black spruce population during the Pleistocene era. Our observations signal a need for a thorough reexamination of several conifer species complexes in which natural hybridization is known to occur.

Genetic Markers↗

PubMed1976

Group selections among laboratory populations of Tribolium.

Selection at the population level or group selection is defined as genetic change that is brought about or maintained by the differential extinction and/or proliferation of populations. Group selection for both increased and decreased adult population size was carried out among laboratory populations of Tribolium castaneum at 37-day intervals. The effect of individual selection within populations on adult population size was evaluated in an additional control series of populations. The response in the group selection treatments occurred rapidly, within three or four generations, and was large in magnitude, at times differing from the controls by over 200%. This response to selection at the populational level occurred despite strong individual selection which caused a decline in the mean size of the control populations from over 200 adults to near 50 adults in nine 37-day intervals. "Assay" experiments indicated that selective changes in fecundity, developmental time, body weight, and cannibalism rates were responsible in part for the observed treatment differences in adult population size. These findings have implications in terms of speciation in organisms whose range is composed of many partially isolated local populations.

Animals↗

PubMed2003

Why do species exist? Insights from sexuals and asexuals.

Why does life diversify into the more or less discrete entities we recognise as species? Two main explanations have been proposed: i) species are a consequence of adaptation to different ecological niches, ii) species are a consequence of sexual reproduction and reproductive isolation. Phylogenetic studies of case-study groups can provide insights into the relative importance of divergent selection and isolation for speciation, but it can be difficult to infer causes of speciation unambiguously. The example of North American tiger beetles from the genus Cicindela is discussed. An alternative approach is to compare diversification between related sexual and asexual taxa to infer the relative importance of the two explanations. We outline expected patterns of diversification in sexual and asexual lineages under different scenarios using coalescent theory. Whether sexuals or asexuals diversify to a greater extent depends on the balance among various stages of diversification, particularly on the effects of sexual reproduction on rates of adaptive evolution. Rotifers offer a unique system to test these ideas, allowing comparison of patterns of genetic and functional morphological diversification in sexual (bdelloid) and asexual (monogonont) clades.

Journal Article↗

PubMed2006

Comparative phylogeography of woodland reptiles in California: repeated patterns of cladogenesis and population expansion.

The ultimate goal of comparative phylogeographical analyses is to infer processes of diversification from contemporary geographical patterns of genetic diversity. When such studies are employed across diverse groups in an array of communities, it may be difficult to discover common evolutionary and ecological processes associated with diversification. In order to identify taxa that have responded in a similar fashion to historical events, we conducted comparative phylogeographical analyses on a phylogenetically and ecologically limited set of taxa. Here, we focus on a group of squamate reptiles (snakes and lizards) that share similar ecological requirements and generally occupy the same communities in the western USA. At a gross level, deep genetic division in Contia tenuis, Diadophis punctatus, Elgaria multicarinata, the Charina bottae complex, and Lampropeltis zonata are often concordant in the Transverse Ranges, the Monterey Bay and Sacramento-San Joaquin Delta region, and the southern Sierra Nevada in California. Molecular clock estimates suggest that major phyletic breaks within many of these taxa roughly coincide temporally, and may correspond to important geological events. Furthermore, significant congruence between the phylogeographies of E. multicarinata and L. zonata suggests that the succession of vicariance and dispersal events in these species progressed in concert. Such congruence suggests that E. multicarinata and L. zonata have occupied the same communities through time. However, across our entire multi-taxon data set, the sequence of branching events rarely match between sympatric taxa, indicating the importance of subtle differences in life history features as well as random processes in creating unique genetic patterns. Lastly, coalescent and noncoalescent estimates of population expansion suggest that populations in the more southerly distributed clades of C. tenuis, D. punctatus, E. multicarinata, and L. zonata have been stable, while populations in more northerly clades appear to have recently expanded. This concerted demographic response is consistent with palaeontological data and previous phylogeographical work that suggests that woodland habitat has become more restricted in southern California, but more widespread in the North during Holocene warming. Future phylogeographical work focusing on allied and ecologically associated taxa may add insight into the ecological and evolutionary processes that yield current patterns of genetic diversity.

Animals↗

PubMedDate not supplied

[Progress of ecological parasitology--parasite communities].

Many of the major development in the field of parasite community ecology have been due to a switch in focus from a search for pattern to investigation of the processes that produce those patterns. This switch has been accompanied by a recognition that different processes operate at the scale of the individual host (processes determining host specificity and attributes of the niches of the parasites), within the unit of habitat (processes determining population dynamics, exchange of parasites, and transmission), and among units of habitat (processes determining colonization, extinction, or local speciation of parasites). Further developments are likely to depend upon the coordinated use of models, experimental approaches, and field observations aimed at clarifying the conditions under which the processes at each scale became particularly important.

Animals↗

PubMed2003

Components of reproductive isolation between the monkeyflowers Mimulus lewisii and M. cardinalis (Phrymaceae).

Evolutionists have long recognized the role of reproductive isolation in speciation, but the relative contributions of different reproductive barriers are poorly understood. We examined the nature of isolation between Mimulus lewisii and M. cardinalis, sister species of monkeyflowers. Studied reproductive barriers include: ecogeographic isolation; pollinator isolation (pollinator fidelity in a natural mixed population); pollen competition (seed set and hybrid production from experimental interspecific, intraspecific, and mixed pollinations in the greenhouse); and relative hybrid fitness (germination, survivorship, percent flowering, biomass, pollen viability, and seed mass in the greenhouse). Additionally, the rate of hybridization in nature was estimated from seed collections in a sympatric population. We found substantial reproductive barriers at multiple stages in the life history of M. lewisii and M. cardinalis. Using range maps constructed from herbarium collections, we estimated that the different ecogeographic distributions of the species result in 58.7% reproductive isolation. Mimulus lewisii and M. cardinalis are visited by different pollinators, and in a region of sympatry 97.6% of pollinator foraging bouts were specific to one species or the other. In the greenhouse, interspecific pollinations generated nearly 50% fewer seeds than intraspecific controls. Mixed pollinations of M. cardinalis flowers yielded >75% parentals even when only one-quarter of the pollen treatment consisted of M. cardinalis pollen. In contrast, both species had similar siring success on M. lewisii flowers. The observed 99.915% occurrence of parental M. lewisii and M. cardinalis in seeds collected from a sympatric population is nearly identical to that expected, based upon our field observations of pollinator behavior and our laboratory experiments of pollen competition. F1 hybrids exhibited reduced germination rates, high survivorship and reproduction, and low pollen and ovule fertility. In aggregate, the studied reproductive barriers prevent, on average, 99.87% of gene flow, with most reproductive isolation occurring prior to hybrid formation. Our results suggest that ecological factors resulting from adaptive divergence are the primary isolating barriers in this system. Additional studies of taxa at varying degrees of evolutionary divergence are needed to identify the relative importance of pre- and postzygotic isolating mechanisms in speciation.

Adaptation, Biological↗

PubMed1990

Aldolase DNA polymorphism in subterranean mole-rats: genetic differentiation and environmental correlates.

We analysed the genetic diversity and environmental correlates of the aldolase A and B genes by means of restriction endonucleases (DNA RFLP analysis), in the four chromosomal species (2n = 52, 54, 58 and 60) of the actively speciating subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel. The results indicated that: (i) both aldolase genes are highly polymorphic; (ii) fragment frequencies and fragment profiles display geographical patterns and significant ecological correlates; (iii) discriminant analysis largely succeeded in separating the four chromosomal species on the basis of variation of aldolase RFLPs.

Animals↗

PubMed1990

The interplay of population dynamics and the evolutionary process.

Long-term maintenance of genetic diversity is affected by ecological forces that are driven in turn by current levels of genetic variation. The strength of population regulation and the consequent patterns of population fluctuations determine the likelihood of genetic changes considered pivotal for rapid speciation. However, genetic diversity in the susceptibility to regulatory forces can reduce the magnitude of such fluctuations and minimize the likelihood of genetic revolutions. A group of populations that experiences local extinctions and recolonizations may hold lower levels of genetic diversity than in the absence of such extinctions, but local adaption, which provides enhanced genetic diversity, can reduce the likelihood of local extinctions. Tightly regulated populations experience different selection pressures than poorly regulated populations, although tighter regulation itself can evolve. When genotypic variation affects the outcome of interspecific interactions on a local scale, this effect, coupled with appropriate spatial variation, can enhance the resilience of the interactive system.

Animals↗

PubMed2002

Sexual isolation and speciation in bacteria.

Like organisms from all other walks of life, bacteria are capable of sexual recombination. However, unlike most plants and animals, bacteria recombine only rarely, and when they do they are extremely promiscuous in their choice of sexual partners. There may be no absolute constraints on the evolutionary distances that can be traversed through recombination in the bacterial world, but interspecies recombination is reduced by a variety of factors, including ecological isolation, behavioral isolation, obstacles to DNA entry, restriction endonuclease activity, resistance to integration of divergent DNA sequences, reversal of recombination by mismatch repair, and functional incompatibility of recombined segments. Typically, individual bacterial species are genetically variable for most of these factors. Therefore, natural selection can modulate levels of sexual isolation, to increase the transfer of genes useful to the recipient while minimizing the transfer of harmful genes. Interspecies recombination is optimized when recombination involves short segments that are just long enough to transfer an adaptation, without co-transferring potentially harmful DNA flanking the adaptation. Natural selection has apparently acted to reduce sexual isolation between bacterial species. Evolution of sexual isolation is not a milestone toward speciation in bacteria, since bacterial recombination is too rare to oppose adaptive divergence between incipient species. Ironically, recombination between incipient bacterial species may actually foster the speciation process, by prohibiting one incipient species from out-competing the other to extinction. Interspecific recombination may also foster speciation by introducing novel gene loci from divergent species, allowing invasion of new niches.

Bacteria↗

PubMed2002

Speciation and the establishment of zonation in an intertidal barnacle: specific settlement vs. selection.

The tropical barnacle Tetraclita forms a belt on hard substrates in the intertidal zone of the Red Sea. Based on morphological data, three distinct species were suggested to exist, occupying different vertical levels - T. barnesorum, T. rufotincta and T. achituvi. In this study we used molecular (12S mitochondrial ribosomal DNA) and ecological data to examine whether this morphological variability reflects genetic differences, or is a result of environmental factors. Adults and spats, collected from settlement plates, were censused and screened genotypically using single strand conformation polymorphism (SSCP) analysis, and settlement dynamics was recorded. We provide evidence for the existence of only two distinct species, and point out both phenotypic plasticity and convergence within and between the proposed species. Cyprids of T. achituvi settle specifically at the lower part of the Tetraclita belt, and feature one phenotype. In contrast, T. rufotincta, occupying the upper and middle portions of the Tetraclita belt, settles throughout the range, shows phenotypic plasticity (three variants), and presumably undergoes selection at the lower part. Thus, the vertical zonation of Tetraclita is produced by the combination of pre-settlement and post-settlement factors, in T. achituvi and T. rufotincta, respectively. The examined system may offer a model in which to study the mechanisms underlying sympatric speciation.

Animals↗

PubMed2004

Molecular evidence of speciation between island and continental populations of Anopheles (Cellia) sundaicus (Diptera: Culicidae), a principal malaria vector taxon in Southeast Asia.

Anopheles sundaicus s.l. is a principal malaria vector taxon on islands and along the coastal areas of Southeast Asia. It has a wide geographical distribution and exhibits a high level of ecological and behavioral variability. Study of this taxon is crucial for understanding its biology and implementing effectise vector control measures. We compared populations of An. sundaicus from Vietnam, Thailand, and Malaysian Borneo by using two mitochondrial DNA markers: cytochrome oxidase I and cytochrome b. Genetic divergence, geographic separation, and cladistic analysis of relationships revealed the presence of two cryptic species: Anopheles sundaicus s.s. on Malaysian Borneo and An. sundaicus species A in coastal areas of Thailand and Vietnam. A polymerase chain reaction (PCR) assay was developed to easily identify these two species throughout their geographic distributions. The assay was based on sequence characterized amplified region derived from random amplified polymorphic DNA. This PCR identification method needs to be validated and adapted for the recognition of other possible species in the Sundaicus Complex.

Animals↗

PubMed2005

Molecular phylogeny and evolution of the freshwater eels genus Anguilla based on the whole mitochondrial genome sequences.

Molecular phylogenetic analyses were conducted using the whole mitochondrial genome sequences of all 18 species/subspecies of the freshwater eels genus Anguilla to infer their phylogenetic relationships and to evaluate hypotheses about the possible dispersal routes of this genus. The Bayesian and maximum likelihood analyses using a total of 15,187 sites of mitochondrial DNA sequences suggested that A. mossambica was the most basal species of anguillid eel, and that the other species (except for A. borneensis) formed three geographic clades: Atlantic (two species), Oceania (three species), and Indo-Pacific (11 species). The present study clearly indicated a sister relationship between the Atlantic and Oceanian species, which now have distantly separated geographic distributions. This suggests that the previous hypotheses to estimate the dispersal route of anguillid eels into the Atlantic Ocean based on the current geographic distribution of species are unsupported by the present more complete analysis. Alternatively, the unique geographic distribution of the present day species in the genus Anguilla appears to have resulted from multiple dispersal events. Although the age of the beginning of speciation among anguillid eels was tentatively estimated as 20 million years ago using a calibration for bony fishes of 7.3x10(-4) substitutions/site/million years, it is possible that this divergence time was underestimated because of the ecological characteristics of these fishes. The results of the present study suggest that the hypotheses for the dispersal route and divergence time of the genus Anguilla should be reconsidered.

Anguilla↗

PubMed1996

Allelic diversity and gene genealogy at the self-incompatibility locus in the Solanaceae.

The self-incompatibility (S) locus of flowering plants offers an example of extreme polymorphism maintained by balancing selection. Estimates of recent and long-term effective population size (Ne) were determined for two solanaceous species by examination of S-allele diversity. Estimates of recent Ne in two solanaceous species differed by an order of magnitude, consistent with differences in the species' ecology. In one species, the evidence was consistent with historical population restriction despite a large recent Ne. In the other, no severe bottleneck was indicated over millions of years. Bottlenecks are integral to founder-event speciation, and loci that are subject to balancing selection can be used to evaluate the frequency of this mode of speciation.

Alleles↗

PubMed1999

Molecular identification of chromosomal forms of Anopheles gambiae sensu stricto.

The Afrotropical malaria vectors Anopheles gambiae sensu stricto and An. arabiensis, responsible for more than 3/4 of the world Plasmodium falciparum inoculations, are members of the Anopheles gambiae complex, a group consisting of six sibling species. The nominal species (An. gambiae s.s.) is by far the most anthropophilic vector and its adaptation to man and his environment involves further ongoing speciation processes. This fact is shown by the existence of a number of incipient taxonomic units characterised by different chromosomal arrangements derived from the presence of polymorphic paracentric inversions. This speciation process is centered in West Africa, where five so-called 'chromosomal forms' have been described, designated with a non-Linnean nomenclature: Forest, Bissau, Savanna, Bamako, and Mopti. Studies on the distribution and the ecology of these incipient species have highlighted specific adaptations to eco-ethological parameters, which might reflect on their relative efficiency as malaria vectors. Cytogenetic analysis, in spite of some inherent difficulties, has proved to be a powerful tool for the identification of An. gambiae sibling species and the individual chromosomal forms. Yet, modern molecular tools are now available, providing alternative faster low-cost technologies, and we discuss here their relative merits.

Animals↗

PubMed2026

Life in sediments fosters 'sexual' speciation in the Shewanella baltica complex.

Understanding how intra- and interspecific differentiation arises in natural microbial populations is central to explaining the processes that drive bacterial evolution. Motivated by the co-occurrence of multiple putative genospecies closely related to Shewanella baltica in Baltic Sea sediments, we investigated the genomic structure of this species complex across fine spatial scales. We analyzed 112 genome sequences from strains collected across several sediment cores and depths (0-6 cm) at Vaxön (Stockholm archipelago, Sweden) as well as earlier isolates from this site and allopatric strains from surrounding locations obtained from both sediments and the water column. Using a reverse-ecology population genomics approach, we found unprecedented genomic diversification among sediment-associated strains, which form a species complex resolving into three cohesive evolutionary groups (G1, G2, and G3) with distinct signatures of metabolic specialization including sulfite respiration. While G1 consists predominantly of a single species (S. baltica) with high gene turnover, G2 and G3 comprise an array of divergent putative genospecies and previously reported species consistently recovered from sediments. Patterns of homologous recombination indicate that diversification of the lineages within G2 and G3 is primarily recombination-driven ('sexual') and is associated with specialization in sulfite reduction and utilization of certain carbon sources. The extent of diversity uncovered here far exceeds that reported for S. baltica from other environments, suggesting that a sediment-associated lifestyle promotes the emergence of novel genotypes. These findings expand the known limits of sympatric speciation in prokaryotes beyond subspecific ecotypes, demonstrating that bacterial species can diverge and persist as distinct lineages in the absence of spatial segregation and at microgeographic scales. Furthermore, our results suggest that collective interactions and ecological differentiation can structure sediment-associated bacterial populations strongly enough to drive divergence at the species level.

Journal Article↗

PubMed1985

The evolutionary significance of sexual selection.

A model for the joint evolution of a secondary sexual male trait Z and a female mating preference Y is discussed. Recurrence relations for the moments of (Z, Y) are given under the assumption that the traits are binormally distributed. It is shown that female preference for a male character can lead to an equilibrium distribution of the male trait with non-zero variances. The conditions under which the distribution is stable, are given. Unstable situations, in which a continued exaggeration of the male trait occurs, are described. It is demonstrated that the effect of sexual selection on the evolution of the male trait depends on the intensity of natural selection, i.e. the effect of the sexual selection increases when the intensity of natural selection is reduced. The effect of the female preference on the male trait also increases with increasing availability of males. This provides a link to several ecological conditions which have generally been known to be correlated with the degree of sexual selection. Furthermore, it is demonstrated that perturbations away from the equilibrium may cause rapid evolution of the male character, eventually leading to speciation.

Animals↗

PubMed2006

Reinforcement and the genetics of hybrid incompatibilities.

Recent empirical studies suggest that genes involved in speciation are often sex-linked. We derive a general analytic model of reinforcement to study the effects of sex linkage on reinforcement under three forms of selection against hybrids: one-locus, two-locus, and ecological incompatibilities. We show that the pattern of sex linkage can have a large effect on the amount of reinforcement due to hybrid incompatibility. Sex linkage of genes involved in postzygotic isolation generally increases the strength of reinforcement, but only if genes involved in prezygotic isolation are also sex linked. We use exact simulations to test the accuracy of the approximation and find that qualitative predictions made assuming weak selection can hold when selection is strong. Our simulations also show that incompatibilities that evolve in allopatry by drift or weak selection are likely to be lost by swamping during secondary contact, even when selection against hybrids is strong.

Alleles↗