PubMed Health⌕ Search

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 325 records · Page 18Linked to original sources
PubMed2002

Mating signal variation and bimodality in a mosaic hybrid zone between Chorthippus grasshopper species.

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are easily distinguished by male calling song and the number of stridulatory pegs on the hind femur, and form a mosaic hybrid zone in northern Spain. In this paper, we fit a two-dimensional cline to variation in male calling song characters, which are of particular interest as they are likely to be involved in mate choice by females. As with variation in peg number, local habitat makes only a small contribution in explaining deviations in mean song score from clinal expectations. However, the fitted width of the cline for song characters is significantly narrower than for peg number, suggesting that mating signals may be associated with reduced hybrid fitness in the field and that recombination rates are sufficient to allow clines for different characters to diverge in width. Despite this, estimates for the overall elevation in linkage disequilibrium at the zone center, based on covariance between peg and song characters, reveal a substantial overrepresentation of parental genotypes at the cline center relative to the expectations of a tension zone of similar width. Examination of covariance at individual sites reveals that this inflated estimate of linkage disequilibrium is caused by several sites where the distribution of phenotypes is effectively bimodal. This substantial variation in linkage disequilibrium at the cline center could result from local variation in the strength of assortative mating or selection against hybrids, or may reflect the long-distance colonization of empty habitat from outside the hybrid zone, which would continually create new contacts between parental genotypes at the cline center. Hybrid zones like this, in which strong linkage disequilibrium occurs in some situations but not in others, are of particular relevance to speciation research and allow investigation of the spread of combinations of alleles through different genetic and ecological backgrounds.

Animals↗
PubMed2005

A critical review of the biogeochemistry and ecotoxicology of selenium in lotic and lentic environments.

Anthropogenic activities resulting in elevated selenium (Se) levels in aquatic ecosystems can result in teratogenic and reproductive effects in fish and waterfowl. However, relationships between observed effects and exposure concentrations or body burdens are ambiguous. Therefore, it is critical to identify factors that affect Se ecotoxicity before defining adequate protective environmental regulations. One important political debate questions if Se ecotoxicity differs between standing (lentic) and flowing (lotic) waters and, if so, how this should be incorporated into the definition of protective criteria. In the present review, we compile and discuss the scarce literature regarding Se ecotoxicity in lotic systems, and we compare it to the substantial body of evidence for lentic systems. General differences between lentic and lotic systems with respect to ecology, hydrology, and biogeochemistry are identified and related to Se ecotoxicity. The limited knowledge regarding Se speciation in the biomagnification process is reviewed and put in context. Fundamental considerations suggest that Se ecotoxicity in lotic systems should be reduced compared to lentic systems, but we conclude that this statement is not substantiated by the existing data. Additionally, we identify critical gaps of knowledge that must be resolved in future studies before the argument can be decided conclusively.

Animals↗
PubMed2006

On the abundance of polyploids in flowering plants.

The wide distribution of polyploidy among plants has led to a variety of theories for the evolutionary advantages of polyploidy. Here we claim that the abundance of polyploidy may be the result of a simple ratcheting process that does not require evolutionary advantages due to the biological properties of organisms. The evolution of polyploidy is a one-way process in which chromosome number can increase but not decrease. Using a simple mathematical model, we show that average ploidal level within a plant lineage can continually increase to the levels observed today, even if there are ecological or physiological disadvantages to higher ploidy. The model allowed us to estimate the average net speciation and polyploidy rates for ten angiosperm genera. Based on these estimates, the model predicts distributions of ploidal levels statistically similar to those observed in nine of the 10 genera.

Biological Evolution↗
PubMed1997

[Geography of chromosomes of natural populations of the shrews Sorex araneus and Suncus murinus].

The geographic distribution of chromosome races of two shrew species (Sorex araneus and Suncus murinus) was analyzed on the basis of published data and personal results. It was shown that expansion of both species was accompanied by fixation of different chromosome rearrangements (mainly Robertsonian translocations) in isolates. Chromosome polymorphism studied from the viewpoint of ecology and geography of these species allows reconstruction of their evolutionary history and understanding of the speciation process.

Animals↗
PubMed2025

Genomic analyses of three Acanthus L. species provide insight into polyploidization-driven speciation and evolution.

Allopolyploidy fundamentally influences plant evolution, yet the genomic dynamics of allotetraploidization remain incompletely understood. We investigated Acanthus tetraploideus (2n = 4x = 96), an ecologically significant allotetraploid true mangrove from Indo-West Pacific intertidal zones. Our prior integrative investigations indicate that A. tetraploideus originated through hybridization of the diploid species A. ilicifolius and A. ebracteatus with subsequent chromosome doubling. Here, we present complete chromosome-scale genome assemblies for all three species, representing the first genomic resources for true mangrove polyploid research. Our analysis reveals that the three species have experienced at least four rounds of polyploidization events, with the most recent, approximately 53 mya, possibly an Acanthus-specific event. The allotetraploid A. tetraploideus, which emerged between 1.5 and 2.2 mya, has A. ebracteatus as its maternal progenitor and A. ilicifolius as its paternal one. Through a comprehensive genomic comparison and analysis of homoeologous gene expression, we propose a gradual evolutionary trajectory for allotetraploidy in A. tetraploideus. Despite the allotetraploidization event dating back to around 2 mya, A. tetraploideus retains a high degree of colinearity with its ancestral genomes, with the majority (76.2%) of duplicated genes retained and no significant sub-genome bias in gene expression. Furthermore, we have identified positive selection in specific genes that may facilitate the adaptation of Acanthus mangrove species to their intertidal habitats. These findings establish A. tetraploideus as a model for studying allopolyploid evolution while providing new insights into mangrove speciation processes.

Genome, Plant↗
PubMed2001

Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish.

Mechanisms of speciation in cichlid fish were investigated by analyzing population genetic models of sexual selection on sex-determining genes associated with color polymorphisms. The models are based on a combination of laboratory experiments and field observations on the ecology, male and female mating behavior, and inheritance of sex-determination and color polymorphisms. The models explain why sex-reversal genes that change males into females tend to be X-linked and associated with novel colors, using the hypothesis of restricted recombination on the sex chromosomes, as suggested by previous theory on the evolution of recombination. The models reveal multiple pathways for rapid sympatric speciation through the origin of novel color morphs with strong assortative mating that incorporate both sex-reversal and suppressor genes. Despite the lack of geographic isolation or ecological differentiation, the new species coexists with the ancestral species either temporarily or indefinitely. These results may help to explain different patterns and rates of speciation among groups of cichlids, in particular the explosive diversification of rock-dwelling haplochromine cichlids.

Animals↗
PubMed1990

The Spalacidae: evolutionary history, speciation and population biology.

The evolutionary history of Spalacidae is reviewed taxonomically, paleontologically and neontologically. We focused selectively on taxonomy, biogeography, paleontology and evolutionary origins, chromosomal evolution, population biology and the species concept in Spalacidae. We concluded that the taxonomy of Spalacidae needs a modern revision based on chromosome and molecular-genetic data, beside that of morphology, physiology and behavior. The subterranean Spalacidae originated probably from a muroid-cricetoid stock in Asia Minor or vicinity, in Upper Oligocene times and adaptively radiated underground in the Balkans, steppic Russia and Middle East, extending into North Africa. The major important evolutionary feature in peripatric or allopatric speciation and adaptive radiation was karyotypic evolution, primarily through Robertsonian changes. More than 30 karyotypes (2n = 38-62; NF = 72-124) earlier represented by 8 classical species, occur primarily allopatrically or parapatrically, with only marginal sympatry, across the Eastern Mediterranean range of the family. Most karyotypes represent biospecies adapted at multiple organizational levels to their different ecologies. A short overview is presented on population biology and life history parameters of the Spalacidae which result in K-selected, "equilibrium species". Speciation in action and adaptive radiation embracing molecular and organismal adptations to the subterranean unique ecotope and to four different climatic regimes, have been multidisciplinarily studied in the Israeli Spalax ehrenbergi superspecies.

Animals↗
PubMed1999

Evolution of a mitochondrial cytochrome b gene sequence in the species-rich genus sebastes (Teleostei, Scorpaenidae) and its utility in testing the monophyly of the subgenus Sebastomus.

The ecologically diverse and species-rich rockfishes (Sebastes) are a useful group for the study of marine speciation. The monophyly of the genus is generally accepted, as is the validity of most of the numerous species found along the West Coast of North America. However, the subgeneric groupings that would help in the proposal and interpretation of various speciation schemes are poorly supported based on widely overlapping morphological characters. The use of genetic characters provides an alternative approach. In this study, we present the first quantitative analysis supporting the monophyly of all 14 species of the subgenus Sebastomus among 54 congeners. The structural features and evolution of the 750 bp of the cytochrome b gene used to test the monophyly were similar to those of other vertebrates. Low levels of intrageneric sequence divergence (<10%) and incipient levels of saturation at third-codon positions were found in the gene. The monophyly of Sebastomus was supported in extensive phylogenetic analyses using distance, cladistic, and likelihood methods. Further corroboration was obtained from permutation- and simulation-based statistical tests.

Animals↗
PubMed2005

Small clades at the periphery of passerine morphological space.

Among passerine birds (order Passeriformes), tribe- to family-level clades with five or fewer species are more frequent than one would expect from a homogeneous speciation and extinction process. Previous analyses also suggested that small clades tend to be marginal geographically and/or ecologically. In this study, I use principal component (PC) scores based on eight log-transformed measurements of the wing, tail, leg, and beak to test the hypothesis that small clades (<or=5 species) occupy peripheral positions in morphological space. Species in smaller clades exhibited higher absolute deviations and greater standard deviations on PC axes 4, 6, and 7, reflecting peripheral positions associated with relatively long toes, sometimes in contrast with short legs, and relatively small beaks compared with other birds. These extreme morphological characters are related to foraging on hard substrates, such as rock or bark, or feeding from perched positions or in dense vegetation. The implication that these small clades are protected from extinction at the periphery of morphological and, by inference, ecological space suggests that more detailed studies of the evolution and ecology of species in small clades should be a priority.

Adaptation, Physiological↗
PubMed2003

Radiation, diversity, and host-plant interactions among island and continental legume-feeding psyllids.

Island archipelagos and insect-plant associations have both independently provided many useful systems for evolutionary study. The arytainine psyllid (Sternorrhyncha: Hemiptera) radiation on broom (Fabaceae: Genisteae) in the Canary Island archipelago provides a discrete system for examining the speciation of highly host-specific phytophagous insects in an island context. Phylogenetic reconstructions based on three datasets (adult and nymph morphological characters, and two mitochondrial DNA regions: part of the small subunit rRNA, and part of cytochrome oxidase I, cytochrome oxidase II and the intervening tRNA leucine) are generally consistent. The combined molecular tree provides a well-supported estimate of psyllid relationships and shows that there have been several colonizations of the Macaronesian islands but that only one has resulted in a significant radiation. Psyllid diversification has apparently been constrained by the presence of suitable host groups within the genistoid legumes, and the diversity, distribution, and abundance of those groups. The phylogeny, by indicating pairs of sister species, allows putative mechanisms of speciation to be assessed. The most common conditions associated with psyllid speciation are geographical allopatry with a host switch to closely related hosts (six examples), or geographical allopatry on the same host (four examples). Where allopatric speciation involves a host switch, these have all been to related hosts. There is some evidence that switches between unrelated host plants may be more likely in sympatry. Only one sister pair (Aryrtainilla cytisi and A. telonicola) and the putative host races of Arytinnis modica are sympatric but on unrelated hosts, which may be a necessary condition for sympatric speciation in these insects. Where several psyllids share the same host, resources appear to be partitioned by ecological specialization and differing psyllid phenology.

Animals↗
PubMed2007

Speciation of sulfur from filamentous microbial mats from sulfidic cave springs using X-ray absorption near-edge spectroscopy.

Most transformations within the sulfur cycle are controlled by the biosphere, and deciphering the abiotic and biotic nature and turnover of sulfur is critical to understand the geochemical and ecological changes that have occurred throughout the Earth's history. Here, synchrotron radiation-based sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to examine sulfur speciation in natural microbial mats from two aphotic (cave) settings. Habitat geochemistry, microbial community compositions, and sulfur isotope systematics were also evaluated. Microorganisms associated with sulfur metabolism dominated the mats, including members of the Epsilonproteobacteria and Gammaproteobacteria. These groups have not been examined previously by sulfur K-edge XANES. All of the mats consisted of elemental sulfur, with greater contributions of cyclo-octasulfur (S8) compared with polymeric sulfur (Smicro). While this could be a biological fingerprint for some bacteria, the signature may also indicate preferential oxidation of Smicro and S8 accumulation. Higher sulfate content correlated to less S8 in the presence of Epsilonproteobacteria. Sulfur isotope compositions confirmed that sulfur content and sulfur speciation may not correlate to microbial metabolic processes in natural samples, thereby complicating the interpretation of modern and ancient sulfur records.

Epsilonproteobacteria↗
PubMed2002

Gene transfer in bacteria: speciation without species?

Although Bacteria and Archaea reproduce by binary fission, exchange of genes among lineages has shaped the diversity of their populations and the diversification of their lineages. Gene exchange can occur by two distinct routes, each differentially impacting the recipient genome. First, homologous recombination mediates the exchange of DNA between closely related individuals (those whose sequences are sufficient similarly to allow efficient integration). As a result, homologous recombination mediates the dispersal of advantageous alleles that may rise to high frequency among genetically related individuals via periodic selection events. Second, lateral gene transfer can introduce novel DNA into a genome from completely unrelated lineages via illegitimate recombination. Gene exchange by this route serves to distribute genes throughout distantly related clades and therefore may confer complex abilities--not otherwise found among closely related lineages--onto the recipient organisms. These two mechanisms of gene exchange play complementary roles in the diversification of microbial populations into independent, ecologically distinct lineages. Although the delineation of microbial "species" then becomes difficult--if not impossible--to achieve, a cogent process of speciation can be predicted.

Bacteria↗
PubMed2005

Out of Tanganyika: genesis, explosive speciation, key-innovations and phylogeography of the haplochromine cichlid fishes.

BACKGROUND: The adaptive radiations of cichlid fishes in East Africa are well known for their spectacular diversity and their astonishingly fast rates of speciation. About 80% of all 2,500 cichlid species in East Africa, and virtually all cichlid species from Lakes Victoria (approximately 500 species) and Malawi (approximately 1,000 species) are haplochromines. Here, we present the most extensive phylogenetic and phylogeographic analysis so far that includes about 100 species and is based on about 2,000 bp of the mitochondrial DNA. RESULTS: Our analyses revealed that all haplochromine lineages are ultimately derived from Lake Tanganyika endemics. We find that the three most ancestral lineages of the haplochromines sensu lato are relatively species poor, albeit widely distributed in Africa, whereas a fourth newly defined lineage - the 'modern haplochromines' - contains an unparalleled diversity that makes up more than 7% of the worlds' approximately 25,000 teleost species. The modern haplochromines' ancestor, most likely a riverine generalist, repeatedly gave rise to similar ecomorphs now found in several of the species flocks. Also, the Tanganyikan Tropheini are derived from that riverine ancestor suggesting that they successfully re-colonized Lake Tanganyika and speciated in parallel to an already established cichlid adaptive radiation. In contrast to most other known examples of adaptive radiations, these generalist ancestors were derived from highly diverse and specialized endemics from Lake Tanganyika. A reconstruction of life-history traits revealed that in an ancestral lineage leading to the modern haplochromines the characteristic egg-spots on anal fins of male individuals evolved. CONCLUSION: We conclude that Lake Tanganyika is the geographic and genetic cradle of all haplochromine lineages. In the ancestors of the replicate adaptive radiations of the 'modern haplochromines', behavioral (maternal mouthbrooding), morphological (egg-spots) and sexually selected (color polymorphism) key-innovations arose. These might be - together with the ecological opportunity that the habitat diversity of the large lakes provides - responsible for their evolutionary success and their propensity for explosive speciation.

Animals↗
PubMed2004

Genomic evidence for divergence with gene flow in host races of the larch budmoth.

Ecological divergence in the face of gene flow has recently become implicated as a potentially important cause of speciation and adaptive radiation. Here, we develop a genomic approach to test for divergent selection in sympatric host races of the larch budmoth Zeiraphera diniana (Lepidoptera: Tortricidae). We analysed hundreds of amplified fragment length polymorphism markers in 92 individuals in sympatric and allopatric populations, and in two backcross broods used to map the markers to individual chromosomes. The results directly confirm the existence of natural hybridization and demonstrate strong heterogeneity between chromosomes in terms of molecular divergence between host races (the average level of divergence was FST = 0.216). However, genomic heterogeneity was not found when we analysed divergence between geographically separated populations of the same host race. We conclude that the variance of the level of sympatric divergence among chromosomes is the footprint of divergent selection acting on a few linkage groups, combined with appreciable gene flow that homogenizes between-race variation at the remaining linkage groups. These results, coupled with other recent multilocus analyses of sister species pairs, demonstrate that selection-driven sympatric phase of genetic divergence in the presence of gene flow is a likely feature of speciation.

Analysis of Variance↗
PubMed2004

Chromosome evolution in Neotropical Danainae and Ithomiinae (Lepidoptera).

Chromosome numbers are given for 1011 populations of 242 species, representing the full range of taxa (49 of the about 52 presently recognized genera) in the Neotropical Nymphalid butterfly subfamily Ithomiinae (prime movers for mimicry rings), including many additional geographical subspecies from 47 regions from Mexico and the Caribbean islands throughout all tropical South American countries to southern Brazil. Twelve Neotropical Danainae (in 3 genera), all but one with n=29-31, and the Australian Tellervo (n=32) served as sister groups for comparison. The numbers range near-continuously from n=5 to n=120 with modal values (33-84 counts) at n=12-18, and only 16 and 26 counts at the usual modal number of all butterfly groups, n=30-31. Superimposition of these changes in karyotype on a cladistic phylogeny of the subfamily indicates possible early halving of the complement to n about 14-15, followed by much variation in each genus and tribe. While at least 17 species in 15 genera show stable karyotypes over much of the Neotropics, at least 40 species show large geographical variation in number of chromosomes, rarely accompanied by any evidence for reduction in fertility or incipient speciation. The evolutionary opportunism of the members of this subfamily probably accompanies their known population biology and community ecology: they are common, shade-loving, highly gregarious (occurring in small multispecies "pockets" in deep forest) and often migratory as a community when the environment becomes unfavorable (too hot or dry).

Americas↗
PubMed2025

Genomic resequencing unravels species differentiation and polyploid origins in the aquatic plant genus Trapa.

Trapa L. is a non-cereal aquatic crop with significant economic and ecological value. However, debates over its classification have caused uncertainties in species differentiation and the mechanisms of polyploid speciation. This study employed whole-genome resequencing together with the fruit morphology of 229 Trapa accessions (153 Asian and 76 North American samples) to elucidate species differentiation and polyploidization events in Trapa. For the species with AA genome and large fruits, clear genetic differentiation was found between two clades with different geographic origins, that is, from the Yangtze River and Amur River basins. The invasive AA species in North America (T. natans) was identified as originating from the Amur River based on genetic and morphological similarities, while all the cultivated accessions were AA species originating from the Yangtze River with severe genetic impoverishment. The separation of the two BB species with small seeds, that is, T. incisa and T. maximowiczii, was strongly supported by both morphological and genetic evidence. For the tetraploids, Asian and North American tetraploids were revealed to have distinct evolutionary origins. Asian allotetraploids (AABB) originated through hybridization between AA diploids from the Yangtze River Basin and BB diploids T. maximowiczii, supported by nuclear and chloroplast evidence. In contrast, the invasive North American tetraploids (T. bispinosa var. iinumai) exhibited an AACC-like genome, suggesting an independent polyploidization involving an unknown "CC" diploid. These findings provide critical insights into Trapa's complex evolutionary history, polyploidizations, and invasive origins, offering a genomic foundation for the conservation and sustainable utilization of the underutilized aquatic crop amid global environmental challenges.

Polyploidy↗
PubMed1961

The origin of the treponematoses.

An attempt is made to explain along Darwinian lines the steps by which the treponematoses evolved and how they came to have their present distributions and characteristics. The original ancestors of the treponemes would have been free-living organisms, but various forms of symbiosis with larger creatures would in time lead to the development of parasitism with varying degrees of pathogenicity. Modern man may have acquired his treponemes from his ungeneralized primate ancestors and taken them with him on his migrations over the world. Isolation of man in different continents, especially after the end of the Ice Age, would lead to speciation in both man and his parasites; this would account for the features of pinta in Central America. Ecological isolations would produce syphilis and yaws, the latter being successful in warm areas where no clothes were worn or overcrowding was gross, and syphilis being successful in colder climates but not in endemic yaws areas where so many people were immune by puberty.A syphilis organism has little chance of survival if it fails to infect the genitalia. This is perhaps the reason for congenital infections in that disease. The organotropic properties of syphilis treponemes may be the results of repeated passage through the foetus; the conditions for survival in the foetus are much different from those in the mother, so that organotropic rather than genitotropic strains would be selected.

Animals↗