RESUMO
AbstractPhenotypic differentiation within polytypic species is often attributed to selection, particularly when selection might be acting on a trait that serves as a signal for predator avoidance and mate choice. We evaluated this hypothesis by examining phenotypic and genotypic clines between populations of the strawberry poison frog Oophaga pumilio, a polytypic species that exhibits aposematic color pattern variation that is thought to be subject to both natural and sexual selection. Our aim was to assess the extent of admixture and to estimate the strength of selection acting on coloration across a region of Panama where monomorphic populations of distinctly colored frogs are separated by polymorphic populations containing both color variants alongside intermediately colored individuals. We detected sharp clinal transitions across the study region, which is an expected outcome of strong selection, but we also detected evidence of widespread admixture, even at sites far from the phenotypic transition zone. Additionally, genotypic and phenotypic clines were neither concordant nor coincident, and with one exception, selection coefficients estimated from cline attributes were small. These results suggest that strong selection is not required for the maintenance of phenotypic divergence within polytypic species, challenging the long-standing notion that strong selection is implicit in the evolution of warning signals.
Assuntos
Anuros , Seleção Sexual , Humanos , Animais , Anuros/genética , Fenótipo , Genótipo , Panamá , Seleção GenéticaRESUMO
Urbanization often substantially influences animal movement and gene flow. However, few studies to date have examined gene flow of the same species across multiple cities. In this study, we examine brown rats (Rattus norvegicus) to test hypotheses about the repeatability of neutral evolution across four cities: Salvador, Brazil; New Orleans, USA; Vancouver, Canada; and New York City, USA. At least 150 rats were sampled from each city and genotyped for a minimum of 15 000 genome-wide single nucleotide polymorphisms. Levels of genome-wide diversity were similar across cities, but varied across neighbourhoods within cities. All four populations exhibited high spatial autocorrelation at the shortest distance classes (less than 500 m) owing to limited dispersal. Coancestry and evolutionary clustering analyses identified genetic discontinuities within each city that coincided with a resource desert in New York City, major waterways in New Orleans, and roads in Salvador and Vancouver. Such replicated studies are crucial to assessing the generality of predictions from urban evolution, and have practical applications for pest management and public health. Future studies should include a range of global cities in different biomes, incorporate multiple species, and examine the impact of specific characteristics of the built environment and human socioeconomics on gene flow.
Assuntos
Fluxo Gênico , Genótipo , Polimorfismo de Nucleotídeo Único , Brasil , Colúmbia Britânica , Cidades , Análise por Conglomerados , Nova Orleans , Cidade de Nova IorqueRESUMO
Diversification of freshwater fishes on islands is considered unlikely because the traits that enable successful colonization-specifically, broad salinity tolerances and the potential for oceanic dispersal-may also constrain post-colonization genetic differentiation. Some secondary freshwater fish, however, exhibit pronounced genetic differentiation and geographic structure on islands, whereas others do not. It is unclear what conditions give rise to contrasting patterns of differentiation because few comparative reconstructions of population history have been carried out for insular freshwater fishes. In this study, we examined the phylogeography of Hart's killifish (Rivulus hartii) across Trinidad, with reference to neighboring islands and northern South America, to test hypotheses of colonization and differentiation derived from comparable work on co-occurring guppies (Poecilia reticulata). Geographic patterns of mitochondrial DNA haplotype variation and microsatellite genotype variation provide evidence of genetic differentiation of R. hartii among islands and across Trinidad. Our findings are largely consistent with patterns of geographically structured ancestry and admixture found in Trinidadian guppies, which suggests that both species share a history of colonization and differentiation and that post-colonization diversification may be more common among members of insular freshwater fish assemblages than has been previously thought.
Assuntos
Ciprinodontiformes/genética , DNA Mitocondrial/genética , Especiação Genética , Animais , Ciprinodontiformes/classificação , DNA Mitocondrial/química , Água Doce , Variação Genética , Haplótipos , Repetições de Microssatélites/genética , Filogeografia , Poecilia/classificação , Poecilia/genética , Dinâmica Populacional , Trinidad e Tobago , Índias OcidentaisRESUMO
It has been proposed that a moving hybrid zone can be a mechanism for the spread of adaptive traits in phase III of Wright's shifting balance model of evolution. Here I present an example of a moving hybrid zone in warningly colored Heliconius butterflies, a system which is considered to be a possible case of shifting balance evolution. Having moved approximately 47 km in 17 years, the hybrid zone shift has led to the H. erato hydara color pattern rapidly displacing the adjacent H. erato petiverana pattern. The movement is potentially due to dominance drive augmenting a slight selective advantage of H. erato hydara over H. erato petiverana, which is largely consistent with theoretical conditions favoring the success of phase III.
Assuntos
Evolução Biológica , Borboletas/fisiologia , Animais , Borboletas/anatomia & histologia , Epistasia Genética , Geografia , Modelos Estatísticos , Modelos Teóricos , PanamáRESUMO
Anartia fatima and Anartia amathea (Lepidoptera: Nymphalidae) are sister taxa whose ranges abut in a narrow hybrid zone in eastern Panama. At the center of the zone, hybrids are abundant, although deviations from Hardy-Weinberg and linkage disequilibria are strong, due in part to assortative mating. We measured differences across the zone in four wing color-pattern characters, three allozyme loci, and mitochondrial haplotype. Wing pattern, allozyme, and mitochondrial clines were coincident (i.e., had the same positions) and concordant (i.e.. all markers had similar cline shapes, about 28 km wide). Repeated samples demonstrated that the hybrid zone has been moving eastwards at an average rate of 2.5 km/year over the past 20 years, accompanied by an equivalent movement of the mtDNA cline. No introgression of mtDNA haplotypes were found in the ''wake" of the moving cline, as might be expected for a neutral marker. The concordance of morphological and mtDNA clines between 1994 and 2000, in spite of hybrid zone movement, suggests strong epistasis between the mitochondrial genome and nuclear loci. Cline movement is achieved mainly by pure fatima immigrating into amathea populations; hybrids had little effect, and were presumably outcompeted by fitter pure fatima genotypes. This movement can be explained if random dispersal of 7-19 km x gen(1/2) is coupled with a competitive advantage to A. fatima genomes of 2-5%. Hybrid zone motion is equivalent to Phase III of Wright's shifting balance. Hybrid zone movement has rarely been considered likely in the past, but our results show that it may be more important in biogeography and evolution than generally realized.