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Recent Divergence (recent + divergence)
Selected AbstractsREPLICATED EVOLUTION OF INTEGRATED PLASTIC RESPONSES DURING EARLY ADAPTIVE DIVERGENCEEVOLUTION, Issue 4 2006Kevin J. Parsons Abstract Colonization of a novel environment is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. Local adaptation in the new environment occurs through the accumulation and integration of character states that positively affect fitness. The role played by plastic traits in adaptation to a novel environment has generally been ignored, except for variable environments. We propose that if conditions in a relatively stable but novel environment induce phenotypically plastic responses in many traits, and if genetic variation exists in the form of those responses, then selection may initially favor the accumulation and integration of functionally useful plastic responses. Early divergence between ancestral and colonist forms will then occur with respect to their plastic responses across the gradient bounded by ancestral and novel environmental conditions. To test this, we compared the magnitude, integration, and pattern of plastic character responses in external body form induced by shallow versus open water conditions between two sunfish ecomorphs that coexist in four postglacial lakes. The novel sunfish ecomorph is present in the deeper open water habitat, whereas the ancestral ecomorph inhabits the shallow waters along the lake margin. Plastic responses by open water ecomorphs were more correlated than those of their local shallow water ecomorph in two of the populations, whereas equal levels of correlated plastic character responses occurred between ecomorphs in the other two populations. Small but persistent differences occurred between ecomorph pairs in the pattern of their character responses, suggesting a recent divergence. Open water ecomorphs shared some similarities in the covariance among plastic responses to rearing environment. Replication in the form of correlated plastic responses among populations of open water ecomorphs suggests that plastic character states may evolve under selection. Variation between ecomorphs and among lake populations in the covariance of plastic responses suggests the presence of genetic variation in plastic character responses. In three populations, open water ecomorphs also exhibited larger plastic responses to the environmental gradient than the local shallow water ecomorph. This could account for the greater integration of plastic responses in open water ecomorphs in two of the populations. This suggests that the plastic responses of local sunfish ecomorphs can diverge through changes in the magnitude and coordination of plastic responses. Although these results require further investigation, they suggest that early adaptive evolution in a novel environment can include changes to plastic character states. The genetic assimilation of coordinated plastic responses could result in the further, and possibly rapid, divergence of such populations and could also account for the evolution of genes of major effect that contribute to suites of phenotypic differences between divergent populations. [source] TIME TO THE MOST RECENT COMMON ANCESTOR AND DIVERGENCE TIMES OF POPULATIONS OF COMMON CHAFFINCHES (FRINGILLA COELEBS) IN EUROPE AND NORTH AFRICA: INSIGHTS INTO PLEISTOCENE REFUGIA AND CURRENT LEVELS OF MIGRATIONEVOLUTION, Issue 1 2002Cortland K. Griswold Abstract We analyzed sequences from a 275-bp hypervariable region in the 5, end of the mitochondrial DNA control region in 190 common chaffinches (Fringilla coelebs) from 19 populations in Europe and North Africa, including new samples from Greece and Morocco. Coalescent techniques were applied to estimate the time to the most recent common ancestor (TMRCA) and divergence times of these populations. The first objective of this study was to infer the locations of refugia where chaffinches survived the last glacial episode, and this was achieved by estimating the TMRCA of populations in regions surrounding the Mediterranean that were unglaciated in the late Pleistocene. Although extant populations in Iberia, Corsica, Greece, and North Africa harbor haplotypes that are basal in a phylogenetic tree, this information alone cannot be used to infer that these localities served as refugia, because it is impossible to infer the ages of populations and their divergence times without also considering the population genetic processes of mutation, migration, and drift. Provided we assume the TMRCAs of populations are a reasonable estimate of a population's age, coalescent-based methods place resident populations in Iberia, Corsica, Greece, and North Africa during the time of the last glacial maximum, suggesting these regions served as refugia for the common chaffinch. The second objective was to determine when populations began diverging from each other and to use this as a baseline to estimate current levels of gene flow. Divergence time estimates suggest that European populations began diverging about 60,000 years before present. The relatively recent divergence of populations in North Africa, Italy, and Iberia may explain why classic migration estimates based on equilibrium assumptions are high for these populations. We compare these estimates with nonequilibrium-based estimates and show that the nonequilibrium estimates are consistently lower than the equilibrium estimates. [source] Genetic structure of the European polecat (Mustela putorius) and its implication for conservation strategiesJOURNAL OF ZOOLOGY, Issue 1 2006C. Pertoldi Abstract During the last century, the European polecat Mustela putorius populations in most of Europe declined and survived in fragmented patches, because of habitat alterations and direct persecution. To assess the genetic consequences of the demographic decline and to describe the spatial pattern of genetic diversity, 250 polecats sampled at seven localities from five European countries , Poland, Denmark (southern Denmark and northern Denmark), Spain, Belgium (eastern and western) and the Netherlands , were screened by means of nine microsatellite loci. Genetic diversity estimated by mean expected heterozygosity (HE) and allelic richness (AR) were moderately high within populations [range: 0.50 (northern Denmark) ,HE,0.64 (Poland) and 1.33,AR,7.80] as compared with other carnivores and mustelids. Bottleneck tests suggested that polecat populations in southern Denmark and Poland have declined recently and populations from northern Denmark and the Netherlands have expanded recently, whereas the remaining populations did not show any sign of demographic change. Recent demographic changes could suggest that some of the populations are still not in equilibrium, which could partly explain the relatively high genetic variability observed in polecat populations despite the drastic decline in population size observed in several European countries. A significant heterozygote deficiency [FIS=0.19; 0.01,95% confidence interval (CI),0.32] suggests substructuring within the total European sample. Partitioning of the genetic variation among sampling locations (FST=0.14; 0.06,95% CI,0.23) and pairwise FST between localities (range: 0.01,FST,0.37) without any correlation with the geographic distances between localities were found, suggesting a recent divergence and a restriction of gene flow between populations and the action of genetic drift. An assignment test showed that the Polish and the northern Danish populations were the most unique, whereas the other populations were partially admixed. Factorial component analysis tests indicate a subdivision of the total sample into two distinct groups: one including the samples from Poland and the two Danish localities and the second group comprising the remaining localities investigated. The observed pattern of genetic differentiation is suggested to be due to two main routes of recolonization after the last glacial period. To compare the results obtained with microsatellite data, the most variable region of the mitochondrial DNA (d-loop) was sequenced and different phylogenetic reconstructions and genetic diversity analyses based on nucleotide (,) and haplotype diversity (h) measures within populations were performed using a subsample of populations. The lack of well-defined geographical structure, as well as the reduced level of mitochondrial DNA variability (,: 0.00274±0.00038; h: 0.876±0.028) that was found, has been previously reported in several studies on different carnivores and supports the hypothesis of post-glacial recolonization from southern or eastern refugees of Europe as suggested by the microsatellite data. Implications for conservation strategies of the polecat at the European level are discussed. [source] Speciation with gene flow could be commonMOLECULAR ECOLOGY, Issue 9 2008PATRIK NOSIL Abstract The likelihood of speciation in the face of homogenizing gene flow (i.e. without complete geographical isolation) is one of the most debated topics in evolutionary biology. Demonstrating this phenonemon is hampered by the difficulty of isolating the effects of time since population divergence vs. gene flow on levels of molecular genetic differentiation. For example, weak genetic differentiation between taxa could be due to recent divergence, gene flow, or a combination of these factors. Nonetheless, a number of convincing examples of speciation with gene flow have recently emerged, owing in part to the development of new analytical methods designed to estimate gene flow specifically. A recent example of speciation with gene flow in salamanders (Niemiller et al. 2008) further advances our understanding of this phenonemon, by showing that gene flow between cave and spring salamanders was ongoing during speciation, rather than having occurred after a long period of allopatric divergence. Future work on the ecological and genetic factors reducing gene flow will likely increase our understanding of the conditions that faciliate divergence in the face of gene flow. [source] The ecological differentiation of asexual lineages of cotton aphids: alate behaviour, sensory physiology, and differential host associationsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2009ADRIANA J. NAJAR-RODRÍGUEZ The cotton aphid (Aphis gossypii Glover) is a cosmopolitan pest species consisting of various host plant-associated lineages that appear to have different patterns of insecticide resistance, electrophoretic banding, and reproductive output across alternative host species. Debate continues as to whether these differences represent intraspecific variation or indicate a complex of cryptic or sibling species. We studied the host plant-related ecology of two asexual lineages of A. gossypii associated with the families Malvaceae and Cucurbitaceae, respectively, in particular the host plant finding and acceptance processes of the alate forms. The two lineages proved to be differentiated across host plants in terms of: (1) their landing and settling behaviour, nymphal production rate, and subsequent colony establishment (i.e. nymphal survival and development) and (2) their sensory abilities in relation to host plant-derived odours. Furthermore, genetic structuring according to host plant type was detected using the gene for elongation factor 1-,. The magnitude of the genetic differentiation across lineages was low, perhaps indicating a relatively recent divergence. The results demonstrate: (1) the presence of (at least) two cryptic species within the current definition of A. gossypii, as anticipated in previous studies, and (2) the practicalities of using a multidisciplinary approach to understanding the ,limits' of asexual species. If sexuals can be generated from each of these lineages, this conclusion will be open to further testing. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 503,519. [source] | ||||||||||