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At least 145 records · Page 8Linked to original sources
PubMed1998

A temperature cline in copy number for 412 but not roo/B104 retrotransposons in populations of Drosophila simulans.

The copy number of the retrotransposable element 412 of Drosophila simulans from populations collected worldwide shows a negative correlation with minimum temperature. No association was detected for the roo/B104 element. The possibility that selective pressures might regulate the 412 copy number in these natural populations is supported by detection of selection against the detrimental effects of 412 insertions (estimated by the proportion of insertions on the X chromosome in comparison with the autosomes) but not roo/B104. These data reveal different spatial patterns for two element families, and strongly suggest that some factors in the environment, such as temperature, may interfere with the control of retrotransposition, thus affecting important aspects of genomic evolution.

Animals↗
PubMed2006

Temporal cline in a hybrid zone population between Fraxinus excelsior L. and Fraxinus angustifolia Vahl.

The two closely related ash species Fraxinus excelsior L. (common ash) and Fraxinus angustifolia Vahl (narrow-leaved ash) have a broad contact zone in France where they hybridize. However, little is known about the local structure of hybrid zone populations and the isolation mechanisms. We assessed the potential effect of floral phenology on the structure of a riparian ash hybrid zone population in central France. The distribution of flowering times was unimodal and lay between the flowering periods of the two species. Using microsatellite markers, we detected isolation by time, which has possibly originated from assortative mating. Multivariate analyses indicated that morphological variation is not distributed at random with respect to flowering times. Spatial autocorrelation analyses showed that temporal and spatial patterns were tightly linked. Interestingly, despite the fact that the population shows isolation by time, neighbourhood size and historical dispersal variance (sigma = 63 m) are similar to those detected in pure stands of F. excelsior where individuals flower rather synchronously and hermaphrodites are not the most frequent sexual type. Trees flowering at intermediate dates, which comprised the majority of the population, produced on average more flowers and fruits. We detected no significant differences in floral parasite infections relative to reproductive timing, although there was a tendency for late flowering trees to suffer from more gall attack. We discuss the impact of temporal variation in fitness traits and their possible role in the maintenance of the hybrid zone.

Adaptation, Physiological↗
PubMed2006

Phylogeography and the geographic cline in the armament of a seed-predatory weevil: effects of historical events vs. natural selection from the host plant.

Japanese camellia (Camellia japonica) and its seed predator, the camellia weevil (Curculio camelliae), provide a notable example of a geographic mosaic of coevolution. In the species interaction, the offensive trait of the weevil (rostrum length) and the defensive trait of the plant (pericarp thickness) are involved in a geographically-structured arms race, and these traits and selective pressures acting on the plant defence vary greatly across a geographical landscape. To further explore the geographical structure of this interspecific interaction, we tested whether the geographical variation in the weevil rostrum over an 800-km range along latitude is attributed to local natural selection or constrained by historical (phylogeographical) events of local populations. Phylogeographical analyses of the mitochondrial DNA sequences of the camellia weevil revealed that this species has experienced differentiation into two regions, with a population bottleneck and subsequent range and/or population expansion within each region. Although these phylogeographical factors have affected the variation in rostrum length, analyses of competing factors for the geographical variation revealed that this pattern is primarily determined by the defensive trait of the host plant rather than by the effects of historical events of populations and a climatic factor (annual mean temperature). Thus, our study suggests the overwhelming strength of coevolutionary selection against the effect of historical events, which may have limited local adaptation.

Animals↗
PubMed1991

Transferrin polymorphisms in Japanese populations: north-south cline in the distribution of the TF*C2 allele.

Allele frequencies for human transferrin (TF) subtypes were determined using serum samples from Japanese subjects living in Fukui prefecture, Japan, and compared with other Japanese populations using isoelectric focusing (IEF) and immunoblotting. The application of IEF revealed considerable heterogeneity in the TF system, enhancing its potential value for anthropologic and genetic studies. So far, TF subtypes of about 27,000 Japanese individuals from 35 population groups have been analyzed to evaluate the degree of genetic variation at the TF locus. Possible geographic and biologic factors are discussed.

Alleles↗
PubMed1990

Diversity of some gene frequencies in European and Asian populations. V. Steep multilocus clines.

Regions of abrupt genetic change, which result from either rapid spatial change of selective pressures or limited admixture, were investigated in Europe and Asia on the basis of eight red cell markers typed in 960 samples. Two methods were employed, one based on genetic distances and one on evaluation of the first derivative of the surfaces representing allele-frequency variation. Genetic divergence tends to be maximal between populations that are separated by physical factors (mountain ranges and seas) but also separated by cultural barriers (different language affiliation). This suggests that mating isolation, rather than adaptive response to environmental change, accounts for spatially abrupt genetic change at the loci studied and that cultural differences associated with language contribute to isolating populations. Although selection may have determined two wide allele-frequency gradients, the genetic structure of European and Asian populations seems primarily to reflect isolation by distance when investigated on a small scale and migration patterns (or absence of migration) when investigated on a larger scale.

Alleles↗