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At least 109 records · Page 6Linked to original sources
PubMed2001

Experimental evidence for a demographic cline in Panstrongylus megistus populations.

The population biology of three populations of Panstrongylus megistus was compared to determine possible influence on the behaviour and epidemiological importance of this species. The results demonstrated differences in terms of egg eclosion time, nymphal mortality and development rates, and feeding and defaecation rates. These differences appeared to follow a geographical cline, primarily reflecting different degrees of adaptation to domestic habitats.

Animals↗
PubMed2004

Genetic variation in a cline in a living intertidal snail arose in the Neogastropoda over 100 million years ago.

To understand how species adapt and evolve it is necessary to appreciate the relationship between genetic variation and the environment. Here, the fossil record and molecular data from different lineages of the marine Gastropoda are used to understand the evolution of genetic variations found in the nuclear gene for mitochondrial malate dehydrogenase (mMDH; EC 1.1.1.37) in the living intertidal Muricid snail, Nucella lapillus. Assuming a molecular clock, DNA sequences of mMDH indicate that two variants found in N. lapillus, mMDH(9) and mMDH(10), may have arisen as long as 144 MY (million years) ago and at least prior to the evolution of the Muricidae approximately 112-90 MY ago. The Muricidae contain by far the greatest majority of the Neogastropoda specialized for life in the intertidal habitat. In N. lapillus the mMDH(9) and mMDH(10) variants covary with variations in other biochemically defined loci, inherited phenotypic traits (shell shape and physiology) and karyotype frequencies to differentiate two distinct nuclear haplotypes that are associated with different temperature environments. The variations in shell shape that are associated with the haplotypes of N. lapillus represent adaptations to temperature stress and similar variations occur in other related intertidal molluscs whose lineages are much older than Nucella, which arose around 25 million years ago. It is suggested that the divergence of the mMDH variants found in N. lapillus may reflect an ancient genetic event, such as a chromosomal mutation, perhaps involving variation in other linked traits that together became important in the subsequent evolution of the marine Gastropoda.

Adaptation, Biological↗
PubMed2003

Grouping of Y-STR haplotypes discloses European geographic clines.

Y-STR haplotypes are widely studied in Europe and an extensive databasing effort has been conducted (http://www.ystr.org). The distribution of these haplotypes has been considered to present no evidence for substructure at central and southern European level. This picture contrasts with the one that results from Y haplogroups defined by binary markers. This paradox has been solved by admitting that the high STR mutation rate and corresponding recurrence has erased geographic structuration. This explanation prompted us to reanalyse Y-STR haplotypes distribution bearing in mind the commonly admitted model for the generation of diversity in these markers, namely the stepwise mutation model (SMM) and, thus, taking the molecular distance between haplotypes into consideration. Accordingly, we have studied the European distribution of the two most frequent haplotypes in the Iberian Peninsula and their one step neighbours using the European samples deposited in the Y STR database (http://www.ystr.org). For the first group we found a clear-cut decreasing W-E gradient, while for the second the highest frequencies were found in the Iberian Peninsula (3.98% in Portugal and 3.85% in Spain), dropping to 2.88% in France and showing a less well defined SW-NW gradient. Furthermore, we have tested the agreement between haplotype groups and binary markers haplogroups in a random sample of 292 individuals from Northern Portugal. Our results demonstrate that (a) Y-STR haplotype data can be used for wide-scale anthropological approaches disclosing information that has been considered only available through binary markers and (b) forensic use of continental databases needs careful refinement, due to the macro-geographic pattern now evidenced.

Chromosomes, Human, Y↗
PubMed2000

Geographical clines for quantitative traits in natural populations of a tropical drosophilid: Zaprionus indianus.

We analyzed natural populations of Zaprionus indianus in 10 Indian localities along a south-north transect (latitude: 10-31 degrees 3 N). Size traits (body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait value increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhibited a non-significant but negative correlation with latitude. Sex dimorphism, estimated as the female/male ratio, was very low in Z. indianus, contrasting with results already published in other species. Genetic variations among populations were also analyzed according to other geographic parameters (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal bristles, a multiple regression technique evidenced a significant effect of both latitude and altitude, but in opposite directions. Genetic variations were also correlated to climate, and mainly with average year temperature. Taking seasonal variations into account failed however to improve the predictability of morphometrical variations. The geographic differentiation of Z. indianus for quantitative traits suggests adaptive response to local conditions, especially to temperature, but also reveals a complex situation according to traits investigated and to environmental parameters, which does not match results on other drosophilid species.

Altitude↗
PubMed2003

Clines: a reductionist model.

A piecewise linear model is used to provide a caricature of the nonlinear equation describing genetic variation due to migration and local natural selection in an inhomogeneous bounded habitat. The conditions for which nontrivial spatially-dependent steady state solutions exist are analytically determined together with these solutions for three distinct scenarios. For the usual case of no flux (Neumann) boundary conditions, explicit solutions require additional information to fix the genetic frequency within the habitat. This difficulty can be bypassed in two of the scenarios considered (this is an artifact of the model), but in the remaining scenario it is necessary to take into account the connection with the initial data to explicitly determine the steady state frequency. Some numerical examples are considered for each of the scenarios to illustrate the analytical results that are the primary focus of the work presented here.

Gene Frequency↗