EVOLUTIONARY DIVERGENCE IN DIRECTIONS OF HIGH PHENOTYPIC VARIANCE IN THE OSTRACODE GENUS POSEIDONAMICUS
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Abstract:
Trait variation and covariation are understood to influence the response of populations to natural selection on generational time scales, but their role, if any, in shaping long-term macroevolutionary divergence is still unclear. The present study uses the rich fossil record of the ostracode genus Poseidonamicus to reconstruct in great detail the evolutionary history of a set of landmark-based morphometric characters. This reconstruction included two kinds of evolutionary inferences: ancestor-descendant transitions among populations repeatedly sampled at the same location and divergence between lineages measured as independent contrasts on a phylogeny. This reconstructed history was then used to test if evolutionary changes were concentrated in directions (traits or combinations of traits) with high phenotypic variance. Two different statistics of association between evolution and variation tested the null hypothesis that evolutionary changes occur in random directions with respect to trait variability. The first of these measured the similarity between the directions of evolutionary change and the axis of maximum variance, and the second measured the degree to which evolutionary changes were concentrated in directions of high phenotypic variation. Randomization tests indicated that both kinds of evolutionary inferences (ancestor-descendant and phylogenetic contrasts) occurred preferentially in directions of high phenotypic variance (and close to the axis of maximal variation), suggesting that within-population variation can structure long-term divergence. This effect decayed after a few million years, but at least for one metric, never disappeared completely. These results are consistent with Schluter's genetic constraints model in which evolutionary trajectories on adaptive landscapes are deflected by variation within and covariation among traits.Keywords:
Divergence (linguistics)
A three-dimensional picture of the horizontal velocity divergence is constructed at seven times, at twelve-hour intervals, with use of observed winds as a basis for divergence computations. No level of non-divergence is found; however, a surface of least divergence and a level of least divergence are located at each of the seven times, and their behavior is noted. A defense of the method includes comparison of vertical velocities computed by another method, and by the same method but with application of various types and degrees of smoothing. Principle conclusions are (1) that a surface of least divergence can be located but is not a physically significant surface, (2) that vertical velocities computed from the integrated low-level divergence correlate very well with the precipitation pattern, (3) that various kinds and degrees of smoothing do not appreciably change the order of magnitude of the divergence, and (4) that interesting diurnal variations in divergence intensity occur when values at 0300 GCT and 1500 GCT are compared.
Divergence (linguistics)
Smoothing
Intensity
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Spatial and temporal variability of divergence is analysed over equatorial East Africa. According to the analysis, seasonal march of upper level divergence is bimodal. There is peak upper level divergence during March‐April‐May and October‐November‐December. Analysis of upper level divergence at synoptic hours reveals that peak divergence occurs in the afternoon over the inland areas. Over the coastal areas, peak upper level divergence occurs at night. Spectral analysis results indicate that there is existence of oscillations in upper level divergence. These oscillations vary in terms of their periodicities and the amount of variance that they account for in the observed divergence.
Divergence (linguistics)
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Divergence (linguistics)
Degree (music)
Genetic divergence
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