We compiled a database of microevolution on contemporary time scales in nature (47 source articles; 30 animal species), comprising 2649 evolutionary rates in darwins (proportional change per million years) and 2151 evolutionary rates in haldanes (standard deviations per generation). Here we demonstrate how quantitative rate measures can provide general insights into patterns and processes of evolution. The frequency distribution of evolutionary rates was approximately log-normal, with many slow rates and few fast rates. Net selection intensities estimated from haldanes were on average lower than selection intensities commonly measured directly in natural populations. This difference suggests that natural selection could easily accomplish observed microevolution but that the intensities of selection typically measured in nature are rarely maintained for long (otherwise observed evolutionary rates would be higher). Traits closely associated with fitness (life history traits) appear to evolve at least as fast as traits less closely tied to fitness (morphology). The magnitude of evolutionary difference increased with the length of the time interval, particularly when maximum rates from a given study were considered. This pattern suggests a general underlying tendency toward increasing evolutionary diversification with time. However, evolutionary rates also tended to decrease with time, perhaps because longer time intervals average increasingly disparate rates over time, or because evolution slows when populations approach new optima or as genetic variation is depleted. In combination, our results suggest that macroevolutionary transitions may ultimately arise through microevolution occasionally 'writ large' but are perhaps temporally characterized by microevolution 'writ in fits and starts'.
"The absence of a clear relationship between environment and morphology could be the result of selection-driven adaptation lagging behind environmental change, where populations may exhibit maladaptive morphologies during transitional response periods (Maynard Smith, 1978). For example, a population of stream fish inhabiting a recently impounded river may not exhibit morphological characteristics typical of a species found in a lentic environment because it may require many generations for advantageous attributes to emerge after impoundment (Kinnison & Hendry, 2001; Smith & Bernatchez, 2008; Cureton & Broughton, 2014). Alternatively, an environmental condition might not exhibit sufficient variation to serve as a significant driver of phenotypic change or diversification (Binning & Chapman, 2010). "
"STATISTICAL ANALYSES Analyses for the first two questions were performed separately on each of four different metrics: Darwins, Darwin numerators, Haldanes, and Haldane numerators. The reason for using both rates and numerators is that phenotypic changes sometimes scale with time interval and sometimes do not (Kinnison and Hendry 2001; Westley 2011). The data did not meet assumptions of normality (Shapiro–Wilks test; 0.279 ࣘ W ࣘ 0.953; P < 0.001), and so nonparametric tests were performed to address the first question. "
[Show abstract][Hide abstract] ABSTRACT: Cope's rule, wherein a lineage increases in body size through time, was originally motivated by macro-evolutionary patterns observed in the fossil record. More recently, some authors have argued that evidence exists for generally positive selection on individual body size in contemporary populations, providing a micro-evolutionary mechanism for Cope's rule. If larger body size confers individual fitness advantages as the selection estimates suggest, thereby explaining Cope's rule, then body size should increase over micro-evolutionary time scales. We test this corollary by assembling a large database of studies reporting changes in phenotypic body size through time in contemporary populations, as well as studies reporting average breeding values for body size through time. Trends in body size were quite variable with an absence of any general trend, and many populations trended toward smaller body sizes. Although selection estimates appear to support Cope's rule, our results suggest that actual rates of phenotypic change for body size do not. We discuss potential reasons for this discrepancy and its implications for the understanding of Cope's rule. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
"The distribution of genetic variation within and among populations of a species is determined by the interaction between natural selection and neutral evolutionary processes such as drift and gene flow. While evolutionary change can be very fast with measurable genetic change occurring over only a few generations , , the pace of evolution and its final outcome depends on several factors such as genetic diversity , , ecological and evolutionary costs associated with adaptive change, and interactions with other evolutionary forces. Specifically, gene flow and genetic drift may disturb the effects of divergent selection and prevent local adaptation (e.g. "
[Show abstract][Hide abstract] ABSTRACT: The way environmental variation shapes neutral and adaptive genetic variation in natural populations is a key issue in evolutionary biology. Genome scans allow the identification of the genetic basis of local adaptation without previous knowledge of genetic variation or traits under selection. Candidate loci for divergent adaptation are expected to show higher FST than neutral loci influenced solely by random genetic drift, migration and mutation. The comparison of spatial patterns of neutral markers and loci under selection may help disentangle the effects of gene flow, genetic drift and selection among populations living in contrasting environments. Using the gastropod Radix balthica as a system, we analyzed 376 AFLP markers and 25 mtDNA COI haplotypes for candidate loci and associations with local adaptation among contrasting thermal environments in Lake Mývatn, a volcanic lake in northern Iceland. We found that 2% of the analysed AFLP markers were under directional selection and 12% of the mitochondrial haplotypes correlated with differing thermal habitats. The genetic networks were concordant for AFLP markers and mitochondrial haplotypes, depicting distinct topologies at neutral and candidate loci. Neutral topologies were characterized by intense gene flow revealed by dense nets with edges connecting contrasting thermal habitats, whereas the connections at candidate loci were mostly restricted to populations within each thermal habitat and the number of edges decreased with temperature. Our results suggest microgeographic adaptation within Lake Mývatn and highlight the utility of genome scans in detecting adaptive divergence.
PLoS ONE 07/2014; 9(7):e101821. DOI:10.1371/journal.pone.0101821 · 3.23 Impact Factor
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