Freshwater fishes exhibit high morphological divergence, suggesting that they evolved to exploit specific habitats that differ in their environmental stressors [ 33, 34].
The high levels of molecular and morphological divergence suggest that Chaetomys belongs to an early radiation of the Erethizontidae that may have occurred in the Early Miocene, and should be assigned to its own subfamily, the Chaetomyinae.
Such rapid divergence is especially notable in the diversity through time plot of the olfactory bulbs (Fig 1b), which presents a recent, high peak in morphological divergence suggesting that interspecific differences in olfactory bulb volume are the result of a recent evolutionary divergence.
The results of this study suggest that by ignoring morphological divergence between populations that lack detectable genetic divergence we may be missing an opportunity to conserve evolutionary significant levels of biodiversity and to uncover the evolutionary hot spots that drive adaptive divergence.
For example, small-bodied dolphins of the genera Cephalorhynchus and Lagenorynchus occupy temperate waters in the Southern Hemisphere and share similarities in their distribution and pattern of morphological and genetic (exclusively mtDNA) divergence that have been interpreted as being the result of dispersal corridors present during inter-glacial periods in the Plio-Pleistocene [ 7, 8].
The second goal of the study is to investigate morphological divergence between populations that share common ecological conditions.
Sequencing revealed patterns of geographic coherence and divergence that were not revealed in morphological analysis.
In contrast to existing morphological hypotheses, we found that most Endeostigmata (rare deep-soil mites known from the Devonian) represent a major basal divergence that occurred prior to the split between the two hyperdiverse acariform lineages, Sarcoptiformes and Trombidiformes.
Irrespective of the specific adaptive significance of morphological and behavioral divergence between populations of swamp sparrows, differences in bill size and plumage as well as the timing of reproduction and molt in experimental groups provide evidence of divergence that is the result of local adaptation to different environments rather than to phenotypic plasticity.
Although the morphogenetic factors that contribute to morphological divergence remain unclear, our results suggest that the gudgeon populations in Lake Biwa show a state of resource polymorphism associated with differences in the bottom environment.
