This raises some further points about inferring causality: increased dimensionality of niche divergence might promote speciation, reduced gene flow might allow divergence in a greater number of niche dimensions, or these two processes feed back on one another [77], [87], [88].
Relaxed molecular clock models allow divergence time dating and "relaxed phylogenetic" inference, in which a time tree is estimated in the face of unequal rates across lineages.
Open image in new window Fig. 7 The plate is slightly convex in lateral profile and the screws do not lock onto the plate, allowing divergence as it guides correction through the physis Open image in new window Fig. 8 This 15-year-old boy, with documented growth hormone deficiency and comparatively short stature, had received tibial staples a year before this radiograph.
In this analysis, we assumed a normal TMRCA distribution, allowing divergence dates to vary symmetrically.
This less parameterized model also allowed divergence time to be estimated more precisely, suggesting the split between Brown-cheeked and Water Rails occurred ~534,000 years ago 955% CI 275,000-990,000 years).
These differences could simply be the result of population bottlenecks and/or periods of allopatry that allowed divergence to rapidly accumulate between the populations, and the hybridization is due to recent secondary contact.
Rather, there are likely to be a number of dynamic combinations of a genome or transcriptome to produce a phenome, and these combinations will differ between plants depending on both the environment and evolutionary distance that allows divergence.
Although our data does not allow for divergence time estimates between Oreina speciosissima ecotypes, it seems likely that they diverged relatively recently.
And how are these mechanisms exploited over evolutionary time to allow for divergence and to give rise to new functions and ultimately species?
Common criticisms are that bidirectional CI (the mode that most obviously can promote reciprocal reductions in gene flow) will be uncommon in nature, that levels of CI are insufficient to allow genetic divergence, and that CI is not effective in promoting the evolution of premating isolation.
It is possible to speculate, however, that the recent evolution of Tetraodontiformes did not last long enough to allow specific divergence of the genome and hence of aqp1b.
