One possibility is that initial divergence coincided with the separation of the southern landmasses, which was initiated about 180 million years ago (Scotese 2001) and continued until about 30 million years ago (McLoughlin 2001).
The initial divergence of the two sequences is roughly exponential, each pair of terms being different by an amount greater than that of the preceding pair by a roughly constant factor.
However, to date we have only assumed that allopatry was maintained from the point of initial divergence.
Our analyses reveal that initial divergence is restricted to a small fraction of the genome, largely clustered around known wing-patterning genes.
Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades.
However, an initial divergence of the cortisol- and IBMX-mediated effects was observed among the up-regulated nuclear receptor genes: cortisol induced their expression levels, while IBMX lead to their repression.
Alternatively, initial divergence among allopatric populations in trophic niche could have lead to different levels of exposures to parasites transmitted via the food chain such as acanthocephalans, which in turn may select for different MHC alleles.
In addition, the initial divergence within the NA OPXV appears to have occurred much earlier than the apparently more recent and/or rapid radiation of known Old World OPXV.
In contrast to the apparent stepwise fashion of divergences in Nomascus, the radiation of Hylobates gibbons began with an initial divergence at 4.17 mya, followed by a split between H. lar and H. pileatus at 2.90 mya and nearly contemporaneous molecular divergences between two additional species pairs (H. moloch and H. klossii, H. muelleri and H. agilis) at 2.77 and 2.62 mya, respectively.
Our results indicate that complete loss of UGT1A6 mediated glucuronosyltransferase activity occurred via pseudogene fixation following divergence of the Felidae from all other feliform families approximately 37 MYA, and prior to the initial divergence of the extant felid lineages 11 MYA.
However paleodistribution modelling (e.g. Moussalli & Dolman, unpublished models) [and see 16] suggest that rainforest was continuous across this region during past cooler, wetter climatic conditions (∼7500-6000 YBpossiblyibly allowing for interactions between S-RED and BLUE since their initial divergence.
