Species divergence

Desdevises, Y., Jovelin, R., Jousson, O. and Morand, S. (2000) Comparison of ribosomal DNA sequences of Lamellodiscus spp. (Monogenea, Diplectanidae) parasitising Pagellus (Sparidae, Teleostei) in the North Mediterranean Sea species divergence and coevolutionary interactions. International Journal for Parasitology 30, 741-746. 

Substitutions at conservative and variable sites have been used to trace evolutionary relationships. These studies assume that the longer the time since two species diverged from each other, the larger the number of differences in a certain polypeptide s primary structure. For example, humans and chimpanzees are believed to have diverged relatively recently (perhaps only four million years ago). This presumption, based principally on fossil and anatomical evidence, is supported by cytochrome c primary sequence data, because the protein is identical in both species. Animals such as kangaroos, whales, and sheep, whose cytochrome c molecules each differ by 10 residues from the human protein, are all believed to have evolved from a common ancestor that lived over 50 million years ago. 

Although the most common unsaturated fatty acids in plants are derived from oleic acid, a wide range of unusual fatty acids are found in the seed oils of different species. Divergent plastid acyl-ACP desaturases have been shown to account for some of this diversity. For example, Coriandrum sativum achieves seed oils rich in A -18 1 (pet-roselinic acid) by desaturation of 16 0 at the A position followed by elongation, while Thunbergia alata attains a similar oil by direct A -desaturation of 16 0. A single acyl-ACP desaturase from Hedera helix can even produce A -dienes (E. Whittle, 2005). 

Comparison of the amino acid sequences of hemoglobin and myoglobin from different species of animals shows that the chains from phylogenetically (evolutionarily) related species are similar. The number of differences increases with species that are phylogenetically more separated. On the assumption that proteins evolve at a constant rate, the number of differences between two homologous proteins is proportional to the time at which the species diverged during evolution. 

DNA patterns have shown us that modem man is very similar to all the apes ineluding Asian Orangutans, African Gorillas and Chimpanzees. The time at which each of the various species diverged from each other remains a matter of considerable uncertainty in academic circles. Estimates are little more than tentative speculations based on assumed average mutation rates and an arbitrary sizing of the time scale. 

Verrell, P. A., 2003, Population and species divergence of chemical cues that influence male recognition of females in desmognathine salamanders, rAo/ogv 109 577-586. 

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