speciation
Darwin's legacy
20-11-2008 15:49
Darwin’s legacy is still very vivid and doubtless
will continue to be. A recent paper by Parent et al.
(2008) reviews the colonization and diversification
of the Galápagos terrestrial fauna. Snails are one of
the groups that have diversified on this archipelago.
Of the 10 land snail genera present on the islands,
only the bulimulids show a huge radiation. Much is,
however, still unknown - not only of snails but also
of other groups - and e.g. even the sister group of
the Galápagos bulimulids has not been ascertained
till now. One of the reasons is that no reliable
molecular clock for the group is known. As a
non-vagile group, land snails are among the animals
for which many single island endemics are to be
expected. Parent & Crispi (2006) found a
combination of both within-island and between-island
speciation and the relative importance of genetic
drift and selection in within-island diversifications
of this group is not known.
While the speciation processes are affected by colonization and extinction, the geographical dynamics of the whole archipelago has to be taken into account, where change of sea levels undoubtedly created or ceased possibilities for gene flow.
The analogy with the tepui ‘islands’ in Guayana are strikingly. Perhaps I will come back at this issue later, when hopefully more phylogenetic data are known.
Incidentally I came across another paper on the Galápagos earlier this week (Estes et al., 2000). It is a detailed reconstruction of the journey of Darwin within the archipelago. Where was Darwin in the Galápagos and what did he see? Based both on bibliographic sources and revisiting the islands in the same period of the year, the authors were still able to see the geological features noted by Darwin. However, in contrast, the flora and fauna has changed considerably since the Beagle landed on the islands.
The reconstruction was possible thanks to the detailed field notes taken during that expedition and the fact that they have been preserved. Again and again, I cannot help to stress the importance of taking field notes and storing them at a place where they will be available for future scientists.
References:
Estes, G., Grant, K.T. & Grant, P.R., 2000. Darwin in Galápagos: his footsteps through the archipelago. - Notes and Records of the Royal Society London 54: 343-368.
Parent, C.E. Caccone, A. & Petren, K., 2008. Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biographical synthesis. - Phliosopical Transactions of the Royal Society, B 363: 3347-3361.
Parent, C.E. & Crespi, B.J., 2006. Sequrntial colonization and diversification of Galápagos endemic land snail genus Bulimulus (Gastropoda, Stylommatophora). - Evolution 60: 2311-2328.
While the speciation processes are affected by colonization and extinction, the geographical dynamics of the whole archipelago has to be taken into account, where change of sea levels undoubtedly created or ceased possibilities for gene flow.
The analogy with the tepui ‘islands’ in Guayana are strikingly. Perhaps I will come back at this issue later, when hopefully more phylogenetic data are known.
Incidentally I came across another paper on the Galápagos earlier this week (Estes et al., 2000). It is a detailed reconstruction of the journey of Darwin within the archipelago. Where was Darwin in the Galápagos and what did he see? Based both on bibliographic sources and revisiting the islands in the same period of the year, the authors were still able to see the geological features noted by Darwin. However, in contrast, the flora and fauna has changed considerably since the Beagle landed on the islands.
The reconstruction was possible thanks to the detailed field notes taken during that expedition and the fact that they have been preserved. Again and again, I cannot help to stress the importance of taking field notes and storing them at a place where they will be available for future scientists.
References:
Estes, G., Grant, K.T. & Grant, P.R., 2000. Darwin in Galápagos: his footsteps through the archipelago. - Notes and Records of the Royal Society London 54: 343-368.
Parent, C.E. Caccone, A. & Petren, K., 2008. Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biographical synthesis. - Phliosopical Transactions of the Royal Society, B 363: 3347-3361.
Parent, C.E. & Crespi, B.J., 2006. Sequrntial colonization and diversification of Galápagos endemic land snail genus Bulimulus (Gastropoda, Stylommatophora). - Evolution 60: 2311-2328.