Biogeography of the genus Phelsuma
All species of the genus Phelsuma occur on islands located in the south-western Indian Ocean, except Phelsuma dubia that is also found on mainland Africa in coastal Kenya and Tanzania. This species probably arrived there only recently, most likely by cargo vessels as the main distribution area is around the ancient merchant ports of Mombassa, Dar-Es-Salaam and Zanzibar (on Zanzibar Island).
It is generally accepted that the phylogenetic origin of the genus Phelsuma lies on the island of Madagascar. From there the genus has colonized the other Indian Ocean islands and East Africa.
The Mascarene Plateau probably played a key role in the evolution of certain species, especially in the ones from the current Mascarene Islands (Réunion, Mauritius and Rodrigues). The now submerged islands on this plateau had probably the function of stepping stones for a number of plant species, the dodo and Phelsuma.
On the Seychelles archipelago, fragments of the ancient Gondwana continent, the genus has a relatively poor representation with only two species (Phelsuma astriata and Phelsuma sundbergi) present, but is still, together with Madagascar, the oldest landmass of the genus' range. These two species are closely related to the Madagascar forms and more distinct from the Mascarene forms. This implies that the Phelsuma species from the Seychelles are younger than those on the Mascarene Islands, although that the Seychelles are millions of years older.
The same is true for the Andaman Islands, only one species (Phelsuma andamanensis) occurs here and has not evolved like the Mascarene forms, remaining closer to Seychelles or Madagascar species. Implying that Phelsuma andamanensis only recently arrived on the Andaman Islands.
Due to the young age of the Comoro Islands and the proximity to Madagascar, it is almost certain that this archipelago is colonized from here. The genus is represented on the islands with six species (Phelsuma v-nigra, Phelsuma robertmertensi, Phelsuma nigistriata, Phelsuma comorensis, Phelsuma laticauda and Phelsuma dubia).
Madagascar has due to its size and the many ecological niches the richest Phelsuma fauna. On the other hand this richness in species implies that the genus Phelsuma is relatively young. The many cases of coexistence of certain forms, occupying identical niches (e.g. Phelsuma mutabilis and Phelsuma modesta), are proof that the genus is in an early stage of evolution. This coexistence can only be temporary and one species will supersede the other.
Normally species richness is a sign of recent colonization of an area or island. Species evolve then to occupy the diverse ecological niches under different selection pressures. The colonization of the entire island of Madagascar by the genus Phelsuma finds probably its origin in the fact that its ancestor became diurnal. The capability to move, feed and breed during daytime opened a window of opportunity for the genus resulting in a fast evolution and huge biomass of Phelsuma species on the island.
