 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 (R�union,
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. |
