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Several house gecko species of the genus Hemidactylus are almost cosmopolitan lizards, with distributions that have probably been shaped by natural transoceanic dispersal as well as by more recent human introductions. Here we revise the Hemidactylus populations of Madagascar and compare them genetically with populations from other sites in the Indian Ocean region. Morphological data strongly confirm the occurrence of three Hemidactylus species on Madagascar: Hemidactylus frenatus, distributed along the western coast of Madagascar; H. platycephalus, restricted to the north-west and the widespread H. mercatorius that occurs throughout the island, including coastal areas at sea level as well as big cities (Antananarivo, Fianarantsoa) at altitudes of 1200–1300 m above sea level. Analyses of partial sequences of the 16S rRNA gene in 46 Hemidactylus specimens from Madagascar, East Africa, South Asia, and the Comoro and Mascarene archipelagos demonstrated the presence of a fourth species, H. brooki, on the Mascarenes (Réunion, Rodrigues, and Mauritius) and Comoros (Moheli). The Malagasy populations of H. platycephalus were genetically uniform and differentiated from the African and Comoroan specimens studied. H. frenatus had a relatively low genetic differentiation over the whole region with no recognizable phylogeographical structure, indicating more recent colonizations or introductions. In contrast, H. mercatorius showed a strong phylogeographical structure of haplotypes, with two distinctly different lineages in Madagascar. Moreover, all Malagasy specimens differed strongly from the single African specimen included. This indicates that populations of H. mercatorius in Madagascar have a long history that predates human settlement. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 115–130. [ABSTRACT FROM AUTHOR]

Diurnal dwarf geckos of the genus Lygodactylus are distributed in tropical and subtropical regions and live in highly diverse habitats. The genus currently comprises 79 species and several candidates for new species or subspecies. Most of these taxa occur in Sub-Saharan Africa and Madagascar, with only two described species in South America. Although the main center of diversity of Lygodactylus currently is Africa, the genus probably has a Malagasy origin, followed by two or three independent transoceanic dispersal events between Madagascar and Africa and one trans-Atlantic dispersal from Africa to South America. A few species colonised islands in the Western Indian Ocean belonging to the Zanzibar Archipelago and to the Îles Éparses. Here we examined L. grotei pakenhami from Pemba Island, L. insularis from Juan de Nova, and L. verticillatus from Europa Island to clarify their taxonomic status and their origin. Concerning L. grotei pakenhami and L. insularis, preceding studies pointed to a relation to species of the African L. capensis group. In contrast, L. verticillatus on Europa Island is considered to be conspecific with Malagasy populations. Therefore, we conducted a phylogenetic study of the African L. capensis group and the Malagasy L. verticillatus group, and examined color pattern, selected morphological characters and two mitochondrial markers (ND2 for African and 16S rRNA for Malagasy Lygodactylus). Lygodactylus grotei pakenhami from Pemba and L. grotei from mainland Africa cannot be distinguished by their scalation, but their reciprocal monophyly suggested by mitochondrial DNA, conspicuously different coloration (both in adults and hatchlings) and their high genetic distances (16.3% in ND2) support the hypothesis that these taxa represent two distinct species. Consequently, we elevate L. grotei pakenhami to species level, as Lygodactylus pakenhami Loveridge, 1941. Lygodactylus pakenhami is endemic to Pemba Island which was possibly separated from the African mainland during the late Miocene or Early Pliocene (6 million years ago). The simplest explanation for the existence of L. pakenhami on Pemba is vicariance. A recent, human-mediated transportation is excluded, as the molecular data clearly indicate a longer period of isolation. Lygodactylus insularis has been supposed to be related to the taxa 'capensis' or 'grotei'. However, it is impossible to discern the relationship of L. insularis, L. capensis and L. grotei by means of scalation or coloration alone. Our molecular phylogenetic analyses reveal that L. insularis is embedded within the L. capensis group, clearly indicating its African origin. The single gene (ND2) as well as the multigene analyses fully support a closer common origin of L. insularis and L. capensis than of L. insularis and L. grotei. However, the position of L. insularis within the clade formed by L. insularis, L. nyaneka, L. capensis sensu stricto and six L. aff. capensis groups is not clearly resolved. Lygodactylus insularis is endemic on Juan de Nova Island, an old low elevation atoll. That all L. insularis mitochondrial sequences are very similar to each other and together form a monophyletic lineage is in agreement with the hypothesis of a single dispersal event to the island. For the L. verticillatus population from Europa Island our mitochondrial data suggest close relationships to conspecific samples from the coastal regions of south-western Madagascar. As we found no relevant morphological or genetic differences between the insular and the Malagasy populations of L. verticillatus, and no remarkable genetic variation within the monophyletic lineage on Europa, we suggest a single, very recent dispersal event, perhaps human-mediated. Although the genus Lygodactylus colonised Africa, islands in the Gulf of Guinea, South America and some islands in the Western Indian Ocean, it seems-compared to other lizard genera-to be only moderately successful in transoceanic long-distance dispersal.

Previous genetic studies of frogs from Mayotte Island (a French Overseas Department in the Comoros Archipelago) in the Western Indian Ocean have provided evidence for oceanic dispersal in amphibians, which is a rare phenomenon due to the osmotic intolerance of amphibians to saline water. Using an integrative approach including morphological, bioacoustic, and genetic evidence, we here confirm that these frogs correspond to two new species and are the only representatives of the family Mantellidae not endemic to Madagascar. Blommersia transmarina sp. nov. differs from its sister taxon, B. wittei, by several morphological differences including larger body size (snout-vent length up to 34.5 mm) and by slight differences in advertisement calls. Boophis nauticus sp. nov. differs from its closest relatives, B. tephraeomystax and B. doulioti, by slight morphological differences (including larger body size), a reddish (vs. silvery or golden) iris coloration in life, and slightly different advertisement calls. The two new species differ from their closest relatives by a substantial genetic differentiation, with pairwise genetic distances > 5% in the mitochondrial 16S rRNA gene, and based on the limited available data, also by distinct differences in nuclear DNA. They also are both larger than their closest relatives from Madagascar and B. transmarina sp. nov. is the largest Blommersia species, suggesting a moderate form of island gigantism. The Madagascan sister species B. wittei and B. doulioti are among the relatively few amphibian species occurring in the arid western biomes of the island, are adapted to open landscape, and reproduce in stagnant water bodies, which we hypothesize may represent important preadaptations for successful overseas colonization.

Amphibians are thought to be unable to disperse over ocean barriers because they do not tolerate the osmotic stress of salt water. Their distribution patterns have therefore generally been explained by vicariance biogeography. Here, we present compelling evidence for overseas dispersal of frogs in the Indian Ocean region based on the discovery of two endemic species on Mayotte. This island belongs to the Comoro archipelago, which is entirely volcanic and surrounded by sea depths of more than 3500 m. This constitutes the first observation of endemic amphibians on oceanic islands that did not have any past physical contact to other land masses. The two species of frogs had previously been thought to be nonendemic and introduced from Madagascar, but clearly represent new species based on their morphological and genetic differentiation. They belong to the genera Mantidactylus and Boophis in the family Mantellidae that is otherwise restricted to Madagascar, and are distinguished by morphology and mitochondrial and nuclear DNA sequences from mantellid species occurring in Madagascar. This discovery permits us to update and test molecular clocks for frogs distributed in this region. The new calibrations are in agreement with previous rate estimates and indicate two further Cenozoic transmarine dispersal events that had previously been interpreted as vicariance: hyperoliid frogs from Africa to Madagascar (Heterixalus) and from Madagascar to the Seychelles islands (Tachycnemis). Our results provide the strongest evidence so far that overseas dispersal of amphibians exists and is no rare exception, although vicariance certainly retains much of its importance in explaining amphibian biogeography.