Lygodactylus verticillatus

Röll, Beate, Sanchez, Mickaël, Gippner, Sven, Bauer, Aaron M., Travers, Scott L., Glaw, Frank, Hawlitschek, Oliver & Vences, Miguel, 2023, Phylogeny of dwarf geckos of the genus Lygodactylus (Gekkonidae) in the Western Indian Ocean, Zootaxa 5311 (2), pp. 232-250 : 245-246

4.3. Lygodactylus verticillatus

Lygodactylus verticillatus from Madagascar and from Europa Island do not differ in scalation ( Boettger 1913; Pasteur 1965). The slight difference in the number of precloacal pores mentioned by Pasteur (1965) was not supported by this study. Both populations show a very similar variation in coloration and in patterning. Thus, L. verticillatus from Madagascar and Europa cannot be distinguished by their external appearance or by the number of precloacal pores.

The most basal node within L. verticillatus separates specimens from the southern Malagasy localities Sakaraha and Isalo from all other samples. Sakaraha lies approximately 135 km from Toliara on the main road to the Isalo National Park. The remaining sister subgroup consists of specimens exclusively from the coastal regions of Madagascar, approximately from Morondava southwards to Toliara, and the insular population. We cannot exclude an inland origin of the L. verticillatus from Europa Island. However, based on our morphological and genetic dataset, it seems more likely that the nearest relatives of the insular L. verticillatus are conspecifics from populations in the coastal regions of south-western Madagascar.

We found no relevant morphological differences, and only weak genetic differences between the Malagasy and the insular population, and only weak genetic variation within the monophyletic lineage of Europa Island. This agrees with the hypothesis of a relatively recent colonization as suggested by Pasteur (1965).

Europa Island is 355 km west-northwest from Toliara or 300 km southwest from Cap Saint-Vincent close to Morombe, 529 km east-northeast from Inhambane ( Mozambique) and approximately 600 km south of Juan de Nova ( Caceres 2003; Fricke et al. 2013). It is nearly circular (6 × 7 km) with a total area of 30 km 2 ( Caceres 2003) and represents the largest island of the Îles Éparses. Europa Island belongs to the group of ‘modern’ isolated seamounts in the Channel, possibly developed during Oligocene to Miocene times ( Courgeon et al. 2016). Lygodactylus verticillatus could have reached Europa Island recently by natural transoceanic dispersal or by human-mediated dispersal. While a natural dispersal would be supported by flows westward from Madagascar to mainland Africa ( Ali & Huber 2010), a much simpler and thus more parsimonious alternative explanation is ship-borne dispersal. Lygodactylus verticillatus could have arrived at Europa Island e.g., with ships of Malagasy fishermen seasonally searching for nesting chelonians, or with ships of European (French) settlers who started their settlement from Toliara and lived on the island from approximately 1860 to the 1920s ( Fricke et al. 2013). The amount of genetic variation found within Europa (three haplotypes differing by up to two mutations in 16S) would be in agreement with either (i) ship-borne dispersal or (ii) natural dispersal of multiple individuals, or (iii) natural dispersal of a single individual at a somewhat deeper point in time, with subsequent in-situ genetic diversification. Support for either of these hypotheses could come from a denser sampling of Malagasy populations: the presence of haplotypes identical to those on Europa in Malagasy populations would allow to reject the third hypothesis, and given that simultaneous or repeated natural dispersal to such a small islet is rather unlikely, ship-borne introduction would in this case remain as the most probable hypothesis. Only if the presence of the Europa haplotypes in Madagascar could be reasonably excluded, the third hypothesis would be supported.

Lygodactylus verticillatus is adapted to dry climatic conditions. In south-western Madagascar, the species inhabits shrubs and trees in semi-arid areas as well as fences and walls in human settlements ( Puente et al. 2009). On Europa Island, it is widely distributed and occurs in most natural habitats on rocks, shrubs, trees and in a dry euphorbia forest as well as in human settlements ( Brygoo 1966; Sanchez et al. 2015, 2019). The conditions for L. verticillatus in the coastal regions of south-western Madagascar and on Europa are very similar, facilitating the survival on the island.