Lygodactylus insularis, Boettger, 1913

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 : 244-245

4.2. Lygodactylus insularis

Lygodactylus insularis is an endemic species on Juan de Nova, a very small island with a total area of approximately 5 km 2, 280 km from mainland Africa (East Mozambique) and 120 km to the nearest point on the Malagasy coast ( Caceres 2003; Lambs et al. 2016). Pasteur (1965) already included L. insularis in the L. capensis group and assumed that L. insularis originated from either L. c. capensis or L. c. grotei . Lygodactylus capensis and L. insularis share the same number of precloacal pores and a superficially similar coloration of the adults. However, they strongly differ in the status of the subcaudals and in the appearance of their hatchlings. It is thus impossible to discern the relationships 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 and, in so far, supporting Pasteur (1965). While the single gene as well as the multigene analyses fully support closer relationships between L. insularis and L. capensis than between L. insularis and L. grotei , the position of L. insularis within the clade formed by L. insularis , L. nyaneka , L. capensis sensu stricto and six L. aff. capensis lineages (provisionally named as “groups”; here, the last two of these are referred to as L. capensis sensu lato) is not clearly resolved. For a taxonomic revision of the L. capensis complex—one is stated to be in progress by Travers et al. unpublished (in Marques et al. 2020)—we strongly recommend a broader incorporation of genetic markers to resolve the conflicting topologies since our multigene dataset consists of only few markers especially for L. nyaneka and for the numerous groups forming L. capensis sensu lato. The clade including L. grotei and L. pakenhami is defined as the sister clade of L. insularis , L. nyaneka and L. capensis sensu lato. Lygodactylus insularis is recovered as a monophyletic group based on mtDNA, probably resulting from a single dispersal event. Furthermore, the species based on the sampling herein exhibits little intraspecific genetic variability, possibly due to the tiny size of the island resulting in a panmictic population.

Members of the genus Lygodactylus successfully crossed the Mozambique Channel from mainland Africa back to Madagascar one or perhaps two times (R̂ll et al. 2010; Mezzasalma et al. 2017; Gippner et al. 2021). The ancestor of L. insularis probably began at least one further traverse in eastward direction ending on Juan de Nova, an island in the middle of the channel. Juan de Nova developed as the uplifted top of a seamount that probably was formed during the Cretaceous along the Davie Fracture ( Riaux-Gobin & Witkowski 2012). Ali & Hedges (2022) suggest that it may have remained emerged as a low elevation atoll since the Early Palaeocene. In such a scenario, the dispersal of the ancestors of L. insularis may have taken place as early as 22.3 (confidence interval 15.6–30.2) mya, the stem age of the L. capensis group estimated in the Lygodactylus timetree of Gippner et al. (2021). Results of palaeogeographic reconstructions and palaeo-oceanographic modelling suggest strong surface currents in the Mozambique Channel flowing from northeast Mozambique and Tanzania eastward towards Madagascar during the Palaeogene (66 to 23 mya), which would support this scenario ( Ali & Huber 2010). While the main contemporary direction of oceanic surface currents is westward, the situation in the Mozambique Channel is very complex with numerous eddies and possible countercurrents ( Hawlitschek et al. 2016a). This also suggests that dispersal could have occurred during a more recent period of mainly westward marine currents.

An alternative hypothesis, dispersal via short-lived Cenozoic land-bridges between mainland Africa and Madagascar (e.g., Mazza et al. 2019; Masters et al. 2020), is disputed and has been ruled out based on current geological reconstructions (e.g., Ali & Huber 2010; Ali & Hedges 2022).

It also must be emphasized that despite a reasonable sampling of Eastern Africa, especially Mozambique (with L. capensis group sequences from 14 localities available so far), it is possible that a still undiscovered species representing the sister lineage of L. insularis may exist in this region. A somewhat similar situation was uncovered in the frogs of the Ptychadena mascariensis complex in which the sister lineage of the Malagasy species has only been recorded from a small area of Malawi and could have easily been overlooked without intensive sampling efforts ( Zimkus et al. 2017). If a closer relative of L. insularis was found on the African mainland, it would lead to younger age estimates of the colonization event of Juan de Nova by these geckos.