The application of genetic studies to populations of widespread animals and plants in recent years has revealed that many widespread ‘species’ are in fact made up of several different cryptic species, which resemble one-another closely (or even completely) but are in fact genetically distinct and incapable of reproducing with one another. This has profound implications for the conservation of the species in question, as it often becomes apparent that ‘species’ thought to have widespread distributions and large population sizes are often made up of several smaller populations with much more limited distributions, which are much more vulnerable to extinction.
In a paper published in the Bonn zoological Bulletin in June 2014, Philipp Wagner of the Department of Biology at Villanova University and Zoologisches Forschungsmuseum Alexander Koenig, Adam Leaché of the Department of Biology & Burke Museum of Natural History and Culture at the University of Washington and Matthew Fujita of the Department of Biology at the University of Texas at Arlington, describe four new species of Forest Geckos that had previously been assumed to be populations of the species Hemidactylus fasciatus, which has recently been found to be a cluster of cryptic species. While these species are very similar morphologically, they do show differences in size and colouration, which enables them to be distinguished.
The species Hemidactylus fasciatus was first described in 1842, based upon specimens from the collection of the British Museum (now the Natural History Museum), and it is unclear exactly where the holotype originated (in taxonomy a single specimen is designated as the holotype, against which any subsequent specimens can be compared; when species are split those specimens determined to be of the same species as the holotype retain the original species name, whilst those determined to be of a different species are assigned a new name). Wagner et al. conclude that this specimen belongs to a large population that includes all specimens west of the Dahomey Gap (a gap in continuous forest running from eastern Ghana to western Nigeria and reaching from the grasslands of the Sahel south to the Gulf of Guinea), including Geckos from Guinea, Liberia, Côte d’Ivoire and Ghana.
Living specimen of Hemidactylus fasciatus from Liberia. Wagner et al. (2014).
Hemidactylus fasciatus (as now defined) is a large Forest Gecko, reaching 172 mm in length. It is pale grey in colour, with dark crossbands on its dorsal side (back), and lacks any form of spots or coloured tubercles. It has a broad, dark band collecting its eyes to the dark stripe on the back of its neck, and a pale upper lip.
The first new species described is named Hemidactylus kyaboboensis, meaning ‘from Kyabobo’, in reference to the Kyabobo National Park in the Volta region of Ghana. This species is known only from patches of discontinuous moist semi-deciduous rainforest within the Dahomey Gap, in the Togo Hills of eastern Ghana and the Missahöhe forests of Togo. Hemidactylus kyaboboensis is a medium sized Forest Gecko, reaching about 140 mm in length. It is grey in colour with darker crossbands on its dorsal surface, though these are less distinct than in Hemidactylus fasciatus, and it has prominent whitish spots and stripes. It has a narrower band connecting its eyes to the stripe on its neck, and a darker upper lip.
Living specimen of Hemidactylus kyaboboensis from the Kyabobo National Park. Wagner et al. (2014).
The second new species described is named Hemidactylus eniangii, in honour of the Nigerian herpetologist and conservation biologist Edem Eniang, who helped to collect the specimens from which this species was described in Cross River National Park, Nigeria. Hemidactylus eniangii is a medium sized Forest Gecko reaching about 140 mm in length. It is grey in colour with distinct darker bands, a narrow band connecting the eye to the neck stripe and a dark upper lip.
The holotype of Hemidactylus eniangii. Wagner et al. (2014).
The third new species described is named Hemidactylus coalescens, in reference to the method used to determine the species within the group (coalescent-based Bayesian analysis of 1,087 single nucleotide polymorphisms). It is a medium sized Forest Gecko, reaching 174 mm in length, grey in colour with narrow darker crossbands on its dorsal surface, and a very fine line connecting the eye to the neck stripe. Hemidactylus coalescens is found in the Congolian rainforest south of the Sanaga River, including southern Cameroon, Gabon and Congo.
Living specimen of Hemidactylus coalescens from the Campo Region of Cameroon. Wagner et al. (2014).
The final new species is named Hemidactylus biokoensis, meaning ‘from Bioko’, in reference to Bioko Island, an Equatorial Guinean territory in the Gulf of Guinea, to which it is endemic. Hemidactylus biokoensis is a medium sized Forest Gecko reaching 166.7 mm in length. It is pale in colour with darker crossbands on its back, and ligher spots on these bands. The stripe connecting the eye to the neck stripe is narrow.
Living specimen of Hemidactylus biokoensis from the Reserva científica de la Caldera de San Carlos on Bioko Island. Wagner et al. (2014).
The rainforests of West and Central Africa are not continuous in extent, being broken up by areas of savannah grassland and dry forest, that are thought to have expanded into areas of continuous wet forest during the last Pleistocene glaciation, and never completely retreated. These drier areas serve as barriers to moisture-loving species such as Forest Geckos, and are likely to have led to fragmentation of an original population into smaller groups, which then became genetically isolated. These African forests appear to be home to a large number of highly localized Reptile and Amphibian species, which probably have their roots in forest fragmentation during the Pleistocene.
See also
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