Cryptic diversity in pygmy chameleons (Chamaeleonidae: Rhampholeon) of the Eastern Arc Mountains of Tanzania, with description of six new species
Michele Menegon, Division of Biology & Conservation Ecology, School of Science & the Environment, Manchester Metropolitan University
John V. Lyakurwa, Department of Sustainable Agriculture and Biodiversity Ecosystem Management, Nelson Mandela African Institute of Science and Technology
Simon P. Loader, Department of Life Sciences, The Natural History Museum
Krystal A. Tolley, South African National Biodiversity Institute, Kirstenbosch Research Centre
Many of the best-known species radiations (e.g., Darwin’s finches, Caribbean Anolis, African cichlids) are characterised by high species richness with substantial morphological disparity among species. However, species radiations can also be characterised by genetic diversification with little ecological or phenotypic divergence between species. Typically, these species are distributed allopatrically, but in ecologically similar areas (Gittenberger, 1991; Losos and Mahler, 2010). Chameleons in the genus Rhampholeon are an example of such a radiation (e.g., Branch et al., 2014). They are morphologically conservative, exhibit-ing limited phenotypic diversity, despite notable genetic divergence that has accumulated over millions of years in isolation (Branch et al., 2014; Hughes et al., 2018).
Most Rhampholeon species occur in fragmented and ecological-ly isolated mountains in East Africa, where species have evolved in allopatry (Menegon et al., 2009; Branch et al., 2014; Hughes et al.,2018). The species essentially occur in ecologically similar forests on isolated mountains of the Eastern Arc Mountains, the Albertine Rift, and the sky islands of Mozambique and Malawi. Their phenotypic similarity however has resulted in difficulties diagnosing and identifying species using morphological characters (e.g., Menegon et al.,2002; Fisseha et al., 2013).One particular radiation demonstrating morphologi-cal conservatism is the Rhampholeonuluguruensis/moyerispecies complex from the Eastern Arc Mountains, which shows large phylogenetic diversity across its distribution (Fisseha et al., 2013). However, external morphological diversity appears to be low. For example, Rhampholeon uluguruensis from the Uluguru Mountains (Tilbury and Emmrich, 1996) was the first Rhampholeon found in the Eastern Arc Mountains to bear a soft, tuberculated ros-tral process. This feature is similar to that of Rhampholeon nchisiensis (Loveridge, 1953) from the Southern Highlands of Tanzania and Malawi, and of Rhampholeon bouleng-eri (Steindachner, 1911) from the montane forests of the Albertine Rift. Subsequently, the morphological analysis of Rhampholeon individuals from the Kihanga and Kito-lomero valleys of the Uzungwa Scarp Nature Reserve bore strong resemblance to R. uluguruensis but were distin-guished by the number of their interorbital scales and the number and arrangement of hemipenial papillae (Men-egon et al., 2002).
These differences became the basis for describing a new species, R. moyeri (Menegon et al., 2002). Phylogenetic analyses that have incorporated wide geographic coverage across the Eastern Arc Mountains have shown highly divergent lineages within R.moyeriwith distinct lineages endemic to single mountain blocks (Matthee et al., 2004; Fisseha et al., 2013).Furthermore, R. uluguruensis, restricted to the Uluguru Mountains, is deeply divergent from other members of the clade (Fisse-ha et al., 2013). Moreover, there are two highly divergent clades from the Uzungwa Scarp Nature Reserve populations, both currently assigned to R. moyeri suggesting that R. moyeri as currently understood is paraphyletic (Fisseha et al., 2013), with specimens in the type series assignable to both these clades. One clade is restricted to the Kito-lomero valley and was provisionally designated as R. cf.uluguruensis, whereas the other clade is from Kihanga (the type locality for R. moyeri). In addition, two previously unknown but highly divergent clades were found from the Nguu and the Nguru Mountains, the latter of which is more closely related to Rhampholeon beraduccii (Mariaux and Tilbury, 2006) than to the species in the R. uluguruensis/moyeri complex.
Despite substantial genetic differences shown in these studies, there are few identifiable and diagnosable morphological traits to separate lineages (e.g., Menegon et al., 2002; Mariaux et al., 2006; Fisseha et al., 2013; Branch et al., 2014). Given the results from phylogenetic studies on R. uluguruensis/moyeri complex (e.g., Fisseha et al., 2013), the complex contains a number of unrecognised spe-cies. We combine existing data with new data from six candidate species of Rhampholeon from the Eastern Arc Mountains in a phylogenetic analysis (including Uzungwa Scarp Nature Reserve in the Udzungwa Mts; Mafwom-ero Forest Reserve in the Rubeho Mts; Mkingu Nature Reserve in the Nguru Mts; Mount Kanga, in the Nguru landscape; Mamiwa Kisara Forest Reserve in the Ukaguru Mts; and Nguu North and Kilindi Forest Reserves in the Nguu Mts). Using combined data, we provide taxonomic descriptions of six new species and outline, based on their distribution, the conservation status of these new species.
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