Snakes are among the least-studied vertebrate taxa in Africa, largely because of their secretive behavior, considerable morphological conservatism, and complex biogeographic patterns that confound taxonomic resolution. Dipsadoboa, however, offered an unusual opportunity. Unlike many snake groups, these lizards, frogs, and frog egg specialists are commonly encountered, with more than 1,500 records available in online repositories and large numbers of specimens housed in museum collections. Despite this wealth of material, most species and subspecies had never been assessed in a phylogenetic framework, leaving confidence in the current morphology-based taxonomy limited and species boundaries uncertain.

To close this gap, the research team compiled tissue samples from fieldwork and museum loans representing all recognized species across the entire distributional range of the genus. The final dataset comprised new genetic material from 152 Dipsadoboa samples plus 39 sequences retrieved from GenBank, analyzed alongside an outgroup of 25 colubrid genera. The researchers generated data for three mitochondrial markers: 16S ribosomal RNA, cytochrome b, and NADH dehydrogenase subunit 4, producing a concatenated dataset of 2,227 base pairs. Phylogenetic relationships were inferred using both maximum likelihood and Bayesian inference approaches, with the maximum likelihood analyses performed in IQ-TREE and Bayesian analyses conducted in MrBayes, each with rigorous convergence and support assessments.

The results strongly confirmed the monophyly of Dipsadoboa and recovered the genus as sister to Crotaphopeltis, consistent with most previous phylogenetic proposals. Four major well-supported clades emerged from the analyses, corresponding largely to the morphological species groups proposed by Rasmussen in 1993: the aulica, duchesnii, unicolor, and werneri groups, plus one deeply divergent lineage corresponding to D. kageleri. Species delimitation analyses using ASAP and ABGD methods recovered 14 clusters in the cytochrome b dataset and 18 clusters in the 16S dataset, suggesting substantial cryptic diversity across the genus that current taxonomy does not capture.

Among the most striking findings was the revelation that D. duchesnii, D. brevirostris, and D. guineensis are likely conspecific, with sequence divergences falling within the intraspecific range. Conversely, several widely distributed taxa showed pronounced genetic structure. D. viridis, for example, exhibited five mitochondrial lineages distributed along the Upper and Lower Guinean forests, while D. underwoodi comprised two highly divergent allopatric populations from the Upper Guinean and Lower Guinean forests that appear to have separated roughly 6 million years ago. The nominotypical subspecies D. unicolor unicolor from the Upper Guinean forests was recovered as sister to D. viridis, whereas D. unicolor viridiventris from the Albertine Rift grouped with the West African D. riparia, rendering D. unicolor the only species recovered as paraphyletic.

Divergence time estimates, calculated using secondary calibration points in BEAST with an uncorrelated lognormal clock, indicated that after splitting from Crotaphopeltis approximately 25 million years ago, diversification within Dipsadoboa began in the early Miocene, around 22 million years ago. This initial split separated the aulica group from the remaining lineages. The werneri group diverged approximately 19.5 million years ago, followed by the separation of the duchesnii group from the unicolor group at approximately 17 million years ago. The unicolor group then began to diverge around 14.5 million years ago, with a subsequent radiation during the mid to late Miocene, and the most recent diversification within the duchesnii group occurring during the Plio-Pleistocene between roughly 4 and 2 million years ago.

Biogeographic reconstructions using the BioGeoBEARS package identified the DEC+J model as the best-fitting scenario, revealing low dispersal rates, negligible extinction, and a significant role for founder-event speciation. According to this model, East Africa is the most probable origin of the genus, with a probability of 0.31, though a combined origin spanning southern and eastern Africa or East to Central Africa cannot be entirely ruled out. Within the genus, the aulica and werneri groups are both inferred to have originated in East Africa, while the clade containing the duchesnii and unicolor groups likely originated in the tropical forests of Central Africa with a probability of 0.77. These results suggest at least three independent colonization events of the Upper Guinean forests from the Lower Guinean-Congolian forests.

The temporal and geographic patterns uncovered in the study align remarkably well with Africa’s geological and climatic history. The formation of the East African Rift, which began developing during the mid to late Miocene, and Miocene climatic fluctuations that shifted the distribution of forest and savanna habitats across the continent likely promoted lineage isolation and diversification, particularly through the persistence of climatic refugia on East African inselbergs. Within the Congo Basin, at least four diversification events are inferred to have occurred during the mid and late Miocene, consistent with savanna expansion driving multiple vicariant events and subsequent secondary contacts during forest expansions.

The study confirms Rasmussen’s earlier suggestion that the Lower Guinean forests within the Congo Basin represent the main diversity hotspot for Dipsadoboa, while highlighting the Eastern Afromontane region as pivotal for the genus’s origin and early diversification. The researchers emphasize that because the phylogenetic inference relies solely on mitochondrial data, the results should be interpreted as a working hypothesis for a set of candidate species. Future studies incorporating nuclear loci and morphological data will be essential to critically examine species boundaries and resolve the taxonomic status of several candidate taxa, including the problematic D. kageleri and the genetically distinct lineages within the unicolor group.

Beyond its taxonomic implications, the work establishes a robust framework for future integrative evolutionary and conservation research on African forest and wooded savanna snakes. Accurate species delimitation, improved assessments of species distributions, and a better understanding of evolutionary history are all essential for informing conservation priorities and management strategies in understudied regions of Africa, where many reptile species remain data-deficient. As forests continue to contract under increasing environmental pressure, the hidden diversity revealed in Dipsadoboa serves as a vivid reminder of how much evolutionary heritage still awaits discovery on the African continent.

Subject of Research: Diversity, origin, and biogeography of a widely distributed genus of African tree snakes ( Colubridae , Dipsadoboa )

Article Title: Diversity, origin, and biogeography of a widely distributed genus of African tree snakes ( Colubridae , Dipsadoboa )

Article References: Lobón-Rovira, J., Basham, E. W., Gvozdik, V., Greenbaum, E., Badjedjea, G., Bamba-Kaya, A., Champagne, P. S., Dobbins, B. A., Kusamba, C., Loader, S. P., Lyakurwa, J. V., Kouete, M. T., Masudi, F. M., Menegon, M., Nečas, T., Penner, J., Rödel, M.-O., Tobi, E., Tolley, K. A., … Jongsma, G. F. M. (2026). Diversity, origin, and biogeography of a widely distributed genus of African tree snakes (Colubridae, Dipsadoboa). Frontiers of Biogeography, 19, Article e195124. https://doi.org/10.21425/fob.19.195124

Image Credits: AI Generated

DOI: 10.21425/fob.19.195124

Keywords: Diversity, origin, biogeography, widely, distributed, genus, African, tree, snakes, Colubridae, Dipsadoboa, scientific research