Photos from Addis ababa, courtesy Elias Bayou

Biogeographic Patterns in the Trioceros affinis Species Complex of the Ethiopian Montane Belt

Introduction

The Trioceros affinis species complex represents a geographically isolated and morphologically variable group of chameleons endemic to the montane forests of the Ethiopian Highlands. These populations are distributed across deeply fragmented forest systems, shaped by elevation, climate gradients, and tectonic features such as the Great African Rift. Despite being erroneously referred to as "Rüppell's Desert Chameleon" across multiple databases (e.g., iNaturalist, The Reptile Database), members of the affinis complex are exclusively montane forest dwellers, often associated with Coffea arabica cultivation zones above 2500 m a.s.l. (Koppetsch, Nečas, and Wipfler 2021).

This paper clarifies taxonomic composition, critiques vernacular naming, and highlights the need for further integrative revision. Important historical contributions—including Tilbury's paratype collection (Tilbury 1996), Nečas's long-term documentation and early recognition of divergent Bale taxa (Nečas 1999), and broader systematics frameworks (e.g., Glaw 2016)—are synthesized to build a coherent view of the complex's diversity.

Misnomers and Vernacular Confusion

The name "Rüppell's Desert Chameleon" is misleading. Though Trioceros affinis was indeed described by Rüppell (1845), the term "desert" fails to represent its humid montane ecology. Another widespread name—"Beardless Ethiopian Montane Chameleon"—partially distinguishes T. affinis from sympatric forms such as T. harennae and T. bitaeniatus, yet does not account for beardless relatives like T. baalebicornutus and T. wolfgangboehmei (Koppetsch et al. 2021).

Taxonomic Composition and Distribution

The complex includes both formally described and provisional species, each restricted to montane zones separated by ecological and tectonic boundaries:

• Trioceros affinis s.str. . – Illubabor and Kaffa

• Trioceros wolfgangboehmei – Northern Bale Mountains (Koppetsch, Nečas, and Wipfler 2021)

• Trioceros cf. affinis sp. nov. – Shoa, Gondar

• Trioceros cf. affinis sp. nov. – Harrar

• Trioceros cf. affinis sp. nov. – Djam Djam

• Trioceros cf. affinis sp. nov. – Dorse

• Trioceros cf. affinis sp. nov. – Unknown locality

These populations show significant morphological divergence, particularly in cranial ornamentation, scalation, and body proportions. A formal species delimitation effort integrating morphometrics, molecular data, and ecological niche modeling is urgently needed.

Historical Contributions and Field Legacy

Tilbury (1996) collected a paratype of T. wolfgangboehmei near Goba—this specimen was later used in the species' formal description (Koppetsch et al. 2021). Nečas (1999) documented the Bale forms and recognized their divergence as early as the 1990s, based on field studies and photographic archives. Glaw (2016) did not describe Ethiopian taxa directly but contributed broader phylogenetic frameworks that contextualize Eastern Afromontane chameleons within the Trioceros lineage.

Conclusion

The Trioceros affinis complex offers a compelling case study in montane speciation, biogeographic isolation, and vernacular misrepresentation. A comprehensive revision is essential—not only for scientific clarity but to guide conservation efforts amid deforestation and agroexpansion in Ethiopia's remaining forest remnants.

References

• Glaw, Frank. 2016. A Field Guide to Amphibians and Reptiles of Madagascar. 3rd edition. Vences & Glaw Verlag.

• Koppetsch, Tim, Petr Nečas, and Benjamin Wipfler. 2021. "A New Species of Chameleon of the Trioceros affinisSpecies Complex (Squamata, Chamaeleonidae) from the Northern Slopes of the Bale Mountains, Ethiopia." Zoosystematics and Evolution 97(1):169–182.

• Nečas, Petr. 1999. Chameleons: Nature's Hidden Jewels. Kirschner & Seufer Verlag.

• Tilbury, Colin. 1996. Field notes and paratype collection of T. wolfgangboehmei, Bale Mountains, Ethiopia. (Unpublished data cited in Koppetsch et al. 2021).

• Rüppell, Eduard. 1845. "Neue Wirbelthiere zu der Fauna von Abyssinien gehörig." Museum Senckenbergianum. Frankfurt am Main.