On the status of Calumma cf. radamanus in NW Madagascar

By Petr Nečas

Abstract

Calumma radamanus (Mertens, 1933) is a small Malagasy chameleon long misclassified within the Calumma nasutumcomplex but revalidated through integrative taxonomic studies. Field observations in Montagne d'Ambre and Nosy Komba reveal populations provisionally referred to C. cf. radamanus, yet exhibiting distinct morphological traits, particularly in rostral appendage form and coloration. Comparative analyses suggest that these populations may represent separate, undescribed taxa. Their occurrence in microendemic refugia highlights the urgent need for molecular phylogenetic studies and underscores ethical concerns regarding specimen collection. Conservation contexts differ markedly: Montagne d'Ambre enjoys statutory protection as a national park, while Nosy Komba remains unprotected and vulnerable to tourism and agricultural pressures. These findings contribute to ongoing debates on cryptic diversity, biogeographical isolation, and conservation priorities in northern Madagascar.

Keywords: Calumma cf. radamanus, Nosy Komba, Montagne d'Ambre, Madagascar, chameleon, distribution, conservation, microendemism

Introduction

Calumma radamanus (Mertens, 1933) is a small chameleon distinguished by the presence of a soft rostral appendage and the absence of occipital flaps. For decades it was confused within the Calumma nasutum complex, but integrative taxonomic work combining osteology, morphology, and genetics has revalidated it as a distinct species (Benarson & Nečas, 2025).

Prötzel et al. (2020) provided a detailed account of its morphological variation and documented its distribution in northeastern Madagascar, ranging from Tampolo to Ambatondradama at elevations between 7 and 500 m. On the basis of these findings, and in the absence of alternative described taxa, current consensus among herpetologists is that all northern Madagascar records of small Calumma species with a soft rostral appendage and lacking occipital flaps should be provisionally referred to C. radamanus.

Field observations (Nečas, pers. obs. 2019, 2026) and expert communications (Prötzel, in litt.) reinforce this pragmatic approach, though they also highlight the likelihood of cryptic diversity within the complex (Raxworthy, 1994; D'Cruze et al., 2008). A comprehensive revision integrating molecular phylogenetics, morphometrics, and biogeography remains urgently needed to resolve the taxonomy of these populations.

Geographic and Geological Context of Montagne d'Ambre and Nosy Komba

Montagne d'Ambre, rising in northern Madagascar near Antsiranana, is a volcanic massif that reaches elevations above 1,400 meters. Its geology is dominated by basaltic and trachytic formations, the result of Miocene to Pliocene volcanic activity. The massif functions as a highland island of humid forest within an otherwise drier northern landscape, creating a pronounced ecological gradient. Its montane rainforest, cloud forest, and crater lakes are sustained by orographic rainfall, making Montagne d'Ambre a biodiversity hotspot and a critical refuge for microendemic reptiles and amphibians. The volcanic substrate and isolation of the massif have contributed to the persistence of unique faunal assemblages, with dispersal barriers reinforced by surrounding savannah and dry forest (Andreone et al., 2000; D'Cruze et al., 2008; Raxworthy, 1994).

Nosy Komba, by contrast, is a small volcanic island situated between Nosy Be and the mainland of the Ambanja District. It is characterized by a central volcanic cone rising to about 622 meters, composed of basaltic flows linked to the same intraplate magmatic events that shaped Nosy Be. The island's steep slopes and rugged terrain have limited human settlement, preserving patches of humid forest despite increasing tourism pressure. Geographically, Nosy Komba is separated from the mainland by shallow straits and mangrove belts, which act as effective biogeographical barriers. This insularity, combined with its volcanic origin, has fostered a distinctive reptile fauna, including several chameleon species whose distributions are restricted to the Ambanja island complex (Andreone et al., 2000; Blumgart et al., 2017; The Reptile Database, 2025; IUCN, 2025).

Observations

Calumma cf. radamanus 1 - Montagne d'Ambre

In December 2019, during a night excursion, a female Calumma cf. radamanus was observed in degraded forest edge at perch height 7,5m on a Litchi tree, shaded by larger trees in Montagne d'Ambre, Diana Region, NW Madagascar about 500m from the entrance to the National Park, at an altitude of about 870 m a.s.l.

In January 2026, also during a night excursion, another female Calumma cf. radamanus was observed in degraded forest edge along the road at perch height 1,5m on a bush, shaded by larger trees in the same area, about 300m from thew first locality at an altitude of about 900 m a.s.l.

The animals showed features typical for C. cf. radamanus (sensu Prötzel et al., 2020):

• small size,
• body scalation sub-homogenous with strongly enlarged round flat to semi-lenticular scales on the outer side of the extremities,
• no dorsal crest,
• head with relatively large eyes and weakly expressed cranial crests,
• casque slightly exceeding the level of the dorsum
• no occipital flaps,
• rostral flap small, with smooth margin, situated dorso-rostrally above the snout tip, developed like a tiny ridge rather than a flap, reaching along the canthi rostrales to 40% of the distance to the rostral margin of orbit, just slightly exceeding the snout.

The sub-temporal and parietal areas were covered with strongly enlarged, flat, round scales.

The overall coloration was beige to brownish orange, almost homogeneously alternated with groups of 4 to 6 scales coloured light green. The enlarged scales on extremities were somewhat darker. There were single blue scales scattered irregularly along the tail and legs. Across the body, three faint darker spindle-like stripes were present, lighter in the centre of the widest area. The head was of same base colour as the body. From the rostral flap, which was marked dorsally with darker hue, a similarly darker coloured line crossed the eye turrets to run across the temporal area to fade at the posterior margin of the head. The enlarged scales of the parietal region were darker brown centrally with a lighter margin, giving this area a reticulated pattern; the sub-temporal (cheek) ones were coloured light green, while three of them, just above the mouth angle, were prominently light blue.

Clear character displacement was evident when compared with the syntopic, similarly sized Calumma linotum, identifiable even in females:

Calumma cf. radamanus 2 - Nosy Komba

In December 2019, during a night excursion, a female Calumma cf. radamanus was observed in degraded forest at perch height 2m on a bush, shaded by larger trees in central Nosy Komba, Ambanja District, Diana Region, NW Madagascar at an altitude of about 320 m a.s.l.

The animal showed features typical for C. cf. radamanus (sensu Prötzel et al., 2020):

• small size,
• body scalation sub-homogenous with strongly enlarged round flat to semi-lenticular scales on the outer side of the extremities,
• no dorsal crest,
• head with relatively large eyes and weakly expressed cranial crests,
• casque slightly exceeding the level of the dorsum
• no occipital flaps.

The sub-temporal and parietal areas were covered with strongly enlarged, flat, round scales.

The overall coloration was beige to brownish orange, almost homogeneously alternated with groups of 4 to 6 scales coloured light green in the dorsal half of the flanks and brownish-blueish in the lower one. The enlarged scales on extremities were somewhat darker. The head was of yellowish colour visibly lighter than the body. The rostral flap was yellowish with few darker spots situated in a centrally oriented horizontal faint line. A darker coloured line started just before the nostril and crossed the eye turrets to run across the temporal area to fade before the posterior margin of the head. The enlarged scales of the parietal region, same as the sub-temporal (cheek) ones were coloured light green.

Contrary to typical C. radamanus and C. cf. radamanus 1 from Montagne d'Ambre, the rostral flap was not small, but prominent, rounded, serrated and situated in front of the snout tip.

Clear character displacement was evident when compared with with the syntopic, similarly sized Calumma linotum, identifiable even in females:

All three specimens were photographed and left undisturbed.

Morphometric data (based on photo reference scaling):

Comparison of C. cf. radamanus 1 and 2

Based on the detailed comparison, it is probable that, although provisionally referred to C. radamanus due to the above‑mentioned logic, the Montagne d'Ambre population appears morphologically much closer to C. radamanus s.str.than the population from Nosy Komba. It is very likely that at least the latter, if not both, represent separate taxa. The Nosy Komba specimen exhibits a feature not typical for C. radamanus: a serrated rostral flap. In Montagne d'Ambre, the syntopic species Calumma linotum possesses a prominent serrated rostral flap, so the regular non‑serrated flap remains sufficient to differentiate C. radamanus and stays typical without the necessity of change (Rand, 1961; Prötzel et al., 2020; Benarson & Nečas, 2025). By contrast, the Nosy Komba population may have evolved a serrated flap as an optical differentiation against the smooth‑edged rostral flap of Calumma boettgeri. This could be a feasible explanation for the observed differences. However, as the differences in the form of the rostral flap, in fine morphology and size are otherwise significant, it remains possible that the two populations are not conspecific and may even both—or at least the Nosy Komba population—be not conspecific with C. radamanus.

When males are secured, more can be said about their affinities. DNA analysis could shed light on their phylogeny and relationships, but such work was beyond the scope of the non‑invasive observations undertaken without disturbing or collecting the animals and without taking DNA samples. The populations appear restricted to tiny refugia, and collecting specimens would cross ethical boundaries given their conservation status.

Chameleonocenoses

The chameleonocenoses (compiled based on literature data and own observations) show two distinct sympatric assemblages, each with its own ecological and taxonomic dynamics.

Montagne d'Ambre

This massif supports a high diversity of Calumma species (C. amber, C. ambreense, C. linotum, C. cf. radamanus) alongside large-bodied Furcifer taxa (F. oustaleti, F. pardalis, F. petteri, F. timoni) and several leaf chameleons of the genus Brookesia. The sympatry here is striking:

• Calumma lionotum and C. cf. radamanus overlap, yet are morphologically distinct, particularly in rostral appendage form.
• C. amber and C. ambreense are both microendemics of the massif, reinforcing Montagne d'Ambre's role as a diversification hotspot.
• The coexistence of multiple Brookesia species (antakarana, tuberculata) highlights niche partitioning at the forest floor level.

Nosy Komba

The island hosts fewer Calumma taxa, but the assemblage is equally interesting: C. boettgeri, C. cf. radamanus, and F. pardalis occur alongside Brookesia ebenaui, B. minima, and B. stumpffi.

• The sympatry of C. boettgeri and C. cf. radamanus is particularly important. The serrated rostral flap in the Nosy Komba C. cf. radamanus may function as an optical differentiation against the smooth flap of C. boettgeri, consistent with Rand's (1961) hypothesis that ornamentation serves species recognition.
• F. pardalis occurs in both Montagne d'Ambre and Nosy Komba, acting as a widespread generalist that overlaps with microendemic taxa.
• The presence of three Brookesia species on Nosy Komba suggests strong microhabitat partitioning even within a small island environment.

The sympatric occurrence of multiple Calumma species in both sites underscores the role of ornamentation and fine morphology in species recognition and reproductive isolation. Rand (1961) argued that sympatric chameleons never share identical ornaments, and your data fit this pattern: serrated vs. smooth rostral flaps, presence vs. absence of occipital flaps, and differences in crest development all serve as distinguishing signals.

Montagne d'Ambre represents a montane diversification center, while Nosy Komba illustrates island microendemism with optical differentiation pressures. Together, they highlight how sympatry drives morphological divergence and may conceal cryptic taxa within what is currently referred to as C. radamanus.

Conservation Context and Threats

Montagne d'Ambre National Park, situated in northern Madagascar, represents one of the earliest legally protected landscapes in the country. Established in 1958, the park encompasses 30,538 hectares of volcanic highlands clothed in evergreen rainforest. Classified under IUCN Category II, it is managed by Madagascar National Parks and enjoys full statutory protection. Its conservation significance is underscored by recognition as an Alliance for Zero Extinction site, an Important Bird Area, and a Key Biodiversity Area (IUCN, 2025). The park shelters six species of lemurs, including locally endemic taxa, and is equally notable for its herpetofaunal diversity. Numerous reptiles inhabit its forests, including endemic chameleons, leaf-tailed geckos, and snakes, making Montagne d'Ambre a cornerstone of northern Malagasy biodiversity (Andreone et al., 2000; D'Cruze et al., 2008).

By contrast, Nosy Komba, a small volcanic island near Nosy Be, covers approximately 2,500 hectares but lacks formal designation within Madagascar's protected area system (IUCN, 2025; The Reptile Database, 2025). It has no IUCN category and is not legally protected, though it hosts conservation research initiatives led by non-governmental organizations. Despite its ecological richness, particularly in reptiles and amphibians, Nosy Komba remains vulnerable to tourism and agricultural pressures, illustrating the precariousness of biodiversity outside statutory frameworks.

References

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Benarson, E. S., & Nečas, P. (2025). Ecological and taxonomic notes on Calumma radamanus (Mertens, 1933) in the Antalaha Region of Northeastern Madagascar. Archaius, 2(2), 2–15.

D'Cruze, N., Köhler, J., Franzen, M., & Glaw, F. (2008). A conservation assessment of the amphibians and reptiles of the Forêt d'Ambre Special Reserve, north Madagascar. Madagascar Conservation & Development, 3(1), 44–54.

IUCN. (2025). Calumma radamanus. The IUCN Red List of Threatened Species. Retrieved from www.iucnredlist.org

Mertens, R. (1933). Chamaeleo radamanus sp. nov. Senckenbergiana Biologica, 15, 1–10.

Prötzel, D., Glaw, F., Ratsoavina, F. M., Vences, M., & Köhler, J. (2020). Morphological variation and distribution of Calumma radamanus. Salamandra, 56(1), 40–55.

Rand, A. S. (1961). A suggested function of the ornamentation of East African forest chameleons. Copeia, 1961(4), 411–414. https://doi.org/10.2307/1439582

Raxworthy, C. J. (1994). A rainforest survey of amphibians, reptiles and small mammals at Montagne d'Ambre, Madagascar. Biological Conservation, 69(3), 195–204.

The Reptile Database. (2025). Calumma radamanus. Retrieved from www.reptile-database.org