Field Notes: Calumma gastrotaenia and the Paradox of Parasites and Habitat Loss

An intriguing observation from the field in eastern Madagascar: populations of the stump-nosed chameleon (Calumma gastrotaenia) in the Manambato (Masohely) / Mitsinjo / Andasibe region present a striking ecological contrast regarding parasite load and habitat pressures.

The Maromizaha Forest: Resilient Populations Amid Chronic Infestation

In the undisturbed rainforests of the Maromizaha (Eastern Escarpment), Calumma gastrotaenia populations remain remarkably robust throughout the year across all age and sex groups.

However, individuals here are chronically parasitized by blood-sucking mites, which can be found on this species consistently year-round. Despite this heavy, persistent ectoparasite load, the host population shows no apparent ill effects; the lizards maintain high vitality, robust body conditions, and stable population densities.

Andasibe-Mitsinjo: A Dramatic Population Collapse

In stark contrast, the situation in the Andasibe-Mitsinjo area tells a troubling story of decline. Once common, Calumma gastrotaenia has nearly vanished from parts of this well-known zone:

• 2024: Only a single specimen sighting was reported by local guides.
• 2025: Just 6 specimens were sighted across the entire area.

Unraveling the Causes of Decline

While the chronic presence of mites in Maromizaha appears to be a natural, well-tolerated host-parasite dynamic, the collapse in Andasibe-Mitsinjo points to acute anthropogenic and environmental stressors:

1. Lighting and Microclimate Modification: Alterations to the forest canopy and edge effects modify humidity and temperature, critically impacting sensitive montane forest species.
2. Habitat Fragmentation: Ongoing biotope modification restricts dispersal and genetic flow.
3. The Silent Trap—Desmodium uncinatum: The proliferation of the invasive tick-trefoil (Desmodium uncinatum) poses a lethal mechanical threat. Its adhesive, hook-bearing trichomes (burrs) catch and entangle vulnerable neonates, juveniles, and even adults, pinning them down and leading to starvation and death.

While natural parasites like mites may be easily shrugged off by healthy ecosystems, compounded environmental degradation and invasive flora present a lethal synergy that targeted conservation efforts urgently need to address.