A Tarsal Spur Aberration in Chamaeleo calyptratus
It is widely recognized that certain species of the genus Chamaeleo possess a remarkable secondary sexual characteristic: the male tarsal spur. This is exemplified by species such as Chamaeleo africanus, C. arabicus, C. calyptratus, C. dilepis, C. monachus, and others. The tarsal spur has been utilized as a key diagnostic feature for distinguishing between species (e.g., C. calcaricarens from C. africanus and C. incognitus from C. dilepis). In some species, the spur is consistently present in males while being consistently absent in females. In others, such as Chamaeleo zeylanicus and certain populations of C. dilepis, substantial variation in the spur's presence, absence, and size occurs among females.
The exact function of the tarsal spur remains unknown. To date, no observations have been published indicating that chameleons actively use this structure. Furthermore, there have been no documented cases of females selecting males based on the spur's presence; this is improbable since males approach females from various angles—either from the front or the rear—making the spur less visible. Similarly, no evidence supports the notion that males identify females based on the absence of the spur. In both scenarios, other, less conspicuous traits, such as casques, crests, body shapes, enlarged scales, and color patterns, as well as behavioral patterns, including "pancaking," body inflation, and specific movements, appear to play a more significant role in sex determination. Nevertheless, the tarsal spur holds considerable importance for sex differentiation in scientific research and breeding programs in captivity.
It has been repeatedly reported that, due to inbreeding and incorrect incubation temperatures, the presence or absence of the tarsal spur in the Yemen chameleon,
Chamaeleo calyptratus, can be altered. The following aberrations are documented:
presence of an underdeveloped tarsal spur in both males and females,
absence of the tarsal spur in males, and
presence of a fully developed tarsal spur in females.
This is the first reported case of a unilateral deviation: a female exhibiting a fully developed tarsal spur on the left hind foot, while the spur is absent on the right side. This case likely represents further evidence of genetic deterioration within this species due to extensive inbreeding in captivity.