Why cordylid lizards are black at the south-western tip of Africa
Date
2009-03
Authors
Janse van Rensburg, D. A.
Mouton, P. le F. N.
Van Niekerk, Adriaan
Journal Title
Journal ISSN
Volume Title
Publisher
Blackwell Publishing Ltd
Abstract
There is a high incidence of melanism among the cordylid lizards of Africa and it
was suggested that melanism has a thermoregulatory function in these species. One
prediction of the thermal melanism hypothesis would be that melanistic cordylid
species would be restricted to cool environments. The aim of our study was to
determine the climatic conditions with which melanistic cordylids are currently
associated.Distributional data for the eight melanistic cordylid taxa occurring at the
south-western tip of Africa were obtained from the CapeNature State of Biodiversity
database. Using GIS and principal component analyses, the climatic variables
best describing the geographical distribution of melanistic cordylids were investigated.
We found that several melanistic cordylid populations show a distinct
association with a high incidence of fog and cloud cover, underscoring the thermal
melanism hypothesis. Several other populations, however, do not show such an
association. We conclude that some species, such as Pseudocordylus capensis, have a
morphology that provides them with great flexibility in habitat use, allowing them to
overcome the constraints of melanism in warm environments. The available
information suggests that melanism in cordylids evolved during the Miocene in
response to the development of the cold Benguela Current along the west coast of
Africa.We also conclude that viviparity, a sit-and-wait foraging strategy and a rockdwelling
lifestyle would have preadapted cordylids for survival in cool conditions
brought about by the development of the cold Benguela Current. These conditions
would have been unfavourable for oviparous, active-foraging lizards. The cooccurrence
ofmelanistic lizards andmelanistic molluscs at the Landdroskop locality
casts some doubt on improved heating rates as the only explanation for melanism in
cordylids, because molluscs are not heliothermic baskers.
Description
The original publication is available at http://onlinelibrary.wiley.com/
Keywords
Cordylid lizards -- Africa, Southwestern, Cordylids -- Melanism -- Effect of climate on -- Africa, Southwestern, Thermoregulation, Vivipartity
Citation
Janse Van Rensberg, D. A., Mouton, P. le F. N. & Van Niekerk, A. 2009. Why cordylid lizards are blackat the south-western tip of Africa. Journal of Zoology, 278, 333-341, http://onlinelibrary.wiley.com/