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A composite of a series of video images illustrating how the Malagasy dwarf chameleon’s tail curls and contacts the substrate during locomotion. |
The Malagasy
Dwarf Chameleons (Brookesia sp) are unusual for several reasons. They
are exceptionally small for members of the Chamaeleonidae, they are very
terrestrial (most chameleons are very arboreal), they have very short tails
(most chameleons have relatively long tails), and they have bodies that mimic
dried leaves. Several recent papers report on some interesting aspects on these interesting lizards.
Boistel et al.
(2010) examined the walking behavior of these lizards and found that while they
have grasping feet used to hold on to narrow substrates, they also place the
tail on the substrate when walking on broad substrates to improve their
stability. Using three-dimensional synchrotron X-ray phase-contrast imaging,
the authors demonstrate a set of unique specializations in these unusual
lizards. 3D reconstructions of the vertebrae inside the tail show morphological
specializations that explain this ability. The tail tip is relatively mobile
because there are fewer and finer vertebrae with stronger ventral tendons. The
tail is therefore able to bend and provide the chameleon with a fifth point of
contact with the ground. The inner ear morphology also is involved in balance.
It has a highly specialized structure so that the ear could be adapted to
detecting weak accelerations and help to correct posture. The high-resolution
images obtained at the ESRF (The European Synchrotron Radiation Facility) were
crucial in order to visualize the tail tendons, this could not have been
accomplished with conventional X-ray technology. Also, the detailed
reconstruction of the inner ears enabled precise comparison of the subtle
structures within each species’ ear. The authors point out that it will be interesting
to compare Brookesia's adaptations
with those of genus Rhampholeon, an
independent lineage of small ground-dwelling chameleons to test whether a
similar tail-assisted locomotor mechanism is present.
Randrianantoandro
et al. (2010) examined the abundance of chameleons at eight locations in Madagascar
and found that in deciduous forest in Menabe, western Madagascar. Brookesia brygooi was the most abundant
species, with a population density estimated at
35 per hectare. Furcifer
species were less common, with densities of
about 7.2 per hectare for F.
labordi, 3.0 per hectare for Furcifer sp. and 1.3 per hectare F. oustaleti. Abundance of B. brygooi varied with altitude and the
authors did not detect any clear problems created by logging. However, a lack of
information about the chameleons diurnal habitat use is needed to assess the
tolerance of these lizards to forest degradation. However, Rakotondravony et
al. (2010) report that common species in original forest (e.g., Brookesia)
were completely lacking in fragments.
Andrews and
Karsten (2010) examined molecular phylogenies of chameleons and found that
oviparity (egg-laying) is ancestral. Viviparity (live birth) has apparently evolved
at least twice in the chameleons, once in Bradypodion
and again in members of the Trioceros
bitaeniatus clade. Viviparous species tend to be medium-sized as a result
of convergence from either small-sized ancestors or large-sized ancestors,
respectively. Also viviparous species do not differ from oviparous species in
clutch size, hatchling size, or the trade-off between clutch and hatchling
size. The authors found that the basal chameleons (Brookesia, Rhampholeon
and Rieppeleon) are small-sized and
have developmental rates comparable with those of other lizards. However, the
more derived chameleons (Calumma, Chamaeleo, Trioceros and Furcifer)
are mostly large and all have relatively slow developmental rates. Some
of the derived chameleon clades also exhibit developmental arrest (the embryo goes
into stasis) and incubation periods may be extended to 6–10 months or more.
Developmental arrest is apparently an adaptation to dry, highly seasonal
climates where the time period favorable for oviposition and hatching is short. Long
incubation periods thus ensure that hatching occurs when temperatures, rainfall,
and food availability are appropriate for the young.
Literature
Andrews, R. M.
and K. B. Karsten. 2010. Evolutionary innovations of squamate reproductive and
developmental biology in the family Chamaeleonidae. Biological Journal of the Linnean Society, 100: 656–668. doi:
10.1111/j.1095-8312.2010.01442.x
Boistel, R., A.
Herrel, G. Daghfous, P.-A. Libourel, E. Boller, P. Tafforeau, and V. Bels.
2010. Assisted walking in Malagasy dwarf chamaeleons. Biology Letters 2010 : rsbl.2010.0322v1-rsbl20100322.
Rakotondravony,
D., A. Raselimanana, J. Ratsimbazaf, J. S. Sparks, L. Wilmé and J. U. Ganzhorn.
2010. Patterns of species change in anthropogenically disturbed forests of
Madagascar. Biological Conservation 143:2351-2362.
Randrianantoandro,
C., B. Razafimahatratra, M. Soazandry, J. Ratsimbazafy, R. K. B. Jenkins. 2010.
Habitat use by chameleons in a deciduous forest in western Madagascar. Amphibia -Reptilia 31:27-35.