Functional consequences of morphological differentiation between populations of the Cape Dwarf Chameleon (Bradypodion pumilum)

Department of Botany and Zoology, University of Stellenbosch, Matieland 7602, South Africa
Biological Journal of the Linnean Society (Impact Factor: 2.26). 10/2011; 104(3):692 - 700. DOI: 10.1111/j.1095-8312.2011.01764.x

ABSTRACT Variation in phenotype between species or populations of the same species living in different habitats is often explained in an adaptive context with local habitat differences driving selection on morphological traits relevant in a given ecological context. Previous studies have demonstrated significant differences in limb and tail morphology between populations of the Cape Dwarf Chameleon (Bradypodion pumilum) living in closed vs. open habitats. However, the adaptive nature of the observed differences remains unclear. Here, we quantify the structural habitat use in two different populations, test whether the random habitat differs between the two sites and whether or not chameleons select perches randomly. Next, we test whether morphology is correlated with structural habitat use and test for differences in performance between populations. Our results demonstrate that habitats are structurally different, that chameleons in the two populations use perches of different diameters and that, in one of the populations, chameleons select relatively wider perches than available at random. Performance traits (hand and tail grip performance and sprint speed) are correlated with morphology (hand size, tail length and tibia length) and differ between sexes and populations. Moreover, performance is dependent on dowel size. These results suggest that differences in performance between populations are indeed adaptive and indicate the existence of true ecomorphs in chameleons of the genus Bradypodion. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 692–700.

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Available from: Anthony Herrel, Sep 26, 2015
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    • "Perch diameter availability and sleeping perch use have been quantified, and differ between the morphs. The woodland morph sleeps on larger diameter (2.82 mm) perches than the fynbos morph (1.98 mm) (Herrel et al., 2011). However, few data exist for daytime perch use, which is critical given that these chameleons are diurnal. "
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    ABSTRACT: Arboreal lizards are extremely effective at moving in structurally complex habitats, including surfaces of varying diameter and incline. Chameleons exemplify this by exhibiting a number of morphological specializations for moving in these habitats, including the use of prehensile feet and tail to grasp branches. Despite their unique morphology and behaviour, little is known about how locomotor movements vary between species. In addition, some species, such as the Cape Dwarf Chameleon, Bradypodion pumilum, consist of two morphs that differ in ecology, morphology, and behaviour. The two morphs can be found in either closed canopy woodland habitat or relatively open fynbos habitat. The morph that occupies the woodland habitat tends to be larger and utilizes larger diameter perches. Although their ecological and morphological divergence is established, whether this translates into differences in three-dimensional kinematics of locomotion is not known. Given the potentially strong selective pressures from structurally different habitats, kinematic differences might reveal the functional basis of incipient speciation. We determined that the two morphs diverge significantly in multidimensional kinematic space, and that this occurs for the forelimb and hindlimb independently. These differences outweigh the effects of substrate within each morph, although the differences between morphs were more pronounced on the vertical treatments.
    Biological Journal of the Linnean Society 05/2015; 116:27-40. DOI:10.1111/bij.12566 · 2.26 Impact Factor
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    • "This finding is not altogether surprising considering chameleons move extremely slowly and tend to use crypsis instead of running to avoid predation (Brain 1961; Burrage 1973; Tolley & Burger 2007). These results also indicate that sprint speed is not just a by-product of limb length, as suggested as a possible explanation for performance differences between open and closed-canopy B. pumilum forms (Herrel et al. 2011). Indeed, the combination of limbs and feet correlated best with sprint speed for each form, but this appears to be simply a function of body size. "
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    ABSTRACT: 1. Evidence that morphological traits associated with particular environments are functionally adapted to those environments is a key component to determining the adaptive nature of radiations. Adaptation is often measured by testing how organisms perform in diverse habitats, with performance traits associated with locomotion thought to be amongst the most ecologically relevant. 2. We therefore explored whether there are relationships between morphology, locomotor performance traits (sprint speed, forefoot and tail grip strength on broad and narrow dowels) and microhabitat use in five phenotypic forms of a recent radiation of dwarf chameleon - the Bradypodion melanocephalum-B. thamnobates species complex - to determine whether morphological differences previously identified between the forms are associated with functional adaptations to their respective habitats, which can be broadly categorised as open or closed canopy vegetation. 3. The results showed significant differences in both absolute and relative performance values between the phenotypic forms. Absolute performance suggests there are two phenotypic groups – strong (B. thamnobates and Type B) and weak (B. melanocephalum and Types A and C). Relative performance differences highlighted the significance of forefoot grip strength among these chameleons, with the closed canopy forms (B. thamnobates, Types B and C) exceeding their open canopy counterparts (B. melanocephalum, Type A). Little to no differences were detected between forms with respect to sprint speed and tail strength. These results indicate that strong selection is acting upon forefoot grip strength and has resulted in morphological adaptions that enable each phenotypic form to conform with the demands of its habitat. 4. This study provides evidence for the parallel evolution of forefoot grip strength among dwarf chameleons, consistent with the recognition of open and closed canopy ecomorphs within the genus Bradypodion.
    Functional Ecology 01/2014; 28(3):702-713. DOI:10.1111/1365-2435.12210 · 4.83 Impact Factor
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    • "The common fiscal (Lanius collaris) was used as a model predator by Stuart-Fox et al. (2006a), who found that Bradypodion transvaalense readily avoided these predators (see Chapter 6), and these authors considered that common fiscals are likely to exert a strong selection on chameleon antipredator responses. However, the substantial grip of some individual chameleons (see Herrel et al. 2011; Chapter 4) may help them to escape predation from at least some shrikes. In Cape Town, an adult common fiscal was seen trying to remove an adult Bradypodion pumilum from its perch on a reed by using its weight to hang from a single limb (G.A. Millar, personal communication). "
    01/2013: pages 85-113; University of California Press.
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