Impacts of temperature on performance in two species of South African dwarf chameleons,<i>Bradypodion pumilum</i>and<i>B. occidentale</i>

Segall, Marion; Tolley, Krystal A.; Vanhooydonck, Bieke; Measey, John; Herrel, Anthony

doi:10.1242/jeb.092353

Cited by 6 publications

(7 citation statements)

References 52 publications

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“…Fasted states involved starving lizards for a 48‐h period prior to measuring T pref in the thermal gradient (Segall et al. ). All lizards defecated during this period.…”

Section: Methodsmentioning

confidence: 99%

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Differences in the thermal physiology of adult Yarrow's spiny lizards (Sceloporus jarrovii) in relation to sex and body size

Beal

Lattanzio

Miles

2014

Ecology and Evolution

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Sexual size dimorphism (SSD) is often assumed to reflect the phenotypic consequences of differential selection operating on each sex. Species that exhibit SSD may also show intersexual differences in other traits, including field-active body temperatures, preferred temperatures, and locomotor performance. For these traits, differences may be correlated with differences in body size or reflect sex-specific trait optima. Male and female Yarrow's spiny lizards, Sceloporus jarrovii, in a population in southeastern Arizona exhibit a difference in body temperature that is unrelated to variation in body size. The observed sexual variation in body temperature may reflect divergence in thermal physiology between the sexes. To test this hypothesis, we measured the preferred body temperatures of male and female lizards when recently fed and fasted. We also estimated the thermal sensitivity of stamina at seven body temperatures. Variation in these traits provided an opportunity to determine whether body size or sex-specific variation unrelated to size shaped their thermal physiology. Female lizards, but not males, preferred a lower body temperature when fasted, and this pattern was unrelated to body size. Larger individuals exhibited greater stamina, but we detected no significant effect of sex on the shape or height of the thermal performance curves. The thermal preference of males and females in a thermal gradient exceeded the optimal temperature for performance in both sexes. Our findings suggest that differences in thermal physiology are both sex- and size-based and that peak performance at low body temperatures may be adaptive given the reproductive cycles of this viviparous species. We consider the implications of our findings for the persistence of S. jarrovii and other montane ectotherms in the face of climate warming.

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“…Fasted states involved starving lizards for a 48‐h period prior to measuring T pref in the thermal gradient (Segall et al. ). All lizards defecated during this period.…”

Section: Methodsmentioning

confidence: 99%

“…The T pref of all lizards was measured first in a fasted state and then in a fed state. Fasted states involved starving lizards for a 48-h period prior to measuring T pref in the thermal gradient (Segall et al 2013). All lizards defecated during this period.…”

Section: Thermal Preferencementioning

confidence: 99%

Differences in the thermal physiology of adult Yarrow's spiny lizards (Sceloporus jarrovii) in relation to sex and body size

Beal

Lattanzio

Miles

2014

Ecology and Evolution

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“…Chameleons were first allowed to thermoregulate in a sun/shade setting to attain their preferred body temperature (between 28 and 32°C; see Segall et al 2013). All performance trials were then performed at ambient temperature.…”

Section: P E R F O R M a N C Ementioning

confidence: 99%

Linking microhabitat structure, morphology and locomotor performance traits in a recent radiation of dwarf chameleons

et al. 2014

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Summary 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 among the most ecologically relevant. 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–Bradypodion 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 categorized as open or closed‐canopy vegetation. 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 adaptations that enable each phenotypic form to conform with the demands of its habitat. 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.

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“…Chameleons were allowed to thermoregulate in a sun/shade setting to obtain their preferred body temperature (between 28–32°C [44] ). In vivo bite force was then measured in Newtons (N) at ambient temperature using an isometric force transducer (Kistler type 9203, ±500 N) connected to a bite plate and a Kistler charge amplifier (type 5995A, Kistler Inc., Winterthur, Switzerland) [3] , [4] .…”

Section: Methodsmentioning

confidence: 99%

Sexual Dimorphism in Bite Performance Drives Morphological Variation in Chameleons

et al. 2014

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Phenotypic performance in different environments is central to understanding the evolutionary and ecological processes that drive adaptive divergence and, ultimately, speciation. Because habitat structure can affect an animal’s foraging behaviour, anti-predator defences, and communication behaviour, it can influence both natural and sexual selection pressures. These selective pressures, in turn, act upon morphological traits to maximize an animal’s performance. For performance traits involved in both social and ecological activities, such as bite force, natural and sexual selection often interact in complex ways, providing an opportunity to understand the adaptive significance of morphological variation with respect to habitat. Dwarf chameleons within the Bradypodion melanocephalum-Bradypodion thamnobates species complex have multiple phenotypic forms, each with a specific head morphology that could reflect its use of either open- or closed-canopy habitats. To determine whether these morphological differences represent adaptations to their habitats, we tested for differences in both absolute and relative bite performance. Only absolute differences were found between forms, with the closed-canopy forms biting harder than their open-canopy counterparts. In contrast, sexual dimorphism was found for both absolute and relative bite force, but the relative differences were limited to the closed-canopy forms. These results indicate that both natural and sexual selection are acting within both habitat types, but to varying degrees. Sexual selection seems to be the predominant force within the closed-canopy habitats, which are more protected from aerial predators, enabling chameleons to invest more in ornamentation for communication. In contrast, natural selection is likely to be the predominant force in the open-canopy habitats, inhibiting the development of conspicuous secondary sexual characteristics and, ultimately, enforcing their overall diminutive body size and constraining performance.

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Impacts of temperature on performance in two species of South African dwarf chameleons,Bradypodion pumilumandB. occidentale

Cited by 6 publications

References 52 publications

Differences in the thermal physiology of adult Yarrow's spiny lizards (Sceloporus jarrovii) in relation to sex and body size

Differences in the thermal physiology of adult Yarrow's spiny lizards (Sceloporus jarrovii) in relation to sex and body size

Linking microhabitat structure, morphology and locomotor performance traits in a recent radiation of dwarf chameleons

Sexual Dimorphism in Bite Performance Drives Morphological Variation in Chameleons

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