Testing the predictability of morphological evolution in contrasting thermal environments.

Gaining the ability to predict population responses to climate change is a pressing concern. Using a "natural experiment," we show that testing for divergent evolution in wild populations from contrasting thermal environments provides a powerful approach, and likely an enhanced predictive power for responses to climate change. Specifically, we used a unique study system in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity, adjacent to populations in ambient-temperature water. We focused on morphological traits across six pairs from warm and cold habitats. We found that fish from warm habitats tended to have a deeper mid-body, a subterminally orientated jaw, steeper craniofacial profile, and deeper caudal region relative to fish from cold habitats. Our common garden experiment showed that most of these differences were heritable. Population age did not appear to influence the magnitude or type of thermal divergence, but similar types of divergence between thermal habitats were more prevalent across allopatric than sympatric population pairs. These findings suggest that morphological divergence in response to thermal habitat, despite being relatively complex and multivariate, are predictable to a degree. Our data also suggest that the potential for migration of individuals between different thermal habitats may enhance nonparallel evolution and reduce our ability to predict responses to climate change.

A force-measuring and behaviour-recording system consisting of 24 individual 3D force plates for the study of single limb forces in climbing animals on a quasi-cylindrical tower.

This study describes the design of a new force measuring array with a quasi-cylindrical surface for measuring the 3D ground reaction forces of animals climbing on a surface with high curvature. This force-measuring array was assembled from 24 individual 3D force sensors, each with a resolution at the millinewton (mN) level, which were installed from top to bottom in four columns and six rows, with sensors in neighbouring columns staggered in height. Three cameras were used to simultaneously record the climbing behaviours of animals (in these experiments tree frogs) on the cylinder-like force measuring array. We were thus able to simultaneously record the ground reaction forces of each of the four limbs of tree frogs (here six individuals of the Chinese gliding or flying frog, Rhacophorus dennysi, with forelimb spans in the range 163-201 mm) climbing or descending both smooth and rough surfaces on a quasi-cylindrical structure with an overall diameter of 79 mm. We describe the design and calibration of the individual force sensors, their installation and arrangement on the quasi-cylindrical climbing tower, the recording of ground reaction forces and climbing behaviour, data transformations necessitated by the angular relationship of neighbouring sensors, and data processing using MATLAB scripts. Additionally, we present preliminary data on the use of a clamping grip by climbing frogs and the existence of small pull-off forces that aid toe-pad detachment at the end of each locomotor stance phase.

The biomechanics of tree frogs climbing curved surfaces: a gripping problem.

The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the 44 and 13 mm diameter cylinders, frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualise substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots.