Relationships between dietary breadth and flexibility in jaw movement: A case study of two recently diverged insular populations of Podarcis lizards

The kinematics of lizard feeding are the result of complex interactions between the craniocervical, the hyolingual, and the locomotor systems. The coordinated movement of these elements is driven by sensory feedback from the tongue and jaws during intraoral transport. The kinematics of jaw movements have been suggested to be correlated with the functional characteristics of the prey consumed, such as prey mobility and hardness. However, whether and how dietary breadth correlates with the flexibility in the behavioral response has rarely been tested, especially at the intraspecific level. Here we tested whether an increase in dietary breadth was associated with a greater behavioral flexibility by comparing two recently diverged populations of insular Podarcis lizards differing in dietary breadth. To do so, we used a stereoscopic high-speed camera set-up to analyze the jaw kinematics while offering them different prey types. Our results show that prey type impacts kinematics, especially maximum gape, and maximum opening and closing speed. Furthermore, the behavioral flexibility was greater in the population with the greater dietary breadth, suggesting that populations which naturally encounter and feed on more diverse prey items show a greater ability to modulate their movements to deal with variation in functionally relevant prey properties. Finally, the more generalist population showed more stereotyped movements suggesting a finer motor control.

Flexibility in locomotor-feeding integration during prey capture in varanid lizards: effects of prey size and velocity

Feeding movements are adjusted in response to food properties, and this flexibility is essential for omnivorous predators as food properties vary routinely. In most lizards, prey capture is no longer considered to solely rely on the movements of the feeding structures (jaws, hyolingual apparatus), but instead is understood to require the integration of the feeding system with the locomotor system (i.e., coordination of movements). Here, we investigate flexibility in the coordination pattern between jaw, neck and forelimb movements in omnivorous varanid lizards feeding on four prey types varying in length and mobility: grasshoppers, live newborn mice, adult mice and dead adult mice. We test for bivariate correlations between 3D locomotor and feeding kinematics, and compare the jaw-neck-forelimb coordination patterns across prey types. Our results reveal that locomotor-feeding integration is essential for the capture of evasive prey, and that different jaw-neck-forelimb coordination patterns are used to capture different prey types. Jaw-neck-forelimb coordination is indeed significantly altered by the length and speed of the prey, indicating that a similar coordination pattern can be finely tuned in response to prey stimuli. These results suggest feed-forward as well as feedback modulation of the control of locomotor-feeding integration. As varanids are considered to be specialized in the capture of evasive prey (although they retain their ability to feed on a wide variety of prey items), flexibility in locomotor-feeding integration in response to prey mobility is proposed to be a key component in their dietary specialization.

Quantitative analysis of the effect of prey properties on feeding kinematics in two species of lizards

Studies of the functional morphology of feeding have typically not included an analysis of the potential for the kinematics of the gape cycle to vary based on the material properties of the prey item being consumed. Variation in prey properties is expected not only to reveal variation in feeding function,but allows testing of the functional role of the phases of the gape cycle. The jaw kinematics of two species of lizards are analyzed when feeding trials are conducted using quantitative control of prey mass, hardness and mobility. For both species, there were statistically significant prey effects on feeding kinematics for all the prey properties evaluated (i.e. prey mass, hardness and mobility). Of these three prey properties, prey mass had a more significant effect on feeding kinematics than prey hardness or mobility. Revealing the impact of varying prey properties on feeding kinematics helps to establish the baseline level of functional variability in the feeding system. Additionally,these data confirm the previously hypothesized functional role of the slow open (SO) phase of the gape cycle as allowing for physical conformation of the tongue to the surface of the food bolus in preparation for further intraoral transport.

The functional significance of the lower temporal bar inSphenodon punctatus

One of the major conundrums in the evolution of vertebrate cranial design is the early loss and frequent redevelopment of the lower temporal bar in diapsids. Whereas it has been proposed that the reduction of the lower temporal bar allows for an increase in jaw adductor mass and bite force, this has never been tested experimentally. As the sole recent representative of the Rhynchocephalia, Sphenodon punctatus is different from other extant lepidosaurians in having a fully diapsid skull and in using translation to shear food rather than using the typical puncture-crushing of other lizards. In the present study, we show that S. punctatus has lower bite forces compared with extant lepidosaurians. Moreover, dissection of the jaw muscles of an adult S. punctatus shows that the mass of the external jaw adductor muscle is significantly smaller than that of lizards, probably accounting for the lower measured bite forces. An analysis of the transport cycles suggests a less efficient prey transport in S. punctatuscompared with an agamid lizard of similar size in terms of handling time and number of cycles needed to crush similar prey. Modelling of biting in S. punctatus suggests a different role of the jaw adductor muscles during biting and a clear functional role for the lower temporal bar. Future finite element models may provide better insights into the function of the lower temporal bar in S. punctatus.