From micro to macroevolution: drivers of shape variation in an island radiation of Podarcis lizards.

Phenotypictraits have been shown to evolve in response to variation in the environment. However, the evolutionary processes underlying the emergence of phenotypic diversity can typically only be understood at the population level. Consequently, how subtle phenotypic differences at the intraspecific level can give rise to larger-scale changes in performance and ecology remains poorly understood. We here tested for the covariation between ecology, bite force, jaw muscle architecture, and the three-dimensional shape of the cranium and mandible in 16 insular populations of the lizards Podarcis melisellensis and P. sicula. We then compared the patterns observed at the among-population level with those observed at the interspecific level. We found that three-dimensional head shape as well as jaw musculature evolve similarly under similar ecological circumstances. Depending on the type of food consumed or on the level of sexual competition, different muscle groups were more developed and appeared to underlie changes in cranium and mandible shape. Our findings show that the local selective regimes are primary drivers of phenotypic variation resulting in predictable patterns of form and function. Moreover, intraspecific patterns of variation were generally consistent with those at the interspecific level, suggesting that microevolutionary variation may translate into macroevolutionary patterns of ecomorphological diversity.

INTRAMUSCULAR ADMINISTRATION OF KETAMINE-MEDETOMIDINE ASSURES STABLE ANAESTHESIA NEEDED FOR LONG-TERM SURGERY IN THE ARGENTINE TEGU SALVATOR MERIANAE.

To define a protocol of anesthesia for long-duration invasive surgery in a lizard, eight young adult Argentine tegus ( Salvator merianae) of mean body weight 3.0 kg (interquartile range [IQR] 3.40-2.65) were anesthetized with a mixture of ketamine (K) and medetomidine (M) at 19°C, injected intramuscularly and equally distributed in the four limbs. As the experimental surgery procedure required a prolonged deep anesthesia with a good myorelaxation (between 16 and 21 hr), reinjections were required and reflexes were checked during surgery. Times for anesthetic induction, anesthetic reinjection, and recovery periods were recorded for five different combinations of ketamine-medetomidine: 1) 66 mg/kg K + 100 µg/kg M; 2) 80 mg/kg K + 100 µg/kg M; 3) 100 mg/kg K + 130 µg/kg M; 4) 125 mg/kg K + 200 µg/kg M; and 5) 150 mg/kg K + 200 µg/kg M. The effect on the recovery speed of the postoperative atipamezole injection was also evaluated. The median induction time was 30 (IQR 35-27.5) min with no statistical difference between all the concentrations tested. The first reinjection of half a dose was administered after a mean of 5 hr (5.64 hr, IQR 5.95-4.84) as were the subsequent reinjections of a quarter dose (3.99 hr, IQR 5.98-3.23). Intramuscular administration of the ketamine-medetomidine combination is a simple, rapid, and efficient anesthesia for long-term surgery (>12 hr). A mix of 100 mg/kg ketamine and 200 µg/kg medetomidine, with reinjections every 4 hr of half a dose of the previous injection can maintain a good quality of anesthesia for at least 16 hr. The injection of atipamezole after the surgery reverses the effects of medetomidine and permits a reduction of the recovery period.

Effects of testosterone on morphology, performance and muscle mass in a lizard.

Because sexual selection pressures are high in sexually dimorphic organisms, morphological, physiological and performance traits are often studied in a sexual selection context. The proximate mechanisms underlying evolutionary change in these traits, however, remain largely unstudied. Here, we examined the role of steroids in shaping morphology and physiological performance in males of a sexually dimorphic lizard (Gallotia galloti). We compared morphology and physiological performance of males with experimentally elevated testosterone levels to sham-operated males. Before surgery, inter-individual variation in plasma testosterone levels correlated positively with bite force capacity. Administration of exogenous testosterone resulted in an increase of the mass of both jaw closing and locomotory muscles compared with sham-operated individuals, but the responsiveness varied considerably among muscle groups. In contrast to our expectations, the dramatic testosterone-induced changes in muscle masses did not result in concordant changes in bite force performance or sprint speed.

Ontogeny of performance in vertebrates.

When competing for food or other resources, or when confronted with predators, young animals may be at a disadvantage relative to adults because of their smaller size. Additionally, the ongoing differentiation and growth of tissues and the development of sensory-motor integration during early ontogeny may constrain performance. Because ectothermic vertebrates show different growth regimes and energetic requirements when compared to endothermic vertebrates, differences in the ontogenetic trajectories of performance traits in these two groups might be expected. However, both groups of vertebrates show similar patterns of changes in performance with ontogeny. Evidence for compensation, resulting in relatively high levels of performance in juveniles relative to adults, appears common for traits related to locomotor and defensive behaviors. However, there is little evidence for compensation in traits associated with feeding and foraging. We suggest that this difference may be due to different selective regimes operating on locomotor versus feeding traits. As a result, relatively high levels of locomotor performance in juveniles and relatively high levels of feeding performance in adults are observed across a wide range of vertebrate groups.