Does foraging mode affect metabolic responses to feeding？ A study of pygopodid lizards

Foraging mode （ambush vs. active） profoundly affects many aspects of organismal biology, including metabolic rates and their relationship with food intake. Previous studies on snakes suggest that ambushers tend to have lower standard metabolic rates （SMR） and higher energetic costs of digestion and assimilation of prey （specific dynamic action, or SDA） than do active foragers. However, phylogenetic considerations may be at least partly responsible for such patterns, as foraging mode is strongly conserved evolutionarily and most SDA studies have focused on species from only two lineages of ambush foragers （pythonid and viperid snakes） and one lineage of active foragers （colubrid snakes）. We sought to deconfound the effects of phylogeny and foraging mode, investigating SMR and SDA in two closely related pygopodid lizards, the common scaly-foot Pygopus lepidopo- dus （active forager） and Burton＇s legless lizard Lialis burtonis （ambush forager）. Consistent with the pattern seen in snakes, L. burtonis exhibits a significantly lower SMR and a higher SDA than does P lepidopodus. The magnitude of SDA in L. burtonis is comparable to that of some pythons and vipers, providing yet more evidence for the remarkable convergence between this species and ambush-foraging snakes [Current Zoology 59 （5）： 618-625, 2013].

Behavioral thermoregulation is highly repeatable and unaffected by digestive status in Agama atra

The precision and the extent of behavioral thermoregulation are likely to provide fitness benefits to ectotherms.Yet the factors driving variation in selected or preferred body temperature(T_(set))and its usefulness as a proxy for optimal physiological temperature(Topt)are still debated.Although T_(set)is often conserved among closely related species,substantial variation at the individual,population and species level has also been reported.However,the repeatability(calculated as the intra-class correlation coefficient)of T_(set)is generally low.One factor that influences T_(set)is feeding status,with fed reptiles typically showing higher T_(set),a process thought to aid meal digestion.Here,using experiments simulating realistic feeding and fasting regimes in Agama atra,a heliothermic lizard from southern Africa,we test if T_(set)and its repeatability under these 2 states significantly differ.Daily T_(set)ranged from 33.7 to 38.4℃,with a mean(±SE)of 36.7±0.1℃ for fed and 36.6±0.1℃ for unfed individuals.Comparisons of repeatability showed that females tend to be more consistent in the selection of body temperature than males,but not significantly so regardless of feeding status.We report some of the highest repeatability estimates of T_(set)to date(full range:0.229–0.642),and that the weak positive effects of feeding status on T_(set)did not increase its repeatability.In conclusion,one of the major prerequisites for natural selection,consistent among-individual variation,is present,making the adaptive significance of T_(set)considerably more plausible.