ANDRES, D.L.; MACKIE, R.I.; SECOR, S.M.; ESPINOZA, R.E.; California State Univ., Northridge; Univ. of Illinois, Urbana-Champaign; Univ. of Alabama, Tuscaloosa; California State Univ., Northridge: Can the cost of diet switching explain the evolution of herbivory in reptiles?

Herbivory is rare in reptiles and speculation on why herbivory has evolved spans more than 40 years. When fed insects or meat, captive herbivorous reptiles grow faster, reach a larger size, and produce more offspring. If eating insects is advantageous for captive herbivorous reptiles, then why don’t herbivores seasonally switch to eating insects in the wild? We tested the hypothesis that diet switching is energetically costly for herbivorous lizards. Changes in diet were expected to cause changes in the gut milieu (e.g., pH). Such changes may make conditions unfavorable for resident fiber-degrading bacteria, thus altering the microbial community and causing a concomitant decline in digestive efficiency for the host. To test these hypotheses, desert iguanas (Dipsosaurus dorsalis) were fed ground alfalfa or crickets for 5 weeks, switched to the alternative diet for 5 weeks, then switched back to the original diet for 5 weeks. Feces were collected during this period to test if diet switches were associated with changes in (1) digestive efficiency (dry-matter digestibility) or (2) the microbial community of the gut (via numerical analysis of fecal banding profiles using PCR-DGGE). We also compared gross morphology and physiology (pH and rates of nutrient transport) of lizard guts across diet treatments. Diet switches caused changes in gut morphology, pH, and digestive efficiency, and these changes were correlated with changes in the endosymbiont community. If diet switching alters gut structure and function, as well as disturbs the endosymbiont community, then switching back and forth from eating insects and plants may not provide an advantage to herbivorous lizards in nature.