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Changes in Digestive Performance and Gut Structure and Function in a Newly Herbivorous Lizard

Although evolution is generally thought to happen over long timescales, examples of rapid evolutionary change are becoming more common. One example, a population of Italian Wall Lizards (Podarcis sicula) in Croatia has become primarily herbivorous and morphologically distinct from its source population in ~30 generations. By studying what these animals are ingesting and digesting, we can investigate if their physiology and morphology are optimized for their diets. The Adaptive Modulation Hypothesis posits diet specialization should lead to gut specialization. With previously documented changes in diet and gut structure in these lizards, we hypothesized concomitant changes in gut function to accommodate a plant diet. Indeed, we found the herbivorous population was more efficient at digesting plants than the source population lizards. Thus, we compared the gut morphology and physiology of the herbivorous population, its source population, and two outgroup populations of P. sicula to discern the mechanisms of their digestive capabilities. We expected the plant−eating population would have increased gut length and intestinal surface area to absorb nutrients. We found differences in gut length by population and sex, but not in intestinal cross sectional area. We anticipated higher carbohydrase activities in the herbivorous population, but have found inconsistent patterns across populations and enzymes. In experiments underway, we predicted the herbivorous population would have increased microbial fermentation and food transit time, as is found in other herbivorous lizards. In progress metabolic measurements aim to investigate effects of diet and diet specialization on performance. Our study addresses mechanisms of how diet specializations arise and their effects on fitness.

Digestive Physiology; Physiological Performance; Gut; Lizard; Podarcis sicula

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