Feeding Rates in the Swordtail Fish Xiphophorus multilineatus: A Model System for Genetic Variation in Nutritional Programming.

A better understanding of the role of appetite regulation in obesity and metabolic disorders requires consideration of both genetic and developmental influences on appetite. Previously we detected genetic differences in responses to nutritional programming (e.g., the permanent influence that nutrition in early life has on the physiological and metabolic states in adults) on a presumed measure of appetite (feeding rate) in the swordtail fish Xiphophorus multilineatus. In this study we validate that feeding rate is a good measure of appetite, by first demonstrating that it is repeatable and correlated with food consumed when controlling for body size. Second, we detected a significant positive correlation between juvenile growth rates and feeding rates measured in adult males, when growth has ceased. In addition, feeding rates explained significant variation in the size of the nuchal hump, a fat deposit that develops after sexual maturity. Finally, we show that the feeding rates of "courter" males were significantly greater than "sneaker" males, alternative reproductive tactics that are influenced by variation in the Mc4r gene on the Y-chromosome. Our results suggest that examining feeding rate in X. multilineatus could provide valuable insights into how nutritional programming influences appetite independently from food intake, as well as insights into the mechanisms that produce the correlation between delayed maturation and faster growth rates of the courter males as compared with the sneaker males that mature early and grow slower in this species.