GROWTH AND REPRODUCTION OF HISPID COTTON RATS (SIGMODON HISPIDUS) IN RESPONSE TO NATURALLY-OCCURRING LEVELS OF DIETARY-PROTEIN

Hispid cotton rats (Sigmodon hispidus) ingest both monocotyledon (mono cot) and dicotyledon (dicot) plants, ostensibly to balance intake of n utrients. On the Texas coastal prairie, monocots are more abundant, re quire less handling time, and have more fiber and soluble carbohydrate s than dicots, which contain more protein, lipid, water, energy, and m inerals. Because availability of protein may be limiting here, cotton rats were raised on artificial diets that mimicked protein content of either monocots (4%) or dicots (11%). Body mass, growth rate, and leng th of hind foot were lower and liver mass was higher in individuals fe d a monocot-protein diet. Tissue protein, but not lipid, content was h igher in individuals fed a dicot-protein diet. First estrus occurred a t the same body mass on both diets, but slower growth on a monocot-pro tein diet resulted in females being 50% older at first estrus. Cotton rats must ingest dicots to obtain sufficient protein for growth and re production because monocots are not a complete food source.