Inter-individual variation in the diet within a group of Japanese macaques and its relationship with social structure investigated by stable isotope and DNA analyses.

We investigated individual variation in diet in relation to age-sex class and kin relationship in 28 of 40 members of a small group of wild Japanese macaques (Macaca fuscata). We used stable isotope ratios from hair as an index of individual dietary profiles, genetic relatedness as an index of kin relationship, and mitochondrial DNA (mtDNA) haplotype as a marker of being an immigrant or native member of the group. The range of carbon and nitrogen stable isotope ratios from hair of individual macaques (δ13C: -24.1‰ to -22.6‰, δ15N:3.8-5.5‰), which reflected their diet over a period of ~ 6 months, implied small individual variation in diet. The results of PERMANOVA implied that there were no significant effects of age class, sex, or mtDNA haplotype on hair stable isotope ratios between individuals, or on the variation in individual diet. However, the isotope values of males with mtDNA haplotypes that differed from those of the native females appeared to differ from those of other group members, which implies that immigrant males might have had a different diet profile from that of native group members. Furthermore, there was a weak correlation trend between genetic relatedness and differences in stable isotope ratios between pairs of individuals. Differences in stable isotope values were more marked in pairs with a more distant genetic relationship. This implies that within the group, closely related kin tended to forage together to avoid competing for food. However, this effect might have been weak because the size of the group was small relative to the size of the food patches, thereby reducing competition.

Seasonal and sexual variation in the diet and gastrointestinal features of the sika deer in western Japan: implications for the feeding strategy.

Sexual and seasonal variation in diet quality and the gastrointestine have important implications for forage acquisition and the feeding strategy. We assessed the botanical and chemical compositions of the diet and the gastrointestinal macrostructure of the sika deer (Cervus nippon) in western Japan. The sexual dimorphism-body size hypothesis predicts that smaller females will have a better diet than larger males to meet a higher nutritional demand due to a higher metabolic rate. According to the optimal digestion theory, the gut of larger males will retain a greater quantity of digesta of poor forage to compensate for the reduction in net energy obtained per unit of digesta. The relatively greater omasum content in winter than in summer was the only feature consistent with this prediction. This may suggest that the omasum is the organ that most sensitively reflects diet quality, because the summer diet quality is little better than that in winter. Contrary to predictions, the botanical composition of the diet did not show a sexual difference, but females had greater relative weights of stomach contents, tissues, and hindgut segments (small and large Intestines, and cecum-colon), and a relatively greater small Intestine length than males in summer. Further, females had greater relative weights of abomasum contents, ruminoreticulum tissue, and small Intestine in summer than in winter, but no seasonal variation in gastrointestinal features was detected in males. The sexual variation in diet and in the gastrointestine in summer suggest that lactating females Intake more forage and maintain more digesta in the gut, due to not body size but to higher energy requirements for lactation. The greater gut fill and tissue weight of females in summer than in winter likely resulted from a nutrient demand from lactation greater than that from gestation.

Sexual variations in food quality and gastrointestinal features of sika deer (Cervus nippon) in Japan during winter: implications for feeding strategy.

We assessed sexual variation in food quality and gut macrostructure in adult male and pregnant female sika deer, Cervus nippon (Temminck, 1838), in Japan during winter. These variations might have important implications relative to sexual differences in habitat use, forage acquisition, and digestive strategy. According to the sexual dimorphism-body size hypothesis the larger males would feed on poorer forage and have heavier stomach contents and heavier intestine contents and longer intestines than smaller females. However, the food quality in rumen contents of males was higher than, or at least similar with, that of pregnant females. In correspondence to food quality, the relative weights of stomach contents and intestines with contents, the relative lengths of intestines to the lengths of body and total intestines in pregnant females were similar to adult males. The relative weights of omasum and abomasum tissues in pregnant females were greater than in males. Our findings suggest sexual differences in feeding strategy in sika deer in Japan during winter. To meet greater nutritional demands of high metabolic rate and gestation, pregnant females seemed to maintain a greater volume of digesta in guts and had more stomach tissues than expected by the sexual dimorphism-body size hypothesis to compensate for poorer forage quality.