ON STRUCTURAL CHARACTERISTICS AND MORPHOPHYSIOLOGICAL ADAPTATION OF THE SPRINGBOK (ANTIDORCAS MARSUPIALIS) DIGESTIVE SYSTEM

Gross intestinal morphometry and allometry in ruminants

While some descriptions of ruminants' dietary adaptations suggest that the length of the intestinal tract reflects the proportion of grass or browse in the diet, this assumption has been questioned. We collated data on body mass (BM), as well as small intestine, caecum, colon/rectum, large and total intestine length in 68 ruminant species, and, while accounting for the phylogenetic structure of the dataset, evaluated both allometric scaling and the potential influence of diet, digestive physiology or climate proxies on measures of intestine length. Intestinal length generally scaled to BM at an exponent higher than the 0.33 expected due to geometry. Diet or digestive physiology proxies did not have an influence on any intestinal length measures, though some proxies indicating more arid natural habitats were positively correlated with measures of the large intestine. The relative size of a forestomach compartment, the omasum, was negatively correlated with intestine length. The results indicate that intestine length measures provide little indication of feeding type or digestive physiology, but rather indicate adaptations to aridity. Higher-than-geometry scaling of intestinal length may be related to the necessity of maintaining geometric (or metabolic) scaling of intestinal surface area while keeping gut diameter, and hence the diffusion distances, small. The way in which space trade-offs determine the macroanatomy of different organs in the abdominal cavity, such as the omasum and the intestine, deserves further investigation.

Synergistic effects of seasonal rainfall, parasites and demography on fluctuations in springbok body condition

1. Seasonality of rainfall can exert a strong influence on animal condition and on host-parasite interactions. The body condition of ruminants fluctuates seasonally in response to changes in energy requirements, foraging patterns and resource availability, and seasonal variation in parasite infections may further alter ruminant body condition. 2. This study disentangles the effects of rainfall and gastrointestinal parasite infections on springbok (Antidorcas marsupialis) body condition and determines how these factors vary among demographic groups. 3. Using data from four years and three study areas, we investigated (i) the influence of rainfall variation, demographic factors and parasite interactions on parasite prevalence or infection intensity, (ii) whether parasitism or rainfall is a more important predictor of springbok body condition and (iii) how parasitism and condition vary among study areas along a rainfall gradient. 4. We found that increased parasite intensity is associated with reduced body condition only for adult females. For all other demographic groups, body condition was significantly related to prior rainfall and not to parasitism. Rainfall lagged by two months had a positive effect on body condition. 5. Adult females showed evidence of a 'periparturient rise' in parasite intensity and had higher parasite intensity and lower body condition than adult males after parturition and during early lactation. After juveniles were weaned, adult females had lower parasite intensity than adult males. Sex differences in parasitism and condition may be due to differences between adult females and males in the seasonal timing of reproductive effort and its effects on host immunity, as well as documented sex differences in vulnerability to predation. 6. Our results highlight that parasites and the environment can synergistically affect host populations, but that these interactions might be masked by their interwoven relationships, their differential impacts on demographic groups, and the different time-scales at which they operate.

Convergent evolution in feeding types: salivary gland mass differences in wild ruminant species

In the ongoing debate about divergent evolutionary morphophysiological adaptations of grazing and browsing ruminants, the size of the salivary glands has received special attention. Here, we report the most comprehensive dataset on ruminant salivary glands so far, with data on the Glandula parotis (n=62 species), Gl. mandibularis (n=61), Gl. buccalis ventralis (n=44), and Gl. sublingualis (n=30). All four salivary gland complexes showed allometric scaling with body mass (BM); in all cases, the 95% confidence interval for the allometric exponent included 0.75 but did not include 1.0 (linearity); therefore, like other parameters linked to the process of food intake, salivary gland mass appears to be correlated to metabolic body weight (BM0.75), and comparisons of relative salivary gland mass between species should rather be made on the basis of BM0.75 than as a percentage of BM. In the subsequent analyses, the percentage of grass (%grass) in the natural diet was used to characterize the feeding type; the phylogenetic tree used for a controlled statistical evaluation was entirely based on mitochondrial DNA information. Regardless of phylogenetic control in the statistical treatment, there was, for all four gland complexes, a significant positive correlation of BM and gland mass, and a significant negative correlation between %grass in the natural diet and gland mass. If the Gl. parotis was analyzed either for cervid or for bovid species only, the negative correlation of gland mass and %grass was still significant in either case; an inspection of certain ruminant subfamilies, however, suggested that a convergent evolutionary adaptation can only be demonstrated if a sufficient variety of ruminant subfamilies are included in a dataset. The results support the concept that ruminant species that ingest more grass have smaller salivary glands, possibly indicating a reduced requirement for the production of salivary tannin-binding proteins.