Sodium Provision and Wild Cottontail Rabbits: Morphological Change in Adrenal Glands

• Published in: The Journal of wildlife management 1992-10, Vol.56 (4), p.669-676
• Main Authors: McCreedy, Clark D., Weeks, Harmon P.
• Format: Article
• Language: English
• Subjects: Adrenal cortex; Adrenal glands; Animal and plant ecology; Animal morphology; Animal physiology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Male animals; Mammalia; Nutrition; Pregnancy; Rabbits; Rats; Sodium; Sylvilagus floridanus; Vertebrata
• ISSN: 0022-541X; 1937-2817
• DOI: 10.2307/3809459

A direct relationship exists between sodium (Na) nutrition and morphology of the mammalian adrenal cortex, but little research on the relationship between soil Na levels and herbivore populations exists. Consequently, we assessed the effect of Na on wild cottontail rabbits (Sylvilagus floridanus) inhabiting Na poor soils in southcentral Indiana by characterizing their adrenal mass and histology prior to, and following, provision of supplemental Na. Data and tissues were collected at annual (1985-87) hunter check stations and during the 1987 breeding season at the Atterbury Fish and Wildlife Area. Nutrient supplements, consisting of either deionized water (controls) or 150 meq aqueous NaCl, were delivered via dripper bottles to 4 replicates of each treatment throughout the spring and summer of 1986-87. Additionally, NaCl was delivered via impregnated pegs through winter 1986 and spring 1987. Hypotheses tests relative to the 1985 harvest served to evaluate adrenal morphology with respect to treatments prior to experimental manipulation. During the 1985 pretreatment period there was no evidence (P ≤ 0.99, n = 828) of extant differential adrenal morphology by treatment type. Following introduction of supplements, adrenal mass (mg/g body mass) declined uniformly across age (adult, juvenile) and sex classes among rabbits with access to ancillary Na (1986: P ≤ 0.05, n = 422; 1987: P ≤ 0.10, n = 456). Relative area of the adrenal cortex declined uniformly (P ≤ 0.05) in response to Na provision. Although mass and cortical area declined in response to sodium, the cortical area of the zona glomerulosa, in which the hormone aldosterone is produced, did not additionally decline, but did differ by sex. The marked response of the adrenal gland to Na provision suggests that, within Na poor environments, Na nutrition may be a valid management concern.