Effects of saline intake, sex, and season on Pekin duck osmoregulatory organ masses and comparison with wild Mallards

Abstract

Osmoregulatory organ masses of freshwater Mallards (Anas platyrhynchos) do not differ between the sexes, but drinking saline induces changes that are sexually disparate in some organs. We examined relative size of organ masses of male and female Pekin ducks (that were domesticated from Mallards) and compared their responses to saline intake with those of Mallards. Organ masses of male and female Mallards do not differ in size. The liver and kidneys are heavier in female Pekin ducks and their digestive tract (except for the proventriculus and duodenum) is longer and heavier; male Pekin ducks have heavier salt glands. Mallards acclimated to saline drinking water have enlarged salt glands but not kidneys, adrenal glands, or Harderian glands, their proventriculus tends to be shorter and lighter, the jejunum longer in males, and the ileum longer and heavier in both sexes. In Pekin ducks that drink saline, the salt and Harderian glands are larger and their kidneys (but not adrenal glands) tend to be larger; the proventriculus is unaffected, but the small intestine is lighter, but not shorter, in females. Body, salt gland, Harderian gland, ventriculus, and duodenum masses vary seasonally in Pekin ducks. Discussion considers the effects of season and sex on relative organ masses and how saline-induced changes in them reflect domestication and may influence salt tolerance.