Size and growth of viscer in the southern elephant seal, Mirounga leonina (L.)

Abstract

Relative size and relative growth of the viscera of elephant seals ranging in age from birth to 16 yr were studied. Individual organs were measured and weighed within an hour of death. The data were subjected to regression analyses, making use of the logarithmic transformation of the allometric equation. Fat-free body weight was the independent variable in the analyses, to avoid apparent growth patterns which could be attributable to large fluctuations in the body fat only. The relative weight data established normal values for organ weight in elephant seals in different phases of growth, although it was recognized that relative weight did change within growth phases in some organs, i.e, those whose growth coefficient was significantly greater or less than 1.000. Changes of relative weight of some organs were particularly marked in phase 1 of growth (suckling phase), when very rapid body weight growth occurred. The relative size of most organs was similar to that in other mammals. The stomach was relatively smaller than other carnivore stomachs, and the liver was relatively larger than in terrestrial mammals but similar to that in cetaceans. The relative length and weight of the small intestine were very much greater than in other carnivores. The spleen was relatively very large. The possible reasons for the difference in relative size of these organs in elephant seals and other mammals are discussed. Growth gradients of most organs did not alter significantly between or within growth phases. Exceptions to this pattern were noted and illustrated for the stomach, liver, pancreas, heart, reproductive tract, and eyes. The interpretation of the growth patterns of different organs was that changes in growth gradients occurred in those organs whose functional significance changed during postnatal life. The functional significance of most organs did not alter markedly within or between growth phases, and in those organs no change in growth pattern occurred throughout postnatal life.