Intra-uterine Selection Due to Maternal-fetal Incompatibility of Blood Types in the Whales*

Since its discovery, it had been generally considered that blood type was hereditarily neutral characteristics free from natural selection. Thereafter many observations were reported on the correlations between blood types and hemolytic diseases in newborn or erythroblastosis foetalis and differential survival in intrauterine life such as rate of fertility and of miscarriage and in extra-uterine life for human and some other mammalian species (reviewed in Race and Sanger, 1959, pp. 310-312). These knowledges have led to rise of discussions on natural selections relating to blood groups. Series of recent papers on human blood groups by Matsunaga (1953, 1954, 1959), Matsunaga and Itoh (1953, 1954, 1958), Simmons et al. (I 960), Grubb and Sjostedt (1955), and Jakobowicz et al. (1961) furnish more evidences from these view-points. Basing upon the results of the Antarctic whaling investigation in 1960/61 season, Fujino (1962) describes that differential percentage pregnancies by blood groups were seen in both species of the Antarctic pigmy-blue and the fin whales, and that hemolytic antibodies were positively detected from isoserums of fin whales. Then he states that the facts in these observations strongly suggest incidence of miscarriages of fetuses caused by maternal-feta! incompatibility of blood types in whales and that these frequencies of occurrence will closely relate to gene frequencies of blood types of the population. Results of further observations in 1961/62 Antarctic season (Fujino, unpublished data) confirm the differential rates of pregnancy stated above. In the present paper, at first are described the results of observation, that is a) differential apparent rates of pregnancy by blood groups and b) hemolytic properties ofisoserums as the evidences suggesting intra-uterine selection in whales. Secondly, after basing upon knowledges about intra-uterine selection and its compensatory mechanism in human (Matsunaga, 1954), quantitative relationships between selection and fitness are discussed, and the prenatal mortality rate is estimated for actual population of whales.