Development of the Columbian black-tailed deer (Odocoileus hemionus columbianus) during the fetal period

Abstract

This study of 88 fetuses of the Columbian black-tailed deer (Odocoileus hemionus columbianus) from a single wild-ranging population has yielded values of k in the heterogonic growth formula for 18 measurable attributes. Length measurements of the ear pinna and the elements of the legs have the highest coefficients during prenatal development. This is in marked contrast with circumstances subsequent to birth.There is no evidence of an anterior-posterior trend in growth in diameter of parts of the trunk. In the legs, each component of the hind limb grows faster than the corresponding part of the foreleg. This departs from the patterns of postnatal growth where there is slight anterior precedence.During fetal development, unlike postnatal development, cranial and rostral segments of the skull grow at the same rate.Regional variation in growth rate of different body parts is extensive and even in twin pairs may involve several characteristics, sometimes departing in different directions.In mixed-sex twins either sex can be more developed than its littermate but there is strong evidence for male dominance in size. This is apparent also in comparison of single fetuses of equal developmental stage.Comparison with fetal growth patterns of the mule deer (Odocoileus hemionus hemionus) and the white-tailed deer (Odocoileus virginianus) reveals that the subspecies of hemionus possess generally similar patterns. However, both races of this species differ from virginianus in a number of features of relative growth.Many structural changes occur at a smaller fetal size in columbianus than in hemionus or virginianus in keeping with the smaller adult size of the former. The heterogonic growth constants of columbianus and hemionus for five segments upon which comparison can be made are similar, but differ from those of the species virginianus. It appears, therefore, that patterns of relative growth are closely similar within the species even where there are considerable differences in mature size of the subspecies. Interspecies differences occur even where ultimate size and general proportions may be similar.