Teat functionality varies, and mammals that are primarily monotocous
like cattle have four functional teats, whereas humans, primates, elephants, sheep and goats have two (Anderson et al., 1982).
Across small to large ungulates comprised mostly of monotocous
species, birth mass scales to the 0.75 power of body mass of the dam, meaning smaller dams give birth to larger neonates in proportion to the dams body size (Robbins and Robbins, 1979).
Larger fetuses of monotocous
species are more prone to maldisposition than relatively small ovoid fetuses of polytocous species (Jackson, 1995).
Mammalian species can be divided into two groups, monotocous and polytocous, by the number of progeny per birth.
In order to identify important genes that underlie the differences between monotocous and polytocous species, a novel approach focusing on the evolutionary genetic differences between the two groups of species was applied.
Human, chimpanzee, orangutan, macaque, panda, horse, cow and dolphin were selected as monotocous species, and mouse, rat, dog, cat, pig and Tasmanian devil were selected as polytocous species with the platypus as an outgroup.
As monotocous and polytocous species are not monophyletic, the inference of episodic evolutionary history from which their traits formed through convergent evolution is somewhat complicated.
Bharal is a monotocous
species and rarely breeds before two years of age (Schaller 1977, Wegge 1979).
I fitted 4 allometric relationships according to the life history traits (birth mass and early growth rate) and to the species-specific litter size (polytocous and monotocous species).
As expected, a strong positive relationship occurred between birth mass (BW) and adult body mass (ABW) in both monotocous (Ln (BW) = -1.366 + 0.902 Ln (ABW); r = 0.977, P < 0.0001) and polytocous (Ln (BW) = -3.274 + 1.059 Ln (ABW); r = 0.892, P = 0.0029) species.
I can thus also conclude that moose allocate energy to maternal care as a monotocous species during the gestation period but as a polytocous species during the lactation period.
Firstly, the variance of female lifetime reproductive success will be expected to be greater in polytocous than in monotocous
species because, for the latter, family effects cannot occur within a single year.