On the presence and absence of suckling order in polytocous mammals.

Mammals have developed a variety of suckling behaviours ranging from tenacious nipple attachment in some rodents and marsupials to once-a-day suckling in rabbit. However, a common feature of suckling that was found in many mammals is the suckling order, or a partial preference to suckle a particular teat (teat fidelity) or part of the udder (suckling preference). A lack of suckling order is observed only in a few mammals. In this article, the possible background of the presence or absence of suckling order in eutherian polytocous mammals is discussed either from the maternal investment or sibling competition point of view. Characteristics related to maternal investment in species in which the suckling order has already been studied at least partially, were classified using C4.5 algorithm (J48 classifier in Weka 3.8.1), and decision tree was built. In the context of sibling competition, an extensive form game (game theory) was predicted to show the optimal suckling strategy considering the basic relations among littermates in two situations (littermates of equal strength/dominance and littermates with different strength/dominance). Although no ultimate conclusion can be drawn, it appears that the suckling order is typical for species whose reproductive system requires a lower maternal investment (up to one litter/year, monogamy, biparental care, lower litter birth weight); and, it appears that the suckling order is inherent to the weaker (inferior) siblings.