Development of behavior in the litter huddle in rat pups: Within‐ and between‐litter differences

Abstract

Early postnatal growth in mammals can be considerably influenced by litter size and often differs among littermates in relation to birth mass. In a study of Long Evans laboratory rats we asked whether within- and between-litter differences in body mass and growth are related to behavioral development during early postnatal life. For this, we analyzed the amount of general motor activity and the display of directed, seemingly goal-oriented interactions within the litter huddle in previsual pups. During the study period from postnatal days 2 to 11, we found significant changes in pup behavior, showing a nonlinear, quadratic shape. General motor activity and, more specifically, the display of behaviors apparently directed to reaching central positions in the litter huddle increased during the first postnatal days and then decreased again. However, pups from small litters that grow more rapidly than pups from large litters, showed a faster increase in both behaviors, whereas the young from large litters reached a higher maximum. We also found striking within-litter differences in the amount of directed behavior performed by light and heavy pups, with higher levels in the former group, most probably because light pups that have a less favorable body mass-to-volume ratio and more often occupy peripheral positions in the litter huddle, make a greater effort to reach thermally favorable central positions. In conclusion, our study shows there to be consistent between-litter as well as within-litter differences in behavioral patterns during early life. These differences might have important implications for an individual's long-term behavioral and physiological performance.

The effect of siblings on early development: A potential contributor to personality differences in mammals

“…They also occupy more central, thermally advantageous positions in the litter huddle while expending significantly less time in presumably energetically costly efforts to gain these by climbing over or pushing between littermates than their lighter sibs, a pattern we have also found in newborn rats ( Fig. 4; Bautista, García-Torres, et al, 2008;Bautista, García-Torres, Prager, Hudson, & Rödel, 2010).…”

“…In conditions of sustained cold, as can be the case for low-bodymass young occupying the periphery of the huddle, BAT stores can be rapidly depleted, resulting in a life-threatening situation in which the cool, moribund young can no longer successfully compete in the brief daily scramble for nipples (Fig. 5;Bautista et al, 2003; (2008) and Bautista et al (2010). Gilbert et al, 2007; cf.…”

Within‐litter variance in early rat pup–mother interactions and adult offspring responses to novelty

“…Prior studies have shown that neonate weight is related to neonate huddling (Bautista, García-Torres, Prager, Hudson, & Rödel, 2010) and may predict maternal licking rates (Cavigelli et al, 2010). Litter and sex effects were controlled by centering variables to the family mean for same-sex siblings.…”

Early development influences ontogeny of personality types in young laboratory rats

“…In mammals, for example, the number of litter siblings can vary considerably, as it is the case in many rodents and lagomorphs, and has been shown to influence the early physiological and physical development (reviewed in Hudson & Trillmich, 2008;Hudson et al, 2011;Mock & Parker, 1997). Most importantly, animals born to larger litters usually show a lower body mass development until weaning and beyond (Bautista, Garcia-Torres, Prager, Hudson, & Rödel, 2010;Mendl, 1988;Rödel, Prager, Stefanski, von Holst, & Hudson, 2008). But also other physiological parameters, such as the development of HPA axis functionality are reported to be slower in young from larger litters (Rödel, Meyer, Prager, Stefanski, & Hudson, 2010).…”