Differential development of body equilibrium among littermates in the newborn rabbit

Abstract

Interest is growing among psychobiologists and behavioral ecologists in the role of sibling relations in shaping individual development and life histories. In litters of domestic rabbits Oryctolagus cuniculus the heaviest pups at birth are more likely to survive the critical first postnatal week, they compete more effectively with littermates for milk and well-insulated positions in the litter huddle, and are the heaviest at weaning. Here we report that high birth weight pups are also better able to maintain body equilibrium. Testing pups' ability to maintain equilibrium when placed on a 15 degrees ramp for 2 min each day during the first postnatal week, we found that pups showed a continual daily improvement in their ability to maintain balance while moving on the ramp, rarely lost balance by postnatal day 8, and that heavier pups could maintain balance better and earlier than their lighter littermates. Better ability to maintain body equilibrium, however achieved, may help explain heavier pups' advantage in competing for vital resources such as milk and in gaining access to better-insulated positions in the litter huddle. It also provides further support for the usefulness of birth weight, not only as an absolute measure but also relative to the weight of other littermates, as a predictor of different developmental trajectories, behavioral and physiological, among same-age siblings in this mammal.

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

“…First, the greater body mass of pups from small litters might have been associated with earlier neuromuscular maturation and greater energetic resources, enabling them to engage in directed behaviors ahead of same-age but lighter members of large litters (cf. Foxcroft et al, 2006;Muciño et al, 2009). Second, having fewer littermates and thus fewer potential huddling partners might have motivated them to more actively seek thermally advantageous positions in the huddle at an earlier (more vulnerable) age.…”

“…The existence of such a link is supported by studies in several mammalian species showing that young with low postnatal growth or body mass often have reduced motor abilities or poorer muscle development in comparison to same-age but heavier offspring (laboratory rat Rattus norvegicus: Gramsbergen & Westerga, 1992;Salas, 1972; domestic pig Sus scrofa : Foxcroft et al, 2006; domestic rabbit Oryctolagus cuniculus : Muciño, Bautista, Jímenez, Martínez-Gómez, & Hudson, 2009). Furthermore, the importance of sibling presence or interactions among them for an individual's behavioral development, including the acquisition of social skills, has been highlighted both in studies of birds (Edwards, 1989) and mammals (Bekoff, 1977;Nunes, Muecke, Sanchez, Hoffmeier, & Lancaster, 2004;Rödel, Starkloff, Bruchner, & von Holst, 2008;Uriarte, Ferreira, Rosa, Sebben, & Lucion, 2008).…”

Early development influences ontogeny of personality types in young laboratory rats

“…However, due to the strong effects of starting body mass-overriding the effects of litter size-we suggest that the individual body mass and size directly and causally affect the ontogeny of personality traits. We propose that, starting from birth, an animal's perception of its environment strongly depends on its physical state, such as its body size or mass, which in turn can strongly influence individual behavioral performance and motor abilities (Gramsbergen & Westerga, 1992;Muciño et al, 2009;Salas, 1972). This could also apply to experimental test situations, where smaller or larger pups may experience the height of a platform or the area of an open field in a different way, which in turn might considerably affect their responses.…”

“…The existence of such a link between early development and behavior is supported by studies in different mammal species including humans, showing that young with low birth mass, weaning mass or postnatal growth often have reduced motor abilities (Gramsbergen & Westerga, 1992;Muciño, Bautista, Jímenez, Martínez-Gómez, & Hudson, 2009;Rickards et al, 1993;Salas, 1972) and behavioral performance (e.g., diving capabilities in elephant seals Mirounga leonine : Hindell et al, 1999).…”

Optimizing temperament through litter size in short‐lived, iteroparous mammals in seasonal environments

“…Most importantly, the lower share of milk available to the individual offspring born to larger litters limits their postnatal growth and thus body mass around weaning and beyond (Mendl, 1988;Rödel, Hudson, & von Holst, 2008), and hence affects the individual capability and agility of the young (Bautista, Garcia-Torres, Prager, Hudson, & Rödel, 2010;Muciño, Bautista, Jímenez, Martínez-Gómez, & Hudson, 2009). Furthermore, the number of siblings present during early postnatal life and the interactions among them might have priming effects for later behavioral tactics and interactions with conspecifics.…”