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

Abstract

Although most mammals grow up in the company of same or different age sibs (or half sibs), surprisingly little attention has been given to how relations among them might influence the development of individual differences in morphology, physiology, and behavior. Here we review evidence from our work on domestic and wild European rabbits, and more recently on laboratory rats, mice, and domestic cats, supporting the proposition that in mammals early sibling relations contribute to the development of individual differences in these three domains and thereby to long-term behavioral differences of the kind we might consider part of an animal's behavioral style or personality. First we report a consistent and marked negative relation between litter size and individuals' body mass at birth and weaning, as well as marked within-litter differences in prenatal body mass and placental efficiency. We then report individual differences in preweaning behaviors associated with these morphological variables such as position occupied in the litter huddle and development of motor ability, as well as physiological differences in thermoregulation, immune parameters, and endocrine indicators of stress. Finally, we report first evidence from wild rabbits that early relations among littermates may have long-term consequences for individual differences in behavioral style. We conclude that in mammals, individual differences in early growth, physiology and behavior potentially important for the development of animal personality, are shaped to an appreciable extent by early sibling relations and that this little-researched field deserves closer attention.

Early development influences ontogeny of personality types in young laboratory rats

“…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). Such significant differences in the physical and physiological development are not only apparent among litters but also within litters between pups born with higher and lower starting mass (Bautista, Garcia-Torres, Martínez-Gómez, & Hudson, 2008;Hudson et al, 2011;Rödel, Bautista, García-Torres, Martínez-Gómez, & Hudson, 2008).…”

“…These studies show that individuals can be assigned to distinct groups or at least can be ordered along a continuum with respect to parameters such as, for example, their levels of boldness, aggressiveness, or tendency to explore novel environments. This gives rise to several questions on the proximate causes (Hudson et al, 2011), physiological correlates (Kralj-Fišer, Weiß, & Kotrschal, 2010), adaptive value (Boon, Réale, & Boutin, 2007;Eccard & Rödel, 2011;Réale, Martin, Coltman, Poissant, & Festa-Bianchet, 2009), and evolution of this phenomenon (Wolf, Van Doorn, Leimar, & Weissing, 2007), which is often referred to as animal personality, behavioral Developmental Psychobiology Heiko G. Rö del 1 syndrome, temperament, or coping style Mason, 1984).…”

“…In particular, features of the early development, which can play an important role in shaping individual life histories (Kaiser & Sachser, 2009;Lindström, 1999;Lummaa & Clutton-Brock, 2002;Rödel, von Holst, & Kraus, 2009;Sachser, Hennessy, & Kaiser, 2011), may also have the potential to be involved here. 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).…”

Unfolding personalities: The importance of studying ontogeny

“…Sulloway (2010) has suggested that one major force leading to such differential development of personality is character displacement as observed in different closely related species such as the Darwin's finches. In this sense then niche construction is a very active process that is most likely to occur in closed social systems like children within one family, chicks in a nest or young within one litter (Hudson, Bautista, Reyes-Meza, Morales-Montor, & Rödel, 2011). In such a situation where competition for the same resources becomes extreme any small differentiation in use of the environment will diminish competitive and potentially agonistic interactions and reward social differentiation.…”

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

“…Increasing evidence suggests that aggression and coping style of an individual animal can depend on the conditions experienced during early life, including the size of the litter it is born into (reviewed in Hudson, Bautista, Reyes, Morales Montor, & Rödel, 2011). Individuals of small litters of rats and rabbits were more aggressive and bolder compared to individuals of the same species and same sex that were born into larger ones (Rödel & Meyer, 2011;.…”