Factors influencing the expression of behaviour: maternal effects

The expression of behaviour, in general, in mammals can be influenced by multiple factors. I’ll start by explaining how maternal effects may influence an offspring’s behaviour.

Maternal effects have been defined by Wolf & Wade (2009) as “the causal influence of the maternal genotype or phenotype on the offspring phenotype.” While the mother’s genotype can influence the phenotype of the offspring, maternal effects are mediated through the mother’s phenotype (Wolf & Wade 2009). Maternal effects can influence the young while they are still in utero or during the early postnatal period (Liu et al. 1997). These maternal effects, primarily hormonally driven, have either a direct or an indirect organising effect on an offspring’s behavioural phenotype, hence these can be termed “organisational effects”. These organisational hormonal effects can create permanent, non-reversible changes in neural substrates underlying behaviour (Elekonich & Robinson, 2000).

Females may directly influence the offspring through cross placental hormonal transmission during gestation (Soares et al. 2010). Reproductive hormones, such as oestrogen (Goebelsmann etal. 1972) and stress hormones, such as cortisol (Van den Bergh et al. 2005) can be passed across the placenta during gestation. Furthermore, there is strong evidence that these hormones influence a variety of different behaviours (e.g. spatial memory and ability, Williams et al. 1990; Williams & Meck 1991; social behaviour, Mogi et al. 2014). For example, early exposure to oxytocin improves alloparental responsiveness in ICR mice (Fig. 1).

Fig. 1. Domestic mouse Mus musculus domesticus, ICR strain 

(Unknown: picture accessed 08 December 2014; 17h39) 

(http://www.taconic.com/icr)

Females can also influence an offspring’s phenotype indirectly through provision of postnatal care. Numerous studies have shown that variations in the quality and quantity of maternal care can influence their offspring’s behaviour later in life (e.g. Champagne et al. 2001; Jia et al. 2011). A classic example is seen in rats (Francis et al. 1999). Females that receive high levels of postnatal care during early development become mothers that also show high levels of care to their own offspring (Francis et al. 1999). Importantly, both sons and daughters are influenced by maternal effects. In African striped mice Rhabdomys pumilio (Fig. 2), sons experiencing high levels of care from their mothers show correspondingly high levels of paternal care to their own offspring later (Rymer & Pillay 2011).

Fig. 2 African striped mouse family Rhabdomys pumilio  

(Tasmin Rymer: personal picture)

 

In my next post, I explain how activational effects influence the expression of behaviour.