The development of paternal care

Although increasing in popularity, relatively few studies have investigated the how paternal care behaviour develops and is expressed, and what role fathers play in these processes.Bester-Meredith &Marler (2003) showed that a decrease in paternal care behaviour by California mouse Peromyscus californicus results in sons also showing lower levels of care, possibly because vasopressin expression in the bed nucleus of the stria terminalis (BNST) facilitates this behaviour. However, Bredy et al. (2004) found no apparent influence of paternal care on the development of the hippocampus, the area of the brain that secretes vasopressin.

Behaviour, in general, is influenced genetically and non-genetically (e.g. learning, Cushing & Kramer 2005), although behavioural expression can be more strongly influenced either by environmental or genetic components. For example, offspring feeding rate in long-tailed tits Aegithalos caudatus (Fig. 1) has a significant heritable component (MacColl & Hatchwell 2003), whereas paternal state is strongly regulated by environmental cues in meadow voles Microtus pennsylvanicus (Fig. 2), a species that is rarely paternal (Parker& Lee 2001). However, few studies have looked at the relative influence of both genetic and non-genetic factors on the development of paternal care.

 

Fig. 1 Long-tailed tit Aegithalos caudatus
(Tim Edelsten: picture accessed 28 July 2014; 12h53)
(http://www.birdskorea.org/Birds/Birdnews/BK-BN-Review-2007.shtml)

Fig. 2 Juvenile meadow vole Microtus pennsylvanicus
(Unknown: picture accessed 28 July 2014; 12h59)
(http://natchem.wordpress.com/2010/06/04/the-genetics-of-monogamy-guys-girls-you-better-read-this/)




In two recent studies, Prof. Neville Pillay (University of the Witwatersrand) and I demonstrated the importance of both non-genetic (Rymer & Pillay 2011a) and genetic (Rymer & Pillay 2011b) factors on the developmental of paternal care behaviour in biparental African striped mice Rhabdomys pumilio (Fig. 3). We found that mothers are particularly important for the development of paternal care behaviour in their sons (Rymer & Pillay 2011a). Sons raised by their mothers only show heightened levels of paternal care as adults, as mothers compensate for the absence of the father by increasing the amount of maternal care invested in their sons (Rymer & Pillay 2011a). Interestingly, there appears to be little genetic heritability of paternal care either down the matriline or the patriline (Rymer & Pillay 2011b), suggesting that the development of paternal care in striped mice in strongly regulated by environmental factors.

Fig. 3 Juvenile striped mice Rhabdomys pumilio

(Gaby Schmohl: picture accessed 28 July 2014; 16h10)
(http://www.stripedmouse.com/site1_3.htm)


In my next blog, I’ll make a start on those factors influencing the expression of paternal care.

The evolution of paternal care

According to classic sexual selection theory, the lifetime reproductive success of males is predominantly determined by the number of matings achieved and the number of offspring sired, not the number of offspring helped to raise (Trivers 1972). This occurs as male mammals are unable to provide parental care during the prenatal period (Orians 1969; Queller 1997). However, the very occurrence of paternal care in some mammals indicates that the evolutionary benefits of providing care must have outweighed the costs associated with lost mating opportunities (Gubernick & Teferi 2000).


Two hypotheses, that are not mutually exclusive, have been proposed for the evolution of paternal care, namely the “mating constraints hypothesis” (Orians 1969; Queller 1997) and the “male care hypothesis” (Smuts & Gubernick 1992). The “mating constraints hypothesis” proposes that males that are ecologically and/or socially constrained from securing additional reproductive opportunities will provide paternal care (Orians 1969; Queller 1997). Mating behaviour is often regulated by social conditions, in particular, population density, which in turns regulates whether males remain with females or move on to find additional opportunities. This is classically observed in African striped mice Rhabdomys pumilio (Fig. 1). When population density is low, males adopt a roaming strategy, visiting several females and showing no paternal care (Schradin 2008). In contrast, when population density is high, males become territorial breeders, defending a group of females and showing paternal care (Schradin 2008).

Fig. 1 African striped mice Rhabdomys pumilio 
(Lars Müller: picture accessed 12 July 2014; 14h30)
(http://www.stripedmouse.com/site1_1.htm)

The “male care hypothesis” predicts that males will provide care under three circumstances (Smuts& Gubernick 1992): 1) When the certainty of paternity is low, males will provide paternal care in exchange for future mating opportunities. Low certainty of paternity should place strong selection pressure on males not to provide care to young that are unlikely to be kin (Møller & Cuervo 2000) as providing care is energetically expensive and could influence a male’s ability to breed the following season (Houston et al. 2005). However, staying with the female and caring for her young could lead to the formation of a pair bond and further matings, which increases the certainty of paternity later. Furthermore, even though a male may show decreased body condition by caring, the costs could be offset by the benefits gained through raising strong, healthy offspring. This is seen in owl monkeys Aotus azarai (Fernandez-Duque et al. 2008; Wolovichet al. 2008; Fig. 2). 

  

Fig. 2 Owl monkeys Aotus azarai 

(Unknown. Picture accessed 12 July 2014; 14h25)

(http://mamiferosdomundo.blogspot.com.au/2013/04/aotus-azarae-macaco-da-noite-de-azara.html)

2) Males will provide care when the certainty of paternity is high, as providing care to biological offspring increases the father’s lifetime reproductive success if the offspring survive to reproduce themselves; and 3) Males may provide care when it provides a direct benefit to the offspring, through enhanced development, growth or survival. For example, rodent pups require exogenous heat (through huddling) to ensure growth and survival, as they are unable to thermoregulate (Wang & Novak 1994). By providing care, males reduce heat loss from their young and enhance their survival, thereby enhancing their survival and growth, as seen in California mice Peromyscus californicus (Gubernick & Teferi 2000; Fig. 3). It is thought that this last circumstance is the most likely explanation for the evolution of paternal care (Woodroffe & Vincent 1994).

Fig. 3 California mice Peromyscus californicus 

(Unknown. Picture accessed 12 July 2014; 14h35) 

(http://abcnews.go.com/Technology/bpa-chemical-found-environment-reproductive-scientists-report/story?id=18506698)

In my next blog, I’ll take you through the development of paternal care.