PRINCIPALES RASGOS de la DIALÉCTICA MATERIALISTA de MAR

Parental care: correlated traits

In fish, there is a wide literature showing females prefer larger males in species that show biparental or paternal care (Downhower and Brown 1980; Noonan 1983; Keenleyside et al. 1985; Goto 1987; Bisazza and Marconato 1988; Cote and Hunte 1989; Rogers and Barlow 1991). Larger and more dominant males are more likely to be of higher physiological quality (e.g., Chellappa and Huntingford 1989; Guderley and Couture 2005) and female mate choice for larger males might mask a preference for better physiological condition, thereby also selecting for condition-dependence of male traits (Bonduriansky and Rowe 2005).

The condition of a male or his quality in terms of parental care is often related to his size. For example, guarding is one of the most common forms of parental care in fish and there appears to be a large male advantage in nest defence. Larger males are better at acquiring and guarding spawning sites (Bisazza and Marconato 1988; Lindström 1988) and their ability to obtain better quality nesting sites could also contribute to an increased survival rate of eggs (Hastings 1988; Cote and Hunte 1989; Kvarnemo et al. 1998). Guarding is a foraging limiting activity (Kraak and Videler 1991; Kraak 1996; Payne et al. 2002), and males have been shown to lose weight by the end of the caring period (Coleman and Fischer 1991; Maekawa et al. 1996; Jones and Reynolds 1999; Skolbekken and Utne-Palm 2001) which selects for males that are initially in better condition. Where dominance does not equate to increased parental care, however, females often choose overall paternal quality over male fighting ability (Forsgren 1997; Wong 2004; Wong and Candolin 2005).

Other factors effecting female choice - filial cannibalism

Females also choose mates based on other male traits such as courtship (Knapp and Warner 1991; Östlund and Ahnesjö 1998), nest characteristics (Sargent and Gebier 1980), and number of eggs in a nest. The incidence of females preferentially choosing to lay their eggs with males who already have eggs in their nest is widespread (Marconato and Bisazza 1986; Unger and Sargent 1988; Cote and Hunte 1989; Petersen 1990; Kraak and Groothuis 1994; Forsgren et al. 1996; Goulet 1998; Reynolds and Jones 1999; Jennions and Polakow 2001; Okuda et al. 2002). There may be several reasons for this: (1) to reduce the risk of males eating the whole clutch or abandoning the nest by increasing total clutch size (Rohwer 1978); (2) to reduce the proportion of her eggs that are eaten during care (e.g., Forsgren et al. 1996); (3) to increase male parental investment by increasing clutch size (e.g., Coleman et al. 1985; Karino and Arai 2006); and (4) to increase the chance that a male is a high quality parent (mate choice copying) (Kraak and Videler 1991).

If the costs of care are too great (or the benefits too small), males often eat their own eggs (filial cannibalism) or desert the brood to regain condition to invest in future reproduction (FitzGerald 1992b; Marconato et al. 1993; Kraak 1996; Okuda and Yanagisawa 1996; Kvarnemo et al. 1998; Marques 2003). This behaviour is adaptive for males, who benefit in terms of resource consumption but represents a loss of investment for the female. Expenditure on small clutches presents a low return on investment which may be better allocated to future broods, so whole clutch filial cannibalism is usually found when males have small or low quality clutches (Petersen 1990; Sargent 1992; Smith 1992; Svensson et al. 1998; Manica 2002a; Lissaker et al. 2003; Manica 2003; Karino and Arai 2006). Experimental reductions of clutches have shown that parents have a threshold below which a clutch is totally cannibalised (Lavery and Keenleyside 1990) or a male will abandon his eggs (Jennions and Polakow 2001). Females who preferentially lay eggs in nests where there are already eggs present will increase the clutch size of a male’s brood and therefore decrease the likelihood of losing her investment to whole clutch filial cannibalism or desertion.

Males do not always eat the entire clutch; sometimes they eat only a portion of their eggs. Partial clutch cannibalism is theorised to be a method of regaining energy lost from care to invest into current or future offspring (Unger and Sargent 1988; Forsgren et al. 1996; Reynolds and Jones 1999). The behaviour is therefore adaptive as it can reduce the loss of condition and increase a male’s overall reproductive success by increasing the hatching success of the current reproductive event and maintaining condition for future clutches (Sargent 1985; Smith and Wootton 1995). As with whole clutch/or

cannibalism, females who choose to lay eggs in nests where there are already eggs present will dilute the effect of partial cannibalism on her eggs by increasing the total clutch size.

Evidence that males devote greater amounts of parental investment into larger clutches is widespread in fish (Coleman et al. 1985; Sargent 1988; Forsgren et al. 1996; Karino 1997; Jennions and Polakow 2001; Suk and Choe 2002; Manica 2003; Karino and Arai 2006) though some studies have found no relationship between clutch size and effort (Knapp and Warner 1991; Skolbekken and Utne-Palm 2001). Females who preferentially lay their eggs to maximise their mates clutch size should be at a selective advantage and receive direct benefits for this behaviour. Finally, it has been suggested that a female preference for males with large broods might be adaptive because the number of eggs present in the nest is probably a reliable predictor of the survival chances of the eggs (Kraak and Videler 1991). Overall parental investment is also affected by the environmental conditions, such as temperature (Skolbekken and Utne-Palm 2001; Cooke et al. 2003) and oxygen level (Lissaker et al. 2003).