Does Experience Affect the Outcome of Male-Male Contests in the Burying Beetle, Nicrophorus quadripunctatus?

The bigger individual in a fight usually wins unless the smaller individual is a resident or has recently won a fight. I conducted three experiments on the effects of body size, residency, and fight history on the outcome of male-male fights in a burying beetle. Fights were staged between an intruding male and the male of a male-female pair. When males differed in size, the larger male usually won regardless of residency or individual fight histories. Residents and winners of previous fights won only when competing males were similar in size. Hence, male body size largely determines the outcomes of fights in this beetle. 1. Introduction Fighting between males over mating opportunities is a widespread phenomenon in the animal kingdom and has received much empirical attention [1]. Fighting ability is often correlated with morphological and physiological attributes such as body size, weaponry, and ornaments [1], but these are not the only attributes that may determine fighting ability. It has been hypothesized that the “prior residence effect” can also affect the outcome of fighting contests in accordance with the convention “resident wins, intruder retreats” [2]. A third effect is the “winner-loser effect,” in which winners are more likely to win again and losers are more likely to lose again [3]. These two effects sometimes counteract morphological and physiological attributes (e.g., [4]). The complex parental behaviour of burying beetles (Nicrophorus: Silphidae) has been well-studied (reviewed in [5, 6]). Nicrophorus exploits small vertebrate carrions as food for its young. A male-female pair prepares a carcass by burying it, removing its hair, and rounding it into a ball. Eggs are then laid in the soil adjacent to the carrion ball. After hatching, the larvae crawl to the carrion ball, where they are fed by parental regurgitations. Nicrophorus is generally monogamous [7–9], and both sexes display intense intrasexual competition [10, 11]. Two or more individuals of both sexes often locate the same carcass, but usually only a single dominant pair eventually occupies the carcass. Resident males are more likely to be injured than resident females [12], and males have a greater tendency to guard [13, 14]. Contests between males are expected to be more intense than those between females. Larger individuals of Nicrophorus usually win contests among conspecifics in N. humator [10] or in N. quadripunctatus [11]. However, the presence of the winner effect is supported by a previous study of N. humator [15], and it is possible that other attributes affect the