Here, we manipulated both age and social experience of male burying beetles (N. vespilloides) to investigate their effects on contest behavior, contest outcome, and winner loser effects.
We independently manipulated age and social experience of focal male beetles used in our experiment, and investigated their effects on contest behavior and outcome using a 2×2 factorial design.
As residual reproductive value is likely to influence contest behavior via effects on motivation rather than fighting ability, these studies provide further, albeit indirect, evidence that age effects on contest behavior that result from variation in residual reproductive value may be weak when fighting ability plays a prominent role in determining contest outcome.
Only 24 of the 47 males (51.1%) who won aggressive contests scored higher than their rival on PC2 (binomial p = 1.000), and the magnitude of the difference in PC2 between males had no effect on contest outcome (χ2 = 0.365, p = 0.546, Nagelkerke R2 = 0.010).
The numbers of previous contests experienced by focus fish and by opponent fish had no effect on contest outcome and were removed from the model.
Neither sex nor body size had a significant effect on contest duration when both settled and tied contests were included in a Cox regression (β sex) = 0.71 for males compared to females, z = 1.54, p = 0.12; β(RSD) = 5.83, z = 1.16, p = 0.25; interaction sex and RSD: LRT, χ = 0.71, df = 1, p = 0.398).
As, however, olfactory signals produced by contestants (Barata et al. 2007) could influence the behavior of fish in later contests, we confirmed that the number of previous contests on the same day had no effect on the activities of the contestants (generalized linear model testing the effects of contest number on the rates of charges and displays; all p values >0.2).
Here, we independently manipulate male age and social experience to examine their effects on male contest behavior in the burying beetle Nicrophorus vespilloides.
Cumulative link models (CLM) were built in the package "ordinal" (Christensen 2010) to test for sex-specific effects of RSD on contest outcome, which was coded as an ordinal response variable (with levels "loser," "tied," and "winner").
Our results show that not only was there no difference between young and old males in their ability to win a contest (i.e. no effect of age on contest outcome), but there was also no effect of male age on male motivation to win a contest (i.e. no effect of age on contest behavior).
Both males were placed onto the carcass at the same time to avoid any effects of ownership on contest behavior or outcome as previous studies have shown that resource holders are more likely to win contests in N. vespilloides (Otronen 1988).
