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Unformatted text preview: ORIGINAL PAPER Defending young biparentally: female risk-taking with and without a male in the burying beetle, Nicrophorus pustulatus Stephen T. Trumbo Received: 3 August 2006 /Revised: 14 April 2007 /Accepted: 18 April 2007 /Published online: 11 May 2007 # Springer-Verlag 2007 Abstract A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk- taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothe- sized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female. Keywords Parental care . Brood defense . Infanticide . Parental effort . Cooperation Introduction Parental defensive effort and willingness to take risks, like other contest behavior, will vary with resource-holding potential (Parker 1974 ) and the relative value of winning a contest by the two contestants (Houston and McNamara 1988 ). A parent defending against a potentially infanticidal intruder might be expected to take few risks when the probability of a successful outcome is low and defensive effort of the parent is unlikely to alter the outcome (reviews in van Schaik and Janson 2000 ). Similarly, if the intruder has low resource-holding potential or the reproductive value of committing infanticide is low, then the intruder is not expected to take risks. In both cases, injuries are expected to be infrequent. The greatest escalation of potentially infanticidal encounters and the highest proba- bility of injury are expected when both the parent and intruder place a high value on a successful outcome and...
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This note was uploaded on 04/14/2008 for the course BIOL 115 taught by Professor Diggs during the Fall '07 term at Austin College.
- Fall '07