Defense of Territories by Male-Female Pairs in the Red-Backed Salamander (Plethodon cinereus)

Abstract

Both adult males and females of the Red-Backed Salamander (Plethodon cinereus) maintain feeding territories under cover objects (rocks and logs on the forest floor) during the summer noncourtship and autumn and spring courtship seasons. Previous research found that, during the summer, 28% of the adults occurred as male-female pairs under cover objects, whereas male-male and female-female pairs rarely occurred. Therefore, we tested the hypothesis that male-female pairs codefend territories against intruders during the courtship season and that such codefense extends into the noncourtship summer. During October 1996 and June 1997, we collected male-female pairs, single males, and single females at Mountain Lake Biological Station, Virginia. In laboratory experiments, we employed six randomized treatments during the courtship season (n = 27 pairs) but only the first two treatments during the noncourtship season (n = 29 pairs). The treatments were the male-female pair confronting (1) a single male intruder and (2) a single female intruder, the male resident alone confronting (3) a single male intruder and (4) a single female intruder, and the female resident alone confronting (5) a single male intruder and (6) a single female intruder. During the courtship season, intruding males did not spend significantly different amounts of time on territories defended by a male-female pair versus territories defended by a single salamander (male or female) from the pair. However, during the courtship season intruding females did spend significantly less time on territories defended by a male-female pair versus territories defended by a single salamander (male or female) from the pair. Male and female intruders spent significantly less time on territories defended by a pair during the courtship season compared to the noncourtship season. During both the courtship and noncourtship seasons, males in pairs spent significantly more time in aggression toward intruding males than did their female partners, and females in pairs spent significantly more time in aggression toward intruding females than did their partners. Thus, our experiment suggests that male-female pairs as residents can codefend territories but not in a cooperative manner. Because paired male residents were more aggressive to male intruders, whereas paired female residents were more aggressive to female intruders, we suggest that males in pairs may not be willing to pass up future polygynous relationships, and females in pairs may not be willing to pass up future polyandrous relationships.