Defense of territories by male-female pairs in the Red-Backed Salamander (Plethodon cinereus)

Both adult males and females of the Red-Backed Salamander (Plethodon cinere us) maintain feeding territories under cover objects (rocks and logs on the forest Boor) during the summer noncourtship and autumn and spring courtshi p seasons. Previous research found that, during the summer, 28% of the adul ts occurred as male-female pairs under cover objects, whereas male-male and female-female pairs rarely occurred. Therefore, we tested the hypothesis t hat male-female pairs codefense territories against intruders during the co urtship 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. I n laboratory experiments, we employed six randomized treatments during: the courtship season (n = 27 pairs) but only the first two treatments during t he noncourtship season (n = 29 pairs). The treatments were the male-female pair confronting (1) a single male intruder and (2) a single female intrude r, the male resident alone confronting (3) a single male intruder and (4) a single female intruder, and the female resident alone confronting (5) a si ngle male intruder and (6) a single female intruder. During the courtship s eason, intruding males did not spend significantly different amounts of tim e 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 te rritories defended by a male-female pair versus territories defended by a s ingle salamander (male or female) from the pair, hlale 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 cour tship and noncourtship seasons, males in pairs spent significantly more tim e in aggression toward intruding males than did their female partners, and females in pairs spent significantly more time in aggression toward intrudi ng females than did their partners. Thus, our experiment suggests that male -female pairs as residents can codefend territories but not in a cooperativ e manner. Because paired male residents were more aggressive to male intrud ers, whereas paired female residents were more aggressive to female intrude rs, we suggest that males in pairs may not be willing to pass up future pol ygynous relationships, and females in pairs may not be willing to pass up f uture polyandrous relationships.