Body condition and order of arrival affect cooperative nesting behaviour in four-toed salamanders Hemidactylium scutatum

Joint nesting is defined as two or more conspecific females laying eggs in the same nest. Female four-toed salamanders may lay and brood eggs in a solitary nest, lay eggs in a joint nest and brood them along with eggs of other females, or lay eggs in a joint nest that is brooded by another female. Using data from a 9-year study in mesocosms, I found that body condition index scores were associated with nesting behaviour. Joint nesters who stayed with the nest were in the best condition, whereas joint nesters who deserted the nest were in the worst condition. Solitary nesters, who almost always stayed with their nests, were in intermediate condition. Nesting behaviour was also a function of whether a female founded or joined a nest. Females that laid eggs first in what ultimately became a joint nest tended to stay regardless of relative body condition. Nest joiners stayed if they were in relatively good condition, but deserted if they were in relatively poor condition. Nest founders may tolerate nest joiners because there is no cost to doing so, they cannot nest again within a season, and the costs of fighting to exclude a potential nest joiner are prohibitive. Body condition of individuals varies in populations and may often affect costs and benefits of nesting decisions. Therefore, the inclusion of body condition variation into models of joint nesting will lead to a more predictive theory of nesting and breeding decisions.