Pair-living in the absence of obligate biparental care in a lizard: trading off sex and food?

A pair-living social organisation can typically be explained by obligate biparental care. We investigated pair-living in the absence of biparental care in the Australian sleepy lizard, Tiliqua rugosa, which forms exceptionally strong pair bonds. We fitted 10 lizards, five male-female pairs, with Global Positioning System (GPS) recorders and continuously monitored social associations and separations between active pair partners, based on location records taken every 10min over 3mo. Males temporarily separated and reunited the pair more frequently than females, but females also contributed to the maintenance of the pair bond. These behavioural data were consistent with the hypothesis that females successfully coerce males into associations with one female. Lower frequencies of social association between pair partners once mating had finished support this interpretation. Males that are coerced into pair associations appear to experience higher costs of pair-living than females, because males initiated temporary separations of the pair more frequently than females. Males showed higher movement activity and remained active later each day. This sex bias in activity may be an important mechanism to mitigate the higher costs of pair-living for males. Costs for males might include within-pair competition for food as females appear more competitive. Our study provides detailed empirical data on a lizard pair bond and provides important insights into pair-living in the absence of biparental care.