Estimating ancestral states of a communicative display:: a comparative study of Cyclura rock iguanas

In this study we describe the signature headbob displays of seven of the eight extant species of Cyclura iguanas using data collected from the field and from captive animals. We used phylogenetic comparative methods to estimate the ancestral states of several measures of the headbob displays, including number of headbobs and the duration of headbobs and inter-bob pauses. Divergence in the headbob display among species has been substantial, with some major changes occurring within only a few (about six) generations. Otherwise, results are consistent with those obtained previously for other lizards which suggest that there is an evolutionary limit on the total duration of headbob displays. Differences in the results obtained using different phylogenetic methods suggest that although estimates of ancestral states are reasonably robust to violations of evolutionary assumptions, we cannot determine the standard errors of those ancestral phenotypes accurately without more detailed information about the types of forces (e.g. selection, drift) underlying evolutionary change in these traits. In particular, within-species variation had a substantial impact on the standard errors of estimated ancestral states, and should be included in such estimations whenever possible. Finally, our results emphasize the importance of conserving behavioural as well as genetic diversity in trying to preserve endangered species for possible reintroduction into the wild. (C) 1998 The Association for the Study of Animal Behaviour.