Fluctuating asymmetry and body morphology in relation to population bottlenecks of introduced birds in New Zealand.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The introduction of exotic bird species to New Zealand (NZ) from the United Kingdom (UK) over 100 years ago unintentionally created an ideal study system to examine potential changes in developmental stability due to bottleneck effects. In this study I measured fluctuating asymmetry (FA; random deviations from symmetry between bilaterally symmetrical traits) in 13 species of introduced birds in NZ. FA has been used for conservation purposes as an early warning system of increased developmental instability (DI; the inability to cope with random genetic or environmental perturbations during development). I evaluated DI using FA in several anatomical external and internal morphological traits, and compared differences in body morphology between introduced and source populations in relation to the bottleneck size. I also examined FA in nestlings in two closely related introduced species that passed through two different-sized population bottlenecks. Differences in FA in relation to bottleneck severity were only observed in external traits. FA in external traits in some NZ populations differed from their UK counterparts, but it was in the opposite direction than predicted. FA in external traits varied significantly across NZ populations of introduced species - the most severe bottlenecks species exhibited higher levels of FA than species that passed through larger bottlenecks. There were no patterns in FA and bottleneck size for skeletal traits, most likely due to differences in environmental and genetic stressors resulting in species- and characterspecific FA relationships. Nestling FA was the same for both species, despite the large difference in bottleneck size. FA did decrease over the nestling period, although not at the same rate for each trait, most likely due to the differing costs of development, functional importance, and other environmental stressors that might influence FA in each trait differently. Overall changes in body morphology occurred in four species introduced to NZ, and all species exhibited some changes in trait morphology but were not related to bottleneck size. Finally, the proportion of deformities (deviations from normal phenotype) was higher in NZ than in UK suggesting passing through a bottleneck increased the probability of abnormalities. Although the associations between FA, body morphology and bottleneck severity are complex, my results confirm that measures of morphology have the potential of being useful indicators of DI in the management of endangered species.