Population variation of the North Island rifleman (Acanthisitta chloris granti): Implications for conservation management

Abstract

Effective conservation management of threatened species involves the preservation of both adaptive diversity and evolutionary potential. One of the key steps in forming a cohesive and effective conservation management plan is therefore the analysis of levels of variation across a species distribution, particularly for fragmented species which show discontinuous distributions. Discussion regarding the analysis of fundamental units for conservation has been ongoing. The terms Evolutionarily Significant Unit (ESU) and Management Unit (MU) have been proposed to represent sub-populations which represent distinct units of diversity and therefore have distinct evolutionary potential. While debate around appropriate definition of conservation units continues, most definitions outline the need for integration of both genotypic and phenotypic data. This research aimed to analyse levels of both genotypic and phenotypic variation across isolated populations of the North Island rifleman (Acanthisitta chloris granti). The analysis of variation across rifleman populations involved four studies analysing population variation in genetic, morphological and behavioural traits. Results indicate that the North Island distribution of rifleman is characterized by three divergent genetic lineages including the sole insular population, two populations in the south-east of the North Island and the remaining mainland populations. Several key areas with very low genetic diversity were also identified. Morphological variation was measured in terms of size and plumage colouration and was found to vary on a spatial scale. The population in the Eastern Ranges in particular was characterised by significantly brighter and more colourful male plumage which may be associated with increased levels of sexual selection as a result of competition for mates at high densities. This finding was supported by an analysis of breeding behaviour variation which found that levels of cooperative breeding were found only in this high density population. Structural components of rifleman call vocalisations were also found to vary on a spatial scale, however playback experiments indicated that these variations do not result in reduced conspecific recognition in a territorial context. The results of these analyses were used to provide key recommendations for future conservation management of the rifleman, particularly with regard to the use of translocation. This study provides evidence for the diagnosis of at least three MUs across the North Island, however further analysis incorporating nuclear genetic markers may find evidence of ESUs.