Data from: Evidence for Bergmann's rule and not allopatric subspeciation in the threatened kaka (Nestor meridionalis)

Species of conservation concern characterized by small and declining populations greatly benefit from proactive management approaches such as population translocations. Because they often show intra-specific genetic and phenotypic variation, which can result from drift or differential selective pressures between habitats, understanding the distribution of such variation and its underlying processes is a prerequisite to develop effective management guidelines. Indeed, translocations among genetically differentiated populations potentially locally adapted are discouraged in order to avoid outbreeding depression, while translocations among populations characterized by high gene flow with no evidence for local adaptation are encouraged. Here, we first test whether 2 recognized subspecies, the North Island kaka (Nestor meridionalis septentrionalis) and South Island kaka (Nestor meridionalis meridionalis) of New Zealand fit a scenario of allopatric subspeciation following the separation of the North and South Islands at the end of the Pleistocene using 1 mtDNA (n = 96) and 9 microsatellite markers (n = 126). We then test whether morphological differences among the 2 subspecies support a pattern of local adaptation, comparing phenotypic divergence (P ST) and the level of divergence by drift alone (F ST) among populations. We find little population structure between islands, ruling out allopatric subspeciation in kaka. Further, P ST exceeds F ST, supporting an adaptive latitudinal size cline consistent with Bergmann’s rule. These results therefore suggest that using neutral genetic diversity alone can be misleading when identifying management units and that the nature of phenotypic variation should be considered in translocations efforts. We finally discuss North and South Island management units but suggest that cross-island translocation be allowed.

针对种群规模微小且持续衰退的保育关注物种，主动保育策略（如种群易地保护）可使其获得显著收益。这类物种常存在由遗传漂变或生境间差异化选择压力所引发的种内遗传与表型变异，明晰此类变异的分布格局及其形成机制，是制定有效保育管理指南的必要前提。事实上，为避免远交衰退，应避免在遗传分化显著且可能已产生本地适应的种群间开展易地保护；而在基因交流频繁、无本地适应迹象的种群间则可推行易地保护措施。本研究首先以线粒体DNA（mtDNA，样本量n=96）与9组微卫星标记（样本量n=126）为分析工具，检验新西兰境内两个已被认定的亚种——北岛卡卡鹦鹉（Nestor meridionalis septentrionalis）与南岛卡卡鹦鹉（Nestor meridionalis meridionalis）是否符合更新世末期南北岛分离后形成的异域亚种分化模式。随后，本研究通过比较表型分化系数（PST）与仅由遗传漂变驱动的种群分化水平（遗传固定指数FST），检验两个亚种间的形态差异是否支持本地适应格局。研究结果显示，南北岛间几乎不存在种群遗传结构，这排除了卡卡鹦鹉存在异域亚种分化的可能。此外，PST显著高于FST，表明其存在符合伯格曼法则（Bergmann’s rule）的适应性纬度体型梯度。因此，本研究结果提示，在划定保育管理单元时仅依赖中性遗传多样性可能产生误导，易地保护工作中应充分考量表型变异的本质。我们最终针对南北岛提出了保育管理单元方案，但建议允许跨岛种群易地保护。