Structure and genetic diversity of Ixora margaretae an endangered species: a baseline study for conservation and restoration of natural dry forest of New Caledonia

The dry forests of New Caledonia are an excep- tional ecosystem because of their numerous endemic botan- ical species and their highly diversified fauna of insects, mollusks, reptiles and birds. Unfortunately, the area of the dry forests has been significantly reduced, mainly by human activities. Ecological, phenological and genetic analysis of Ixora margaretae, a symbolic species of the sclerophyll forest, has revealed contrasting traits among natural stands. The division of the natural range and then the separation of forest islands has greatly reduced the existing genetic vari- ability of this species. The genetic diversity is strongly structured in genetic clusters which correspond well to spe- cific ecotypes according to the environmental conditions and the forest types. Furthermore, genetic analysis of the reproductive and non-reproductive trees as well the half- sib families obtained by complete protection of mother trees has revealed substantial genetic drift which has resulted in increased loss of allelic variability. The total consumption of seeds by mainly rats confirms the ob- served absence of natural regeneration. All these results show that measures taken to protect the stands of dry forests will not be enough to maintain sufficient genetic variability of I. margaretae populations in the long term. Assisted regeneration with control of the increase in var- iability will be necessary to maintain the biodiversity of the species. The results obtained for I. margaretae must be confirmed with other symbolic species in order to take the necessary measures for the effective preservation of the dry forests in New Caledonia.

新喀里多尼亚干旱森林是一类极具特殊性的生态系统，其拥有数量众多的特有植物物种，以及物种高度丰富的昆虫、软体动物、爬行动物与鸟类区系。遗憾的是，受人类活动主导影响，该区域干旱森林的面积已出现显著缩减。针对硬叶常绿林（sclerophyll forest）的标志性物种Ixora margaretae开展的生态学、物候学与遗传学分析显示，其天然林分存在显著的性状分化。自然分布区的分割以及森林岛的隔离效应，大幅降低了该物种的现有遗传变异水平。该物种的遗传多样性呈现强烈的遗传簇（genetic clusters）结构，且各遗传簇与对应环境条件及森林类型下的特定生态型（ecotypes）高度契合。此外，通过对生殖与非生殖植株、以及通过母株完全保护获得的半同胞家系（half-sib families）开展遗传分析，研究人员发现存在显著的遗传漂变现象，进而导致等位基因变异进一步丢失。主要由鼠类造成的种子全面消耗，也印证了该物种自然更新缺失的观测结果。综上所有研究结果可见，仅采取保护干旱森林天然林分的措施，不足以长期维持Ixora margaretae种群的充足遗传变异。需通过调控遗传变异增长的辅助更新手段，方能维系该物种的生物多样性。本研究针对Ixora margaretae的发现，需在其他标志性物种中加以验证，以便为新喀里多尼亚干旱森林的有效保护制定针对性措施。