Inferred vs Realized Patterns of Gene Flow: An Analysis of Population Structure in the Andros Island Rock Iguana

Ecological data, the primary source of information on patterns and rates of migration, can be integrated with genetic data to more accurately describe the realized connectivity between geographically isolated demes. In this paper we implement this approach and discuss its implications for managing populations of the endangered Andros Island Rock Iguana, Cyclura cychlura cychlura. This iguana is endemic to Andros, a highly fragmented landmass of large islands and smaller cays. Field observations suggest that geographically isolated demes were panmictic due to high, inferred rates of gene flow. We expand on these observations using 16 polymorphic microsatellites to investigate the genetic structure and rates of gene flow from 188 Andros Iguanas collected across 23 island sites. Bayesian clustering of specimens assigned individuals to three distinct genotypic clusters. An analysis of molecular variance (AMOVA) indicates that allele frequency differences are responsible for a significant portion of the genetic variance across the three defined clusters (Fst = 0.117, p0.01). These clusters are associated with larger islands and satellite cays isolated by broad water channels with strong currents. These findings imply that broad water channels present greater obstacles to gene flow than was inferred from field observation alone. Additionally, rates of gene flow were indirectly estimated using BAYESASS 3.0. The proportion of individuals originating from within each identified cluster varied from 94.5 to 98.7%, providing further support for local isolation. Our assessment reveals a major disparity between inferred and realized gene flow. We discuss our results in a conservation perspective for species inhabiting highly fragmented landscapes.

作为阐明迁移模式与速率的核心信息源，生态数据可与遗传数据整合联用，从而更精准地描述地理隔离同类群（deme）间的实际连通性。本研究采用该研究思路，并探讨其在濒危物种安德罗斯岛岩鬣蜥（Cyclura cychlura cychlura）种群管理中的应用价值。该鬣蜥为巴哈马安德罗斯岛特有物种，其栖息的陆块由大型岛屿与小型礁屿组成，呈现高度破碎化特征。过往野外观测表明，由于此前推断的较高基因流速率，这些地理隔离的同类群曾被认为处于随机交配状态。本研究以此前的观测为基础，利用16个多态性微卫星标记（microsatellite），对采自23个岛屿样点的188只安德罗斯岛岩鬣蜥开展遗传结构与基因流速率分析。对个体进行贝叶斯聚类分析后，可将其划分为3个独立的基因型簇。分子方差分析（AMOVA）结果显示，在这3个划定的簇中，等位基因频率差异对整体遗传变异的贡献占比显著（Fst=0.117, p=0.01）。这些基因型簇与大型岛屿及被宽阔强流水道分隔的卫星礁屿存在显著关联。本研究结果表明，宽阔水道对基因流的阻碍作用远超仅通过野外观测推断的程度。此外，本研究借助BAYESASS 3.0软件间接估算了基因流速率：各鉴定簇内的个体来源占比介于94.5%至98.7%之间，进一步佐证了种群的局部隔离性。本研究评估揭示了推断基因流与实际基因流之间存在显著差异。最后，本研究从保护生物学视角，针对栖息于高度破碎化生境的物种，对上述研究结果展开了讨论。