Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA.
San Diego Zoo Wildlife Alliance, Escondido, CA, USA.
J Hered. 2021 Dec 17;112(7):590-601. doi: 10.1093/jhered/esab058.
Three subspecies of Northern Bahamian Rock Iguanas, Cyclura cychlura, are currently recognized: C. c. cychlura, restricted to Andros Island, and C. c. figginsi and C. c. inornata, native to the Exuma Island chain. Populations on Andros are genetically distinct from Exuma Island populations, yet genetic divergence among populations in the Exumas is inconsistent with the 2 currently recognized subspecies from those islands. The potential consequences of this discrepancy might include the recognition of a single subspecies throughout the Exumas rather than 2. That inference also ignores evidence that populations of C. cychlura are potentially adaptively divergent. We compared patterns of population relatedness in a three-tiered host-parasite system: C. cychlura iguanas, their ticks (genus Amblyomma, preferentially parasitizing these reptiles), and Rickettsia spp. endosymbionts (within tick ectoparasites). Our results indicate that while C. c. cychlura on Andros is consistently supported as a separate clade, patterns of relatedness among populations of C. c. figginsi and C. c. inornata within the Exuma Island chain are more complex. The distribution of the hosts, different tick species, and Rickettsia spp., supports the evolutionary independence of C. c. inornata. Further, these patterns are also consistent with two independent evolutionarily significant units within C. c. figginsi. Our findings suggest coevolutionary relationships between the reptile hosts, their ectoparasites, and rickettsial organisms, suggesting local adaptation. This work also speaks to the limitations of using neutral molecular markers from a single focal taxon as the sole currency for recognizing evolutionary novelty in populations of endangered species.
三种北巴哈马岩鬣蜥亚种，Cyclura cychlura，目前被认可：C. c. cychlura，仅限于安德罗斯岛，和 C. c. figginsi 和 C. c. inornata，原产于埃克苏马群岛链。安德罗斯岛上的种群在遗传上与埃克苏马岛的种群不同，但埃克苏马群岛上的种群遗传分化与这两个岛屿上目前认可的两个亚种不一致。这种差异的潜在后果可能包括在整个埃克苏马群岛只承认一个亚种，而不是两个亚种。这种推断也忽略了 C. cychlura 种群可能存在适应性分化的证据。我们比较了一个三层宿主-寄生虫系统中的种群亲缘关系模式：C. cychlura 鬣蜥、它们的蜱（属 Amblyomma，优先寄生这些爬行动物）和共生的 Rickettsia 属内共生体（在蜱的外寄生虫内）。我们的结果表明，虽然安德罗斯岛上的 C. c. cychlura 一直被支持为一个独立的分支，但埃克苏马群岛链上 C. c. figginsi 和 C. c. inornata 种群之间的亲缘关系模式更为复杂。宿主、不同的蜱种和共生的 Rickettsia 属的分布支持了 C. c. inornata 的进化独立性。此外，这些模式也与 C. c. figginsi 内的两个独立的进化上有意义的单位一致。我们的研究结果表明，爬行动物宿主、它们的外寄生虫和立克次体生物之间存在协同进化关系，表明存在局部适应。这项工作也说明了使用单一焦点分类群的中性分子标记作为识别濒危物种种群进化新颖性的唯一货币的局限性。
