The cryptic and the apparent reversed: lack of genetic differentiation within the morphologically diverse plexus of the planktonic foraminifer Globigerinoides sacculifer
The cryptic and the apparent reversed: lack of genetic differentiation within the morphologically diverse plexus of the planktonic foraminifer Globigerinoides sacculifer
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DOI：
10.1666/0094-8373-39.1.21
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发表时间：
2013-12-01
期刊：
影响因子：
2.7
通讯作者：
Kucera, Michal
中科院分区：
文献类型：
--
作者：
Andre, Aurore;Weiner, Agnes;Kucera, Michal
先前对现存浮游有孔虫的遗传研究已经提供了证据，表明这些生物中传统的、严格的物种形态学定义低估了它们的生物多样性。在这里，我们报告了第一个与此模式相反的案例。现代（亚）热带植物丛（plexus Globigerinoides sacullifer）具有较大的形态变异，这导致丛内形态学末端成员的分类名称大量增加。为了明确其形态型的分类地位，并研究其目前部分分离的（亚）热带种群之间的遗传连通性，我们在全球海洋（亚）热带地表水中收集的所有最近形态型的丛丛中进行了两个核糖体RNA区域（SSU和its -1）的全球调查。出乎意料的是，我们发现丛内的遗传变异极低，遗传和形态差异之间没有相关性，这表明分类上的过度解释。考虑到其在（亚）热带大西洋和印度-太平洋的部分分离范围及其年龄（早中新世），形态种内的遗传同质性是出乎意料的。在快速进化的ITS-1区域的序列变异表明大西洋单倍型的存在，这表明相对最近（末次冰期）的隔离事件，随后从印度-太平洋恢复到大西洋的单向基因流动。这是浮游有孔虫中第一个形态物种的形态变异性超过其rDNA遗传变异性的例子。这种浮游有孔虫形态和遗传多样性不一致的证据可能使对其化石记录中进化模式的解释复杂化。
Previous genetic studies of extant planktonic foraminifera have provided evidence that the traditional, strictly morphological definition of species in these organisms underestimates their biodiversity. Here, we report the first case where this pattern is reversed. The modern (sub)tropical species plexus Globigerinoides sacculifer is characterized by large morphological variability, which has led to the proliferation of taxonomic names attributed to morphological end-members within the plexus. In order to clarify the taxonomic status of its morphotypes and to investigate the genetic connectivity among its currently partly disjunct (sub)tropical populations, we carried out a global survey of two ribosomal RNA regions (SSU and ITS-1) in all recent morphotypes of the plexus collected throughout (sub)tropical surface waters of the global ocean. Unexpectedly, we find an extremely reduced genetic variation within the plexus and no correlation between genetic and morphological divergence, suggesting taxonomical overinterpretation. The genetic homogeneity within the morphospecies is unexpected, considering its partly disjunct range in the (sub)tropical Atlantic and Indo-Pacific and its old age (early Miocene). A sequence variant in the rapidly evolving ITS-1 region indicates the existence of an exclusively Atlantic haplotype, which suggests an episode of relatively recent (last glacial) isolation, followed by subsequent resumption of unidirectional gene flow from the Indo-Pacific into the Atlantic. This is the first example in planktonic foraminifera where the morphological variability in a morphospecies exceeds its rDNA genetic variability. Such evidence for inconsistent scaling of morphological and genetic diversity in planktonic foraminifera could complicate the interpretation of evolutionary patterns in their fossil record.