Abstract
Elphidium macellum is a benthic foraminifer commonly found in the Patagonian fjords. To test whether its highly variable morphotypes are ecophenotypes or different genotypes, we analysed 70 sequences of the SSU rRNA gene from 25 specimens. Unexpectedly, we identified 11 distinct ribotypes, with up to 5 ribotypes co-occurring within the same specimen. The ribotypes differ by varying blocks of sequence located at the end of stem-loop motifs in the three expansion segments specific to foraminifera. These changes, distinct from typical SNPs and indels, directly affect the structure of the expansion segments. Their mosaic distribution suggests that ribotypes originated by recombination of two or more clusters of ribosomal genes. We propose that this expansion segment polymorphism (ESP) could originate from hybridization of morphologically different populations of Patagonian Elphidium. We speculate that the complex geological history of Patagonia enhanced divergence of coastal foraminiferal species and contributed to increasing genetic and morphological variation.
Highlights
Member of the family Elphidiidae [1], Elphidium macellum is a common species of benthic foraminifera that occurs in coastal marine environment
The initial aim of the present study was to establish the phylogenetic position of E. macellum among elphidiids and to test whether its high morphological variations were indicative of cryptic speciation or whether they were induced by environmental factors
Considering the exceptional intra-genomic variability and the extraordinary ‘fragmented’ design of the SSU rDNA described above, the present study strongly suggests the occurrence of recombination within different sets of the SSU rRNA gene of E. macellum
Summary
Member of the family Elphidiidae [1], Elphidium macellum is a common species of benthic foraminifera that occurs in coastal marine environment. An interesting feature of Elphidiidae, is the high morphological variability observed between individuals of the same species and often within the same population [5,6,7]. These morphological variations are especially well documented in the case of E. macellum from Patagonia [8,9]. The taxonomic classification of elphidiids remains unclear and nothing is known about the molecular aspect of this intra-specific variability
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