Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, Sagitta elegans and S. setosa

• Published in: Marine Biology
• Main Authors: Peijnenburg, K, T C A, van Haastrecht, E, K, Fauvelot, Cécile
• Other Authors: Institut de Recherche pour le Développement (IRD), Ecologie marine tropicale des océans Pacifique et Indien (ENTROPIE Nouvelle-Calédonie ), Institut de Recherche pour le Développement (IRD Nouvelle-Calédonie )-Délégation Ifremer de Nouvelle-Calédonie, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de la Nouvelle-Calédonie (UNC)-Centre National de la Recherche Scientifique (CNRS), Institute for Biodiversity and Ecosystem Dynamics - IBED (NETHERLANDS), Institute for Biodiversity and Ecosystem Dynamics (IBED)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2005
• Subjects: [SDV.EE]Life Sciences [q-bio]/Ecology; environment; North East Atlantic
• Online Access: https://ird.hal.science/ird-03044192; https://ird.hal.science/ird-03044192/document; https://ird.hal.science/ird-03044192/file/Peijnenburg_et_al_2005_MarBiol.pdf; https://doi.org/10.1007/s00227-005-0041-2

International audience Sagitta elegans and S. setosa are the two dominant chaetognaths in the NorthEast (NE) Atlantic. They are closely related and have a similar ecology and life history, but differ in distributional ranges. Sagitta setosa is a typical neritic species occurring exclusively above shelf regions, whereas S. elegans is a more oceanic species with a widespread distribution. We hypothesised that neritic species, because of smaller and more fragmented populations, would have been more vulnerable to population bottlenecks resulting from range contractions during Pleistocene glaciations than oceanic species. To test this hypothesis we compared mitochondrial Cytochrome Oxidase II DNA sequences of S. elegans and S. setosa from sampling locations across the NE Atlantic. Both species displayed very high levels of genetic diversity with unique haplotypes for every sequenced individual and an approximately three times higher level of nucleotide diversity in S. elegans (0.061) compared to S. setosa (0.021). Sagitta setosa mitochondrial DNA (mtDNA) haplotypes produced a star-like phylogeny and a uni-modal mismatch distribution indicative of a bottleneck followed by population expansion. In contrast, S. elegans had a deeper mtDNA phylogeny and a multi-modal mismatch distribution as would be expected from a more stable population. Neutrality tests indicated that assumptions of the standard neutral model were violated for both species and results from the McDonald-Kreitman test suggested that selection played a role in the evolution of their mitochondrial DNA. Congruent with these results, both species had much smaller effective population sizes estimated from genetic data when compared to census population sizes estimated from abundance data, with a factor of $10 8-10 9 difference. Assuming that selective effects are comparable for the two species, we conclude that the difference in genetic signature can only be explained by contrasting demographic histories. Our data are consistent with the hypothesis that in ...