Latitudinal distribution of polyplacophorans along the South-eastern Pacific coast: unravelling biases in geographical diversity patterns

Abstract

Latitudinal diversity patterns in marine species are commonly estimated from literature records, which at times are incomplete and/or biased. Advances in molecular phylogenetics have contributed to avoid this bias, clarifying the identity of the species, improving our knowledge of species diversity and distribution. With the aim to identify biogeographic biases, we compiled and compared range distribution data of polyplacophorans along the South-eastern Pacific (SEP) coast (0 degrees-56 degrees S) generated from: (i) literature review (LIT dataset) and (ii) Operational Taxonomic Units (OTUs dataset), based on the analysis of 8949 individuals obtained from field sampling and biological collections. Cytochrome oxidase I (COI) and 16S rRNA of 104 specimens were used for genetic identification of conflictive morphospecies. Multivariate analysis (nMDS, PERMANOVA) were applied to test differences between datasets (LIT, OTUs) and also between biogeographic ecoregions. Just like prior studies based on literature reviews, the richness of LIT species showed an increase with latitude. Contrastingly, OTUs' richness peaked at intermediate latitudes showing a bell-shaped distribution, indicating that the LIT dataset was flawed by inaccuracies in the identification and location of polyplacophoran species on the South-eastern Pacific, causing an overestimation of their geographic ranges. Our results contrast with the previous richness patterns described for the SEP polyplacophorans, where species richness was reported to increase with latitude. Both an overestimation of geographic ranges and inaccuracies in the identification of species cause these differences. Biogeographical studies should be conducted on the basis of a comprehensive review of specimens with verifiable occurrences, and incorporate as far as possible genetic analysis to define the identity of conflicting morphospecies, in order to improve the estimation of species richness and the understanding of marine biodiversity.