Widely distributed red algae often represent hidden introductions, complexes of cryptic species or species with strong phylogeographic structure

Abstract

Despite studies suggesting that most seaweeds are poor dispersers, many red algal species are reported to have circumglobal distributions. Such distributions have mostly been based on morphological identifications, but molecular data have revealed a range of issues with morphologically defined species boundaries. Consequently, the real distribution of such reportedly circumglobal species must be questioned. In this study, we analyzed molecular data sets (rbcL gene) of nine species in the Rhodomelaceae for which samples were available from widely spaced geographical locations. Three overall patterns were identified: (i) species showing strong phylogeographic structure (i.e., phylogenetic similarity correlates with geographical provenance), often to the point that populations from different locations could be considered as different species (Lophosiphonia obscura, Ophidocladus simpliciusculus, Polysiphonia villum, and Xiphosiphonia pinnulata); (ii) species with a broad distribution that is explained, in part, by putative human-mediated transport (Symphyocladia dendroidea and Polysiphonia devoniensis); and (iii) non-monophyletic complexes of cryptic species, most with a more restricted distribution than previously thought (Herposiphonia tenella, Symphyocladia dendroidea, and the Xiphosiphonia pennata complex that includes the species Xiphosiphonia pinnulata and Symphyocladia spinifera). This study shows that widely distributed species are the exception in marine red algae, unless they have been spread by humans.

Complete Mitochondrial Genomes Reveal Population-Level Patterns in the Widespread Red Alga Gelidiella fanii (Gelidiales, Rhodophyta)

“…However, pairwise divergence in rbcL was 0-0.5%, a value lower than interspecific divergences (0.8-0.9%) in the Gelidiales, with the exception of a closely related sibling species (Boo et al, 2014). The pairwise divergences in rbcL fell within the large range of reported rhodomelacean divergences, e.g., 0.4-1% in Symphyocladiella dendroidea (Montagne) D.Bustamante, B.Y.Won, S.C.Lindstrom and T.O.Cho, and 0.3-0.7% in Melanothamnus harveyi (Bailey) Díaz-Tapia and Maggs (Díaz-Tapia et al, 2018). Pairwise divergence within or between species is a relative value rather than an absolute criterion for species recognition.…”

“…The broad range of G. fanii, spanning the east and west margins of the Indo-Pacific Ocean, is part of an interesting biogeographical story. In contrast, recent molecular studies have revealed that many so-called widespread species are introduced, misidentified species, or consisted of a complex of local cryptic species (Won et al, 2009;Sherwood et al, 2010;Boo et al, 2018;Díaz-Tapia et al, 2018;Leliaert et al, 2018). That said, this and previous studies have recently distinguished G. fanii from its very similar and widespread congener, G. acerosa, with which it has been long confused.…”

Reassessment of the genus Lophurella (Rhodomelaceae, Rhodophyta) from Australia and New Zealand reveals four cryptic species

“…As a result, in the macroalgae including the family Rhodomelaceae, cryptic diversity is commonly discovered when molecular assisted taxonomy is used for species diversity assessments (e.g. Guillemín et al, 2016;Savoie & Saunders, 2016Saunders et al, 2017;Díaz-Tapia et al, 2018a). New cryptic species have been detected as the result of comparing sequence data for specimens of the presumed same species from distant locations (e.g.…”

<italic>Alsidium oliveiranum</italic> sp. nov. (Rhodomelaceae, Rhodophyta), an overlooked species from the southwestern Atlantic based on morphology and DNA sequence data

“…The discovery of new species is often related to the finding of cryptic diversity, both when comparing molecular data of specimens from dis-DNA was extracted from silica gel-dried material following Saunders and McDevit (2012). Polymerase chain reaction (PCR) amplification was carried out for rbcL using the primers F2/R1452, F7/RrbcsStart, F7/R893 or F57/rbcLrevNEW (Freshwater and Rueness 1994, Mamoozadeh and Freshwater 2011, Saunders and Moore 2013, Díaz-Tapia et al 2018 and for cox1 using the primers GwsFn/Cox1R1 (Saunders 2008, Le Gall andSaunders 2010) or GazF1/GazR1 (Saunders 2005). Reactions were performed in a total volume of 25 µL, consisting of 5 µL 5× MyTaq reaction buffer, 0.7 µL 10 µM of forward and reverse primers, 0.125 µL 1 U/µL My Taq DNA Polymerase (Bioline, London, UK), 17.475 µL MilliQ water and 1 µL template DNA.…”

“…Our outgroup selection was based on the phylogenomic analyses of the major lineages of the Rhodomelaceae that resolved a clade formed by the Chondrieae and Laurencieae as sister to the Alsidieae (Díaz-Tapia et al 2017). tant locations or from the same region (e.g., Zuccarello et al 2015, Muangmai et al 2016, Savoie and Saunders 2016, Díaz-Tapia et al 2018, Schneider et al 2018. More surprisingly, some species with conspicuous morphological differences regarding other members of the family remained unnoticed.…”