Understanding processes at the origin of species flocks with a focus on the marineAntarctic fauna

Abstract

Species flocks (SFs) fascinate evolutionary biologists who wonder whether such striking diversification can be driven by normal evolutionary processes. Multiple definitions of SFs have hindered the study of their origins. Previous studies identified a monophyletic taxon as a SF if it displays high speciosity in an area in which it is endemic (criterion 1), high ecological diversity among species (criterion 2), and if it dominates the habitat in terms of biomass (criterion 3); we used these criteria in our analyses. Our starting hypothesis is that normal evolutionary processes may provide a sufficient explanation for most SFs. We thus clearly separate each criterion and identify which biological (intrinsic) and environmental (extrinsic) traits are most favourable to their realization.The first part focuses on evolutionary processes. We highlight that some popular putative causes of SFs, such as key innovations or ecological speciation, are neither necessary nor sufficient to fulfill some or all of the three criteria. Initial differentiation mechanisms are diverse and difficult to identify a posteriori because a primary differentiation of one type (genetic, ecological or geographical) often promotes other types of differentiation. Furthermore, the criteria are not independent: positive feedbacks between speciosity and ecological diversity among species are expected whatever the initial cause of differentiation, and ecological diversity should enhance habitat dominance at the clade level. We then identify intrinsic and extrinsic factors that favour each criterion. Low dispersal emerges as a convincing driver of speciosity. Except for a genomic architecture favouring ecological speciation, for which assessment is difficult, high effective population sizes are the single intrinsic factor that directly enhances speciosity, ecological diversity and habitat dominance. No extrinsic factor appeared to enhance all criteria simultaneously but a combination of factors (insularity, fragmentation and environmental stability) may favour the three criteria, although the effect is indirect for habitat dominance.We then apply this analytical framework to Antarctic marine environments by analysing data from 18 speciose clades belonging to echinoderms (five unrelated clades), notothenioid fishes (five clades) and peracarid crustaceans (eight clades). Antarctic shelf environments and history appear favourable to endemicity and speciosity, but not to ecological specialization. Two main patterns are distinguished among taxa. (i) In echinoderms, many brooding, species-rich and

Benthic ecoregionalization based on echinoid fauna of the Southern Ocean supports current proposals of Antarctic Marine Protected Areas under IPCC scenarios of climate change

“…Front account for about 10% of all known echinoid species reported worldwide (Saucède et al, 2014) (Saucède et al, 2014); a similar pattern was also found in other marine groups (Chenuil et al, 2018;Clarke, 2008;Lecointre et al, 2013;Saucède et al, 2014). The speciose families Cidaridae and Schizasteridae in the Antarctic (Poulin & Féral, 1996), which represent about 65% of all Antarctic echinoid species, are also highly endemic to the Antarctic continental shelf with 81% and 67% of endemic species, respectively (David et al, 2005;Pearse, Mooi, Lockhart, & Brandt, 2009;Pierrat et al, 2012;Saucède et al, 2014).…”

“…The speciose families Cidaridae and Schizasteridae in the Antarctic (Poulin & Féral, 1996), which represent about 65% of all Antarctic echinoid species, are also highly endemic to the Antarctic continental shelf with 81% and 67% of endemic species, respectively (David et al, 2005;Pearse, Mooi, Lockhart, & Brandt, 2009;Pierrat et al, 2012;Saucède et al, 2014). This high level of endemicity and the prevalence of a taxonomically limited number of speciose groups were found in many other marine groups in the Antarctic, and particularly on the continental shelf where species flocks were identified (Chenuil et al, 2018;Clarke & Crame, 2010;Eastman, 2000;Lecointre et al, 2013). Endemicity is even more pronounced in the less-extended sub- (David et al, 2005;Fabri-Ruiz et al, 2018;Guillaumot et al, 2018;Saucède et al, 2014).…”

Key stages in the evolution of the Antarctic marine fauna

“…Molecular phylogenetic evidence also suggests that the amphipod genus Epimeria , which forms a species flock at the present day in the Southern Ocean, can be traced back to an initial Middle or Late Eocene Antarctic radiation (Verheye, Backeljau, & d'Udetem d'Acoz, ). There is a particularly strong pulse of diversification immediately after the MMCT (Chenuil et al., ; Verheye et al., ).…”

Phylogenomics of an extra-Antarctic notothenioid radiation reveals a previously unrecognized lineage and diffuse species boundaries

“…In addition to extrinsic environmental factors, intrinsic factors (such as dispersal ability, genetic architecture or chromosomal instability; see [3]) specific to Patagonotothen might have played a role in the diversification of this clade. This is suggested, for example, by their comparison with the evolutionary history of Eleginops maclovinus , another notothenioid species occurring along the Patagonian coast.…”