Dwarf brooder versus giant broadcaster: combining genetic and reproductive data to unravel cryptic diversity in an Antarctic brittle star

Abstract

Poecilogony, or multiple developmental modes in a single species, is exceedingly rare. Several species described as poecilogenous were later demonstrated to be multiple (cryptic) species with a different developmental mode. The Southern Ocean is known to harbor a high proportion of brooders (Thorson's Rule) but with an increasing number of counter examples over recent years. Here we evaluated poecilogony vs. crypticism in the brittle star Astrotoma agassizii across the Southern Ocean. This species was initially described from South America as a brooder before some pelagic stages were identified in Antarctica. Reproductive and mitochondrial data were combined to unravel geographic and genetic variation of developmental modes. Our results indicate that A. agassizii is composed of seven well-supported and deeply divergent clades (I: Antarctica and South Georgia; II: South Georgia and Sub-Antarctic locations including Kerguelen, Patagonian shelf, and New Zealand; III-VI-VII: Patagonian shelf, IV-V: South Georgia). Two of these clades demonstrated strong size dimorphism when in sympatry and can be linked to differing developmental modes (Clade V: dwarf brooder vs. Clade I: giant broadcaster). Based on their restricted geographic distributions and on previous studies, it is likely that Clades III-VI-VII are brooders. Clade II is composed of different morphological species, A. agassizii and A. drachi, the latter originally used as the outgroup. By integrating morphology, reproductive, and molecular data we conclude that the variation identified in A. agassizii is best described as crypticism rather than poecilogony.

Dispersal Reduction: Causes, Genomic Mechanisms, and Evolutionary Consequences

“…1e), with non-buoyant lineages typically restricted to single landmasses [34]. Similarly, transitions from planktonic (dispersive) to benthic/brooding (non-dispersive) larval development have occurred in numerous marine invertebrate taxa [35][36][37], with major implications for biogeography and genetic connectivity ( [38][39][40] and Fig. 1f).…”

Pragmatic Assignment of Species Groups Based on Primary Species Hypotheses: The Case of a Dominant Component of the Southern Ocean Benthic Fauna

“…Thorough taxonomic reinvestigation of these species groups (and others where cryptic species are inferred, such as Sands et al, 2015;Jossart et al, 2019) is likely to have significant lag time as investment in taxonomic expertise is declining in general (Wägele et al, 2011). Expert (taxonomic) species identification is essential in studies of biodiversity and ecology (Bortolus, 2008) as identification failures due to crypsis and unappreciated errors in identification may result in poor management decisions, erroneous interpretations of experimental results and inaccurate species distributions in large databases.…”

Unexpected molecular and morphological diversity of hemichordate larvae from the Neotropics

“…There are numerous and diverse examples of how DNA barcoding can bring hidden diversity to light. Studies of seemingly cosmopolitan species of marine invertebrates commonly uncover cryptic taxa (e.g., Barroso, Klautau, Solé‐Cava, & Paiva, ; Collin, ; Cornils Wend‐Heckmann & Held, ; Jossart, Sands, & Sewell, ; Kawauchi & Giribet, ; Pérez‐Portela, Arranz, Rius, & Turon, ), and previous barcoding studies of larvae have discovered local diversity that was not appreciated from studies of adults (Barber & Boyce, ; Collin, Venera‐Pontón, Driskell, Macdonald, Chan, et al, ; Mahon et al, ; Maslakova et al unpublished data). Here we sextupled the documented species diversity of acorn worms reported for the Tropical Eastern Pacific, with only moderate sampling effort of planktonic larvae.…”