Planktotrophic Brachiopod Larvae from the Pacific and Caribbean of Panama

Abstract

Lingulids and discinids are the only brachiopods that exhibit life histories that include a feeding planktonic stage usually referred to as a “larva”. We collected planktotrophic brachiopod larvae from the Pacific and Caribbean coasts of Panama and took a DNA barcoding approach with mitochondrial cytochrome c oxidase subunit I (COI), mitochondrial ribosomal 16S, and nuclear ribosomal 18S genes to identify those larvae and to estimate their diversity in the region. We observed specimens from both coasts with distinct morphologies typical of lingulid and discinid larvae. COI and 16S were sequenced successfully for the lingulid larvae but failed consistently for all discinid larvae. 18S was sequenced successfully for larvae from both families. Sequence data from each gene revealed one lingulid operational taxonomic unit (OTU) from Bocas del Toro on the Caribbean coast, and one lingulid OTU from the Bay of Panama on the Pacific coast. These OTUs differed by >20% for COI, >10% for 16S and ~0.5% for 18S. Both OTUs clustered with GenBank sequences of Glottidia species, the only genus of lingulids in the Americas, but were distinct from G. pyramidata the only species reported for the Caribbean. Analysis of 18S sequence data for discinid larvae recovered 2 OTUs, one exclusively from the Pacific and one with a mixture of Pacific and Caribbean larvae. The 18S marker does not provide enough resolution to distinguish between species, and comparisons with GenBank sequences suggest that one OTU includes Pelagodiscus species, while the other may include Discradisca species. When compared with other marine invertebrates, our surveys of brachiopod larvae through DNA barcoding show relatively low levels of diversity for Panama.

Analysis of the juvenile shell ofLingula anatina(Brachiopoda: Linguliformea) provides insight into the evolution of life cycles of fossil brachiopods

“…The lingulide mantle therefore forms and grows at three developmental stages: within the egg envelope, at the pelagic stage, and after settlement. Until settlement, however, the shell remains totally organic and transparent (Paine 1963; Collin et al 2019).

Figure 1.Scheme of the ornamentation of the dorsal valve of juvenile Lingula anatina .

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“…Although the superfamily Linguloidea appeared in the early Cambrian, only two genera, Lingula Bruguière, 1797 and Glottidia Dall, 1870, have survived to the present. The microstructure and morphology of juvenile shells of lingulides remain completely unknown, because the published photographs of the juvenile lingulide shells do not provide any clear information on their structure (Paine 1963; Chuang 1977; Collin et al 2019) and descriptions in the literature are absent. The lingulides, however, may be regarded as a key group for understanding the evolution of brachiopod ontogeny, because they appeared in the early Cambrian and because many authors now infer that their life cycle, in which the shell forms at the planktonic stage, is ancestral for all other brachiopod life cycles (e.g., Ushatinskaya 2016; Zhang et al 2018).…”

DNA barcoding of echinopluteus larvae uncovers cryptic diversity in neotropical echinoids

“…Surveys of adults are typically used for documenting the diversity of marine animals, but they may be of limited value for taxa whose adults are difficult to collect or occur at depths not easily reached with SCUBA diving. In the few cases where larval diversity has been surveyed, it has resulted in the discovery of more or different species than those documented in adult surveys from the same location (Barber & Boyce 2006;Collin, Venera-Pontón, Driskell, Macdonald, & Boyle, 2019a;b;Collin et al 2019;Mahon, Thornhill, Norenburg, & Halanych, 2010). This pattern may be due in part to the choice of study taxa, as these previous studies focused on nemerteans, phoronids, and hemichordates, groups in which adult diversity is likely to be severely underestimated.…”

How I wonder what you are: Can DNA barcoding identify the larval asteroids of Panama?

“…Surveys of marine invertebrate larvae are a powerful tool for the detection of hidden diversity (Barber & Boyce, 2006; Collin, et al., 2019; Collin et al, 2019a, 2019b; Mahon et al., 2010). They may be particularly effective at capturing deep‐water, small, or infaunal species that are difficult to collect as adults by use of standard sampling techniques, and thus provide an independent assessment of diversity that complements species lists based solely on studies of adults (Collin, et al., 2020; Mahon et al., 2010; Sewell & Jury, 2011).…”