Vicariance and convergence in Magellanic and New Zealand long-looped brachiopod clades (Pan-Brachiopoda: Terebratelloidea)

• Published in: Zoological journal of the Linnean Society 2011-07, Vol.162 (3), p.631-645
• Main Authors: COHEN, BERNARD L., BITNER, MARIA A., HARPER, ELIZABETH M., LEE, DAPHNE E., MUTSCHKE, ERIKA, SELLANES, JAVIER
• Format: Article
• Language: English
• Subjects: Aerothyris; Brachiopoda; COI mtDNA; Liothyrella; Magellania; Marine; molecular clocks; molecular systematics; parapatric clades; radial ornament; rDNA; rib; Terebratella; Terebratella sanguinea
• ISSN: 0024-4082; 1096-3642
• DOI: 10.1111/j.1096-3642.2010.00682.x

Phylogenetic reconstructions using parsimony, maximum likelihood (ML), and Bayesian relaxed molecular clock analyses of ∼2850 nucleotides of nuclear‐encoded small and large subunit ribosomal DNAs (SSU and LSU rDNAs) from 14 long‐looped (terebratelloid) ingroup and four short‐looped (terebratulidine) outgroup brachiopod taxa, together with ML analyses of ∼663 nucleotides of mitochondrial cytochrome oxidase subunit 1 (cox1) from 12 terebratelloid taxa, show that deep divergence separates taxa endemic to waters in the vicinity of New Zealand from those with a Magellanic distribution around South America and Antarctica. This deep divergence also separates Magellanic Terebratella dorsata from New Zealand Terebratella sanguinea, showing that they are not congeneric. Instead, they belong to separate ‘Magellanic’ (MAG) and ‘New Zealand’ (NZ) clades that first diverged about 82 Mya (95% highest posterior density, 48–120 Mya), correlating with separation between the NZ and Antarctic tectonic plates. Sequence analyses also reveal (1) that the Antarctic endemic taxa Magellania fragilis and Magellania joubini are not congeneric with Magellania venosa, suggesting that their previous placement in Aerothyris should be restored, and (2) that divergence between Antarctic and NZ species of the terebratulide Liothyrella occurred much later than plate separation, perhaps because of continuing gene flow caused by long‐lived larvae. The topology of the rDNA and cox1 gene trees implies that radial ornament of the shell (‘ribbing’) has been gained (and/or lost) independently within the MAG and NZ clades. Radial ribs are widespread in articulate brachiopods throughout the Phanerozoic, but no comparisons of brachiopod rib morphology and morphogenesis have been published. Our comparisons of transverse shell mid‐sections in the scanning electron microscope reveal no obvious evidence of differences in morphology between independently gained ribs. We also consider several ways in which ribs may affect fitness, including effects on hydrodynamics. Only scanty and inconclusive evidence is available, but we suggest that effects (if any) are likely to be of small magnitude; adaptive value of brachiopod shell ribs remains to be demonstrated. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162, 631–645.