|Their day in the sun: molecular phylogenetics and origin of photosymbiosis in the 'other' group of photosymbiotic marine bivalves (Cardiidae: Fraginae)|
Kirkendale, L. (2009). Their day in the sun: molecular phylogenetics and origin of photosymbiosis in the 'other' group of photosymbiotic marine bivalves (Cardiidae: Fraginae). Biol. J. Linn. Soc. 97(2): 448-465
In: Biological Journal of the Linnean Society. Academic Press: London; New York. ISSN 0024-4066, more
Evolution; Phylogenetics; Zooxanthellae; Cardiidae Lamarck, 1809 [WoRMS]; Marine
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The subfamily Fraginae (Cardiidae) is a morphologically diverse group of small-bodied marine clams inhabiting shallow seas worldwide. Like the exclusively photosymbiotic giant clams (Cardiidae: Tridacninae), some fragines are known to host zooxanthellae photosymbionts. However, surveys to widely determine photosymbiotic status and the lack of a comprehensive phylogeny have hindered attempts to track the evolution of photosymbiosis in the group. Worldwide sampling of all fragine genera and subgenera with phylogenetic reconstructions based on four gene regions [nuclear (28S) and mtDNA (16S, cytochrome oxidase I, cytochrome b)] does not support a monophyletic Fraginae. Sampled taxa form four restructured clades: (1) the 'Fragum' group, (2) the 'Trigoniocardia' and 'Ctenocardia' groups, (3) the 'Parvicardium' group and (4) the 'Papillicardium' group. Maximum likelihood analyses strongly support a clade of European cardiids uniting species from three subfamilies. Live examination of > 50% of species reveals that less than half of derived genera and subgenera host photosymbionts, supporting a single and relatively late origin of photosymbiosis in the Fraginae. The evolutionary implications for a small and little modified earliest diverging photosymbiotic lineage are discussed.