Several groups of marine fishes and squids form mutualistic bioluminescent symbioses with luminous bacteria. The dependence of the animal on its symbiont for light production, the animal's specialized anatomical adaptations for harboring bacteria and controlling light emission, and the host family bacterial species specificity characteristic of these associations suggest that bioluminescent symbioses are tightly coupled associations that might involve coevolutionary interactions. Consistent with this possibility, evidence of parallel cladogenesis has been reported for squid-bacterial associations. However, genetic adaptations in the bacteria necessary for and specific to symbiosis have not been identified, and unlike obligate endosymbiotic associations in which the bacteria are transferred vertically, bacterially bioluminescent hosts acquire their light-organ symbionts from the environment with each new host generation. These contrasting observations led us to test the hypotheses of species specificity and codivergence in bioluminescent symbioses, using an extensive sampling of naturally formed associations. Thirty-five species of fish in seven teleost families (Chlorophthalmidae, Macrouridae, Moridae, Trachichthyidae, Monocentridae, Acropomatidae, Leiognathidae) and their light-organ bacteria were examined. Phylogenetic analysis of a taxonomically broad sampling of associations was based on mitochondrial 16S rRNA and cytochrome oxidase I gene sequences for the fish and on recA, gyrB and luxA sequences for bacteria isolated from the light organs of these specimens. In a fine-scale test focused on Leiognathidae, phylogenetic analysis was based also on histone H3 subunit and 28S rRNA gene sequences for the fish and on gyrB, luxA, luxB, luxF and luxE sequences for the bacteria. Deep divergences were revealed among the fishes, and clear resolution was obtained between clades of the bacteria. In several associations, bacterial species identities contradicted strict host family bacterial species specificity. Furthermore, the fish and bacterial phylogenies exhibited no meaningful topological congruence; evolutionary divergence of host fishes was not matched by a similar pattern of diversification in the symbiotic bacteria. Re-analysis of data reported for squids and their luminous bacteria also revealed no convincing evidence of codivergence. These results refute the hypothesis of strict host family bacterial species specificity and the hypothesis of codivergence in bioluminescent symbioses.

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Sparid fishes consist of approximately 115 species in 33 genera that are broadly distributed in tropical and temperate coastal waters. Although several phylogenetic analyses were conducted based on specific molecular markers, their classification remains unresolved. Here, we present the most comprehensive molecular phylogeny of the family Sparidae to date, based on cytochrome b (cyt-b) genes. We determined 18 sequences of sparids and conducted phylogenetic analyses among 72 individuals representing 66 sparids with 23 outgroup species. Phylogenetic trees were constructed according to partitioned Maximum Likelihood (ML) and Bayesian methods. The phylogenetic analyses were conducted on two different data sets (including all positions; RY-coding). The phylogenetic trees showed monophyly of the family Sparidae with a different taxon, centracanthid Spicara. The subfamilies in the Sparidae in all trees are non-monophyletic and do not agree with current classification of the subfamilies. The genera Acanthopagrus, Cheimerius, Dentex, Diplodus, Pagellus, Pagrus, and Spicara are also non-monophyletic and their classifications should be revised based on the phylogenetic relationships and reinvestigation of morphological characters. The sparids are divided into three major clades, A, B and C, respectively in the ML tree based on all codon positions, whereas clade C was paraphyletic in the other trees. The species in clade C are known to be present in the eastern Pacific to western Atlantic, whereas those in clades A and B are distributed in various oceanic regions. Some sub-clades in clades A and B consist of species that are distributed in defined local regions. We further investigated evolutionary patterns of 87 morphological characters by ancestral character-state reconstruction according to the parsimony criteria. The results suggested high evolutionary plasticity of the characters in sparids, indicating that it causes species-diversity and taxonomic confusion at various taxonomic levels, and that such convergent evolution may occur more frequently also in other coastal fishes.

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