Does evolutionary innovation in pharyngeal jaws lead to rapid lineage diversification in labrid fishes?

Abstract

BackgroundMajor modifications to the pharyngeal jaw apparatus are widely regarded as a recurring evolutionary key innovation that has enabled adaptive radiation in many species-rich clades of percomorph fishes. However one of the central predictions of this hypothesis, that the acquisition of a modified pharyngeal jaw apparatus will be positively correlated with explosive lineage diversification, has never been tested. We applied comparative methods to a new time-calibrated phylogeny of labrid fishes to test whether diversification rates shifted at two scales where major pharyngeal jaw innovations have evolved: across all of Labridae and within the subclade of parrotfishes.ResultsDiversification patterns within early labrids did not reflect rapid initial radiation. Much of modern labrid diversity stems from two recent rapid diversification events; one within julidine fishes and the other with the origin of the most species-rich clade of reef-associated parrotfishes. A secondary pharyngeal jaw innovation was correlated with rapid diversification within the parrotfishes. However diversification rate shifts within parrotfishes are more strongly correlated with the evolution of extreme dichromatism than with pharyngeal jaw modifications.ConclusionThe temporal lag between pharyngeal jaw modifications and changes in diversification rates casts doubt on the key innovation hypothesis as a simple explanation for much of the richness seen in labrids and scarines. Although the possession of a secondarily modified PJA was correlated with increased diversification rates, this pattern is better explained by the evolution of extreme dichromatism (and other social and behavioral characters relating to sexual selection) within Scarus and Chlorurus. The PJA-innovation hypothesis also fails to explain the most dominant aspect of labrid lineage diversification, the radiation of the julidines. We suggest that pharyngeal jaws might have played a more important role in enabling morphological evolution of the feeding apparatus in labrids and scarines rather than in accelerating lineage diversification.

Explosive morphological diversification of spiny-finned teleost fishes in the aftermath of the end-Cretaceous extinction

“…Instead, the radiation of these particular percomorph clades has been linked to the ascendance of scleractinian-dominated reefs in the early Palaeogene (Kiessling 2008). The correlation between ecological association with reefs and elevated rates of diversification demonstrated for some modern acanthomorph clades (Alfaro et al 2007(Alfaro et al , 2009a, combined with strong evidence for reefs as cradles of biodiversity throughout the Phanerozoic (Kiessling et al 2010), lends weight to this hypothesis. However, potential decoupling of rates of taxonomic diversification and morphological change (cf.…”

Cryptic lineage divergence in marine environments: genetic differentiation at multiple spatial and temporal scales in the widespread intertidal goby Gobiosoma bosc

“…The lack of phenotypic divergence associated with the formation of independent lineages in G. bosc is striking, both when compared with dramatic radiations in other marine fish groups such as labrid fishes (Alfaro, Brock, Banbury, & Wainwright, 2009), and with other lineages within the Gobiidae (Rüber et al, 2003). Well-known cases of cryptic divergence in fish include weakfish (Santos, Hrbek, Farias, Schneider, & Sampaio, 2006) and bonefishes of the genus Albula (Colborn, Crabtree, Shaklee, Pfeiler, & Bowen, 2001), and among gobies, G. bosc is not alone in showing cryptic divergence.…”

Ecological variation in South American geophagine cichlids arose during an early burst of adaptive morphological and functional evolution

“…The Crenicichla clade may have colonized the predatory, ram-feeding adaptive peak early in Neotropical cichlid history, and this may have excluded some other Neotropical cichlids lineages from filling similar roles; for example, relatively elongate-bodied piscivores in the tribe Heroini are only found in Central America and not in South America [18]. The feeding biomechanics observed in Crenicichla may represent a key innovation [52] and if so it may have contributed to cichlid diversity and to shape the structure of fish communities in South America [38].…”