Ecomorphology of a predatory deep-sea fish family: does trophic specialization drive hyperspeciation?

Two of the main drivers speciation among aquatic vertebrates are physical isolation (e.g., lakes and streams) micro-niche availability tropical reefs). In both regards, mesopelagic domain open ocean, Earth’s second largest cumulative ecosystem (behind only bathypelagic domain), would seem retardant. Ocean circulation makes rare on contemporary geological time/space scales, lack substrate precludes stable micro-niches. Paradoxically, some pelagic taxa demonstrate much higher-than-expected species richness regional scales. A prime example is dragonfish family Stomiidae, most speciose fishes, owing largely to subfamily Melanostomiinae (scaleless black dragonfishes), which contributes 222 320 described species. Within genera, differentiated almost solely by form jugular-positioned, bioluminescent barbel, a structure putatively linked feeding (via prey luring). The relationship between diversity (both systematic morphological) diet within has not been previously examined, primarily due sample size limitation. Herein, morphology 16 melanostomiine dragonfishes from Gulf Mexico were examined ascertain whether diversification in this fish clade based specialization, as case with many other families Cichlidae). Gut content analysis revealed rather small spectrum across wide predators, exhibiting piscivory centered regionally abundant lanternfishes (Myctophidae). Lesser numbers preyed upon bristlemouths (Gonostomatidae), oceanic basslets (Howellidae), bigscales (Melamphaidae), dragonfishes, while three selected for cephalopod prey. No consumed macrocrustaceans decapod shrimps), despite their numerical prevalence potential Regarding functional morphology, dissimilarity was driven mostly barbel length, vertical oral gape, horizontal maxillary gape. There no robust morphological-dietary relationships amongst melanostomiines, dietary lower than morphological diversity. These results suggest that factors, perhaps conspecific recognition and/or sexual selection related spawning, may be primary hyperspeciation micro-habitat-poor environment.