A morphological novelty for feeding and sound production in the yellowtail clownfish

Acoustic and postural displays in a miniature and transparent teleost fish, Danionella dracula

Acoustic behavior is widespread across vertebrates, including among fishes. We report robust acoustic displays during aggressive interactions for a laboratory colony of Danionella dracula, a miniature and transparent species of teleost fish closely related to zebrafish (Danio rerio), which are hypothesized to be sonic based on the presence of a hypertrophied muscle associated with the male swim bladder. Males produce bursts of pulsatile sounds and a distinct postural display-extension of a hypertrophied lower jaw, a morphological trait not present in other Danionella species-during aggressive, but not courtship interactions. Females show no evidence of sound production or jaw extension in such contexts. Novel pairs of size-matched or -mismatched males were combined in resident-intruder assays where sound production and jaw extension could be linked to individuals. In both dyad contexts, resident males produced significantly more sound pulses than intruders. During heightened sonic activity, the majority of highest sound producers also showed increased jaw extension. Residents extended their jaw more than intruders in size-matched, but not -mismatched contexts. Larger males in size-mismatched dyads produced more sounds and jaw extensions compared to their smaller counterparts, and sounds and jaw extensions increased with increasing absolute body size. These studies establish D. dracula as a sonic species that modulates putatively acoustic and postural displays during aggressive interactions based on residency and body size, providing a foundation for further investigating the role of multimodal displays in a new model clade for neurogenomic and neuroimaging studies of aggression, courtship, and other social interactions.

First use of acoustic calls to distinguish cryptic members of a fish species complex

Although molecular methods and bioacoustical analysis have been used to uncover cryptic species, the combination of both methodologies is still rare. The humbug damselfish complex, Dascyllus aruanus, is composed of at least two species with Dascyllus aruanus in the Pacific Ocean and Dascyllus abudafur in the Indian Ocean. However, genetic data suggest that additional species could be found. Therefore, we aimed to determine whether the sounds produced by different populations of fish could help to distinguish cryptic species. Recordings of chase and courtship sounds were made on humbug damselfish populations from Madagascar, Taiwan and French Polynesia. Chase sound features are more variable than courtship sounds, suggesting more constraints on courtship sounds, since they would contribute to premating isolation. Comparison between courtship sounds show the variation in acoustic features between Taiwan and Madagascar align with genetic differences, supporting that sounds could discriminate cryptic species in Teleosts. Moreover, differences in both acoustic features and genetic data are also found between Taiwan and French Polynesia, suggesting two clearly distinct populations. Consequently, the name D. emamo can be resurrected for the Polynesian humbug damselfish. External phenotype traits do not allow the distinction between populations, illustrating that only behaviour has been modified.