Meeting Abstract
Intraspecific aggression has led to some of the most extravagant examples of animal display, weaponry, and ornamentation; used for awing admirers, intimidating rivals, or injuring would-be assailants. This is especially clear in the Neotropics, where in freshwater habitats, high species richness leads to all manner of animal ornamentation and display. For example, catfishes use venomous spines to deter predators, garishly-colored cichlids display to favored females and rival males, while drab knifefishes ‘catcall’ with electric signals. Other fishes scrap it out more directly; piranhas and other serrasalmids defend their nests and foraging territories from conspecifics and confamilials alike, regularly chasing and biting each other. We surveyed serrasalmid morphology with micro-computed tomography, and discovered that piranhas have a high prevalence of skeletal injury. Damage was particularly common on the bony, armored keel, which we propose defends against conspecific aggression. Piranha schools may also face aggression from confamilial parasites in sheep’s clothing: scale-feeding wimple piranhas. We examine the ontogeny of feeding morphology in Catoprion mento, one of the few piranhas which scale-feed through to adulthood. Few characters distinguish Catoprion from piranhas which scale-feed solely as juveniles, suggesting it retains some paedomorphic characters to adulthood. The robust teeth and elongate lower jaw in this taxon are critical to scale-feeding performance, leveraging scales and mucus from prey. Overall however, the unspecialized nature of the feeding apparatus in Catoprion suggest that transitions to (or away) from scale-feeding are mediated by small changes in developmental timing.
