What’s the Point Form and Function of the Caudal Barb in Stingrays


Meeting Abstract

P1-19  Thursday, Jan. 4 15:30 – 17:30  What’s the Point? Form and Function of the Caudal Barb in Stingrays CHABAIN, J*; KOLMANN, M/A; SUMMERS, A/P; CHABAIN, Jules; FHL, Univ. of Montpellier, France; FHL, Univ. of Washington, Wash.; FHL, Univ. of Washington, Wash. jules.chabain@hotmail.fr

Animal weaponry are diverse and serve a variety of roles; from the asymmetrically-sized and largely-ceremonial chela of fiddler crabs, to the venomous spurs of male platypuses, these structures can defend against predators, intimidate rivals, or attract mates. Stingrays (Myliobatiformes) are the most ecologically-diverse lineage within the modern elasmobranchs (sharks and rays) and have an enlarged, venomous caudal barb formed from hypertrophied dermal denticles, which these rays use to defend themselves from predators. Barbs display diverse morphologies. We used micro-computed tomography to examine barbs from over 40 species, representing the major families in Myliobatiformes; including Potamotrygonidae (Potamotrygon, Plesiotrygon), Dasyatidae (Dasyatinae, Neotrygonidae), Myliobatidae (Rhinoptera), Urotrygonidae (Urotrygon, Urobatis), Urolophidae, and Gymnuridae . As expected barb shape was distinctive with each species, with previously undescribed variation in morphometry and meristics. For example, the spine of Paratrygon aiereba is distinguished by large rounded base, with large bilaterally symmetrical central serrations, and an overall teardrop shape. In contrast, the spine of Plesiotrygon iwamae is largely covered by small disorderly serrations, along a uniform beam-like shape. In cross section, barb morphology is also variable and can be oval, triangular, or more complex. We used a phylogenetic framework to assess the variability of barb shape stems from inheritance or if there is an ecological signal as well. We generate functional hypotheses to explain barb morphological diversity using analogies with edged weapons, different sword and arrow shapes, which are specialized for either slashing or puncture.

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