Grouping behaviour impacts on the parasitic pressure and squamation of sharks

Abstract

The evolution of grouping behaviour involves a complex trade-off of benefits and costs. Among the latter, an increase in the risk of parasitic transmission is a well-documented phenomenon that has likely promoted the evolution of defensive mechanisms in aquatic vertebrates. Here, we explore the relationship between grouping behaviour, parasitic richness (∼parasitic pressure), and the evolution of potential defensive traits in the squamation of sharks through phylogenetic, standard and zero-inflation regression models. Our results demonstrate that sharks that frequently aggregate show increased parasitic pressure, which may constitute an agent of selection. Accordingly, their squamation is characterized by large-scale crown insertion angles and low-scale coverage, which are interpreted as traits that compromise parasite attachment and survival. These traits are less evident in regions of the body and ecological groups that are subjected to high abrasive stress or increased drag. Thus, the squamation of sharks responds to a compromise between various functions, where protective and hydrodynamic roles prevail over the rest (e.g. ectoparasitic defence and bioluminescence aiding). This work establishes a quantitative framework for inferring parasitic pressure and social interaction from squamation traits and provides an empirical basis from which to explore these phenomena through early vertebrate and chondrichthyan evolution.

Aligning paleobiological research with conservation priorities using elasmobranchs as a model

“…Because shark teeth can be identified to species (Naylor and Marcus 1994;Cappetta 2012;Paillard et al 2021), biological processes related to these traits can be explored over microevolutionary scales. Shark dermal denticles also encode biological information (e.g., body size, mobility, position in the water column, schooling behavior, and bioluminescence), although they are less taxonomically resolved than teeth (Reif 1985;Raschi and Tabit 1992;Dillon et al 2017;Ferrón and Botella 2017;Ferrón and Palacios-Abella 2022). Additionally, elasmobranch vertebral rings preserve life-history traits such as growth rates and age (Daiber 1960;Shimada 2008).…”

The multidimensional spectrum of eco‐evolutionary relationships between sharks and remoras

“…If relationships persist for a sufficient length of time and with sufficient fitness effects, they may become ecoevolutionary in nature, resulting in some degree of coevolutionary dynamic between the respective populations (Dixit, 2024;Provorov & Vorob'ev, 2012). Sharks (Elasombranchii) are associated with a wide range of other taxa, including prey (Heithaus & Vaudo, 2004), predators (Heithaus, 2001;Heithaus & Vaudo, 2004), competitors, and parasites (Brena et al, 2018;Brunnschweiler, 2006;Ferrón & Palacios-Abella, 2022;Heithaus, 2001). In these cases, the nature of interspecific interactions is relatively simple from an eco-evolutionary perspective.…”

First recorded occurrence of the parasitic barnacle (Anelasma squalicola) on a Greenland shark (Somniosus microcephalus) in the Canadian Arctic

“…Parasites play diverse roles in aquatic ecosystems and can in many instances drive changes to the behaviour, physiology and population dynamics of their hosts (Barber et al ., 2000; Ferrón & Palacios‐Abella, 2022; Krkošek et al ., 2011; Slavík et al ., 2017). As with most teleost fishes, elasmobranchs globally are known to host numerous ecto‐ and endoparasite species (Caira & Healy, 2004).…”