A tale of two antennules: the performance of crab odour-capture organs in air and water

Abstract

Odour capture is an important part of olfaction, where dissolved chemical cues (odours) are brought into contact with chemosensory structures. Antennule flicking by marine crabs is an example of discrete odour capture (sniffing) where an array of chemosensory hairs is waved through the water to create a flow-no flow pattern based on a narrow range of speeds, diameters of and spacings between hairs. Changing the speed of movement and spacing of hairs at this scale to manipulate flow represents a complicated fluid dynamics problem. In this study, we use numerical simulation of the advection and diffusion of a chemical gradient to reveal how morphological differences of the hair arrays affect odour capture. Specifically, we simulate odour capture by a marine crab (Callinectes sapidus) and a terrestrial crab (Coenobita rugosus) in both air and water to compare performance. We find that the antennule morphologies of each species are adaptions to capturing odours in their native habitats. Sniffing is an important part of odour capture for marine crabs in water where the diffusivity of odorant molecules is low and flow through the array is necessary. On the other hand, flow within the hair array diminishes odour-capture performance in air where diffusivities are high. This study highlights some of the adaptations necessary to transition from water to air.

Ocean acidification alters foraging behaviour in Dungeness crab through impairment of the olfactory pathway

“…Chemical cues are critical in marine environments for mediating important behaviours including those related to feeding, mating and reproduction, predator–prey interactions, social interactions, and orientation (de la Haye et al, 2012; Kim et al, 2016; Richardson et al, 2021; Wang & Wang, 2020). Antennular flicking is a natural olfactory behaviour in crabs that is used to detect chemical cues in the surrounding seawater (Schmitt & Ache, 1979; Waldrop et al, 2016), akin to sniffing in other animals. This is especially important for the Dungeness crab as an opportunistic scavenger in the benthos that relies heavily on chemoreception to locate food (Holsman et al, 2003; Stevens et al, 1982).…”

“…The antennules of crustaceans bear chemosensory sensilla (i.e. aesthetascs) in the outer flagellum segment, which at their base house olfactory sensory neuron (OSN) clusters underneath a thin cuticle (Harzsch & Krieger, 2018; Schmitt & Ache, 1979; Solari et al, 2017; Waldrop et al, 2016). The antennules are necessary for odour capture and routine flicking of the antennules (i.e.…”

Scent of death: Evolution from sea to land of an extreme collective attraction to conspecific death

“…However, such an explanation is undermined by the extreme sensory specializations, both of the marine and terrestrial species. Indeed, analyses of antennule morphologies in marine and terrestrial crabs (Waldrop, Miller, & Khatri, ) have revealed that each is highly adapted to capturing odors within their native habitats, sea and land, respectively. Given how specialized marine and terrestrial species are in morphological hardware for sensing localized chemical plumes within their respective environments, it suggests millions of years of natural selection has ensured optimal sensing and adaptive responses within each of these quite different environments.…”

A novel mechanism of mixing by pulsing corals

“…The marine crab Callinectes sapidus flicks its antennules in such a way that new fluid is brought into the hair array during the rapid downstroke and is trapped within the array during the upstroke (Koehl, 2006;Waldrop et al, 2015). This gives sufficient time for odorants to be taken up via diffusion while bringing in new fluid to sample during each flick (Waldrop et al, 2016).…”