Abstract
Although many lineages of terrestrial crustaceans have poor olfactory capabilities, crabs in the family Coenobitidae, including the terrestrial hermit crabs in the genus Coenobita, are able to locate food and water using olfactory antennae (antennules) to capture odors from the surrounding air. Terrestrial hermit crabs begin their lives as small marine larvae and must find a suitable place to undergo metamorphosis into a juvenile form, which initiates their transition to land. Juveniles increase in size by more than an order of magnitude to reach adult size. Since odor capture is a process heavily dependent on the size and speed of the antennules and physical properties of the fluid, both the transition from water to air and the large increase in size during ontogeny could impact odor capture. In this study, we examine two species of terrestrial hermit crabs, Coenobita perlatus H. Milne-Edwards and Coenobita rugosus H. Milne-Edwards, to determine how the antennule morphometrics and kinematics of flicking change in comparison to body size during ontogeny, and how this scaling relationship could impact odor capture by using a simple model of mass transport in flow. Many features of the antennules, including the chemosensory sensilla, scaled allometrically with carapace width and increased slower than expected by isometry, resulting in relatively larger antennules on juvenile animals. Flicking speed scaled as expected with isometry. Our mass-transport model showed that allometric scaling of antennule morphometrics and kinematics leads to thinner boundary layers of attached fluid around the antennule during flicking and higher odorant capture rates as compared to antennules which scaled isometrically. There were no significant differences in morphometric or kinematic measurements between the two species.
Highlights
Capturing chemical signals from the environment is an important task to many animals in both air and water
Scaling of the olfactory antennae and flicking kinematics of terrestrial hermit crabs Many crustaceans rely on flicking antennules with arrays of chemosensory aesthetascs in order to capture odors in their environments
These animals increase in size over an order of magnitude during growth, and since the fluid dynamics of odor capture rely heavily on the size and speed of the antennules during flicking, the animals’ ability to capture odors may change during ontogeny
Summary
Capturing chemical signals (odors) from the environment is an important task to many animals in both air and water. Crustaceans use the information derived from odors to find food and mates, identify conspecifics, and avoid predators (Dusenbery, 1992; Atema, 1995; Zimmer & Butman, 2000; Diaz et al, 1999; Pardieck et al, 1999; Ferner, Smee & Chang, 2005; Lecchini et al, 2010; Hazlett, 1969; Caldwell, 1979; Gleeson, 1980; Gleeson, 1982; Keller, How to cite this article Waldrop et al (2014), Scaling of olfactory antennae of the terrestrial hermit crabs Coenobita rugosus and Coenobita perlatus during ontogeny. The olfactory organ of malacostracan crustaceans consists of chemosensory sensillae (aesthetascs) arranged in an array on the lateral flagellum each of their first antennae (antennules) (Fig. 1A). Crustaceans move their antennules back and forth through the water in a motion called flicking (Fig. 1A). Each flick is a sniff, or the capture of a discrete sample of odor-containing water
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