Insect-Like Olfactory Adaptations in the Terrestrial Giant Robber Crab

Abstract

The robber crab (Birgus latro), also known as the coconut crab, is the world's largest land-living arthropod, with a weight reaching 4 kg and a length of over half a meter. Apart from the marine larval stage, this crab is fully terrestrial, and will actually drown if submerged in water. A transition from sea to land raises dramatically new demands on the sensory equipment of an animal. In olfaction, the stimulus changes from hydrophilic molecules in aqueous solution to mainly hydrophobic in the gaseous phase. The olfactory system of land crabs thus represents an excellent opportunity for investigating the effects of the transition from sea to land. Have land crabs come to the same solutions as other terrestrial animals, or is their olfactory sense characterized by unique innovations? Here, we show that the robber crab has evolved an olfactory sense with a high degree of resemblance to the insect system. The similarities extend to physiological, behavioral, and morphological characters. The insect nose of the robber crab is a striking example of convergent evolution and nicely illustrates how similar selection pressures result in similar adaptation.

Digestive enzymes of two brachyuran and two anomuran land crabs from Christmas Island, Indian Ocean

“…B. latro is an omnivore with a distinct preference for items such as fruits, seeds and animal material which are high in carbohydrate, lipid and protein (linton and greenaway 2007;Wilde et al 2004) ( Table 1). They are capable of travelling large distances, up to 1 km per day, and possess an excellent olfactory ability which allow them to seek out their preferred food (Stensmyr et al 2005;greenaway 2001;Fletcher et al 1990). Terrestrial hermit crabs such as C. perlatus are nocturnal and are restricted to areas near the shore such as beaches and terrace forest (Hartnoll 1988).…”

Identified antennular near-field receptors trigger reflex flicking in the crayfish

“…Snow, 1975a;Snow, 1975b;Schmitt and Ache, 1979;Mellon, 1997;Koehl et al, 2001;Mead and Koehl, 2000;Stensmyr et al, 2005;Mellon and Reidenbach, 2011). The very small size of aesthetasc sensilla (10m in diameter at the base by 100m long in crayfish) dictates that their Reynolds numbers -a measure of the ratio of inertial to viscous fluid forces -will also be small.…”

New electroantennography method on a marine shrimp in water

“…In lobsters, odors may depolarize or hyperpolarize ORNs, and different pathways are directly linked to opposing outputs: excitatory and inhibitory receptor potentials coexist in the same ORN and the response type (excitation or inhibition) is not a property of the stimulant but it depends on the ORN (Doolin et al, 2001;McClintock and Ache, 1989;Michel et al, 1991). Positive EAG responses were obtained in robber crab, hermit crab and daphnia (Krång et al, 2012;Simbeya et al, 2012;Stensmyr et al, 2005). In the marine hermit crab P. bernhardus, EAG responses to amines were positive, and responses to acids were negative (Krång et al, 2012 The development of the EAG method in shrimp opens a large field of possibilities for studying antennular chemoreception in decapods and maybe other crustaceans.…”

“…This technique is widely used in screening moth pheromones (Roelofs, 1984). In crustaceans, EAG measurements were performed in aerial conditions on two terrestrial crabs, the giant robber crab Birgus latro (Stensmyr et al, 2005) and the hermit crab Coenobita clypeatus (Krång et al, 2012), and in the marine hermit crab Pagurus berhnardus (Stensmyr et al, 2005). Two papers reported very briefly EAG recordings, with no technical demonstration, from freshwater crustaceans: the branchiopoda Daphnia spp.…”