The hermit crab's nose—antennal transcriptomics

Katrin C Groh,Heiko Vogel,Marcus C Stensmyr,Bill S Hansson,Ewald Grosse-Wilde

doi:10.3389/fnins.2013.00266

Katrin C Groh, Heiko Vogel + Show 3 more

Open Access

https://doi.org/10.3389/fnins.2013.00266

Copy DOI

Abstract

In the course of evolution, crustaceans adapted to a large variety of habitats. Probably the most extreme habitat shift was the transition from water to land, which occurred independently in at least five crustacean lineages. This substantial change in life style required adaptations in sensory organs, as the medium conveying stimuli changed in both chemical and physical properties. One important sensory organ in crustaceans is the first pair of antennae, housing their sense of smell. Previous studies on the crustacean transition from water to land focused on morphological, behavioral, and physiological aspects but did not analyze gene expression. Our goal was to scrutinize the molecular makeup of the crustacean antennulae, comparing the terrestrial Coenobita clypeatus and the marine Pagurus bernhardus. We sequenced and analyzed the antennal transcriptomes of two hermit crab species. Comparison to previously published datasets of similar tissues revealed a comparable quality and GO annotation confirmed a highly similar set of expressed genes in both datasets. The chemosensory gene repertoire of both species displayed a similar set of ionotropic receptors (IRs), most of them belonging to the divergent IR subtype. No binding proteins, gustatory receptors (GRs) or insect-like olfactory receptors (ORs) were present. Additionally to their olfactory function, the antennules were equipped with a variety of pathogen defense mechanisms, producing relevant substances on site. The overall similarity of both transcriptomes is high and does not indicate a general shift in genetic makeup connected to the change in habitat. IRs seem to perform the task of olfactory detection in both hermit crab species studied.

Highlights

Crustaceans successfully conquered a variety of habitats, including backwater and freshwater as well as marine and terrestrial habitats
Beyond the abstract level of GO terms we focused on olfaction, the main sensory task of the antennules
We propose a hermit crab olfactory transduction mechanism comparable to the one found in lobster (Hatt and Ache, 1994)

Summary

Introduction

Crustaceans successfully conquered a variety of habitats, including backwater and freshwater as well as marine and terrestrial habitats. At least five lineages of crustaceans independently succeeded in the transition from water to land (Bliss and Mantel, 1968; Powers and Bliss, 1983) Such substantial changes in environment require extensive adaptation, for example regarding metabolism, water and ion balance, and behavior. In the marine hermit crab Pagurus bernhardus the aesthetascs are long and slender (Hansson et al, 2011) while in its terrestrial relative Coenobita clypeatus they are short and blunt (Krång et al, 2012) This change is probably an adaptation to function in air rather than water, comparable to its terrestrial relatives Coenobita compressus (Ghiradella et al, 1968a,b) and Birgus latro (Stensmyr et al, 2005). Investigations of the terrestrial hermit crab Birgus latro, a close relative of C. clypeatus, suggested that the adaptation of the olfactory organs is insectlike (Rittschof and Sutherland, 1986; Greenaway, 2003; Stensmyr et al, 2005)

Objectives

Methods

Results