Functional anatomy and ion regulatory mechanisms of the antennal gland in a semi-terrestrial crab, Ocypode stimpsoni.

Jyuan-Ru Tsai,Hui-Chen Lin

doi:10.1242/bio.20147336

Abstract

ABSTRACTBrachyuran crabs from diverse habitats show great differences in their osmoregulatory processes, especially in terms of the structural and physiological characteristics of the osmoregulatory organs. In crustaceans, the antennal glands are known to be important in osmoregulation, and they play a functional role analogous to that of the vertebrate kidney. Nevertheless, the detailed structure and function of the antennal glands in different species have rarely been described. The aim of this study is to investigate the role of the antennal gland in ion regulation by examining the ultrastructure of the cells and the distribution of the ion regulatory proteins in each cell type in the antennal gland of a semi-terrestrial crab. The results showed that Na+, K+-ATPase activity significantly increased in the antennal gland after a 4-day acclimation in dilute seawater and returned to its original (day 0) level after 7 days. Three major types of cells were identified in the antennal gland, including coelomic cells (COEs), labyrinthine cells (LBRs) and end-labyrinthine cells (ELBRs). The proximal tubular region (PT) and distal tubular region (DT) of the antennal gland consist of LBRs and COEs, whereas the end tubular region (ET) consists of all three types of cells, with fewer COEs and more ELBRs. We found a non-uniform distribution of NKA immunoreactivity, with increasing intensity from the proximal to the distal regions of the antennal gland. We summarise our study with a proposed model for the urine reprocessing pathway and the role of each cell type or segment of the antennal gland.

Highlights

Osmoregulation is an important process in aquatic crustaceans
The Na+, K+-ATPase (NKA) activity of the antennal gland When the crabs were transferred from 35% to 5% seawater, the antennal gland NKA activity increased on the 1st day after transfer to 5% diluted seawater and attained a significant difference on the 4th day (F(3,25)510.17, p,0.01, n55–11), decreased to the control (35%) level on the 7th day (Fig. 1)
In the past, the gills have been hypothesised to be the principal osmoregulatory organ in brachyuran crabs, and numerous studies have shown that the posterior gills are especially important in ion

Summary

Introduction

Osmoregulation is an important process in aquatic crustaceans. Osmoregulators maintain their haemolymph or urine osmolality during environmental stresses. The overall osmoregulatory process involves absorbing or excreting ions between the environmental medium and the body fluid through osmoregulatory organs, such as gills, antennal glands and the gut in decapod crustaceans (Chung and Lin, 2006; Freire et al, 2008). The antennal gland is involved in the anion transporting process to modulate the loss of ions due to urine excretion (Holliday and Miller, 1984; De Vries et al, 1994; Pequeux, 1995; Morris, 2001; Freire et al, 2008). In the euryhaline mud crab Scylla paramamorsain, Na+, K+-ATPase (NKA) activity in the antennal glands increased slightly after crabs were transferred to diluted seawater for 12 hr (Chung and Lin, 2006)

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