Microanatomy and Histochemistry of the Salt Glands of the Kentish Plover, Charadrius alexandrines (Aves, Charadriidae)

Bashir M Jarrar

doi:10.3844/ojbsci.2009.75.80

Abstract

Problem statement: Histological and histochemical investigations on the salt glands of birds are very limited. The present study was performed to characterize the microanatomy and histochemistry of the salt glands of the Kentish plover (Charadrius alexandrines). Approach: Salt glands of the bird under study were fixed, dehydrated, cleared, impregnated and blocked out by paraffin wax. Paraffin sections were utilized in histological and histochemical examinations to characterize the structure and chemical contents of these glands. Results: The Kentish plover had a well developed bilateral seromucous salt glands lie in the supraorbital depression of the frontal bone. Each gland is about 0.18 g and had lobular arrangement consisted of one cell thick secretory tubules enmeshed in tiny blood capillaries. The tubules radiate from central canals that drain in a main duct of 3-4 mm in length and opens into the external nares. The secretory tubules were lined by a single layer of principal cells and opens in intercalated ducts followed by striated ducts. The employed histochemical tests indicated that seretory tubules elaborate proteins and acid mucosubstances but are devoid of glycogen and neutral mucosubstances while the intertubular stroma showed metachromatic, alcianophilic and PAS reactivity. Conclusion/Recommendations: The results of the present study revealed that salt glands of Kentish plover are active adaptive tool of osmoregulation to control the amount of water needed by this bird. More research is needed to understand the adaptation of the seabirds to the physiological stress of the salt load.

Highlights

Drinking seawater and feeding on saline marine food put physiological stress on marine birds to reduce the salt load and to eliminate excess electrolytes
There are several species of plovers in Saudi Arabia with the Kentish plovers (Charadrius alexandrinus) is the most common. It is seen throughout the year in the Gulf coast of Saudi Arabia, Jizan and on the Farasan Islands with increasing presence in most subtropical and tropical parts of the world
The structure of the salt glands of the Kentish plover as seen by the results of the present study can be considered as an adaptive tool of osmoregulation to control the amount of water needed by this bird

Summary

INTRODUCTION

Drinking seawater and feeding on saline marine food put physiological stress on marine birds to reduce the salt load and to eliminate excess electrolytes. Birds inhabit freshwater ponds possess significantly small or inactive salt glands while seabirds who have limited or no excess to freshwater are equipped with well developed specialized salt glands[1,2]. These glands allow marine birds to maintain water and ion concentration balance by excreting salt from seawater they ingest with their food. It is seen throughout the year in the Gulf coast of Saudi Arabia, Jizan and on the Farasan Islands with increasing presence in most subtropical and tropical parts of the world This species breeds on sandy coasts and brackish inland lakes and is uncommon on fresh water. The present study was performed to characterize the microanatomy and histochemistry of the salt gland of Charadrius alexandrinus

MATERIALS AND METHODS

RESULTS

CONCLUSION