ABSTRACT
Male fiddler crabs (genus Uca) have an enlarged major claw that is used during fights. In most species, 50% of males have a major claw on the left and 50% on the right. In Uca vocans vomeris, however, less than 1.4% of males are left-clawed. Fights between opponents with claws on the same or opposite side result in different physical alignment of claws, which affects fighting tactics. Left-clawed males mainly fight opposite-clawed opponents, so we predicted that they would be better fighters due to their relatively greater experience in fighting opposite-clawed opponents. We found, however, that (i) a left-clawed male retains a burrow for a significantly shorter period than a size-matched right-clawed male, (ii) when experimentally displaced from their burrow, there is no difference in the tactics used by left- and right-clawed males to obtain a new burrow; however, right-clawed males are significantly more likely to initiate fights with resident males, and (iii) right-clawed residents engage in significantly more fights than left-clawed residents. It appears that left-clawed males are actually less likely to fight, and when they do fight they are less likely to win, than right-clawed males. The low-level persistence of left-clawed males is therefore unlikely to involve a frequency-dependent advantage associated with fighting experience.
Subject(s)
Brachyura/physiology , Functional Laterality/physiology , Aggression , Animals , Behavior, Animal/physiology , Male , Reproduction , Social DominanceABSTRACT
A discoid organ, 'pereopodal disk (PD)', was found on the medial surface of the basipodite of each pereopod, except the third and the fourth, in an estuarine amphipod, Melita setiflagella. The silver methods showed that PD is an extrabranchial ion-permeable area of the body surface. The ultrastructural study revealed that PD is covered by a thin and soft cuticle layer suggesting high permeability to gases and ions, and is composed of a thick, transporting-type epithelium. This epithelium is characterized by deep basal infolding systems (BIS) of cell membranes exceeding two-thirds of the epithelial thickness and complicated interdigitations between adjacent epithelial cells, both associated with many mitochondria. Apical infolding systems (AIS) are shallow and not accompanied by any mitochondria. These characteristics resemble those of the sternal epithelia and form a striking contrast in the polarity of the infoldings to the gill epithelia, which are characterized by a well-developed AIS and sparse BIS. The results suggest that this unique organ may be involved in the active transport of electrolytes to maintain constant osmotic pressures of the body fluids under widely fluctuating salinities of the estuarine environments.
ABSTRACT
Sternomoera yezoensis has specialized sterna with 21 sternal gills in addition to six pairs of coxal gills. Despite a common high permeability to chloride ions, the epithelia of these two kinds of gills are diametrically opposed in the polarity of the cell membrane-mitochondria complex. The coxal gill epithelium (4-6 microm thick) is characterized by a well-developed AIS (apical infolding system) associated with a huge number of large mitochondria. The AIS exceeds two-thirds of the epithelial thickness and forms a highly sophisticated, subcuticular labyrinth. On the contrary, the sternal gill epithelium, an extension of the sternal epithelium proper, is extremely thick (10-15 microm) and is characterized by a very deep BIS (basolateral infolding system) associated with numerous slender mitochondria. The BIS reaches nine-tenths of the epithelial thickness and forms a giant, baso-lateral labyrinth. Shallower, less elaborate AIS and BIS without mitochondrial association originate from the opposite sides of these epithelia. Although AIS and BIS interpenetrate in the sternal gill epithelium, they never communicate. The results indicate that in addition to the coxal gills, the sterna with the sternal gills function as transporting as well as respiratory organs, though the functional difference between these two kinds of gills remains to be elucidated.
ABSTRACT
By electron microscopy of the coxal gills in two species of estuarine amphipod crustaceans, Grandidierella japonica and Melita satifragella, we found a patch-like, specialized tissue area which consisted of unique cells closely resembling the salt-excreting cells in the gill of the brine shrimp and so-called chloride cells in teleost gills. These cells were characterized by an abundance of mitochondria, two kinds of extensive networks of cytoplasmic tubules, well-developed lamellar infoldings of the basal cell membrane, sparse microvillous projections of the apical border, and numerous large vacuoles with several incomplete partitions. The large (60 nm in diameter) and the small (30 nm) cytoplasmic tubular networks were found in the basal and the apical portions of the cell, respectively. The large networks, which were both directly and indirectly (through the lamellar system) continuous with the basal cell membrane, were regarded as extensions of the cell membrane. Both the outer walls and the partition walls of the vacuoles were reinforced with a parallel array of microtubules. The results suggest that this unique tissue plays an important role in the active transport of electrolytes to maintain a constant osmotic pressure of the hemolymph under widely fluctuating salinities of the estuarine environments.
