Athanas

Abstract: An alpheid shrimp,Athanas kominatoensis, inhabiting a Japanese purple sea urchin was shown to be a partially protandrous hermaphrodite. They settled mainly in summer and spent the first reproductive season as males. Smaller males changed into females the following spring, but larger ones remained males throughout their lives. Sex change was socially controlled, as has been known in some fishes. In contrast to the fishes, however, subordinates changed their sex as the best of a bad situation in this shrimp. Most larger individuals lived singly or in sexual pairs, not tolerating others of the same sex on a host. The larger a male was, the more likely he was to be found with a female. On the contrary, males smaller than 3 mm were tolerated by larger males to some extent and had chances to cohabit and copulate with larger females. This made it advantageous to be functional as a male at first. Though the secondary sex change from female to male is theoretically expected, it is hardly realized because of the short life span. Hermaphroditism in this shrimp can be explained by the size-advantage model as a special case.

Abstract: During the Balgim-84 Expedition, carried out from both sides of the Straits of Gibraltar (Atlantic Ocean: Gulf of Cadiz and Mediterranean Sea: Alboran Sea), in depths between 137 and 2,142 m, 3,559 specimens of decapods belonging to 122 species were captured. Many of these species are rare, of biogeographic al interest and represent new records for the area. For some species, anatomical details are given. A specimen of Plesionika may be a new species. The collection of Calocarides coronatus, Sympagurus acinops, Monodaeus guinotae, Periclimenes kornii, Alpheus talismani, Athanas amazone, Merhippolyte ancitrosta, Eualus cf. lebourae, Plesionika williamsi, Pontophilus cf. abyssi, Spongicoloides evolutus, Spongicoloides profundus, Odontozona edwardsi, Catapaguroides iris and Strobopagurus gracilipes, among others, represents new records for the Mediterranean Sea, eastern Atlantic, and Iberian waters.

Abstract: The occurrence of protandrous hermaphroditism is demonstrated in the alpheid shrimp Athanas indicus (Coutiere), a species which lives in symbiosis with the sea urchin Echinometra mathaei (de Blainville) in Indo-Pacific coral systems. Protandry is partial (true males persist in the population), and male sexual types (true males and sex-changers) do not differ in their external morphological characteristics. The female reproductive success is enhanced by increased body size (clutch size is positively correlated with body mass). In males, however, the effects of body dimension on reproductive success are contradictory. On the one hand, size seems to be uninfluential, because sperm production commences when the males are still very small, female-male pair formation was not observed, and mating occurs during a brief encounter; on the other hand, fighting, where the largest individual is more likely to win, is frequent. One scenario based on the socioecological milieu of A. indicus suggests that the smallest male in a group must exhibit great plasticity in his behavior to achieve reproductive output. Several options, including leaving the group, changing sex, waiting for some misfortune to strike the dominant males, or else sneaking copulations, are possible, but none are totally rewarding. The resulting behavior will therefore depend on "making the best of a bad situation."