Wittmann 1995d
Wittmann 1995d
WITTMANN, K. J., 1995d: Reproductive adaptations in Antarctic meso- to bathypelagic Mysidacea (Crustacea). In: Deep-sea and extreme shallow-water habitats: affinities and adaptations. Vienna Deep Sea Symposium 1995 (abstract): 1 p.
A highly diverse marine fauna is found in and above the shelf in high-Antarctic regions. Animals are adapted to extremely low temperatures with very small annual variations of -2 to 0°C. Among mysid shrimps (Mysidacea) that frequently occur in 100-700 m depths, one finds special morphological adaptations in both sexes such as modified inner branches of the antennae. The males of many species show large to giant penes, some even extending beyond body size. Several species that are new to science show a variety of characteristic morphological features involving glandiform structures and/or penes with erectile tissue, previously unknown for the entire group. Females show no obvious specializations. This leads to the assumption that copulation and fertilization proceed in a manner similar to that known from species in warmer climates, where the eggs are fertilized in the brood pouch. From December to February, freshly hatched postmarsupial stages are completely absent and adult males are very rare. In contrast, subadult females and adults with empty brood pouches are very frequent. Among females which carry young, most have embryonated eggs. Those with nauplioid larvae are more rare, but still more frequent than those with postnauplioid larvae. These observations suggest that the reproductive cycle proceeds similar to that in the Arctic. The animals accumulate storage materials during summer and gain sexual maturity in early autumn. Presumably in March and April the eggs are deposited in the brood pouch and copulation takes place. Shortly thereafter the males die. The larvae develop in the brood pouch during autumn and winter. After about eight months of development they are liberated from the brood pouch in early summer, when they can profit from the plankton boom by fast individual growth. In the Antarctic, the sexual morphological peculiarities are interpreted as being adaptive for males. They have the chance to reproduce once in their lifetime during a very short period. If copulation proceeds as quickly as in species of temperate climates, it would be crucial for males to use their modified antennulae to detect females ready for mating and to introduce their penes into the brood pouch as fast as possible. Here, the giant penes may be useful to gain precedence in mating, or may even favour higher precision in the transfer of gametes. In order to transfer the genes to the next generation, fitness for survival may lose importance in favour of fitness for reproduction. In this sense, it can be of advantage to bear highly efficient giant penes for mating, even if this is inconvenient for normal activities such as swimming.
reproductive adaptations; Antarctic
Mysidacea