MATING AND ROLE OF SEMINAL RECEPTACLES IN THE REPRODUCTIVE-BIOLOGY OFTHE SPIDER CRAB MAJA-SQUINADO (DECAPODA, MAJIDAE)

The reproductive biology of the spider crab Maja squinado was analyzed based on monthly samples from an 18-month study carried out in Galici a (NW Spain) and laboratory experiments holding primiparous and multip arous females in captivity with and without males. The seminal recepta cles of adult females were analyzed and their relationship with the pr esence and developmental stage of the eggs and the gonad maturity stag e was determined. Gonad maturation in primiparous females began one or two months after the pubertal moult. Females having gonads in an adva nced stage of development made their appearance in December and the fi rst spawning took place in mid-winter or early spring. The percentage of ovigerous females from March to September was similar to 75%. As th e incubation period progressed, the ovaries became mature again in ord er to carry out the next spawning. Under experimental conditions the b reeding cycle started earlier in multiparous females, during their sec ond yearly cycle, than in primiparous ones. After mating, female spide r crabs store sperm in seminal receptacles and this sperm is used in t he fertilization of eggs immediately prior to spawning. The analyses o f seminal receptacles consisted of the estimation of fullness and the number of differentiated sperm masses. The number of masses ranged bet ween 0 and 6 in field samples (median for females with stored sperm = 1) and was positively correlated with fullness. Differences in colour and volume of individual masses showed that, at least in some cases, f emales carried out successive matings with long intervals in between. This storage mechanism allowed females to fertilize successive broods without remating (as was also shown under experimental conditions). Ju venile females from shallow waters did not have developed seminal rece ptacles which indicated that mating was not possible until the onset o f maturity. Postpubertal females in shallow waters (August to October) , including animals participating in aggregations, always showed empty receptacles. The seasonality of receptacle fullness showed that matin g involved hard-shelled females and occurred in deep water during the autumn migration from juvenile habitats or in the wintering habitats, during the last stages of gonad maturation (November to February). Aft er fertilization ovigerous females continued to store sperm, but the v olume was lower than in non-ovigerous females. Mating may occur in ovi gerous females, particularly in the final period of incubation, becaus e in females with broods almost ready to hatch, both new and older spe rm masses were seen in the receptacles (distinguished by colour and si ze). The fullness of the receptacles decreased both in ovigerous and n on-ovigerous females in the final phase of the annual breeding cycle ( August-October), however, some sperm was still available. In the labor atory, mating was observed, and no courtship nor postcopulatory guardi ng was recorded. The analysis of receptacles from laboratory experimen ts indicated that primiparous and multiparous females showed differenc es in the seasonality of mating in the first phase of the breeding cyc le (September-January), related to differences in the timing of gonad maturation and hatching. Mating occurred in the final stages of gonad maturation, a short time before hatching, and matings were detected in ovigerous females. Multiple matings were also evident, to a greater e xtent than in the field, probably due to the higher availability of ma les. Females underwent over four successive spawnings in the laborator y without having to recopulate, and the incubation lasted on the avera ge from 40 to 58 days (similar to 18 and 16 degrees C respectively) an d the mean duration between hatching and the next spawning was 3.4 day s. It is estimated that most females carry out three successive spawni ngs during the annual cycle. (C) 1998 Elsevier Science B.V.