María Andrea Gavio

LATITUDINAL VARIATION IN POPULATION STRUCTURE AND REPRODUCTIVE PATTERN OF THE ENDEMIC SOUTH AMERICAN SHRIMP ARTEMESIA LONGINARIS (DECAPODA: PENAEOIDEA)

Abstract Population structure and reproductive maturity of females were investigated in the shrimp Artemesia longinaris Bate, 1888 from coastal waters of northern São Paulo State (Brazil, 23°S) and Mar del Plata (Argentina, 38°S) from June 2001 to May 2002. Monthly collections were taken by commercial shrimp fishing boats equipped with bottom trawl nets. Population parameters from size frequency distributions and size (carapace length = CL) of female reproductive maturity were analyzed and compared from the two sampling areas. Latitudinal trends in reproductive parameters of A. longinaris were shown in overall body size and size of reproductive maturity, both of which were smaller in females from the tropical location than those from the cold-temperate sampling area. Largest females (> 30 mm CL) were collected in Argentina, while Brazilian specimens reached maximum size at 27 mm CL. The smallest size of female sexual maturity was estimated at 13.6 mm CL in Brazilian samples compared to 22.1 mm CL calculated for those from Argentina. Populations from both regions exhibited a bimodal size distribution in the spring, with the peak at small body size probably corresponding to recent recruits and the peak at larger body size to reproductive females or shrimps migrating in from deeper waters or other latitudinal regions. In late spring and summer, an intrusion of the cold South Atlantic Coastal Water mass was observed which lowered water temperature and stimulated plankton production, the primary food source for the larvae of a typically cold-temperate species such as A. longinaris. The trend of increasing body size and delay of sexual maturity with increasing latitude appears to be correlated with the decreasing water temperature and increasing plankton productivity at higher latitudes.

Morphology and function of the reproductive tract of the spider crab Libinia spinosa (Crustacea, Brachyura, Majoidea): pattern of sperm storage

Morphology and function of the male reproductive tract, female spermatheca and patterns of sperm storage were assessed in the crab Libinia spinosa using histological methods. Testes are characterized by the presence of peripheral spermatogonia and different sequences of sperm maturity. Spermatophores begin to be packed in the last portion. The vas deferens consists of three sections: anterior, with undeveloped spermatophores and free sperm; median, with well-developed spermatophores; and posterior with granular secretions. Female spermathecae are of the ventral type, with a velum separating dorsal and ventral chambers. Live individuals were kept in the laboratory and arranged in pairs. An experiment was conducted toward the end of the reproductive season, in which males with the right gonopod excised were placed with receptive females. After mating, females were killed and the spermathecae dissected for histological study and observation of the pattern of sperm storage. Spermatozoa were found forming discrete sperm packages. New ejaculates can fill the entire spermatheca or be restricted to the ventral chamber; sperm are rounded, with a distinguishable acrosomal core. Old ejaculates are restricted to the dorsal chamber and are of irregular shape and larger size; an acrosomal core was not distinguishable. The secretions produced by the glandular epithelium of the dorsal chamber of the spermathecae are likely to have a role in the removal of dead sperm.

Morphometric and gonad maturity of the spider crab Libinia spinosa (Crustacea: Brachyura: Majoidea: Epialtidae) in Argentina

Morphometric and gonad maturity of Libinia spinosa on the coast of Mar del Plata, Argentina, were assessed. In both sexes various morphometric features were measured to determine the morphometric maturity, and through macroscopic inspection of gonads and analysis of its content, different stages of gonad maturity were described and the physiological maturity was estimated. In females, the carapace width ranged from 8 to 5 6. 5 mm while in males from 4 .6 to 8 1 . 97 mm. The size at which 50 % of females were morphometrically mature was calculated at 40 .6 mm. Based on the allometric growth of the abdomen, two morphometric groups of females were recognized as juvenile and adult phases. In males, results of principal component analysis showed that the most suitable variables that efficiently represent the size and sexual differentiation factor were the carapace width and cheliped length respectively. The size at which 50 % of males were morphometrically mature was estimated at 5 8. 9 mm. Based on the allometry of the cheliped growth, two morphometric groups were recognized as immature and mature phases. Males maintained under laboratory conditions moulted and growth was related to regular and terminal moults. Males reached their terminal moult at a wide size-range, from 4 8. 5 mm to 6 1 . 4 mm of carapace width. This terminal moult coincided with the size of morphometric maturity. In both sexes four stages of gonad development were described, two corresponded to immature phases and two to mature phases. The size at which 50 % of females and males reached gonad maturity was LC 50 = 40.33 mm and LC 50 = 33 .6 mm, respectively. In females, both morphometric and gonad maturity occurred at a similar size. In males, gonad maturity is acquired prior to morphometric maturity, thus three different types of males were characterized: (1) those with small carapace width and cheliped, without spermatophores in their vas deferens; ( 2 ) those with large carapace width and small cheliped, bearing spermatophores in their vas deferens; and ( 3 ) those with large carapace width and cheliped, bearing spermatophores in their vas deferens.

Evaluation of Alternative Life History Hypotheses for the Sand Shrimp Crangon Franciscorum (Decapoda: Caridea)

Abstract Caridean shrimps are unique among decapod crustaceans in showing a great diversity of sexual systems, including gonochorism, protandry, protandry with primary females and simultaneous hermaphroditism. Crangon franciscorum (Stimpson, 1859) (Crangonidae), an ecologically and economically significant species from the Pacific coast of North America, has been assumed to be gonochoristic. Earlier population studies concluded that average lifespan is longer in females than in males, and that the latter die in or emigrate from estuaries after mating. This was believed to explain a recurrently observed “shrinking” of average male size starting during the fall of the first year of life. We investigated an alternative hypothesis according to which this species is a protandric hermaphorodite, and disappearance of large males from the population reflects sex change rather than death or emigration. We present several pieces of evidence in support of the alternative hypothesis: (i) ovarian development in males undergoing sex change, (ii) presence of atrophied vas deferens in secondary females, and (iii) observation of sex change in individuals kept in captivity. Our results are supported by histological study of the gonads, careful description of secondary sexual characters, and monthly sampling of an estuarine population (Grays Harbor, Washington). Tracking an identifiable year-class (1980) and combining field and laboratory data allowed us to assemble a life history schedule, including growth and a calendar of significant reproductive events. We discuss the implications of our results for the interpretation of survey data and studies on population dynamics.

Receptivity of female Neohelice granulata (Brachyura, Varunidae): different strategies to maximize their reproductive success in contrasting habitats

The extent of the receptive period may determine the mating strategies employed by female crabs to obtain mates. Here, we studied the receptivity of female Neohelice granulata (Dana, 1851) in the laboratory, including the form of the vulvae and the anatomy of the seminal receptacle (SR). We examined the factors that influence the duration of receptivity by comparing two populations inhabiting contrasting habitats: Mar Chiquita Coastal lagoon (MCL), which is an oligo-polyhaline estuary, and San Antonio Oeste (SAO), which is an eu-hyperhaline marine bay. Non-receptive females have immobile vulva opercula, while receptive females have mobile opercula. Histological sections of the SR showed that the degree of epithelium secretions was associated with the receptive stage of females, and they may be involved in the maintenance of viable sperm and in the dehiscence of spermatophores. The existence of a special tissue at the junction of the oviduct and the SR was described and proposed as an internal mechanism influencing the timing of ovulation. The duration of receptivity was dependent on the SR load and the capacity to lay eggs. Thus, females with empty SR exhibited longer receptivity and did not lay eggs, while those with full SR exhibited shorter receptivity and always laid eggs. Interpopulation differences showed that females from SAO had shorter receptivity and heavier SR and laid eggs more frequently than females from MCL. Based on our results, we suggest that N. granulata females can adjust the duration of their receptivity and control the moment of fertilization according to different internal mechanisms related to the morphology of the vulvae, the fullness of the SR and anatomical attributes of the SR. An important consequence of this control is greater sperm competition. The extent of the receptive period and the number of times that a female could become receptive in a single reproductive season may also depend on the habitat characteristics.

Mercury distribution in estuarine environments from Argentina: the detoxification and recovery of salt marshes after 15 years

Total Hg contents from abiotic (surface sediments and suspendedparticulate matter) and biological (crabs, fishes and halophytes)compartments from Bahía Blanca estuary and Mar Chiquita CoastalLagoon, Argentina, have been monitored since the 1980s. At BahíaBlanca estuary, high Hg concentrations were recorded during the early1980s in surface sediments (0.34 ± 0.22 μg/g) andsuspended particulate matter (0.19 ± 0.10 μg/g). Fishspecies, Mustelus schmitti (0.89 ± 0.29 μg/g), Paralichthys brasiliensis (0.85 ± 0.18 μg/g) and Micropogonias furnieri (0.37 ± 0.11 μg/g) also presentedhigh Hg concentrations. The large industrial nucleus located within theestuary has been identified as the main metal source for this environment.Hg contents from the same area during 1996–1998 were significantlylower: surface sediments (0.164 ± 0.023 μg/g), suspendedparticulate matter (0.048 ± 0.0017 μg/g), fish Micropogonias furnieri (0.13 ± 0.02 μg/g) and crab Chasmagnathus granulata (0.334 ± 0.071 μg/g). This trendof environmental detoxification is probably related with (i) thetechnological changes incorporated by the local industry, (ii) a mostadequate management of industrial effluents, and (iii) the removal ofgreat sediment volume by dredging and refill.During the 1980s Mar Chiquita Lagoon Hg concentrations reached 0.08± 0.01 μg/g in surface sediments and 0.09 ±0.025 μg/g in suspended particulate matter, and 0.14 ±0.04 μg/g in the fish Basilichthys bonariensis and 0.22 ±0.08 μg/g in Paralichthys brasiliensis, and 0.08 ±0.01 μg/g in the crab C. granulata, Hg concentrations werelower than at Bahía Blanca. Remote Hg sources for this Coastal Lagoonand atmospheric and stream transport of Hg is proposed as major Hgsources, since no Hg point sources exists nearby. Mercury concentrationsrecorded in the 1996–1998 period were lower than those recorded inthe previous decade: surface sediments (0.019 ± 0.004 μg/g), suspended particulate matter (0.030 ± 0.008 μg/g), halophyte Spartina densiflora (0.013 ± 0.008 μg/g) or crab C. granulata (0.011 ± 0.009 μg/g).Both Hg bioaccumulation and biomagnification processes were verified inBahía Blanca estuary and in Mar Chiquita Coastal Lagoon. This apparentrecovery of both estuarine environments deserves to be carefully analyzed,in order to fully understand the foundations of these processes.

Reproductive System and Size Maturity of the Paddle Crab Ovalipes trimaculatus (Brachyura: Portunidae) Along the Argentine Coast

Ovalipes trimaculatus (de Haan, 1833) is a commercial species captured in the Mar del Plata coast, Argentina. However, no studies were conducted in order to study its population features neither its reproductive biology. The morphometric and physiological maturity of both sexes, the histology of the female seminal receptacle and ovary, and the ultrastructure of the male gonopods were studied in the present paper. In females, morphometric maturity (44.6 mm of carapace width, CW) was acquired prior to physiological maturity (54.6 mm CW). By contrast, in males, physiological maturity (46.6 mm CW) was acquired prior to morphometric maturity (52.3 mm CW). The ovary is connected to the dorsal part of the seminal receptacle. Neither Spermatophores, nor sperm packets were found inside the seminal receptacle; instead free spermatozoids were observed indicating that sperm from different males is probably mixed favoring sperm competition. The ultrastructure of the male gonopods was similar to the described for other Brachyura. Different types of setae and the presence of internal rosette glands were described and probable functions were suggested.

Comparison of Mating Behavior and Copulation in Male Morphotypes of the Spider Crab Libinia spinosa (Brachyura: Majoidea: Epialtidae)

ABSTRACT The mating behavior of the spider crab Libinia spinosa Milne Edwards 1834 was studied in the laboratory. Two male morphotypes as morphometrically immature (MI) with small chelae and morphometrically mature (MM) with large chelae were used in non competitive and competitive mating trials. The liberation of putative hormones by receptive females to attract males was studied. We examined whether male body or cheliped size influence mate acquisition and copulation. The liberation of putative hormones by receptive females could not be demonstrated because males did not behave differently among four treatments exposed to water from 1) ovigerous females, 2) non ovigerous females, 3) males, and 4) a control of water unexposed to crabs. Under non competitive and competitive scenarios, copulation occurred immediately after physical contact between partners, thus a contact pheromone could be involved. The copulatory behavior and the time of copulation were similar between both male morphotypes. In non-competitive mating trials, MI males copulated successfully with females, and immediately after the mating pairs decoupled. By contrast, MM males displayed a post-copulatory guarding behavior that consisted of holding the female with the major cheliped and carrying her around the aquarium. In a competitive scenario, MM males guarded females for several hours by either caging them within the legs, or holding them out of the water when MI males approached. MI males of larger sizes than MM males did not gain mates and avoided agonistic interactions with MM males; thus, large chelae size is a more decisive trait than large body size for mate acquisition.

Are semi-terrestrial crabs threatened by human noise? Assessment of behavioural and biochemical responses of Neohelice granulata (Brachyura, Varunidae) in tank

This study examined the effects of human lab-generated noise (sweep tone) on the behaviour and biochemistry of a semi-terrestrial crab (Neohelice granulata). The experiment was carried out in tanks equipped with video- and audio-recording systems on a total of seventy-eight specimens. In total, 42 experimental trials with sweep-tone exposure and control conditions were performed using crabs in single and group layouts. After a habituation period of 30 min, the locomotor and acoustic (sound signals emitted by the crabs) behaviours were monitored for 30 min. During this time, the animals in sweep-tone conditions were exposed to ascending sweeps in a bandwidth range of 2.5-25 kHz. Exposure to sweep-tone noise produced significant changes in the number of signals emitted, locomotor behaviours and plasma parameters, such as haemolymph total haemocyte count and glucose, lactate and total protein concentrations, revealing that human noise could represent a disturbance for this crustacean species.