Tomás Luppi

Predation risk modifies behaviour by shaping the response of identified brain neurons.

ABSTRACT Interpopulation comparisons in species that show behavioural variations associated with particular ecological disparities offer good opportunities for assessing how environmental factors may foster specific functional adaptations in the brain. Yet, studies on the neural substrate that can account for interpopulation behavioural adaptations are scarce. Predation is one of the strongest driving forces for behavioural evolvability and, consequently, for shaping structural and functional brain adaptations. We analysed the escape response of crabs Neohelice granulata from two isolated populations exposed to different risks of avian predation. Individuals from the high-risk area proved to be more reactive to visual danger stimuli (VDS) than those from an area where predators are rare. Control experiments indicate that the response difference was specific for impending visual threats. Subsequently, we analysed the response to VDS of a group of giant brain neurons that are thought to play a main role in the visually guided escape response of the crab. Neurons from animals of the population with the stronger escape response were more responsive to VDS than neurons from animals of the less reactive population. Our results suggest a robust linkage between the pressure imposed by the predation risk, the response of identified neurons and the behavioural outcome. Highlighted Article: Crabs from an isolated population under high risk of predation show stronger neuronal and behavioural responses to visual threats than those from a population at low risk of predation.

Functional morphology of the female reproductive system of a crab with highly extensible seminal receptacles and extreme sperm storage capacity

We studied the functional morphology of the female reproductive system of the purple stone crab Danielethus crenulatus. The most remarkable feature is the relative storage capacity and extensibility of the seminal receptacles. These receptacles are a pair of simple sacs that lack internal structures dividing the internal lumen. Differences in seminal receptacle size and contents are accompanied by conspicuous changes in receptacle lining at a tissue level. Full seminal receptacles contain discrete sperm masses formed by hardened fluid and densely packed spermatophores. Different sperm masses are likely from different mates and their stratified disposition within the seminal receptacles is compatible with rival sperm displacement and last sperm precedence. Additionally, the anatomical structure of the vulva and vagina suggest active female control over copula. We discuss our results in the general context of sperm storage in brachyurans and the implications for the mating system of this species.

HABITAT RELATED VARIATION IN REPRODUCTIVE TRAITS AMONG INTERTIDAL CRABS FROM THE SOUTHWESTERN ATLANTIC

ABSTRACT The reproductive traits of three coastal grapsoid crabs from the southwestern Atlantic, Neohelice granulata (Dana, 1851), Cyrtograpsus angulatus Dana, 1851 and C. altimanus Rathbun, 1914, were compared under the hypothesis that more energy is diverted to maintenance (and less to reproduction) in the upper intertidal and/or in estuaries than in the lower marine intertidal or subtidal, in order to cope with the harsh, and frequently variable, environmental conditions of semiterrestrial and brackish water habitats. Each species occupies a different habitat along intertidal, as well as estuarine gradients: N. granulata lives in the upper and middle intertidal of salt marshes and mud flats, especially in estuarine waters; C. angulatus lives in the low intertidal and subtidal of estuarine and marine habitats, and C. altimanus is predominantly an intertidal and subtidal marine crab. Results suggested that energy demands imposed by the harsh environmental conditions of the estuarine and semiterrestrial habitats resulted in less energy available for reproduction in N. granulata, evidenced by a shorter breeding season, a reduced reproductive output per clutch and an increased clutch interval. The opposite occurred with C. altimanus: less energy was necessary to cope with the stable marine water, allowing the presence of a long breeding season, a higher reproductive output per clutch and a very short clutch interval. Differences observed between marine and estuarine populations of C. angulatus are comparable with differences between C. altimanus, and N. granulata.

Hatching and larval export of the intertidal crab Neohelice granulata in Mar Chiquita coastal lagoon, Argentina

Synchronization in the events of the reproductive cycle in female Neohelice granulata Dana, 1851 were studied from samples taken weekly and biweekly from September to December 2006 in the Laguna Mar Chiquita. The timing and larval hatching and synchronicity were inferred from numbers of ovigerous females and observing the stages of embryonic development. Synchronization in larval hatching also was observed in females in experiments in dark for a period of 48 hours, at three different salinities (10, 23 and 33 ppm). In addition plankton sampling were performed in order to study larval exportation at the field and its link to the tidal and light/dark cycles. We found that ovigerous females of N. granulata have a marked synchronization in embryonic development which results in that most of berried females are close to hatching within a period of maximum tidal range (days). Within this period, there is a synchronization of hatching at a time scale of hours, governed by environmental conditions. The salinity range used in this study (10-32‰) did not affect hatching synchronicity neither time to hatch. Hatching was synchronized according to endogenous rhythms governed mainly by the tidal cycle and secondarily by the breadth of it. It is also conditioned by the light-dark cycle through an exogenous cycle, so that the hatchings would occur mostly at night high tides.

On the presence of the deep-sea blind lobster Stereomastis suhmi (Decapoda: Polychelidae) in Southwestern Atlantic waters and its circum-Antarctic distribution

Here we report on the presence of the deep-sea blind lobster Stereomastis suhmi in the Southwestern Atlantic. The species identification was based on morphological traits and confirmed with genetic barcoding. The specimen analysed shows little difference from previous descriptions. This work extends the range of S. suhmi in America, where it was previously limited to the Pacific coasts off Chile, to the mouth of the Rio de la Plata, Argentina, and confirms its circumpolar presence with molecular data. A review of all available records shows that the overall distribution of the species is well correlated with the presence of Antarctic Intermediate Waters suggesting that the species habitat is restricted to cold and relatively low-salinity/oxygen-rich waters.

New record of the deep-sea crab Ethusina abyssicola from the Mar del Plata Canyon, Argentina

Ethusina abyssicola Smith, 1884 (Decapoda, Ethusidae) belongs to Ethusidae, a family of small and deep-sea crabs adapted to carrying objects on their backs for camouflage. Ethusina abyssicola is the only species of that genus occurring in the West Atlantic, is distributed from New England, USA to Cape Frio, Brazil, and is one of the best adapted brachyuran crabs to inhabit deep water (up to 5046 m). We reported herein E. abyssicola in the deep and under-explored ‘Mar del Plata Canyon’ (38°01′S, 53°39′W), Argentina. The specimens were taken at 2934 m, which represents the greatest depth record for any brachyuran crab below 25°S in the southwestern Atlantic. Although E. abyssicola from the canyon mostly agree with previous descriptions, their outer orbital spines pointed forward and not outwards as in the original description. The significance of this difference is presently unknown and will require genetic analysis to be clarified.

The ontogeny of the female reproductive system in the parasitic castrator pea crab Calyptraeotheres garthi: Implications for its mating system

The knowledge of the mating system of pea crabs is still fragmentary as it remains dubious whether females copulate in the juvenile and free‐living ‘hard’ or in the obligatory symbiotic stages (adult stage ‘V’ or intermediate stages II to IV). To discriminate between these two possibilities, we analysed the female seminal receptacles, vagina and opercula, and the sperm content in different stages of the pea crab Calyptraeotheres garthi. Our histology and scanning electron microscopy results revealed that in the hard stage the seminal receptacle is simple without secretory epithelia, and vagina and opercula are not controlled by musculature. In stages II to IV, the seminal receptacles, vagina, and opercula are under development and these structures reach maturity in stage V. These results suggest that females become receptive in stage V and not during predating stages. We found no spermatozoa in SR of ‘hard’ and stage II to IV females while these structures were loaded of sperm in most stage V, indicating that females start to mate in stage V. Our results support the notion that males of C. garthi roam among hosts in search for sedentary stage V females, as predicted by Baeza and Thiels ( ) model of mating systems for symbiotic crustaceans. Nevertheless, we failed to reveal whether females mate repeatedly: the accumulation of sperm in larger females might indicate occurrence of multiple copula or a high variability in male sperm transfer.

Hard-shell mating in Neohelice granulata: the role of ecdysone in female receptivity and mate attraction

Most brachyuran females become receptive during the intermolt period, a condition considered “derived”. However, as far as we know, studies testing the existence and function of pheromones in decapods are based on species which have mating linked to molting, a condition considered as “ancestral”. For the first time, we studied some physiological and morphological processes involved in Neohelice granulata intermolt female crabs becoming receptive and potentially attracting males. We found that receptive females have mobile vulvae opercula due to a softening process of the cuticle hinge which showed lower calcium levels compared to the hinge of unreceptive females. Local softening of the hinge was stimulated by a low concentration of ecdysone during the intermolt period. A putative pheromone liberated by receptive females to attract males is presumed to be released through the mobile vulvae and not through the urine.

The larval development of the spider crab Rochinia gracilipes (Crustacea: Majoidea: Epialtidae: Pisinae) reared in the laboratory

ABSTRACT The larval development of the spider crab Rochinia gracilipes Milne-Edwards, 1875 (Crustacea: Decapoda: Brachyura: Majoidea: Epialtidae: Pisinae) is described and illustrated from laboratory-reared larvae. Development consisted of two zoeal stages and one megalopa, following the typical pattern in Majoidea. Zoea I of R. gracilipes, R. debilis and R. carpenteri differed in lengths of the rostral spine of the carapace, in the number of setae and aesthetascs of several head appendages (exopods of antennules, endopods of maxillules, and endopods and scaphognathites of maxillae) and in the length of posterolateral processes of abdominal somites; lateral carapace spines were present only in R. carpenteri and pleopod buds only in R. debilis. Megalopae of Rochinia gracilipes and R. carpenteri differed in several notable characters: a dorsal spine and long rostrum of the carapace, as well as spines in coxa and ischium of pereiopods, appeared only in R. carpenteri, and podobranchiae of the 3rd maxilliped appeared only in R. gracilipes; they also differed in setation of abdomen and pleopods. The comparison of the available information on Pisinae larval development suggested that larval morphology would not help to accurately understand the phylogenetic relationships of this subfamily of spider crabs.