RESUMEN
Abstract Sympatric mud crab species Panopeus americanus and Panopeus austrobesus are found in intertidal environments associated with muddy and rocky habitats in the Western Atlantic coast. Therefore, they are a suitable model system to be used in studies focused on investigating biological coexistence aspects between close species, such as population structure and habitat. The aims of the current study are to describe and compare the distribution of two sympatric mud crab species - P. americanus and P. austrobesus - based on their spatial and temporal distribution, in a low human impact estuarine complex area. The hypothesis that these two species show similar distribution, although one species is more abundant than the other, was herein tested. Sampling was carried out in the intertidal zone of a specific area in Cananeia estuarine complex, São Paulo State, Southeastern Brazil, in different periods of time for two years. Both species presented similar pattern distribution and frequency, with predominance in the middle and high intertidal zones, including all demographic categories. However, Panopeus americanus was more abundant and presented smaller mean size in all sampling zones. The pronounced disparity in size between the species suggests divergent dietary preferences, potentially related to prey size allowing the coexistence of these sympatric and syntopic species. The predominance of these two species in the upper intertidal zones was understood as a strategy for avoiding competition with the intertidal alpheid shrimps.
Resumo As espécies simpátricas de caranguejo-da-lama Panopeus americanus e Panopeus austrobesus são encontradas em ambientes entremarés associados a habitats lamacentos e rochosos, bem como em simpatria na costa do Atlântico Ocidental. Portanto, constituem um sistema modelo adequado para ser utilizado em estudos focados na investigação de aspectos de coexistência biológica entre espécies semelhantes, como estrutura populacional e habitat. Os objetivos do presente estudo são descrever e comparar a microdistribuição de duas espécies simpátricas de caranguejo-da-lama - P. americanus e P. austrobesus - com base na avaliação de sua distribuição espacial e temporal, em uma área estuarina complexa e com baixo impacto antrópico. A hipótese de que estas duas espécies apresentam microdistribuição semelhante, embora uma espécie seja mais abundante que a outra, foi testada. A amostragem foi realizada na zona entremarés de uma área específica do complexo estuarino de Cananeia, Estado de São Paulo, Sudeste do Brasil, em diferentes períodos durante dois anos. Ambas as espécies apresentaram microdistribuição e frequência semelhantes, principalmente nas zonas entremarés média e alta. Entretanto, Panopeus americanus foi mais abundante e apresentou menor tamanho médio em todas as zonas amostrais. A pronunciada disparidade de tamanho entre as espécies sugere preferências alimentares divergentes, potencialmente relacionadas ao tamanho das presas possibilitando a coexistência dessas espécies simpátricas. A predominância dessas duas espécies nas zonas intermareais superiores também indica uma estratégia para evitar a competição com os camarões alfeídeos.
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The life history traits of the snapping shrimp Alpheus carlae were investigated. We evaluated the relative growth, morphological sexual maturity, sexual dimorphism, handedness, fecundity, and egg volume. Sampling was performed monthly in an estuarine region of Cananéia, in the south-eastern coast of Brazil. The following structures were measured to perform the relative growth analysis: length of carapace and second pleonal pleuron, length, width and height of major cheliped propodus, and length of appendix interna and appendix masculina. Juveniles and adults males and females have different growth patterns, indicating distinct strategies of energy allocation. The estimated carapace length at the onset of morphological sexual maturity of females and males was 5.6 mm and 6.2 mm, respectively. The sexual dimorphism of specific body structures was evident, mainly in the appendix interna of females and major cheliped of males. There was no evidence of handedness in females or males. The mean fecundity of females was 364 ± 204 eggs (mean ± SD) eggs and was positively correlated with the carapace length. The egg volume differed between developmental stages I and II, and I and III, with an overall volume increase of 73.23% and 95.45%, respectively. The results contribute to the knowledge about A. carlae and its life history in natural environment.
RESUMEN
Herein, the Zoea I of Synalpheus apioceros is described, followed by a comparative analysis of the first larval stage from Synalpheus. Larvae were obtained from two ovigerous females sampled in Ubatuba, São Paulo. The morphology of the Zoea I of S. apioceros was compared to five other Synalpheus species whose structures were previously described: S. biunguiculatus, S. minus, S. neomeris, S. pectiniger, and S. tumidomanus. A set of unique morphological characteristics was found for S. apioceros: exopod of antennule with 4 aesthetascs and 1 plumose seta; coxal endite of maxillule with 2 simple setae plus 2 plumose setae; basial endite of maxillule with 2 simple setae plus 2 short spines; endopod of maxillule with 1 plumose seta plus 2 simple setae; basial endite of maxilla bilobed with 2 (1 plumose and 1 simple) + 2 (1 plumose and 1 simple) setae; coxal endite of maxilla bilobed with 2 + 1 plumose setae; endopod of maxilla with 3 (1 plumose and 2 simple) terminal setae + 2 simple setae; endopod of first maxilliped unsegmented with 3 terminal simple setae; basis of first maxilliped with 5 spines; endopod of second maxilliped 5-segmented with 0, 0, 0, 1 plumodenticulate, 4 (1 serrate + 3 simple) setae; endopod of third maxilliped 5-segmented with 0, 0, 0, 1 simple, 3 simple setae; pereiopods 1st to 3rd birramous and 4th and 5th uniramous. S. apioceros shows higher morphological similarity with S. minus, followed by S. tumidomanus, S. neomeris and S. pectiniger, probably since these species present extended larval development. Besides the similar morphology among species, the unique attributes presented here are important for the genus' taxonomy, being fundamental for identifying the first larval stages of Synalpheus, as well as for subsidizing information for species identification keys.
Asunto(s)
Decápodos , Animales , Femenino , LarvaRESUMEN
The aims of this study were to describe and illustrate the early larval stages of the snapping shrimp Alpheus brasileiro Anker, 2012 and to review the larval morphology (Zoea I) of the genus Alpheus Fabricius, 1798. Larvae were obtained from two females with embryos collected in an intertidal estuary in Cananéia, São Paulo state, Brazil. The published descriptions of all available Alpheus zoea I (only 14 spp., 4.7%) were used for a comparison of larval morphology. The zoeae I of Alpheus species are very similar, but A. brasileiro can be separated from the other studied species by the following set of characteristics: antennal scale 5-segmented with 11 plumose setae and 2 simple setae; coxal endite of maxillule with 3 simple setae and 2 sparsely plumose setae; and coxal endite of maxilla with 1 simple seta and 1 sparsely plumose seta. The description of early larval development of A. brasileiro indicates consistent characteristics, which, when analyzed along with other morphological, molecular, and biogeographical aspects, can help to elucidate the complex phylogenetic relationships between the species in the group. However, this is the first zoeal description of a member of Alpheus armillatus species complex and it therefore does not permit a comparison. Only with new additional descriptions we will be able to generate a clearer scenario in this field due the high similarity among the species.