Browsing by Author "Baeza, JA"

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    Active brood care in Cancer setosus (Crustacea: Decapoda)
    (2002) Baeza, JA; Fernández, M
    1. Previous studies have shown that oxygen is limiting in embryo masses of marine invertebrates. It has been suggested that several behaviours found in brooding females of brachyuran crabs are used to ventilate and provide oxygen to the embryo masses.
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    Life history of Allopetrolisthes spinifrons, a crab associate of the sea anemone Phymactis clematis
    (2001) Baeza, JA; Stotz, W; Thiel, M
    Allopetrolisthes spinifrons is an ectocommensal crab of the, sea anemone Phymactis clematis. The population biology of A, spinifrons in north central Chile was examined between January and December 1996. During 1996, 74% of P. clematis in the rocky intertidal zone hosted at least one commensal crab. In most cases, one sea anemone was inhabited by a single adult crab, either male or female. A few sea anemones hosted two or more crabs, one usually being an adult and the others juveniles or small crabs that just had recruited to the host. The sex ratio of adult crabs was similar to 1:1 during most months. Reproduction occurred with similar intensity throughout the year as indicated by the continuous presence of reproductive females. Similarly, recruitment of A. spinifrons occurred throughout the year with the exception of late winter when no megalopae and small juveniles were found on sea anemones. Fecundity of female crabs varied between 121 and 5661 eggs per female (6.9-19.2 mm carapace length and was significantly higher during the austral winter (July) than during the summer (December). The fact that most sea anemones were inhabited by a single adult crab indicates that hosts may be monopolized by individual crabs. Resource requirements may prohibit adult crabs from sharing a host individual with another large crab, while adult tolerance towards juveniles may facilitate the maintenance of local populations.
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    Patterns of oxygen supply in embryo masses of brachyuran crabs throughout development
    (2002) Fernández, M; Pardo, LM; Baeza, JA
    Different patterns of variation in oxygen availability throughout development have been observed in embryo masses of brooding species of marine invertebrates, and this variation seems to be related to the strategy to solve the oxygen limitation problem of the broods. As yet, little is known about patterns of oxygen availability and female brooding behavior (abdominal flapping) throughout development in brachyuran crabs, and about which factors trigger abdominal flapping. These issues were experimentally studied in 2 crab species of similar body size (Cancer setosus and Homalaspis plana). In addition, oxygen consumption of crab embryos and 2 potential factors that could trigger changes in female brooding behavior were studied (oxygen partial pressure and non-identified chemical cues produced by the embryos). Optic fibers were used to monitor oxygen partial pressure (pO(2)) in the embryo mass as female behavior was videotaped; optic fibers do not affect female behavior. Microchambers were used to determine oxygen consumption of the embryos. Females carrying early stage embryos connected to containers with water under different treatments were used to evaluate the effect of pO(2) and chemical cues on female behavior. A cyclic pattern in pO(2) was detected in masses of early stage embryos and constant high pO(2) for late stages. As changes in pO(2) in the embryo mass occurred, an increase in oxygen demand by the embryos and an increase in abdominal flapping frequency were detected in both species. Abdominal flapping seems to be affected by low pO(2) in the embryo mass and also by the presence of late stage embryos. These results support previous findings suggesting that oxygen provision to embryos seems to be a critical factor determining parental investment across taxa of marine invertebrates.