Patterns of oxygen supply in embryo masses of brachyuran crabs throughout development: the effect of oxygen availability and chemical cues in determining female brooding behavior

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.