Larvae of female Caecognathia sp. (Isopoda: Gnathiidae) are attracted to male adults and prolong their larval phase in the absence of males

The interaction between males and females (adults and/or larvae) of Caecognathia sp., a parasite of fishes, was studied in the laboratory to investigate the attraction of the opposite sexes and the induction of metamorphosis to adults. We reared the third-stage larvae collected by a light trap to develop them into adults. Their sex ratio was 104 males to 100 females, suggesting that females and males have similar fitness. The attraction experiments using an experimental chamber demonstrate that adult males attract female larvae that were also attracted by the dichloromethane extract of males but not the female extract. The males also induce the praniza females to develop into adults. When there are no males present, females can prolong the larval phase and moreover can spontaneously start to develop into adults after the prolonged larval phase. As in other isopods, the gnathiid female is supposed to be able to copulate immediately after metamorphosis, and the timing of metamorphosis is therefore crucial. The prolongable larval phase in the gnathiid female could be an adaptation to a polygynous, semelparous system and brief copulatory phase after the metamorphosis into adult female.

Indomethacin reproducibly induces metamorphosis in Cassiopea xamachana scyphistomae

Cassiopea xamachana jellyfish are an attractive model system to study metamorphosis and/or cnidarian–dinoflagellate symbiosis due to the ease of cultivation of their planula larvae and scyphistomae through their asexual cycle, in which the latter can bud new larvae and continue the cycle without differentiation into ephyrae. Then, a subsequent induction of metamorphosis and full differentiation into ephyrae is believed to occur when the symbionts are acquired by the scyphistomae. Although strobilation induction and differentiation into ephyrae can be accomplished in various ways, a controlled, reproducible metamorphosis induction has not been reported. Such controlled metamorphosis induction is necessary for an ensured synchronicity and reproducibility of biological, biochemical, and molecular analyses. For this purpose, we tested if differentiation could be pharmacologically stimulated as in Aurelia aurita, by the metamorphic inducers thyroxine, KI, NaI, Lugol’s iodine, H2O2, indomethacin, or retinol. We found reproducibly induced strobilation by 50 μM indomethacin after six days of exposure, and 10–25 μM after 7 days. Strobilation under optimal conditions reached 80–100% with subsequent ephyrae release after exposure. Thyroxine yielded inconsistent results as it caused strobilation occasionally, while all other chemicals had no effect. Thus, indomethacin can be used as a convenient tool for assessment of biological phenomena through a controlled metamorphic process in C. xamachana scyphistomae.

Indomethacin reproducibly induces metamorphosis in Cassiopea xamachana scyphistomae

Cassiopea xamachana jellyfish are an attractive model system to study metamorphosis and/or cnidarian-dinoflagellate symbiosis due to the ease of cultivation of their planula larvae and scyphistomae through their asexual cycle, in which the latter can bud new larvae and continue the cycle without differentiation into ephyrae. Then, a subsequent induction of metamorphosis and full differentiation into ephyrae is believed to occur when the symbionts are acquired by the scyphistomae. Although strobilation induction and differentiation into ephyrae can be accomplished in various ways, a controlled, reproducible metamorphosis induction has not been reported. Such controlled metamorphosis induction is necessary for an ensured synchronicity and reproducibility of biological, biochemical and molecular analyses. For this purpose, we tested if differentiation could be pharmacologically stimulated as in Aurelia aurita, by the metamorphic inducers thyroxine, KI, NaI, lugol's iodine, H2O2, indomethacin, or retinol. We found reproducibly induced strobilation by 50 µM indomethacin after 6 days of exposure, and 10-25 µM after 7 days. Strobilation under optimal conditions reached 80-100% with subsequent ephyrae release after exposure. Thyroxine yielded inconsistent results as it caused strobilation occasionally, while all other chemicals had no effect. Thus, indomethacin can be used as a convenient tool for assessment of biological phenomena through a controlled metamorphic process in C. xamachana scyphistomae.

Indomethacin reproducibly induces metamorphosis in Cassiopea xamachana scyphistomae

Cassiopea xamachana jellyfish are an attractive model system to study metamorphosis and/or cnidarian-dinoflagellate symbiosis due to the ease of cultivation of their planula larvae and scyphistomae through their asexual cycle, in which the latter can bud new larvae and continue the cycle without differentiation into ephyrae. Then, a subsequent induction of metamorphosis and full differentiation into ephyrae is believed to occur when the symbionts are acquired by the scyphistomae. Although strobilation induction and differentiation into ephyrae can be accomplished in various ways, a controlled, reproducible metamorphosis induction has not been reported. Such controlled metamorphosis induction is necessary for an ensured synchronicity and reproducibility of biological, biochemical and molecular analyses. For this purpose, we tested if differentiation could be pharmacologically stimulated as in Aurelia aurita, by the metamorphic inducers thyroxine, KI, NaI, lugol's iodine, H2O2, indomethacin, or retinol. We found reproducibly induced strobilation by 50 µM indomethacin after 6 days of exposure, and 10-25 µM after 7 days. Strobilation under optimal conditions reached 80-100% with subsequent ephyrae release after exposure. Thyroxine yielded inconsistent results as it caused strobilation occasionally, while all other chemicals had no effect. Thus, indomethacin can be used as a convenient tool for assessment of biological phenomena through a controlled metamorphic process in C. xamachana scyphistomae.

Influence of natural settlement cues on the metamorphosis of fiddler crab megalopae, Uca vocator (Decapoda: Ocypodidae)

Megalopae of many decapod crab species accelerate their development time to metamorphosis (TTM) when exposed to natural physical and/or chemical cues characteristic of the parental habitat. In the present study, the influence of natural settlement cues on the moulting rates and development TTM in megalopae of the fiddler crab Uca vocator was investigated. The effects of mud from different habitats (including well-preserved and degraded-polluted mangrove habitats) and conspecific adult 'odours' (seawater conditioned with crabs) on the induction of metamorphosis were compared with filtered pure seawater (control). 95 to 100% of the megalopae successfully metamorphosed to first juvenile crab stage in all treatments, including the control. However, the development TTM differed significantly among treatments. Settlement cues significantly shortened development, while moulting was delayed in their absence. The fact that megalopae responded to metamorphosis-stimulating cues originating from both adult and non-adult benthic habitats demonstrates that settlement in this species may occur in a wider range of habitats within the mangrove ecosystem, including impacted areas.