ABSTRACT
Pycnogonum litorale (Ström) is unpalatable to the common shore crabCarcinus maenas, a generalist predator in the pycnogonid's habitat. A feeding bioassay reveals that the crabs are deterred by ecdysteroids that occur in high levels in all developmental stages ofP. litorale. The total ecdysteroids in the pycnogonids reach 5.9×10(-4) M. The 20-hydroxyecdysone 22-acetate (20E22A), which is the predominant ecdysteroid in the pycnogonids, and 20-hydroxyecdysone (20E), the arthropod molting hormone, were tested for their antifeedant effect onC. maenas. When contained in food pellets in homogeneous concentrations, 20E and 20E22A significantly reduced food consumption at 1.25×10(-4) and 5.0×10(-4) molar levels, respectively. The present results demonstrate for the first time chemical defense in arthropods in a marine predator-prey relationship. Furthermore, they provide evidence that ES contained in one animal can act as feeding deterrents on another animal.
ABSTRACT
In embryos, larvae, and juveniles of Pycnogonum litorale, unusual ecdysteroids have been found at excessively high levels. Concentrations and dynamics of the following eight ecdysteroids were determined by HPLC: 20-hydroxyecdysone, 20-hydroxyecdysone 22-glycolate, (25R) and (25S) isomers of 20,26-dihydroxyecdysone 22-acetate, 22-deoxy-20,26-dihydroxyecdysone, 20-hydroxyecdysone 22-acetate, 22-deoxy-20-hydroxyecdysone, and ecdysone 22-glycolate. The excessively high content of ecdysteroids is found in all developmental stages. Juvenile pycnogonids contain the highest total ecdysteroid amounts ever found in arthropods: 0.1% of their body dry weight. 20-Hydroxyecdysone 22-acetate is the prominent ecdysteroid and represents at all stages of both sexes, 66.2-85.8% of the total ecdysteroids. This compound, as well as all other ecdysteroids without a free 22-OH group, are presumed to be inactive as molting hormones. In contrast to these compounds, 20-hydroxyecdysone is present only in amounts similar to those in other arthropods. Furthermore, it is the only ecdysteroid with its peak at apolysis. It is regarded as the molt-promoting hormone. The origin and function of the other ecdysteroids in different developmental stages are discussed.
Subject(s)
Arthropods/metabolism , Invertebrate Hormones/metabolism , Steroids/metabolism , Aging/metabolism , Animals , Chromatography, High Pressure Liquid , Ecdysteroids , Ecdysterone/analysis , Ecdysterone/metabolism , Embryo, Nonmammalian/chemistry , Embryo, Nonmammalian/metabolism , Female , Invertebrate Hormones/analysis , Larva/chemistry , Larva/metabolism , Male , Morphogenesis , Steroids/analysisABSTRACT
Molting in pycnogonid larvae, Pycnogonum litorale, is accelerated by exposing the animals to 20-hydroxyecdysone at concentrations of 10 to 1000 ppm during Days 5 to 9 after the first ecdysis. Hormone application at the beginning or at the end of the molt cycle, as well as treatment all through the molt cycle, delays or even inhibits the molt by upsetting the sequence of molting processes.
Subject(s)
Arthropods/growth & development , Ecdysterone/pharmacology , Animals , Dose-Response Relationship, Drug , Larva/physiology , Metamorphosis, Biological/drug effectsABSTRACT
Cross-linked and uncross-linked acrylamide polymers were used to alleviate technical difficulties in cryosectioning and autoradiographic processing of marine arthropods (Pycnogonum litorale), larval insect tissues (Sarcophaga bullata), and amphibian (Xenopus laevis) oocytes. Rapidly polymerized cross-linked acrylamide was used to prepare sections from an animal with a hard thick cuticle, P. litorale. Fragmentation and compression artifacts caused by tissue density differences were avoided and internal tissues were well preserved. Our results indicate that closely applied external support eliminates difficulties typically associated with arthropod cryosectioning. Pre-polymerized, uncross-linked acrylamide provided similar protection when used for sectioning larval tissue from S. bullata. Soft tissues under the cuticle were undamaged in tracheal and epidermal preparations. This polymer was also an excellent embedding material for soft tissues such as salivary glands, quickly penetrating tissue cavities and eliminating air bubbles. Uncross-linked acrylamide was used as an embedding and culturing medium for oocytes from X. laevis. The polymers were non-toxic and allowed the preparation of thin frozen sections containing as many as 50 large oocytes per section.
