Egg envelopes and cuticle renewal in Porcellio embryos and marsupial mancas

Abstract

An important adaptation to land habitats in terrestrial isopod crustaceans is development of embryos in a fluid-filled female brood pouch, marsupium. The study brings insight into the structure and protective role of egg envelopes and cuticle renewal during ontogenetic development of Porcellio embryos and marsupial mancas. Egg envelopes cover embryos, the outer chorion until late-stage embryo and the inner vitelline membrane throughout the whole embryonic development. Egg envelopes of Porcellio have relatively simple ultrastuctural architecture compared to Drosophila egg envelopes. Exoskeletal cuticle is produced in late embryonic development by hypodermal cells of the embryo and is renewed in further development in relation to growth of developing embryos and mancas. Cuticle structure and renewal in prehatching late-stage embryos and marsupial mancas exhibit main features of cuticle in adults. Epicuticle is thin and homogenous. The characteristic arrangement of chitin-protein fibers and the dense distal layer in exocuticle are hardly discernible in prehatching embryo and distinct in marsupial mancas. Endocuticle consists of alternating electron dense and electron lucent sublayers and is perforated by pore canals in both stages. Differences from adult cuticle are evident in cuticle thickness, ultrastructure and mineralization. Signs of cuticle renewal in prehatching embryo and marsupial mancas such as detachment of cuticle from hypodermis, partial disintegration of endocuticle and assembly of new cuticle are described.

Formation of the hindgut cuticular lining during embryonic development of Porcellio scaber (Crustacea, Isopoda)

“…These differences indicate that the hindgut cuticle in marsupial mancae does still not perform all functions of the gut cuticle in adults, which could be related to the aqueous environment of the marsupium, among other not exposing the animal to dissication. As described for the exoskeleton (Mrak et al 2012, 2014), morphological characteristics of cuticle renewal in late marsupial mancae are observed also in the hindgut, indicating the renewal of the gut cuticle soon after release of mancae from the marsupium and subsequent molting of the mancae. Bacteria recorded in one specimen of an early marsupial manca were distributed evenly within the contents of the hindgut lumen and no specific attachments to the cuticular lining were observed.…”

“…The marsupial mancae were classified in accordance with the staging system reported by Mrak et al (2012), distinguishing three sequential marsupial manca stages. In this study, three stages of late embryos (stage 16, stage 18 and stage 19) and two stages of marsupial mancae (early marsupial manca and late marsupial manca) were analysed.…”

“…A cuticular matrix with the general characteristics of crustacean exoskeletal cuticle is formed in the last stages of embryonic development. The new cuticle formation in the subsequent marsupial manca stages and the renewal of the exoskeleton in late-stage marsupial mancae have been described by Mrak et al (2012, 2014). Larvae, termed postmarsupial mancae, are released from the marsupium and develop in the external environment until the juvenile stage (Tomescu and Craciun 1987, Brum and Araujo 2007, Montesanto et al 2012).…”

Exoskeletal cuticle differentiation during intramarsupial development of Porcellio scaber (Crustacea: Isopoda)

“…Our results show gradual formation and calcification of the exoskeleton during P. scaber larval development within the marsupium. The exoskeleton provides support for the muscles and is involved in the animal mobility which was observed within the marsupium (Mrak et al, 2012). Elaborated and calcified cuticle also protects the larvae against potential physiological stresses, including osmotic and ionic variations in the marsupial environment.…”

“…Embryos and mancae were isolated from the marsupia of gravid females. Different developmental stages of embryos were identified according to Milatovi c et al (2010) and the marsupial mancae were classified according to Mrak et al (2012). The following stages of embryos were used in this study: mid-stage embryo (stages 10, 13, 14 and 15) and late-stage embryo (stages 16, 18 and 19).…”