Proceedings of the Royal Society B: Biological Sciences
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The extraembryonic serosa protects the insect egg against desiccation

Chris G. C. Jacobs

Chris G. C. Jacobs

Institute of Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands

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Gustavo L. Rezende

Gustavo L. Rezende

Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, RJ 21045-900, Brazil

Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ 28013-602, Brazil

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Gerda E. M. Lamers

Gerda E. M. Lamers

Institute of Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands

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Maurijn van der Zee

Maurijn van der Zee

Institute of Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands

[email protected]

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Published:https://doi.org/10.1098/rspb.2013.1082

    Insects have been extraordinarily successful in occupying terrestrial habitats, in contrast to their mostly aquatic sister group, the crustaceans. This success is typically attributed to adult traits such as flight, whereas little attention has been paid to adaptation of the egg. An evolutionary novelty of insect eggs is the serosa, an extraembryonic membrane that enfolds the embryo and secretes a cuticle. To experimentally test the protective function of the serosa, we exploit an exceptional possibility to eliminate this membrane by zerknüllt1 RNAi in the beetle Tribolium castaneum. We analyse hatching rates of eggs under a range of humidities and find dramatically decreasing hatching rates with decreasing humidities for serosa-less eggs, but not for control eggs. Furthermore, we show serosal expression of Tc-chitin-synthase1 and demonstrate that its knock-down leads to absence of the serosal cuticle and a reduction in hatching rates at low humidities. These developmental genetic techniques in combination with ecological testing provide experimental evidence for a crucial role of the serosa in desiccation resistance. We propose that the origin of this extraembryonic membrane facilitated the spectacular radiation of insects on land, as did the origin of the amniote egg in the terrestrial invasion of vertebrates.

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