The extraembryonic serosa protects the insect egg against desiccation

Area of Science:

• Evolutionary biology
• Developmental genetics
• Insect ecology

Background:

• Insects are highly successful terrestrial organisms, unlike their aquatic crustacean relatives.
• Insect egg adaptation, specifically the serosa, is understudied compared to adult traits like flight.
• The serosa is an insect egg novelty, an extraembryonic membrane secreting a protective cuticle.

Purpose of the Study:

• To experimentally investigate the protective role of the serosa against desiccation.
• To understand the contribution of the serosa to insect terrestrialization.

Main Methods:

• Utilized zerknüllt1 RNA interference (RNAi) to eliminate the serosa in Tribolium castaneum eggs.
• Analyzed egg hatching rates across a range of humidity levels.
• Examined the expression of Tc-chitin-synthase1 in the serosa and its role in cuticle formation.

Main Results:

• Serosa-less eggs showed significantly reduced hatching rates at lower humidities compared to control eggs.
• Knock-down of Tc-chitin-synthase1 resulted in the absence of the serosal cuticle and decreased hatching at low humidity.
• Experimental evidence supports the serosa's critical role in desiccation resistance.

Conclusions:

• The serosa is vital for insect egg survival in terrestrial, arid environments.
• The evolution of the serosa likely facilitated the radiation of insects onto land.
• This finding parallels the role of the amniote egg in vertebrate terrestrialization.