Inherent constraints on a polyfunctional tissue lead to a reproduction-immunity tradeoff

Area of Science:

• Insect physiology
• Molecular biology
• Evolutionary biology

Background:

• The insect fat body is a polyfunctional tissue with roles in metabolism, reproduction, and immunity.
• Understanding how such tissues manage multiple functions simultaneously is crucial for explaining physiological constraints and tradeoffs.
• The tradeoff between immunity and reproduction is a common observation, but its mechanistic basis is often unclear.

Purpose of the Study:

• To investigate the cellular mechanisms underlying functional constraints and tradeoffs in the polyfunctional insect fat body.
• To determine how the fat body balances the demands of reproduction and immune defense.
• To explore the basis for the observed tradeoff between immunity and reproduction in Drosophila melanogaster.

Main Methods:

• Single-nucleus sequencing was used to analyze cellular subpopulations within the Drosophila melanogaster fat body.
• Gene expression patterns were analyzed in response to infection and reproductive status.
• Experimental manipulation using a reversible translation inhibitor was performed to assess protein synthesis capacity.

Main Results:

• The fat body exhibits heterogeneous cellular subpopulations with stable identities under basal conditions.
• Immune response engages the entire tissue, with all subpopulations expressing defense genes.
• Reproductively active, infected females showed ER stress and impaired protein synthesis, including antimicrobial peptide production, which was rescued by a translation inhibitor.

Conclusions:

• The tradeoff between reproduction and immunity in Drosophila melanogaster is linked to the fat body's limited capacity for simultaneous protein translation demands.
• Cellular limitations in polyfunctional tissues may offer a general explanation for widespread physiological and evolutionary tradeoffs.
• This study provides a mechanistic insight into how polyfunctional tissues manage competing physiological demands.