The gut microbiome shapes latitudinal differences in host immunity and pathogen load in a damselfly

Area of Science:

• Evolutionary Biology
• Microbiome Research
• Ecology

Background:

• Latitudinal patterns in fitness traits are crucial for understanding evolution under global warming.
• Mechanisms driving these patterns, particularly the role of the gut microbiome, are poorly understood.
• The gut microbiome is increasingly recognized as a proximate driver of host phenotypes.

Purpose of the Study:

• To investigate if the gut microbiome drives latitudinal differences in immune function and pathogen load in Ischnura elegans damselflies.
• To experimentally test the causal role of gut microbiome transplants in mediating these latitudinal trait variations.
• To assess the impact of thermal regimes on these interactions.

Main Methods:

• Reciprocal gut microbiome transplants between high-latitude (Sweden) and low-latitude (France) damselfly larvae.
• Larvae were exposed to Escherichia coli under different thermal regimes.
• Measurements included mortality, growth rate, immune function (phenoloxidase), pathogen load, and gut microbiome diversity (alpha and beta diversity).

Main Results:

• Low-latitude damselflies exhibited faster life history, lower immune function, and higher pathogen load, confirming thermal adaptation.
• Gut microbiome transplants causally altered host immune function and pathogen load.
• Pathogen exposure increased mortality, particularly under warming conditions.

Conclusions:

• The gut microbiome is a significant proximate driver of latitudinal variation in immune function and pathogen load.
• These findings provide critical insights into the evolutionary adaptation of populations to changing climates.
• The gut microbiome's role in latitudinal trait patterns is an important, yet often overlooked, area in evolutionary ecology.