Between-population differences in constitutive and infection-induced gene expression in threespine stickleback

Area of Science:

• Evolutionary immunology
• Host-parasite coevolution
• Vertebrate immune systems

Background:

• Vertebrate immunity comprises constitutive and inducible defenses, shaped by selective pressures from parasites and pathogens.
• Population-level variation in immune defenses arises through adaptation via constitutive differences, shared inducible responses, or divergent inducible responses.

Purpose of the Study:

• To investigate the relative contributions of different adaptive strategies to among-population divergence in host immune responses to parasites.
• To identify genetic underpinnings of immune adaptation and resistance phenotypes in a natural host-parasite system.

Main Methods:

• Utilized a natural host-parasite model: threespine stickleback (Gasterosteus aculeatus) and the tapeworm Schistocephalus solidus.
• Conducted gene expression analyses to compare constitutive and inducible immune responses across populations.
• Investigated cellular mechanisms of a fibrosis-related resistance phenotype.

Main Results:

• Limited evidence for divergence in constitutive immune gene expression was found.
• Strong signatures of conserved inducible immune responses to the parasite were observed.
• A small number of immune-related genes exhibited divergent inducible responses, potentially influencing infection success.

Conclusions:

• Immune system evolution in response to parasites is characterized by conserved inducible responses rather than divergent constitutive expression.
• A few specific genes may disproportionately contribute to functional differences in infection outcomes.
• This study provides insights into the genetic basis of immune adaptation and resistance mechanisms.