No apparent cost of evolved immune response inDrosophila melanogaster

Abstract

Maintenance and deployment of the immune system are costly and are hence predicted to trade-off with other resource-demanding traits, such as reproduction. We subjected this longstanding idea to test using laboratory experimental evolution approach. In the present study, replicate populations of Drosophila melanogaster were subjected to three selection regimes-I (Infection with Pseudomonas entomophila), S (Sham-infection with MgSO4 ), and U (Unhandled Control). After 30 generations of selection flies from the I regime had evolved better survivorship upon infection with P. entomophila compared to flies from U and S regimes. However, contrary to expectations and previous reports, we did not find any evidence of trade-offs between immunity and other life history related traits, such as longevity, fecundity, egg hatchability, or development time. After 45 generations of selection, the selection was relaxed for a set of populations. Even after 15 generations, the postinfection survivorship of populations under relaxed selection regime did not decline. We speculate that either there is a negligible cost to the evolved immune response or that trade-offs occur on traits such as reproductive behavior or other immune mechanisms that we have not investigated in this study. Our research suggests that at least under certain conditions, life-history trade-offs might play little role in maintaining variation in immunity.

Sexual selection reveals a cost of pathogen resistance undetected in life‐history assays

“…) and the independent experimental evolution study by Gupta et al. (), which likewise found no such evidence. This suggests that, at least in some cases, sexually selected traits are more sensitive to subtle physiological trade‐offs than life‐history traits, as has been proposed on theoretical grounds (Rowe and Houle ; Getty ).…”

“…Although all populations evolved high resistance to their specific pathogenic regimes, no correlated responses were detected in larval viability or developmental time of either sex (on either standard or nutrientpoor diet), larval competitive ability, adult reproductive output, or starvation or desiccation resistance. In an independent evolution experiment starting from a different base population, populations selected for resistance to systemic infection by P. entomophila showed no detectable changes in developmental time, body size, fecundity, life span, egg viability or starvation resistance (Gupta et al 2016). Furthermore, in both experiments, the evolved resistance persisted for 30 (Faria et al 2015) and 15 (Gupta et al 2016) generations after exposure to the pathogen had ceased.…”

“…In an independent evolution experiment starting from a different base population, populations selected for resistance to systemic infection by P. entomophila showed no detectable changes in developmental time, body size, fecundity, life span, egg viability or starvation resistance (Gupta et al. ). Furthermore, in both experiments, the evolved resistance persisted for 30 (Faria et al.…”

“…) and 15 (Gupta et al. ) generations after exposure to the pathogen had ceased. Interpretation of these results is subject to epistemological caveats: it is based on nonrejection of null hypothesis and it remains possible that a trade‐off would be revealed under some other environmental conditions.…”

A newly evolved Drosophila Cytorace-9 shows trade-off between longevity and immune response

“…Not all studies report a trade-off between immunity and other lifehistory traits (Faria et al, 2015;Gupta et al, 2016). Both the studies, elegant in their own right, report no costs of improved immunity after selecting pathogen resistant Drosophila for 30 generations; highlighting the non-ubiquitous nature of immunity-fitness trade-off.…”