Quantitative genetics of immunity and life history under different photoperiods

Abstract

Insects with complex life-cycles should optimize age and size at maturity during larval development. When inhabiting seasonal environments, organisms have limited reproductive periods and face fundamental decisions: individuals that reach maturity late in season have to either reproduce at a small size or increase their growth rates. Increasing growth rates is costly in insects because of higher juvenile mortality, decreased adult survival or increased susceptibility to parasitism by bacteria and viruses via compromised immune function. Environmental changes such as seasonality can also alter the quantitative genetic architecture. Here, we explore the quantitative genetics of life history and immunity traits under two experimentally induced seasonal environments in the cricket Gryllus bimaculatus. Seasonality affected the life history but not the immune phenotypes. Individuals under decreasing day length developed slower and grew to a bigger size. We found ample additive genetic variance and heritability for components of immunity (haemocyte densities, proPhenoloxidase activity, resistance against Serratia marcescens), and for the life history traits, age and size at maturity. Despite genetic covariance among traits, the structure of G was inconsistent with genetically based trade-off between life history and immune traits (for example, a strong positive genetic correlation between growth rate and haemocyte density was estimated). However, conditional evolvabilities support the idea that genetic covariance structure limits the capacity of individual traits to evolve independently. We found no evidence for GÂE interactions arising from the experimentally induced seasonality.

Extra Molting and Selection on Nymphal Growth in the Desert Locust

“…This is in agreement with most studies in insects, though high heritability estimates are sometimes found with no clear explanation (e.g. [ 71 ]). The body weight threshold for adult emergence therefore seems to be genetically canalized, leaving no genetic variance for selection to act on.…”

Intra‐ and trans‐generational effects of larval diet on susceptibility to an entomopathogenic fungus, Beauveria bassiana, in the greater wax moth, Galleria mellonella

“…As maintaining good immune function is energetically costly, there is often a trade‐off between immunity and other costly traits (e.g. Schmid‐Hempel, ; Sadd & Schmid‐Hempel, ; Schulenburg et al ., ; Bascunan‐Garcia et al ., ; Valtonen et al ., ; Hammerschmidt et al ., ). Indeed, in a recent study by Krams et al .…”

“…As maintaining good immune function is energetically costly, there is often a trade-off between immunity and other costly traits (e.g. Schmid-Hempel, 2005;Sadd & Schmid-Hempel, 2009;Schulenburg et al, 2009;Bascunan-Garcia et al, 2010;Valtonen et al, 2010;Hammerschmidt et al, 2012). Indeed, in a recent study by Krams et al (2015) on the same species, a trade-off was found between immune function and growth; individuals fed on standard or high-energy diet grew faster but had weaker encapsulation response than individuals fed on low-energy diet.…”

Storage of Carotenoids in Crustaceans as an Adaptation to Modulate Immunopathology and Optimize Immunological and Life‐History Strategies

“…Under the hypothesis that carotenoid storage is adaptive to fight pathogens, genetic variance and heritability for this trait might therefore be expected. Ample additive genetic variance and heritability have been found for components of the innate immune response in invertebrates . Investigating the genetic basis of carotenoid storage by measuring its heritability and estimating potential genetic correlations with components of the innate immune response as well as other life‐history traits appears of primary importance.…”