Mothers matter: how maternal investment can help offspring to cope with environmental stress

Abstract

Environmental stress can considerably reduce an organism’s reproductive success and survival prospect. Although environmental stress has always been a component of the natural environment of living organisms, the stressors that they are currently exposed to are larger than ever before due to the increasing impact of man on its surroundings. Yet, organisms have several mechanisms at their disposal to buffer the impact of environmental stress. I studied whether an adjustment of maternal investment is such a mechanism. More specifically, I investigated whether mothers adjust their investment in eggs in response to environmental stress and whether maternal investment affects offspring phenotype. To that purpose, I manipulated parasite abundance in nests of great tits (Parus major), a common European bird species, and studied effects on several egg components (size, yolk androgens and eggshell pigmentation) and offspring traits (oxidative stress, constitutive innate immunity, survival and body size, mass and condition). I also studied the combined effect of nutritional stress during nestling development (manipulated via a brood size experiment) and adulthood (manipulated via a foraging cost experiment) on constitutive innate immunity of male and female zebra finches (Taeniapygia guttata). The results show that maternal investment can buffer offspring against environmental stress. However, this is not always the case as it may also aggravate the effects of environmental stressors. Furthermore, the magnitude and direction of maternal investment is variable in relation to several factors, such as the egg and offspring trait under study and the particular nestling involved. Because of the complexity of maternal investment, it is a real challenge to predict how organisms will cope with environmental stress