Maternal food supplementation and perceived predation risk modify egg composition and eggshell traits but not offspring condition

Abstract

Mothers may vary resource allocation to eggs and embryos, which may affect offspring fitness and prepare them for future environmental conditions. The effects of food availability and predation risk on reproduction have been extensively studied, yet their simultaneous impacts on reproductive investment and offspring early life conditions are still unclear. We experimentally manipulated these key environmental elements using a 2×2 full factorial design in wild, free-living pied flycatchers (Ficedula hypoleuca), and measured egg composition, eggshell traits and offspring condition. Eggs laid in food-supplemented nests had larger yolks and thicker shells independently of predation risk, while eggs laid in nests exposed to predator cues had lower levels of immunoglobulins, independent of food supplementation. In nests without predator cues, shell biliverdin content was higher in eggs laid in food-supplemented nests. Incubation was 1 day shorter in food-supplemented nests and shorter incubation periods were associated with higher hatching success, but there were no direct effects of maternal treatment on hatching success. To investigate the impact of maternal treatment (via egg composition) on the offspring, we performed full brood crossfostering after hatching to unmanipulated nests. Maternal treatment did not significantly affect body mass and immunoglobulin levels of offspring. Our results suggest that although prenatal maternal cues affected egg composition, these egg-mediated effects may not have detectable consequences for offspring growth or immune capacity. Unpredictable environmental stressors may thus affect parental investment in the eggs, but parental care may level off costs and benefits of differential maternal egg allocation.

The effects of environmental conditions on eggshell thickness of two North American secondary cavity-nesting birds

“…Two studies on species of flycatchers addressed food availability and eggshell traits. Morosinotto et al (2019) found that Pied Flycatchers supplemented with food had thicker eggshells than those not supplemented with food, suggesting that they were able to invest more resources in eggshell development. Additionally, female Collared Flycatchers ( Ficedula albicollis ) that were in better condition laid thicker eggshells (Hargitai et al 2011).…”

Do maternal allocations towards offspring quality and quantity ameliorate the effects of predators on offspring survival?

“…Other prey responses, such as delaying development, may be compensatory, ameliorating the costs of predator avoidance (Thaler et al., 2012). One type of non‐consumptive effect of predators on prey occurs when mothers exposed to predators change the quantity (hereafter referred to as density) or the quality (hereafter referred to as condition or provisioning) of their offspring (Morosinotto et al., 2019). Predator exposure can alter investment in offspring as parents have less resources to invest in reproduction because they fed less or invested more energy in their own protection, or because of adaptive reproductive allocation decisions.…”