Experimental brood enlargement differentially influences the magnitude of the corticosterone stress response in closely related, co‐occurring songbirds

Abstract

Rearing environments can shape offspring phenotype across taxa, yet little is known about how brood size influences hypothalamic–pituitary axis functioning, whether its expression trades off with growth, and the degree to which these relationships vary between species. We evaluated how brood size influenced nestling physiological (glucocorticoids) and somatic traits (growth), and the extent to which their relationship differed between two closely related, sympatric songbirds when experiencing identical rearing environments. Specifically, we used a cross‐fostering approach to alter brood size and create an experimental gradient of nestmate competition, and then tested whether experimentally manipulated brood sizes resulted in nestlings with altered concentrations of corticosterone and whether corticosterone responses traded off with growth. Nestlings of both species experienced elevated concentrations of baseline and stressor‐induced corticosterone when raised in enlarged broods, relative to control and reduced broods, but neither measurement was found to trade off with growth or be linked to survival to fledging. In contrast, we found divergence in the magnitude of the corticosterone stress response between species across all brood treatments, with greater stressor‐induced corticosterone concentrations found in the Violet‐green Swallow (Tachycineta thalassina) relative to the closely related Tree Swallow (T. bicolor). Our study demonstrated that brood size can lead to changes in offspring corticosterone concentrations in swallows and that nestlings of sympatric species, even those that are closely related and ecologically similar, can diverge in their corticosterone stress response when experiencing identical rearing conditions. We conclude that corticosterone appears to play a key role for balancing energetic demands that arise in the face of nestmate competition in Tachycineta swallows and that elevated concentrations of corticosterone may enhance offspring survival during challenging environmental conditions, such as when brood competition is strong. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13116/suppinfo is available for this article.

Oxidative Stress Experienced during Early Development Influences the Offspring Phenotype

“…In the first case, sibling rivalry in enlarged broods can lead to increased corticosteroid levels in birds (e.g. Hardt et al 2018 and references therein), and corticosteroid levels have been positively associated with OS in vertebrates, likely due to increased free radical production (Costantini et al 2011). Thus, lower glutathione values in birds raised in enlarged broods might be due to glutathione being spent in fighting-off OS or inhibition of glutathione synthesis by free radicals (e.g.…”

Seeing wildlife behavior in a new way: Novel utilization of computer vision for focal reptile videography behavior study

“…Computer vision does have the potential to address interesting and pressing ecological questions (Weinstein 2017), however, rigorous discussion of the challenges, biases, and limitations of such technology remains limited. Previous studies utilizing the specific program used in our study, MotionMeerkat, have sometimes simply mentioned use of the program without adequately discussing, investigating, or addressing its benefits or limitations (Emerson et al 2018, Hardt et al 2018, Lagomarsino and Muchhala 2019). The aim of our current study was to comprehensively evaluate a specific type of computer vision, detection of motion, for a topic with contexts of ethology, conservation, and snakebite management closely linked.…”

Early life parameters and personality affect oxidative status during adulthood in an altricial rodent

“…The stress‐inducing character of increased sibling competition in enlarged broods or larger litters is further supported by studies reporting higher glucocorticoid levels prior to weaning or fledging in offspring developing under such conditions (birds: Gil et al, 2019 ; Hardt et al, 2017 ; Vitousek et al, 2017 ; mammals: Cohas et al, 2021 ; Fey & Trillmich, 2008 , but see: Kozlowski & Ricklefs, 2011 ; Rödel et al, 2010 ). Accordingly, as chronic stress is known to deteriorate an animal's oxidative status (Costantini et al, 2011 ), several studies have found indications of higher oxidative damage and/or lower antioxidant activity in offspring from larger or enlarged broods or litters (Bourgeon et al, 2011 ; Costantini et al, 2006 ; Gibson et al, 2015 ; Gil et al, 2019 , but see: López‐Arrabé et al, 2016 ; Losdat et al, 2010 ).…”