68 Table 1. Developmental Stress: Evidence for Adaptive Phenotypic Effects in Birds Hypothesis type Specialization Specialization Specialization Specialization 1 Developmental Stress Exposure Embryonic exposure to yolk corticosterone Low food accessibility, early-life social isolation (in nestlings/ fledglings) Unpredictable stress regimen (e.g., catching, handling, noise) as fledglings Limited and unpredictable food supply 1 Phenotypic Effects Production of smaller nestlings that achieve faster takeoff speeds (barn swallows, European starlings, great tits: Crino & Breuner, 2015). Enhanced flight as shown by more mature flight muscles, lower wing loading, and better in-flight performance by fledglings (European starlings: Chin et al., 2009). In adulthood, enhanced associative learning (zebra finches: Brust et al., 2014; Kriengwatana et al., 2015; chickens: Goerlich et al., 2012) but impaired hippocampal-dependent contextual learning on spatial tasks (Western scrub-jays: Pravosudov et al., 2005; zebra finches: Kriengwatana et al., 2015). Within 6 days following stress exposure: Enhanced prefrontal cortex-dependent reversal learning (i.e., flexibility relearning a new rewarded location) in a spatial task (Japanese quail; Calandreau et al., 2011). Enhanced food caching intensity and memory for cache location (i.e. spatial memory; black-capped chickadees, tufted titmice, marsh tits: Hurly, 1992; Pravosudov & Grubb, 1997; Pravosudov & Clayton, 2001, 2002). 2 Proposed Function Enhanced flight capacity promotes survival in predator dense environments (as signaled by maternal and embryonic glucocorticoids). Enhanced associative learning (over slower, cognitively-expensive contextual learning) promotes immediate responding to environmental challenges (prevalent in resource-poor environments). Enhanced reversal learning promotes survival in an unpredictable environment. Enhanced food caching and memory for stored food locations promotes survival and reproduction in environments where food is scarce or unpredictable.
69 Specialization Specialization Sensitization Post-hatching exposure to corticosterone Pre-hatching exposure to corticosteroids; post-natal food unpredictability (nestlings and fledglings) Low-quality diet as nestlings In adulthood, more frequent switching between social learning strategies (i.e., discounting of parental information in favor of learning from non-parental adults); weaker affiliation with parents in favor of flock mates; attainment of more central social network positions; improved performance on a novel foraging task; higher quality and quantity of offspring in males (zebra finches: Boogert, Farine, & Spencer, 2014; Crino et al., 2014a, 2014b; Farine et al., 2015). In adulthood: Pre-hatching stress led to increased activity level, exploration in a novel environment, and mimicking of foraging strategies demonstrated by conspecifics; post-hatching stress led to more risktaking to find food and avoidance of foraging strategies demonstrated by conspecifics. Combined pre- and posthatching stress resulted in the highest levels of exploratory and risk-taking behavior (Japanese quail: Boogert et al., 2013; Zimmer et al., 2013). During a brief period of food restriction, adult zebra finches that experienced poor early nutrition were faster to engage in exploratory and foraging behavior (Krause et al., 2009). 1 Timing of developmental stress exposure not specified. 2 Age at testing not specified. In unpredictable environments, exposure to elevated developmental stress (as signaled by glucocorticoids) may indicate one’s parents are struggling to cope with current conditions. If other adults know better, copying them should yield better foraging strategies. Chicks may also be selected to switch to individual trialand-error learning in this context. Elevated corticosterone triggers life history tradeoffs (e.g., shorter lifespan) favoring current over future reproduction. Elevated exploratory and risk-taking behavior under developmentally stressful conditions promotes greater food acquisition. Food unpredictability promotes novel foraging strategies relative to those demonstrated by conspecifics. Rapid exploration and foraging promotes greater food acquisition in a nutritionally poor environment.
1 Running Head: ADAPTATION-BASED AP
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