Abstract
Unfavourable conditions throughout the period of parental care can severely affect growth, reproductive performance, and survival. Yet, individuals may be affected differently, depending on the developmental period during which constraints are experienced. Here we tested whether the nestling phase compared to the fledgling phase is more susceptible to nutritional stress by considering biometry, physiology, sexually selected male ornaments and survival using zebra finches (Taeniopygia guttata) as a model species. As nestlings (day 0–17) or fledglings (day 17–35), subjects were raised either on low or high quality food. A low quality diet resulted in significantly elevated baseline corticosterone titres in both nestlings and fledglings. Subjects showed substantial compensatory growth after they had experienced low quality food as nestlings but catch-up growth did neither lead to elevated baseline corticosterone titres nor did we detect long term effects on biometry, male cheek patch, or survival. The compensation for temporally unfavourable environmental conditions reflects substantial phenotypic plasticity and the results show that costs of catch-up growth were not mediated via corticosterone as a physiological correlate of allostatic load. These findings provide new insights into the mechanisms and plasticity with which animals respond to periods of constraints during development as they may occur in a mistiming of breeding.
Highlights
A key period for vertebrates is early in life when biosynthetic and growth rates are steeper than later in life requiring a high energy and adequate nutrient intake
Effects on corticosterone Nutritional treatment resulted in significantly higher baseline corticosterone concentrations in the low quality group at day 17 (Table 1; Fig. 3 a, b) but there was no such effect at day 35 (Table 1)
The experiments revealed that nestling zebra finches were more susceptible to unfavourable nutritional conditions than fledglings
Summary
A key period for vertebrates is early in life when biosynthetic and growth rates are steeper than later in life requiring a high energy and adequate nutrient intake. Breeding late in the season likely results in the opposite scenario where a period of high food availability during the nestling phase (nestlings stay in the nest and are entirely dependent of parental care) is followed by a period of declining food abundance during the fledgling phase (fledglings leave the nest, start feeding by themselves but are not yet independent of parental care). In most studies showing pronounced phenotypic effects, subjects were exposed to a stressor either throughout the entire period of parental care [2,4,11,12] or only during the nestling period [13,14]. Two studies recently showed that adult birds which had experienced nutritional stress during the nestling period rather than the fledgling period were less able to compensate in terms of management of energy resources (resting metabolic rate and body mass loss under deprivation) [15,16]
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