Environmental effects and life-history variation in birds

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Parents play a critical role in shaping their offspring. Mothers in particular may influence offspring via prenatal transfer of hormones or antibodies and/or via postnatal care. When mothers experience stressful environments, offspring may display differing physiologies and behaviours from offspring of non-stressed mothers. Traditionally, this has been viewed as a non-adaptive consequence of a poor rearing environment. An emerging perspective is that mothers are in fact adjusting their offspring to better cope with subsequent environmental challenges. The relative importance of pre and postnatal cues in shaping offspring has been studied in laboratory animals, but only recently in the wild. The major goal of my proposed research is to use wild birds to test whether pre- and postnatal maternal cues change offspring physiology and behaviour in an adaptive way. In my proposed research, my students and I will address three general questions: (1) What is the role of prenatal hormonal cues in shaping offspring characteristics, and do they increase survival? (2) Do mothers incubate their eggs at different temperatures to adjust offspring characteristics? (3) Does stress impact a mother’s ability to transfer antibodies to her offspring, and does she adjust her response to the number of pathogens in the environment? To test questions 1 and 2, we will study ring-billed gulls. We propose to swap eggs between regions of a gull colony that differ in levels of disturbance. “Mismatched” chicks will receive prenatal maternal cues of one level of disturbance (via their egg), but will be raised in a different level of disturbance; “Matched” chicks will be reared in the same area of the colony in which their eggs were laid (and same level of disturbance). If prenatal cues result in adaptive adjustments in the chicks, we predict chicks from “mismatched” environments will be of lower quality and have lower survival than chicks from “matched” environments. The mothers of “mismatched” chicks will have lower return rates the following year. We will also experimentally manipulate egg corticosterone levels (a hormonal cue of maternal stress), expose captive chicks to differing forms of stress, and measure their behaviour and physiology the following year. Theoretically, mothers may also use egg incubation temperature as a mechanism to adjust their offspring (Question 2). To test this, we will remotely monitor nest temperatures of experimentally stressed/non-stressed mothers. We predict that eggs of stressed mothers will experience greater fluctuations in temperature. If disrupted incubation behaviour is a mechanism for mothers to shape their offspring, we predict chicks from disturbed nests will show a blunted response to stress when compared with chicks from non-disturbed nests. How this occurs is not known, but we will test whether embryos play a role via producing their own hormonal cues of stress. Mothers can transfer antibodies to their eggs, with potential to show favouritism to one sex over the other. Mothers may also allocate antibodies according to the number of pathogens in the environment. Using tree swallows, we will compare antibody levels of eggs from temperate populations with subtropical populations, and test whether nestlings differ in their ability to respond to an immune challenge (Question 3). We predict that when stressed, temperate females will transfer fewer antibodies than will sub-tropical females (where there are more pathogens), with negative consequences for temperate offspring. If maternal stress limits a female’s ability to transfer antibodies prenatally, there may be negative consequences for populations that experience combinations of environmental degradation and the threat of emerging diseases.