Do parental effects mediate adaptation to climate differences? A study in a bird species breeding at different latitudes

To what extent and how organisms adapt to changing or extreme environments has become an urgent biological question. One effective parental response to extreme climatic differences (i.e. breeding season length mediated by temperature and food availability) is altering offspring developmental time through parental effects. I will test how parents adjust pre- and postnatal investment responding to such environmental variation in thorn-tailed rayaditos, Aphrastura spinicauda. This songbird breeds along a wide latitudinal gradient with extreme climatic variation (long to short food peaks, extreme warm to extreme cold environments). I will measure parental adjustment of offspring development in three populations. I expect the high-latitude population (cold environment, short food peaks) to have greater incubation attendance (hypothesis 1) and higher yolk testosterone and thyroid hormones deposition (hypothesis 2), accelerating embryo development. More hormones may increase nestling competitiveness and begging, parental provisioning, and nestling growth (hypothesis 3). First, I will test whether populations differ in egg quality, incubation patterns, nestling begging and fitness, and parental provisioning. Subsequently, I will test the hypotheses as follows:
H1: I will mimic increased incubation attendance using incubators to accelerate embryo developmental time. After relocating hatchlings, I expect higher fledging weight and survival of faster hatching nestlings, interacting with origin.
H2: I will manipulate yolk testosterone and thyroid hormones levels, incubate and hatch the eggs in incubators, revealing whether prenatal maternal effects influence embryo development and fitness, and whether this differs between populations.
H3: Hatchlings from hormone-manipulated, control and untreated eggs will be relocated (incubator to nests) and subjected to standard begging tests. I expect that nestlings from hormonally-augmented eggs will beg more, resulting in accelerated nestling development, higher fledging weight and survival.
The results will show to what extent and how evolution has shaped pre-and postnatal parental effects and phenotypic plasticity for adaptation to different environments.