Maternal effect mediated by yolk corticosterone in the Greater Rhea (Rhea americana)

DELLA COSTA, N.S.; MARTELLA MB,; MARIN RH; NAVARRO JL

Vancouver

Congreso; 27th International Ornithological Congress; 2018

IOCongress 2018 Organizing Society, Bird Studies Canada and Society of Canadian Ornithologists

Yolk corticosterone levels and stress responses in chicks of Greater Rhea vary according to the maternal environment, suggesting that this hormone may act as a maternal effect by which the mother adjusts the offspring phenotype according to the context. However, this adaptive adjustment requires mechanisms that may allow the female to regulate deposition of corticosterone in relation to those conditions that are relevant for its offspring fitness. Therefore, yolk corticosterone levels would vary in a changing environment and should not be correlated with hormone levels in the mother. To explore these hypotheses we quantified: (a) maternal yolk corticosterone levels in eggs collected during different breeding seasons in two captive Greater Rhea populations (one of them exposed to similar environmental conditions and the other to different conditions), and (b) mean fecal glucocorticoid metabolites (FGMs) concentration in each female of a captive population during the egg formation period (7 days before oviposition), and the amount of corticosterone deposited in the yolk. We found that a) Greater Rhea females deposit different yolk corticosterone levels when environmental conditions change during two breeding seasons (61.52 ± 5.36 and 102.49 ± 13.12 ng/g, respectively), and b) yolk corticosterone concentration is not correlated (P = 0.36) with the female´s hormone level. These results suggest the existence of flexible mechanisms that could act at the level of the oocyte, regulating the amount of corticosterone that enters and/or is retained in the yolk of each egg.