Yolk corticosterone and progesterone levels in Greater Rhea (Rhea americana) eggs vary in a changing social environment

DELLA COSTA N. S.; MARTELLA M. B.; BERNAD, LUCÍA; MARIN R. H. (AUTOR CORRESPONDENCIA); NAVARRO, J. L.

JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL GENETICS AND PHYSIOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2022 vol. 337 p. 594 - 599

1932-5223

Maternal hormones in avian egg yolks may signal andprepare offspring for the prevailing conditions. Furthermore, this adjustmentrequires some degree of flexibility in regulating yolk hormone deposition. The GreaterRhea (Rhea americana) is a large ratitebird with a communal nesting system. In this species, we previously found thatyolk hormone deposition varies among eggs of different captive populations andcould influence chicks? physiology and behaviour. However, it is still unknown whetherfemales can modify yolk hormone deposition in a changing social environment. Usinga captive population of Greater Rheas, we quantified yolk corticosterone andprogesterone levels before and after a change in the breeder?s sex ratio from1:1 to 1 female per 2 males. Yolk hormones were measured using radioimmunoassayspreviously validated for this species. We found that females deposited onaverage higher yolk immunoreactive corticosterone and lower yolk immunoreactiveprogesterone after reducing the proportion of females per male. Sincecorticosterone deposited into the yolk comes exclusively from the female?splasma, these results suggest that females had on average higher plasma corticosteronelevels. The change in the sex ratio may increase the events in which femaleswere exposed to male-male competitions, courtships, and matings, leading to anincrease of corticosterone into their plasma and then into their eggs. Since wepreviously found that higher yolk corticosterone and lower yolk progesterone areassociated with the production of chicks that have an attenuated stressresponse, the results of the present study suggest that yolk hormone depositionin the Greater Rhea females is mediated by flexible mechanisms that could adjustdevelopment to the prevailing conditions.