Influence of the rearing system on yolk corticosterone concentration in captive Greater Rheas (Rhea americana)

Abstract

Many environmental conditions elevate plasma corticosterone in laying birds, leading to elevated hormone accumulation in the egg. We investigated whether maternal yolk corticosterone levels in Greater Rheas differ between fresh eggs collected from an intensive (IRS) and a semi-extensive (SRS) rearing system. After HPLC validation, yolk corticosterone was measured using a corticosterone (125) I radio-immunoassay kit. Results (mean ± SE) showed that eggs collected from the IRS exhibited a significantly higher corticosterone concentration than eggs from SRS (89.88 ± 8.93 vs. 45.41 ± 5.48 ng/g yolk, respectively). Our findings suggest that rearing conditions under an intensive scheme (e.g., small pens with bare ground, no direct foraging and handling) might be perceived as more stressful for Greater Rhea females than semi-extensive rearing conditions (e.g., low animal density distributed in extensive areas and direct foraging), which would result in the transfer of higher yolk corticosterone levels. A better understanding of environmental conditions and female traits that affect yolk corticosterone deposition provides a background for future studies concerning the roles of maternal corticosterone on offspring development. Zoo Biol. 35:246-250, 2016. © 2016 Wiley Periodicals, Inc.

Distribution and concentration of maternal progesterone in the yolk of Greater Rhea eggs (Rhea americana)

“…These variable amounts of hormones deposited into egg yolk that could potentially affect embryonic growth and development (von Engelhardt & Groothuis, ), could be explained as the result of context and dose‐dependent optimal strategies to maximize offspring fitness, in which the balance between costs and benefits depends on the prevailing conditions (Muriel et al., ). Consistently, the variation in yolk corticosterone levels observed among eggs of Greater Rhea females bred under different rearing conditions, such as size of pens and presence or lack of natural pastures in the pens (Della Costa et al., ), suggests that yolk steroids in this species could also function as indicators of relevant environmental conditions for the offspring development. Future experimental studies are needed to know whether yolk progesterone levels in Greater Rheas are also regulated under different rearing conditions.…”

“…To our knowledge, corticosterone is the only maternal yolk steroid quantified to date in ratite eggs (Della Costa et al., ), and no information about yolk progesterone is available in this group of birds; therefore, this study aims to characterize the distribution and concentration of maternal yolk progesterone in freshly eggs laid by captive Greater Rhea females bred under similar rearing conditions during two breeding seasons. First, for this purpose, we validated a commercial electrochemiluminescence immunoassay kit for progesterone concentration measurement.…”

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

“…Yolk corticosterone concentration was determined using a 125 I Corticosterone Radioimmunoassay Kit (MP Biomedicals), previously validated for the yolk of Greater Rhea (Della Costa et al, 2016). Although our antibody cross‐reacts with progesterone in a low percentage (2.5%, Della Costa et al, 2016) in comparison with other antibodies (e.g., Quillfeldt et al, 2011; Rettenbacher et al, 2013), we will refer to immunoreactive substances detected by the antibody as “immunoreactive corticosterone”. Hormone quantification was performed in a gamma counter (Counter PC‐RIA‐MAS Stratec Electronic GMBH).…”