Unique oestrogen receptor ligand-binding domain sequence of native parrots: a possible link between phytoestrogens and breeding success.

The New Zealand (NZ) native parrots kākāpō, kākā and kea are classified as critically endangered, endangered and vulnerable respectively. Successful reproduction of kākāpō and kākā is linked to years of high levels of fruiting in native flora (mast years). To assess a possible hormonal link between native plants and reproductive success in these parrots in mast years, we examined the ligand-binding domains (LBD) of the progesterone receptor (PR), androgen receptor (AR), estrogen receptor 1 (ESR1) and estrogen receptor 2 (ESR2) in NZ native (kākāpō, kākā, kea and kākāriki) and non-native (Australian cockatiel) parrots and compared them with those in the chicken. The amino acid sequences for PR, AR, ESR1 and ESR2 shared >90% homology among the NZ parrots, the cockatiel and, in most cases, the chicken. The exception was for the ESR1 LBD, which contained an extra eight amino acids at the C-terminal in all the parrots compared with the chicken and with published sequences of non-parrot species. These results support the notion that the ESR1 LBD of parrots responds differently to putative oestrogenic compounds in native trees in NZ during times of intermittent masting. In turn, this may provide important information for generating parrot-specific bioassays and linkages to steroidogenic activity in native plants.