Kākāpō (Strigops habroptilus) are a critically endangered parrot that is endemic to Aotearoa, New Zealand (NZ). The Kākāpō Recovery Team, Department of Conservation and local iwi have brought this species back from the brink of extinction to ~250 individuals which reside in predator-free off-shore sanctuaries.
Kākāpō breed intermittently every 2-5 years, coinciding with the fruiting of Dacrydium cupressinum (NZ rimu) but the mechanistic link remains a mystery. One hypothesis is that phytoestrogens in rimu fruit bolster endogenous oestrogen levels, which act upon oestrogen receptors (ESR1) in the liver to stimulate egg yolk protein production leading to ovarian follicle maturation1. We have identified an amino acid indel in the ligand-binding domain of ESR1 of kākāpō̄ that may increase their sensitivity to phytoestrogens2 and have obtained preliminary data of oestrogenic activity in crude rimu fruit extracts3.
The study aims were to 1) identify mutations within the ESR1 genes of individual Kākāpō and 2) assess the oestrogenic activity in extracts of rimu.
Mutations within the ESR1 gene of 171 individual Kākāpō were examined using the Kākāpō125+ database. Despite single nucleotide polymorphisms (SNPs) being present within introns of most individuals, only one SNP (TCC<TCG) was present in the coding region in 33 individuals but did not result in an amino acid change (S<S).
The oestrogenic activity of rimu fruit, seeds and unfertilised ovules extracted in range of solvents (methanol, chloroform, acetone and water) were examined using a yeast bioassay transfected with human ESR1. All rimu specimens showed some oestrogenic activity, water-based extracts exhibiting the highest activity.
This study revealed no functional mutations in ESR1 that may impair an individual’s breeding success. Also the presence of rimu-derived phytoestrogens in aqueous extracts mirrors the birds eating habit of crushing the rimu fruit and discarding the chews supporting a physiological role of phytoestrogens in kākāpō.