Socially regulated estrogen in an eavesdropping brood parasite

Abstract

Social regulation of reproductive hormones is a means by which conspecific males and females orchestrate successful reproductive efforts. We investigate whether social cues modify activity within the hypothalamic-pituitary-gonadal (HPG) axis and the specificity of this response in a social parasite that is known to eavesdrop on the communication signals of other species: the brown-headed cowbird (Molothrus ater). Brown-headed cowbirds are obligate brood parasites that do not build nests or care for their own young. Instead, obligate brood parasites leave their eggs in the nest of a host species and therefore must coordinate their breeding attempts with conspecifics as well as potential heterospecific hosts. Here, we explore whether the vocal signals of potential host species can also be used as a social cue that modifies the HPG axis of female brown-headed cowbirds. Results reveal that both conspecific and heterospecific song-exposed females exhibit significantly greater circulating estradiol concentrations as compared to silence-exposed females. While conspecific song induces the greatest elevation in circulating estradiol, there is no significant difference in circulating estradiol levels in females exposed to either conspecific or heterospecific songs. This pattern suggests both song types are effective at evoking a reproductive physiological response. On the other hand, circulating progesterone concentrations did not differ among the song- and silence-exposed groups nor did the size of the female's ovarian follicles. These results indicate that heterospecific vocal communication signals can effectively be used as a social cue that simultaneously provides necessary information regarding breeding status of hosts and modifies breeding condition of the eavesdropper.

Examining the disconnect between prolactin and parental care in avian brood parasites

“…Circulating estrogen concentrations were measured using modified extraction and assay procedures described by References 57–60. Validation of estrogen assays in cowbird plasma was reported in Reference 60 Briefly, steroids were extracted from plasma using 3 mL of diethyl ether. Extracted estrogens resuspended in assay buffer were measured using ELISA assay kits from Cayman Chemical (Ann Arbor, Michigan).…”

Sex roles and sex ratios in animals

“…Interactions with conspecifics also affect female physiology. In vertebrates, one way that male courtship behaviour affects female physiology is by changing the secretion of gonadotropins and oestradiol (Bentley et al, 2000;Cheng, 2003Cheng, , 2008Watts, Edley & Hahn, 2016;Lynch, Azieva & Pellicano, 2018). It is therefore possible that a shift in ASR that changes male courtship behaviour will affect the sex steroid profile of females.…”