To breed or not to breed: endocrine response to mercury contamination by an Arctic seabird

Abstract

Mercury, a ubiquitous toxic element, is known to alter expression of sex steroids and to impair reproduction across vertebrates but the mechanisms underlying these effects are not clearly identified. We examined whether contamination by mercury predicts the probability to skip reproduction in black-legged kittiwakes (Rissa tridactyla) from Svalbard. We also manipulated the endocrine system to investigate the mechanism underlying this relationship. During the pre-laying period, we injected exogenous GnRH (gonadotropin-releasing hormone) to test the ability of the pituitary to release luteinizing hormone (LH, a key hormone for the release of sex steroids and hence breeding) in relation to mercury burden. Birds that skipped reproduction had significantly higher mercury concentration in blood than breeders. Endocrine profiles of these birds also varied based on breeding status (breeders versus non-breeders), mercury contamination and sex. Specifically, in skippers (birds that did not breed), baseline LH decreased with increasing mercury concentration in males, whereas it increased in females. GnRH-induced LH levels increased with increasing mercury concentration in both sexes. These results suggest that mercury contamination may disrupt GnRH input to the pituitary. Thus, high mercury concentration could affect the ability of long-lived birds to modulate their reproductive effort (skipping or breeding) according to ongoing environmental changes in the Arctic, thereby impacting population dynamics.

Demographic consequences of heavy metals and persistent organic pollutants in a vulnerable long-lived bird, the wandering albatross

“…Concerning the proximate mechanisms, Hg, in its methylated form, is known to disrupt reproductive hormones [1] such as the luteinizing hormone, a key pituitary hormone for the onset of breeding [3]. As found in two southern Catharacta skua species [10], Hg negatively impacted hatching probability of albatrosses, but only in individuals previously observed as breeders.…”

The stress of being contaminated? Adrenocortical function and reproduction in relation to persistent organic pollutants in female black legged kittiwakes

“…In a recent study we have shown that moderate levels of mercury could be linked to non-breeding events in kittiwakes from Svalbard (Tartu et al 2013). In our study, however the decision to breed or not was unrelated to blood POP levels (neither to pesticides nor PCBs).…”

“…We studied kittiwakes in one plot of around 117 pairs breeding on cliff ledges at heights of 5-10 m. Female kittiwakes were sampled from 19 May to 7 June 2011, during the pre-laying period (i.e. copulations and nest building period), a key period for reproductive decisions during which females kittiwakes appear highly sensitive to stressors (Goutte et al 2010a(Goutte et al , 2011bTartu et al 2013). …”

“…Thus it is possible that POP levels found in pre-laying kittiwakes were not high enough to alter reproduction. Another possibility is that pesticides and PCBs, contrary to mercury, may not interfere with hormonal pathways involved in non-breeding behaviour, such as GnRH (gonadotropin-releasing hormone) and luteinizing hormone (LH, Tartu et al 2013). …”

Mercury bioaccumulation in the food web of Three Gorges Reservoir (China): Tempo-spatial patterns and effect of reservoir management

“…Mercury (Hg) is an ubiquitous pollutant released to the environment from natural and anthropogenic sources Fitzgerald et al, 1998;Tartu et al, 2013;US Environmental Protection Agency, 2001). Hg bioaccumulates and bioamplifies within the food web (Watras et al, 1998), and poses a potential threat to fish, wildlife and human health (Hammerschmidt and Fitzgerald, 2006;Sandheinrich and Wiener, 2011).…”