Assessment of neuroanatomical and behavioural effects of in ovo methylmercury exposure in zebra finches (Taeniopygia guttata)

•Assessed the long term effects of in ovo MeHg exposure on courtship behavior and associated neuroanatomy in a model songbird species.•Utilized the egg injection method.•No adverse long term effects of in ovo MeHg treatment on courtship behavior or singing were observed in male zebra finches.•An increase in telencephalon volume, with increasing in ovo MeHg concentrations, was measured.

Methylmercury (MeHg) readily crosses the blood brain barrier and is a known neuro-toxicant. MeHg accumulation in the brain causes histopathological alterations, neurobehavioral changes, and impairments to cognitive motor functions in mammalian models. However, in birds the neurotoxic effects of MeHg on the developing pre-hatching brain and consequent behavioral alterations in adult birds have not received much attention. Moreover, passerine birds are poorly represented in MeHg neurotoxicology studies in comparison to other avian orders. Hence in this study, we used the egg injection method to investigate the long term effects of in ovo MeHg exposure on brain histopathology and courtship behavior in a model songbird species, the zebra finch (Taeniopygia guttata). Egg treatment groups included: a low MeHg dose of 0.2 μg Hg g−1 egg, a high MeHg dose of 3.2 μg Hg g−1 egg, and a vehicle control (water). No adverse effects of in ovo MeHg treatment were detected on courtship song quality or on mating behavior in experimental males at sexually maturity which would suggest that observable neurobehavioral effects of MeHg exposure may depend on the timing of exposure during offspring development. However, neuroanatomical analysis indicated an increase in telencephalon volume with increased MeHg concentrations which may suggest a prolonged inflammatory response in this region of the brain.