The Effects of Dietary Mercury Exposure on Male Fertility in the Zebra Finch

Sperm traits, including morphology, number and function, have been linked to fertilization ability and offspring quality in several species. However, many of these traits are artificially influenced by anthropogenic pollutants. Mercury, a globally distributed heavy metal pollutant, has been linked to altered testicular morphology and reduced fertility in many vertebrates. in this study, we exposed domestic male zebra finches (Taenopygia guttata) to dietary mercury at concentrations found in prey species in a highly polluted watershed region. We then compared sperm traits from these males to those of controls, and found a significant effect of mercury on sperm length and variability. Mercury-dosed birds produced shorter, more variable sperm than control males. When paired to female birds with no history of mercury exposure, fewer sperm from mercury-dosed males were found on the egg perivitelline membrane, suggesting that fewer sperm managed to reach the egg within the female reproductive system. Finally, we also found that mercury-exposed males had lower sperm counts compared to control males. to examine if this effect persisted under more natural copulation, we mated male zebra finches to dummy females. We found a similar trend, suggesting that mercury exposure could result in males transferring fewer sperm to females. Taken together, these results suggest that mercury exposure could result in males that produce fewer, smaller, more variable sperm with a reduced ability to reach the egg in the female reproductive tract. This could have strong implications for post-copulatory sexual selection and gene transmission patterns in mercury-affected populations, and may have further consequences in terms of epigenetic effects or developmental disruptions that affect offspring quality