Gonad development and reproductive hormones of invasive silver carp (Hypophthalmichthys molitrix) in the Illinois River

Reproduction is a major component of an animal's life history strategy. Species with plasticity in their reproductive biology are likely to be successful as an invasive species, as they can adapt their reproductive effort during various phases of a biological invasion. Silver carp (Hypophthalmicthys molitrix), an invasive cyprinid in North America, display wide variation in reproductive strategies across both their native and introduced ranges, though the specifics of silver carp reproduction in the Illinois River have not been established. We assessed reproductive status using histological and endocrinological methods in silver carp between April and October 2018, with additional histological data from August to October 2017. Here, we show that female silver carp are batch spawners with asynchronous, indeterminate oocyte recruitment, while male silver carp utilize a determinate pattern of spermatogenesis which ceases in the early summer. High plasma testosterone levels in females could be responsible for regulating oocyte development. Our results suggest that silver carp have high spawning activity in the early summer (May-June), but outside of the peak spawning period, female silver carp can maintain spawning-capable status by adjusting rates of gametogenesis and atresia in response to environmental conditions, while males regress their gonads as early as July. The results of this study are compared to reports of silver carp reproduction in other North American rivers as well as in Asia.

Methylmercury alters proliferation, migration, and antioxidant capacity in human HTR8/SV-neo trophoblast cells

Methylmercury, a potent neurotoxin, is able to pass through the placenta, but its effects on the placenta itself have not been elucidated. Using an immortalized human trophoblast cell line, HTR8/SV-neo, we assessed the in vitro toxicity of methylmercury. We found that 1 μg/mL methylmercury decreased viability, proliferation, and migration; and it had effects on antioxidant genes similar to those seen in neural cells. However, methylmercury led to decreased expression of superoxide dismutase 1 and increased expression of surfactant protein D. HTR cells treated 0.01 or 0.1 μg/mL methylmercury had increased migration rates along with decreased expression of an adhesion gene, cadherin 3, suggesting that low doses of methylmercury promote migration in HTR cells. Our results indicate that trophoblast cells react differently to methylmercury relative to neural cell lines, and thus investigation of methylmercury toxicity in placental cells is needed to understand the effects of this heavy metal on the placenta.