Variation in Response to Methylmercury by Killifish (Fundulus heteroclitus) Embryos

Abstract

Some female killifish (Fundulus heteroclitus) from Montauk, N.Y., produce eggs that are much more resistant to the craniofacial, cardiovascular, and skeletal effects of 0.05 ppm methylmercury than eggs of other females. The following relationships were observed in studying 128 batches of eggs from 85 females fertilized by 35 males. Batches of eggs with a high percentage of noncleaving eggs (NCEs) tended to be most susceptible. Tolerance was also associated with the relation of the date to the lunar spawning cycle and with the number of dorsal fin rays in the females; fish that had ten fin rays produced no unaffected batches, whereas those with eleven or twelve rays produced eggs ranging from very tolerant (unaffected) to very susceptible. A weaker correlation with female weight was seen. Because of the importance of the percentage of NCEs in determining the tolerance of a batch of eggs, the data were reanalyzed after removing all those batches with high rates of (>35 percent) NCEs. This revealed a strong association of tolerance with the stickiness of the eggs in that batches which were very sticky tended to be more resistant. Correlations were also seen with female length and fecundity. No correlations were seen with any measured traits of the males.

Tolerance to Environmental Contaminants in the Mummichog,Fundulus heteroclitus

“…Fish from the polluted site did show higher numbers of fin rays, which may be associated with tolerance. This is similar to our findings that females with higher fin ray counts produce embryos with greater resistance to meHg (Weis and Weis 1982a).…”

“…We initially found that the embryos from reference sites were highly variable in their response to meHg (Figure l a ) , i.e., some females produced eggs that were very resistant to teratogenic effects of meHg, some produced eggs that were susceptible, others produced eggs of intermediate susceptibility (Weis et al 1982a). The resistance of a batch of eggs was associated with certain traits of the female (higher fin ray counts), and was independent of which male fertilized the eggs.…”

Fundulus as the premier teleost model in environmental biology: Opportunities for new insights using genomics

“…This altered rate of embryonic development may protect the highly sensitive embryos by decreasing the time over which they are exposed to methyl mercury. Some evidence suggested that the resistant phenotype in the embryos appeared to be inherited primarily maternally, not paternally, and was correlated with finray count, a characteristic believed to have a large genetic component (Weis et al, 1982). However, additional evidence indicated that methyl mercury-resistant gametes were also produced by resistant adults of both sexes (Khan and Weis, 1987b).…”

Methods for and approaches to evaluating susceptibility of ecological systems to hazardous chemicals.

“…Fish exposed to methylmercury for many years undergo selection such that eggs from these regions are less susceptible to mercury than those from other regions (14,19 (48) exposed to chronic oil pollution are better (49) able to survive continued oil pollution than (50) are organisms from pristine habitats (33). ( 19) The mere presence of some hazardous chemicals changes the susceptibility of (51) many organisms, despite similar exposures (Table 1). For example, susceptibility of (52) fish and birds to mercury is reduced by the (18) presence of selenium (34).…”