Dixon Field Station, Western Ecological Research Center, US Geological Survey, Dixon, California.
Environ Toxicol Chem. 2024 Aug;43(8):1844-1854. doi: 10.1002/etc.5900. Epub 2024 Jun 10.
In birds, mercury embryotoxicity can occur through the transfer of mercury from the female to her eggs. Maternal transfer of mercury can vary by egg position in the laying sequence, with first-laid eggs often exhibiting greater mercury concentrations than subsequently laid eggs. We studied egg mercury concentration, mercury burden (total amount of mercury in the egg), and egg morphometrics by egg position in the laying sequence for two songbirds: tree swallows (Tachycineta bicolor) and house wrens (Troglodytes aedon). Egg mercury concentration in the second egg laid was 14% lower for tree swallows and 6% lower for house wrens in comparison with the first egg laid. These results indicate that in both species, after an initial relatively high transfer of mercury into the first egg laid, a smaller amount of mercury was transferred to the second egg laid. This lower mercury concentration persisted among all subsequently laid eggs (eggs three to eight) in tree swallows (all were 14%-16% lower than egg 1), but mercury concentrations in subsequently laid house wren eggs (eggs three to seven) returned to levels observed in the first egg laid (all were 1% lower to 3% greater than egg 1). Egg size increased with position in the laying sequence in both species; the predicted volume of egg 7 was 5% and 6% greater than that of egg 1 in tree swallows and house wrens, respectively. This change was caused by a significant increase in egg width, but not egg length, with position in the laying sequence. The percentage of decline in mercury concentration with position in the laying sequence was considerably lower in tree swallows and house wrens compared with other bird taxonomic groups, suggesting that there are key differences in the maternal transfer of mercury into songbird eggs compared with other birds. Finally, we performed simulations to evaluate how within-clutch variation in egg mercury concentrations affected estimates of mean mercury concentrations in each clutch and the overall sampled population, which has direct implications for sampling designs. Environ Toxicol Chem 2024;43:1844-1854. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.
在鸟类中，汞的胚胎毒性可以通过雌性向其卵转移汞来发生。母体对汞的转移可能因产卵序列中的卵位置而异，第一批产下的卵通常表现出比随后产下的卵更高的汞浓度。我们研究了产卵序列中卵位置对两种鸣禽的卵汞浓度、汞负担（卵中总汞量）和卵形态计量学的影响：树燕（Tachycineta bicolor）和家鹪鹩（Troglodytes aedon）。与第一批产卵相比，树燕的第二批产卵中的汞浓度低 14%，家鹪鹩的汞浓度低 6%。这些结果表明，在这两个物种中，在最初将相对大量的汞转移到第一批产卵后，转移到第二批产卵的汞量较小。在树燕的所有后续产卵（产卵三至八）中，这种较低的汞浓度一直持续存在（均比产卵一低 14%-16%），但后续家鹪鹩产卵中的汞浓度恢复到在第一批产卵中观察到的水平（均比产卵一低 1%至高 3%）。在这两个物种中，卵大小随产卵序列的位置而增加；预测的卵 7 的体积比树燕和家鹪鹩的卵 1 分别大 5%和 6%。这种变化是由产卵序列中卵宽度的显著增加引起的，但卵长度没有变化。与其他鸟类分类群相比，树燕和家鹪鹩的汞浓度随产卵序列位置的下降百分比要低得多，这表明在将汞转移到鸣禽卵中与其他鸟类相比存在关键差异。最后，我们进行了模拟，以评估卵中汞浓度随产卵序列位置的变化如何影响每个巢中平均汞浓度的估计值以及整个采样种群，这对采样设计有直接影响。环境毒理化学 2024；43：1844-1854。2024 年出版。本文是美国政府的一项工作，在美国属于公有领域。
