Malek Jennafer C, Byers James E
Odum School of Ecology, University of Georgia, Athens, GA, United States of America.
PeerJ. 2018 Jul 2;6:e5046. doi: 10.7717/peerj.5046. eCollection 2018.
Changes in climate are predicted to influence parasite and pathogen infection patterns in terrestrial and marine environments. Increases in temperature in particular may greatly alter biological processes, such as host-parasite interactions. For example, parasites could differentially benefit from increased reproduction and transmission or hosts could benefit from elevated immune responses that may mediate or even eliminate infections. In the southeastern United States, the Eastern oyster, , is infected by the lethal protozoan parasite, . Under field conditions, intertidal (air-exposed) oysters have been found to have significantly higher infection intensity and marginally higher infection prevalence than subtidal (submerged) oysters. During summer, air temperatures are much warmer than water and this exposure of intertidal oysters to higher temperatures is a suggested mechanism for increased infection intensity.
We simulated intertidal exposure using controlled laboratory experiments to determine how host traits (survival and immune response) and parasite infection intensity will respond to elevated air temperature ranging from 27 °C to 53 °C during emersion at low tide. In Georgia, where our work was conducted, the average summer water temperature is 29 °C and the average maximum high air temperature in July is 33 °C (though oysters have been shown to survive at much higher air temperatures).
Host survival declined as temperature increased, with a definitive drop-off between 39-43 °C. Negative effects of air temperature on host immune response (phagocytic activity) were detectable only at extremely high temperatures (47-50 °C) when hosts were suffering acute mortality. Parasite infection intensity peaked at 35 °C.
Our results suggest that an increase in average summer air temperature to 35 °C or higher could affect oyster survival directly through temperature-related impacts in the short-term and indirectly through increased infection intensity over the long-term.
预计气候变化会影响陆地和海洋环境中寄生虫和病原体的感染模式。特别是温度升高可能会极大地改变生物过程，如宿主与寄生虫的相互作用。例如，寄生虫可能会因繁殖和传播增加而不同程度地受益，或者宿主可能会因免疫反应增强而受益，这可能介导甚至消除感染。在美国东南部，东部牡蛎（Crassostrea virginica）受到致命原生动物寄生虫（Haplosporidium nelsoni）的感染。在野外条件下，已发现潮间带（暴露于空气中）牡蛎的感染强度明显高于潮下带（淹没）牡蛎，感染率也略高。在夏季，气温比水温高得多，潮间带牡蛎暴露于较高温度下被认为是感染强度增加的一种机制。
我们通过控制实验室实验模拟潮间带暴露，以确定宿主特征（存活率和免疫反应）以及寄生虫感染强度如何应对低潮时暴露期间27°C至53°C的气温升高。在我们开展研究的佐治亚州，夏季平均水温为29°C，7月平均最高气温为33°C（不过已证明牡蛎能在更高气温下存活）。
宿主存活率随温度升高而下降，在39 - 43°C之间出现明显下降。仅在宿主遭受急性死亡的极高温度（47 - 50°C）下，才检测到气温对宿主免疫反应（吞噬活性）的负面影响。寄生虫感染强度在35°C时达到峰值。
我们的结果表明，夏季平均气温升高至35°C或更高可能在短期内通过与温度相关的影响直接影响牡蛎存活，并在长期内通过增加的（Haplosporidium nelsoni）感染强度间接影响牡蛎存活。
