Department of Evolutionary Biology & Environmental Studies, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Department of Evolutionary Biology & Environmental Studies, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland; Natural History Museum of Vienna, Austria.
J Therm Biol. 2023 Feb;112:103473. doi: 10.1016/j.jtherbio.2023.103473. Epub 2023 Jan 11.
Climate is changing towards both higher average temperatures and more frequent and severe heat waves. Whereas numerous studies have investigated temperature effects on animal life histories, assessments of their immune function are limited. In the size- and colour-dimorphic black scavenger (or dung) fly Sepsis thoracica (Diptera: Sepsidae), we experimentally studied how developmental temperature and larval density influence phenoloxidase (PO) activity, a key enzyme in insect pigmentation, thermoregulation, and immunity. Flies from five latitudinal European populations were raised at three developmental temperatures (18, 24, 30 °C). PO activity increased with developmental temperature differently in the sexes and the two male morphs (black and orange), altering the sigmoid relationship between melanism, i.e. colouration and fly size. PO activity further positively correlated with larval rearing density, potentially because of higher risks of pathogen infection or greater developmental stress following stronger resource competition. Populations varied somewhat in PO activity, body size and colouration, however with no clear latitudinal pattern. Overall our results indicate that morph- and sex-specific PO activity, and thus likely immune function, in S. thoracica depends on temperature and larval density, modifying the underlying putative trade-off between immunity and body size. The strong dampening of the immune system of all morphs at cool temperatures suggests low-temperature stress in this warm-adapted species common in southern Europe. Our results also support the population density dependent prophylaxis hypothesis, which predicts higher investment in immunity when facing limited resource availability and increased pathogen infection probability.
气候正朝着更高的平均温度和更频繁、更严重的热浪方向变化。虽然有许多研究调查了温度对动物生活史的影响，但对其免疫功能的评估是有限的。在大小和颜色二态性的黑腐生蝇（或粪便蝇）Sepsis thoracica（双翅目：Sepsidae）中，我们通过实验研究了发育温度和幼虫密度如何影响酚氧化酶（PO）活性，这是昆虫色素沉着、体温调节和免疫的关键酶。来自欧洲五个纬度的种群的苍蝇在三种发育温度（18、24、30°C）下进行培养。PO 活性在性别和两种雄性形态（黑色和橙色）中随发育温度的不同而增加，改变了黑色素沉着（即颜色和苍蝇大小）之间的 S 形关系。PO 活性还与幼虫饲养密度呈正相关，这可能是由于病原体感染的风险更高，或者在资源竞争加剧后发育压力更大。然而，种群在 PO 活性、体型和颜色方面存在一定差异，但没有明显的纬度模式。总的来说，我们的结果表明，S. thoracica 的形态和性别特异性 PO 活性，以及因此可能的免疫功能，取决于温度和幼虫密度，从而改变了免疫和体型之间潜在的权衡。所有形态在低温下免疫系统的强烈抑制表明，在这种在南欧常见的适应温暖的物种中，低温压力很大。我们的结果也支持种群密度依赖的预防假说，该假说预测在资源有限和病原体感染概率增加的情况下，会对免疫功能进行更高的投资。
