Climatic anomaly affects the immune competence of California sea lions

The past decades have been characterized by a growing number of climatic anomalies. As these anomalies tend to occur suddenly and unexpectedly, it is often difficult to procure empirical evidence of their effects on natural populations. We analysed how the recent sea surface temperature (SST) anomaly in the northeastern Pacific Ocean affects body condition, nutritional status, and immune competence of California sea lion pups. We found that pup body condition and blood glucose levels of the pups were lower during high SST events, although other biomarkers of malnutrition remained unchanged, suggesting that pups were experiencing early stages of starvation. Glucose-dependent immune responses were affected by the SST anomaly; specifically, pups born during high SST events had lower serum concentrations of IgG and IgA, and were unable to respond to an immune challenge. This means that not only were pups that were born during the SST anomaly less able to synthesize protective antibodies; they were also limited in their ability to respond rapidly to nonspecific immune challenges. Our study provides empirical evidence that atypical climatic conditions can limit energetic reserves and compromise physiological responses that are essential for the survival of a marine top predator.

近数十年来，气候异常事件的数量持续攀升。由于此类异常事件往往突发且难以预判，获取其对野生种群影响的实证证据通常颇具难度。我们分析了近期东北太平洋海表温度（sea surface temperature, SST）异常对加州海狮幼崽身体状况、营养状态与免疫功能的影响。研究发现，在海表温度异常偏高事件期间，幼崽的身体状况与血糖水平均有所下降，而其他营养不良相关生物标志物未出现显著变化，这表明幼崽正处于饥饿早期阶段。葡萄糖依赖性免疫应答受到海表温度异常的影响：具体而言，在海表温度偏高事件期间出生的幼崽，其血清IgG与IgA浓度更低，且无法对免疫刺激作出应答。这意味着，在海表温度异常时期出生的幼崽不仅难以合成保护性抗体，还无法快速对非特异性免疫刺激作出应答。本研究提供了实证证据，表明非典型气候条件会限制海洋顶级捕食者的能量储备，并损害其生存所必需的生理应答能力。