Inbreeding reduces fitness of seed beetles under thermal stress

Human-induced environmental change can influence populations both at the global level through climatic warming and at the local level through habitat fragmentation. As populations become more isolated, they can suffer from high levels of inbreeding which contributes to a reduction in fitness, termed inbreeding depression. However, it is still unclear if this increase in homozygosity also results in a corresponding increase in sensitivity to stressful conditions, which could intensify the already detrimental effects of environmental warming. Here, in a fully factorial design, we assessed the life-long impact of increased inbreeding load and elevated temperature on key life history traits in the seed beetle, Callosobruchus maculatus. We found that beetles raised at higher temperatures had far reduced fitness and survival than beetles from control temperatures. Importantly, these negative effects were exacerbated in inbred beetles as a result of increased inbreeding load, with further detrimental effects manifesting on individual eclosion probability and lifetime reproductive success. These results reveal the harmful impact that increasing temperature and likelihood of habitat fragmentation due to anthropogenetic changes in environmental conditions could have on populations of organisms worldwide.

人为活动驱动的环境变化可通过全球尺度的气候变暖与局地尺度的生境破碎化两种途径影响种群。随着种群愈发孤立，其将面临高水平近交（inbreeding）问题，进而导致适合度（fitness）下降，该现象被称为近交衰退（inbreeding depression）。然而目前仍不清楚，纯合性（homozygosity）提升是否会相应增加种群对胁迫环境的敏感性，而这一敏感性增强可能加剧本已有害的气候变暖负面影响。本研究采用完全析因设计，评估了近交负荷（inbreeding load）增加与温度升高对四纹豆象（Callosobruchus maculatus）关键生活史性状的终生影响。研究发现，相较于对照组温度下饲养的个体，高温饲养的豆象适合度与存活率均显著降低。值得注意的是，由于近交负荷增加，近交个体的上述负面影响进一步加剧，且在羽化率（eclosion probability）与终生繁殖成功率方面呈现出额外的有害效应。本研究结果揭示，环境条件的人为改变所引发的温度升高与生境破碎化风险，可能对全球范围内的生物种群造成有害影响。