Data from: Social discrimination by quantitative assessment of immunogenetic similarity

Genes of the major histocompatibility complex (MHC) that underlie the adaptive immune system may allow vertebrates to recognise their kin. True kin-recognition genes should produce signalling products to which organisms can respond. Allelic variation in the peptide-binding region (PBR) of MHC molecules determines the pool of peptides that can be presented to trigger an immune response. To examine whether these MHC peptides also might underlie assessments of genetic similarity, we tested whether Xenopus laevis tadpoles socially discriminate between pairs of siblings with which they differed in PBR amino acid sequences. We found that tadpoles (4 sibships, N=854) associated preferentially with siblings with which they were more similar in PBR amino acid sequence. Moreover, the strength of their preference for a conspecific was directly proportional to the sequence similarity between them. Discrimination was graded, and correlated more closely with functional sequence differences encoded by MHC class I and class II alleles than with numbers of shared haplotypes. Our results thus suggest that haplotype analyses may fail to reveal fine-scale behavioural responses to divergence in functionally expressed sequences. We conclude that MHC-PBR gene products mediate quantitative social assessment of immunogenetic similarity that may facilitate kin recognition in vertebrates.

编码适应性免疫系统的主要组织相容性复合体（major histocompatibility complex, MHC）基因，或可帮助脊椎动物识别亲属。真正的亲属识别基因应当能够产生可供生物体识别响应的信号产物。MHC分子的肽结合区（peptide-binding region, PBR）的等位基因变异，决定了可被呈递以触发免疫应答的肽段库。为探究此类MHC肽段是否同样可作为遗传相似性评估的基础，我们检测了非洲爪蟾（Xenopus laevis）蝌蚪是否会基于同胞间的PBR氨基酸序列差异，产生社会识别偏好。本研究共纳入4个全同胞家系、总计854只蝌蚪，结果显示，相较于PBR氨基酸序列差异更大的同胞，蝌蚪会优先与序列相似性更高的同胞结伴。进一步分析发现，蝌蚪对同种个体的偏好强度，与其二者间的序列相似程度呈正相关。这种识别行为具有梯度性，且与MHC I类、II类等位基因所编码的功能性序列差异的相关性，要高于与共享单倍型数量的相关性。据此可知，仅通过单倍型分析或无法精准揭示针对功能性表达序列差异的精细行为响应。本研究最终表明，MHC-PBR基因产物可介导对免疫遗传相似性的量化社会评估，这一机制或可助力脊椎动物实现亲属识别。