Kin recognition in a butterfly: inferences about its heritability

Some animal species are able to recognise their relatives, cannibalising mostly non-kin individuals, as happens with the caterpillars of the butterfly Heliconius erato phyllis. Here, we established a breeding programme where adults had different coefficients of relatedness (r = 0 and r = 0.5; offspring, respectively with F = 0 and F = 0.25). The caterpillars cannibalised or did not cannibalise sibling eggs, which was used to make inferences on the kin recognition inheritance of non-cannibals, and to estimate its heritability. The parents had both cannibal and non-cannibal phenotypes; crosses were done for all combinations of these phenotypes, which were divided into outbred and inbred. Caterpillars were grown in the laboratory until the adult stage, and were classified as cannibal or non-cannibal after a test with three sibling eggs. The results showed that the mean number of non-cannibal siblings, those that recognise their kin, is larger in inbreds, above 60%, regardless of their parents’ behaviour. Among non-inbred individuals the mean frequency of non-cannibal siblings was around 38%; these differences were statistically significant. The heritability was estimated by four methods. For F = 0 it was around 0.24 ± 0.11, and for F = 0.25 it was around 0.20 ± 0.17. These results, taken together, were discussed in terms of a threshold character: above this threshold the expression of the non-cannibal phenotype is allowed. As for the low values for heritabilities, they were discussed in terms of the theory of traits relevant to both fitness and the resource allocation priority hypothesis.

部分动物物种可识别亲缘个体，且大多会捕食非亲缘个体，红带袖蝶（Heliconius erato phyllis）的幼虫便是此类典型。本研究构建了一套繁育实验体系，供试成虫的亲缘系数（coefficient of relatedness）分别为r=0与r=0.5，对应子代的近交系数（F）分别为0和0.25。幼虫可选择捕食或不捕食同胞卵，以此可推断非捕食者的亲缘识别遗传模式，并估算其遗传力（heritability）。亲本均包含捕食者与非捕食者两种表型；针对两种表型的所有组合进行杂交，并将杂交组分为远交（outbred）与近交（inbred）两类。幼虫在实验室条件下饲养至成虫阶段，并通过3枚同胞卵的捕食测试，将其划分为捕食者与非捕食者两类。结果显示，无论亲本的捕食行为如何，近交组中非捕食同胞（即可识别亲缘个体）的平均占比均高于60%。远交组中非捕食同胞的平均占比约为38%，两组差异具有统计学显著性。本研究通过四种方法估算遗传力：当F=0时，遗传力约为0.24±0.11；当F=0.25时，约为0.20±0.17。综合上述结果，本研究以阈值性状（threshold character）理论展开讨论：当个体的性状值高于该阈值时，即可表达非捕食表型。针对遗传力偏低的现象，则结合适合度相关性状理论与资源分配优先级假说（resource allocation priority hypothesis）进行了分析。