Inbreeding reduces the ability of young to exploit high-resource nurseries

Parents of many species create a “nursery” in which young develop, and variation in this environment can influence offspring phenotype and fitness. Recent studies have demonstrated that behavioral interactions within these nurseries may moderate inbreeding depression. However, whether other features of the nursery impact inbreeding depression, either directly or through secondary impacts on behavior, has been less well studied. Here, I describe two experiments involving the burying beetle, Nicrophorus orbicollis, in which I test (1) whether inbreeding depression is sensitive to the size of the carcass that constitutes the nursery, and (2) whether inbreeding and carcass size influence parental care behavior. In the first experiment, I found that resource abundance in the nursery impacted inbreeding depression in larval mass, a trait that determines adult body size and competitive ability. In low-resource nurseries, inbred and outbred offspring did not differ in mass. However, in high-resource nurseries, inbred larvae were smaller than outbred larvae. This inbreeding-by-environment interaction occurred because the mass of outbred larvae was more responsive to resource abundance than the mass of inbred larvae. Larval survival from dispersal to eclosion exhibited inbreeding depression that was independent of resource abundance. In the second experiment, I found no evidence that the inability of inbred larvae to exploit high-resource nurseries was due to differences in parental behavior. These results suggest that inbred larvae are less able than outbred larvae to take advantage of high resource nurseries; however, further work is necessary to uncover the mechanisms generating this inbreeding-by-environment interaction.

诸多物种的亲代会构建育幼场所（nursery）以抚育子代，该育幼环境的差异会对子代表型与适合度产生影响。已有研究表明，这些育幼场所内的行为交互可缓解近交衰退（inbreeding depression）。然而，育幼场所的其他特征是否会直接或通过影响行为的间接途径对近交衰退产生作用，目前相关研究仍较为匮乏。本研究针对埋葬甲（Nicrophorus orbicollis）开展了两项实验，旨在验证两个问题：其一，近交衰退是否会随构成育幼场所的尸体尺寸发生变化；其二，近交与尸体尺寸是否会影响亲代抚育行为。在第一项实验中，研究发现育幼场所内的资源丰度会对子代幼虫体重相关的近交衰退产生影响——幼虫体重是决定成虫体型与竞争能力的关键性状。在低资源育幼环境中，近交子代与远交子代的体重并无显著差异。但在高资源育幼环境中，近交幼虫的体重显著小于远交幼虫。出现这一近交-环境互作（inbreeding-by-environment interaction）效应的原因在于，远交幼虫的体重对资源丰度的响应程度显著高于近交幼虫。幼虫从扩散至羽化的存活率也存在近交衰退现象，且该效应不受资源丰度的影响。在第二项实验中，并未发现近交幼虫无法利用高资源育幼场所的现象是由亲代抚育行为差异导致的证据。上述结果表明，相较于远交幼虫，近交幼虫更难以利用高资源育幼场所；不过，仍需开展进一步研究以阐明产生该近交-环境互作效应的内在机制。