Data from: Manipulation of parental nutritional condition reveals competition among family members

Parental care is thought to be costly, as it consumes time and energy. Such costs might be reduced in animal parents that raise their young on valuable food sources such as dung or carcasses, as parents are able to invest in self-maintenance by feeding from the same resource. However, this might lower the nutritional value for other family members and, as a consequence, food competition might arise. To promote our understanding of the outcome of such competition, we manipulated the necessity of parents to feed from the resource. Using a full factorial design, we paired food-deprived or well-fed males with food-deprived or well-fed females of burying beetles, which are known to raise their young on vertebrate cadavers. We found that food-deprived parents consumed more of the carrion than those that were well-fed and this had a negative impact on other family members. However, the outcome of the competition depended on the sex of the parents, with females suffering when males fed more and offspring suffering when females fed more. Thus, family life involves selfish elements, as both parents remove resources for the purpose of self-maintenance. However, females show altruistic aspects, as they appear to restrict their food consumption for the benefit of their offspring when paired with a food-deprived male. Interestingly, males extend their stay with the brood when having faced food scarcity prior to reproduction, presumably to replenish their energy reserves. Our study therefore reveals that breeding on shared resources can promote family living, but also results in competition.

亲本抚育（parental care）被认为具有成本，因其会消耗时间与能量。依托粪便、腐尸这类高价值食物来源抚育后代的动物亲本，其抚育成本或可降低——因为亲本可通过取用同一资源开展自我维持的能量投入。然而这或许会降低其他家庭成员所能获得的营养价值，进而可能引发食物竞争。为深化我们对这类竞争结局的认知，我们对亲本取用该资源的必要性进行了调控。我们采用完全析因设计（full factorial design），将禁食或饱腹的雄性埋葬甲（burying beetles）与禁食或饱腹的雌性进行配对——已知该类昆虫会依托脊椎动物腐尸抚育后代。我们发现，禁食的亲本相较于饱腹个体，会消耗更多腐肉，这对其他家庭成员产生了负面影响。但竞争的结局取决于亲本的性别：当雄性取食更多时，雌性会受到不利影响；而当雌性取食更多时，后代则会受到不利影响。由此可见，家族生活中存在自私性元素，因为双亲均会为自我维持而消耗资源。不过雌性也表现出利他性特征：当与禁食的雄性配对时，它们似乎会限制自身的食物摄取，以保障后代的利益。有趣的是，若雄性在繁殖前遭遇过食物匮乏，它们会延长与育幼群（brood）共处的时长，推测是为了补充自身的能量储备（energy reserves）。因此，本研究揭示：依托共享资源开展繁殖，既能够促进家族群居行为的形成，也会引发竞争。