Data from: Why does it take two to tango? lifetime fitness consequences of parental care in a burying beetle

In species that require parental care, each parent can either care for their offspring or leave them in the care of the other parent. For each parent this creates three possible parental care strategies: biparental care, uniparental (male or female) care, and uniparental desertion by either the male or female. The burying beetle, Nicrophorus orbicollis, typically exhibits biparental care of offspring, and thus provides a unique system that allows us to compare the fitness benefits of these parental care strategies in an unconfounded way. In this study, we assess the lifetime fitness of biparental care, uniparental care, and uniparental desertion strategies in both male and female N. orbicollis. Specifically, we tested for increased fitness of the biparental care strategy compared to uniparental care strategies. Second, we test for equality of fitness between uniparental care and uniparental desertion strategies. Surprisingly, biparental care yields lower lifetime fitness for both parents compared to the other two strategies. Also, uniparental care and uniparental desertion strategies yielded equal fitness. The evolution of biparental care in this system is not consistent with the expectation of a mutual fitness benefit. We discuss other potential explanations for the evolution of biparental care in this system.

在需要亲代抚育（parental care）的物种中，每个亲本既可以选择亲自照料后代，也可以将后代托付给另一方抚育。针对单个亲本而言，这一选择衍生出三种可行的亲代抚育策略：双亲共同育幼（biparental care）、单亲（雄性或雌性）育幼（uniparental care），以及雄性或雌性单方实施的单亲弃养（uniparental desertion）。黑埋葬甲（Nicrophorus orbicollis）通常会采用双亲共同育幼的方式照料后代，因此其为我们提供了一个独特的研究体系，能够以无混杂干扰的方式比较不同亲代抚育策略的适合度（fitness）收益。本研究中，我们评估了黑埋葬甲雌雄个体分别采用双亲共同育幼、单亲育幼以及单亲弃养策略时的终生适合度。具体而言，我们首先检验了双亲共同育幼策略相较于单亲育幼策略是否具备更高的适合度；其次，我们检验了单亲育幼与单亲弃养策略的适合度是否相等。令人意外的是，相较于另外两种策略，双亲共同育幼会使雌雄双亲的终生适合度均更低；同时，单亲育幼与单亲弃养策略的适合度并无显著差异。该体系中双亲共同育幼的演化过程，并不符合"双方均可获得适合度收益"的经典预期。我们就此讨论了该体系中双亲共同育幼演化的其他潜在解释。