Testing the Fitness Consequences of the Thermoregulatory and Parental Care Models for the Origin of Endothermy

The origin of endothermy is a puzzling phenomenon in the evolution of vertebrates. To address this issue several explicative models have been proposed. The main models proposed for the origin of endothermy are the aerobic capacity, the thermoregulatory and the parental care models. Our main proposal is that to compare the alternative models, a critical aspect is to determine how strongly natural selection was influenced by body temperature, and basal and maximum metabolic rates during the evolution of endothermy. We evaluate these relationships in the context of three main hypotheses aimed at explaining the evolution of endothermy, namely the parental care hypothesis and two hypotheses related to the thermoregulatory model (thermogenic capacity and higher body temperature models). We used data on basal and maximum metabolic rates and body temperature from 17 rodent populations, and used intrinsic population growth rate (Rmax) as a global proxy of fitness. We found greater support for the thermogenic capacity model of the thermoregulatory model. In other words, greater thermogenic capacity is associated with increased fitness in rodent populations. To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

内温性（endothermy）起源是脊椎动物演化历程中一个令人困惑的科学问题。为解答该问题，学界已提出多种解释模型。针对内温性起源提出的主流模型主要包括有氧能力模型（aerobic capacity model）、体温调节模型（thermoregulatory model）以及亲代抚育模型（parental care model）。本研究的核心论点为：若要对这些备选模型开展比较分析，关键在于明确在内温性演化过程中，自然选择受体温、基础代谢率（basal metabolic rate）与最大代谢率（maximum metabolic rate）的影响强度。本研究围绕三类旨在阐释内温性演化的核心假说展开上述关联的验证，分别为亲代抚育假说，以及与体温调节模型相关的两个子假说：产热能力假说与高体温假说。我们采集了17个啮齿类种群的基础代谢率、最大代谢率与体温数据，并以种群内禀增长率（intrinsic population growth rate, Rmax）作为适合度（fitness）的全局替代指标。研究结果更支持体温调节模型中的产热能力假说。换言之，啮齿类种群的产热能力越强，其适合度越高。据我们所知，本研究首次针对内温性起源相关的体温调节模型与亲代抚育模型，验证了其适合度相关效应。