Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, South Africa.
PLoS One. 2013;8(2):e57969. doi: 10.1371/journal.pone.0057969. Epub 2013 Feb 25.
Sociality and particularly advanced forms of sociality such as cooperative breeding (living in permanent groups with reproductive division of labour) is relatively rare among vertebrates. A suggested constraint on the evolution of sociality is the elevated transmission rate of parasites between group members. Despite such apparent costs, sociality has evolved independently in a number of vertebrate taxa including humans. However, how the costs of parasitism are overcome in such cases remains uncertain. We evaluated the potential role of parasites in the evolution of sociality in a member of the African mole-rats, the only mammal family that exhibits the entire range of social systems from solitary to eusocial. Here we show that resting metabolic rates decrease whilst daily energy expenditure and energy stores (i.e. body fat) increase with group size in social Natal mole rats (Cryptomys hottentotus natalensis). Critically, larger groups also had reduced parasite abundance and infested individuals only showed measurable increases in energy metabolism at high parasite abundance. Thus, in some circumstances, sociality appears to provide energetic benefits that may be diverted into parasite defence. This mechanism is likely to be self-reinforcing and an important factor in the evolution of sociality.
社会性，特别是合作繁殖等高级形式的社会性（生活在具有生殖分工的永久群体中）在脊椎动物中相对较少。寄生虫在群体成员之间的高传播率被认为是社会性进化的一个限制因素。尽管存在这种明显的成本，但社会性已经在包括人类在内的许多脊椎动物类群中独立进化。然而，在这种情况下，寄生虫的成本是如何被克服的仍然不确定。我们评估了寄生虫在非洲鼹鼠科（非洲地鼠）这一物种社会性进化中的潜在作用，非洲地鼠科是唯一表现出从独居到真社会性等一系列社会系统的哺乳动物科。在这里，我们表明在社会性的纳塔尔鼹鼠（Cryptomys hottentotus natalensis）中，休息代谢率随着群体大小的增加而降低，而每日能量支出和能量储存（即体脂肪）则增加。关键的是，较大的群体寄生虫丰度也较低，只有在寄生虫丰度较高时，受感染的个体能量代谢才会出现可测量的增加。因此，在某些情况下，社会性似乎提供了能量益处，这些益处可能被转移到寄生虫防御中。这种机制很可能是自我强化的，是社会性进化的一个重要因素。
