Eldakar Omar Tonsi, Dlugos Michael J, Holt Galen P, Wilson David Sloan, Pepper Johnw
Center for Insect Science, P.O. Box 210088, University of Arizona, Tucson, AZ 85721-0088, USA.
Behaviour. 2010 Aug;147(12):1615-1631. doi: 10.1163/000579510X510520.
In sexual conflict, aggressive males frequently diminish the long-term reproductive success of females in efforts to gain a short-term advantage over rival males. This short-term advantage can selectively favour high-exploitation males. However, just as the over-exploitation of resources can lead to local extinction, the over-exploitation of females in the form of harassment by aggressive males can yield similar consequences resulting in reduced female fecundity, increased female mortality and overall decline in mating activity. This outcome may often be prevented by selection acting at multiple levels of biological organization. Directional selection favouring aggressive exploitation within groups can be balanced by directional selection amongst groups opposing exploitation. Such between-group selection has recently been demonstrated in laboratory studies of water striders, where the conditional dispersal of individuals increased variation amongst groups and influenced the balance of selection toward reduced male aggression. This multilevel selection (MLS) framework also provides predictive value when investigating natural populations differing in their relative strength of selection within versus among groups. For water striders, the consequences of local exploitation cause fitness differences between groups, favouring less aggressive males. Inconsistently flowing ephemeral streams consist of isolated pools that prevent aggressive male water striders from escaping the consequences of local exploitation. We, therefore, predicted that inconsistently flowing ephemeral streams would favour the evolution of less aggressive males than would perennial streams, which allow aggressive males to move more freely and to escape the group-level costs of their aggression. Comparing two neighbouring streams during the mating season, we found that males dispersed naturally between pools at much higher rates in the perennial stream than in the ephemeral stream. As predicted, we found that males from the perennial stream were significantly more aggressive than those from the ephemeral stream. We also found that dispersers were significantly more aggressive than non-dispersers within each stream. These field results illustrate the relevance of the MLS framework in our understanding of the evolution of sexual conflict.
在性冲突中，具有攻击性的雄性常常会降低雌性的长期繁殖成功率，以努力在与竞争对手雄性的较量中获得短期优势。这种短期优势会选择性地青睐高剥削性的雄性。然而，正如对资源的过度开发会导致局部灭绝一样，具有攻击性的雄性以骚扰形式对雌性的过度开发也可能产生类似后果，导致雌性繁殖力下降、死亡率增加以及交配活动总体减少。这种结果通常可以通过在生物组织的多个层面上起作用的选择来预防。在群体内部有利于攻击性剥削的定向选择可以被群体之间反对剥削的定向选择所平衡。最近在水黾的实验室研究中证明了这种群体间选择，个体的条件性扩散增加了群体间的变异性，并影响了朝着减少雄性攻击性的选择平衡。当研究群体内部与群体之间选择相对强度不同的自然种群时，这种多层次选择（MLS）框架也具有预测价值。对于水黾来说，局部剥削的后果导致群体之间的适合度差异，有利于攻击性较弱的雄性。水流不稳定的季节性溪流由孤立的水潭组成，这使得具有攻击性的雄性水黾无法逃避局部剥削的后果。因此，我们预测，与常年溪流相比，水流不稳定的季节性溪流将更有利于攻击性较弱的雄性的进化；常年溪流使具有攻击性的雄性能够更自由地移动，从而逃避其攻击行为在群体层面产生的代价。在交配季节比较两条相邻的溪流时，我们发现，常年溪流中雄性在水潭之间自然扩散的速率比季节性溪流中的要高得多。正如预测的那样，我们发现常年溪流中的雄性比季节性溪流中的雄性攻击性明显更强。我们还发现，在每条溪流中，扩散者比非扩散者的攻击性明显更强。这些实地研究结果说明了多层次选择框架在我们理解性冲突进化中的相关性。
