Bel-Venner M C, Dray S, Allainé D, Menu F, Venner S
Expression et Evolution des Comportements, Université Henri Poincaré Nancy, BP 239, 54506 Vandoeuvre-les-Nancy, France.
Proc Biol Sci. 2008 Jan 7;275(1630):77-82. doi: 10.1098/rspb.2007.1278.
Sexual selection theory traditionally considers choosiness for mates to be negatively related to intra-sexual competition. Males were classically considered to be the competing, but not the choosy, sex. However, evidence of male choosiness is now accumulating. Male choosiness is expected to increase with an individual's competitive ability, and to decrease as intra-sexual competition increases. However, such predictions have never been tested in field conditions. Here, we explore male mate choice in a spider by studying size-assortative pairing in two natural sites that strongly differ in the level of male-male competition. Unexpectedly, our results demonstrate that mate choice shifts from opportunism to high selectivity as competition between males increases. Males experiencing weak competition did not exhibit size-related mating preferences. By contrast, when competition was intense we found strong size-assortative pairing due to male choice: while larger, more competitive males preferentially paired with larger, more fecund females, smaller males chose smaller females. Thus, we show that mating preferences of males vary with their competitive ability. The distinct preferences exhibited by males of different sizes seem to be an adaptive response to the lower reproductive opportunities arising from increased competition between males.
性选择理论传统上认为对配偶的挑剔程度与同性间竞争呈负相关。传统观念认为，雄性是竞争的一方，而非挑剔的一方。然而，如今雄性挑剔的证据正在不断积累。预计雄性的挑剔程度会随着个体竞争能力的增强而增加，随着同性间竞争的加剧而降低。然而，这些预测从未在野外条件下得到验证。在此，我们通过研究两个雄性间竞争程度差异很大的自然栖息地中的体型配对情况，来探究一种蜘蛛中雄性的配偶选择。出乎意料的是，我们的结果表明，随着雄性间竞争的增加，配偶选择从机会主义转变为高度选择性。经历弱竞争的雄性没有表现出与体型相关的交配偏好。相比之下，当竞争激烈时，我们发现由于雄性选择而出现了强烈的体型配对：体型较大、更具竞争力的雄性优先与体型较大、繁殖力更强的雌性交配，而体型较小的雄性则选择体型较小的雌性。因此，我们表明雄性的交配偏好会随着其竞争能力而变化。不同体型雄性表现出的不同偏好似乎是对雄性间竞争加剧导致的较低繁殖机会的一种适应性反应。
