Data from: 'Prudent habitat choice': a novel mechanism of size-assortative mating

Assortative mating, an ubiquitous form of nonrandom mating, strongly impacts Darwinian fitness and can drive biological diversification. Despite its ecological and evolutionary importance, the behavioural processes underlying assortative mating are often unknown, and in particular, mechanisms not involving mate choice have been largely ignored so far. Here, we propose that assortative mating can arise from ‘prudent habitat choice’, a general mechanism that acts under natural selection, and that it can occur despite a complete mixing of phenotypes. We show that in the cichlid Eretmodus cyanostictus size-assortative mating ensues, because individuals of weaker competitive ability ignore high-quality but strongly competed habitat patches. Previous studies showed that in E. cyanostictus, size-based mate preferences are absent. By field and laboratory experiments, here we showed that (i) habitat quality and body size are correlated in this species; (ii) territories with more stone cover are preferred by both sexes in the absence of competition; and (iii) smaller fish prudently occupy vacant territories of worse quality than do larger fish. Prudent habitat choice is likely to be a widespread mechanism of assortative mating, as both preferences for and dominance-based access to high-quality habitats are generic phenomena in animals.选型交配（assortative mating）是一种广泛存在的非随机交配（nonrandom mating）形式，对达尔文适合度（Darwinian fitness）具有显著影响，并可推动生物多样化进程。尽管其在生态与进化层面的重要性已得到学界认可，但选型交配背后的行为机制仍多未被阐明，尤其是不涉及配偶选择的交配机制，迄今基本被忽视。 本研究提出，选型交配可源于审慎栖息地选择（prudent habitat choice）——这是一种受自然选择（natural selection）作用的通用机制——且即便种群内表型完全混合，该机制仍可引发选型交配。研究表明，在慈鲷（cichlid）埃氏桨鳍丽鱼（Eretmodus cyanostictus）中，体型选型交配（size-assortative mating）得以发生，原因在于竞争能力较弱的个体会回避优质但竞争激烈的栖息地斑块（habitat patch）。 既往研究已证实，该物种不存在基于体型的配偶偏好。本研究通过野外与实验室实验进一步证明：其一，该物种的栖息地质量与个体体型存在相关性；其二，在无竞争的前提下，雌雄个体均偏好石块覆盖度更高的领地（territory）；其三，相较于体型较大的个体，体型较小的个体更倾向于审慎地占据质量较差的空置领地。 审慎栖息地选择或许是一种广泛存在的选型交配机制，因为对优质栖息地的偏好以及基于优势地位的优质栖息地获取权，在动物界均属于普遍现象。