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形式，可显著影响达尔文适合度（Darwinian fitness）并推动生物多样化进程。尽管其生态与进化意义重大，但学界对选型交配背后的行为机制仍缺乏清晰认知，尤其是不涉及配偶选择（mate choice）的相关机制，迄今仍被大幅忽视。本文提出，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，该机制仍可催生选型交配。研究显示，在丽鱼科（cichlid）鱼类饰鳍丽鱼（Eretmodus cyanostictus）中，体型选型交配（size-assortative mating）确实存在，这是因为竞争能力较弱的个体，会主动回避那些高质量但竞争激烈的栖息地斑块（habitat patches）。既往研究表明，饰鳍丽鱼并不存在基于体型的配偶偏好（size-based mate preferences）。本文通过野外与室内实验证实：其一，该物种的栖息地质量与个体体型存在相关性；其二，在无竞争的条件下，雌雄个体均偏好石块遮蔽物（stone cover）更多的领地；其三，相较于体型更大的个体，体型较小的个体更审慎地选择占据质量较差的空领地（vacant territories）。审慎栖息地选择大概率是一种广泛存在的选型交配机制，因为对高质量栖息地的偏好，以及基于优势地位的高质量栖息地获取权（dominance-based access），都是动物界的普遍现象。