Data from: Behavioral isolation due to cascade reinforcement in Lucania killifish

Reinforcement occurs when behavioral isolation is strengthened between species due to selection against hybridization in sympatry. Mate preferences and their target traits may change in sympatry as a consequence of reinforcement. This can potentially generate further behavioral isolation within species if sympatric populations evolve extreme preferences or traits that cause them to reject individuals from foreign populations as mates or be rejected as mates. This process is known as cascade reinforcement. We measured behavioral isolation between sympatric and allopatric populations of Lucania killifish to determine whether isolation evolves due to reinforcement between species and whether reinforcement affects preferences within species, consistent with the cascade reinforcement hypothesis. We measured mate preferences in both sexes between species (Lucania parva vs. Lucania goodei) and within species (among populations of L. parva). Between species, both male and female preferences for conspecifics were highest in sympatric populations. Within species, L. parva females from sympatric populations preferred their own native males over foreign males. Allopatric L. parva females and all L. parva males showed no preferences within species. Within species, behavioral isolation showed no association with ecological variables, such as salinity. Thus, reinforcement is a primary factor generating behavioral isolation in Lucania killifish, creating strong preferences in both sexes among species and leading to cascade reinforcement of female mate preference within species.

当同域分布（sympatry）的物种种群间因选择压力淘汰杂交个体而强化行为隔离（behavioral isolation）时，即发生生殖强化（reinforcement）。作为生殖强化的结果，配偶偏好（mate preferences）及其目标性状（target traits）可能在同域种群中发生改变。若同域种群演化出极端配偶偏好或性状，导致其拒绝外来种群个体作为配偶，或被外来种群拒绝交配，则可能进一步在种群内部产生行为隔离。这一过程被称为级联生殖强化（cascade reinforcement）。
我们以溪鳉属（Lucania）鱼类为研究对象，测量了其同域与异域分布（allopatry）种群间的行为隔离，以验证两个核心问题：一是物种间的行为隔离是否由生殖强化演化而来，二是生殖强化是否会影响物种内部的配偶偏好，从而符合级联生殖强化假说。我们分别测定了物种间（矮溪鳉Lucania parva vs. 古德溪鳉Lucania goodei）以及物种内（矮溪鳉不同种群间）的两性配偶偏好。
在物种间层面，同域种群的雌雄个体对同种个体（conspecifics）的配偶偏好均最强。在物种内层面，来自同域种群的矮溪鳉雌性更偏好本土雄性而非外来雄性；而异域矮溪鳉雌性以及所有矮溪鳉雄性均未表现出种内配偶偏好。此外，种内行为隔离与盐度（salinity）等生态变量无显著关联。
综上，生殖强化是溪鳉属鱼类行为隔离形成的核心驱动因素，不仅在物种类群间催生了两性的强烈配偶偏好，还引发了物种内部雌性配偶偏好的级联生殖强化。