The role of abiotic and biotic factors in the unequal body shape diversification of a Gondwanan fish radiation (Otophysi:Characiformes)

Understanding why some clades diversify greatly, while others do not, is a
major goal of evolutionary biology. Both abiotic and biotic factors are
important in driving unequal morphological diversity across the tree of
life. However, few studies have quantified how differences in abiotic
habitat and community composition influence unequal morphological
diversification in spatiotemporally diffuse radiations. Here we use
geometric morphometrics, abiotic habitat data generated by Geographic
Information Systems (GIS) analyses, evolutionary simulations, and
phylogenetic comparative methods to determine whether random evolution,
habitat variation, competition for niches or a combination of factors
influenced the unequal body shape diversity of a Gondwanan freshwater fish
radiation. We find that neotropical characiform lineages, which exhibit
substantially more body shape diversity than their African counterparts,
occupy significantly more slope and elevation habitats than African
lineages. Differences in habitat occupation between the continental
radiations occur by a combination of competition with cypriniform fishes
in Africa restricting access to higher slope and elevation habitats and
significantly more low elevation and slope habitat available in the
neotropics. Our findings suggest that spatiotemporally widespread
radiations, like the Characiformes, do not diversify across homogenized
habitats and biotic assemblages, with differences in community structure
and physical habitat important in driving unequal morphological
diversification.

探明为何部分演化支（clade）能够发生大规模多样化，而另一部分则无法实现，是演化生物学的核心研究目标之一。非生物与生物因子均是驱动生命之树各处形态多样性不均等分布的关键因素。然而，目前鲜有研究量化分析非生物生境差异与群落组成变化，如何影响时空弥散式辐射演化类群的不均等形态多样化进程。本研究借助几何形态测量学（geometric morphometrics）、地理信息系统（GIS）分析生成的非生物生境数据、演化模拟以及系统发育比较方法，旨在探究随机演化、生境变异、生态位竞争，或是多因子共同作用，是否影响了冈瓦纳淡水鱼类辐射演化类群的不均等体形多样性。研究发现，新热带区脂鲤形目支系的体形多样性远高于其非洲对应支系，且它们占据的坡地与海拔生境也显著多于非洲支系。两大大陆辐射演化类群的生境利用差异，源于两方面因素的共同作用：一是非洲地区的鲤形目鱼类竞争限制了脂鲤形目支系对高海拔与坡地生境的利用；二是新热带区拥有远更多的低海拔与坡地生境。本研究结果表明，诸如脂鲤形目这类时空分布广泛的辐射演化类群，并未在均质化生境与生物群落中发生多样化；群落结构与物理生境的差异，是驱动不均等形态多样化的关键因素。