Moray Camile, Hua Xia, Bromham Lindell
Division of Ecology, Macroevolution and Macroecology, Evolution and Genetics, Research School of Biology, Australian National University, Brinkin, 0200, Australia.
BMC Evol Biol. 2015 May 19;15:90. doi: 10.1186/s12862-015-0379-0.
Salt tolerance in plants is rare, yet it is found across a diverse set of taxonomic groups. This suggests that, although salt tolerance often involves a set of complex traits, it has evolved many times independently in different angiosperm lineages. However, the pattern of evolution of salt tolerance can vary dramatically between families. A recent phylogenetic study of the Chenopodiaceae (goosefoot family) concluded that salt tolerance has a conserved evolutionary pattern, being gained early in the evolution of the lineage then retained by most species in the family. Conversely, a phylogenetic study of the Poaceae (grass family) suggested over 70 independent gains of salt tolerance, most giving rise to only one or a few salt tolerant species. Here, we use a phylogenetic approach to explore the macroevolutionary patterns of salt tolerance in a sample of angiosperm families, in order to ask whether either of these two patterns - deep and conserved or shallow and labile - represents a common mode of salt tolerance evolution. We analyze the distribution of halophyte species across the angiosperms and identify families with more or less halophytes than expected under a random model. Then, we explore the phylogenetic distribution of halophytes in 22 families using phylogenetic comparative methods.
We find that salt tolerance species have been reported from over one-third of angiosperm families, but that salt tolerant species are not distributed evenly across angiosperm families. We find that salt tolerance has been gained hundreds of times over the history of the angiosperms. In a few families, we find deep and conserved gains of salt tolerance, but in the majority of families analyzed, we find that the pattern of salt tolerant species is best explained by multiple independent gains that occur near the tips of the phylogeny and often give rise to only one or a few halophytes.
Our results suggest that the pattern of many independent gains of salt tolerance near the tips of the phylogeny is found in many angiosperm families. This suggests that the pattern reported in the grasses of high evolutionary lability may be a common feature of salt tolerance evolution in angiosperms.
植物的耐盐性很罕见，但在不同的分类群中都能发现。这表明，尽管耐盐性通常涉及一系列复杂性状，但它在不同的被子植物谱系中已多次独立进化。然而，耐盐性的进化模式在不同科之间可能有很大差异。最近对藜科（藜科）的系统发育研究得出结论，耐盐性具有保守的进化模式，在该谱系进化早期获得，然后被该科的大多数物种保留。相反，对禾本科（禾本科）的系统发育研究表明，耐盐性有70多次独立获得，大多数仅产生一个或几个耐盐物种。在这里，我们使用系统发育方法来探索被子植物科样本中耐盐性的宏观进化模式，以询问这两种模式——深度且保守或浅度且不稳定——是否代表耐盐性进化的常见模式。我们分析了盐生植物物种在被子植物中的分布，并识别出盐生植物数量多于或少于随机模型预期的科。然后，我们使用系统发育比较方法探索22个科中盐生植物的系统发育分布。
我们发现超过三分之一的被子植物科都报道了耐盐物种，但耐盐物种在被子植物科中的分布并不均匀。我们发现，在被子植物的历史上，耐盐性已经获得了数百次。在少数科中，我们发现了深度且保守的耐盐性获得，但在大多数分析的科中，我们发现耐盐物种的模式最好由系统发育树末端附近的多次独立获得来解释，这些获得通常仅产生一个或几个盐生植物。
我们的结果表明，在许多被子植物科中都发现了系统发育树末端附近耐盐性多次独立获得的模式。这表明禾本科中报道的高进化不稳定性模式可能是被子植物耐盐性进化的一个共同特征。
