Nitta Joel H, Watkins James E, Davis Charles C
Department of Organismic and Evolutionary Biology and Harvard University Herbaria, Harvard University, 22 Divinity Avenue, Cambridge, MA, 02138, USA.
Department of Biology, Colgate University, 13 Oak Drive, Hamilton, NY, 13346, USA.
New Phytol. 2020 Sep;227(6):1885-1899. doi: 10.1111/nph.16607. Epub 2020 May 19.
The expansion of angiosperm-dominated forests in the Cretaceous and early Cenozoic had a profound effect on terrestrial biota by creating novel ecological niches. The majority of modern fern lineages are hypothesized to have arisen in response to this expansion, particularly fern epiphytes that radiated into the canopy. Recent evidence, however, suggests that epiphytism does not correlate with increased diversification rates in ferns, calling into question the role of the canopy habitat in fern evolution. To understand the role of the canopy in structuring fern community diversity, we investigated functional traits of fern sporophytes and gametophytes across a broad phylogenetic sampling on the island of Moorea, French Polynesia, including > 120 species and representatives of multiple epiphytic radiations. While epiphytes showed convergence in small size and a higher frequency of noncordate gametophytes, they showed greater functional diversity at the community level relative to terrestrial ferns. These results suggest previously overlooked functional diversity among fern epiphytes, and raise the hypothesis that while the angiosperm canopy acted as a complex filter that restricted plant size, it also facilitated diversification into finely partitioned niches. Characterizing these niche axes and adaptations of epiphytic ferns occupying them should be a priority for future pteridological research.
被子植物主导的森林在白垩纪和早新生代的扩张通过创造新的生态位对陆地生物群产生了深远影响。大多数现代蕨类植物谱系被认为是对这种扩张的响应而产生的，特别是那些辐射到树冠层的蕨类附生植物。然而，最近的证据表明，附生习性与蕨类植物多样化率的增加并无关联，这使得树冠层栖息地在蕨类植物进化中的作用受到质疑。为了了解树冠层在构建蕨类植物群落多样性中的作用，我们在法属波利尼西亚的莫雷阿岛进行了广泛系统发育采样，调查了蕨类植物孢子体和配子体的功能性状，涵盖超过120个物种以及多个附生辐射类群的代表。虽然附生植物在体型较小和非心形配子体频率较高方面表现出趋同，但相对于陆生蕨类植物，它们在群落水平上表现出更大的功能多样性。这些结果表明蕨类附生植物中存在以前被忽视的功能多样性，并提出了一个假设，即虽然被子植物树冠层起到了限制植物大小的复杂过滤器的作用，但它也促进了向精细划分的生态位的多样化。确定这些生态位轴以及占据它们的附生蕨类植物的适应性应该是未来蕨类植物学研究的重点。
