Not only in the temperate zone: independent gametophytes of two vittarioid ferns (Pteridaceae, Polypodiales) in East Asian subtropics
Not only in the temperate zone: independent gametophytes of two vittarioid ferns (Pteridaceae, Polypodiales) in East Asian subtropics
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DOI：
10.1007/s10265-016-0897-x
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发表时间：
2017-03-01
影响因子：
2.8
通讯作者：
Chiou, Wen-Liang
中科院分区：
文献类型：
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作者：
Kuo, Li-Yaung;Chen, Cheng-Wei;Chiou, Wen-Liang
独立配子体蕨类植物在维管植物中是独特的，因为它们是无孢子体的，通过无性繁殖来维持配子体世代的种群数量。这类蕨类植物最初发现于温带，通常假设起源于（亚）热带，随后由于冰川时期气候变化导致孢子体灭绝。据推测，独立的蕨类配子体不太可能分布在热带和亚热带，因为气候相对稳定，受冰川影响较小。然而，目前的研究表明，东亚亚热带地区有两种独立的配子体蕨类植物。本研究利用同源种的质体DNA序列（trnL-L-F和matK + ndhF + chlL数据集）和综合采样（接近80%）对这些独立的蕨类配子体进行分子鉴定和分化时间估计。这两种配子体独立的蕨类植物属于单蕨属（vittarioids, Pteridaceae），在东亚没有遗传相同的孢子体种。对一个物种来说，种群间的分化时间意味着孢子最近的海外扩散发生在更新世。通过对这两种单倍体的离地和原位育性的检测，发现配子体不存在或很少存在的两种单倍体存在前合子不育性，这种前合子不育性可能与它们缺乏功能性孢子体有关。野外观察和生境调查表明，微生境条件可能与这种前合子不育有关。这些发现表明，更新世冰川时期的气候变化是否导致了非温带独立配子体蕨类植物的生态生理不适应。此外，本文还对种群水平上蕨类配子体独立性的分类提出了新的定义。我们期望对热带和亚热带蕨类配子体区系的进一步研究将进一步阐明非温带蕨类配子体独立性的生物地理意义。
Independent gametophyte ferns are unique among vascular plants because they are sporophyteless and reproduce asexually to maintain their populations in the gametophyte generation. Such ferns had been primarily discovered in temperate zone, and usually hypothesized with (sub)tropical origins and subsequent extinction of sporophyte due to climate change during glaciations. Presumably, independent fern gametophytes are unlikely to be distributed in tropics and subtropics because of relatively stable climates which are less affected by glaciations. Nonetheless, the current study presents cases of two independent gametophyte fern species in subtropic East Asia. In this study, we applied plastid DNA sequences (trnL-L-F and matK + ndhF + chlL datasets) and comprehensive sampling (similar to 80%) of congeneric species for molecular identification and divergence time estimation of these independent fern gametophytes. The two independent gametophyte ferns were found belonging to genus Haplopteris (vittarioids, Pteridaceae) and no genetic identical sporophyte species in East Asia. For one species, divergence times between its populations imply recent oversea dispersal(s) by spores occurred during Pleistocene. By examining their ex situ and in situ fertility, prezygotic sterility was found in these two Haplopteris, in which gametangia were not or very seldom observed, and this prezygotic sterility might attribute to their lacks of functional sporophytes. Our field observation and survey on their habitats suggest microhabitat conditions might attribute to this prezygotic sterility. These findings point to consideration of whether recent climate change during the Pleistocene glaciation resulted in ecophysiological maladaptation of non-temperate independent gametophyte ferns. In addition, we provided a new definition to classify fern gametophyte independences at the population level. We expect that continued investigations into tropical and subtropical fern gametophyte floras will further illustrate the biogeographic significance of non-temperate fern gametophyte independence.