Perley Danielle S, Jesson Linley K
Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, Canada E3B5A3.
Department of Biology, University of New Brunswick, 10 Bailey Dr, Fredericton, Canada E3B5A3 Faculty of Biology, University of Marburg, Karl-von-Frisch-Str. 8, D-35043 Marburg, Germany.
Am J Bot. 2015 Apr;102(4):555-65. doi: 10.3732/ajb.1400494. Epub 2015 Apr 6.
Over 50% of bryophytes have separate sexes, and numerous transitions have occurred between combined and separate sexes. Polyploidy and hybridization is one proximate mechanism hypothesized to cause evolutionary transitions to hermaphroditism in bryophytes because sex is expressed at the haploid stage and in nonpolyploid dioecious species males have a single V chromosome and females a U. Hermaphroditism can arise if gametophytes of allopolyploids have both U and V chromosomes. We examined the association between polyploidy and hermaphroditism in the bryophyte genus Atrichum, which has species where gametophytes can be haploid, diploid, or triploid, and some species have hermaphroditic individuals.
We generated phylogenies of Atrichum from sequences of three plastid regions (rbcL, rps4, and trnL-trnF) and the second intron for the nuclear gene Leafy/Floricaula to further understand the relationships among haploid, diploid, and triploid species, and those with combined or separate sexes.
The existence of multiple sequences of Leafy/Floricaula in diploid and triploid, but not haploid, individuals is consistent with independent allopolyploid origins of the diploid and triploid species. Allopolyploidy was associated with a likely gain in hermaphroditism in triploid Atrichum undulatum and possibly diploid A. altecristatum, but not in the allopolyploid A. crispulum (diploid at the gametophyte level).
These results highlight a role for hybridization and polyploidy in sexual system evolution, but the presence of diploid (allopolyploid) dioecious species suggest that other factors may influence the maintenance of sexual systems after an evolutionary transition.
超过50%的苔藓植物具有不同的性别，并且在两性融合和性别分离之间发生了多次转变。多倍体和杂交是一种被认为导致苔藓植物向雌雄同体进化转变的直接机制，因为性别在单倍体阶段表达，并且在非多倍体雌雄异株物种中，雄性有一条V染色体，雌性有一条U染色体。如果异源多倍体的配子体同时具有U和V染色体，就会产生雌雄同体现象。我们研究了苔藓植物仙鹤藓属中多倍体与雌雄同体之间的关联，该属物种的配子体可以是单倍体、二倍体或三倍体，并且有些物种存在雌雄同体的个体。
我们根据三个叶绿体区域（rbcL、rps4和trnL-trnF）的序列以及核基因叶状/花椰菜基因的第二个内含子构建了仙鹤藓属的系统发育树，以进一步了解单倍体、二倍体和三倍体物种之间以及具有两性融合或性别分离的物种之间的关系。
在二倍体和三倍体个体中存在多个叶状/花椰菜基因序列，但单倍体个体中没有，这与二倍体和三倍体物种独立的异源多倍体起源一致。异源多倍体与三倍体波叶仙鹤藓以及可能的二倍体高褶仙鹤藓中雌雄同体现象可能性的增加有关，但在配子体水平为二倍体的异源多倍体皱叶仙鹤藓中并非如此。
这些结果突出了杂交和多倍体在性系统进化中的作用，但二倍体（异源多倍体）雌雄异株物种的存在表明，在进化转变后，其他因素可能会影响性系统的维持。
