Cryptic species of Asplenium nidus complex from the East Malesia region and their speciation process.

野蕨是东半球热带地区最常见的附生蕨类植物之一。它有简单的叶子，没有任何特殊的附属物，缺乏良好的物种识别可能是由于缺乏良好的分类特征。最近，我们对东马来半岛（马来半岛、苏门答腊、爪哇、婆罗洲）和马达加斯加的a .nidus进行了详细的遗传变异分析。我们收集了许多地区的叶片材料，确定了rbcL序列，并进行了人工杂交实验。我们在这些地区发现了大约50种隐种。利用杂交实验结果和杂交样品间rbcL序列的差异，探讨了该蕨类植物生殖隔离的进化过程。序列差越大，杂交实验得到的杂种数量越少。然而，在少数情况下，尽管rbcL差异很小，但生殖隔离很强。这可能意味着生殖屏障有时会很快形成。还观察到，只有当杂交的亲本种族中有一个是母亲时，才能获得杂种。这意味着生殖隔离只在一个杂交方向上形成。在果蝇中也观察到类似的现象，这被认为是由于负责基因编码在x染色体上。然而，蕨类植物，包括A.nidus是雌雄同体，它们不能有x染色体。因此，在蕨类植物中观察到这种单向亲和性是非常有趣的。

Asplenium nidus is one of the most common epiphytic fern species in the Old World tropics. It has simple leaves without any particular appendages, and the lack of good species recognition might be due to the lack of good taxonomic characters. Recently, we made a detailed analysis of the genetic variation of A.nidus in the East Malesia region (Malay peninsula, Sumatra, Java, Borneo) and Madagascar. We collected leaf materials from many localities and determined rbcL sequences and also made artificial crossing experiments. We found about 50 cryptic species in these regions. Using the results of crossing experiments and rbcL sequence differences between crossed samples, we also discussed evolutionary process of reproductive isolation in this fern group. As the sequence difference got larger, number of hybrids obtained through crossing experiments became smaller. However, in a few cases, reproductive isolation was strong even though rbcL difference was small. It might means reproductive barrier is sometimes formed quickly. It was also observed that hybrids were obtained only when one of the crossed parental race was mother. It means that reproductive isolation is formed only in one direction of crossing. Similar phenomena have been observed in Drosophila and this was considered due to that responsible genes are coded on X-chromosomes. However, ferns including A.nidus are hermaphrodites and they cannot have X-chromosomes. Therefore, it is very interesting that such the one directional crossability was observed in ferns.