64
N. Murakami et al.
4 Discussion
We found three rbeL sequence types among plants from a small area of Mt. Halimun
National Park which were all identified as A. nidus according to Holttum's (1974)
classification. Based on the molecular phylogenetic tree obtained, it was determined
that these three rbeL types are distantly related to each other. Thus, their origin is
certainly old, and it is not likely that they recently speciated in Mt. Halimun.
In this work, the three rbeL types were found to have different ecological preferences as well. The types A and B mixed on Mt. Halimun, but even in sympatric
populations, their habitats were differentiated as to their relative position on tree
trunks. The type C occurs mostly parapatrically, with distribution at higher elevations. Distances among the populations were within a range of a few km, and therefore gene exchange through spores between the populations of C and the other two
rbeL types should happen frequently. There was no better evidence of their
dispersability than the fact that the type C was also distributed at mid-elevations
(1400-1900 m) of Mt. Gede, which is 50-60 km apart from Mt. Halimun. Still,
their ecological preferences arc recognizable, and we can conclude that the three
rbeL types have different niches.
Thus, these three rbeL types are both genetically and ecologically differentiated. They have been treated as conspecific so far because it is difficult to distinguish them only by morphology. However, it is evident that biologically they belong to different entities, and should be taxonomically treated as three separate
species.
In the present study, we showed sequence variations of the rbeL gene even in a
fern species complex which is morphologically hard to distinguish. Based on this
information, we concluded that the three rbeL types found in Mt. Halimun belong
to ditferent biological units. It is becoming easier to determine partial sequences of
particular genes. Such molecular techniques are useful even for monographic works
which try to delimit species, especially morphologically similar taxa like ferns.
Ecological (habitat) comparison is also a powerful method to recognize different biological units with similar morphology, especially when they are sympatrically distributed. Murakami and Moran (1993) recognized four species of the
Hymenasplenium obtusifolium complex (H. obtusifolium, H. riparium, H.
repandulum, H. volubile) based on their differentiated habitats (subaquatic,
Iithophytic, epiphytic on large tree trunks, and epiphytic on thin trees, respectivcly)
in addition to morphological and molecular (restriction fragment length polymorphism analysis of whole chloroplast DNA) data of their mixed populations in
Panama. Murakami et a1. (1998) distinguished a new species H. inthanonense from
the most closely related species, H. eheilosorum, using habitat differentiation in
addition to morphological and molecular (rbeL nucleotide sequences) information.
If populations defined by molecular markers belong to different biological units,
they should also have differentiated niches. Otherwise, they would not be able to
coexist for a long time in nature. Searching for coincidence between molecular and
N. Murakami et al.
4 Discussion
We found three rbeL sequence types among plants from a small area of Mt. Halimun
National Park which were all identified as A. nidus according to Holttum's (1974)
classification. Based on the molecular phylogenetic tree obtained, it was determined
that these three rbeL types are distantly related to each other. Thus, their origin is
certainly old, and it is not likely that they recently speciated in Mt. Halimun.
In this work, the three rbeL types were found to have different ecological preferences as well. The types A and B mixed on Mt. Halimun, but even in sympatric
populations, their habitats were differentiated as to their relative position on tree
trunks. The type C occurs mostly parapatrically, with distribution at higher elevations. Distances among the populations were within a range of a few km, and therefore gene exchange through spores between the populations of C and the other two
rbeL types should happen frequently. There was no better evidence of their
dispersability than the fact that the type C was also distributed at mid-elevations
(1400-1900 m) of Mt. Gede, which is 50-60 km apart from Mt. Halimun. Still,
their ecological preferences arc recognizable, and we can conclude that the three
rbeL types have different niches.
Thus, these three rbeL types are both genetically and ecologically differentiated. They have been treated as conspecific so far because it is difficult to distinguish them only by morphology. However, it is evident that biologically they belong to different entities, and should be taxonomically treated as three separate
species.
In the present study, we showed sequence variations of the rbeL gene even in a
fern species complex which is morphologically hard to distinguish. Based on this
information, we concluded that the three rbeL types found in Mt. Halimun belong
to ditferent biological units. It is becoming easier to determine partial sequences of
particular genes. Such molecular techniques are useful even for monographic works
which try to delimit species, especially morphologically similar taxa like ferns.
Ecological (habitat) comparison is also a powerful method to recognize different biological units with similar morphology, especially when they are sympatrically distributed. Murakami and Moran (1993) recognized four species of the
Hymenasplenium obtusifolium complex (H. obtusifolium, H. riparium, H.
repandulum, H. volubile) based on their differentiated habitats (subaquatic,
Iithophytic, epiphytic on large tree trunks, and epiphytic on thin trees, respectivcly)
in addition to morphological and molecular (restriction fragment length polymorphism analysis of whole chloroplast DNA) data of their mixed populations in
Panama. Murakami et a1. (1998) distinguished a new species H. inthanonense from
the most closely related species, H. eheilosorum, using habitat differentiation in
addition to morphological and molecular (rbeL nucleotide sequences) information.
If populations defined by molecular markers belong to different biological units,
they should also have differentiated niches. Otherwise, they would not be able to
coexist for a long time in nature. Searching for coincidence between molecular and