Functional Androdioecy in Critically Endangered Gymnocladus assamicus (Leguminosae) in the Eastern Himalayan Region of Northeast India
Dayanandan S (2014) Functional Androdioecy in Critically Endangered Gymnocladus assamicus (Leguminosae) in the Eastern
Himalayan Region of Northeast India. PLoS ONE 9(2): e87287. doi:10.1371/journal.pone.0087287
Functional Androdioecy in Critically Endangered Gymnocladus assamicus (Leguminosae) in the Eastern Himalayan Region of Northeast India
Baharul Islam Choudhury 0
Mohammed Latif Khan 0
Selvadurai Dayanandan 0
Kamal Bawa, University of Massachusetts, United States of America
0 1 Forest and Evolutionary Genomics Laboratory, and Centre for Structural and Functional Genomics, Biology Department, Concordia University , Quebec , Canada , 2 Que bec Centre for Biodiversity Sciences , Montre al, Quebec , Canada , 3 Department of Forestry, North Eastern Regional Institute of Science & Technology , Nirjuli, Arunachal Pradesh , India
Gymnocladus assamicus is a critically endangered tree species endemic to Northeast India, and shows sexual dimorphism with male and hermaphrodite flowers on separate trees. We studied phenology, reproductive biology and mating system of the species. The flowers are small, tubular, odorless and last for about 96 hours. Pollen grains in both morphs were viable and capable of fertilization leading to fruit and seed set. Scanning electron micrographs revealed morphologically similar pollen in both male and hermaphrodite flowers. The fruit set in open pollinated flowers was 43.61 percent, while controlled autogamous and geitonogamous pollinations yielded 76.81 and 65.58 percent fruit set respectively. Xenogamous pollinations between male and hermaphrodite flowers resulted in 56.85 percent fruit set and pollinations between hermaphrodite flowers yielded 67.90 percent fruit set. This indicates a functionally androdioecious mating system and pollination limited fruit set in G. assamicus. Phylogenetic analyses of Gymnocladus and the sister genus Gleditsia are needed to assess if the androdioecious mating system in G. assamicus evolved from dioecy as a result of selection for hermaphrodites for reproductive assurance during colonization of pollination limited high altitude ecosystems.
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Funding: This work was supported by Department of Science and Technology, New Delhi (Sanction no. SR/SO/PS-16/2002) to M.L.K. Partial support of FRQNT
and NSERC to BC and SD is greatly acknowledged. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the
manuscript.
Competing Interests: The authors have declared that no competing interests exist.
The tree genus Gymnocladus (Leguminosae) comprises five species
[1] distributed in the Eastern North America and Eastern Asia [2],
and considered to have originated in the Eastern Asia during the
Eocene and migrated across the Bering land bridge to North
America [4]. G. diocus (L.) K. Koch is restricted to North America,
while G. angustifolius (Gagnep.) J.E. Vidal is confined to Vietnam.
The remaining three species, G. chinensis Baill., G. assamicus Kanjilal
ex P.C. Kanjilal and G. burmanicus Parkinson are distributed in the
region bordering India, China and Myanmar (Burma). The
geographical ranges of G. assamicus and G. chinensis within India are
restricted to the Northeastern states [3]. G. assamicus is a critically
endangered tree species with declining populations [5]. Extensive
field surveys and environmental niche modelling (ENM) studies
revealed existence of only a few remnant populations of the species
confined to moist areas on hilly slopes and stream banks in the
West Kameng and Tawang districts of Arunachal Pradesh [6].
The mating system of the genus Gymnocladus has been broadly
described as polygamous, unisexual, bisexual or dioecious [79].
Although G. chinensis is considered as a polygamous species [7], no
detailed studies on floral biology or the breeding system of
Gymnocladus species exist. We studied floral biology of G. assamicus
and discovered an androdioecious mating system where male and
hermaphrodite flowers are produced on separate trees.
Androdioecy is a rare mating system [1012], and since Darwins [14]
original report on the androdioecy, no reliable evidence for the
occurrence of androdioecy was reported until 1922 [13]. To date,
about 50 plants and 36 animal species have been described as
androdioecious [15]. In contrast, dioecy (occurrence of male and
female plants) and gynodioecy (occurrence of female and
hermaphrodite plants) are known to occur in approximately 6%
[16] and 10% [17] of angiosperms respectively. Since the first
confirmed report of androdioecy in Datisca glomerata (Datiscaceae)
[18], several reports of androdioecy have been published [12,19
22]. During the last two decades, several plant species have been
described as androdioecious on the basis of morphology. However,
detailed studies have revealed that many such species are
functionally dioecious or cryptic dioecy with sterile pollen in
morphologically hermaphroditic flowers [23]. Only few plant
species inclu (...truncated)