Table of Contents

16 May 2012, Volume 50 Issue 3
Cover illustration: Evolution of the life cycle traced by a phylogeny. The filled gray cells are diploid and the open cells are haploid. F, fertilization; M, meiosis; MI, mitosis. See QIU et al., pp. 171–194 in this issue.
  • Yin-Long QIU, Alexander B. TAYLOR, Hilary A. MCMANUS
    J Syst Evol. 2012, 50(3): 171-194.
    All sexually reproducing eukaryotes have a life cycle consisting of a haploid and a diploid phase, marked by meiosis and syngamy (fertilization). Each phase is adapted to certain environmental conditions. In land plants, the recently reconstructed phylogeny indicates that the life cycle has evolved from a condition with a dominant free-living haploid gametophyte to one with a dominant free-living diploid sporophyte. The latter condition allows plants to produce more genotypic diversity by harnessing the diversity-generating power of meiosis and fertilization, and is selectively favored as more solar energy is fixed and fed into the biosystem on earth and the environment becomes more heterogeneous entropically. Liverworts occupy an important position for understanding the origin of the diploid generation in the life cycle of land plants. Hornworts and lycophytes represent critical extant transitional groups in the change from the gametophyte to the sporophyte as the independent free-living generation. Seed plants, with the most elaborate sporophyte and the most reduced gametophyte (except the megagametophyte in many gymnosperms), have the best developed sexual reproduction system that can be matched only by mammals among eukaryotes: an ancient and stable sex determination mechanism (heterospory) that enhances outcrossing, a highly bimodal and skewed distribution of sperm and egg numbers, a male-driven mutation system, female specialization in mutation selection and nourishment of the offspring, and well developed internal fertilization. The study of evolution of the land plant life cycle requires a multidisciplinary approach that considers morphology, development, genetics, phylogeny, ecology, and evolution in an integrated fashion, and will deepen our understanding of plant evolution.
  • Original Articles
  • Hui GAO, Dong-Mei GUO, Wen-Juan LIU, Jin-Hua RAN, Xiao-Quan WANG
    J Syst Evol. 2012, 50(3): 195-205.
    The 4-coumarate:coenzyme A ligase (4CL) is the branch point enzyme that channels the general phenylpropanoid metabolism into specific lignin and flavonoid biosynthesis branches. Genetic engineering experiments on the 4CL gene have been carried out in many species, but the precise functions of different gene members are still unresolved. To investigate the evolutionary relationships and functional differentiation of the 4CL gene family, we made a comprehensive evolutionary analysis of this gene family from 27 species representing the major lineages of land plants. The phylogenetic analysis indicates that both vascular and seed plant 4CL genes form monophyletic groups, and that three and two 4CL classes can be recognized in gymnosperms and angiosperms, respectively. The evolutionary rate and frequency of duplication of the 4CL gene family are much more conserved than that of the CAD/SAD (cinnamyl/sinapyl alcohol dehydrogenase) gene family, which catalyzes the last step in monolignol biosynthesis. This may be due to different selective pressures on these genes whose products catalyze different steps in the biosynthesis pathway. In addition, we found two new major classes of 4CL genes in gymnosperms.
  • Chen-Yang LIAO, Stephen R. DOWNIE, Yan YU, Xing-Jin HE
    J Syst Evol. 2012, 50(3): 206-217.
    Biogeographical patterns and diversification processes of Asia-centered angiosperm groups have been significantly affected by the multistage uplift of the Himalayas–Tibetan Plateau since the Late Tertiary. The divergence time of the largely East Asian Angelica group (Apiaceae, subfamily Apioideae, tribe Selineae) was initially analyzed using Beast and nrDNA internal transcribed spacer sequence data from 96 representatives of tribe Selineae and relatives. Further analyses of the biogeographical history of the Angelica group were carried out using Beast, S-Diva, Rasp, and Lagrange on datasets containing all or some of the following loci: nrDNA internal and external transcribed spacers; cpDNA rps16 intron; and cpDNA rps16-trnK, rpl32-trnL, and trnL-trnT intergenic spacers. The results suggested that the Angelica group was originally present in the East Palearctic during the global cooling of the late Middle Miocene (13.6 Mya) and that the Angelica s.s. clade originated in the same region at 10.2 Mya. Subsequent diversifications of the Angelica s.s. clade intensified in the East Palearctic during the middle Late Miocene (10.0–7.0 Mya) and in the eastern Himalayan Zone during the late Pliocene and Pleistocene (<4.0 Mya). These diversifications likely corresponded with plateau uplift-driven climatic changes. Considering elevational reconstructions, the differential responses to altitude appear to be the primary factor explaining the recent radiation of the group in the eastern Himalayas. The North American species of the Angelica group were retrieved as polyphyletic and their migrations involved six independent dispersals to North America at least since the middle Late Miocene, including four times from northeast Asia and twice from Europe.
  • Wen-Bin YU, De-Zhu LI, Hong WANG
    J Syst Evol. 2012, 50(3): 218-226.
    Pedicularis (Orobranchaceae) is a common high altitude genus of the Himalayas that may be affected by pollination limitation. Using Pedicularis lachnoglossa from Yulong (Jade Dragon) Snow Mountain in Lijiang (Yunnan Province, southwest China), we investigated the effects of high altitude habitats on the process of pollination and seed production. Floral biology, pollinator foraging behavior, breeding system, and pollination efficiency were examined using observation and exclusionary techniques. Pedicularis lachnoglossa was found to be entomophilous and exclusively pollinated by Bombus friseanus and B. yunnanicola. Our results indicated that pollination limitation in P. lachnoglossa was not significant. Under open pollination, approximately 80% of flowers were successfully pollinated and developed to fruits, and about 38% of ovules developed to mature seeds. Bumblebee pollination is highly precise and efficient in P. lachnoglossa, because its flowering phenology and floral characters enhance the foraging of bumblebees on flowers. This study supports that animal pollination plays a crucial role in the outbreeding of the early flowering Pedicularis. The evolution of floral specification in Pedicularis has the advantages of adaptation to bumblebee pollination in adverse high altitude habitats.
  • Jian-Ping HAN, Lin-Chun SHI, Xiao-Chen CHEN, Yu-Lin LIN
    J Syst Evol. 2012, 50(3): 227-234.
    Many species in the family Lamiaceae have been widely used for the treatment of coronary heart disease, stroke, and other conditions, and authenticating each of these species has become an important topic of research. Due to the lack of distinct phenotypic differences between the species, morphological identification is often inaccurate. In the third Consortium for the Barcode of Life, the combination of matK and rbcL was recommended as the universal barcode for plants, but this combination resolved only 70% of the species; the psbA-trnH intergenic region and internal transcribed spacer (ITS)/ITS2 were required for further study. In this study, we compared the sequences of the four candidate barcodes (matK, rbcL, ITS2, and psbA-trnH), among different species of Lamiaceae medicinal plants based on three selection criteria: intraspecific and interspecific genetic divergences; Wilcoxon signed-rank tests; and species identification ability. The results showed that ITS2 was the most variable region of the four tested barcodes. Of 672 samples collected from 314 species, ITS2 successfully identified 78.3% at the species level and 100% at the genus level. This strategy could widen the optimal range of divergence levels for the identification of Lamiaceae medicinal plants.
    J Syst Evol. 2012, 50(3): 235-243.
    We aimed to detect physiological characteristics that clearly varied among the closely-related Cladosporium sphaerospermum-like species. We isolated the fungi identified as C. sphaerospermum s.l. based on traditional morphological criteria from various locations and substrata, and redefined this initial identification by the molecular phylogenetic methods. The isolates were identified as only C. sphaerospermum and C. halotolerans. We analyzed the substrate-utilization of 95 carbon sources using the Biolog system and made statistical comparisons of isolates by their abilities to grow at different osmolarities. The substrate-utilization patterns separated the isolates into two groups corresponding to the molecular data, and the osmotolerance was different between the species. We first showed that C. sphaerospermum and C. halotolerans were diverse not only at the molecular level but also at the ecological and the physiological levels, by analyzing substrate-utilization patterns and osmotolerance. Furthermore, we showed the potential utility of the Biolog system for discriminating among closely-related fugal species.
  • Syed Mudassir JEELANI, Santosh KUMARI, Raghbir Chand GUPTA
    J Syst Evol. 2012, 50(3): 244-257.
    As a part of our program to explore and evaluate genetic diversity of flowering plants of the Kashmir Himalayas, meiotic studies have been carried out on 150 wild species. Of these, Caltha alba (2n= 32), Delphinium roylei (2n= 16), D. uncinatum (2n= 16), Ranunculus palmatifidus (2n= 28), and Sedum heterodontum (2n= 14) have been cytologically worked out for the first time. New intraspecific diploid or polyploid cytotypes have been recorded for Alchemilla vulgaris (2n= 34, 96), Arabis amplexicaulis (2n= 16), Impatiens amphorata (2n= 14), I. racemosa (2n= 12), I. sulcata (2n= 16, 12), Meconopsis latifolia (2n= 14), Potentilla supina (2n= 14), Saxifraga cernua (2n= 16), Sium latijugam (2n= 24), and Vicatia coniifolia (2n= 44). Four species, Arabidopsis thaliana (2n= 10), Berberis vulgaris (2n= 28), Potentilla nubicola (2n= 14), and P. sericea (2n= 28), have been cytologically reported for the first time from India. A large number of meiotic abnormalities have been observed in most of these species, leading to a reduction in pollen fertility and production of heterogeneous-sized pollen grains.
    J Syst Evol. 2012, 50(3): 258-266.
    Cambodian aquatic ecosystems are extremely diversified and constitute major preservation targets. However, the species composition, diversity, and distribution of the inhabiting algal communities are largely unknown. During a sample collection carried out in the Angkor and Banteay Srei monuments area in 2010, several unknown diatom taxa were found in various population densities in the artificial lakes surrounding these temples. Detailed light and scanning electron microscopy observations allowed the description of five of them (Pinnularia cambodiana, P. shivae, Gomphonema angkoricum, G. paradaphnoides, and Frustulia lacus-templi) as taxa new to science. Differential diagnostic criteria with respect to similar taxa, together with the ecological and environmental implications of these findings, are briefly discussed.