Bing Hong Huang

Changes of diet and dominant intestinal microbes in farmland frogs

BackgroundAgricultural activities inevitably result in anthropogenic interference with natural habitats. The diet and the gut microbiota of farmland wildlife can be altered due to the changes in food webs within agricultural ecosystems. In this work, we compared the diet and intestinal microbiota of the frog Fejervarya limnocharis in natural and farmland habitats in order to understand how custom farming affects the health of in vivo microbial ecosystems.ResultsThe occurrence, abundance, and the numbers of prey categories of stomach content were significantly different between the frogs inhabiting natural and farmland habitats. In addition, differences in the abundance, species richness, and alpha-diversity of intestinal microbial communities were also statistically significant. The microbial composition, and particularly the composition of dominant microbes living in intestines, indicated that the land use practices might be one of factors affecting the gut microbial community composition. Although the first three dominant microbial phyla Bacteroidetes, Firmicutes, and Proteobacteria found in the intestines of frogs were classified as generalists among habitats, the most dominant gut bacterial phylum Bacteroidetes in natural environments was replaced by the microbial phylum Firmicutes in farmland frogs. Increased intestinal microbial richness of the farmland frogs, which is mostly contributed by numerous microbial species of Proteobacteria, Actinobacteria, Acidobacteria, and Planctomycetes, not only reflects the possible shifts in microbial community composition through the alteration of external ecosystem, but also indicates the higher risk of invasion by disease-related microbes.ConclusionsThis study indicates that anthropogenic activities, such as the custom farming, have not only affected the food resources of frogs, but also influenced the health and in vivo microbial ecosystem of wildlife.

Diversification, Biogeographic Pattern, and Demographic History of Taiwanese Scutellaria Species Inferred from Nuclear and Chloroplast DNA

The ragged topography created by orogenesis generates diversified habitats for plants in Taiwan. In addition to colonization from nearby mainland China, high species diversity and endemism of plants is also present in Taiwan. Five of the seven Scutellaria species (Lamiaceae) in Taiwan, for example, are endemic to the island. Hypotheses of multiple sources or in situ radiation have arisen to explain the high endemism of Taiwanese species. In this study, phylogenetic analyses using both nuclear and chloroplast markers revealed the multiple sources of Taiwanese Scutellaria species and confirmed the rapid and recent speciation of endemic species, especially those of the “indica group” composed of S. indica, S. austrotaiwanensis, S. tashiroi, and S. playfairii. The common ancestors of the indica group colonized first in northern Taiwan and dispersed regionally southward and eastward. Climate changes during glacial/interglacial cycles led to gradual colonization and variance events in the ancestors of these species, resulting in the present distribution and genetic differentiation of extant populations. Population decline was also detected in S. indica, which might reflect a bottleneck effect from the glacials. In contrast, the recently speciated endemic members of the indica group have not had enough time to accumulate much genetic variation and are thus genetically insensitive to demographic fluctuations, but the extant lineages were spatially expanded in the coalescent process. This study integrated phylogenetic and population genetic analyses to illustrate the evolutionary history of Taiwanese Scutellaria of high endemism and may be indicative of the diversification mechanism of plants on continental islands.

Population genetic structure, local adaptation, and conservation genetics of Kandelia obovata

Topographic changes during the Pleistocene glacial/interglacial cycles affected the distribution of coastline mangroves and influenced their population genetic structure. The submergence of the continental shelf off southeast China during the postglacial age caused coastline expansions and resulted in the colonization of mangroves. Here, we performed multilocus genome scans using amplified fragment-length polymorphisms to explore the effects of topography and natural selection in structuring Kandelia obovata populations. Long-term isolation by the Taiwan Strait since the end of the last glacial maximum, which obstructed gene flow, differentiated the Taiwanese and Chinese populations. Founders that colonized from both outlets of the Taiwan Strait were sourced from the northern South China Sea and the Ryukyus, thereby creating a melting pot in the Taiwan Strait. Inner-strait currents played roles as vectors for propagule dispersal among populations. Upon examination of the allele-frequency distributions of outlier loci, most negative outliers reflected the widespread polymorphisms shared by common ancestors. Furthermore, significant differentiation in the genetic components of positive outliers between this and other populations and the negative correlation with geographic distance suggested the presence of geography- or latitude-independent population divergence. Restored populations were compared with their sources and revealed biased sampling of nursery seedlings, which caused within-population substructures and reduced effective population sizes. This study indicated that multiple factors affect the population structure of the mangroves off southeast China.

Genetic relationships and ecological divergence in Salix species and populations in Taiwan

Linking ecology with evolutionary biology is important to understand how environments drive population and species divergence. Phenotypically diverse Salix species, such as lowland riparian willow trees and middle- to high-elevation multistemmed shrubs and alpine dwarf shrubs, provide opportunities for studying genetic divergence driven by ecological factors. We used amplified fragment length polymorphism (AFLP) to quantify the genetic variation of 185 individuals from nine populations of four Salix species in Taiwan. Our phylogenetic analyses distinguished two riparian species and the separation of riparian species from multistemmed and dwarf shrub species. Variance partitioning for the total data found that environment explained a substantially larger proportion of genetic variation than geography. However, no genetic variation was explained by geography alone when only compared within and between species. Spatially structured regional environmental effects explained more variation than pure environments in most comparisons within and between species, suggesting that unmeasured environmental variables and/or past demographic histories played important roles in shaping population and species divergence. Based on forward selection analysis, annual mean temperature, aspect, and fraction of absorbed photosynthetically active radiation were the most influential ecological factors in shaping genetic variation within and between species. Nevertheless, different combinations of environmental variables correlated significantly with genetic variation within and between species. We identified eight AFLP loci that potentially evolved under selection intraspecifically using different outlier detection methods. These loci correlated with more than one environmental variable, suggesting local adaptation along environmental gradients at the population level.

Asymmetric Introgression in the Horticultural Living Fossil Cycas Sect. Asiorientales Using a Genome-Wide Scanning Approach

The Asian cycads are mostly allopatric, distributed in small population sizes. Hybridization between allopatric species provides clues in determining the mechanism of species divergence. Horticultural introduction provides the chance of interspecific gene flow between allopatric species. Two allopatrically eastern Asian Cycas sect. Asiorientales species, C. revoluta and C. taitungensis, which are widely distributed in Ryukyus and Fujian Province and endemic to Taiwan, respectively, were planted in eastern Taiwan for horticultural reason. Higher degrees of genetic admixture in cultivated samples than wild populations in both cycad species were detected based on multilocus scans by neutral AFLP markers. Furthermore, bidirectional but asymmetric introgression by horticultural introduction of C. revoluta is evidenced by the reanalyses of species associated loci, which are assumed to be diverged after species divergence. Partial loci introgressed from native cycad to the invaders were also detected at the loci of strong species association. Consistent results tested by all neutral loci, and the species-associated loci, specify the recent introgression from the paradox of sharing of ancestral polymorphisms. Phenomenon of introgression of cultivated cycads implies niche conservation among two geographic-isolated cycads, even though the habitats of the extant wild populations of two species are distinct.

Recurrent positive selection and heterogeneous codon usage bias events leading to coexistence of divergent pigeon circoviruses.

The capsid genes from 14 pigeon circovirus (PiCV) sequences, collected from Taiwan between 2009 and 2010, were sequenced and compared with 14 PiCV capsid gene sequences from GenBank. Based on pairwise comparison, PiCV strains from Taiwan shared 73.9-100% nucleotide identity and 72-100% amino acid identity with those of the 14 reported PiCV sequences. Phylogenetic analyses revealed that Taiwanese PiCV isolates can be grouped into two clades: clade 1 comprising isolates from Belgium, Australia, USA, Italy and China, and clade 2 showing close relation to isolates from Germany and France. Recurrent positive selection was detected in clade 1 PiCV lineages, which may contribute to the diversification of predominant PiCV sequences in Taiwan. Further observations suggest that synonymous codon usage variations between PiCV clade 1 and clade 2 may reflect the adaptive divergence on translation efficiency of capsid genes in infectious hosts. Variation in selective pressures acting on the evolutionary divergence and codon usage bias of both clades explains the regional coexistence of virus sequences congeners prevented from competitive exclusion within an island such as Taiwan. Our genotyping results also provide insight into the aetiological agents of PiCV outbreak in Taiwan and we present a comparative analysis of the central coding region of PiCV genome. From the sequence comparison results of 28 PiCVs which differs in regard to the geographical origin and columbid species, we identified conserved regions within the capsid gene that are likely to be suitable for primer selection and vaccine development.

Positive Selection and Functional Divergence of R2R3-MYB Paralogous Genes Expressed in Inflorescence Buds of Scutellaria Species (Labiatae)

Anthocyanin is the main pigment forming floral diversity. Several transcription factors that regulate the expression of anthocyanin biosynthetic genes belong to the R2R3-MYB family. Here we examined the transcriptomes of inflorescence buds of Scutellaria species (skullcaps), identified the expression R2R3-MYBs, and detected the genetic signatures of positive selection for adaptive divergence across the rapidly evolving skullcaps. In the inflorescence buds, seven R2R3-MYBs were identified. MYB11 and MYB16 were detected to be positively selected. The signature of positive selection on MYB genes indicated that species diversification could be affected by transcriptional regulation, rather than at the translational level. When comparing among the background lineages of Arabidopsis, tomato, rice, and Amborella, heterogeneous evolutionary rates were detected among MYB paralogs, especially between MYB13 and MYB19. Significantly different evolutionary rates were also evidenced by type-I functional divergence between MYB13 and MYB19, and the accelerated evolutionary rates in MYB19, implied the acquisition of novel functions. Another paralogous pair, MYB2/7 and MYB11, revealed significant radical amino acid changes, indicating divergence in the regulation of different anthocyanin-biosynthetic enzymes. Our findings not only showed that Scutellaria R2R3-MYBs are functionally divergent and positively selected, but also indicated the adaptive relevance of regulatory genes in floral diversification.

Tracing evolutionary relicts of positive selection on eight malaria-related immune genes in mammals

Plasmodium-induced malaria widely infects primates and other mammals. Multiple past studies have revealed that positive selection could be the main evolutionary force triggering the genetic diversity of anti-malaria resistance-associated genes in human or primates. However, researchers focused most of their attention on the infra-generic and intra-specific genome evolution rather than analyzing the complete evolutionary history of mammals. Here we extend previous research by testing the evolutionary link of natural selection on eight candidate genes associated with malaria resistance in mammals. Three of the eight genes were detected to be affected by recombination, including TNF-α, iNOS and DARC. Positive selection was detected in the rest five immunogenes multiple times in different ancestral lineages of extant species throughout the mammalian evolution. Signals of positive selection were exposed in four malaria-related immunogenes in primates: CCL2, IL-10, HO1 and CD36. However, selection signals of G6PD have only been detected in non-primate eutherians. Significantly higher evolutionary rates and more radical amino acid replacement were also detected in primate CD36, suggesting its functional divergence from other eutherians. Prevalent positive selection throughout the evolutionary trajectory of mammalian malaria-related genes supports the arms race evolutionary hypothesis of host genetic response of mammalian immunogenes to infectious pathogens.

Characterization of 24 transferable microsatellite loci in four skullcaps (Scutellaria, Labiatae)

PREMISE OF THE STUDY Transferable polymorphic microsatellite loci for four skullcaps, Scutellaria indica, S. taiwanensis, S. austrotaiwanensis, and S. playfairii, were developed for future studies of the mating system and population structure of these species. Interspecific amplification was also tested in various Scutellaria species. METHODS AND RESULTS Twelve novel polymorphic microsatellite loci were isolated from four S. taiwanensis specimens, and seven are interspecifically transferable. Microsatellite loci developed from S. austrotaiwanensis in a previous study were also analyzed in the other three species, and 12 loci were found to be transferable. Allele numbers of the total 24 loci for S. indica, S. taiwanensis, S. playfairii, and S. austrotaiwanensis are two to four, two, two to five, and two to three, respectively, with an expected heterozygosity ranging from 0.114-0.661, 0.062-0.499, 0.280-0.730, and 0.268-0.662, respectively. The interspecies transferability of these 24 loci was further tested in another 10 Scutellaria species, including three species native to Taiwan. Seventeen loci were found to be interspecifically amplifiable, especially among the Taiwan native species. CONCLUSIONS These highly polymorphic and transferable loci will be useful for future studies of the mating system of closely related Scutellaria species.

Continuation of the genetic divergence of ecological speciation by spatial environmental heterogeneity in island endemic plants

Divergent selection plays a critical role not only as a speciation driver but also in maintaining post-speciation divergence. In the absence of direct evidence, ancestral interspecific gene flow between incipient species can reflect ancient selective pressure for ecological speciation. In the present study, two late-Pleistocene diverged species endemic to Taiwan, Scutellaria playfairii and S. tashiroi, were spatially and ecologically partitioned with partial overlap. Multilocus genome-scan analyses and in silico evaluation revealed ancestral interspecific gene flow but distinct genetic compositions, implying that adaptive divergence contributed to their speciation. Ecological niche modeling and principal component analysis suggested incomplete divergent niches between the two species; the species distribution is therefore consistent with Hutchinson’s metaphor of multidimensional hypervolume niches rather than attributable to a single factor. Constraint ordination analysis supported this inference of a combination of variables explaining the genetic structure. The rare occurrence of hybrids in the sympatric population suggested hybrid breakdown, providing further evidence of divergent selection blocking gene flow. The correlation of environmental variables with integrated genetic components demonstrated that environmental heterogeneity maintains the species and population differentiation. This study highlights the importance of environmental heterogeneity and divergent selection for the rapid speciation and recent diversification of island plants.