Indigenous Congener Research Articles

Comparative analysis of mitochondrial genomes of invasive weed Mikania micrantha and its indigenous congener Mikania cordata

Mikania micrantha and Mikania cordata are two distinct species in China. The former is notorious as one of the top 100 worst invasive species, whereas the latter is an indigenous species harmless to native plants or the environment. They form an ideal congener pair for comparative studies aimed at deeply understanding the invasion mechanisms of the exotic weed. In this study, we have assembled and annotated the mitogenomes of both species using Illumina and PacBio sequencing data and compared their characteristic differences. The complete mitogenome of M. micrantha is a double-stranded DNA with a length of 336,564 bp, while the mitogenome of M. cordata exhibits a branching structure, consisting of two small circular molecules and six linear molecules, with a combined length totaling 335,444 bp. Compared to M. cordata, M. micrantha has less SSRs, tandem repeats, dispersed repeats, mitochondrial protein coding genes (PCGs). The two plants show similar codon usage patterns. This comparative study has revealed the structure and function of the mitogenomes of the two species and laid a solid foundation for investigating the effects of gene loss and duplication on the development of invasive traits in M. micrantha.

Phytoremediation potential of hybrids of the exotic plant Xanthium strumarium and its native congener Xanthium sibiricum for cadmium-contaminated soils

Exotic plants could play an essential role in the restoration of heavy metal-contaminated soil. This study evaluated the tolerance of and extraction of cadmium (Cd) by ZCR (CR♀ × LT♂), hybrids of Xanthium strumarium (LT, exotic species) and X. sibiricum (CR, indigenous congener), and their parental species under different Cd treatments (0, 10, 40, and 80 mg·kg−1). The results showed that the hybrids had significantly improved tolerance to Cd. Under Cd stress, the biomass of ZCR increased by more than 50% on average compared with that of CR. Moreover, the hybrids showed a more remarkable ability to transport Cd from the root to the shoot. The Cd content of the shoots of ZCR increased by 128.33, 147.22, and 252.63% when treated with 10, 40, and 80 mg·kg−1 Cd, respectively. ZCR stored more than 70% of Cd in litter leaves, thereby reducing the toxic effects of Cd on photosynthesis and growth. The results showed that ZCR showed excellent Cd tolerance and enrichment in the presence of Cd. The hybrids of Xanthium strumarium and its native congener X. sibiricum may remediate soil Cd pollution. Novelty statement With the changing world economy and increasing human activities, exotic plants have become a global issue of common concern to the international community. This study describes new findings on using hybrids of the exotic plant of Xanthium strumarium and its native congener Xanthium sibiricum for the restoration of cadmium-contaminated soils. Under Cd stress, the hybrids' biomass, tolerance, and ability to accumulate Cd were significantly higher than that of X. sibiricum, indicating that hybrids gained useful heavy metal extraction traits from X. strumarium.

Comparison of the Ability to Control Water Loss in the Detached Leaves of Wedelia trilobata, Wedelia chinensis, and Their Hybrid.

In the process of biological invasion, hybridization between invasive species and native species is very common, which may lead to the formation of hybrids with a stronger adaptability. The hybrid of Wedelia trilobata (an alien invasive species) and Wedelia chinensis (an indigenous congener) has been found in South China. In our previous study, we found that the hybrid showed heterosis under cadmium stress. However, the results of this experiment demonstrated that the leaves of the hybrid had no heterosis in controlling water loss. The results showed that the water loss rate of W. trilobata was the slowest, that of W. chinensis was the fastest, and that of the hybrid was in the middle. Compared with W. chinensis and the hybrid, W. trilobata accumulated more abscisic acid (ABA) in leaves to control water loss. After the leaves were detached, W. chinensis leaves suffered the most serious damage, the lowest maximum photochemical efficiency, the most serious membrane lipid peroxidation, and the largest accumulation of malondialdehyde and reactive oxygen species. Compared with W. chinensis and its hybrid, the leaves of W. trilobata could accumulate more antioxidant enzymes and antioxidants, and the total antioxidant capacity was the strongest. The results demonstrate that the ability of the hybrid to reduce water loss was lower than that of W. trilobata, but higher than that of W. chinensis. They showed that the drought resistance of the hybrid may be higher than that of W. chinensis, and it might threaten the survival of W. chinensis.

Full-length transcriptome analysis of Phytolacca americana and its congener P. icosandra and gene expression normalization in three Phytolaccaceae species

BackgroundPhytolaccaceae species in China are not only ornamental plants but also perennial herbs that are closely related to human health. However, both large-scale full-length cDNA sequencing and reference gene validation of Phytolaccaceae members are still lacking. Therefore, single-molecule real-time sequencing technology was employed to generate full-length transcriptome in invasive Phytolacca americana and non-invasive exotic P. icosandra. Based on the transcriptome data, RT-qPCR was employed to evaluate the gene expression stability in the two plant species and another indigenous congener P. acinosa.ResultsTotal of 19.96 Gb and 19.75 Gb clean reads of P. americana and P. icosandra were generated, including 200,857 and 208,865 full length non-chimeric (FLNC) reads, respectively. Transcript clustering analysis of FLNC reads identified 89,082 and 98,448 consensus isoforms, including 86,989 and 96,764 high-quality ones. After removing redundant reads, 46,369 and 50,220 transcripts were obtained. Based on structure analysis, total 1675 and 1908 alternative splicing variants, 25,641 and 31,800 simple sequence repeats (SSR) as well as 34,971 and 36,841 complete coding sequences were detected separately. Furthermore, 3574 and 3833 lncRNA were predicted and 41,676 and 45,050 transcripts were annotated respectively. Subsequently, seven reference genes in the two plant species and a native species P. acinosa were selected and evaluated by RT-qPCR for gene expression analysis. When tested in different tissues (leaves, stems, roots and flowers), 18S rRNA showed the highest stability in P. americana, whether infested by Spodoptera litura or not. EF2 had the most stable expression in P. icosandra, while EF1-α was the most appropriate one when attacked by S. litura. EF1-α showed the highest stability in P.acinosa, whereas GAPDH was recommended when infested by S. litura. Moreover, EF1-α was the most stable one among the three plant species whenever germinating seeds or flowers only were considered.ConclusionFull-length transcriptome of P. americana and P. icosandra were produced individually. Based on the transcriptome data, the expression stability of seven candidate reference genes under different experimental conditions was evaluated. These results would facilitate further exploration of functional and comparative genomic studies in Phytolaccaceae and provide insights into invasion success of P. americana.

The hybridization between Sphagneticola trilobata (L.) Pruski and Sphagneticola calendulacea (L.) Pruski improved the tolerance of hybrid to cadmium stress

Hybridization is common between invasive and native species and may be accompanied by invasive evolution. The hybrid of Sphagneticola trilobata (alien invasive species) and Sphagneticola calendulacea (indigenous congener) was found in South China. According to previous studies, the hybrid performed weak environmental adaptability in comparison with parents. However, based on the results from this study, the hybridization significantly improved the tolerance of the hybrid to cadmium (Cd) stress (200 μmol L−1). Under Cd stress, the hybrid lines showed lowest level of oxidative damage and the highest level of photosynthetic efficiency. Compared with the parents, the hybrid utilized more active detoxification strategies, such as the cell walls of the leaves and roots adsorbed 88% and 95% Cd, respectively, reducing the amount of Cd entering cells; moreover, most of the Cd that entered cells was transformed into less toxic chemical forms through the reduction of the highly toxic chemical forms; furthermore, it accumulated a large number of phytochelatins to bind Cd2+ and reduced the damage of organelles by Cd2+. The results demonstrate that hybridization between S. trilobata and S. calendulacea improved the adaptability of the new hybrid species to Cd stress and may pose a greater threat to the survival of the native parent species in the presence of serious water and soil pollution.

Comparative chloroplast genomics between the invasive weed Mikania micrantha and its indigenous congener Mikania cordata: Structure variation, identification of highly divergent regions, divergence time estimation, and phylogenetic analysis

Mikania micrantha and Mikania cordata are the only two species in genus Mikania (Asteraceae) in China. They share very similar morphological and life-history characteristics but occupy quite different habitats. Most importantly, they generate totally different ecological consequences. While M. micrantha has become an exotic invasive weed, M. cordata exists as an indigenous species with no harmful effects on native plants or habitats. As a continuous study of our previously reported M. micrantha chloroplast (cp) genome, in this study we have further sequenced the M. cordata cp genome to (1) conduct a comparative genome analysis to gain insights into the mechanism of invasiveness; (2) develop cp markers to examine the population genetic adaptation of M. micrantha; and (3) screen variable genome regions of phylogenetic utility. The M. cordata chloroplast genome is 151,984 bp in length and displays a typical quadripartite structure. The number and distribution of protein coding genes, tRNA genes, and rRNA genes of M. cordata are identical to those of M. micrantha. The main difference lays in that the pseudogenization of ndhF and a 118-bp palindromic repeat only arises in M. cordata. Fourteen highly divergent regions, 235 base substitutions, and 58 indels were identified between the two cp genomes. Phylogenetic inferences revealed a sister relationship between M. micrantha and M. cordata whose divergence was estimated to occur around 1.78 million years ago (MYA). Twelve cpSSR loci were detected to be polymorphic and adopted to survey the genetic adaptation of M. micrantha populations. No cpSSR loci were found to undergo selection. Our results build a foundation to examine the invasive mechanism of Mikania weed.

Comparative analysis of growth and physiological traits between the natural hybrid Sphagneticola trilobata × calendulacea and its parental species

Biological invasion is a global environmental issue. Hybridization is considered a stimulus for evolution of invasiveness. It is thus essential to evaluate the invasive potential of new hybrids before management strategies are designed and implemented for them, especially, using performance‐related traits. Comparing growth and physiological traits between invasive species and their non‐invasive congeners is an effective way to identify invasive traits and to predict the invasive potential of species. However, few studies have evaluated the invasive potential of new hybrids by comparative analysis of these traits. We examined the invasive potential of a recently confirmed natural hybrid between the invasive Sphagneticola trilobata, one of the 100 worst invasive species worldwide, and its indigenous congener S. calendulacea. We compared growth and physiological responses of the hybrid and its parental species to different light conditions (open, natural light; shade, 25% of natural light) by conducting a common garden experiment. We then used discriminant analysis to identify those growth and physiological traits that are most different between the invasive and the non‐invasive species. We found that S. trilobata had a higher growth rate, photosynthetic capacity and resource use efficiency than S. calendulacea in both the open and the shade environments, and the hybrid was more similar to S. trilobata than to S. calendulacea in these traits. Discriminant analysis suggested that the hybrid is more similar to S. trilobata than to S. calendulacea for a number of traits associated with performance, and that the hybrids had less invasive potential in the shade than in the open environment. These results indicate that the hybrid has a high invasive potential and could be an efficient invader in both open and shade environments.

Biotic interactions under climate warming: temperature-dependent and species-specific effects of the oligochaete Chaetogaster limnaei on snails

Biological invasions impose severe threats to biodiversity, and the extent of this phenomenon is predicted to intensify under climate warming. Only a few investigators have examined how temperature interacts with other environmental variables to affect competition between native and invasive species. Physa acuta, an invasive freshwater snail in Europe, often outcompetes the indigenous congener Physa fontinalis. Both species are hosts of the oligochaete Chaetogaster limnaei limnaei (CL). We examined how the growth rates of the 2 competing physid species are co-affected by CL infestation (0, 10, 20 CL/snail) and temperature regime (15, 20, 25°C). Physa acuta grew faster than P. fontinalis. Warmer temperatures strongly favored growth rates of P. acuta, whereas P. fontinalis hardly profited from increased temperatures. CL infestation reduced the growth rates of both physids, but affected P. acuta more strongly than P. fontinalis. At the highest CL infestation level, the growth rates of both species were equal at 15 and 20°C, and faster growth of P. acuta occurred only at 25°C. Thus, using only the temperature response of a species to predict its reaction to climate warming is insufficient because biotic interactions can strongly affect species’ responses to temperature change. Additional host-preference experiments showed that physids were preferentially infested compared to Radix balthica and Bithynia tentaculata, 2 species that commonly co-occur with the physids. We showed the clear competitive superiority of P. acuta over P. fontinalis, but environmental conditions exist in which their fitness-relevant growth rates do not differ. CL infestation can reduce the competitive superiority of P. acuta, so CL might facilitate the co-existence of the 2 species. In general, its density-dependent effects and different selectivity for snail species may make CL an agent that structures snail communities in the field, a role that has been underestimated.

Is a new invasive herb emerging? Molecular confirmation and preliminary evaluation of natural hybridization between the invasive Sphagneticola trilobata (Asteraceae) and its native congener S. calendulacea in South China

Sphagneticola trilobata is an invasive herb in South China. Here, we reported some morphological intermediates between S. trilobata and the indigenous congener S. calendulacea in the field for the first time, which were suspected to be hybrids. Morphological and molecular methods were used to test this hybrid origin hypothesis, and eco-physiological parameters were measured to evaluate the hybrid’s invasion potential. The hybrid origin hypothesis was confirmed by analysis of microsatellite and nrITS sequences. Bayesian assignment analysis based on six microsatellite loci genotypes separated the studied individuals into three groups, which corresponded to the two parent species and the putative hybrids that were identified on the basis of leaf morphology. The hybrid individuals were categorized as F1 hybrids with membership coefficients (Qi values) close to 0.5. Phylogenetic analysis based on nrITS data showed that the putative hybrid individuals possessed two types of species-level divergent clones, and were inseparate with S. trilobata clade and S. calendulacea clade, respectively. The maternally-inherited chloroplast marker atpB-rbcL demonstrated that the invasive species functioned as the pollen donors. Ecophysiological studies on photosynthesis, specific leaf area (SLA), leaf nutrient concentration, and construction cost in the parental species and the hybrid demonstrated that the hybrid showed slightly lower or equivalent growth potential compared to the invasive species and significant higher energy-use efficiency than both parents. As such, it seems that a new invasive herb is emerging. As a consequence of this hybridization, the native species S. calendulacea may be disappearing rapidly, which presents a major concern for conservation efforts.

Parity and disparity between two Chama oysters: the reproductive biology of the Indo‐Pacific C. pacifica Broderip, invasive to the Mediterranean Sea; and C. savignyi Lamy, indigenous to the Red Sea

AbstractThe Indo‐Pacific oyster Chama pacifica Broderip, 1835 (Mollusca, Bivalvia, Chamidae) is rarely found in the Northern Red Sea reefs of Eilat (Gulf of Aqaba), where it is outnumbered by its indigenous congener, Chama savignyi Lamy, 1921. The influx of Eritrean biota from the Red Sea into the Mediterranean Sea via the Suez Canal has led to the formation of massive Chama oyster beds along the Eastern Mediterranean shore. However, unlike the Northern Red Sea, the Eastern Mediterranean Chama beds are dominated by C. pacifica oysters, whereas C. savignyi is absent from this region. In an attempt to understand this difference in their respective distribution, the reproductive biology of both species was compared. Histological analysis of the male and female gonads, monitored monthly from March 2009 to August 2010 in both regions, revealed a similar reproductive cycle, comprising six stages: onset of gametogenesis, advanced gametogenesis, ripe, ready to spawn, spent and sexual rest. Female gonads demonstrated an additional, seventh stage – restoration, coinciding with inferred spawning of ripe gametes. Both species were found to be dioecious spawners, with a single, annual, temperature‐dependent inferred spawning period. Chama pacifica was found to reproduce efficiently in maximal Mediterranean seawater temperatures not experienced by the Northern Red Sea Chama populations. This study demonstrates the high invasive potential of an oyster species despite its rarity in its source region.

Tar spot disease on Norway maple in North America: Quantifying the impacts of a reunion between an invasive tree species and its adventive natural enemy in an urban forest

The invasion of Norway maple (Acer platanoides) into North American forests is considered to have deleterious effects on native flora richness. One explanation for Norway maple's success is that it may have escaped its natural enemies and thus is less predated upon than its indigenous congener, sugar maple (Acer saccharum). However, Norway maple has been recently reunited with one of its natural enemies from Europe, Rhytisma acerinum, an adventive fungus that causes tar spot disease. The study reported here quantified the impacts of the disease on the growth and survival of Norway maple. In the urban forest of Mount Royal, we compared the growth of maple saplings and trees before the disease was first observed and after tar spot outbreaks of 2006 and 2007. We found a strong link between the outbreak of the disease and a very sharp decline in sapling and tree growth, together with high mortality of Norway maple saplings that could not be attributed to normal senescence or detrimental climatic conditions. While Norway maple usually exhibits higher growth rates than sugar maple, the reverse situation was observed after the epidemics. Our results suggest that the invasion potential of Norway maple could be reduced by the exotic disease.

Acclimation of photosystem II to high temperature in two Wedelia species from different geographical origins: implications for biological invasions upon global warming

More intense, more frequent, and longer heat waves are expected in the future due to global warming, which could have dramatic ecological impacts. However, few studies have involved invasive species. The aims of this study were to examine the effect of extreme heating (40/35 degrees C for 30 d) on the growth and photosynthesis of an alien invasive species Wedelia trilobata and its indigenous congener (Wedelia chinensis) in South China, and to determine the development of this invasive species and its potential adaptive mechanism. In comparison with W. chinensis, W. trilobata suffered less inhibition of the relative growth rate (RGR) and biomass production due to high temperature, which was consistent with the changes of photosystem II (PSII) activity and net photosynthetic rate (P(n)). High temperature caused a partial inhibition of PSII, but the adverse effect was more severe in W. chinensis. Measurement of the minimum fluorescence (F(o)) versus temperature curves showed that W. trilobata had a higher inflexion temperature of F(o) (T(i)), indicating greater thermostability of the photosynthetic apparatus. Moreover, comparisons of absorbed light energy partitioning revealed that W. trilobata increased xanthophyll-dependent thermal dissipation (Phi(NPQ)) under high temperature, while retaining the higher fraction of absorbed light allocated to photochemistry (Phi(PSII)) relative to W. chinensis. The results suggest that the invasive W. trilobata has a high thermostability of its photosynthetic apparatus and an effective regulating mechanism in energy partitioning of PSII complexes to minimize potential damage and to retain greater capability for carbon assimilation. These factors confer greater heat stress tolerance compared with the native species. Therefore, the invasive W. trilobata may become more aggressive with the increasingly extreme heat climates.

Elevated CO2 increases energy-use efficiency of invasive Wedelia trilobata over its indigenous congener

Increasing atmospheric CO2 concentration is regarded as an important factor facilitating plants invasions by stimulating invasive species growth. However, the physiological mechanisms by which invasive plants increase at the expense of existing native plants are poorly understood. Plant growth is always related to energy-use process including energy assimilation and expenditure, and thus examination of energetic properties could provide mechanistic insight into growth responses to increased CO2. The aims of this study were to examine the effect of rising CO2 on the growth and energetic properties of alien invasive species (Wedelia trilobata (L.) Hitchc.) and its native congener (Wedelia chinensis (Osbeck.) Merr.) in South China, and to determine if the specific energetic properties of invasive species at elevated CO2 favoring its growth. Elevated CO2 stimulated a greater increase in biomass production for invasive W. trilobata (58.9%) than for its indigenous congener (48.1%). Meanwhile, elevated CO2 altered the energetic properties differently upon species. For invasive W. trilobata, elevated CO2 significantly increased total energetic gain via photosynthetic activity (A total), but decreased energetic cost of biomass construction (CC), and thus enhanced photosynthetic energy-use efficiency (PEUE) by 85.3%. In contrast, the indigenous W. chinensis showed a slight increase in PEUE by 43.8%. Additionally, W. trilobata individuals grown in elevated CO2 increased energy allocation towards stems. Statistic analysis revealed significant associations between growth characteristics (relative growth rate and biomass) and energetic properties (CC and PEUE), suggesting the greater growth stimulation in invasive species could be partly explained by its specific energetic properties in elevated CO2 concentration. The invasive species showed a greater increase in energy-use efficiency under elevated CO2, which consequently facilitated its growth. It might be a physiological mechanism promoting success of invasion with ongoing increase in atmospheric CO2 concentration.

Gas Exchange Characteristics of the Invasive Species Mikania Micrantha and its Indigenous Congener M. Cordata (Asteraceae) in South China

In South China, the photosynthetic characteristics of an invasive exotic weed Mikania micrantha H.B. Kunth and its indigenous close congener Mikania cordata (Burm. f.) B.L. Robinson were studied. Mikania micrantha exhibited a greater biochemical capacity for photosynthesis than M. cordata, as the former had higher V(subscript cmax) and J(subscript max), which lead to its higher maximum assimilation rate A(subscript max) values. Similar light compensation point, apparent quantum yield (α), and dark respiration (R(subscript d)), suggested a similar shade-tolerance. Higher A(subscript max), light saturating point, and CO2 saturating point give M. micrantha greater potential to acclimate to brighter environments and a larger pool of available carbon. These differences in photosynthetic characteristics could be a basis for their niche partitioning. The leaf traits of the native and invasive Mikania species were as follows; higher construction cost (CC), lower specific leaf area (SLA), as well as lower mass-based leaf N and photosynthetic nitrogen-use efficiency (PNUE) for the native species, but M. micrantha had lower area-based leaf N. The higher water use efficiency (WUE) and δ^13C observed in M.micrantha was probably due to its high photosynthetic capacity and not to reduced stomatal conductance, explaining the absence of any trade-off between WUE and PNUE.

Comparative evaluation of Cotesia flavipes and C. sesamiae (Hymenoptera: Braconidae) for the management of Chilo partellus (Lepidoptera: Pyralidae) in Kenya

AbstractCotesia flavipes Cameron, a gregarious larval endoparasitoid native to the Indo-Australian region, was imported from Pakistan and released in Kenya in 1993 for management of the exotic stemborer, Chilo partellus (Swinhoe). Recent reports confirmed the successful establishment of the parasitoid in three locations in Kenya and in northern Tanzania. Functional response studies on this parasitoid and an indigenous congener, Cotesia sesamiae (Cameron), indicated that C. flavipes had a higher searching ability and attacked more larvae when Chilo partellus was the host. When a native stemborer, Sesamia calamistis Hampson, was the host, there was no significant difference between numbers attacked by both parasitoids. Numerical response studies showed that Cotesia flavipes produced more total progeny and female progeny per female parasitoid on Chilo partellus than did Cotesia sesamiae. No significant difference in progeny production was detected between the two parasitoids on S. calamistis. Functional and numerical responses tested in the laboratory gave the same ranking of the two parasitoids on the two hosts as in the field. This study suggests that Cotesia flavipes is a more efficient parasitoid and it is anticipated that it will contribute to the control of both exotic and native stemborers in Kenya.

The Effects of Herbivory by a Mite, Aculus hyperici, and Nutrient Deficiency on Growth in Hypericum Species

The combined effects of herbivory by a mite, Aculus hyperici Liro, and a deficiency of nutrients on plant growth were measured for Hypericum perforatum L. and H. gramineum J.Forst. grown in a glasshouse. The results are discussed in relation to the biological control of H. perforatum, an introduced weed in southern Australia, relative to growth of its indigenous congener, H. gramineum. Growth of both species was reduced when infested with the mite, although the growth of H. perforatum was reduced by more than that of H. gramineum. Nutrient deficiencies also reduced growth of both species, especially of roots. Imposition of nutrient deficiency on mite-infested plants caused multiplicative reductions in plant growth equivalent to the product of the proportional reductions caused by either herbivory or nutrient deficiency alone.