Effects of physiological integration on defense strategies against herbivory by the clonal plant Alternanthera philoxeroides

Aims The plant-herbivore interaction is one of the most fundamental inter-actions in nature.Plants are sessile organisms,and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory.Here,we aimed to determine the defense strategies against insect herbivores in the creeping invasive plant Alternanthera philoxeroides.Methods We tested the defense response of A.philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a pol-yphagous sap-feeding insect Planococcus minor.We also tested the mechanisms triggering defense responses of A.philoxeroides by including treatments of artificial leaf removal and jasmonic acid application.Furthermore,we examined the effect of physiological integration on these defense strategies.Important Findings The combination of artificial leaf removal and jasmonic acid appli-cation produced a similar effect to that of leaf-feeding by the real herbivore.Physiological integration influenced the defense strat-egies of A.philoxeroides against herbivores,and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores.Our study highlights the importance of physio-logical integration and modular plasticity for understanding the consequences of herbivory in clonal plants.

Trans-generational effects in the clonal invader Alternanthera philoxeroides

Aims Recent studies have revealed heritable phenotypic plasticity through vegetative generations.In this sense,changes in gene regulation induced by the environment,such as DNA methylation(i.e.epigenetic changes),can result in reversible plastic responses being transferred to the offspring generations.This trans-generational plasticity is expected to be especially relevant in clonal plants,since reduction of sexual reproduction can decrease the potential for adaptation through genetic variation.Many of the most aggressive plant invaders are clonal,and clonality has been suggested as key to explain plant invasiveness.Here we aim to determine whether trans-generational effects occur in the clonal invader Alternanthera philoxeroides,and whether such effects differ between populations from native and non-native ranges.Methods In a common garden experiment,parent plants of A.philoxeroides from populations collected in Brazil(native range)and Iberian Peninsula(non-native range)were grown in high and low soil nutrient conditions,and offspring plants were transplanted to control conditions with high nutrients.To test the potential role of DNA methylation on trans-generational plasticity,half of the parent plants were treated with the demethylating agent,5-azacytidine.Important Findings Trans-generational effects were observed both in populations from the native and the non-native ranges.Interestingly,trans-generational effects occurred on growth variables(number of ramets,stem mass,root mass and total mass)in the population from the native range,but on biomass partitioning in the population from the non-native range.Trans-generational effects of the population from the native range may be explained by a‘silver-spoon’effect,whereas those of the population from the non-native range could be explained by epigenetic transmission due to DNA methylation.Our study highlights the importance of trans-generational effects on the growth of a clonal plant,which could help to understand the mechanisms underlying expansion success of many clonal plants.

Differences in physiological integration between invasive and noninvasive introduced clonal species of Carpobrotus

Aims Clonal growth is associated with invasiveness in introduced plant species,but few studies have compared invasive and noninvasive introduced clonal species to investigate which clonal traits may underlie invasiveness.To test the hypothesis that greater capacity to increase clonal growth via physiological integration of connected ramets increases invasiveness in clonal plants,we compared the effects of severing connections on accumulation of mass in the two species of the creeping,succulent,perennial,herbaceous genus Carpobrotus that have been introduced on sand dunes along the Pacific Coast of northern California,the highly invasive species Carpobrotus edulis and the co-occurring,noninvasive species Carpobrotus chilensis.Methods Pairs of ramets from four mixed populations of the species from California were grown in a common garden for 3 months with and without severing the stem connecting the ramets.To simulate the effect of clones on soils in natural populations,the older ramet was grown in sand amended with potting compost and the younger in sand alone.Important Findings Severance decreased net growth in mass by~60%in C.edulis and~100%in C.chilensis,due mainly to the negative effect of severance on the shoot mass of the younger ramet within a pair.Contrary to the hypothesis,this suggests that physiological integration increases growth more in the less invasive species.However,severance also decreased allocation of mass to roots in the older ramet and increased it in the younger ramet in a pair,and the effect on the younger ramet was about twice as great in C.edulis as in C.chilensis.This indicates that the more invasive species shows greater phenotypic plasticity in response to physiological integration,in particular greater capacity for division of labor.This could contribute to greater long-term growth and suggests that the division of labor may be a trait that underlies the association between clonal growth and invasiveness in plants.

四大洲食用昼花属的比较入侵生态学:对养分和竞争的响应

入侵生物学的两个关键假设是,某些特征是外来物种入侵的基础,且这些特征是在引入期间或之后选择的。我们通过关注两个可能赋予入侵性的特征来检验这些假设,即营养增加引起的较高生长加速和竞争引起的较低生长减速。我们对采自非洲、澳洲、欧洲和北美洲的4个食用昼花属(Carpobrotus)品种进行了比较。为了测试高入侵物种莫邪菊(Carpobrotus edulis)对这些特征的选择,我们将原产于南非的植株与入侵其他3个地区的植株进行了比较。在一个同质园中繁殖植株。然后,在添加或不添加养分的情况下单独培育子代,并在不添加养分的情况下将子代与另一个食用昼花属品种一起、或与欧洲的一种共生本土物种马兰草(Ammophila arenaria)一起培育。不同品种的食用昼花属对营养物质的反应并无差异,在入侵性更强的物种中,竞争反应的负面性也没有减弱。然而,与本土莫邪菊相比,添加营养物质引起外来莫邪菊更高的生长加速。此外,在处理开始时,两种入侵物种每分株的鲜质量高于两种非入侵物种。我们的研究结果表明,引种可以选择入侵物种对营养富集的反应进行选择,也证明了外来植物的体积和入侵性之间的关联。

Is the ballan wrasse (Labrus bergylta) two species? Genetic analysis reveals within-species divergence associated with plain and spotted morphotype frequencies

The ballan wrasse(Labrus bergylta)is a marine fish belonging to the family Labridae characterized by 2 main morphotypes that occur in sympatry:spotty and plain.Previous studies have revealed differences in their life-history traits,such as growth and maturation;however,the genetic relationship between forms is present­ly unknown.Using 20 recently developed microsatellite markers,we conducted a genetic analysis of 41 and 48 spotty and plain ballan wrasse collected in Galicia(northwest Spain).The 2 morphotypes displayed highly sig­nificant genetic differences to each other(F_(ST)=0.018,P<0.0001).A similar degree of genetic differentiation(F_(ST)=0.025,P<0.0001)was shown using the STRUCTURE clustering approach with no priors at K=2.In this case,the frequency of spotty and plain morphotypes was significantly different(χ^(2)=9.46,P=0.002).It is con­cluded that there is significant genetic heterogeneity within this species,which appears to be highly associated with the spotty and plain forms,but not completely explained by them.Given the previously demonstrated bio­logical differences between morphotypes,and the present genetic analyses,we speculate about the convenience of a taxonomic re-evaluation of this species.

Population structure and range expansion:the case of the invasive gastropod Cyclope neritea in northwest Iberian Peninsula

Biotic invasions have a reputation for unpredictable behavior.Here,we report how slight changes in human activity responsible for the introduction and range expansion of a non-native mollusk have led to detectable differences in the genetics of the invasion.Cyclope neritea is a non-predatory gastropod introduced to 2 areas of the European Atlantic:the northwest Iberian Peninsula(NWIP)and the French Atlantic coast(FAC).Shellfish seabed farming is intense in both areas but focuses on different commercial species.Using mitochondrial gene sequences,the lower genetic diversity recorded along the NWIP suggests a more homogeneous range of source populations than in the FAC.Unlike FAC,genetic diversity and haplotype composition in the NWIP correlate with the date of first occurrence of C.neritea at each site rather than with geographical location.Although this pattern evokes the genetic signature expected under a serial-founder colonization model from a single initial enclave,a comparison with samples from potential source populations suggests that the NWIP probably experienced several independent reintroductions.The jump dispersal pattern of C.neritea in the NWIP,together with the observation that populations established in the same year are genetically undifferentiated,point to human transport as the most plausible explanation for the current range expansion.Despite evidence for human-mediated dispersal,C.neritea managed to develop a seemingly non-random genetic pattern in the NWIP.It is suggested that caution must be exerted when interpreting genetic patterns in invaders.

Effects of resource sharing directionality on physiologically integrated clones of the invasive Carpobrotus edulis

Aims One of the key traits associated with clonal growth in plants is the capacity for physiological integration,which allows resource sharing between connected ramets within a clonal system.Resource transport is expected to occur following a source–sink relationship:from ramets established in rich patches to ramets growing in poor patches.However,some experiments have shown that acropetal transport(from basal to apical modules)usually exceeds basipetal transport(from apical to basal ramets).In this study,we aimed to determine the resource transport directionality in physiologically integrated modules of the invader Carpobrotus edulis.Methods We conducted two manipulative experiments under common garden conditions that studied the effect of different nutrient levels located at different positions(basal,medial and apical)on connected and disconnected clonal systems of C.edulis.We compared the biomass partitioning patterns and final biomass of ramets to elucidate whether the effect of physiological integration is affected by the directionality of the resource transport.Important Findings Results indicate a prevalent acropetal transport of resources in C.edulis,with a developmentally programmed division of labor where basal ramets were specialized in obtaining soil-based resources and apical ramets specialized in aboveground growth.This biomass partitioning pattern was not affected by the nutrient conditions in which basal or apical ramets were growing,although the highest benefit was achieved by apical ramets growing under the most stressed conditions.This developmentally programmed division of labor is expected to increase the lateral growth of C.edulis,and therefore could have meaningful implications for the expansion of this invasive species.