Perennial Populations Research Articles

Perenniality induces high inbreeding depression in self-fertilising species

When predicting the fate and consequences of recurring deleterious mutations in self-fertilising populations most models developed make the assumption that populations have discrete non-overlapping generations. This makes them biologically irrelevant when considering perennial species with overlapping generations and where mating occurs independently of the age group. The few models studying the effect of perennial life-histories on the genetic properties of populations in the presence of self-fertilisation have done so considering age-dependent selection. They find low levels of inbreeding depression in perennial populations that do not explain empirical observations. Here we propose a simple deterministic model in continuous time with selection at different fitness traits and feedback between population fitness and size. We find that a perennial life-history can result in high levels of inbreeding depression in spite of inbreeding, due to higher frequencies of heterozygous individuals at the adult stage. We also propose that there may be demographic advantages for self-fertilisation that are independent of reproductive success.

The importance of recurrent reproductive events for Ruppia maritima seed bank viability in a highly variable estuary

Submerged aquatic vegetation (SAV) that recruits from seed may be favored over species that maintain populations through clonal reproduction as estuaries become more dynamic under upstream hydrologic changes and sea level rise. We examined recruitment in an SAV species Ruppia maritima (wigeongrass) at the hydrologically variable Everglades-Florida Bay ecotone. We hypothesized that the R. maritima seed bank depends upon large reproductive events occurring at least annually. Vegetation biomass, nutrient allocation, sexual reproduction, seed set and sediment seed bank viability were examined when reproductive meadows were present and following senescence. Within a meadow, total seed bank densities were high (>20,000m−2). However, 85% of seeds had germinated, leaving a small persistent seed bank, and most germinations did not successfully produce seedlings. Only 25% of intact (potentially viable) seeds were viable (<768 seedsm−2) to create a persistent seed bank. As reproductive shoots senesced, all vegetation completely died and 2750seedsm−2 entered the seed bank (40seedsg−1 biomass), increasing total seed bank viability from <4 to ∼20%. Reproductive R. maritima meadows can produce numerous seeds if not nutrient-limited during “windows of opportunity”; however, lack of a persistent seed bank, high germination rate and total vegetation mortality following reproduction indicate a reliance on reproductive events for population regeneration. Under lower hydrologic variability, perennial populations of R. maritima and other SAV could be sustained through vegetative reproduction, thereby reducing dependence on sexual reproduction. Otherwise, SAV in variable environments like this ecotone will remain dependent recurrent reproductive events to sustain recruitment and vegetation maintenance.

Acetohydroxyacid synthase (AHAS) amino acid substitution Asp376Glu in Lolium perenne: effect on herbicide efficacy and plant growth

Recently, the acetohydroxyacid synthase (AHAS) amino acid substitution Asp376Glu was detected in a Lolium perenne population originating in France. This is the first documented occurrence of the Asp376Glu single-nucleotide polymorphism in a Lolium species. The effects on herbicide efficacy and plant fitness are presented. Separation of the original population into different genetic subgroups allowed the comparison of different L. perenne AHAS genotypes according to their susceptibility to AHAS-inhibiting herbicides. Root and shoot biomass accumulation as well as tiller production was analysed for resistant and sensitive populations. Genotype-specific AHAS activity and inhibition were studied in vitro, using recombinant Arabidopsis thaliana DNA. Plants expressing the AHAS Asp376Glu genotype were resistant against mesosulfuron + iodosulfuron, pyroxsulam and propoxycarbazone. To imazamox, reduced susceptibility for dosages below 140 g a.i. ha−1 was observed. In the absence of herbicide, no significant impact of the Asp376Glu genotype on shoot biomass and tiller accumulation could be observed, whereas root biomass of the Asp376Glu genotype was significantly reduced by 68 % compared to the AHAS genetic wild type. The AHAS enzyme study revealed reduced AHAS enzyme rate of 48 % for the Asp376Glu genotype compared to the AHAS genetic wild type. This study highlights the role of the amino acid exchange on resistance profile against the most relevant AHAS-inhibiting herbicides. First indications were found that fitness of the Asp376Glu genotype is hampered.

SoloSchistocephalus solidustapeworms are nasty

Trophically transmitted parasites must trade-off own growth on one hand and energy drain from the intermediate host on the other hand, since killing the host before transmission to the next host is a dead end for both parasites and hosts. This challenge becomes especially intriguing when multiple parasites find themselves within the same individual host. The tapeworm Schistocephalus solidus may gain more than 98% of its final body mass within few months infecting its three-spined stickleback (Gasterosteus aculeatus) intermediate host. During these months the tapeworms may achieve a mass even larger than its host. We studied virulence of single and multiple infections of S. solidus, by comparing body condition of wild stickleback hosts in two perennial stickleback populations located at high latitudes, and each population was studied in two different years. Our results demonstrated multiple compared with single infections to be a highly significant predictor of the condition of stickleback hosts, with multiple-infected hosts having relatively higher body condition. However, this applied only after adjusting for parasite mass, which was another significant predictor for host condition. Thus, our results suggested that, at a given parasite mass, S. solidus was more harmful towards their host's body condition in single compared with multiple infections.

Glyphosate-resistant Lolium multiflorum and Lolium perenne populations from New Zealand are also resistant to glufosinate and amitrole

This study examined if glyphosate-resistant populations of Lolium multiflorum and Lolium perenne from some New Zealand vineyards were still susceptible to glufosinate and amitrole. The response of plants of one glyphosate-resistant population of L. multiflorum, population A, and two glyphosate-resistant L. perenne populations, populations J and O, to glufosinate and amitrole were evaluated and compared to susceptible populations in two dose–response experiments. Based on the herbicide rates giving 50% reduction in growth (GR50 values), populations A, J and O were 3.9, 4.5 and 3.8 times more resistant to glufosinate respectively, compared to the susceptible populations in a glufosinate dose–response experiment. Populations A, J and O were also found to be 2.9, 5.0 and 13.1 times more resistant to amitrole respectively, in an amitrole dose–response experiment. Very similar results were obtained when both dose–response experiments were repeated. This is the first confirmed report of weed species that have developed multiple-resistance to glyphosate, glufosinate and amitrole. These are the three main herbicides currently used for weed control in New Zealand vineyards.

Life‐history traits and geographical divergence in wild rice ( Oryza rufipogon ) gene pool in Indochina Peninsula region

Indochina Peninsula is the primary centre of diversity of rice and lies partly in the centre of origin of cultivated rice (Oryza sativa) where the wild ancestor (Oryza rufipogon) is still abundant. The wild gene pool is potentially endangered by urbanisation and the expansion of agriculture, and by introgression hybridisation with locally cultivated rice varieties. To determine genetic diversity and structure of the wild rice of the region we genotyped nearly 1000 individuals using 20 microsatellite loci. We found ecological differentiation in 48 populations, distinguishable by their life-history traits and the country of origin. Geographical divergence was suggested by isolation of the perennial Myanmar populations from those of Cambodia, Laos and Thailand. The annual types would be most likely to have lost genetic variation because of genetic drift and inbreeding. The growing of cultivated and wild rice together, however, gives ample opportunities for hybridisation, which already shows signs of genetic mixing, and will ultimately lead to replacement of the original wild rice gene pool. For conservation we suggest that wild rice should be conserved ex situ in order to prevent introgression from cultivated rice, along with in situ conservation in individual countries for the recurrent evolutionary process through local adaptation, but with sufficient isolation from cultivated rice fields to preserve genetic integrity of the wild populations.

An ultraviolet floral polymorphism associated with life history drives pollinator discrimination in Mimulus guttatus.

• Ultraviolet (UV) floral patterns are common in angiosperms and mediate pollinator attraction, efficiency, and constancy. UV patterns may vary within species, yet are cryptic to human observers. Thus, few studies have explicitly described the distribution or ecological significance of intraspecific variation in UV floral patterning. Here, we describe the geographic distribution and pattern of inheritance of a UV polymorphism in the model plant species Mimulus guttatus (Phrymaceae). We then test whether naturally occurring UV phenotypes influence pollinator interactions within M. guttatus.• We document UV patterns in 18 annual and 19 perennial populations and test whether UV pattern is associated with life history. To examine the pattern of inheritance, we conducted crosses within and between UV phenotypes. Finally, we tested whether bee pollinators discriminate among naturally occurring UV phenotypes in two settings: wild bee communities and captive Bombus impatiens.• Within M. guttatus, perennial populations exhibit a small bulls-eye pattern, whereas a bilaterally symmetric runway pattern occurs mainly in annual populations. Inheritance of UV patterning is consistent with a single-locus Mendelian model in which the runway phenotype is dominant. Bee pollinators discriminate against unfamiliar UV patterns in both natural and controlled settings.• We describe a widespread UV polymorphism associated with life history divergence within Mimulus guttatus. UV pattern influences pollinator visitation and should be considered when estimating reproductive barriers between life history ecotypes. This work develops a new system to investigate the ecology and evolution of UV floral patterning in a species with extensive genomic resources.

Evaluation of genetic variation among wild rice populations in Cambodia

A total of 448 samples in five natural populations of wild rice (Oryza rufipogon) were collected in Cambodia. They were examined using 12 SSR and two chloroplast markers to evaluate the degree of variation among populations and the genetic structure within populations. In the two annual populations, the number of plants with homozygous alleles at all 12 SSR loci were high (66.3% and 79.5%), suggesting that these plants propagate mainly through self-pollination. In the three perennial populations, no individuals had all homozygous genotypes, but redundant genotypes resulted from clonal propagation were observed. Percentages of the redundant genotypes were highly varied (3.6%, 29.2% and 86.0%). This may be due to the different stable levels of environmental conditions. As for chloroplast genome, most of the wild plants showed the same chloroplast types as most Indica-type cultivars have. However, plants with different chloroplast types were maintained, even in the same population. In tropical Asian countries, many wild rice populations were observed under similar ecological conditions examined in this study. Therefore, the present results concerning population structure will be important to further elucidate genetic features of wild rice, and will also give strong clues to utilize and conserve wild natural genetic resources.

The potential of novel Festulolium (2n = 4x = 28) hybrids as productive, nutrient‐use‐efficient fodder for ruminants

AbstractThe field performance and potential future use of F1 Lolium multiflorum and Lolium perenne × Festuca arundinacea var. glaucescens and Festuca mairei hybrids (2n = 4x = 28) are described. Foliar trait expression in the hybrids was largely determined by the Lolium rather than their Festuca parent ensuring maintenance of high‐forage quality. All four Festulolium populations comprised high‐yielding genotypes, but the L. multiflorum populations were particularly erect and tall, while the L. perenne populations had significantly higher numbers of tillers and were prostrate. Forage yields of the Festulolium populations assessed in field plot trials were either not significantly different from, or were superior to leading L. multiflorum and L. perenne cultivars used as controls. Endogenous plant proteases contribute to excessive proteolysis in the rumen which causes environmental N pollution. Protein degradation due to plant‐mediated proteolysis was assessed by in vitro exposure of leaves to the environmental conditions of the rumen (39°C, anaerobic) and calculated based on the time taken for protein levels to be reduced to half their original levels (t½). Leaf proteins were significantly more stable in L. multiflorum × F. arundinacea var. glaucescens and L. perenne × F. arundinacea var. glaucescens F1 hybrids (t½ 18–21 h) than in their respective Lolium parental genotypes (t½ 4–5 h), and there was a highly significant genome interaction. The t½ in the majority of the L. multiflorum × F. arundinacea var. glaucescens F1 hybrids studied often exceeded 24 h, whereas t½ of their Lolium and Festuca parents was consistently &lt;14 h. Although inferior to the F1, F. arundinacea var. glaucescens genotypes tested had significantly greater t½ than L. perenne under rumen‐simulated conditions. Significant variation in protein stability was apparent within the F1 and their respective parent species' groups. The initial protein content of the F1 hybrids was lower than their respective parents, but following 24‐h exposure to anoxia at 39°C, the protein content of both parent and hybrid genotypes was similar. The differences in protein stability between parental and hybrid genotypes was due to the greater rate of protein decline observed in the Lolium genotypes. Hence, uptake of these Festulolium hybrids as forage crops has potential to directly mitigate environmental impact of livestock farming without affecting production capacity.

омплексна оцінка стану популяцій степових багаторічників України на прикладі Iris pumila

омплексна оцінка стану популяцій степових багаторічників України на прикладі Iris pumila

Quantitative trait loci analysis to study the genetic regulation of non-polar metabolites in perennial ryegrass

In recent years advances in quantitative trait loci (QTL) mapping of complex metabolomics traits have been made in plants. This study is a two-phase experiment in which we have profiled transesterified non-polar metabolites in a Lolium perenne population consisting of parents, F1 and 325 F2 genotypes. These were grown in a replicated field trial, then analysed in batches by a targeted approach using gas-chromatography mass spectrometry (GC–MS), which identified 17 metabolites. The metabolite data was analysed using a mixed model that included random effects of field replicate, laboratory batch and technical replication to derive genotype means for QTL mapping. Using a linkage map of 326 markers, mainly Diversity Array Technology markers, QTLs were detected for seven of the metabolites. The most heritable metabolite was octacosanol, where a single QTL on linkage group four explained 42 % of the trait variance.

Persistence of Zostera marina L. (eelgrass) seeds in the sediment seed bank

Two separate field experiments in the Newport River/Back Sound, North Carolina (NC) and the lower Chesapeake Bay (CB), Virginia were conducted in 2007 and 2008 to quantify the effects of time (6, 12, 15months), seed source (mixed-annual, perennial NC; perennial CB), site (local environmental factors), and sediment type (fine, coarse) on the persistence of Zostera marina seeds in the sediment seed bank. It is here, at the southern limit of the species distribution along the western Atlantic, that the probability of population loss may be high and the importance of a seed bank in the resilience and recovery of these populations great. Experimental results indicate that viability of both NC and CB seeds decreased significantly after just 6months in the sediment following the seasonal period of maximum germination and continued to decline over time with no seeds viable remaining in CB cores and <5% of seeds remaining viable after 15months in NC treatments. In these experiments time was the overriding factor affecting the persistence Z. marina seed banks for all treatments in both NC and CB and viability was not significantly affected by seed source, site, or sediment type. Based on the results of the in situ experiments, mixed-annual and perennial Zostera marina populations in North Carolina and perennial populations in Virginia produce transient seed banks (seeds viable <12months). The lack of a persistent seed bank may reduce the resilience of Z. marina at the limits of the species distribution to repeated stress events. As a result these populations may be particularly susceptible to disturbance with only a limited capacity for recovery if sexual reproduction is impaired.

Molecular relationships between Australian annual wild rice, Oryza meridionalis, and two related perennial forms

BackgroundThe perennial, Oryza rufipogon distributed from Asia to Australia and the annual O. meridionalis indigenous to Australia are AA genome species in the Oryza. However, recent research has demonstrated that the Australian AA genome perennial populations have maternal genomes more closely related to those of O. meridionalis than to those found in Asian populations of O. rufipogon suggesting that the Australian perennials may represent a new distinct gene pool for rice.ResultsAnalysis of an Oryza core collection covering AA genome species from Asia to Oceania revealed that some Oceania perennials had organellar genomes closely related to that of O meridionalis (meridionalis-type). O. rufipogon accessions from New Guinea carried either the meridionalis-type or rufirpogon-type (like O. rufipogon) organellar genomes. Australian perennials carried only the meridionalis-type organellar genomes when accompanied by the rufipogon-type nuclear genome. New accessions were collected to better characterize the Australian perennials, and their life histories (annual or perennial) were confirmed by field observations. All of the material collected carried only meridionalis-type organellar genomes. However, there were two distinct perennial groups. One of them carried an rufipogon-type nuclear genome similar to the Australian O. rufipogon in the core collection and the other carried an meridionalis-type nuclear genome not represented in the existing collection. Morphologically the rufipogon-type shared similarity with Asian O. rufipogon. The meridionalis-type showed some similarities to O. meridionalis such as the short anthers usually characteristic of annual populations. However, the meridionalis-type perennial was readily distinguished from O. meridionalis by the presence of a larger lemma and higher number of spikelets.ConclusionAnalysis of current accessions clearly indicated that there are two distinct types of Australian perennials. Both of them differed genetically from Asian O. rufipogon. One lineage is closely related to O. meridionalis and another to Asian O. rufipogon. The first was presumed to have evolved by divergence from O. meridionalis becoming differentiated as a perennial species in Australia indicating that it represents a new gene pool. The second, apparently derived from Asian O. rufipogon, possibly arrived in Australia later.

Regeneration patterns of natural populations of herbaceous perennials in spruce forests of the Carpathians

According to the results of the long-term (1974–2011) monitoring of permanent sample plots at the Institute of Ecology of the Carpathians, National Academy of Sciences of Ukraine, located at the upper border of spruce forests of the Carpathians, patterns of characteristic stages of self-regeneration (regeneration) of the subpopulation structure of Soldanella hungarica Simonk. after severe local damage are generalized. It is found that, under experimental conditions, these point exposures do not cause the general destabilization of population processes. However, they initiate behavioral responses for the mobilization of the population reserve of S. hungarica on nearby areas. The varying role of individual and group effects in these processes is revealed. The conclusion of the decisive importance of the vitality composition for the results of local regeneration of the S. hungarica population is made. It is stated that the self-regeneration of the S. hungarica structure on the experimental plots is a time-consuming process that requires several decades.

Major QTLs for critical photoperiod and vernalization underlie extensive variation in flowering in the Mimulus guttatus species complex

Species with extensive ranges experience highly variable environments with respect to temperature, light and soil moisture. Synchronizing the transition from vegetative to floral growth is important to employ favorable conditions for reproduction. Optimal timing of this transition might be different for semelparous annual plants and iteroparous perennial plants. We studied variation in the critical photoperiod necessary for floral induction and the requirement for a period of cold-chilling (vernalization) in 46 populations of annuals and perennials in the Mimulus guttatus species complex. We then examined critical photoperiod and vernalization QTLs in growth chambers using F(2) progeny from annual and perennial parents that differed in their requirements for flowering. We identify extensive variation in critical photoperiod, with most annual populations requiring substantially shorter day lengths to initiate flowering than perennial populations. We discover a novel type of vernalization requirement in perennial populations that is contingent on plants experiencing short days first. QTL analyses identify two large-effect QTLs which influence critical photoperiod. In two separate vernalization experiments we discover each set of crosses contain different large-effect QTLs for vernalization. Mimulus guttatus harbors extensive variation in critical photoperiod and vernalization that may be a consequence of local adaptation.

Water availability and population origin affect the expression of the tradeoff between reproduction and growth in Plantago coronopus

Investment in reproduction and growth represent a classic tradeoff with implication for life history evolution. The local environment can play a major role in the magnitude and evolutionary consequences of such a tradeoff. Here, we examined the investment in reproductive and vegetative tissue in 40 maternal half-sib families from four different populations of the herb Plantago coronopus growing in either a dry or wet greenhouse environment. Plants originated from populations with an annual or a perennial life form, with annuals prevailing in drier habitats with greater seasonal variation in both temperature and precipitation. We found that water availability affected the expression of the tradeoff (both phenotypic and genetic) between reproduction and growth, being most accentuated under dry condition. However, populations responded very differently to water treatments. Plants from annual populations showed a similar response to drought condition with little variation among maternal families, suggesting a history of selection favouring genotypes with high allocation to reproduction when water availability is low. Plants from annual populations also expressed the highest level of plasticity. For the perennial populations, one showed a large variation among maternal families in resource allocation and expressed significant negative genetic correlations between reproductive and vegetative biomass under drought. The other perennial population showed less variation in response to treatment and had trait values similar to those of the annuals, although it was significantly less plastic. We stress the importance of considering intraspecific variation in response to environmental change such as drought, as conspecific plants exhibited very different abilities and strategies to respond to high versus low water availability even among geographically close populations.

Higher-order bud production increases tillering capacity in the perennial caespitose grass Scribner’s Panicum (Dichanthelium oligosanthes)

The persistence and dynamics of perennial grass populations strongly depend on tiller recruitment from the bud bank. Because of the structural organization of grasses as populations of phytomers, bud production and tillering are constrained by morphology. An infrequent trait observed in only a few caespitose grasses is the branching of buds to produce higher-order buds prior to tiller development. We studied bud bank dynamics in Dichanthelium oligosanthes (Schult.) Gould a C3 perennial caespitose grass widely distributed in the eastern Great Plains. A hierarchy of bud development occurred in D. oligosanthes, with primary buds branching to produce secondary, tertiary, and quaternary buds. This higher-order bud production increased the overwintering propagule supply for spring recruitment by 4.5 times, and more than half of successful tiller recruits originated as higher-order buds. The temporal patterns of higher-order bud production and development suggest that growing season length may be an important factor determining the extent of higher-order bud production and subsequent year tiller natality in D. oligosanthes. Higher-order bud production likely has important consequences for the population dynamics of grasses. It may increase bud bank densities and tillering capacity, buffer population dynamics, and increase intraclonal tiller densities and resource consolidation in caespitose grasses.

Quantitative trait locus mapping of genomic regions controlling herbage yield in perennial ryegrass

Genetic control of herbage yield—a complex trait of fundamental importance to agricultural productivity—was characterized in a perennial ryegrass biparental mapping population (I×S). Seasonal and combined growth score estimates of herbage yield (GS) were obtained from a trial conducted at three sites in New Zealand, over 2 years. Twenty-nine quantitative trait loci (QTL) for GS were identified on an I×S genetic linkage map constructed using simple sequence repeat (SSR) markers. Most QTL explained less than 15% of the phenotypic variation. QTL consistency was low among and within trial sites and years but 17 QTL were observed in more than one environment or season. QTL on linkage groups (LG) 1, 2, 4 and 6 were most consistent, based on numbers of QTL co-located at these positions and persistence of their allelic effects. SSR markers from consistent QTL positions may be beneficially applied in marker-assisted selection to enhance genetic gain for herbage yield in ryegrass breeding.

Water resources management in central northern Namibia using empirically grounded modelling

In this paper, a new methodology for the analysis and assessment of water supply regimes is presented. The problems of water supply management in developing countries are multidimensional and interdependent. Conventional methods, which only deal with separated and isolated issues, are not appropriate to deal with these problems. The method presented here, however, can comprehend the whole system. Therefore, using this method, conclusions for the management of adapted institutional and technological transformations can be drawn. In this study, relevant system variables of a problem context are identified, and their interdependencies are assessed and interpreted. This is done by using a method of qualitative interview analysis (grounded theory) and a cybernetic modelling approach (sensitivity analysis). In doing so, it is possible to identify outstanding variables which are essential to understand the system. These variables reveal the weakest links, driving forces, systemic stabilisers and the sustainability indicators of the system. The case study area is the Cuvelai-Etosha-Basin in central northern Namibia where a large-scale water supply system has been established. The water supply in the region is determined by the dependence on external water resources, high precipitation variability, absence of perennial rivers, saline groundwater, population growth and urbanisation.

Population Structure and Genetic Diversity among Eelgrass (Zostera marina) Beds and Depths in San Francisco Bay

The seagrass Zostera marina is widely distributed in coastal regions throughout much of the northern hemisphere, forms the foundation of an important ecological habitat, and is suffering population declines. Studies in the Atlantic and Pacific oceans indicate that the degree of population genetic differentiation is location dependent. San Francisco Bay, California, USA, is a high-current, high-wind environment where rafting of seed-bearing shoots has the potential to enhance genetic connectivity among Z. marina populations. We tested Z. marina from six locations, including one annual population, within the bay to assess population differentiation and to compare levels of within-population genetic diversity. Using 7 microsatellite loci, we found significant differentiation among all populations. The annual population had significantly higher clonal diversity than the others but showed no detectible differences in heterozygosity or allelic richness. There appears to be sufficient input of genetic variation through sexual reproduction or immigration into the perennial populations to prevent significant declines in the number and frequency of alleles. In additional depth comparisons, we found differentiation among deep and shallow portions in 1 of 3 beds evaluated. Genetic drift, sweepstakes recruitment, dispersal limitation, and possibly natural selection may have combined to produce genetic differentiation over a spatial scale of 3-30 km in Z. marina. This implies that the scale of genetic differentiation may be smaller than expected for seagrasses in other locations too. We suggest that populations in close proximity may not be interchangeable for use as restoration material.