Shrub Lavandula Latifolia Research Articles

Transgenerational epigenetics: Inheritance of global cytosine methylation and methylation-related epigenetic markers in the shrub Lavandula latifolia.

The ecological and evolutionary significance of natural epigenetic variation (i.e., not based on DNA sequence variants) variation will depend critically on whether epigenetic states are transmitted from parents to offspring, but little is known on epigenetic inheritance in nonmodel plants. We present a quantitative analysis of transgenerational transmission of global DNA cytosine methylation (=proportion of all genomic cytosines that are methylated) and individual epigenetic markers (=methylation status of anonymous MSAP markers) in the shrub Lavandula latifolia. Methods based on parent-offspring correlations and parental variance component estimation were applied to epigenetic features of field-growing plants ('maternal parents') and greenhouse-grown progenies. Transmission of genetic markers (AFLP) was also assessed for reference. Maternal parents differed significantly in global DNA cytosine methylation (range = 21.7-36.7%). Greenhouse-grown maternal families differed significantly in global methylation, and their differences were significantly related to maternal origin. Methylation-sensitive amplified polymorphism (MSAP) markers exhibited significant transgenerational transmission, as denoted by significant maternal variance component of marker scores in greenhouse families and significant mother-offspring correlations of marker scores. Although transmission-related measurements for global methylation and MSAP markers were quantitatively lower than those for AFLP markers taken as reference, this study has revealed extensive transgenerational transmission of genome-wide global cytosine methylation and anonymous epigenetic markers in L. latifolia. Similarity of results for global cytosine methylation and epigenetic markers lends robustness to this conclusion, and stresses the value of considering both types of information in epigenetic studies of nonmodel plants.

Within-plant variation in seed size and inflorescence fecundity is associated with epigenetic mosaicism in the shrub Lavandula latifolia (Lamiaceae).

Sub-individual variation in traits of homologous structures has multiple ecological consequences for individuals and populations. Assessing the evolutionary significance of such effects requires an improved knowledge of the mechanisms underlying within-plant phenotypic heterogeneity. The hypothesis that continuous within-plant variation in some phenotypic traits can be associated with epigenetic mosaicism was examined. Fifteen individuals of the long-lived, evergreen Mediterranean shrub Lavandula latifolia were studied. Five widely spaced 'modules', each consisting of a single inflorescence plus all its subtending basal leaves, were collected from each shrub. Genomic DNA was extracted from leaf samples and genome-wide cytosine methylation determined by reversed phase high-performance liquid chromatography (HPLC) with spectrofluorimetric detection. The number and mean mass of seeds produced were determined for each inflorescence. An assessment was made of whether (1) leaves from different modules in the same plant differed significantly in global DNA cytosine methylation, and (2) mosaicism in cytosine methylation contributed to explain variation across modules in number and size of seeds. Leaves from different modules in the same plant differed in global DNA cytosine methylation. The magnitude of epigenetic mosaicism was substantial, as the variance in DNA methylation among modules of the same shrub was greater than the variance between individuals. Number and mean mass of seeds produced by individual inflorescences varied within plants and were quadratically related to cytosine methylation of subtending leaves, with an optimum at an intermediate methylation level (approx. 25 %). The results support a causal link between global cytosine methylation of leaves in a module and the size and numbers of seeds produced by the associated inflorescence. It is proposed that variation in global DNA methylation within L. latifolia shrubs may result from the concerted action of plant sectoriality and differential exposure of different plant parts to some environmental factor(s) with a capacity to induce durable epigenetic changes.

Genetic and epigenetic divergence between disturbed and undisturbed subpopulations of a Mediterranean shrub: a 20-year field experiment.

Little is known on the potential of ecological disturbance to cause genetic and epigenetic changes in plant populations. We take advantage of a long‐term field experiment initiated in 1986 to study the demography of the shrub Lavandula latifolia, and compare genetic and epigenetic characteristics of plants in two adjacent subplots, one experimentally disturbed and one left undisturbed, 20 years after disturbance. Experimental setup was comparable to an unreplicated ‘Before‐After‐Control‐Impact’ (BACI) design where a single pair of perturbed and control areas were compared. When sampled in 2005, plants in the two subplots had roughly similar ages, but they had established in contrasting environments: dense conspecific population (‘Undisturbed’ subpopulation) versus open area with all conspecifics removed (‘Disturbed’ subpopulation). Plants were characterized genetically and epigenetically using amplified fragment length polymorphism (AFLP) and two classes of methylation‐sensitive AFLP (MSAP) markers. Subpopulations were similar in genetic diversity but differed in epigenetic diversity and multilocus genetic and epigenetic characteristics. Epigenetic divergence between subpopulations was statistically unrelated to genetic divergence. Bayesian clustering revealed an abrupt linear boundary between subpopulations closely coincident with the arbitrary demarcation line between subplots drawn 20 years back, which supports that genetic and epigenetic divergence between subpopulations was caused by artificial disturbance. There was significant fine‐scale spatial structuring of MSAP markers in both subpopulations, which in the Undisturbed one was indistinguishable from that of AFLP markers. Genetic differences between subpopulations could be explained by divergent selection alone, while the concerted action of divergent selection and disturbance‐driven appearance of new methylation variants in the Disturbed subpopulation is proposed to explain epigenetic differences. This study provides the first empirical evidence to date suggesting that relatively mild disturbances could leave genetic and epigenetic signatures on the next adult generation of long‐lived plants.

Lognormal distribution of individual lifetime fecundity: insights from a 23‐year study

Individual variance in lifetime fecundity within populations is a life-history parameter of crucial evolutionary and ecological significance. However, knowledge of its magnitude and underlying mechanisms in natural populations is biased toward short-lived taxa. This paper summarizes results of a 23-year study on a population of the Mediterranean shrub Lavandula latifolia. We document the within-population pattern of individual variation in instantaneous and lifetime fecundity (as estimated by inflorescence production) and explore the mechanisms producing the lognormal distribution of individual fecundities by means of an individual-based simulation model. Throughout the study period, a few individuals consistently produced most inflorescences while the majority of plants exhibited moderate-to-low fecundities. The shape of yearly distributions of annual fecundities varied little across years, and most annual fecundity distributions did not depart significantly from a lognormal. The distribution of individual lifetime fecundity did not depart from lognormality. Despite the simplicity of the premises of our simulation model, it was remarkably successful at predicting the shapes of fecundity distributions and the early establishment of a persistent fecundity hierarchy. The agreement between model results and empirical data supports the view that multiplicative interactions of randomly varying environmental effects can play a central role in determining individual variation in lifetime fecundity in L. latifolia, and suggests that environmental stochasticity can be decisive in the genesis of strong fecundity hierarchies in long-lived plants.

Adding a third dimension to the edge of a species' range: altitude and genetic structuring in mountainous landscapes

In addition to the topographical and ecological barriers, other landscape features may also subtly influence the patterns of gene flow and spatial genetic structuring at species' borders. This paper focuses on the role played by altitudinal gradients that characterize mountainous landscapes. We formulate and test the hypothesis that when the distribution boundaries of plant species intersect mountainous landscapes, altitudinal gradients in ecological conditions may considerably enhance population subdivision and genetic structuring at the regional level. Using amplified fragment length polymorphism markers, we studied genetic diversity and differentiation in a set of 21 peripheral populations of the evergreen shrub Lavandula latifolia Med. (Labiatae) at its southernmost distribution limit in the Betic mountain ranges of southern Spain. Population size and abundance, and within-population genetic diversity, varied predictably with altitude, being highest at middle elevations and declining steadily towards both the upper and lower altitudinal distribution margins. Genetic differentiation tended to follow the opposite trend. These altitudinal patterns result from variation with elevation in the relative influence of gene flow and drift on the distribution of genetic variation. Genetic drift prevails around the upper and lower altitudinal limits, whereas a situation closer to a drift-gene flow equilibrium exists at the center of the altitudinal distribution. Altitudinal variation in the relative influences of gene flow and drift appears as an essential element in the interpretation of regional genetic structuring of L. latifolia at its mountainous distribution edge, and a factor which may influence the evolutionary potential of peripheral populations and the likelihood of local adaptation.

Plant generalization on pollinators: species property or local phenomenon?

Despite recent increased interest in the frequency and evolutionary consequences of generalization in plant-pollinator systems, little is known on whether plant generalization on pollinators actually is a species-level trait. This paper addresses the following questions for the insect-pollinated shrub Lavandula latifolia: (1) Are different populations of this pollinator-generalist plant similarly generalized? (2) Within a highly generalized population, are all plants similarly pollinator-generalists? Comparable values for richness in pollinator species were obtained from individual- or population-specific rarefaction curves as the projected number of distinct pollinator species implicated in 100 flower visits (S(RAR100)). Simple counts of pollinator species recorded per individual or population (S(OBS)) were weakly or nonsignificantly correlated with corresponding S(RAR100) figures and closely correlated with flower visitation frequency. The pollination system of L. latifolia was highly generalized at the regional level, but populations differed greatly in pollinator species richness (S(RAR100)). Within the population intensively studied, individual plants had quite variable degrees of generalization, comparable in magnitude to variation among populations. It is concluded that generalization was not an invariant, species-level property in L. latifolia. Furthermore, pollinator diversity estimates based on S(OBS) data may be heavily contingent on aspects related to both research design (sampling effort) and biological phenomena (variation in pollinator abundance or visitation rates), which may either mask or distort underlying ecological patterns of interest.

INDIVIDUAL DIFFERENCES IN PROGENY VIABILITY INLAVANDULA LATIFOLIA: A LONG-TERM FIELD STUDY

Despite its potential importance as a source of fitness variation in natural plant populations, few studies have so far examined long-term patterns of individual dif- ferences in progeny viability under natural conditions. This paper reports on a six-year field study on the differences in progeny viability (defined here as the probability of seeds contributing an established, prereproductive juvenile to the population), and its two com- ponents (seedling emergence and seedling survivorship), for the Mediterranean evergreen shrub Lavandula latifolia. The main objectives of the study were (1) to assess whether individual plants actually differ in the viability of their progeny under natural conditions, and (2) to determine if naturally occurring levels of variation in viability may modify individual differences in fecundity. Seed progenies from 14 maternal parents belonging to one population were sown at 10 field sites differing broadly in habitat type and soil char- acteristics, and seedling emergence and survival subsequently were monitored for six years. Maternal parents differed significantly in progeny viability because of both differential seedling emergence and seedling survivorship, and variation in either of these parameters was not significantly related to maternal differences in seed size. Differences in seedling survivorship were more important than differences in seedling emergence as determinants of maternal variation in progeny viability. While individual differences in seedling emer- gence remained consistent across sowing sites, there was a strong parent 3 sowing site interaction on seedling survivorship, and the rank of maternal parents with regard to this variable varied erratically among sowing sites. A significant inverse relationship existed across maternal parents between seed production and progeny viability, which was not mediated by differences in seed size, thus suggesting a trade-off between the number and quality of the progeny produced by L. latifolia plants. Although maternal differences in seed production were about twice as important as differences in progeny viability in de- termining maternal differences in juvenile recruitment, viability differences should not be disregarded a priori as unimportant sources of fitness differences. Results of this study stress the importance of conducting long-term, direct field assessments of individual dif- ferences in progeny viability across a range of environments encompassing the conditions actually faced by the species.

Agrobacterium tumefaciens-mediated transformation of the aromatic shrub Lavandula latifolia

Transgenic plants of the aromatic shrub Lavandula latifolia (Lamiaceae) were produced using Agrobacterium tumefaciens-mediated gene transfer. Leaf and hypocotyl explants from 35–40-day old lavender seedlings were inoculated with the EHA105 strain carrying the nptII gene, as selectable marker, and the reporter gusA gene with an intron. Some of the factors influencing T-DNA transfer to L. latifolia explants were assessed. Optimal transformation rates (6.0 ± 1.6% in three different experiments) were obtained when leaf explants precultured for 1 day on regeneration medium were subcultured on selection medium after a 24 h co-cultivation with Agrobacterium. Evidence for stable integration was obtained by GUS assay, PCR and Southern hybridisation. More than 250 transgenic plants were obtained from 37 independent transformation events. Twenty-four transgenic plants from 7 of those events were successfully established in soil. β-glucuronidase activity and kanamycin resistance assays in greenhouse-grown plants from two independent transgenic lines confirmed the stable expression of both gusA and nptII genes two years after the initial transformation. Evidence from PCR data, GUS assays and regeneration in the presence of kanamycin demonstrated a 1:15 Mendelian segregation of both transgenes among seedlings of the T1 progeny of two plants from one transgenic L. latifolia line.

Flower-to-Seedling Consequences of Different Pollination Regimes in an Insect-Pollinated Shrub

Insect pollinators of the Mediterranean shrub Lavandula latifolia (Labiatae) differ in components of pollinating effectiveness that may influence seed production and progeny quality. This study tests the prediction that L. latifolia flowers exposed to pollination regimes differing in pollinator composition should differ in their expected contribution to population recruitment in the field, as measured in terms of established seedlings, because of differences in seed production, progeny quality, or both. Using a randomized complete block design, two pollination regimes were induced during a 3-wk period on each of 15 L. latifolia plants by alternately exposing flowers in the two halves of each shrub to natural pollinators during two nonoverlapping diurnal periods (0930–1630, MD regime; dawn to 0930 and 1630 to dusk, R regime). The two pollination regimes differed in pollinator composition. The importance as flower visitors of butterflies and small bees was greater during the MD regime, which was also characterized by higher flower visitation rate and higher probability of visitation per time unit of individual flowers. MD flowers set proportionally more fruits, and each fruit contained more seeds, than R flowers. Seed production per inflorescence was also greater in MD than in R half-plants. Seeds from the MD and R regimes did not differ significantly in either mean mass, probability of germination under laboratory conditions, or probability of producing a seedling when planted in a greenhouse. When planted in the field, seeds originating from MD flowers had a greater probability of producing a seedling than those originating from R flowers, the difference being greatest where soil characteristics were most adverse for early seedling growth. In the field, MD and R seedlings did not differ in post-emergence survival rate and size of eventual survivors. The estimated average probability (±1 se) of one ovule eventually producing one third-year, established seedling in the home environment was significantly greater for MD (0.0192 ± 0.0041) than for R (0.0085 ± 0.0020) flowers. This demographic advantage of MD ovules was mainly accounted for by the greater seedling emergence rate of MD seeds, and only secondarily by the greater fruit- and seed-set of MD flowers. Observed patterns may be explained by a combination of increased outcrossing derived from the greater relative importance of small bees and butterflies as pollinators, and increased gametophytic competition resulting from increased overall visitation rates to individual flowers during the MD pollination regime. This study suggests that even relatively minor differences in pollinator composition and abundance may have a measurable demographic impact on plant populations.

FLOWER-TO-SEEDLING CONSEQUENCES OF DIFFERENT POLLINATION REGIMES IN AN INSECT-POLLINATED SHRUB

Insect pollinators of the Mediterranean shrub Lavandula latifolia (Labiatae) differ in components of pollinating effectiveness that may influence seed production and progeny quality. This study tests the prediction that L. latifolia flowers exposed to pollination regimes differing in pollinator composition should differ in their expected contribution to population recruitment in the field, as measured in terms of established seedlings, because of differences in seed production, progeny quality, or both. Using a randomized complete block design, two pollination regimes were induced during a 3-wk period on each of 15 L. latifolia plants by alternately exposing flowers in the two halves of each shrub to natural pollinators during two nonoverlapping diurnal periods (0930-1630, MD regime; dawn to 0930 and 1630 to dusk, R regime). The two pollination regimes differed in pollinator composition. The importance as flower visitors of butterflies and small bees was greater during the MD regime, which was also characterized by higher flower visitation rate and higher probability of visitation per time unit of individual flowers. MD flowers set pro- portionally more fruits, and each fruit contained more seeds, than R flowers. Seed production per inflorescence was also greater in MD than in R half-plants. Seeds from the MD and R regimes did not differ significantly in either mean mass, probability of germination under laboratory conditions, or probability of producing a seedling when planted in a greenhouse. When planted in the field, seeds originating from MD flowers had a greater probability of producing a seedling than those originating from R flowers, the difference being greatest where soil characteristics were most adverse for early seedling growth. In the field, MD and R seedlings did not differ in post-emergence survival rate and size of eventual survivors. The estimated average probability ( 61 SE) of one ovule eventually producing one third- year, established seedling in the home environment was significantly greater for MD (0.0192 6 0.0041) than for R (0.0085 6 0.0020) flowers. This demographic advantage of MD ovules was mainly accounted for by the greater seedling emergence rate of MD seeds, and only secondarily by the greater fruit- and seed-set of MD flowers. Observed patterns may be explained by a combination of increased outcrossing derived from the greater relative importance of small bees and butterflies as pollinators, and increased gametophytic com- petition resulting from increased overall visitation rates to individual flowers during the MD pollination regime. This study suggests that even relatively minor differences in pol- linator composition and abundance may have a measurable demographic impact on plant populations.

Microclimate and Individual Variation in Pollinators: Flowering Plants are More than Their Flowers

Variation in pollinator composition at the individual plant level is an important prerequisite for plant specialization on pollinators that does not seem to have been investigated previously. I studied variation in pollinator composition in a southeastern Spanish population of the insect—pollinated shrub Lavandula latifolia (Labiatae) and examined its correlates, with particular reference to the distinction between factors intrinsic (flower morphology, nectar standing crop, size of floral display) and extrinsic (sunlight regime, ambient temperature, humidity) to the plants. L. latifolia shrubs differed significantly in all intrinsic variables measured, in average irradiance levels (due to site—dependent variation in timing and duration of insolation periods), and in pollinator composition at both the species and other levels. Individual variation in pollinator composition was largely due to differences among insect taxa in their foraging responses to the sunlight mosaic. While some pollinators foraged indiscriminately over that mosaic, others preferred sites characterized by high irradiance. Variation among plants in intrinsic variables was unrelated to differences in pollinator composition, which depended significantly only on the sunlight regime associated with each plant's location in the habitat. Site—specific effects in pollination will generally act to reduce the likelihood of selective pressures by animals on plant traits. Their importance should be greatest in habitats characterized by patchiness in environmental variables that affect pollinator behavior and in plants with pollinator assemblages dominated by ectothermic species.

Dissecting Factors Responsible For Individual Variation in Plant Fecundity

This paper analyses, on an individual plant basis, the various components determining seed production in the evergreen shrub Lavandula latifolia (Labiatae), in order to estimate their relative contributions to individual differences in fecundity. The relationships between fecundity and age, size, and growth rate are also examined. Experimental pollination and watering were done in an attempt to alter natural patterns of partial fecundity components. Fecundity of individual plants is partitioned into its absolute (number of inflorescences, number of flowers per inflorescence) and relative (fruits/flower and seeds/fruit) partial components, and the following questions are addressed: (1) Are the individual differences in relative components of fecundity? (2) What are the proportional contributions of relative and absolute components of fecundity to individual variation in seed production? (3) Are relative measures of reproductive success reliable predictors of individual differences in fecundity? (4) When induced experimentally, do changes in partial fecundity components translate into modifications of the population's ranking of absolute fecundities? Fecundity depended more on plant size than age, was unrelated to growth rate, and was limited by water, but not pollen, availability. Individual plants differed in all components of fecundity examined, and differences were consistent among years. The proportional contributions of the various components to individual differences in fecundity were very unequal. Almost all variation among plants in seed production (°90% of variance) was explained by the variances and covariances of number of inflorescences and number of flowers per inflorescence. Variation among plants in the two relative components (fruit and seed set), even though statistically significant, had a negligible influence on individual differences in fecundity. These patterns remained invariant despite significant modification of flower production and fruit set induced by artificially watering a part of the study population. Fruit and seed set alone are unreliable indicators of individual differences in the maternal component of fitness in L. latifolia, and a review of relevant literature indicates that this probably applies to other polycarpic plants as well. Plant reproductive biology studies may make erroneous inferences if they consider exclusively data on relative fruit and seed set, and neglect the absolute components of individual differences in fecundity. It is proposed that, to circumvent these potential problems, demographic aspects and absolute estimates of seed output on a per individual basis should be examined in addition to the customarily employed fruit and seed set measures.