Irène Till-Bottraud

Plant resource-use strategies: the importance of phenotypic plasticity in response to a productivity gradient for two subalpine species

BACKGROUND AND AIMS Functional traits are indicators of plant interactions with their environment and the resource-use strategies of species can be defined through some key functional traits. The importance of genetic variability and phenotypic plasticity in trait variations in response to a common environmental change was investigated in two subalpine species. METHODS Two species with contrasted resource-use strategies, Dactylis glomerata and Festuca paniculata, were grown along a productivity gradient in a greenhouse experiment. Functional traits of different genotypes were measured to estimate the relative roles of phenotypic plasticity and genetic variability, and to compare their levels of phenotypic plasticity. KEY RESULTS Trait variability in the field for the two species is more likely to be the result of phenotypic plasticity rather than of genetic differentiation between populations. The exploitative species D. glomerata expressed an overall higher level of phenotypic plasticity compared with the conservative species F. paniculata. In addition to different amplitudes of phenotypic plasticity, the two species differed in their pattern of response for three functional traits relevant to resource use (specific leaf area, leaf dry matter content and leaf nitrogen content). CONCLUSIONS Functional trait variability was mainly the result of phenotypic plasticity, with the exploitative species showing greater variability. In addition to average trait values, two species with different resource-use strategies differed in their plastic responses to productivity.

VARIATION OF REPRODUCTIVE TRAITS IN RHODODENDRON FERRUGINEUM L. (ERICACEAE) POPULATIONS ALONG A SUCCESSIONAL GRADIENT

Sexual and vegetative reproduction in the alpine species Rhododendron ferrugineum was studied along a successional sequence (meadow → open heathland → closed heathland) at two sites and in a wet heathland. This study aims to determine (1) the characteristics of sexual reproduction in R. ferrugineum populations (2) when and how these populations develop layering (adventitious rooting) and (3) whether reproductive traits and reproductive strategies develop relative to the degree of population closure and maturity. The variables used to describe sexual reproduction were inflorescence density (per m(2) of Rhododendron cover), number of flowers per inflorescence and per m(2) of Rhododendron cover, and seeds production (per fruit and m(2) of Rhododendron cover). Flowering and fruiting phenologies were also recorded. For describing clonal development, we investigated layering variables such as length and annual growth rate of prostrate stems, rooting occurence and ramet density. The results show that the direction toward which the clones extend is mainly determinated by the topography, and that layering steadily increases with increasing population closure and maturity. Reproductive potential of R. ferrugineum is enormous (0.4–2.4 million seeds m(-2)) but reproductive effort remains low with respect to total biomass of seeds (3–21 g m(-2)). Reproductive effort of R. ferrugineum populations could be reduced as a conterpart of layering development only when the shrub draws more matter and energy in layering stems than to aerial stems. The variations in reproductive traits observed on our sites could be due to primarily to phenotypic response to variable microhabitat features, rather than to genetically deterministic processes.

Stamen dimorphism in Rhododendron ferrugineum (Ericaceae): development and function

The function of stamen dimorphism in the breeding system of the alpine shrub Rhododendron ferrugineum was studied in two populations in the French Alps. This species has pentameric flowers with two whorls of stamens: an inner whorl of five long stamens and an outer whorl of short stamens. We studied the development of stamens from buds to mature flowers (measurement of the filament, anther, and style lengths at five successive phenological stages) and compared the size and position of reproductive organs at maturity in control and partially emasculated flowers (removal of long-level stamens) to determine whether the presence of long-level stamens constitutes a constraint for the development of the short-level ones. Stamen dimorphism can be observed early in stamen development, from the bud stage of the year prior to flowering. At this early stage, meiosis had already occurred. Emasculation of the long-level stamens induced the short-level ones to grow longer than in normal conditions. We also performed seven pollination treatments on ten randomly chosen individuals in each population, and the number of seeds following each treatment was recorded. Results from these treatments showed that R. ferrugineum produced spontaneous selfed seeds in the absence of pollinators. However, no seed was produced when short-level stamens were emasculated and pollinators excluded, suggesting that long-level stamens are not responsible for selfing in the absence of pollinators and that reproductive assurance is promoted by short-level stamens.

Pollen aperture heteromorphism. Variation in pollen-type proportions along altitudinal transects in Viola calcarata.

Some species produce pollen grains with different aperture numbers within a single individual (pollen aperture heteromorphism). In the pansy Viola diversifolia, aperture number is positively correlated with pollen germination speed, and negatively correlated with viability. In V. calcarata, young five-aperturate pollen grains germinate faster than four-aperturate ones. Heteromorphism could thus be favoured when pollination is unpredictable, as plants produce both very competitive and long-lived pollen grains. Depending on the efficiency of the pollinators, different proportions of pollen types will be optimal. In insect-pollinated species, such as V. calcarata, pollination efficiency generally decreases as elevation increases. We therefore expect a decrease in mean aperture number as altitude increases. This was found in four transects (out of six). Pollinator activity therefore has a potential impact on pollen morphology.Some species produce pollen grains with different aperture numbers within a single individual (pollen aperture heteromorphism). In the pansy Viola diversifolia, aperture number is positively correlated with pollen germination speed, and negatively correlated with viability. In V. calcarata, young five-aperturate pollen grains germinate faster than four-aperturate ones. Heteromorphism could thus be favoured when pollination is unpredictable, as plants produce both very competitive and long-lived pollen grains. Depending on the efficiency of the pollinators, different proportions of pollen types will be optimal. In insect-pollinated species, such as V. calcarata, pollination efficiency generally decreases as elevation increases. We therefore expect a decrease in mean aperture number as altitude increases. This was found in four transects (out of six). Pollinator activity therefore has a potential impact on pollen morphology.

Multi-stemmed trees of Nothofagus pumilio second-growth forest in Patagonia are formed by highly related individuals

BACKGROUND AND AIMS Multi-stemmed trees (tree clusters) in Nothofagus pumilio, a dominant tree species in Patagonia, are very uncommon and are restricted to the edge of second-growth forests following human-provoked fires. No vegetative reproduction has been reported so far. The genetic structure of multi-stemmed trees of this species was investigated and it was hypothesized that genets within a cluster were more closely related than average in the population. METHODS Fifteen clusters (composed of at least three purported stems) and 15 single trees were sampled at the edge of a second-growth forest and genotyped using two amplified fragment length polymorphism (AFLP) primer pairs. We obtained 119 polymorphic markers that allowed clonality to be determined, together with sibship structure and relatedness among samples. KEY RESULTS Clonality was detected in seven clusters but all clusters had at least two different genotypes. Full sibs were found exclusively within clusters and in all clusters. Within a cluster, stems that were not identified as full sibs were often half sibs. Relatedness values for the full sibs and half sibs were higher than the theoretical values of 0·5 and 0·25 but the relatedness between clusters was very low. CONCLUSIONS Tree clusters that are merged at the edge of the second-growth forest of N. pumilio are composed of stems of the same genotype and of other genotypes that are highly related (but not always). It is suggested that this peculiar genetic structure results from a combination of several causes, including selection for merging of related individuals.

Display Size Preferences and Foraging Habits of High Andean Butterflies Pollinating Chaetanthera lycopodioides (Asteraceae) in the Subnival of the Central Chilean Andes

ABSTRACT In our study, we asked whether butterflies visiting Chaetanthera lycopodioides (Asteraceae) in the subnival at 3450 m a.s.l. in the central Andes prefer larger floral displays. To answer this question, we compared the population distribution of display sizes with the distribution of visited display sizes at two sites. Six high elevation butterflies: Faunula leucoglene (Satyridae) (the dominant species), Hylephila sp. (Hesperiidae), Phulia nymphula (Pieridae), Vanessa terpsichore (Nymphalidae), Tatochila mercedis (Nymphalidae), and Yramea modesta (Nymphalidae) were reported as visitors. Butterflies tended to discriminate against plants with a single open head, preferring larger display sizes at both sites. Butterflies visited few plants per bout (mean: 3.1–4.5) and probed increasingly smaller proportions of the open heads per plant with increasing display size (overall mean: 45.8–48.4%). Results suggest that high elevation butterflies tend to prefer larger display sizes over smaller ones, but final choices are conditioned by the relative abundance of each display size in a population. Although previous studies show that butterflies prefer larger artificial individual flowers over smaller ones, our work appears to constitute the first report of butterfly preference for larger floral displays in any plant species or ecosystem.

Conservation unit status inferred for plants by combining interspecific crosses and AFLP

Hybridization and introgression are common in plants and lead to morphological similarity between species and taxonomic confusion. This gene flow with closely related species can complicate efforts to determine whether an endangered taxon is evolutionarily distinctive and should be identified as a separate conservation unit. Potentilla delphinensis is a rare and threatened endemic species of the Southern French Alps. Two common related taxa (P. grandiflora and P. thuringiaca) are morphologically similar and occur in the same geographical locations. Thus, whether P. delphinensis represents a reliable conservation unit remained unclear. Our evaluation procedure based on a combination of molecular biology and interspecific crosses was used to define taxa within these plants. Plants were sampled from a total of 23 single and mixed localities for the three supposed taxa and were genotyped with 68 polymorphic Amplified Fragment Length Polymorphism (AFLP) loci. Fourty-one seedlings from interspecific crosses were obtained and genotyped. Amplified Fragment Length Polymorphism markers identified four genetically distinct units (P. delphinensis, P. grandiflora and two distinct groups of P. thuringiaca). All individuals of P. delphinensis formed a homogeneous and distinct taxon. This taxon was most probably an old allopolyploid from P. grandiflora and the related group of P. thuringiaca. Interspecific crosses gave low seed set and low germination rate. Furthermore, assignment test indicated that seedlings obtained from interspecific crosses were essentially apomictic rather than hybrids. These results suggest that a reproductive barrier exists between the different taxa. In conclusion, all results supported P. delphinensis as a true biological species and justified its conservation unit status. A surprising outcome of this work was the evidence of a potential new cryptic species. This study demonstrated the need to combine a molecular marker-based approach and pollination experiments for an accurate evaluation of plant taxa.

Genetic Diversity of Cypripedium calceolus at the Edge and in the Centre of Its Range in Europe

The patterns of genetic diversity in 14 Cypripedium calceolus populations were investigated in two distant regions, located inside its continuous range (Biebrza valley, NE Poland) and close to the periphery of its range (Alps, SE France). The genetic variation at the species level was found to be relatively high (P% = 37.5%, H o = 0.145) as compared with that observed in other endangered or rare species. The mean genetic diversity for both European regions did not differ significantly, except for P% (42.5% for Biebrza valley, 34.1% for Alps, p < 0.001). The Biebrza valley yielded almost twice as many genotypes, but genotypic diversity (as measured by G/N and Ĝ/N) was higher in populations from the Alps. This could mean that asexual reproduction is more intense in populations in the Biebrza valley than in the Alps. The results from PCA, UPGMA and AMOVA analyses showed clear genetic differences in C. calceolus between the two European regions. The Mantel test showed positive and significant associations between genetic and geographic distances among populations situated in the Biebrza valley (r 2 = 0.37, p < 0.05), but not among the Alpine populations (r 2 = -0.25, p > 0.05). Our data showed that substantial loss of genetic diversity in C. calceolus most likely occurs rather at the population than at the species level.

CHAETANTHERA ACHENO-HIRSUTA (TOMBESI) ARROYO, A.M.R.DAVIES & TILL-BOTTRAUD ELEVATED TO SPECIES, NEW FOR THE FLORA OF CHILE

Chaetanthera acheno-hirsuta (Tombesi) Arroyo, A.M.R. Davies & Till-Bottraud (Asteraceae: Mutisieae), previamente conocida cerca del limite superior de la vegetacion (> 3900 m) en el lado este de la Cordillera de los Andes en la provincia de San Juan, Argentina, es citada para Chile en base a seis colecciones recogidas en la Cordillera de los Andes de la III Region (Region de Atacama) entre 3500-4000 m. La especie nueva para la flora de Chile esta basada en Chaetanthera pulvinata (Phil.) Hauman var. acheno-hirsuta Tombesi, aqui elevada al nivel de especie. Chaetanthera acheno-hirsuta pertenece al subgenero Egania. Sus parientes mas cercanos, basado en caracteristicas morfologicas, son C. apiculata (J.Remy) Benth. & Hook.f. and C. acerosa (J. Remy) Benth. & Hook.f. Se distingue de C. pulvinata (Phil.) Hauman por la ausencia de dimorfismo sexual, las bracteas maculatas, verde-oscuras, y los aquenios densamente pubescentes.