Floral reduction in Crepis tectorum (Asteraceae): tradeoffs and dominance relationships

The present investigation of Crepis tectorum examines the extent to which tradeoffs and patterns of dominance contribute to the association between flower size (head width) and degree of self-fertility among populations adapted to rock outcrops. Partial correlation analyses of phenotypic data from a F2 generation derived from a cross between two outcrop plants and of family means representing one of the parent populations indicate that small-flowered plants fail to reallocate resources to flower and fruit production, that small flower size offers little or no advantage in terms of autofertility, and that floral reduction has little influence on the rate of flower development. Hence, it may be necessary to invoke factors other than tradeoffs to explain the decline in flower size associated with the evolution of autogamy in C. tectorum. Comparison of parent and Fl hybrid means in the crossing experiment suggests incomplete dominance in the alleles for large flower size. Under the assumption that Fl hybrid means reflect the average degree of dominance across loci, I propose inbreeding depression as the basis for some of the reduction in floral morphology.     

Does inbreeding promote evolutionary reduction of flower size? Experimental evidence from Crepis tectorum (Asteraceae)

? Premise of the study: Small, autogamous flowers have evolved repeatedly in the plant kingdom. While much attention has focused on the mechanisms that promote the shift to autogamy, there is still a paucity of information on the factors that underlie the reduction of flower size so prevalent in selfing lineages. In this study of Crepis tectorum, I examine the role of inbreeding, acting alone or together with selection, in promoting evolutionary reduction of flower size. ? Methods: Experimental crosses were performed to produce progeny populations that differed in inbreeding and (or) selection history. Progenies were grown in two different environments and scored for flower size and other characters. ? Key results: Inbreeding depressed flower and fruit size, but also caused changes in flowering time and the number of heads produced. Despite some inconsistencies in the results for the last progeny generation, the decline in flower size was persistent over generations, consistent across environments, and similar in magnitude to the effects of selection for small flower size and the floral reduction inferred to have taken place during the shift toward autogamy within the study species. The floral size reduction was largely independent of changes in overall vigor, and there was considerable adaptive potential in flower size (measured by sib analyses and parent-offspring comparisons) after inbreeding. ? Conclusions: The results of this study indicate that inbreeding can promote evolutionary reduction of flower size and highlight the close, persistent association between flower and fruit size in the study species.     

Life-history variation and allometry for sexual size dimorphism in Pacific salmon and trout

Allometry for sexual size dimorphism (SSD) is common in animals, but how different evolutionary processes interact to determine allometry remains unclear. Among related species SSD (male : female) typically increases with average body size, resulting in slopes of less than 1 when female size is regressed on male size: an allometric relationship formalized as 'Rensch's rule' . Empirical studies show that taxa with male-biased SSD are more likely to satisfy Rensch's rule and that a taxon's mean SSD is negatively correlated with allometric slope, implicating sexual selection on male size as an important mechanism promoting allometry for SSD. I use body length (and life-history) data from 628 (259) populations of seven species of anadromous Pacific salmon and trout (Oncorhynchus spp.) to show that in this genus life-history variation appears to regulate patterns of allometry both within and between species. Although all seven species have intraspecific allometric slopes of less than 1, contrary to expectation slope is unrelated to species' mean SSD, but is instead negatively correlated with two life-history variables: the species' mean marine age and variation in marine age. Second, because differences in marine age among species render SSD and body size uncorrelated, the interspecific slope is isometric. Together, these results provide an example of how evolutionary divergence in life history among related species can affect patterns of allometry for SSD across taxonomic scales.     

Understanding reproductive allometry in turtles: A slippery “slope”

Measures of reproductive output in turtles are generally positively correlated with female body size. However, a full understanding of reproductive allometry in turtles requires logarithmic transformation of reproductive and body size variables prior to regression analyses. This allows for slope comparisons with expected linear or cubic relationships for linear to linear and linear to volumetric variables, respectively. We compiled scaling data using this approach from published and unpublished turtle studies (46 populations of 25 species from eight families) to quantify patterns among taxa. Our results suggest that for log–log comparisons of clutch size, egg width, egg mass, clutch mass, and pelvic aperture width to shell length, all scale hypoallometrically despite theoretical predictions of isometry. Clutch size generally scaled at ~1.7 to 2.0 (compared to an isometric expectation of 3.0), egg width at ~0.5 (compared to an expectation of 1.0), egg mass at ~1.1 to 1.3 (3.0), clutch mass at ~2.5 to 2.8 (3.0), and pelvic aperture width at 0.8–0.9 (1.0). We also found preliminary evidence that scaling may differ across years and clutches even in the same population, as well as across populations of the same species. Future investigators should aspire to collect data on all these reproductive parameters and to report log–log allometric analyses to test our preliminary conclusions regarding reproductive allometry in turtles.     

Native perennial grasses show evolutionary response to Bromus tectorum (cheatgrass) invasion

Invasive species can change selective pressures on native plants by altering biotic and abiotic conditions in invaded habitats. Although invasions can lead to native species extirpation, they may also induce rapid evolutionary changes in remnant native plants. We investigated whether adult plants of five native perennial grasses exhibited trait shifts consistent with evolution in response to invasion by the introduced annual grass Bromus tectorum L. (cheatgrass), and asked how much variation there was among species and populations in the ability to grow successfully with the invader. Three hundred and twenty adult plants were collected from invaded and uninvaded communities from four locations near Reno, Nevada, USA. Each plant was divided in two and transplanted into the greenhouse. One clone was grown with B. tectorum while the other was grown alone, and we measured tolerance (ability to maintain size) and the ability to reduce size of B. tectorum for each plant. Plants from invaded populations consistently had earlier phenology than those from uninvaded populations, and in two out of four sites, invaded populations were more tolerant of B. tectorum competition than uninvaded populations. Poa secunda and one population of E. multisetus had the strongest suppressive effect on B. tectorum, and these two species were the only ones that flowered in competition with B. tectorum. Our study indicates that response to B. tectorum is a function of both location and species identity, with some, but not all, populations of native grasses showing trait shifts consistent with evolution in response to B. tectorum invasion within the Great Basin.     

Reproductive allometry in Malaysian rain forest trees: Biomechanics versus optimal allocation

Summary Quantitative predictions of reproductive allometry in iteroparous plants may be derived from two bodies of theory: biomechanics and optimal allocation theory. Biomechanical theory predicts allometric scaling exponents between reproductive (R) and vegetative (V) biomass in the range of 0.44–1.33, while very general models of life history evolution predictR–V exponents > 1 in all cases. These predictions are examined in light of allometric patterns of flower and fruit production in 32 species of Malaysian rain forest trees. Among these species the mean estimatedR–V exponents are in the range 1.8–2.0 for staminate flower, pistillate flower and fruit production. This range of exponent values provides unambiguous support for some of the general predictions of optimal allocation models, but not for biomechanical theory. Optimal allocation models also predict a positive relationship between species size andR–V slope and a positive relationship between species size andR–V intercept parameters. The latter, but not the former prediction is supported by the data.R–V allometries in sexes of dioecious species were also found to differ in intercept, though not slope, reflecting smaller sizes at reproductive onset in staminate trees. Further critical examinations of reproductive allometry are encouraged as a relatively unexplored avenue for increasing the contact of theory and data in studies of life history evolution in long-lived organisms such as tropical trees.     

Geographical variation in allometry in the guppy (Poecilia reticulata)

Variation in static allometry, the power relationship between character size and body size among individuals at similar developmental stages, remains poorly understood. We tested whether predation or other ecological factors could affect static allometry by comparing the allometry between the caudal fin length and the body length in adult male guppies (Poecilia reticulata) among populations from different geographical areas, exposed to different predation pressures. Neither the allometric slopes nor the allometric elevations (intercept at constant slope) changed with predation pressure. However, populations from the Northern Range in Trinidad showed allometry with similar slopes but lower intercepts than populations from the Caroni and the Oropouche drainages. Because most of these populations are exposed to predation by the prawn Macrobrachium crenulatum, we speculated that the specific selection pressures exerted by this predator generated this change in relative caudal fin size, although effects of other environmental factors could not be ruled out. This study further suggests that the allometric elevation is more variable than the allometric slope.     

Production of male flowers does not decrease with plant size in insect‐pollinated Sagittaria trifolia,contrary to predictions of size‐dependent sex allocation

Abstract It has been proposed that relative allocation to female function increases with plant size in animal‐pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size‐dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect‐pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high‐density population, 48% of ramets were male without female flowers, but in the low‐density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal‐pollinated plants, pointing towards further studies to test the hypothesis of size‐dependent sex allocation using different allocation currencies.     

Arbuscular mycorrhizal fungi alter plant allometry and biomass-density relationships

Background and Aims

Plant biomass–density relationships during self-thinning are determined mainly by allometry. Both allometry and biomass–density relationship have been shown to vary with abiotic conditions, but the effects of biotic interactions have not been investigated. Arbuscular mycorrhizal fungi (AMF) can promote plant growth and affect plant form. Here experiments were carried out to test whether AMF affect plant allometry and the self-thinning trajectory.

Methods

Two experiments were conducted on Medicago sativa L., a leguminous species known to be highly dependent on mycorrhiza. Two mycorrhizal levels were obtained by applying benomyl (low AMF) or not (high AMF). Experiment 1 investigated the effects of AMF on plant growth in the absence of competition. Experiment 2 was a factorial design with two mycorrhizal levels and two plant densities (6000 and 17 500 seeds m⁻²). Shoot biomass, root biomass and canopy radius were measured 30, 60, 90 and 120 d after sowing. The allometric relationships among these aspects of size were estimated by standardized major axis regression on log-transformed data.

Key Results

Shoot biomass in the absence of competition was lower under low AMF treatment. In self-thinning populations, the slope of the log (mean shoot biomass) vs. log density relationship was significantly steeper for the high AMF treatment (slope = –1·480) than for the low AMF treatment (–1·133). The canopy radius–biomass allometric exponents were not significantly affected by AMF level, but the root–shoot allometric exponent was higher in the low AMF treatment. With a high level of AMF, the biomass–density exponent can be predicted from the above-ground allometric model of self-thinning, while this was not the case when AMF were reduced by fungicide.

Conclusions

AMF affected the importance of below-ground relative to above-ground interactions and changed root vs. shoot allocation. This changed allometric allocation of biomass and altered the self-thinning trajectory.     

SEASONAL CHANGES IN SIZE STRUCTURE OF SARGASSUM AND TURBINARIA POPULATIONS (PHAEOPHYCEAE) ON TROPICAL REEF FLATS IN THE SOUTHERN RED SEA1

Seasonal variation in density, thallus length and biomass, population size structure, and allometric length‐biomass relationships was investigated in populations of Sargassum ilicifolium (Turner) C. Agardh, Sargassum subrepandum (Forssk.) C. Agardh, and Turbinaria triquetra (J. Agardh) Kütz. (Phaeophyceae) on shallow reef flats in the southern Red Sea. Thallus length and biomass varied strongly with season, with the highest values occurring in the cooler months. Thallus densities showed no significant temporal variation. Log‐total biomass versus log‐density relationships were positive throughout the growth season without any decrease in the slope of the relationship. In two populations, biomass‐density combinations approached the interspecific biomass‐density line, but the massive annual shedding of modules occurred before self‐thinning would set in. Allometric length‐biomass relationships varied with season in all populations and were associated with seasonal module initiation, growth, and shedding. Evidence of a strong asymmetric competition was found in two high‐density populations. These populations showed a predominance of small thalli during peak development, asymmetrical Lorenz curves, increasing Gini coefficients, and increasing thallus length relative to biomass during the main growth phase. In two other less crowded populations, small thalli were absent during peak development, Lorenz curves were symmetrical, and Gini coefficients decreased during the main growth phase. In these populations, size equalization appears to be due to responses at the modular level rather than size‐dependent mortality. We conclude that changes in size structure in this highly seasonal environment are determined by module dynamics, modified by asymmetric competition in some populations, with a minor role of recruitment and no regulatory effect of self‐thinning.     

How plant allometry influences bud phenology and fruit yield in two Vaccinium species

Background and AimsUnderstanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants’ allometric traits, which are predictors of fruit production.MethodsWe measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass.Key ResultsDuring the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log–log scale model.ConclusionsGrowing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.     

Fruit size and shape: Allometry at different taxonomic levels in bird-dispersed plants

Summary The likelihood that a plant's seeds will be dispersed by fruit-eating birds may depend upon the size and shape of its fruits. Assuming that elongate fruits can be swallowed more easily than spherical fruits of equal volume and that plant fitness is enhanced by seed dispersal by many individuals and species of birds, natural selection should favour increasing fruit elongation with increasing fruit size in bird-dispersed plants. According to this view, this allometric pattern would be adaptive. Alternatively, fruit shape in bird-dispersed plants may be constrained by development or phylogeny. To determine whether there was any evidence to support the adaptive allometry hypothesis, we examined allometric relationships between length and diameter in fruits and seeds in a group of neotropical bird-dispersed plant species. Using the major axis technique, we regressed ln(diameter) on ln(length) for fruits and seeds at various taxonomic levels: (1) within individual trees ofOcotea tenera (Lauraceae) (2) among 19 trees within a population ofO. tenera, as well as among pooled fruits from multiple trees within 20 other species in the Lauraceae, (3) among 25 sympatric species within a plant family (Lauraceae) and (4) among 167 species representing 63 angiosperm families within a plant community in Monteverde, Costa Rica. At most taxonomic levels, a tendency for fruit length to increase more rapidly than fruit diameter among fruits (negative allometry) occurred more frequently than expected by chance. Estimated slopes of the regressions of fruit length on fruit diameter were < 1 within 15 of the 19 individualO. tenera trees, among tree means withinO. tenera, among pooled fruits within 16 of the 20 other species in the Lauraceae, among species means within the Lauraceae and among means of all bird-dispersed species in the lower montane forests of Monteverde. Seed allometry showed similar patterns, although for both fruits and seeds the broad confidence intervals of the slopes estimated by major axis regression overlapped 1 in many cases. Among the 63 Monteverde family means, fruit length and diameter scaled isometrically. Based on measurements of ontogenetic changes in fruit shape in a single species,O. viridifolia, we found no evidence that negative allometry in fruit shape within the Lauraceae was an inevitable consequence of developmental constraints. Instead, increasing elongation of fruits and seeds in certain plant taxa is consistent with adaptation to gape-limited avian seed dispersers. Contrary results from vertebrate-dispersed species from Malawi and Spain may reflect differences between the New and Old World in plant taxa, seed dispersers or evolutionary history.     

THE GEOGRAPHICAL MOSAIC OF COEVOLUTION IN A PLANT–POLLINATOR MUTUALISM

Although coevolution is widely accepted as a concept, its importance as a driving factor in biological diversification is still being debated. Because coevolution operates mainly at the population level, reciprocal coadaptations should result in trait covariation among populations of strongly interacting species. A long-tongued fly ( Prosoeca ganglbaueri ) and its primary floral food plant ( Zaluzianskya microsiphon ) were studied across both of their geographical ranges. The dimensions of the fly's proboscis and the flower's corolla tube length varied significantly among sites and were strongly correlated with each other. In addition, the match between tube length of flowers and tongue length of flies was found to affect plant fitness. The relationship between flower tube length and fly proboscis length remained significant in models that included various alternative environmental (altitude, longitude, latitude) and allometric (fly body size, flower diameter) predictor variables. We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length.     

The geographical mosaic of coevolution in a plant-pollinator mutualism.

Although coevolution is widely accepted as a concept, its importance as a driving factor in biological diversification is still being debated. Because coevolution operates mainly at the population level, reciprocal coadaptations should result in trait covariation among populations of strongly interacting species. A long-tongued fly (Prosoeca ganglbaueri) and its primary floral food plant (Zaluzianskya microsiphon) were studied across both of their geographical ranges. The dimensions of the fly's proboscis and the flower's corolla tube length varied significantly among sites and were strongly correlated with each other. In addition, the match between tube length of flowers and tongue length of flies was found to affect plant fitness. The relationship between flower tube length and fly proboscis length remained significant in models that included various alternative environmental (altitude, longitude, latitude) and allometric (fly body size, flower diameter) predictor variables. We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length.     

Ambulacral growth allometry in edrioasteroids: functional surface‐volume change in ontogeny and phylogeny

McKinney, M. L. & Sumrall, C. D. 2010: Ambulacral growth allometry in edrioasteroids: functional surface‐volume change in ontogeny and phylogeny. Lethaia, Vol. 44, pp. 102–108. Most organisms do not maintain geometric similarity as they grow, in large part because of surface‐volume interactions. Because respiratory and food‐acquiring organs are dependent on surface area, which increases more slowly than volume, organisms have evolved many strategies to increase the efficiency of, and/or the functional surface areas of these organs. Here, we report some preliminary results comparing area of the feeding apparatus (ambulacra) versus the volume of the theca for a suite of isorophid edrioasteroid species at various ontogenetic sizes. Regression of log (ambulacral area) on log (thecal volume) indicates a strongly constrained allometric pattern whereby the ontogenies of all measured species fall on or near the same line (r² = 0.962, n = 55), with a slope (k) = 0.654 (± 0.018). This slope and associated 0.05 standard error (0.618–0.690) is within the bounds of that expected from increasing surface area to keep pace with the metabolic demands of increasing thecal size. This allometric value is also comparable to the size scaling of metabolism and respiratory and feeding surfaces in many living and a few fossil invertebrates (k ～ 0.5–0.9). The edrioasteroid species analysed show a very wide variety of changes in ambulacral length, width and sinuosity, documenting many different patterns for achieving the same goal of increasing surface area to keep pace with volume increase. There is no evidence of increasing feeding efficiency. □Edrioasteroid, allometry, ambulacrum, surface‐volume, echinoderm.     

Reduced fecundity in small populations of the rare plant Gentianopsis ciliate (Gentianaceae)

Habitat destruction is the main cause for the biodiversity crisis. Surviving populations are often fragmented, i.e., small and isolated from each other. Reproduction of plants in small populations is often reduced, and this has been attributed to inbreeding depression, reduced attractiveness for pollinators, and reduced habitat quality in small populations. Here we present data on the effects of fragmentation on the rare, self-compatible perennial herb Gentianopsis ciliata (Gentianaceae), a species with very small and presumably well-dispersed seeds. We studied the relationship between population size, plant size, and the number of flowers produced in 63 populations from 1996-1998. In one of the years, leaf and flower size and the number of seeds produced per fruit was studied in a subset of 25 populations. Plant size, flower size, and the number of seeds per fruit and per plant increased with population size, whereas leaf length and the number of flowers per plant did not. The effects of population size on reproduction and on flower size remained significant if the effects were adjusted for differences in plant size, indicating that they could not be explained by differences in habitat quality. The strongly reduced reproduction in small populations may be due to pollination limitation, while the reduced flower size could indicate genetic effects.     

Morphological characteristics of leaf epidermis and size variation of leaf, flower and fruit in different ploidy levels in Buddleja macrostachya (Buddlejaceae)

Buddleja macrostachya (Buddlejaceae) is a widespread shrub native to the Sino-Himalayan mountains and beyond. It has been found to occur at two ploidy levels, hexaploid, 2n=6x=114 and dodecaploid, 2n=12x=228. To determine if morphological characters might be used as indicators of ploidy levels, we measured floral and fruit length, relative and absolute leaf size, trichome density on both leaf surfaces, and stomatal density and length in different populations of B. macrostachya. In general, flower and fruit length, absolute leaf size, and stomatal length increased with an increase at ploidy level (P<0.01), whereas adaxial cell and stomatal density decreased with an increase at ploidy level (P<0.01). We found no conspicuous differences in relative leaf size (P>0.05) in different populations. Other characters studied such as trichome type, cuticular membrane and ornamentation of stomata, cell and stomatal shape, and anticlinal wall pattern were quite constant in this species. Thus it appears that flower and fruit length, absolute leaf size, and stomatal frequency and length can be used to distinguish hexaploid from dodecaploid cytotypes either in the field or in herbarium specimens.     

药物植物桃儿七不同种群种子产量初步研究

对药用植物桃儿七5个不同种群种子产量的研究表明：各种群中每花平均胚珠数、每果实平均种子数及种群平均结实率与种群所在的海拔高度呈正相关;不同种群个体平均胚珠数的变异范围为58.97-87.97,平均种子数变异范围为40.02-80.58,平均结籽率变异范围为61.29%-91.60%;果料内单粒种子平均干重与种群分布海拔呈明显负相关,与果实内种子数呈弱负相关;同一种群在不同年份间平均各上子产量差异不大;种子产量除主要受个体营养状况影响外,还受海拔及其它因素的影响;果实内种子数与果实大小及重量呈正相关,但单粒种子平均重量与果实大小及果实内种子总重量无显著相关。     

Variation in pollen limitation and floral parasitism across a mating system transition in a Pacific coastal dune plant: evolutionary causes or ecological consequences?

Background and Aims Evolutionary transitions from outcrossing to self-fertilization are thought to occur because selfing provides reproductive assurance when pollinators or mates are scarce, but they could also occur via selection to reduce floral vulnerability to herbivores. This study investigated geographic covariation between floral morphology, fruit set, pollen limitation and florivory across the geographic range of Camissoniopsis cheiranthifolia, a Pacific coastal dune endemic that varies strikingly in flower size and mating system.Methods Fruit set was quantified in 75 populations, and in 41 of these floral herbivory by larvae of a specialized moth (Mompha sp.) that consumes anthers in developing buds was also quantified. Experimental pollen supplementation was performed to quantify pollen limitation in three large-flowered, outcrossing and two small-flowered, selfing populations. These parameters were also compared between large- and small-flowered phenotypes within three mixed populations.Key Results Fruit set was much lower in large-flowered populations, and also much lower among large- than small-flowered plants within populations. Pollen supplementation increased per flower seed production in large-flowered but not small-flowered populations, but fruit set was not pollen limited. Hence inadequate pollination cannot account for the low fruit set of large-flowered plants. Floral herbivory was much more frequent in large-flowered populations and correlated negatively with fruit set. However, florivores did not preferentially attack large-flowered plants in three large-flowered populations or in two of three mixed populations.Conclusions Selfing alleviated pollen limitation of seeds per fruit, but florivory better explains the marked variation in fruit set. Although florivory was more frequent in large-flowered populations, large-flowered individuals were not generally more vulnerable within populations. Rather than a causative selective factor, reduced florivory in small-flowered, selfing populations is probably an ecological consequence of mating system differentiation, with potentially significant effects on population demography and biotic interactions.