Consequences of inter-population crosses on developmental stability and canalization of floral traits in Dalechampia scandens (Euphorbiaceae)

Congruence between changes in phenotypic variance and developmental noise in inter-population hybrids was analysed to test whether environmental canalization and developmental stability were controlled by common genetic mechanisms. Developmental stability assessed by the level of fluctuating asymmetry (FA), and canalization by the within- and among-individual variance, were measured on several floral traits of Dalechampia scandens (Euphorbiaceae). Hybridization affected canalization. Both within- and among-individual phenotypic variance decreased in hybrids from populations of intermediate genetic distance, and strongly increased in hybrids from genetically distant populations. Mean-trait FA differed among cross-types, but hybrids were not consistently more or less asymmetric than parental lines across traits. We found no congruence between changes in FA and changes in phenotypic variance. These results suggest that developmental stability (measured by FA) and canalization are independently controlled. This study also confirms the weak relationship between FA and the breakdown of coadapted gene complexes following inter-population hybridization.     

DEVELOPMENTAL STABILITY IN LEAVES OF CLARKIA TEMBLORIENSIS (ONAGRACEAE) AS RELATED TO POPULATION OUTCROSSING RATES AND HETEROZYGOSITY

Four natural populations of Clarkia tembloriensis, whose levels of heterozygosity and rates of outcrossing were previously found to be correlated, are examined for developmental instability in their leaves. From the northern end of the species range, we compare a predominantly selfing population (t? = 0.26) with a more outcrossed population (t? = 0.84), which is genetically similar. From the southern end of the range, we compare a highly selfing population (t? = 0.03) with a more outcrossed population (t? = 0.58). We measured developmental stability in the populations using two measures of within-plant variation in leaf length as well as calculations of fluctuating asymmetry (FA) for several leaf traits. Growth-chamber experiments show that selfing populations are significantly more variable in leaf length than more outcrossed populations. Developmental instability can contribute to this difference in population-level variance. Plants from more homozygous populations tend to have greater within-plant variance over developmentally comparable nodes than plants from more heterozygous populations, but the difference is not significant. At the upper nodes of the plant, mature leaf length declines steadily with plant age, allowing for a regression of leaf length on node. On average, the plants from more homozygous populations showed higher variance about the regression (MSE) and lower R² values, suggesting that the decline in leaf length with plant age is less stable in plants from selfing populations than in plants from outcrossing populations. Fluctuating asymmetry (FA) was calculated for four traits within single leaves at up to five nodes per plant. At the early nodes of the plant where leaf arrangement is opposite, FA was also calculated for the same traits between opposite leaves at a node. Fluctuating asymmetry is significantly greater in the southern selfing population than in the neighboring outcrossed population. Northern populations do not differ in FA. Fluctuating asymmetry can vary significantly between nodes. The FA values of different leaf traits were not correlated. We show that developmental stability can be measured in plants using FA and within-plant variance. Our data suggest that large differences in breeding system are associated with differences in stability, with more inbred populations being the least stable.     

There is no heterotic effect upon developmental stability in the ventral side of the skull within the house mouse hybrid zone

Fluctuating asymmetry (FA) of a body is expected to be related to an organism's developmental instability. We studied patterns of FA in the ventral side of the skull along a transect across the central-European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. We found that FA was not significantly different between introgression classes relative to differences between localities within those classes and that the within-class differences were much larger than differences between individual-signed asymmetries within localities. However, if year was added to the same analysis as another factor, FA was not significantly different among localities within the same introgression class. When individual asymmetries were plotted against individual hybrid indices, hybrids appeared more asymmetric than individuals from outside of the zone. Thus contrary to previous studies, we did not find lower FA indicating heterotic effect in hybrids for the traits studied. It is suggested that the impact of hybridization on FA in the ventral side of the mouse skull is negligible or overwhelmed by other factors.     

Perfect is best: low leaf fluctuating asymmetry reduces herbivory by leaf miners

Fluctuating asymmetry (FA) represents small, random variation from symmetry and can be used as an indicator of plant susceptibility to herbivory. We investigated the effects of FA of two oak species, Quercus laevis and Q. geminata, and the responses of three herbivore guilds: leaf miners, gallers, and chewers. To examine differences in FA and herbivory between individuals, 40 leaves from each tree were collected, and FA indices were calculated. To examine differences in FA and herbivory within-individuals, we sampled pairs of mined and unmined leaves for asymmetry measurements. Differences in growth of leaf miners between leaf types were determined by tracing 50 mines of each species on symmetric leaves and asymmetric leaves. Asymmetric leaves contained significantly lower concentrations of tannins and higher concentrations of nitrogen than symmetric leaves for both plant species. Both frequency of asymmetric leaves on plants and levels of asymmetry positively influenced the abundance of Brachys, Stilbosis and other leaf miners, but no significant relationship between asymmetry and herbivory was observed for Acrocercops. Brachys and Stilbosis mines were smaller on asymmetric leaves, but differences in mine survivorship between symmetric and asymmetric leaves were observed only for Stilbosis mines. This study indicated that leaf miners might use leaf FA as a cue to plant quality, although differential survivorship among leaf types was not observed for all species studied. Reasons for the different results between guilds are discussed.     

Covariation of fluctuating asymmetry, herbivory and chemistry during birch leaf expansion

Fluctuating asymmetry (FA) is used to describe developmental instability in bilateral structures. In trees, high FA of leaves has been assumed to indicate the level of environmental or genetic stress, and for herbivores leaves from such trees have been shown to be in some cases (though not invariably) of higher quality compared to trees with symmetrical leaves. We demonstrated that FA of birch leaves correlated positively with growth rate of leaves, and with the amount of leaf biomass consumed by larvae of the geometrid Epirrita autumnata. Since asymmetry per se cannot define leaf quality for a herbivore, we determined the biochemical compounds which covary with the degree of foliage FA, in order to elucidate relationships between leaf FA, chemistry and herbivory. High foliar FA was characteristic of birches with high initial concentrations, and rapid seasonal decline in the concentrations of gallic acid and hydrolysable tannins, and with rapid seasonal changes in the concentrations of flavonoid-glycosides and sugars. In contrast, leaf FA was not related to concentrations of proanthocyanidins, protein-bound amino acids or soluble phenylalanine, the precursor of proanthocyanidins and proteins with aromatic amino acids. The positive correlation between leaf FA and consumption by E. autumnata was presumably related to the previously demonstrated compensatory consumption of E. autumnata to high concentrations of foliar gallotannins. Furthermore, sugars are well-known feeding stimulants. We propose that the variable results in studies correlating leaf FA and herbivory may stem from variable chemical associations of FA in different plants and of species-specific effects of compounds on insects. Received: 15 July 1999 / Accepted: 24 September 1999     

Fluctuating asymmetry of leaves is a poor indicator of environmental stress and genetic stress by inbreeding in Silene vulgaris

Fluctuating asymmetry (FA) is often used as a measure of developmental instability and has been proposed as an indicator of both environmental and genetic stress. However, the empirical evidence for the effects of stress on FA in plants is inconsistent, and there are few controlled experimental studies. We analyzed different distance- and shape-based measures of the fluctuating asymmetry of the leaves of clonally replicated self- and cross-pollinated lineages of Silene vulgaris (Moench) Garcke (Caryophyllaceae) grown under a control and seven different stress treatments (drought, copper, simulated herbivory, and two levels of nutrient deficiency and of shade). Overall, FA differed among stress treatments, but was not generally higher under stress and even reduced in some treatments. Different measures of FA were only weakly correlated. Inbreeding increased only one measure of leaf FA, and only under high stress intensities. Our findings suggest that in S. vulgaris leaf fluctuating asymmetry does not serve as an indicator of environmental stress or of genetic stress by inbreeding.     

Leaf trait variation on Erythroxylum tortuosum (Erythroxylaceae) and its relationship with oviposition preference and stress by a host‐specific leaf miner

It has been suggested that plant physical and chemical traits vary considerably in space and time. Hence, leaf‐mining insects may adjust their oviposition in response to leaf attributes representing high quality. Moreover, herbivorous insects can modify leaf morphology by acting as stressors, increasing, for example, fluctuating asymmetry (FA) levels. Here, we investigate oviposition preference in Agnippe sp.2, a leaf‐mining moth of Erythroxylum tortuosum, in relation to differences in leaf nutritional quality (i.e. levels of water, nitrogen and tannin content), leaf area (i.e. quantity of resource hypothesis) and FA. We also verify whether temporal variation in plant nutritional quality emerges as an alternative hypothesis to explain oviposition distribution in time, and whether this leaf miner is a stress‐causing agent, increasing FA during larval development. Mined leaves and leaves with and without eggs were periodically collected from plants located in a Cerrado fragment in Brazil. In the laboratory, leaf traits were assessed (using image analysis software) and quantified (biochemical analysis) according to the aims previously determined. Oviposition probability did not change in relation to variations in nitrogen, tannins and FA of leaves. However, leaf‐miner females preferred to oviposit on leaves having large areas and low water contents. It was also verified that new leaves of E. tortuosum, which carried most leaf‐miner eggs, presented significantly lower tannins and greater levels of nitrogen and water than old leaves. The oviposition choice exhibited by leaf miners was found to be non‐random because they appear to use resource quantity and water content as cues as where to lay their eggs. The temporal variation of plant nutritional quality is likely to influence the time of leaf‐miner oviposition; and leaf FA was not increased during larval feeding, suggesting that these herbivores do not cause variations in FA levels.     

Flight motor patterns of locusts responding to thermal stimuli

Correctional and intentional steering manoeuvres in locusts differ in several important respects. The most profound difference between the two is the production of large forewing asymmetries in angle of elevation during the downstroke in intentional steering that are not obvious in correctional steering. We investigated the flight motor patterns during intentional steering responses to a radiant heat source. We found asymmetries in the timing of forewing first basalar (m97) activity on the left and right sides that were strongly and positively correlated with forewing asymmetries. Timing asymmetry in the second basalar (m98) and pleuroalar (m85) muscles was not significantly different from the changes observed in m97. The hindwing first basalar (m127) shifted its asymmetry in the opposite direction. The forewing subalar muscle (m99) did not shift its asymmetry with the same magnitude as m97, but instead was phase-shifted relative to m97 on the left and right sides, suggesting its role as a supinator. We conclude that large asymmetries in the elevation angle of the forewings during the downstroke, as are evident in intentional steering, are generated by bulk shifts in the activation times of forewing depressor muscles to cause a relative shift in the time of stroke reversals of the two forewings. Accepted: 19 June 1998     

Heteroblasty in the moss,Aphanoregma patens (Physcomitrella patens), results from progressive modulation of a single fundamental leaf developmental programme

Abstract

Leaves at the apex of a mature Aphanoregma patens (Hedw.) Lindb. (Physcomitrella patens (Hedw.) Bruch Schimp. in B.S.G.) gametophore differ markedly in size and form from those at its base. To determine how these differences are produced during development, we first examined qualitative and quantitative differences between successive leaves along the stem and among leaves at different developmental stages. Differences between successive leaves were slight and cumulative. Local changes in cell number and size combined to produce a regularly shaped and approximately bilaterally symmetrical leaf suggesting that cell division and cell expansion are regionally regulated and coordinated at the organ level. The midrib and marginal teeth are discrete characters, which were prefigured by changes in cell shape in leaves that lacked these characters. In leaf primordia, cell proliferation was responsible for most of the changes in leaf form and size early in development and may have continued as cell expansion took over as the primary contributor to leaf growth and morphogenesis. Thus, leaf heteroblasty in Physcomitrella probably results from modulation of a single developmental programme by external and/or internal forces, which alter progressively in intensity as a gametophore grows. We applied exogenous cytokinin and auxin separately to growing cultures to explore their effects on leaf growth. Cytokinin and auxin stimulated leaf cell division and leaf cell elongation, respectively. Also, young upper leaves of gametophores exposed to exogenous auxin closely resembled basal leaves of untreated plants. Therefore, endogenous cytokinins and auxins may be among the modulating internal forces involved in leaf morphogenesis and the establishment of leaf heteroblasty.     

Sex, secondary compounds and asymmetry. Effects on plant–herbivore interaction in a dioecious shrub

We analysed the links between herbivory, anthraquinone content and developmental instability of leaves in Rhamnus alpinus, taking into account possible effects of sexual dimorphism. The amount of leaf loss caused by herbivores averaged 3%, rarely exceeding 25%. Leaf losses were evenly distributed in the shrubs, with highest variability among leaves of the same shoot, thus hiding possible shrub, sex or population effects. This pattern of herbivory implies a shifting of caterpillars from one leaf to another before consuming all readily available material. We suggest that this behaviour might be triggered by a short-term change in leaf palatability by means of an increase in the production of secondary compounds. Supporting this hypothesis, we have found a higher anthraquinone content in damaged leaves compared with undamaged ones. The leaves of male plants exhibited a higher concentration of anthraquinones than those of females, which contrasts with classic hypotheses. We relate this to the lower rate of biomass increase in males, which should allow them to allocate more resources to defence. Leaves showed fluctuating asymmetry (FA), but we did not find any relationship between the degree of asymmetry and sex, herbivory or anthraquinone content at any level considered. Therefore, FA cannot be considered as an indicator of susceptibility to damage by herbivores or of the ability to induce the production of defensive compounds in R. alpinus.     

Persistence of subtle departures from symmetry over multiple molts in individual brachyuran crabs: Relevance to developmental stability

Fluctuating asymmetry (FA) is generally viewed as a population-level character. It is described by some measure of the variance of the difference between the right and left sides for a collection of individuals. Very little is known of the developmental origins of FA, despite the fact that FA is widely used to estimatedevelopmental stability. We present a novel technique for examining the growth trajectory of the asymmetries that give rise to FA, and we explore two sample data sets for the brachyuran crabHemigrapsus nudus. We have traced the fate of these small, random deviations from perfect symmetry through three successive molts of individual crabs. Invertebrates that molt, and hence grow in discrete steps, provide an easily preserved record of their growth. Model II regressions of measurements from one molt versus the previous molt can help describe the stability of subtle departures from symmetry over time. Although any number of different patterns may occur, we identify four general cases: a) asymmetries vary at random throughout growth (random determination), b) asymmetries remain unchanged in sign and magnitude (constant asymmetries), c) asymmetries increase in proportion to character size and hence increase with growth (size-dependent asymmetries), and d) asymmetries persist, but are reduced in magnitude (damped asymmetries). Data from tenHemigrapsus nudus, measured for between 21 and 28 metrical, limb-segment characters over three successive molts, yielded associations most similar to our pattern ‘b’, although some subtle departures in the direction of pattern ‘c’ were also observed. Persistent asymmetries accounted for 26% and 20% of the variance among asymmetries between molts 1 and 2, and molts 2 and 3 respectively. Thus, in spite of large and rapid increments in the external size of the crab, these subtle asymmetries tended to persist in both direction and magnitude, from molt to molt. This result suggests either i) that individual crabs have a genetic predisposition towards asymmetry in a particular direction but contribute to a continuous and normal distribution ofR-L differences at the population level, or ii) that these subtle asymmetries arose at some earlier ontogenetic stage and were preserved through growth. Either interpretation has important ramifications for the study of FA. The first suggests that under some circumstances FA may not provide a valid measure of developmental instability, because subtle departures from symmetry in an individual may have a genetic basis. The second implies that subtle departures from bilateral symmetry are not ‘corrected’ as an individual grows.     

Herbivory-induced stress: Leaf developmental instability is caused by herbivore damage in early stages of leaf development

Herbivory is a major source of plant stress and its effects can be severe, decreasing plant fitness, or subtle, affecting the development of leaves by influencing the normal pattern of growth and expansion of leaf blades. Fluctuating asymmetry (FA) analysis is recognized as a measure of plant stress, and can be used to evaluate subtle effects of herbivory on the imperfect growth of bilaterally symmetrical traits, such as leaves. One general issue is that authors usually consider FA as an indicator of stress, which can attract herbivores (plant stress hypothesis), and studies showing that herbivores themselves affect leaf symmetry (herbivory-induced stress hypothesis) are scarce, with mixed results. Here, we investigated the relationship between herbivory by thrips and leaf FA in Banisteriopsis malifolia and Heteropterys escallonifolia (Malpighiaceae). Pseudophilothrips obscuricornis is a free-living, non-pest, sucking species that feeds mainly on leaf buds. We hypothesized that herbivory by thrips in the early stages of leaf development would provoke increased FA levels in mature leaves. The results showed that thrips herbivory rate was low, affecting barely more than 1% of the leaf blade. Nonetheless, thrips-attacked leaves of B. malifolia and H. escallonifolia presented increases of 15 and 27% in leaf asymmetry, respectively, compared to uninjured leaves, corroborating the herbivory-induced stress hypothesis. Since herbivory by thrips in leaf buds was related to significant increases in the stress of mature leaves, we assume that under these circumstances, FA can be used as a biomarker for plant stress following herbivory damage. To be useful as a biomarker of stress, FA in plants must be investigated with caution, taking into account the natural history of the herbivore species and timing of leaf damage.     

Co-Ordination of Cell Division and Tissue Expansion in Sunflower, Tobacco, and Pea Leaves: Dependence or Independence of Both Processes?

Abstract Temporal analyses of cell division and tissue expansion in pea, tobacco, and sunflower leaves reveal that both processes follow similar patterns during leaf development. Relative cell division and relative tissue expansion rates are maximal and constant during early leaf development, but they decline later. In contrast, relative cell expansion rate follows a bell-shaped curve during leaf growth. Cell division and tissue expansion have common responses to temperature, intercepted radiation, and water deficit. As a consequence, final leaf area and cell number remain highly correlated throughout a large range of environmental conditions for these different plant species, indicating that cell division and tissue expansion are co-ordinated during leaf development. This co-ordination between processes has long been explained by dependence between both processes. Most studies on dicotyledonous leaf development indicate that leaf expansion rate depends on the number of cells in the leaf. We tested this hypothesis with a large range of environmental conditions and different plant species. Accordingly, we found a strong correlation between both absolute leaf expansion rate and leaf cell number. However, we showed that this relationship is not necessarily causal because it can be simulated by the hypothesis of independence between cell division and tissue expansion according to Green's theory of growth (1976). Received 23 February 2000; accepted 3 March 2000     

Reproducibility of fluctuating asymmetry measurements in plants: Sources of variation and implications for study design

Fluctuating asymmetry (FA), i.e. small, non-directional deviations from perfect symmetry in morphological characters, increases under genetic and/or environmental stress. Ecological and evolutionary studies addressing FA became popular in past decades; however, their outcomes remain controversial. The discrepancies might be at least partly explained by inconsistent and non-standardised methodology. Our aim was to improve the methodology of these studies by identifying factors that affect the reproducibility of FA measurements in plant leaves. Six observers used a highly standardised measurement protocol to measure FA using the width, area and weight of the same set of leaves of 10 plant species that differed in leaf size, shape of the leaf margin and other leaf traits. On average, 24% of the total variation in the data was due to measurement error. Reproducibility of measurements varied with the shape of leaf margin, leaf size, the measured character and the experience of the observer. The lowest reproducibility of the width of leaf halves was found for simple leaves with serrate margins and the highest for simple leaves with entire margins and for compound pinnate leaves. The reproducibility was significantly lower for the weight of leaf halves than for either their width or area, especially for plants with small leaves. The reproducibility was also lower for measurements made by experienced observers than by naïve observers. The size of press-dried leaves decreased slightly but significantly relative to fresh leaves, but the FA of press-dried leaves adequately reflected the FA of fresh leaves. In contrast, preservation in 60% ethanol did not affect leaf size, but it decreased the width-based values of FA to 89.3% of the values measured from fresh leaves. We suggest that although reproducibility of leaf FA measurements depends upon many factors, the shape of the leaf margin is the most important source of variation. We recommend, whenever possible, choosing large-leaved plants with entire leaf margins as model objects for studies involving measurements of FA using the width of leaf halves. These measurements should be conducted with high accuracy from images of fresh or press-dried leaves.     

The effect of fluctuating asymmetry and leaf nutrients on gall abundance and survivorship

Fluctuating asymmetry (FA) is defined as small and random deviations from perfect symmetry in otherwise bilaterally symmetrical traits. Usually, plants under stress have a higher nutritional quality and are preferred by insect herbivores. Here, we examined the relationship among leaf FA of Bauhinia brevipes (Fabaceae), nutrients and the occurrence of Schizomyia macrocapillata (Cecidomyiidae: Diptera). We evaluated whether: (i) FA was related to S. macropillata abundance and survivorship; (ii) FA correlated with the levels of foliar nutrients (macro- and micronutrients, and organic carbon); and (iii) S. macropillata abundance was related to leaf nutrients. The results showed a positive relationship between FA and gall abundance. S. macrocapillata survivorship was five times higher in B. brevipes individuals with high FA levels, but this difference was not significant. The influence of nutrients in B. brevipes FA was negligible, except for foliar nitrogen, which was 7.3% higher in plants with low FA levels. The abundance of S. macrocapillata was negatively related to nitrogen levels, but gall survivorship was not affected by this nutrient. We found evidence for a causal relationship between FA and gall occurrence, since S. macropillata gall oviposition occurs in young undeveloped leaves, thus mature leaves show an increase in FA. Nonetheless, in this system, neither FA nor nitrogen influenced gall survivorship.     

Plant growth in relation to ontogenetic changes in productive characteristics of individual leaves I. growth and productive characteristics ofHelianthus annuus andZinnia elegans leaves

Growth and productive characteristics of successive leaves were ontogenetically examined using sunflower and zinnia plants grown in the field. For the purpose of more advanced comprehension, ontogenetic behavior of productive characteristics was formulated with the schematic leaf growth model. The largest leaf in zinnia appeared around the middle leaf order, but did not show the highest photosythetic rate. The decreasing pattern of relative leaf area expansion rate did not significantly differ among individual leaves, and seemed inherent to species. The ontogenetic changes in net photosynthetic rate per unit leaf area showed convex curves, while those in dark respiratory rate per unit leaf area rapidly decreased with leaf development and then became constant. In part, the rapid increase of photosynthetic rate in young leaves was supported by enhancement of light utilization efficiency, along with increase of chlorophyll content. The approach of leaf angle to the horizontal was more or less accompanied by photosynthetic development and leaf expansion. It was suggested that photosynthetic maturation in leaves of the sun-leaf type appears at leaf age equivalent to 0.35 to 0.46 of leaf life span. Ontogenetic pattern of all productive characteristics basically differed little among successive leaves.     

Is thermal time adequate for expressing the effects of temperature on sunflower leaf development?

We have tested whether the effects of temperature on sunflower leaf growth could be documented by using thermal time. The rates of leaf expansion and of cell division were analysed in leaves located at two positions on the stem, and a spatial analysis of expansion rate was carried out. Experiments were performed in growth chamber (stable conditions), in the field or in a greenhouse (fluctuating conditions). We compared three methods for characterizing the rate and the duration of expansion. Responses to leaf temperature were consistent only when expansion was characterized as a two-phase process — a period of exponential expansion (constant relative expansion rate, RER ) followed by a decrease in RER . RER and relative cell division rate ( RDR ) responded linearly to temperature with a common response curve for all studied conditions. This response curve was also common to all studied zones within a leaf and to leaves at two positions on the stem. The reciprocals of the durations of the periods of exponential expansion, non-zero expansion and non-zero division were also linearly related to leaf temperature with common response curves in a given leaf zone. The x -intercepts of all these response curves and of the response curve of leaf initiation rate to temperature did not significantly differ in an analysis of covariance, with a common value of 4·8 °C. The expression of time in cumulative degree days, with a base temperature of 4·8 °C, resulted in a unique time course of RER and cell division rate regardless of temperature. These results suggest that a powerful 'program' of leaf development exists in a sunflower plant.     

Leaf asymmetry as a developmental constraint imposed by auxin-dependent phyllotactic patterning

In a majority of species, leaf development is thought to proceed in a bilaterally symmetric fashion without systematic asymmetries. This is despite the left and right sides of an initiating primordium occupying niches that differ in their distance from sinks and sources of auxin. Here, we revisit an existing model of auxin transport sufficient to recreate spiral phyllotactic patterns and find previously overlooked asymmetries between auxin distribution and the centers of leaf primordia. We show that it is the direction of the phyllotactic spiral that determines the side of the leaf these asymmetries fall on. We empirically confirm the presence of an asymmetric auxin response using a DR5 reporter and observe morphological asymmetries in young leaf primordia. Notably, these morphological asymmetries persist in mature leaves, and we observe left-right asymmetries in the superficially bilaterally symmetric leaves of tomato (Solanum lycopersicum) and Arabidopsis thaliana that are consistent with modeled predictions. We further demonstrate that auxin application to a single side of a leaf primordium is sufficient to recapitulate the asymmetries we observe. Our results provide a framework to study a previously overlooked developmental axis and provide insights into the developmental constraints imposed upon leaf morphology by auxin-dependent phyllotactic patterning.     

Strategies of leaf expansion in Ficus carica under semiarid conditions

Leaf area expansion, thickness and inclination, gas exchange parameters and relative chlorophyll content were analysed in field‐grown fig (Ficus carica L.) leaves over time, from emergence until after full leaf expansion (FLE). Ficus carica leaves showed a subtle change in shape during the early stages of development, and FLE was reached within ca. 30 days after emergence. Changes in leaf thickness and inclination after FLE demonstrated good adaptation to environmental conditions during summer in areas with a Mediterranean climate. Changes in gas exchange parameters and relative chlorophyll content showed that F. carica is a delayed‐greening species, reaching maximum values 20 days after FLE. Correlation analysis of datasets collected during leaf expansion, confirmed dependence among structural and functional traits in F. carica. Pn was directly correlated with stomatal conductance (Gs), transpiration (E), leaf area (LA) and relative chlorophyll content up to FLE. The effect of pruning on leaf expansion, a cultural technique commonly applied in this fruit tree, was also evaluated. Although leaf development in pruned branches gave a significantly higher relative leaf area growth rate (RGR_l) and higher LA than non‐pruned branches, no significant differences were found in other morphological and physiological traits, indicating no pruning effect on leaf development. All studied morphological and physiological characteristics indicate that F. carica is well adapted to semiarid conditions. The delayed greening strategy of this species is discussed.     

Courtship and genetic quality: asymmetric males show their best side

Fluctuating asymmetry (FA), the small random deviations from perfect morphological symmetry that result during development, is ubiquitous throughout the animal kingdom. In many species, FA seems to play a role in mate choice, perhaps because it signals an individual''s genetic quality and health. However, the relationship between an individual''s FA and behaviour is generally unknown: what do more asymmetric individuals do about their own asymmetry? We now show for the first time that individuals respond behaviourally to their own morphological FA in what appears to be an adaptive manner. During courtship, male guppies exhibiting high FA in ornamental colour, bias their displays towards their more colourful body side, thus potentially increasing their attractiveness by exaggerating the quantity of their orange signal. This appears to be a strictly behavioural male response to cues provided by females, as it does not occur when males court a non-reactive model female. Whether inferior males realize any mating advantage remains uncertain, but our study clearly demonstrates a behavioural response to random morphological asymmetries that appears to be adaptive. We propose that the tendency to show or otherwise use a ‘best side’ is common in nature, with implications for sexual signalling and the evolution of more pronounced asymmetries.