Effects of artificial defoliation on reproductive allocation in the common vetch,Vicia sativa (Fabaceae: Papilionoideae)

Previous field experiments have shown that, for the annual herb Vicia sativa, leaf area lost to herbivory results in reduced number of fruit (pods) produced per plant as well as fewer seeds per pod. We conducted a controlled garden experiment to determine the precise relationship between level of defoliation and various measures of maternal fitness through fruit and seed. We employed manual clipping of individual leaflets of newly produced leaves to 25% increments of damage (from 0% to 100%) over the entire period of development and flowering of these annual herbs, harvesting pods when filled but not dehisced. We found significant reduction in number of pods, number of seeds, total seed mass, and individual seed mass with leaf area lost. Even with the highest levels of defoliation over the life of the individual, plants still produced a substantial number of pods and seeds. Seeds produced by plants in all treatment groups showed similar percentages of germination and time to germination.     

Reproductive system and pattern of genetic variation in two Limnanthes species

Summary Several populations of two species of the genus Limnanthes, (L. alba, an outbreeder and L. floccosa, an inbreeder) were examined with respect to variability of fifteen quantitative characters, allozyme variation at 11 loci, and response to different pollination conditions and moisture stress. Nearly equal amounts of phenotypic variability were found in the two species. L. alba had higher within-family variability than L. floccosa, but this result was highly heterogeneous among characters. A study of between- and within-population variance estimates did not reject the null hypothesis that L. alba and L. floccosa are similar with regard to the partitioning and amount of variability for quantitative characters. However, allozyme variation at 11 loci in a large number of populations showed L. alba to be highly polymorphic in contrast to the virtual monomorphism within L. floccosa populations. The average number of alleles per locus in L. alba and L. floccosa was 1.97 and 1.02, respectively, and on an average, L. alba and L. floccosa populations had 63% and 3% loci with polymorphism, respectively. Three groups of allozyme allelic combinations emerged which correlated well with the taxonomic delineation of allogamous L. alba, three semi-autogamous L. floccosa forms and two autogamous L. floccosa forms.All taxa showed a significant reduction in the seed output per plant due to moisture stress. L. alba suffered a further loss of fecundity under the paucity of pollinators, L. floccosa ssp. floccosa showed no significant effect from this factor, whereas L. floccosa ssp. grandiflora exhibited a curvilinear response which peaked at partial pollination and decreased to a lower level at full pollination.The geographic distribution of the two species with regard to the temperature and rainfall distribution did not suggest L. floccosa to be living in drier marginal areas. Patterns of variation in flowering time showed L. alba to be less variable than L. floccosa. Overall, there seemed to be little direct support for the thesis that inbreeding species originated from outcrossing taxa in marginal environments as a direct adaptation to a shortened growing season of xeric environments and to the lack of pollinators. Alternative hypotheses suggest that autogamy in L. floccosa might have evolved as a reproductive isolating barrier acting through either cleistogamy or divergence in flowering times.     

The plastic reproductive allocation of the cruciferous perennialRorippa indica in response to different degrees of feeding damage

The degree of feeding damage in the wild to the cruciferous perennial Rorippa indica (L.) Hieron ranged from 0% (not damaged) to 100% (heavily damaged). However, “not damaged” and “heavily damaged” individuals did not differ in the relative suitability of their intrinsic traits for P. rapae, which caused the heaviest damage on the plant. Therefore, the different degrees of feeding damage may be due to variability in the extrinsic traits of the plant, that is, it may be determined by the habitat conditions where individual plants exist. Furthermore, R. indica allocated more resource to seed production at the expense of the roots when it was experimentally subjected to heavy leaf damage. The result suggested that R. indica individuals may escape, by means of seed dispersal and seed dormancy, from unfavorable habitats where they are heavily damaged by herbivores.     

Reproductive allocation and costs in gynodioecious Leucopogon melaleucoides (Ericaceae): implications for the evolution of gender dimorphism

In dioecious species, females typically allocate more resources to reproduction and incur greater costs of reproduction than males. In gynodioecious species, sex-based differences in reproductive allocation (RA) and costs have been less studied. Such knowledge, however, is relevant to address how females establish and increase in frequency in populations. We examine RA and reproductive costs by comparing fruit set, the proportion of biomass allocated to reproduction, and the responses of fruit set and vegetative growth to shoot defoliation in females and hermaphrodites in gynodioecious Leucopogon melaleucoides. Relative to hermaphrodites, females exhibited a two-fold fruit set advantage. Female fruit set increased proportionately with flower number, but hermaphrodite fruit set was reduced on plants with more flowers. Sex-based differences in allocation to other traits were small. Thus, female RA at flowering was similar to hermaphrodite RA, but was 1.4-fold greater at fruiting. Relative to controls, defoliation reduced fruit set and the percentage of shoots that produced new vegetative growth similarly in both sexes. However, females had a lower proportion of shoots with new growth overall. Further, defoliation on females reduced the dry mass of new growth by 44% compared with controls, whereas hermaphrodites were not affected. These results indicate a trade-off between reproduction and vegetative growth, and greater female costs of reproduction, particularly under resource-limiting conditions. In the absence of compensatory traits to offset higher female reproductive costs, such trade-offs have the potential to retard the spread of females in gynodioecious populations.     

Seasonal variation in nitrogen storage reserves in the roots of leafy spurge (Euphorbia esula) and responses to decapitation and defoliation

Seasonal fluctuations of carbohydrates and nitrogenous components in the roots of the noxious perennial leafy spurge ( Euphorbia esula L.) are strongly associated with overwintering strategy, Amino acids and distinct soluble proteins accumulate during fall and remain at elevated levels throughout winter. The formation of carbohydrate reserves in roots was not significantly affected by decapitation or selective defoliation; however, maximum amino acid and soluble protein contents were markedly reduced. In particular, the accumulation pattern of a 26 kDa protein was altered. This protein may play a role in plant conditioning and regenerative potential.     

State of the reproductive system of populations of species of the genus Glycyrrhiza L. (Fabaceae)

Reproductive features of the valuable medicinal herbs Glycyrrhiza glabra L., G. uralensis Fisch., and G. korshinskyi Grig. were investigated; an assessment was made of the state of the reproductive systems of populations located under introduction conditions in the Central Urals and in the zone contact of the species ranges in the southern cis-Urals. The states of the male and female reproductive systems, seed productivity elements, pollination features, and the viability of seeds produced by different pollination treatments were studied. For the three Glycyrrhiza species, the seed productivity indices were found to decrease considerably starting from the early stages of development of the female reproductive system and continuing to seed maturity. A quantitative analysis of seed productivity elements taking into account the flowering duration of the species showed that the seed production system of the species is very efficient; even in the introduced populations located north of the range, it is able to produce viable seeds in years with favorable growing conditions. Qualitative and quantitative indices of the reproductive system were used to characterize samples from the zone of contact between the ranges. Embryological analysis confirmed the possibility of interspecific hybridization and the prevalence of hybrid forms among the samples. A broad distribution of interspecific hybridization in Glycyrrhiza in various parts of the ranges is assumed. Glycyrrhiza species are characterized by seed and vegetative reproduction. Vegetative reproduction is limited in space but efficiently ensures reproduction of individuals and formation of vegetative clones. Seed reproduction is characterized by indices such as amphimictic seed formation, strict entomophily, and interspecific compatibility. Seed reproduction is a factor that controls the possibility of wide propagation of the genetic material in space and, hence, the formation of mixed and hybrid populations leading to a higher intraspecific and interspecific diversity of the genus.     

Ecophysiological responses to light availability in three Blechnum species (Pteridophyta, Blechnaceae) of different ecological breadth

In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse microhabitats ranging from large gaps to heavily shaded understoreys. We hypothesised that differences in the ecological breadth of three co-occurring Blechnum species would be associated with differences in magnitude of ecophysiological responses to light availability. We quantified the field distribution of each species in relation to diffuse light availability (% canopy openness), and measured in situ variation in photosynthetic capacity (A), dark respiration (R _d) and specific leaf area (SLA) across the light gradient. The response of SLA of each species was also evaluated in a common garden in two light conditions (understorey and forest edge). The three Blechnum species differed significantly in the range of light environments occupied (breadth: B. chilense > B. hastatum > B. mochaenum). Despite significant interspecific differences in average A and R _d, the response of these traits to light availability did not differ among species. However, there was significant interspecific variation in both the mean value and the plasticity of SLA to light availability, the species with least ecological breadth (B. mochaenum) showing a flatter reaction norm (lower response) than its two congeners. This pattern was also found in the common garden experiment. The adjustment of leaf morphology (SLA) to light availability appears to be an important mechanism of acclimation in these Blechnum species. The narrow range of light environments occupied by B. mochaenum may be at least partly attributable to its inability to display phenotypic plasticity in SLA to changes in light availability.     

Phenotypic responses of the twining vine Ipomoea purpurea (Convolvulaceae) to physical support availability in sun and shade

Vines depend on external support to prevent shading by neighbouringplants. Hence, it is important to determine whether shading enhances thephenotypic responses of vines to support availability. I evaluated theconsequences of support availability (a vertical stake) on shoot and leaftraitsof the morning glory Ipomoea purpurea (Convolvulaceae)under full sunlight and extreme shade. It was hypothesised that phenotypicresponses of vines to support availability should be greater in the shade. Inaddition, to investigate possible constraints to such phenotypic responses, thecorrelations among phenotypic traits and the plasticity of such correlationswere evaluated. The phenotypic variation of the main stem length and of thenumber of branches was consistent with the hypothesis, i.e. greater responsestosupport availability in the shade. In contrast, both internode length and leafarea (two traits that showed a significant and positive correlation) decreasedin the sun and increased in the shade with support availability. Petiole lengthdecreased with support in the sun but had no response in the shade. On theotherhand, the number of significant trait correlations found in plants in the sunand supported plants was higher than those of shade and non-supported plants,respectively. Several of the correlations were significantly sensitive to theenvironment. Flowering only occurred in the sun treatment. Whereas no shoot orleaf trait was significantly correlated with flower number in supported plants,both petiole length and shoot biomass showed a significant correlation withsuchestimate of plant fitness in non-supported plants.     

Cost of reproduction in a spring ephemeral species, Adonis ramosa (Ranunculaceae): carbon budget for seed production

BACKGROUND AND AIMS: Spring ephemerals have a specific life-history trait, i.e. shoot growth and sexual reproduction occur simultaneously during a short period from snowmelt to canopy closure in deciduous forests. The aim of this study is to clarify how spring ephemerals invest resources for seed production within a restricted period. METHODS: In order to evaluate the cost of reproduction of a typical spring ephemeral species, Adonis ramosa, an experiment was conducted comprising defoliation treatments (intact, one-third and two-thirds leaf-cutting) and fruit manipulations (control, shading and removal) over two growing seasons. In addition, measurements were made of the movements of carbon assimilated via (13)C tracing. KEY RESULTS: Survival rate was high irrespective of treatments and manipulations. The proportion of flowering plants and plant size decreased as a result of the defoliation treatments over 2 years, but the fruit manipulations did not affect flowering activity or plant size. Seed set and seed number decreased as a result of fruit shading treatment, but the defoliation treatments did not affect current seed production. Individual seed weight also decreased in the second year due to fruit shading. The (13)C tracing experiment revealed that young fruits had photosynthetic ability and current photosynthetic products from leaves were mainly transferred to the below-ground parts, while translocation to fruit was very small even when fruit photosynthesis was restricted by the shading treatment. CONCLUSIONS: Current foliage photosynthetic products are largely stored in the below-ground parts for survival and future growth, and about one-third of the resources for seed production may be attained by fruit photosynthesis. Therefore, the trade-off between current seed production and subsequent growth is weak. The cost of seed production may be buffered by sufficient storage in the below-ground organs, effective photosynthesis under high irradiation and self-assimilation ability of fruits.     

Reproductive effort,fecundity and energy allocation in two species of the genus Perinereis (Polychaeta: Nereididae)

Summary

The reproductive effort in terms of fecundity and energy allocation was studied in two species of semelparous polychaetes belonging to the genus Perinereis, living in the same environment, with different reproductive modalities. There is a great individual variability both in terms of reproductive effort and fecundity. Fecundity varied from 4080 to 15000 oocytes in P. rullieri and from 7000 to 26000 in P. cultrifera; no linear relationship was found between oocyte number and total jaw length utilised as size index. The energy content of germinal and somatic tissues was determined by Differential Scanning Calorimeter (DSC). The reproductive effort was calculated as RE = E_G/(E_G + E_S) where E_G is the total energy in germinal tissues and E_S is the total energy in somatic tissues. Reproductive effort is very high with mean values of 0.62 for P. rullieri and 0.79 for P. cultrifera. The different amounts of energy allocated in germinal tissues can be attributed to the different reproductive modalities—P. rullieri reproduces in the atokous phase whereas P. cultrifera has conserved epitoky in its life-cycle. The lack of correlation between reproductive effort and size index strongly suggests that reproductive allocation does not increase with age. In semelparous species the variability in fecundity and reproductive effort observed cannot be interpreted in terms of a trade-off between fecundity and survival as in iteroparous species. In fact, in semelparous an individual allocates all available resources to reproduction and then dies.     

Correlated responses of root growth and sugar concentrations to various defoliation treatments and rhythmic shoot growth in oak tree seedlings (Quercus pubescens)

Background and Aims

To understand whether root responses to aerial rhythmic growth and contrasted defoliation treatments can be interpreted under the common frame of carbohydrate availability; root growth was studied in parallel with carbohydrate concentrations in different parts of the root system on oak tree seedlings.

Methods

Quercus pubescens seedlings were submitted to selective defoliation (removal of mature leaves, cotyledons or young developing leaves) at appearance of the second flush and collected 1, 5 or 10 d later for morphological and biochemical measurements. Soluble sugar and starch concentrations were measured in cotyledons and apical and basal root parts.

Key Results

Soluble sugar concentration in the root apices diminished during the expansion of the second aerial flush and increased after the end of aerial growth in control seedlings. Starch concentration in cotyledons regularly decreased. Continuous removal of young leaves did not alter either root growth or apical sugar concentration. Starch storage in basal root segments was increased. After removal of mature leaves (and cotyledons), root growth strongly decreased. Soluble sugar concentration in the root apices drastically decreased and starch reserves in the root basal segments were emptied 5 d after defoliation, illustrating a considerable shortage in carbohydrates. Soluble sugar concentrations recovered 10 d after defoliation, after the end of aerial growth, suggesting a recirculation of sugar. No supplementary recourse to starch in cotyledons was observed.

Conclusions

The parallel between apical sugar concentration and root growth patterns, and the correlations between hexose concentration in root apices and their growth rate, support the hypothesis that the response of root growth to aerial periodic growth and defoliation treatments is largely controlled by carbohydrate availability.     

Analytical studies on the responses of sunflower (Helianthus annuus) to various defoliation treatments

The effects of defoliation treatments on plant growth in sunflower (Helianthus annuus) were studied in the field. Four defoliation treatments, 0 (control), 37.4, 56.1 and 93.4% of the total leaf dry weight, were applied to plants that had small third leaves. Decreased leaf weight/whole plant weight (F/W) ratios in defoliated plants rapidly recovered to almost the same ratio as that observed in the control within 12 to 16 days after defoliation according to the degree of defoliation. The mechanism involved in the recovery of the F/W ratio in defoliated plants mainly consisted of three parameters: enhancement of (1) carbon distribution ratios in the leaves, (2) photosynthetic activity in the remaining leaves, and (3) retranslocation of carbon from the stem and/or roots to leaves. Inhibitive effects of defoliation on relative growth rate and net assimilation rate were seen at an early stage, but subsequently both rates became larger in defoliated plants than in controls. Defoliated plants tended to show rapid development and expansion of new leaves, and to show increased specific leaf area and protein synthesis in individual leaves. The sugar content of leaves in defoliated plants was higher than that in controls, while the content in both stem and roots was lower. These responses seem to be advantageous for development of the photosynthetic system. Heights of defoliated plants were clearly depressed according to the degree of defoliation, and this was attributed largely to differences in the elongation rates of the internodes resulting from defoliation.     

Seasonal variation in metabolic rate of a medium-sized frugivore, the Knysna Turaco (Tauraco corythaix)

Many seasonal thermoregulation studies have been conducted on Holarctic birds that live in predictable, highly seasonal climates with severe winters. However, relatively few studies have been conducted on their southern hemisphere Afrotropical counterparts that encounter less predictable climates with milder winters. These latter birds are expected to conserve energy in winter by downregulating their metabolic rates. Therefore in this study, metabolic rate was measured during summer and winter in Knysna Turaco, Tauraco corythaix (Musophagiformes, Musophagidae) (c. 310 g), a non-passerine, in order to test whether there is energy conservation in winter. No overall significant differences in resting metabolic rates over a range of ambient temperatures were observed between winter and summer. However, whole-organism basal metabolic rates were 18.5% higher (p=0.005) in winter than in summer (210.83±15.97 vs. 186.70±10.52 O₂ h⁻¹). Knysna Turacos had broad thermoneutral zones ranging from 20 to 28 °C in winter and 10 to 30 °C in summer. These results suggest that Knysna Turacos show seasonal thermoregulatory responses that represent cold defense rather than energy conservation, which is contrary to what was expected.     

Plasticity of seed output in response to soil nutrients and density in Abutilon theophrasti: implications for maintenance of genetic variation

 Seed output is determined by two processes: resource acquisition and the allocation of resources to seeds. In order to clarify how the reaction norm of seed output is controlled by the phenotypic expression of its two components, we examined the genetic components of plasticity of seed dry mass, plant size, and reproductive allocation under different conditions of soil nutrient availability and conspecific competition among eight families of Abutilon theophrasti. Without competition, the reaction norm of seed mass of the families crossed between the lowest and other nutrient levels, although neither of its components, plant size and reproductive allocation, showed such a response. The crossing reaction norm (i.e., reversal of relative fitnesses of different genotypes along the environmental gradient) of seed mass resulted from (1) a trade-off between plant size and reproductive allocation, and (2) changes in the relative magnitude of genetic variances in plant size and reproductive allocation with soil nutrient availability. While allocation was more important in determining seed mass under limiting nutrient conditions, plant size became more important under high-nutrient conditions. There were no significant genetic variances in seed mass, plant size, and reproductive allocation in the competition treatment, except at the highest nutrient level. The results show that plant competition mitigated the effects of genetic differences in plant performance among the families. We discuss the results in relation to maintenance of genetic variation within a population. Received: 16 August 1996 / Accepted 26 April 1997     

Plasticity of fish body shape. The effects of diet, development, family and age in two species of Geophagus (Pisces: Gichlidae)

Fish body shape is affected by the genetic makeup of an individual as well as environmental influences, such as diet, development, growth rate and nutrition. Fishes in the family Cichlidae exhibit tremendous morphological diversity in body shape and morphology related to feeding. Certain aspects of cichlid feeding morphology have been shown to be plastic in response to different diets but plasticity in body shape has not been examined previously. Plasticity affects ecological interactions, the direction and rate of evolution, and has ramifications for characters used in systematic studies. I examined the effect of different diets: chironomid larvae (bloodworms) and brine shrimp nauplii, on body shape in two species of the Neotropical cichlid genus Geophagus which differ in the size at which young begin feeding on external food sources. The fry of G. brasiliensis , a substrate spawner, begin to feed on external food sources earlier than the fry of G. steindachneri , a mouthbrooder. I hypothesized that the difference in size at first feeding could lead to a difference in the amount of plasticity inducible in the two species. The magnitudes of changes were mostly similar, although G. brasiliensis responded to the different diets with slightly greater changes in some of the head measurements. The pattern of changes in the two species were also similar, with fish fed ferine shrimp nauplii developing longer and shallower heads and shallower bodies and tails than fish fed chironomid larvae. I also examined the consequences of considering family and age as additional factors besides diet in G. steindachneri. Considering family or age as additional factors in the analyses did not change the conclusion that different diets induce differences, albeit small ones, in body shape. I argue that morphological plasticity is dependent on behavioural flexibility and that it may enhance evolutionary morphological diversification.     

Ovarian dynamics and oosorption in two species of predatory lady beetles (Coleoptera: Coccinellidae)

Abstract Ovarian development and oviposition dynamics of two species of lady beetle, Coccinella septempunctata L. and C. transversoguttata richardsoni Brown, are examined in laboratory experiments in which pea aphids (Acyrthosiphon pisum Harris) are provided ad libitum and then removed. Both species respond to prey removal by stabilizing at lower body weights, and by laying progressively fewer and smaller eggs of reduced viability, until oviposition ceases altogether after several days of starvation. Dissections of females after prey removal reveal similar patterns of oosorption in both species. However, C. septempunctata reduces oviposition more rapidly after prey removal than does C. transversoguttata. When prey are again provided, C. septempunctata soon lay as many eggs as previously but C. transversoguttata lay fewer. Females, especially of C. septempunctata, that stop producing and resorb eggs in the absence of prey lay more eggs subsequently than do females that feed continually on prey provided ad libitum and lay eggs throughout the experiment. Thus, although both species are responsive to a rapid change in prey availability, C. septempunctata appears to be especially responsive. Rapid responses to changes in prey availability may contribute to the greater abundance and reproductive success of this introduced species relative to the native C. transversoguttata in western North American alfalfa fields that exhibit widely varying pea aphid densities. However, both species engage in oosorption as a means of reserving resources under poor prey conditions and enhancing future reproductive effort when prey conditions improve.     

Offspring fitness in relation to population size and genetic variation in the rare perennial plant species Gentiana pneumonanthe (Gentianaceae)

Seeds were sampled from 19 populations of the rare Gentiana pneumonanthe, ranging in size from 5 to more than 50,000 flowering plants. An analysis was made of variation in a number of life-history characters in relation to population size and offspring heterozygosity (based on seven polymorphic isozyme loci). Life-his-tory characters included seed weight, germination rate, proportion of seeds germinating, seedling mortality, seedling weight, adult weight, flower production per plant and proportion of plants flowering per family. Principal component analysis (PCA) reduced the dataset to three main fitness components. The first component was highly correlated with adult weight and flowering performance, the second with germination performance and the third component with seed and seedling weight and seedling mortality. The latter two components were considered as being maternally influenced, since these comprised life-history traits that were significantly correlated with seed weight. Multiple regression analysis showed that variation in the first fitness component was mainly associated with heterozygosity and not with population size, while the third fitness component was only correlated with population size and not with heterozygosity. The latter relationship appeared to be non-linear, which suggests a stronger loss of fitness in the smallest populations. The second (germination) component was neither correlated with population size nor with genetic variation. There was only a weak association between population size, heterozygosity and the population coefficients of variation for each life history character. Most correlation coefficients were negative, however, which suggests that there is more variation among progeny from smaller populations. We conclude that progeny from small populations of Gentiana pneumonanthe show reduced fitness and may be phenotypically more variable. One of the possible causes of the loss of fitness is a combination of unfavourable environmental circumstances for maternal plants in small populations and increased inbreeding. The higher phenotypic variation in small populations may also be a result of inbreeding, which can lead to deviation of individuals from the average phenotype through a loss of developmental stability.     

Differences in the compensatory growth of two co-occurring grass species in relation to water availability

We compared the potential for compensatory growth of two grass species from the Mongolian steppe that differ in their ability to persist under grazing: the rhizomatous Leymus chinensis and the caespitose Stipa krylovii, and investigated how this ability might be affected by drought. Plants were grown in a greenhouse under wet and dry conditions and subjected to a clipping treatment (biweekly removal of 75–90% of the aerial mass). Leymus exhibited a much stronger compensatory growth after clipping than Stipa. Leymus showed a significant increase in its relative growth rate (RGR) after clipping, while for Stipa RGR was negatively affected. Clipped Leymus plants maintained leaf productivity levels that were similar to undamaged individuals, while leaf-productivity in clipped Stipa dropped to less than half of that of the controls. In Leymus, there was less compensatory growth under dry than under wet conditions, while in Stipa the compensation was increased under drought. This difference probably reflects the fact that Stipa is more drought-tolerant than Leymus. The greater compensatory growth of Leymus compared to Stipa mainly resulted from a greater stimulation of its net assimilation rate (NAR), and its greater capacity to store and reallocate carbohydrates by clipping. The greater increase in NAR was probably the result of a stronger reduction in self-shading, because Leymus shoots were much denser than those of Stipa, which resulted in a higher increase in light penetration to remaining leaves after clipping. The results of this study suggest that the greater ability of Leymus to persist under grazing is the result of its larger capacity for compensatory growth.