Within-plant distribution of a galling adelgid (Homoptera: Adelgidae): the consequences of conflicting survivorship, growth, and reproduction

Abstract. 1. Adelges cooleyi (Gil.) was rarely found in the top-most whorl of shoots in its host plant Engelmann spruce.
2. The survivorship of the few Adelges fundatrices which did colonize the top whorl was at or near zero for the 3 years in which survivorship was assessed, while survivorship in the bottom whorls was at least 60%.
3. In contrast, when an Adelges fundatrix did survive in the top whorl, her growth and reproductive output, and the growth of her progeny, the gallicolae, were at least double that of bottom whorl fundatrices.
4. The distribution of fundatrices within spruce trees was strongly correlated ( R ²=0.934) with fundatrix fitness (=survivorship × fecundity × growth).
5. We hypothesize that the vigorous growth of top whorl shoots promotes Adelges growth and fecundity, but the earlier growth of these shoots results in low temperature mortality of fundatrices.     

Neighborhood models of plant population dynamics. 2. Multi-species models of annuals

Models are developed for the dynamics of multi-species communities of annual plants that lack seed dormancy. These models explicitly include plastic plant growth, the spatial distribution of individuals, and the fact that individuals interact primarily with nearby individuals. Because the models are based on submodels of individual plants (fecundity, survivorship and dispersal, and how these are affected by inter-individual interactions), they provide explanations of community-level phenomena in terms of the biology of individuals. All model parameters and functional forms may be estimated from data obtained in simple experiments of a single years's duration. The models are used to examine the community-level consequences of some types of inter-individual interactions that have been reported in the ecological literature. In addition, the models are used to demonstrate that dispersal may markedly influence the outcome of competition among plant species, even in a physically homogeneous environment, due to an effect of dispersal on the spatial distribution of individuals.     

Year class splitting in the woodlouse Philoscia muscorum explained through studies of growth and survivorship

Year class splitting has been observed in a population of the terrestrial isopod Philoscia muscorum (Scopoli) in a fixed dune grassland. In this population, individuals born in one season differentiate into two forms, one of which grows to maturity in one year, the other in two.
Laboratory investigations of growth, fecundity and survivorship of individuals showed fundamental positive relationships between rate of growth and the ambient temperature/day light regime and between parental size and the number of offspring produced. Size also affected survivorship, with adults surviving better than juveniles. A link between survivorship and the temperature/day light regime was only obvious in small juveniles.
No direct physiological cause for the year class split could be derived from the laboratory studies, but a trade-off between the need for delayed or early breeding could result in the patterns of growth and reproduction observed in the field population. Delayed breeding allows continued growth of adults and hence larger numbers of offspring. Early breeding allows more growth of juveniles which greatly improves their chances of winter survival.     

Differential invasion success among biotypes: case of Bemisia tabaci

Studies on success or failures of biological invasions by different insect biotypes are scarce and could provide interesting insights into the traits that determine greater or lower ability to invade. Life history traits of invasive whiteflies Bemisia tabaci of the B biotype (known as a worldwide invasive biotype) and of the indigenous biotype Ms (not known as an invader anywhere in the world), both from the island of La Réunion (Indian Ocean), were compared for this purpose. In our study we demonstrated that within a cultivated host plant (tomato), the B biotype differs from the Ms by a combination of several life-history traits. This combination gives the invasive biotype an advantage over the resident both in terms of rapid demographic growth (increased intrinsic rate of increase and associated traits such as short developmental times and high fecundity) and in terms of competition (large adult and offspring sizes), without any recorded trade off. However, in the field the resident biotype remains dominant on non-cultivated hosts (weeds) and in a particular climate (high humidity). This suggests that invasive biotypes are characterized by physiological, morphological and biological adaptations to a disturbed environment created by anthropic activities at different places in the world, while resident biotypes may persist in less altered habitats.     

Consequences of host plant chemical and physical variability to an associated herbivore

The effects of watering and fertilizer treatments on the vigor and biochemistry of the willow,Salix lasiolepis, and subsequent colonization and survivorship of its gallforming herbivore,Euura lasiolepsis, were investigated in two field experiments. Some plants received low (LW), intermediate (MW) or high (HW) levels of water as treatments, while others received no (OF), low (LF) or high (HF) fertilizer levels. In the watering experiment, plant protein concentrations decreased, while growth rate and number of galls per plant increased with increased water treatments. Plant growth proved to be the best correlate of sawfly attack. Sawfly survivorship increased slightly with greater watering, and phenol concentrations showed no pattern among treatments. In the fertilization experiment, leaf protein increased with fertilization, although shoot length, number of galls and survivorship ofE. lasiolepis survivorship were greatest in intermediate treatment plants. In both experiments, plant growth, rather than protein or phenol levels, was the best predictor of sawfly attack and survivorship. In a natural experiment with galls on wild plants, galled tissue had significantly greater protein concentrations and lower phenol concentrations than did ungalled tissue. We suggest that gallformers modify host plant biochemistry within willow galls, which may explain why the chemical parameters of ambient plant quality we tested were less predictive than plant growth.     

Effects of experimental manipulations on the life history pattern of Lymnaea stagnalis appressa say (pulmonata: lymnaeidae)

Field sampling of an Iowa population of Lymnaea stagnalis appressa Say indicated an annual generation pattern, with survivorship to maturity of i percent or less. Estimates of adult fecundity ranged from about 300 to 800 eggs.Density and food manipulations were performed to determine whether density dependent limitation of growth rates, maturation, or fecundity occurs in this fresh water pulmonate snail. Addition of a high quality food resource, spinach, accelerated growth rates, but did not drastically accelerate maturity, nor increase fecundity. Density increments lowered growth rates, delayed maturity, and lowered fecundity, and the addition of spinach did not counteract high densities. Adult densities are fairly low in the field population, and adults are randomly dispersed, indicating little density dependent regulation of fecundity in this population. However, the low survivorship to maturity, response in growth rates with food addition, and increasing survivorship with age and size indicate that juvenile mortality may play an important role in structuring life history patterns in this population.     

Comparative Population Dynamics of an Invading Species in its Native and Novel Ranges

Although the ecology of many exotic invaders has been intensively examined in the novel range, few studies have comparatively explored how population dynamics differ in native and novel parts of an invading plants’ range. The population dynamics of mile-a-minute weed, Polygonum perfoliatum L., was explored in both the native (Japan) and novel (northeastern USA) portions of its range and evaluated using periodic matrix models. Projected per capita population growth rate (λ) varied within and between native and novel range populations. Surprisingly, five of the six populations in the novel range were projected to fail to replace themselves (λ<1) while only two of the four native range populations were projected to decline, although these projections had wider confidence intervals than in the novel habitat. While changes in germination, survivorship, fecundity and seed banking would have equivalent effects on population growth in the invasive habitat, small increases in plant survivorship would greatly increase λ in native populations. The differences between native and novel population growth rates were driven by lower adult survival in the native range caused by annual flooding and higher fecundity. Simulation analyses indicated that a 50% reduction in plant survival would be required to control growing populations in the novel range. Further comparative studies of other invading species in both their native and novel ranges are needed to examine whether the high per capita population growth and strong regulatory effects of adult survival in the native habitat are generally predictive of invasive behavior in novel habitats. Sachiko Araki: (Deceased)     

Mode of origin differentially influences the fitness of parthenogenetic freshwater snails

How parthenogenetic lineages arise from sexual ancestors may strongly influence their persistence over evolutionary time. Hybrid parthenogens often have elevated heterozygosity and ploidy, thus making it difficult to disentangle the influence of reproductive mode, hybridity and ploidy on their relative fitness. By comparing the relative fitness of both hybrid and non-hybrid parthenogens to their sexual ancestors, further insight may be gained into how these three factors influence the maintenance of sexual and parthenogenetic reproduction. In the present study, hybrid and non-hybrid parthenogenetic and sexual snails (Campeloma sp.) were compared for the following characteristics: female size-fecundity curves, offspring size, survivorship, and growth. Compared to nearby sexual populations, triploid hybrid parthenogens from the Florida Gulf coast have similar fecundity and offspring size, five-times higher survivorship, and 60% higher growth. Relative to nearby sexual populations, non-hybrid parthenogenetic C. limum from the Atlantic coast have significantly higher fecundity, smaller offspring size, similar survivorship and slightly lower growth. Given the considerable fitness advantages of parthenogens, especially hybrid parthenogens, it is enigmatic as to why these parthenogens occupy marginal natural habitats.     

Development time and body size in Eupolyphaga sinensis along a latitudinal gradient from China

The responses of organisms to temperature variations may be via short term responses of the phenotype (phenotypic plasticity), or they could involve long-term evolutionary change and adaptation (via selection) to the genotype. These could involve changes to the mean size of the animal or to the thermal reaction norm. We examined the effects of various temperatures (of 22, 25, 28, and 31 °C) on development time, adult body size and preadult survivorship in three populations of the cockroach, Eupolyphaga sinensis (Walker), collected at different latitudes. We found substantial temperature-induced plasticity in development time, body size, and preadult survivorship, indicating that developmental temperatures have strong impacts on growth and life history traits of E. sinensis. Genetic differences for development time, body size, and preadult survivorship were detected among populations, and the three traits exhibited highly significant variations in the responses of different populations to various temperature conditions, indicating genetic differences among populations in terms of thermal reaction norms. We also found that two populations seem to support the beneficial acclimation hypothesis whereas the third mid-latitude population does not. The results are likely because of differences in season length and voltinism, indicating that not only temperature regime but also its interactions with generation time (and development time), voltinism, and season length are likely to have considerable effects on insect development time and body size. Overall, changes in development time, body size, and preadult survivorship in E. sinensis can all be regarded as adaptations to changing thermal regimes.     

A field study using the fungicide benomyl to investigate the effect of mycorrhizal fungi on plant fitness

Summary The effect of vesicular-arbuscular mycorrhiza (VAM) on the fecundity ofVulpia ciliata ssp.ambigua was investigated at two field sites in eastern England by applying the fungicide benomyl to reduce VAM infection. The application of benomyl at the two sites produced very different results. At one site the application of the fungicide reduced the fecundity of plants whereas at the other fecundity was increased. At the first site the reduction in fecundity was linked to a significant reduction in VAM infection on the sprayed plants. The mechanism of the benefit associated with the VAM infection is however unclear: there was no treatment effect on morphology or on phosphorus inflow. At the second site, where fecundity was increased, there was only a negligible amount of VAM infection amongst the unsprayed plants and it is suggested that the increase in fecundity with the application of benomyl may have resulted from a reduction in infection by other, presumably pathogenic, fungi. The value of VAM fungi to the host plant may therefore not be restricted to physiological benefits. They may also provide protection to the plant by competing for space with other species of pathogenic fungi.     

Effects of early resource limitation and compensatory growth on lifetime fitness in the ladybird beetle (Harmonia axyridis)

Acceleration of growth following a period of diet restriction may result in either complete or partial catch-up in size. The existence of such compensatory growth indicates that organisms commonly grow at rates below their physiological maxima and this implies a cost for accelerated growth. We examined patterns of accelerated growth in response to temporary resource limitation, and assayed both short and long-term costs of this growth in the ladybird beetle Harmonia axyridis. Subsequent to the period of food restriction, accelerated growth resulted in complete compensation for body sizes, although we observed greater larval mortality during the period of compensation. There were no effects on female fecundity or survivorship within 3 months of maturation. Females did not discriminate against males that had undergone compensatory growth, nor did we observe effects on male mating behaviour. However, individuals that underwent compensatory growth died significantly sooner when deprived of food late in adult life, suggesting that longer-term costs of compensatory growth may be quite mild and detectable only under stressful conditions.     

Nutrition in terrestrial isopods (Isopoda: Oniscidea): an evolutionary-ecological approach

The nutritional morphology, physiology and ecology of terrestrial isopods (Isopoda: Oniscidea) is significant in two respects. (1) Most oniscid isopods are truly terrestrial in terms of being totally independent of the aquatic environment. Thus, they have evolved adaptations to terrestrial food sources. (2) In many terrestrial ecosystems, isopods play an important role in decomposition processes through mechanical and chemical breakdown of plant litter and by enhancing microbial activity. While the latter aspect of nutrition is discussed only briefly in this review, I focus on the evolutionary ecology of feeding in terrestrial isopods. Due to their possessing chewing mouthparts, leaf litter is comminuted prior to being ingested, facilitating both enzymatic degradation during gut passage and microbial colonization of egested faeces. Digestion of food through endogenous enzymes produced in the caeca of the midgut glands (hepatopancreas) and through microbial enzymes, either ingested along with microbially colonized food or secreted by microbial endosymbionts, mainly takes place in the anterior part of the hindgut. Digestive processes include the activity of carbohydrases, proteases, dehydrogenases, esterases, lipases, arylamidases and oxidases, as well as the nutritional utilization of microbial cells. Absorption of nutrients is brought about by the hepatopancreas and/or the hindgut epithelium, the latter being also involved in osmoregulation and water balance. Minerals and metal cations are effectively extracted from the food, while overall assimilation efficiencies may be low. Heavy metals are stored in special organelles of the hepatopancreatic tissue. Nitrogenous waste products are excreted via ammonia in its gaseous form, with only little egested along with the faeces. Nonetheless, faeces are characterized by high nitrogen content and provide a favourable substrate for microbial colonization and growth. The presence of a dense microbial population on faecal material is one reason for the coprophagous behaviour of terrestrial isopods. For the same reason, terrestrial isopods prefer feeding on decaying rather than fresh leaf litter, the former also being more palatable and easier to digest. Acceptable food sources are detected through distance and contact chemoreceptors. The 'quality' of the food source determines individual growth, fecundity and mortality, and thus maintenance at the population level. Due to their physiological adaptations to feeding on and digesting leaf litter, terrestrial isopods contribute strongly to nutrient recycling during decomposition processes. Yet, many of these adaptations are still not well understood.     

High-throughput Phenotyping and Genomic Selection:The Frontiers of Crop Breeding Converge

Genomic selection (GS) and high-throughput phenotyping have recently been captivating the interest of the crop breeding com-munity from both the public and private sectors world-wide.Both approaches promise to revolutionize the prediction of complex traits,including growth,yield and adaptation to stress.Whereas high-throughput phenotyping may help to improve understanding of crop physiology,most powerful techniques for high-throughput field phenotyping are empirical rather than analytical and compa-rable to genomic selection.Despite the fact that the two method-ological approaches represent the extremes of what is understood as the breeding process (phenotype versus genome),they both consider the targeted traits (e.g.grain yield,growth,phenology,plant adaptation to stress) as a black box instead of dissecting them as a set of secondary traits (i.e.physiological) putatively related to the target trait.Both GS and high-throughput phenotyping have in common their empirical approach enabling breeders to use genome profile or phenotype without understanding the underlying biology.This short review discusses the main aspects of both approaches and focuses on the case of genomic selection of maize flowering traits and near-infrared spectroscopy (NIRS) and plant spectral reflectance as high-throughput field phenotyping methods for complex traits such as crop growth and yield.     

Population biology of <Emphasis Type="Italic">Kosteletzkya pentacarpos</Emphasis> (Malvaceae) in the Llobregat delta (Catalonia,NE of Spain)

Field experiments and wild population monitoring have been performed to study the population biology of the rare long-lived Kosteletzkya pentacarpos (Malvaceae) in the Llobregat delta (Catalonia, NE Spain). Field experiments explored the fate of seeds in soil at different depths, seedling emergence, and seedling survival, growth and flowering with and without canopy cover during the first 2 years of life. They also were used to ascertain the size-related pattern of seedling survivorship and flowering. Field data concerning mortality, growth and fecundity of adult plants were collected yearly in three wild populations for 7–9 years. In old adults (reproducing long before the beginning of the study), ANOVAR tests were performed to compare maximum diameter, total and fertile shoots, and viable seeds per plant between years and populations. New adults (starting flowering the first year of study or in subsequent years) were used to explore, using linear and polynomial regressions, the association of RGR and both total and fertile shoot production with (i) plant size (maximum basal diameter or its logarithm); (ii) plant age (years in adult stage); and (iii) plant age after removing the effect of size and year-to-year fluctuations. In this case, we examined the age-related pattern of the residuals obtained from the regressions with size and year. The study identified the following main demographic features of K. pentacarpos: (i) transient, shallow soil seed bank; (ii) shade tolerance of seedling emergence; (iii) canopy-facilitation of seedling survival and bolting during the first two years of life; (iv) size-related pattern for seedling survivorship but not flowering; (v) exclusive dependence on a fluctuating seed output for reproduction; (vi) rapid adult growth; and (vii) high adult longevity but (viii) rapid depletion of fecundity with age. Seed output was highly constrained by mining insects. The changing size-structure and the decreasing reproductive success of old adults in several populations suggest that K. pentacarpos might undergo a dynamics of population establishment and extinction in the Ricarda marshes. Because of fluctuating reproduction and the lack of a persistent seed bank, the conservation of standing adult populations appears to be a key factor to ensure the persistence of the species.     

Survivorship and fecundity of the radiate and non-radiate morphs of Groundsel,Senecio vulgaris L., raised in pure stand and mixture

British populations of Senecio vulgaris frequently contain two common capitulum morphs (radiate and non-radiate) and one rare intermediate morph. The radiate morph shows a higher maternal rate of intermorph outcrossing than the non-radiate morph and due to the ‘cost of outcrossing’ should decline in frequency, ultimately to be lost from a population. To determine whether the radiate morph exhibits some inherent advantage in fitness to offset the ‘cost of outcrossing’, a comparison was made of the survivorship and fecundity of the radiate and non-radiate morphs raised in pure stands and 1 : 1 mixture at three planting dates (autumn 1983, and spring and autumn 1984). Plants in stands established in spring 1984 were harvested in late August 1984, while plants in stands established in autumn overwintered before being harvested the following summer. In spring planted stands, the two morphs exhibited equivalent survivorships, while the fecundity of the non-radiate morph tended to be greater than the radiate morph. In autumn planted stands, survivorship and Net Reproductive Output (survivorship × fecundity) of the non-radiate morph was greater than that of the radiate morph in mixture, and also in pure stands established in 1983. In no instance was the Net Reproductive Output of either morph significantly greater in mixture than in pure stand. Density had a contrasting effect on morph survivorship and fecundity in the spring and autumn 1984 planted stands. Whereas, in spring stands, fecundity was subject to compensating density dependent regulation while survivorship was density independent, the opposite trend was observed in autumn planted stands. It is concluded that under the conditions of the experiments, the radiate morph exhibited no fitness advantage which might offset the inherent disadvantage it suffers in natural polymorphic populations due to the ‘cost of outcrossing’.     

Adaptation of an outbreaking insect defoliator to chronic nutritional stress

During insect outbreaks, the high number of individuals feeding on its host plant causes a depletion of the food source. Reduced availability and decreased quality of nutrients negatively influence life‐history traits of insects driving them to develop adaptive strategies to persist in the environment. In a laboratory experiment with three repetitions, we tested the effect of chronic nutritional stress on spruce budworm performance during three generations to determine the adaptive strategies employed by the insect to deal with a selection pressure produced by low‐quality diet. Our results show that all tested life‐history traits (mortality, developmental time, pupal mass, growth rate and female fecundity) but female fertility were negatively influenced by the low‐quality diet simulating food depletion during outbreak conditions. However, especially females in the third generation under chronic nutritional stress show an adaptive response in life‐history traits when compared to those reared only one generation on low‐quality diet. Larval developmental time significantly decreased and pupal mass, growth rate and fecundity significantly increased. The study demonstrates the capacity of spruce budworm to react to chronic nutritional stress with adaptations that may be caused by epigenetic parental effects. This information can help to understand the course of an outbreak especially at peak densities and during the collapse.     

Effects of larval density on a natural population of Culex restuans (Diptera: Culicidae): no evidence of compensatory mortality

1. This study investigated the effects of strong density dependence on larval growth, development, and survival of the mosquito Culex restuans (Theobald). It also tested the hypothesis that density reduction early in larval development could result in as many or more individuals surviving to adulthood (compensation or over‐compensation, respectively), or increased reproductive performance via rapid development and greater adult size. 2. In a field study of a natural population of C. restuans, the effects of a 75% lower density on percentage survivorship to adulthood, number of adults, development time, adult size, adult longevity, and size dependent fecundity were tested. 3. No evidence was found of compensation or over‐compensation in adult production, or of effects of lower density on percentage survivorship. Low density yielded significant increases in adult size, adult longevity, and size‐dependent fecundity, and a decrease in development time. 4. Estimated per‐capita population growth rate was significantly greater in the low‐density treatment than in the high‐density treatment. It is inferred that this difference was due to greater per‐capita resources, which increased female size and fecundity, and reduced development time. Greater per‐capita population growth could therefore result from early mortality of larvae, meaning that the hydra effect, which predicts greater equilibrium population with, as opposed to without, extrinsic mortality, may be possible for these mosquitoes.     

Population Dynamics of Evolutionary Change: Demographic Parameters as Indicators of Fitness

I evaluated demographic parameters as indicators of fitness by calculating the net reproductive rate (R₀), exponential rate of change (r), lifetime reproductive success (LRS), and Malthusian parameter (m) for nine genotypes and four phenotypes (two alleles at each of two independent loci) of an age-structured population. The given starting conditions included age-specific survival rates of males and females and age-specific fecundity of females for each genotype (to simplify the problem I presumed no differences in survivorship or fecundity of genotypes with the same phenotype) and the same age structure for each genotype. The prevailing genotype had the greatestm, but it did not have the greatestr,R₀, or LRS, or even the greatest survivorship of either juveniles or adults, or the greatest fecundity. This result indicates thatmis the only correct measure of fitness (i.e., as a predictor of which genotype should prevail from among a group of genotypes) and that comparisons ofr,R₀, LRS, juvenile or adult survival rates, or fecundity may be misleading indicators of which genotype should prevail (i.e., be most “fit”) over time (i.e., be selected for).     

Digestion, growth and reproductive performance of the zoophytophagous rove beetle Philonthus quisquiliarius (Coleoptera: Staphylinidae) fed on animal and plant based diets

The zoophytophagous feeding habits of larvae and adults of the rove beetle, Philonthus quisquiliarius (Gyllenhal) (Coleoptera: Staphylinidae), are reported for the first time. This study evaluates the effects of different feeding regimes on its growth and reproductive performance (i.e., larval growth, adult weight gain, consumption, fecundity and fertility) and digestive physiology. Larvae presented similar growth rates when fed on living animal or on green plant material for 48h. However, higher consumption rates and lower efficiencies of conversion of digested matter to body mass were obtained when leaves were consumed. Adults presented also positive weight gains regardless of the food consumed (plant or animal material). Interestingly, the highest weight gain rate and efficiency of digestion resulted when adults fed on a rearing diet containing nutrients from both animals and plants. Moreover, we have found negative effects upon P. quisquiliarius fecundity and fertility when supplemental plant nutrients were removed from the optimum rearing diet. Physiological adaptations to allow trophic switching between predation and phytophagy have been found, such as the higher ratio of α-amylase activity to protease activity to deal with the inverted protein-carbohydrate ratio of plant versus animal tissues. Furthermore, this species has an arsenal of digestive proteases whose activity is affected by the type of diet ingested. All together, our results suggest that P. quisquiliarius needs certain nutrients, which are obtained only from plant material. This knowledge will help to understand the complex trophic interactions that occur in agroecosystems.     

Effects of microclimate on behavioural and life history traits of terrestrial isopods: implications for responses to climate change

The sensitivity of terrestrial isopods to changes in both temperature and moisture make them suitable models for examining possible responses of arthropod macro-decomposers to predicted climate change. Effects of changes in both temperature and relative humidity on aggregation, growth and survivorship of species of isopods contrasting in their morphological and physiological adaptations to moisture stress have been investigated in laboratory microcosms.All three traits were more sensitive to a reduction in relative humidity of 20–25% than they were to an increase in temperature of 5–6 °C. These results suggest that predicted changes in climate in south east England may reduce the extent to which soil animals stimulate microbial activity and hence carbon dioxide (CO₂) emissions from soils in the future. This may help to mitigate the potential for a positive feedback between increased CO₂ emissions from soils, and increased greenhouse effects causing an increase in soil temperatures.