Effects Of Larval Crowding Research Articles

Effects of larval crowding on the transcriptome of Drosophila simulans.

Larval crowding is one common ecological stressor for many insect species. In Drosophila, high larval density alters multiple widely-studied phenotypes including life-history traits, morphology and behavior. Nevertheless, we still miss a holistic view of the full range of phenotypic changes and the underlying molecular mechanisms. In this study, we analyzed the adult transcriptomes of high and low larval density fly cohorts, and highlighted the molecular basis of the plastic traits. Increased cellular energy metabolism and locomotion, along with reduced reproductive investment, are key responses to high larval density. Moreover, we compared the expression changes among cohorts with different developmental delays caused by larval crowding. The majority of genes induced by larval crowding showed the strongest expression alterations in cohorts with intermediate delay. Furthermore, linear expression changes were observed in genes related to nutrition and detoxification. Comparing different high-density cohorts could provide insights into the varied responses to distinct larval crowding-induced stresses such as space competition, food degradation and waste accumulation.

Spatial and ontogenetic variance in local densities modify selection on demographic traits

Abstract Local density can affect individual performance by altering the strength of species interactions. Within many populations, local densities vary spatially (individuals are patchily distributed) or change across life stages, which should influence the selection and eco‐evolutionary feedback because local density variance affects mean fitness and is affected by traits of individuals. However, most studies on the evolutionary consequences of density‐dependent interactions focus on populations where local densities are relatively constant through time and space. We investigated the influence of spatial and ontogenetic variance in local densities within an insect population by comparing a model integrating both types of local density variance with models including only spatial variance, only ontogenetic variance, or no variance. We parameterized the models with experimental data, then used elasticity and invasion analyses to characterize selection on traits that affect either the local density an individual experiences (mean clutch size) or individuals' sensitivity to density (effect of larval crowding on pupal mass). Spatial and ontogenetic variance reduced population elasticity to effects of local density by 76% and 34% on average, respectively. Spatial variance modified selection and adaptive dynamics by altering the tradeoff between density‐dependent and density‐independent vital rates. In models including spatial variance, strategies that maximized density‐dependent survival were favoured over fecundity‐maximizing strategies even at low population density, counter to predictions of density‐dependent selection theory. Furthermore, only models that included spatial variance, thus linking the scales of oviposition and density‐dependent larval survival, had an evolutionarily stable clutch size. Ontogenetic variance weakened selection on mean clutch size and sensitivity to larval crowding by disrupting the relationship between trait values and performance during critical life stages. We demonstrate that local density variance can strongly modify selection at empirically observed interaction strengths and identify mechanisms for the effects of spatial and ontogenetic variance. Our findings reveal the potential for local density variance to mediate eco‐evolutionary feedback by shaping selection on demographically important traits. Read the free Plain Language Summary for this article on the Journal blog.

Consequences of adaptation to larval crowding on sexual and fecundity selection in Drosophila melanogaster.

Sexual selection is a major force influencing the evolution of sexually reproducing species. Environmental factors such as larval density can manipulate adult condition and influence the direction and strength of sexual selection. While most studies on the influence of larval crowding on sexual selection are either correlational or single-generation manipulations, it is unclear how evolution under chronic larval crowding affects sexual selection. To answer this, we measured the strength of sexual selection on male and female Drosophila melanogaster that had evolved under chronic larval crowding for over 250 generations in the laboratory, along with their controls which had never experienced crowding, in a common garden high-density environment. We measured selection coefficients on male mating success and sex-specific reproductive success, as separate estimates allowed dissection of sex-specific effects. We show that experimental evolution under chronic larval crowding decreases the strength of sexual and fecundity selection in males but not in females, relative to populations experiencing crowding for the first time. The effect of larval crowding in reducing reproductive success is almost twice in females than in males. Our study highlights the importance of studying how evolution in a novel, stressful environment can shape adult fitness in organisms.

Crowded developmental environment promotes adult sex-specific nutrient consumption in a polyphagous fly

BackgroundThe fitness of holometabolous insects depends largely on resources acquired at the larval stage. Larval density is an important factor modulating larval resource-acquisition, influencing adult survival, reproduction, and population maintenance. To date, however, our understanding of how larval crowding affects adult physiology and behaviour is limited, and little is known about how larval crowding affects adult non-reproductive ecological traits. Here, larval density in the rearing environment of the polyphagous fruit fly Bactrocera tryoni (‘Queensland fruit-fly’) was manipulated to generate crowded and uncrowded larval treatments. The effects of larval crowding on pupal weight, adult emergence, adult body weight, energetic reserves, fecundity, feeding patterns, flight ability, as well as adult predation risk were investigated.ResultsAdults from the crowded larval treatment had lower adult emergence, body weight, energetic reserves, flight ability and fecundity compared to adults from the uncrowded larval treatment. Adults from the crowded larval treatment had greater total food consumption (i.e., consumption of yeast plus sucrose) relative to body weight for both sexes compared to adults from the uncrowded treatment. Furthermore, males from the crowded treatment consumed more yeast relative to their body weight than males from the uncrowded treatment, while females from the crowded treatment consumed more sucrose relative to their body weight than females from the uncrowded treatment. Importantly, an interaction between the relative consumptions of sucrose and yeast and sex revealed that the density of conspecifics in the developmental environment differentially affects feeding of adult males and females. We found no effect of larval treatment on adult predation probability. However, males were significantly more likely to be captured by ants than females.ConclusionWe show that larvae crowding can have important implications to ecological traits in a polyphagous fly, including traits such as adult energetic reserve, flight ability, and adult sex-specific nutrient intake. Our findings contextualise the effects of larval developmental conditions into a broad ecological framework, hence providing a better understanding of their significance to adult behaviour and fitness. Furthermore, the knowledge presented here can help us better understanding downstream density-dependent effects of mass rearing conditions of this species, with potential relevance to Sterile Insect Technique.

Effects of larval crowding and nutrient limitation on male phenotype, reproductive investment and strategy in Ephestia kuehniella Zeller (Insecta: Lepidoptera)

Food shortage experienced by juvenile insects affects adult morphology and life-history traits. Developmental plasticity and trade-off between ecological and sexual traits helps maximise individual fitness. Ephestia kuehniella were reared at different larval densities to investigate phenotypic shifts in adult males. Variation in ecological traits (sizes of forewing, head and thorax and adult longevity) and sexual traits (valva and aedeagus, sperm number, mating frequency) were compared. Males that emerged from highest density population (800) had lower body mass and small forewings, head and thorax, suggesting that they could not completely compensate for food shortage. The allometric relationship between body mass and forewing length also changed, and these males had relatively longer wings. This arrangement may enhance dispersal and assist in mate-searching at higher densities. Males from all larval densities achieved similar mating frequency but those from higher density produced fewer eupyrene sperm and had shorter adult lifespan. By mating more frequently and maintaining apyrene sperm production, males increase their reproductive success at sperm competition observed at higher densities. Food stress associated with high density populations did not affect valva and aedeagus size indicating that these traits may be insensitive to external environmental changes because they incur fitness costs to males.

Effects of larval crowding on quantitative variation for development time and viability in Drosophila melanogaster.

Competition between individuals belonging to the same species is a universal feature of natural populations and is the process underpinning organismal adaptation. Despite its importance, still comparatively little is known about the genetic variation responsible for competitive traits. Here, we measured the phenotypic variation and quantitative genetics parameters for two fitness‐related traits—egg‐to‐adult viability and development time—across a panel of Drosophila strains under varying larval densities. Both traits exhibited substantial genetic variation at all larval densities, as well as significant genotype‐by‐environment interactions (GEIs). GEI was attributable to changes in the rank order of reaction norms for both traits, and additionally to differences in the between‐line variance for development time. The coefficient of genetic variation increased under stress conditions for development time, while it was higher at both high and low densities for viability. While development time also correlated negatively with fitness at high larval densities—meaning that fast developers have high fitness—there was no correlation with fitness at low density. This result suggests that GEI may be a common feature of fitness‐related genetic variation and, further, that trait values under noncompetitive conditions could be poor indicators of individual fitness. The latter point could have significant implications for animal and plant breeding programs, as well as for conservation genetics.

Intraspecific competition in the Parthenium beetle Zygogramma bicolorata (Coleoptera: Chrysomelidae): effect of larval crowding on life-history traits

The effects of larval crowding on growth, development and reproductive output of the Parthenium beetle Zygogramma bicolorata Pallister were investigated. Experimental manipulations of larval densities indicated that crowding creates intraspecific competition among the larvae, which negatively affected their growth and development. Larvae at high densities grew more slowly and exhibited longer larval periods compared with those at lower densities. Best-fit curves of developmental rates against larval densities were drawn, which revealed maximum theoretical density for 95% (6 or 15 larvae/63.6 cm 2 ) and 50% developmental rate (1.75 larvae/63.6 cm 2 ), respectively. The reproductive potential of the beetle reared at different larval densities was also observed, but no effect of increased larval densities was observed.

The effects of larval crowding and food type on the size and development of the blowfly, Calliphora vomitoria

The use of entomological evidence in the estimation of the post mortem interval (PMI) often depends on the size and developmental stage of blowfly larvae collected from a corpse. Therefore, factors which can have an effect on the larval size and growth rate can have implications for reliable PMI determinations. This study explores the competitive effects of larval overcrowding on Calliphora vomitoria reared on three different pig tissues – liver, brain and muscle. The competitive feeding environment within the more crowded larval cultures resulted in increased development rates and the production of undersized larvae and adults. Variation in the extent of these effects was observed on each of the three body tissues, highlighting the importance of documenting the positions from which entomological evidence is recovered from a corpse.

Effect of larval crowding on mating competitiveness of Anopheles gambiae mosquitoes

BackgroundThe success of sterile or transgenic Anopheles for malaria control depends on their mating competitiveness within wild populations. Current evidence suggests that transgenic mosquitoes have reduced fitness. One means of compensating for this fitness deficit would be to identify environmental conditions that increase their mating competitiveness, and incorporate them into laboratory rearing regimes.MethodsAnopheles gambiae larvae were allocated to three crowding treatments with the same food input per larva. Emerged males were competed against one another for access to females, and their corresponding longevity and energetic reserves measured.ResultsMales from the low-crowding treatment were much more likely to acquire the first mating. They won the first female approximately 11 times more often than those from the high-crowding treatment (Odds ratio = 11.17) and four times more often than those from the medium-crowding treatment (Odds ratio = 3.51). However, there was no overall difference in the total number of matings acquired by males from different treatments (p = 0.08). The survival of males from the low crowding treatment was lower than those from other treatments. The body size and teneral reserves of adult males did not differ between crowding treatments, but larger males were more likely to acquire mates than small individuals.ConclusionLarval crowding and body size have strong, independent effects on the mating competitiveness of adult male An. gambiae. Thus manipulation of larval crowding during mass rearing could provide a simple technique for boosting the competitiveness of sterile or transgenic male mosquitoes prior to release.

Crowding‐induced responses in a geometrid moth revisited: a field experiment

In Lepidoptera, effects of larval crowding on life history traits may manifest themselves as changes in growth rate and duration of larval period. For the outbreaking geometrid moth, Epirrita autumnata, impacts of crowding have been shown in earlier laboratory studies, and these responses were modified by diet quality. In this study, the aim was to find out the specific nature of crowding effects of E. autumnata in the field. E. autumnata larvae were reared individually and in groups in mesh bags on mountain birch, both on good and poor quality foliage. Three field experiments were carried out with different densities in the crowded treatment (12, 21 and 45 larvae per 100 short shoots of mountain birch), simulating intermediate to severe outbreaks. The study revealed the density interval (12–21) within which impacts of crowding become evident. Significant effects were mostly found with the two highest densities in the crowded treatment combined with poor foliage quality. In those treatments, crowding resulted in 8–12% and 24–33% decrease in pupal mass and larval survival, respectively. The results of the present field experiments, however, did not corroborate the results of earlier laboratory studies: duration of larval period was not substantially affected, net effects of crowding were negative and interactions between crowding and foliage quality were contrary to those obtained in earlier laboratory studies. In many other Lepidoptera as well, the knowledge on responses to crowding may be mostly qualitative since most crowding experiments have been conducted in laboratory.

Environmental effects on cytoplasmic incompatibility and bacterial load in Wolbachia‐infected Drosophila simulans

AbstractThe effects of high temperatures, antibiotics, nutrition and larval density on cytoplasmic incompatibility caused by a Wolbachia infection were investigated in Drosophila simulans. Exposure of larvae from an infected stock to moderate doses of tetracycline led to complete incompatibility when treated females were crossed to infected males; the same doses only caused a partial restoration of compatibility when treated males were crossed to uninfected females. In crosses with treated females, there was a strong correlation between dose effects on hatch rates and infection levels in embryos produced by these females. Ageing and rearing males at a high temperature led to increased compatibility. However, exposing infected females to a high temperature did not influence their compatibility with infected males. Male temperature effects depended on conditions experienced at the larval stage but not the pupal stage. Exposure to 25 °C reduced the density of Wolbachia in embryos compared with a 19 °C treatment. Low levels of nutrition led to increased compatibility, but no effect of larval crowding was detected. These findings show the ways environmental factors can influence the expression of cytoplasmic incompatibility and suggest that environmental effects may be mediated by bacterial density.

Growth and Yield Response of Rice to Rice Water Weevil Injury

Analysis of larval and pupal age-structured data indicates that the soil core sampler–soil separation method underestimates the abundance of early instar rice water weevil, Lissorhoptrus oryzophilus Kuschel. The estimates for bias were used to derive seasonal larval age-structured population estimates for 4 yr of field data from 2 experiments representing untreated and carbofuran treated plots. These estimates were used as input to a physiologically based rice population model to simulate the response of rice to rice water weevil injury. An iterative halving-grid size optimization approach enabled least squares estimation of the larval feeding rate as a function of larval mass, the effect of larval crowding on root mass consumption by larvae, and the effect of larval feeding on root nitrogen uptake efficiency. A statistically based parameterization-verification-validation procedure was used to quantify the robustness of the model at simulating rice straw mass, grain yield, and total above ground mass. The model accurately simulated each of these variables for the range of rice water weevil seasonal age-structured population patterns, and explained 95% of the yield variability in the observed data. In contrast, a multiple linear regression of grain yield as a function of cumulative larval-density degree-days and the timing of peak density explained only 58% of the variability. An analysis of the benefits and costs accrued from the carbofuran treatments suggests that the current rice water weevil action threshold may be too high when infestations begin during early stages of crop growth. Results from sensitivity analyses indicate that the stage of crop growth during which rice water weevil injury occurs greatly affects crop tolerance for root injury, suggesting that optimal timing of rice water weevil controls should take into account both larval density and stage of crop growth.

Effect of larval crowding on adult mating behaviour in Drosophila melanogaster

The effect of larval density on male mating success has been investigated with two strains of Drosophila melanogaster, a wild strain and a mutant strain, under low and high larval competition, and four different genotypic frequencies. The results show a strong sexual selection against mutant males when flies have been raised under low larval competition. Under high larval competition, there is a reduction in mating disadvantage of mutant males. In both instances, a frequency-dependent sexual selection exists. These results explain adequately the evolution of experimental populations where egg to adult viability and male mating success are the most important components of fitness.

Studies on the biology of Attagenus elongatulus Casey (Coleoptera: Dermestidae) and the effects of larval crowding on pupation and life cycle

The rates of pupation of Attagenus elongatulus Casey larvae were reduced by increased larval crowding. Artificial selection reduced the crowding effects and shortened the minimum life cycle. Female fecundity and mating success declined with age. Male potency was not affected by age but mating success declined. Females produced progeny from eggs laid during the first 4 days after mating with over 80% of the larvae produced during the first 2 days.

The Effects of Larval Crowding and Body Size on the Longevity of Adult Drosophila Melanogaster

The Effects of Larval Crowding and Body Size on the Longevity of Adult Drosophila Melanogaster