Context‐dependent effects of cold stress on behavioral,physiological, and life‐history traits of the red flour beetle

Animals are exposed in nature to a variety of stressors. While stress is generally harmful, mild stress can also be beneficial and contribute to reproduction and survival. We studied the effect of five cold shock events versus a single cold shock and a control group, representing three levels of stress (harsh, mild, and no stress), on behavioral, physiological, and life‐history traits of the red flour beetle (Tribolium castaneum, Herbst 1797). Beetles exposed to harsh cold stress were less active than a control group: they moved less and failed more frequently to detect a food patch. Their probability to mate was also lower. Beetle pairs exposed to harsh cold stress frequently failed to reproduce at all, and if reproducing, females laid fewer eggs, which were, as larvae in mid‐development, smaller than those in the control group. However, harsh cold stress led to improved female starvation tolerance, probably due to enhanced lipid accumulation. Harsh cold shock also improved tolerance to an additional cold shock compared to the control. Finally, a single cold shock event negatively affected fewer measured response variables than the harsh cold stress, but also enhanced neither starvation tolerance nor tolerance to an additional cold shock. The consequences of a harsher cold stress are thus not solely detrimental but might even enhance survival under stressful conditions. Under benign conditions, nevertheless, harsh stress impedes beetle performance. The harsh stress probably shifted the balance point of the survival‐reproduction trade‐off, a shift that did not take place following exposure to mild stress.     

The stimulation of immune defence accelerates development in the red flour beetle (Tribolium castaneum)

The timing of the transition between life stages is of key importance for an organism. Depending on the environmental conditions, maturing earlier at a smaller size or maturing later at a larger size can be advantageous for fitness. Exposure to parasites and subsequent immune activation may lead to alterations in development. Immune defence often comes at a cost, such as energy drain towards immune function, which is likely to delay development. On the other hand, animals may react to an anticipated risk of infection with a phenotypically plastic shift in life history, which may more likely lead to accelerated development and earlier maturation. We tested these alternatives in the red flour beetle, Tribolium castaneum. Young larvae were exposed to a non-infectious immune challenge with heat-killed bacteria (either Escherichia coli or Bacillus thuringiensis) and they were followed up for their development, survival, adult size and reproduction. We found that animals that had experienced a bacterial challenge developed into adults earlier than sham-treated beetles, while they did not differ significantly in survival or adult size. Beetles exposed to E. coli produced fewer offspring, while exposure to B. thuringiensis did not affect offspring number. Taken together, our results indicate that T. castaneum is able to speed up its development when facing a risk of infection.     

Separation between maternal and paternal effects on offspring following exposure of adult red flour beetles to two stressors

1. The contribution of non‐genetic maternal effects to offspring performance is well established and the evidence for paternal effects has also been increasing recently. Studies determining the relative contributions of the two parents to offspring success are, however, still rare. 2. In this study, two stressors were applied to adult red flour beetles (Tribolium castaneum) – starvation and cold stress – and a full‐factorial design was used to distinguish between maternal and paternal reproductive decisions and their effects on the offspring. 3. Starvation had a stronger negative effect than cold stress on both males and females, and the likelihood of starved females producing offspring was very low. Furthermore, starved fathers led to lower offspring mass at the larval stage, probably leading to impaired starvation tolerance of the offspring. 4. Cold‐stressed fathers were less likely than unstressed fathers to reproduce, whereas cold‐stressed mothers demonstrated a similar effect by producing fewer offspring. 5. Applying stress probably led to energy saving that came at the expense of reproduction intensity. It is suggested that the smaller offspring mass is a negative consequence of the parental exposure to stress. 6. The differences between the consequences of the two stressors applied and between the relative contribution of each parent could perhaps be explained by the distinct physiological responses of each sex to each of the stressors.     

Identification of microsatellite markers in the red flour beetle,Tribolium castaneum

We isolated and characterized microsatellite markers for the red flour beetle Tribolium castaneum, an important model species for studies in various areas of evolutionary biology and ecology. A microsatellite‐enriched genomic library was constructed and screened with single stranded oligonucleotide probes [(CCT)₁₇, (AAT)₁₇ and (CAG)₁₇]. Forty‐five primer pairs were designed of which 19 pairs produced successful amplification. Polymorphism screening involved beetles from five beetle strains and revealed 15 polymorphic and four monomorphic markers. The development of polymorphic microsatellite markers will facilitate future ecological and genetic studies involving T. castaneum beetles.     

Population density, body size, and phenotypic plasticity of brood size in a burying beetle

Theory predicts that organisms living in heterogeneous environmentswill exhibit phenotypic plasticity. One trait that may be particularlyimportant in this context is the clutch or brood size becauseit is simultaneously a maternal and offspring characteristic.In this paper, I test the hypothesis that the burying beetle,Nicrophorus orbicollis, adjusts brood size, in part, in anticipationof the reproductive environment of its adult offspring. N. orbicollisuse a small vertebrate carcass as a food resource for theiryoung. Both parents provide parental care and actively regulatebrood size through filial cannibalism. The result is a positivecorrelation between brood size and carcass size. Adult bodysize is an important determinant of reproductive success forboth sexes, but only at higher population densities. I testthree predictions generated by the hypothesis that beetles adjustbrood size in response to population density. First, averageadult body size should vary positively with population density.Second, brood size on a given-sized carcass should be larger(producing more but smaller young) in low-density populationsthan in high-density populations. Third, females should respondadaptively to changes in local population density by producinglarger broods when population density is low and small broodswhen population density is high. All three predictions weresupported using a combination of field and laboratory experiments.These results (1) show that brood size is a phenotypically plastictrait and (2) support the idea that brood size decisions arean intergenerational phenomenon that varies with the anticipatedcompetitive environment of the offspring.     

The influence of the ability to disperse on generation length and population size in the flour beetle, Tribolium castaneum

Abstract.

• 1 In Tribolium castaneum Herbst, in which dispersal is genetically determined, it is possible to select for strains that are characterized by high and low dispersal, High dispersal (HD) beetles are better adapted than low dispersal (LD) beetles for colonization, as can be seen from differences that exist between the two groups with regard to several life-history parameters.
• 2 Comparisons were made between the dynamics of seventy-two HD and seventy-two LD populations. Generation length in HD populations was significantly shorter than in LD populations. After 9¹/₂ weeks, in open treatments (from which dispersal away from the set was allowed), HD populations had more beetles than LD populations, whereas in closed treatments (from which dispersal away from the set was not allowed) the opposite was true.
• 3 These findings may explain the maintenance of the genetic variability of dispersal behaviour in natural populations of T.castmeurn.

     

The role of parental age effects on the evolution of aging

Many studies have found that older parents have shorter-lived offspring. However, the evolutionary significance of these findings is poorly understood. We carried out large-scale demographic experiments to examine the direct effect of maternal age and paternal age on offspring aging in inbred and outbred strains of the fruit fly Drosophila melanogaster. We found that the age of mothers and, to a lesser extent, the age of fathers can have a large influence on both offspring longevity and the shape of the age-specific mortality trajectory. In two independent experiments we found that older mothers generally produced shorter-lived offspring, although the exact effect of maternal age on offspring longevity differed among strains. These results suggest that maternal age effects on progeny aging may influence the evolution of aging.     

The effects of Farinocystis tribolii on the growth and development of the flour beetle Tribolium castaneum

Farinocystis tribolii multiplied only in the fatbody of Tribolium castaneum larvae. In the advanced stages of infection, the fatbody was destroyed and the albuminoid granules were completely depleted. Larvae in late stages of infection were “C” shaped. Diseased pupae were flat and straight with the head and mouth parts not completely flexed with the pupal body. Infected pupae failed to develop into adults. Heavily infected adults were distended. Larvae of third, fourth, and fifth instars, although succumbing to the infection ultimately, continued to live even after the healthy larvae of the same age had entered pupation, indicating a prolongation of larval period. Molting was either affected or delayed in infected insects. F. tribolii infection induced a juvenile hormonal effect producing larval-pupal and pupal-adult intermediate forms. Ether extract of spores of F. tribolii when applied on pupae of T. castaneum and final instar nymphs of Dysdercus cingulatus produced adultoids.     

Intraspecific variation in thermal acclimation and tolerance between populations of the winter ant,Prenolepis imparis

Thermal phenotypic plasticity, otherwise known as acclimation, plays an essential role in how organisms respond to short‐term temperature changes. Plasticity buffers the impact of harmful temperature changes; therefore, understanding variation in plasticity in natural populations is crucial for understanding how species will respond to the changing climate. However, very few studies have examined patterns of phenotypic plasticity among populations, especially among ant populations. Considering that this intraspecies variation can provide insight into adaptive variation in populations, the goal of this study was to quantify the short‐term acclimation ability and thermal tolerance of several populations of the winter ant, Prenolepis imparis. We tested for correlations between thermal plasticity and thermal tolerance, elevation, and body size. We characterized the thermal environment both above and below ground for several populations distributed across different elevations within California, USA. In addition, we measured the short‐term acclimation ability and thermal tolerance of those populations. To measure thermal tolerance, we used chill‐coma recovery time (CCRT) and knockdown time as indicators of cold and heat tolerance, respectively. Short‐term phenotypic plasticity was assessed by calculating acclimation capacity using CCRT and knockdown time after exposure to both high and low temperatures. We found that several populations displayed different chill‐coma recovery times and a few displayed different heat knockdown times, and that the acclimation capacities of cold and heat tolerance differed among most populations. The high‐elevation populations displayed increased tolerance to the cold (faster CCRT) and greater plasticity. For high‐temperature tolerance, we found heat tolerance was not associated with altitude; instead, greater tolerance to the heat was correlated with increased plasticity at higher temperatures. These current findings provide insight into thermal adaptation and factors that contribute to phenotypic diversity by revealing physiological variance among populations.     

Characterization and functional analysis of hsp18.3 gene in the red flour beetle,Tribolium castaneum

Small heat shock proteins (sHSPs) are diverse and mainly function as molecular chaperones to protect organisms and cells from various stresses. In this study, hsp 18.3, one Tribolium castaneum species-specific shsp、has been identified. Quantitative real-time polymerase chain reaction illustrated that Tchsp 18.3 is expressed in all developmental stages, and is highly expressed at early pupal and late adult stages, while it is highly expressed in ovary and fat body at the adult period. Moreover, it was up-regulated 4532 ± 396-fold in response to enhanced heat stress but not to cold stress;meanwhile the lifespan of adults in ds-Tchsp 18.3 group reduced by 15.8% from control group under starvation. Laval RNA interference (RNAi) of Tchsp 18.3 caused 86.1%±4.5% arrested pupal eclosion and revealed that Tchsp 18.3 played an important role in insect development. In addition, parental RNAi of Tchsp 18.3 reduced the oviposition amount by 94.7%. These results suggest that Tchsp 18.3 is not only essential for the resistance to heat and starvation stress, but also is critical for normal development and reproduction in T. castaneum.     

Separating parental environment from seed size effects on next generation growth and development in Arabidopsis

Plant growth and development is profoundly influenced by environmental conditions that laboratory experimentation typically attempts to control. However, growth conditions are not uniform between or even within laboratories and the extent to which these differences influence plant growth and development is unknown. Experiments with wild-type Arabidopsis thaliana were designed to quantify the influences of parental environment and seed size on growth and development in the next generation. A single lot of seed was planted in six environmental chambers and grown to maturity. The seed produced was mechanically sieved into small and large size classes then grown in a common environment and subjected to a set of assays spanning the life cycle. Analysis of variance demonstrated that seed size effects were particularly significant early in development, affecting primary root growth and gravitropism, but also flowering time. Parental environment affected progeny germination time, flowering and weight of seed the progeny produced. In some cases, the parental environment affected the magnitude of (interacted with) the observed seed size effects. These data indicate that life history circumstances of the parental generation can affect growth and development throughout the life cycle of the next generation to an extent that should be considered when performing genetic studies.     

Weak evidence for anticipatory parental effects in plants and animals

The evolution of adaptive phenotypic plasticity relies on the presence of cues that enable organisms to adjust their phenotype to match local conditions. Although mostly studied with respect to nonsocial cues, it is also possible that parents transmit information about the environment to their offspring. Such ‘anticipatory parental effects’ or ‘adaptive transgenerational plasticity’ can have important consequences for the dynamics and adaptive potential of populations in heterogeneous environments. Yet, it remains unknown how widespread this form of plasticity is. Using a meta‐analysis of experimental studies with a fully factorial design, we show that there is only weak evidence for higher offspring performance when parental and offspring environments are matched compared with when they are mismatched. Estimates of heterogeneity among studies suggest that effects, when they occur, are subtle. Study features, environmental context, life stage and trait categories all failed to explain significant amounts of variation in effect sizes. We discuss theoretical and methodological reasons for the limited evidence for anticipatory parental effects and suggest ways to improve our understanding of the prevalence of this form of plasticity in nature.     

Genetic variation and co-variation for fitness between intra-population and inter-population backgrounds in the red flour beetle, Tribolium castaneum

Hybrids from crosses between populations of the flour beetle, Tribolium castaneum, express varying degrees of inviability and morphological abnormalities. The proportion of allopatric population hybrids exhibiting these negative hybrid phenotypes varies widely, from 3% to 100%, depending upon the pair of populations crossed. We crossed three populations and measured two fitness components, fertility and adult offspring numbers from successful crosses, to determine how genes segregating within populations interact in inter-population hybrids to cause the negative phenotypes. With data from crosses of 40 sires from each of three populations to groups of five dams from their own and two divergent populations, we estimated the genetic variance and covariance for breeding value of fitness between the intra- and inter-population backgrounds and the sire × dam population interaction variance. The latter component of the variance in breeding values estimates the change in genic effects between backgrounds owing to epistasis. Interacting genes with a positive effect, prior to fixation, in the sympatric background but a negative effect in the hybrid background cause reproductive incompatibility in the Dobzhansky-Muller speciation model. Thus, the sire × dam population interaction provides a way to measure the progress towards speciation of genetically differentiating populations on a trait by trait basis using inter-population hybrids.     

Strain-specific priming of resistance in the red flour beetle, Tribolium castaneum

As invertebrates lack the molecular machinery employed by the vertebrate adaptive immune system, it was thought that they consequently lack the ability to produce lasting and specific immunity. However, in recent years, it has been demonstrated that the immune defence of invertebrates is by far more complicated and specific than previously envisioned. Lasting immunity following an initial exposure that proves protection on a secondary exposure has been shown in several species of invertebrates. This phenomenon has become known as immune priming. In the cases where it is explicitly tested, this priming can also be highly specific. In this study, we used survival assays to test for specific priming of resistance in the red flour beetle, Tribolium castaneum, using bacteria of different degrees of relatedness. Our results suggest an unexpected degree of specificity that even allows for differentiation between different strains of the same bacterium. However, our findings also demonstrate that specific priming of resistance in insects may not be ubiquitous across all bacteria.     

Causes and consequences of variation in offspring body mass: meta‐analyses in birds and mammals

Early survival is highly variable and strongly influences observed population growth rates in most vertebrate populations. One of the major potential drivers of survival variation among juveniles is body mass. Heavy juveniles are better fed and have greater body reserves, and are thus assumed to survive better than light individuals. In spite of this, some studies have failed to detect an influence of body mass on offspring survival, questioning whether offspring body mass does indeed consistently influence juvenile survival, or whether this occurs in particular species/environments. Furthermore, the causes for variation in offspring mass are poorly understood, although maternal mass has often been reported to play a crucial role. To understand why offspring differ in body mass, and how this influences juvenile survival, we performed phylogenetically corrected meta‐analyses of both the relationship between offspring body mass and offspring survival in birds and mammals and the relationship between maternal mass and offspring mass in mammals. We found strong support for an overall positive effect of offspring body mass on survival, with a more pronounced influence in mammals than in birds. An increase of one standard deviation of body mass increased the odds of offspring survival by 71% in mammals and by 44% in birds. A cost of being too fat in birds in terms of flight performance might explain why body mass is a less reliable predictor of offspring survival in birds. We then looked for moderators explaining the among‐study differences reported in the intensity of this relationship. Surprisingly, sex did not influence the intensity of the offspring mass–survival relationship and phylogeny only accounted for a small proportion of observed variation in the intensity of that relationship. Among the potential factors that might affect the relationship between mass and survival in juveniles, only environmental conditions was influential in mammals. Offspring survival was most strongly influenced by body mass in captive populations and wild populations in the absence of predation. We also found support for the expected positive effect of maternal mass on offspring mass in mammals (r_pearson = 0.387). As body mass is a strong predictor of early survival, we expected heavier mothers to allocate more to their offspring, leading them to be heavier and so to have a higher survival. However, none of the potential factors we tested for variation in the maternal mass–offspring mass relationship had a detectable influence. Further studies should focus on linking these two relationships to determine whether a strong effect of offspring size on early survival is associated with a high correlation coefficient between maternal mass and offspring mass.     

Unique maternal and environmental effects on the body morphology of the Least Killifish,Heterandria formosa

An important step in diagnosing local adaptation is the demonstration that phenotypic variation among populations is at least in part genetically based. To do this, many methods experimentally minimize the environmental effect on the phenotype to elucidate the genetic effect. Minimizing the environmental effect often includes reducing possible environmental maternal effects. However, maternal effects can be an important factor in patterns of local adaptation as well as adaptive plasticity. Here, we report the results of an experiment with males from two populations of the poeciliid fish, Heterandria formosa, designed to examine the relative influence of environmental maternal effects and environmental effects experienced during growth and development on body morphology, and, in addition, whether the balance among those effects is unique to each population. We used a factorial design that varied thermal environment and water chemistry experienced by mothers and thermal environment and water chemistry experienced by offspring. We found substantial differences between the two populations in their maternal and offspring norms of reaction of male body morphology to differences in thermal environment and water chemistry. We also found that the balance between maternal effects and postparturition environmental effects differed from one thermal regime to another and among traits. These results indicate that environmental maternal effects can be decidedly population‐specific and, as a result, might either contribute to the appearance of or blur evidence for local adaptation. These results also suggest that local adaptation might also occur through the evolution of maternal norms of reaction to important, and varying, environmental factors.     

Single and multigenerational responses of body mass to atmospheric oxygen concentrations in Drosophila melanogaster : evidence for roles of plasticity and evolution

Greater oxygen availability has been hypothesized to be important in allowing the evolution of larger invertebrates during the Earth’s history, and across aquatic environments. We tested for evolutionary and developmental responses of adult body size of Drosophila melanogaster to hypoxia and hyperoxia. Individually reared flies were smaller in hypoxia, but hyperoxia had no effect. In each of three oxygen treatments (hypoxia, normoxia or hyperoxia) we reared three replicate lines of flies for seven generations, followed by four generations in normoxia. In hypoxia, responses were due primarily to developmental plasticity, as average body size fell in one generation and returned to control values after one to two generations of normoxia. In hyperoxia, flies evolved larger body sizes. Maximal fly mass was reached during the first generation of return from hyperoxia to normoxia. Our results suggest that higher oxygen levels could cause invertebrate species to evolve larger average sizes, rather than simply permitting evolution of giant species.     

Adaptive egg size plasticity for larval competition and its limits in the seed beetle Callosobruchus chinensis

Life‐history theory predicts that females who experienced stressful conditions, such as larval competition or malnutrition, should increase their investment in individual offspring to increase offspring fitness (the adaptive parental hypothesis). In contrast, it has been shown that when females were reared under stressful conditions, they become smaller, which consequently decreases egg size (the parental stress hypothesis). To test whether females adjust their egg volume depending on larval competition, independent of maternal body mass constraint, we used a pest species of stored adzuki beans, Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae: Bruchinae). The eggs of females reared with competitors were smaller than those of females reared alone, supporting the parental stress hypothesis; however, correcting for female body size, females reared with competitors produced larger eggs than those reared in the absence of competition, supporting the adaptive parental hypothesis, as predicted. The phenotypic plasticity in females' investment in each offspring in stressful environments counteracts the constraint of body size on egg size.     

Metamorphosis and adult development of the mushroom bodies of the red flour beetle, Tribolium castaneum

The insect mushroom bodies play important roles in a number of higher processing functions such as sensory integration, higher level olfactory processing, and spatial and associative learning and memory. These functions have been established through studies in a handful of tractable model systems, of which only the fruit fly Drosophila melanogaster has been readily amenable to genetic manipulations. The red flour beetle Tribolium castaneum has a sequenced genome and has been subject to the development of molecular tools for the ready manipulation of gene expression; however, little is known about the development and organization of the mushroom bodies of this insect. The present account bridges this gap by demonstrating that the organization of the Tribolium mushroom bodies is strikingly like that of the fruit fly, with the significant exception that the timeline of neurogenesis is shifted so that the last population of Kenyon cells is born entirely after adult eclosion. Tribolium Kenyon cells are generated by two large neuroblasts per hemisphere and segregate into an early-born delta lobe subpopulation followed by clear homologs of the Drosophila gamma, alpha'/beta' and alpha/beta lobe subpopulations, with the larval-born cohorts undergoing dendritic reorganization during metamorphosis. BrdU labeling and immunohistochemical staining also reveal that a proportion of individual Tribolium have variable numbers of mushroom body neuroblasts. If heritable, this variation represents a unique opportunity for further studies of the genetic control of brain region size through the control of neuroblast number and cell cycle dynamics.