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Data from: Early reproductive success in Drosophila males is dependent on maturity of the accessory gland

In a number of insect taxa, male sexual maturity is not always directly attained at adult eclosion. Sexual maturity is often defined behaviorally as mating success, or physiologically as the point when gametes are produced. Here, we show that the sexual maturation process in males is more complex than previously described and that a measure of maturity also needs to include post-mating traits. In many species mating success is tightly linked with size of the accessory gland (AG). The AG is the production site of a complex cocktail of proteins that are transferred to the female along with the sperm, and which impact on important functions for male reproductive success. Using Drosophila melanogaster we conducted comprehensive behavioral assays of several aspects of male reproductive fitness and demonstrated that the AG has to attain full maturity for males to reach full reproductive competence. We tested males from shortly after, and up to 6 days, post adult eclosion, and considered both pre- and post-copulatory traits. Young males are less likely to gain a mating and show significantly less courtship behavior. Young males that managed to obtain a mating however were inferior in many post-copulatory traits like sperm competitiveness and effectiveness in suppressing female remating. We monitored male AG development over the first 6 days after eclosion and found it to significantly increase in size over the entire period.

Data from: The Urban Heat Island and its spatial scale dependent impact on survival and development in butterflies of different thermal sensitivity

Climate alteration is one of the most cited ecological consequences of urbanization. However, the magnitude of this impact is likely to vary with spatial scale. We investigated how this alteration affects the biological fitness of insects, which are especially sensitive to ambient conditions and well-suited organisms to study urbanization-related changes in phenotypic traits. We monitored temperature and relative air humidity in wooded sites characterized by different levels of urbanization in the surroundings. Using a split-brood design experiment, we investigated the effect of urbanization at the local (i.e., 200 × 200 m) and landscape (i.e., 3 × 3 km) scale on two key traits of biological fitness in two closely related butterfly species that differ in thermal sensitivity. In line with the Urban Heat Island concept, urbanization led to a 1°C increase in daytime temperature and an 8% decrease in daytime relative humidity at the local scale. The thermophilous species Lasiommata megera responded at the local scale: larval survival increased twofold in urban compared to rural sites. Urbanized sites tended to produce bigger adults, although this was the case for males only. In the woodland species Pararge aegeria, which has recently expanded its ecological niche, we did not observe such a response, neither at the local, nor at the landscape scale. These results demonstrate interspecific differences in urbanization-related phenotypic plasticity and larval survival. We discuss larval pre-adaptations in species of different ecological profiles to urban conditions. Our results also highlight the significance of considering fine-grained spatial scales in urban ecology.

Data from: Transgenerational effects modulate density-dependent prophylactic resistance to viral infection in a lepidopteran pest

There is an increasing appreciation of the importance of transgenerational effects on offspring fitness, including in relation to immune function and disease resistance. Here, we assess the impact of parental rearing density on offspring resistance to viral challenge in an insect species expressing density-dependent prophylaxis (DDP); i.e. the adaptive increase in resistance or tolerance to pathogen infection in response to crowding. We quantified survival rates in larvae of the cotton leafworm (Spodoptera littoralis) from either gregarious- or solitary-reared parents following challenge with the baculovirus S. littoralis nucleopolyhedrovirus. Larvae from both the parental and offspring generations exhibited DDP, with gregarious-reared larvae having higher survival rates post-challenge than solitary-reared larvae. Within each of these categories, however, survival following infection was lower in those larvae from gregarious-reared parents than those from solitary-reared, consistent with a transgenerational cost of DDP immune upregulation. This observation demonstrates that crowding influences lepidopteran disease resistance over multiple generations, with potential implications for the dynamics of host–pathogen interactions.

Data from: Subfamily-dependent alternative reproductive strategies in worker honey bees

Functional worker sterility is the defining feature of insect societies. Yet, workers are sometimes found reproducing in their own or foreign colonies. The proximate mechanisms underlying these alternative reproductive phenotypes are key to understanding how reproductive altruism and selfishness are balanced in eusocial insects. In this study we show that in honey bee (Apis mellifera) colonies the social environment of a worker, i.e. the presence and relatedness of the queens in a worker's natal colony and in surrounding colonies, significantly influences her fertility and drifting behaviour. Furthermore, subfamilies vary in the frequency of worker ovarian activation, propensity to drift, and the kind of host colony that is targeted for reproductive parasitism. Our results show that there is an interplay between a worker's subfamily, reproductive state and social environment that substantially affects her reproductive phenotype. Our study further indicate that honey bee populations show substantial genetic variance for worker reproductive strategies, suggesting that no one strategy is optimal under all the circumstances that a typical worker may encounter.

Data from: High temperature intensifies negative density dependence of fitness in red flour beetles

Competition for food, space, or other depletable resources has strong impacts on the fitness of organisms and can lead to a pattern known as negative density dependence, where fitness decreases as population density increases. Yet, many resources that have strong impacts on fitness are nondepletable (e.g., moisture or temperature). How do these nondepletable resources interact with depletable resources to modify negative density dependence? We tested the hypothesis that negative density dependence is modulated by temperature in red flour beetles and tested the prediction that the strength of negative density dependence should decrease as temperature decreases. We measured the number of eggs laid, offspring development time, and the number of offspring that reached maturity at three temperatures and two food treatment combinations as we simultaneously manipulated adult population density. We demonstrated that low temperatures weaken negative density dependence in the number of eggs laid; this pattern was most evident when food was abundant. Density had no effect on development time, but low temperatures increased development time. The percent of eggs that emerged as adults decreased with both density and temperature and increased with food. Temperature, an abiotic driver, can thus modulate density-dependent processes in ectotherms. Therefore, models of population growth for ectotherms should incorporate the effects of temperature.

opencc-zeroDec 2011View details →

Data from: Independent sources of condition dependency and multiple pathways determine a composite trait: lessons from carotenoid-based plumage colouration

Many color ornaments are composite traits consisting of at least four components, which themselves may be more complex, determined by independent evolutionary pathways, and potentially being under different environmental control. To date, little evidence exists that several different components of color elaboration are condition-dependent and no direct evidence exists that different ornamental components are affected by different sources of variation. For example, in carotenoid-based plumage coloration, one of the best-known condition-dependent ornaments, color elaboration stems from both condition-dependent pigment concentration and structural components. Some environmental flexibility of these components has been suggested, but specifically which and how they are affected remains unknown. Here we tested whether multiple color components may be condition-dependent, by using a comprehensive 3 x 2 experimental design, in which we carotenoid supplemented and immune challenged great tit nestlings (Parus major) and quantified effects on different components of coloration. Plumage coloration was affected by an interaction between carotenoid availability and immune challenge. Path analyses showed that carotenoid supplementation increased plumage saturation via feather carotenoid concentration and via mechanisms unrelated to carotenoid-deposition, while immune challenge affected feather length, but not carotenoid concentration. Thus, independent condition-dependent pathways, affected by different sources of variation, determine color elaboration. This provides opportunities for the evolution of multiple signals within components of ornamental traits. This finding indicates that the selective forces shaping the evolution of different components of a composite trait and the trait's signal content may be more complex than believed so far, and that holistic approaches are required for drawing comprehensive evolutionary conclusions.

Data from: The tree balance signature of mass extinction is erased by continued evolution in clades of constrained size with trait-dependent speciation

The kind and duration of phylogenetic topological "signatures" left in the wake of macroevolutionary events remain poorly understood. To this end, we examined a broad range of simulated phylogenies generated using trait-biased, heritable speciation probabilities and mass extinction that could be either random or selective on trait value, but also using background extinction and diversity-dependence to constrain clade sizes. In keeping with prior results, random mass extinction increased imbalance of clades that recovered to pre-extinction size, but was a relatively weak effect. Mass extinction that was selective on trait values tended to produce clades of similar or greater balance compared to random extinction or controls. Allowing evolution to continue past the point of clade-size recovery resulted in erosion and eventual erasure of this signal, with all treatments converging on similar values of imbalance, except for very intense extinction regimes targeted at taxa with high speciation rates. Return to a more balanced state with extended post-extinction evolution was also associated with loss of the previous phylogenetic root in most treatments. These results further demonstrate that while a mass extinction event can produce a recognizable phylogenetic signal, its effects become increasingly obscured the further an evolving clade gets from that event, with any sharp imbalance due to unrelated evolutionary factors.

Data from: The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder

Life-history theory assumes that reproduction entails a cost, and research on cooperatively breeding societies suggests that the cooperative sharing of workloads can reduce this cost. However, the physiological mechanisms that underpin both the costs of reproduction and the benefits of cooperation remain poorly understood. It has been hypothesised that reproductive costs may arise in part from oxidative stress, as reproductive investment may elevate exposure to reactive oxygen species, compromising survival and future reproduction and accelerating senescence. However, experimental evidence of oxidative costs of reproduction in the wild remains scarce. Here, we use a clutch-removal experiment to investigate the oxidative costs of reproduction in a wild cooperatively breeding bird, the white-browed sparrow weaver, Plocepasser mahali. Our results reveal costs of reproduction that are dependent on group size: relative to individuals in groups whose eggs were experimentally removed, individuals in groups that raised offspring experienced an associated cost (elevated oxidative damage and reduced body mass), but only if they were in small groups containing fewer or no helpers. Furthermore, during nestling provisioning, individuals that provisioned at higher rates showed greater within-individual declines in body mass and antioxidant protection. Our results provide rare experimental evidence that reproduction can negatively impact both oxidative status and body mass in the wild, and suggest that these costs can be mitigated in cooperative societies by the presence of additional helpers. These findings have implications for our understanding of the energetic and oxidative costs of reproduction, and the benefits of cooperation in animal societies.

opencc-zeroJun 2019View details →

Data from: Mimicry-dependent lateralization in the visual inspection of foreign eggs by American robins

Brain lateralization, or the specialization of function in the left vs. right brain hemispheres, has been found in a variety of lineages in contexts ranging from foraging to social and sexual behaviours, including the recognition of conspecific social partners. Here we studied whether the recognition and rejection of avian brood parasitic eggs, another context for species recognition, may also involve lateralized visual processing. We focused on American robins (Turdus migratorius), an egg-rejecter host to occasional brood parasitism by brown-headed cowbirds (Molothrus ater) and tested if robins preferentially used one visual hemifield over the other to inspect mimetic vs. non-mimetic model eggs. At the population level, robins showed a significantly lateralized absolute eyedness index (EI) when viewing mimetic model eggs, but individuals varied in left vs. right visual hemifield preference. In contrast, absolute EI was significantly lower when viewing non-mimetic eggs. We also found that robins with more lateralized eye usage rejected model eggs at higher rates. We suggest that the inspection and recognition of foreign eggs represents a specialized and lateralized context of species recognition in this and perhaps in other egg rejecter hosts of brood parasites.

opencc-zeroDec 2010View details →

Data from: Negative frequency-dependent selection of sexually antagonistic alleles in Myodes glareolus

Sexually antagonistic genetic variation, where optimal values of traits are sex-dependent, is known to slow the loss of genetic variance associated with directional selection on fitness-related traits. However, sexual antagonism alone is not sufficient to maintain variation indefinitely. Selection of rare forms within the sexes can help to conserve genotypic diversity. We combined theoretical models and a field experiment with Myodes glareolus to show that negative frequency-dependent selection on male dominance maintains variation in sexually antagonistic alleles. In our experiment, high-dominance male bank voles were found to have low-fecundity sisters, and vice versa. These results show that investigations of sexually antagonistic traits should take into account the effects of social interactions on the interplay between ecology and evolution, and that investigations of genetic variation should not be conducted solely under laboratory conditions.

opencc-zeroDec 2017View details →

Data from: Phenological and fitness responses to climate warming depend upon genotype and competitive neighborhood in Arabidopsis thaliana

1. Increasing temperatures during climate change are known to alter the phenology across diverse plant taxa, but the evolutionary outcomes of these shifts are poorly understood. Moreover, plant temperature-sensing pathways are known to interact with competition-sensing pathways, yet there remains little experimental evidence for how genotypes varying in temperature responsiveness react to warming in realistic competitive settings. 2. We compared flowering time and fitness responses to warming and competition for two near isogenic lines (NILs) of <i>Arabidopsis thaliana</i> transgressively segregating temperature-sensitive and -insensitive alleles for major-effect flowering time genes. We grew focal plants of each genotype in intraspecific and interspecific competition in four treatments contrasting daily temperature profiles in summer and fall under contemporary and warmed conditions. We measured phenology and fitness of focal plants to quantify plastic responses to season, temperature, and competition and the dependence of these responses on flowering time genotype. 3. The temperature-insensitive NIL was constitutively early-flowering and less fit, except in a future-summer climate in which its fitness was higher than the later flowering, temperature-sensitive NIL in low competition. The late-flowering NIL showed accelerated flowering in response to intragenotypic competition and to increased temperature in the summer but delayed flowering in the fall. However, its fitness fell with rising temperatures in both seasons, and in the fall its marginal fitness gain from decreasing competition was diminished in the future. 4. Functional alleles at temperature-responsive genes were necessary for plastic responses to season, warming, and competition. However, the plastic genotype was not the most fit in every experimental condition, becoming less fit than the temperature-canalized genotype in the warm summer treatment. 5. Climate change is often predicted to have deleterious effects on plant populations, and our results show how increased temperatures can act through genotype-dependent phenology to decrease fitness. Furthermore, plasticity is not necessarily adaptive in rapidly changing environments since a non-plastic genotype proved fitter than a plastic genotype in a warming climate treatment.

Data from: The effects of spatial structure, frequency dependence and resistance evolution on the dynamics of toxin-mediated microbial invasions

Recent evidence suggests that interference competition between bacteria shapes the distribution of the opportunistic pathogen Staphylococcus aureus in the lower nasal airway of humans, either by preventing colonization or by driving displacement. This competition within the nasal microbial community would add to known host factors that affect colonization. We tested the role of toxin-mediated interference competition in both structured and unstructured environments, by culturing S. aureus with toxin-producing or nonproducing Staphylococcus epidermidis nasal isolates. Toxin-producing S. epidermidis invaded S. aureus populations more successfully than nonproducers, and invasion was promoted by spatial structure. Complete displacement of S. aureus was prevented by the evolution of toxin resistance. Conversely, toxin-producing S. epidermidis restricted S. aureus invasion. Invasion of toxin-producing S. epidermidis populations by S. aureus resulted from the evolution of toxin resistance, which was favoured by high initial frequency and low spatial structure. Enhanced toxin production also evolved in some invading populations of S. epidermidis. Toxin production therefore promoted invasion by, and constrained invasion into, populations of producers. Spatial structure enhanced both of these invasion effects. Our findings suggest that manipulation of the nasal microbial community could be used to limit colonization by S. aureus, which might limit transmission and infection rates.

Data from: Multiscale evaluation of thermal dependence in the glucocorticoid response of vertebrates

Environmental temperature has profound effects on animal physiology, ecology, and evolution. Glucocorticoid (GC) hormones, through effects on phenotypic performance and life history, provide fundamental vertebrate physiological adaptations to environmental variation, yet we lack a comprehensive understanding of how temperature influences GC regulation in vertebrates. Using field studies and meta- and comparative phylogenetic analyses, we investigated how acute change and broadscale variation in temperature correlated with baseline and stress-induced GC levels. Glucocorticoid levels were found to be temperature and taxon dependent, but generally, vertebrates exhibited strong positive correlations with acute changes in temperature. Furthermore, reptile baseline, bird baseline, and capture stress-induced GC levels to some extent covaried with broadscale environmental temperature. Thus, vertebrate GC function appears clearly thermally influenced. However, we caution that lack of detailed knowledge of thermal plasticity, heritability, and the basis for strong phylogenetic signal in GC responses limits our current understanding of the role of GC hormones in species' responses to current and future climate variation.

Data from: Condition-dependent movement and dispersal in experimental metacommunities

Dispersal and the underlying movement behaviour are processes of pivotal importance for understanding and predicting metapopulation and metacommunity dynamics. Generally, dispersal decisions are condition-dependent and rely on information in the broad sense, like the presence of conspecifics. However, studies on metacommunities that include interspecific interactions generally disregard condition-dependence. Therefore, it remains unclear whether and how dispersal in metacommunities is condition-dependent and whether rules derived from single-species contexts can be scaled up to (meta)communities. Using experimental protist metacommunities, we show how dispersal and movement depend on and are adjusted by the strength of interspecific interactions. We found that the predicting movement and dispersal in metacommunities requires knowledge on behavioural responses to intra- and interspecific interaction strengths. Consequently, metacommunity dynamics inferred directly from single-species metapopulations without taking interspecific interactions into account are likely flawed. Our work identifies the significance of condition-dependence for understanding metacommunity dynamics, stability and the coexistence and distribution of species.

Data from: Size dependency in colour patterns of Western Palearctic carabids

Body colouration is of high evolutionary relevance for most animals. Several competing hypotheses exist regarding the evolutionary reasons for animal colouration ranging from predator avoidance and sexual advertisement to neutral selection. Among these hypotheses, biophysical principles suggest the thermoregulatory importance of dark colouration which in turn strongly depends on species body size. This body size – darkness trade-off is based on sound theoretical background conceptualized in the thermal melanism hypothesis and is confirmed by numerous case studies for individual species. However, evidence for the general relevance of this trade-off on large spatial and taxonomic scale is still missing. Here we specifically focus on this body size – colouration trade-off for a hyper-diverse and cosmopolitan group of insects, namely ground beetles. We combined colour information with trait data and distributional as well as bioclimatic attributes for more than 1,000 carabid species from the entire Western Palearctic. We quantified species-specific body colouration from high-quality, standardised digital photographs using the Munsell colour system. We detect a strong increase of colour darkness with body size from small to medium-sized carabids up to a body size threshold of 15 mm which is consistent with the thermal melanism hypothesis. However, body size showed no effect above this threshold and colour darkness remained constantly high which is in accordance with previous ideas about the size-dependency of thermoregulative control mechanisms (size dependence hypothesis). By demonstrating a strong tendency towards darkness with increasing body size, we illustrate the inter-specific relevance of body colouration for this cosmopolitan group of ectotherms on a continental scale. The putative thermoregulative trade-off between body size and melanism seems to be of significant importance for carabids on a broad spatial scale and may be a general but still underestimated phenomenon for ectotherms in general, although other mechanistic drivers cannot be completely neglected.

opencc-zeroDec 2017View details →

Data from: Distance-dependent aposematism and camouflage in the cinnabar moth caterpillar (Tyria jacobaeae Erebidae)

Defended prey often use distinctive, conspicuous, colours to advertise their unprofitability to potential predators (aposematism). These warning signals are frequently made up of salient, high contrast, stripes which have been hypothesised to increase the speed and accuracy of predator avoidance learning. Limitations in predator visual acuity, however, mean that these patterns cannot be resolved when viewed from a distance, and adjacent patches of colour will blend together (pattern blending). We investigated how saliency changes at different viewing distances in the toxic and brightly coloured cinnabar moth caterpillar (Tyria jacobaeae). We found that although the caterpillars' orange-and-black stripes are highly salient at close-range, when viewed from a distance the colours blend together to match closely those of the background. Cinnabar caterpillars therefore produce a distance-dependent signal combining salient aposematism with targeted background matching camouflage, without necessarily compromising the size or saturation of their aposematic signal.

Data from: Effects of cell-cycle-dependent expression on random fluctuations in protein levels

Expression of many genes varies as a cell transitions through different cell-cycle stages. How coupling between stochastic expression and cell cycle impacts cell-to-cell variability (noise) in the level of protein is not well understood. We analyse a model where a stable protein is synthesized in random bursts, and the frequency with which bursts occur varies within the cell cycle. Formulae quantifying the extent of fluctuations in the protein copy number are derived and decomposed into components arising from the cell cycle and stochastic processes. The latter stochastic component represents contributions from bursty expression and errors incurred during partitioning of molecules between daughter cells. These formulae reveal an interesting trade-off: cell-cycle dependencies that amplify the noise contribution from bursty expression also attenuate the contribution from partitioning errors. We investigate the existence of optimum strategies for coupling expression to the cell cycle that minimize the stochastic component. Intriguingly, results show that a zero production rate throughout the cell cycle, with expression only occurring just before cell division, minimizes noise from bursty expression for a fixed mean protein level. By contrast, the optimal strategy in the case of partitioning errors is to make the protein just after cell division. We provide examples of regulatory proteins that are expressed only towards the end of the cell cycle, and argue that such strategies enhance robustness of cell-cycle decisions to the intrinsic stochasticity of gene expression.

Data from: Patterns of species relatedness created by competitive exclusion depend on species niche differences: evidence from Iberian Atlantic grasslands

It is commonly assumed that closely related species share more similar niches than do distantly related species, thus limiting their ability to coexist and leading to patterns of phylogenetic over-dispersion. On the contrary, recent theoretical developments argue that competitive exclusion may lead to patterns of either over-dispersion, clustering or randomness, depending on the relative importance of niche differences and interspecific competitive ability differences. In this study, we utilized semi-natural grassland communities to test the hypothesis that the pattern of species relatedness generated by competitive exclusion depends on species niche differences. Instead of inferring processes from observed patterns, we experimentally manipulated grassland plots to test the effects of competitive exclusion. We compared grazed plots (in which grazing functioned as an equalizing mechanism and suppressed aboveground competition) with neighbouring plots experimentally excluded from grazing over the course of nine years (in which aboveground competition was not prevented). Weak niche differences between species allowed competitive exclusion to generate phylogenetic clustering, because phylogenetically structured plant canopy height and capacity for lateral spread conferred superior competitive ability to grasses that outcompeted species in all dicot branches. By contrast, moderate niche differences allowed competitive exclusion to result in a random pattern of phylogenetic species assembly, because species niche differences partially counterbalanced competitive exclusion by superior competitors in the grass family. We conclude that patterns of species relatedness created by competitive exclusion in Iberian Atlantic grasslands depend on species niche differences. Competitive exclusion may cause differential patterns of phylogenetic assembly.

Data from: Muscle shortening velocity depends on tissue inertia and level of activation during submaximal contractions

In order to perform external work, muscles must do additional internal work to deform their tissue, and in particular, to overcome the inertia due to their internal mass. However, the contribution of the internal mass within a muscle to the mechanical output of that muscle has only rarely been studied. Here, we use a dynamic, multi-element Hill-type muscle model to examine the effects of the inertial mass within muscle on its contractile performance. We find that the maximum strain-rate of muscle is slower for lower activations and larger muscle sizes. As muscle size increases, the ability of the muscle to overcome its inertial load will decrease, as muscle tension is proportional to cross-sectional area and inertial load is proportional to mass. Thus, muscles that are larger in size will have a higher inertial cost to contraction. Similarly, when muscle size and inertial load are held constant, decreasing muscle activation will increase inertial cost to contraction by reducing muscle tension. These results show that inertial loads within muscle contribute to a slowing of muscle contractile velocities (strain-rates), particularly at the submaximal activations that are typical during animal locomotion.

Data from: Evolution of density-dependent movement during experimental range expansions

Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. While it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intra-strain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general.