Complex multi-trait responses to multivariate environmental cues in a seasonal butterfly

The interplay between abiotic and biotic factors in dispersal decisions in metacommunities

Suitable conditions for species to survive and reproduce constitute their ecological niche, which is built by abiotic conditions and interactions with conspecifics and heterospecifics. Organisms should ideally assess and use information about all these environmental dimensions to adjust their dispersal decisions depending on their own internal conditions. Dispersal plasticity is often considered through its dependence on abiotic conditions or conspecific density and, to a lesser extent, with reference to the effects of interactions with heterospecifics, potentially leading to misinterpretation of dispersal drivers. Here, we first review the evidence for the effects of and the potential interplays between abiotic factors, biotic interactions with conspecifics and heterospecifics and phenotype on dispersal decisions. We then present an experimental test of these potential interplays, investigating the effects of density and interactions with conspecifics and heterospecifics on temperature-dependent dispersal in microcosms of Tetrahymena ciliates. We found significant differences in dispersal rates depending on the temperature, density and presence of another strain or species. However, the presence and density of conspecifics and heterospecifics had no effects on the thermal-dependency of dispersal. We discuss the causes and consequences of the (lack of) interplay between the different environmental dimensions and the phenotype for metacommunity assembly and dynamics. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Temperature- and Diet-Induced Plasticity of Growth and Digestive Enzymes Activity in Spongy Moth Larvae

Temperature and food quality are the most important environmental factors determining the performance of herbivorous insects. The objective of our study was to evaluate the responses of the spongy moth (formerly known as the gypsy moth) [Lymantria dispar L. (Lepidoptera: Erebidae)] to simultaneous variation in these two factors. From hatching to the fourth instar, larvae were exposed to three temperatures (19 °C, 23 °C, and 28 °C) and fed four artificial diets that differed in protein (P) and carbohydrate (C) content. Within each temperature regime, the effects of the nutrient content (P+C) and ratio (P:C) on development duration, larval mass, growth rate, and activities of digestive proteases, carbohydrases, and lipase were examined. It was found that temperature and food quality had a significant effect on the fitness-related traits and digestive physiology of the larvae. The greatest mass and highest growth rate were obtained at 28 °C on a high-protein low-carbohydrate diet. A homeostatic increase in activity was observed for total protease, trypsin, and amylase in response to low substrate levels in the diet. A significant modulation of overall enzyme activities in response to 28 °C was detected only with a low diet quality. A decrease in the nutrient content and P:C ratio only affected the coordination of enzyme activities at 28 °C, as indicated by the significantly altered correlation matrices. Multiple linear regression analysis showed that variation in fitness traits in response to different rearing conditions could be explained by variation in digestion. Our results contribute to the understanding of the role of digestive enzymes in post-ingestive nutrient balancing.

The effect of temperature and invasive alien predator on genetic and phenotypic variation in the damselfly Ischnura elegans: cross-latitude comparison

BACKGROUND

Understanding and predicting how organisms respond to human-caused environmental changes has become a major concern in conservation biology. Here, we linked gene expression and phenotypic data to identify candidate genes underlying existing phenotypic trait differentiation under individual and combined environmental variables. For this purpose, we used the damselfly Ischnura elegans. Egg clutches from replicated high- (southern Sweden) and central-latitude (southern Poland) populations facing different degrees of seasonal time constraints were collected. Damselfly larvae were exposed to experimental treatments: current and mild warming temperatures crossed with the presence or absence of an invasive alien predator cue released by the spiny-cheek crayfish, Faxonius limosus, which is only present in Poland to date. We measured the following traits: larval development time, body size, mass and growth rate, and used the larvae for gene expression analysis by RNA-seq. Data were analysed using a multivariate approach.

RESULTS

We showed latitudinal differences in coping with mild warming and predator cues. When exposed to an increased temperature and a predator cue, central-latitude individuals had the shortest development and the fastest growth compared to high-latitude individuals. There was a general effect of predator cues regarding mass and growth rate reduction independent of latitude. Transcriptome analysis revealed that metabolic pathways related to larval anatomy and development tended to be upregulated in response to mild warming but only in fast-growing central-latitude individuals. Metabolic pathways linked to oxidative stress tended to be downregulated in response to a predator cue, especially in central-latitude individuals.

CONCLUSION

Different phenotypic and transcriptomic responses to environmental factors might be attributed to the variability in I. elegans life history strategies between the two latitudes caused by seasonal time constraints and to its coexistence with the invasive alien predator in nature. By providing insights into how organisms may respond to future anthropogenic changes, our results may be of particular interest in conservation biology.

Effects of anthropogenic stress on hosts and their microbiomes: Treated wastewater alters performance and gut microbiome of a key detritivore ( Asellus aquaticus )

Human activity is a major driver of ecological and evolutionary change in wild populations and can have diverse effects on eukaryotic organisms as well as on environmental and host-associated microbial communities. Although host-microbiome interactions can be a major determinant of host fitness, few studies consider the joint responses of hosts and their microbiomes to anthropogenic changes. In freshwater ecosystems, wastewater is a widespread anthropogenic stressor that represents a multifarious environmental perturbation. Here, we experimentally tested the impact of treated wastewater on a keystone host (the freshwater isopod Asellus aquaticus) and its gut microbiome. We used a semi-natural flume experiment, in combination with 16S rRNA amplicon sequencing, to assess how different concentrations (0%, 30%, and 80%) of nonfiltered wastewater (i.e. with chemical toxicants, nutrients, organic particles, and microbes) versus ultrafiltered wastewater (i.e. only dissolved pollutants and nutrients) affected host survival, growth, and food consumption as well as mid- and hindgut bacterial community composition and diversity. Our results show that while host survival was not affected by the treatments, host growth increased and host feeding rate decreased with nonfiltered wastewater - potentially indicating that A. aquaticus fed on organic matter and microbes available in nonfiltered wastewater. Furthermore, even though the midgut microbiome (diversity and composition) was not affected by any of our treatments, nonfiltered wastewater influenced bacterial composition (but not diversity) in the hindgut. Ultrafiltered wastewater, on the other hand, affected both community composition and bacterial diversity in the hindgut, an effect that in our system differed between sexes. While the functional consequences of microbiome changes and their sex specificity are yet to be tested, our results indicate that different components of multifactorial stressors (i.e. different constituents of wastewater) can affect hosts and their microbiome in distinct (even opposing) manners and have a substantial impact on eco-evolutionary responses to anthropogenic stressors.

Limited sex differences in plastic responses suggest evolutionary conservatism of thermal reaction norms: A meta-analysis in insects

Temperature has a profound effect on the growth and development of ectothermic animals. However, the extent to which ecologically driven selection pressures can adjust thermal plastic responses in growth schedules is not well understood. Comparing temperature-induced plastic responses between sexes provides a promising but underexploited approach to evaluating the evolvability of thermal reaction norms: males and females share largely the same genes and immature environments but typically experience different ecological selection pressures. We proceed from the idea that substantial sex differences in plastic responses could be interpreted as resulting from sex-specific life-history optimization, whereas similarity among the sexes should rather be seen as evidence of an essential role of physiological constraints. In this study, we performed a meta-analysis of sex-specific thermal responses in insect development times, using data on 161 species with comprehensive phylogenetic and ecological coverage. As a reference for judging the magnitude of sex specificity in thermal plasticity, we compared the magnitude of sex differences in plastic responses to temperature with those in response to diet. We show that sex-specific responses of development times to temperature variation are broadly similar. We also found no strong evidence for sex specificity in thermal responses to depend on the magnitude or direction of sex differences in development time. Sex differences in temperature-induced plastic responses were systematically less pronounced than sex differences in responses induced by variations in larval diet. Our results point to the existence of substantial constraints on the evolvability of thermal reaction norms in insects as the most likely explanation. If confirmed, the low evolvability of thermal response is an essential aspect to consider in predicting evolutionary responses to climate warming.

Designing a Seasonal Acclimation Study Presents Challenges and Opportunities

Organisms living in seasonal environments often adjust physiological capacities and sensitivities in response to (or in anticipation of) environment shifts. Such physiological and morphological adjustments (“acclimation” and related terms) inspire opportunities to explore the mechanistic bases underlying these adjustments, to detect cues inducing adjustments, and to elucidate their ecological and evolutionary consequences. Seasonal adjustments (“seasonal acclimation”) can be detected either by measuring physiological capacities and sensitivities of organisms retrieved directly from nature (or outdoor enclosures) in different seasons or less directly by rearing and measuring organisms maintained in the laboratory under conditions that attempt to mimic or track natural ones. But mimicking natural conditions in the laboratory is challenging—doing so requires prior natural-history knowledge of ecologically relevant body temperature cycles, photoperiods, food rations, social environments, among other variables. We argue that traditional laboratory-based conditions usually fail to approximate natural seasonal conditions (temperature, photoperiod, food, “lockdown”). Consequently, whether the resulting acclimation shifts correctly approximate those in nature is uncertain, and sometimes is dubious. We argue that background natural history information provides opportunities to design acclimation protocols that are not only more ecologically relevant, but also serve as templates for testing the validity of traditional protocols. Finally, we suggest several best practices to help enhance ecological realism.

Alternative splicing in seasonal plasticity and the potential for adaptation to environmental change

Seasonal plasticity is accomplished via tightly regulated developmental cascades that translate environmental cues into trait changes. Little is known about how alternative splicing and other posttranscriptional molecular mechanisms contribute to plasticity or how these mechanisms impact how plasticity evolves. Here, we use transcriptomic and genomic data from the butterfly Bicyclus anynana, a model system for seasonal plasticity, to compare the extent of differential expression and splicing and test how these axes of transcriptional plasticity differ in their potential for evolutionary change. Between seasonal morphs, we find that differential splicing affects a smaller but functionally unique set of genes compared to differential expression. Further, we find strong support for the novel hypothesis that spliced genes are more susceptible than differentially expressed genes to erosion of genetic variation due to selection on seasonal plasticity. Our results suggest that splicing plasticity is especially likely to experience genetic constraints that could affect the potential of wild populations to respond to rapidly changing environments.

Little is known about how alternative splicing and other post-transcriptional molecular mechanisms impact plasticity. Steward et al. use transcriptomic and genomic data from the butterfly Bicyclus anynana, finding that splicing plasticity is likely to experience genetic constraints.

Irreversible impact of early thermal conditions: an integrative study of developmental plasticity linked to mobility in a butterfly species

Within populations, phenotypic plasticity may allow adaptive phenotypic variation in response to selection generated by environmental heterogeneity. For instance, in multivoltine species, seasonal changes between and within generations may trigger morphological and physiological variation enhancing fitness under different environmental conditions. These seasonal changes may irreversibly affect adult phenotypes when experienced during development. Yet, the irreversible effects of developmental plasticity on adult morphology have rarely been linked to life-history traits even though they may affect different fitness components such as reproduction, mobility and self-maintenance. To address this issue, we raised larvae of Pieris napi butterflies under warm or cool conditions to subsequently compare adult performance in terms of reproduction performance (as assessed through fecundity), displacement capacity (as assessed through flight propensity and endurance) and self-maintenance (as assessed through the measurement of oxidative markers). As expected in ectotherms, individuals developed faster under warm conditions and were smaller than individuals developing under cool conditions. They also had more slender wings and showed a higher wing surface ratio. These morphological differences were associated with changes in the reproductive and flight performances of adults, as individuals developing under warm conditions laid fewer eggs and flew larger distances. Accordingly, the examination of their oxidative status suggested that individuals developing under warm conditions invested more strongly into self-maintenance than individuals developing under cool conditions (possibly at the expense of reproduction). Overall, our results indicate that developmental conditions have long-term consequences on several adult traits in butterflies. This plasticity likely acts on life history strategies for each generation to keep pace with seasonal variations and may facilitate acclimation processes in the context of climate change.

Predictability of temporal variation in climate and the evolution of seasonal polyphenism in tropical butterfly communities

Phenotypic plasticity in heterogeneous environments can provide tight environment-phenotype matching. However, the prerequisite is a reliable environmental cue(s) that enables organisms to use current environmental information to induce the development of a phenotype with high fitness in a forthcoming environment. Here, we quantify predictability in the timing of precipitation and temperature change to examine how this is associated with seasonal polyphenism in tropical Mycalesina butterflies. Seasonal precipitation in the tropics typically results in distinct selective environments, the wet and dry seasons, and changes in temperature can be a major environmental cue. We sampled communities of Mycalesina butterflies from two seasonal locations and one aseasonal location. Quantifying environmental predictability using wavelet analysis and Colwell's indices confirmed a strong periodicity of precipitation over a 12-month period at both seasonal locations compared to the aseasonal one. However, temperature seasonality and periodicity differed between the two seasonal locations. We further show that: (a) most females from both seasonal locations synchronize their reproduction with the seasons by breeding in the wet season but arresting reproduction in the dry season. In contrast, all species breed throughout the year in the aseasonal location and (b) species from the seasonal locations, but not those from the aseasonal location, exhibited polyphenism in wing pattern traits (eyespot size). We conclude that seasonal precipitation and its predictability are primary factors shaping the evolution of polyphenism in Mycalesina butterflies, and populations or species secondarily evolve local adaptations for cue use that depend on the local variation in the environment.

Multidimensional plasticity in the Glanville fritillary butterfly: larval performance is temperature, host and family specific

Variation in environmental conditions during development can lead to changes in life-history traits with long-lasting effects. Here, we study how variation in temperature and host plant (i.e. the consequences of potential maternal oviposition choices) affects a suite of life-history traits in pre-diapause larvae of the Glanville fritillary butterfly. We focus on offspring survival, larval growth rates and relative fat reserves, and pay specific attention to intraspecific variation in the responses (G × E × E). Globally, thermal performance and survival curves varied between diets of two host plants, suggesting that host modifies the temperature impact, or vice versa. Additionally, we show that the relative fat content has a host-dependent, discontinuous response to developmental temperature. This implies that a potential switch in resource allocation, from more investment in growth at lower temperatures to storage at higher temperatures, is dependent on the larval diet. Interestingly, a large proportion of the variance in larval performance is explained by differences among families, or interactions with this variable. Finally, we demonstrate that these family-specific responses to the host plant remain largely consistent across thermal environments. Together, the results of our study underscore the importance of paying attention to intraspecific trait variation in the field of evolutionary ecology.