Maternal body size as a morphological constraint on egg size and fecundity in butterflies

It is a widespread notion that in arthropods female reproductive output is strongly affected by female size. In butterflies egg size scales positively with female size across species, suggesting a constraint imposed by maternal size. However, in intraspecific comparisons body size often explains only a minor part of the variation in progeny size. We here include representatives of various butterfly families to test the generality of this phenomenon across butterflies. Phenotypic correlations between egg and maternal body size were inconsistent across species: correlations were nonsignificant for Pararge aegeria and Lycaena tityrus, significantly positive for Papilio machaon, significantly negative for Araschnia levana, and contradictory for Pieris napi. Thus, there was no general pattern linking egg size to maternal size, e.g., caused by an allometric relationship. Consequently, there was at best limited evidence for maternal size acting as a morphological constraint on egg size within butterfly species. Realized fecundity depended on maternal size in P. napi and A. levana, but not in P. aegeria, suggesting that maternal size may affect egg number more strongly than egg size. Yet, variation in fecundity was primarily explained by variation in longevity as is expected for income breeders. Heritability estimates across species were rather similar for pupal mass (ranging between 0.14 and 0.19), but more variable for egg size (0.17–0.31)

Disentangling environmental effects on adult life span in a butterfly across the metamorphic boundary

Life span is a central life history trait often showing tremendous variation within populations. Much of this variation can be attributed to environmental factors. In holometabolous insects life stages differ strikingly in physiology and energetic demands, and environmental variation before and after metamorphosis may not necessarily yield identical responses. In this study, we adopted a full-factorial experimental design with two larval and two adult temperatures as well as two larval and three adult feeding treatments (ntotal = 1151). Identical temperatures yielded qualitatively different results depending on the developmental stage. While the lower compared to the higher developmental temperature slightly reduced adult life span, a lower adult temperature substantially increased life span. Food stress in the larval stage slightly reduced life span, as did food stress during the adult stage. Females lived generally longer than males. All factors investigated were involved in interactions with other factors, both within and across life stages. For instance, the qualitative impact of larval food stress depended on adult feeding treatment and adult temperature. Our results suggest that much insight into the causes of variation in life span is to be gained by explicitly considering environmental impacts across developmental stages and potential interactions among different environmental factors

Data from: High temperatures reveal cryptic genetic variation in a polymorphic female sperm storage organ

Variation in female reproductive morphology may play a decisive role in reproductive isolation by affecting the relative fertilization success of alternative male phenotypes. Yet, knowledge of how environmental variation may influence the development of the female reproductive tract and thus alter the arena of post-copulatory sexual selection is limited. Yellow dung fly females possess either three or four sperm storage compartments, a polymorphism with documented influence on sperm precedence. We performed a quantitative genetics study including 12 populations reared at three developmental temperatures complemented by extensive field data to show that warm developmental temperatures increase the frequency of females with four compartments, revealing striking hidden genetic variation for the polymorphism. Systematic genetic differentiation in growth rate and spermathecal number along latitude, and phenotypic covariance between the traits across temperature treatments suggest that the genetic architecture underlying the polymorphism is shaped by selection on metabolic rate. Our findings illustrate how temperature can modulate the preconditions for sexual selection by differentially exposing novel variation in reproductive morphology. This implies that environmental change may substantially alter the dynamics of sexual selection. We further discuss how temperature-dependent developmental plasticity may have contributed to observed rapid evolutionary transitions in spermathecal morphology

Effects of maternal and offspring environmental conditions on growth, development and diapause in latitudinal yellow dung fly populations

Extensive phenotypic plasticity can allow populations to persist in changing environments. Maternal effects represent one important but often neglected source of phenotypic plasticity. Mothers and offspring of 2 high- (northern Norway and central Sweden) and 2 low- (northern and southern Spain) latitude yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) populations were exposed to cold (12 degrees C) and warm (18 degrees C) temperatures and to short (8 h light: 16 h dark) and long (16 h light: 8 h dark) photoperiods in a fully blocked, split-brood common garden design of 8 treatment combinations. We also considered the role of energy content and size of the eggs in producing cross-generational maternal effects on offspring diapause, development time and growth rate. The incidence of diapause strongly declined towards the south, and the northernmost population grew and developed faster in response to perceived seasonal time constraints. There was strong population-specific phenotypic plasticity of all traits in response to offspring temperature and, more weakly, to offspring photoperiod, indicating a genetic basis of plasticity as well as genetic differentiation among populations. There were additional subtle cross-generational maternal effects exerted primarily by the lipid content of the eggs, largely independent of maternal treatment and population. Phenotypic plasticity of life-history traits in the yellow dung fly is predominantly influenced by the growing conditions during larval development, but populations can also respond to changing environments via trans-generational maternal effects

Effects of adult nutrition on female reproduction in a fruit-feeding butterfly : The role of fruit decay and dietary lipids

It was generally believed that butterflies and other holometabolous insects rely primarily on reserves accumulated during the larval stage for reproduction. Recent studies, however, highlight the often fundamental importance of adult nutrition to realize the full reproductive potential. While the importance of carbohydrates is fairly well understood, the role of most other adult-derived substances is only partially resolved. We here focus on the effects of dietary lipids (cholesterol, polyunsaturated fatty acids) and fruit decay (dietary yeast, ethanol) on female reproduction in the tropical, fruit-feeding butterfly Bicyclus anynana (Nymphalidae). We found that banana-fed control females outperformed all other groups fed on sucrose-based diets. Lipids, yeast or ethanol added to a sugar solution did not yield a similarly high reproductive output compared to fruit-fed females. Groups fed fresh or decaying banana showed no differences in reproductive performance. As we could not identify a single pivotal substance, we conclude that resource congruence (the use of nutrient types in a specified ratio) rather than any specific nutrient component is of key importance for maximum reproductive output. Further, dietary quality may affect egg hatching success in spite of no obvious effects on egg size and number. Thus, any implications about potential fitness effects of different diets need to potential fitness effects of different diets need to consider potential fitness effects of different diets need to consider egg (and hatchling) viability in addition to fecundity

No Trade-Off between Growth Rate and Temperature Stress Resistance in Four Insect Species

Although fast growth seems to be generally favored by natural selection, growth rates are rarely maximized in nature. Consequently, fast growth is predicted to carry costs resulting in intrinsic trade-offs. Disentangling such trade-offs is of great ecological importance in order to fully understand the prospects and limitations of growth rate variation. A recent study provided evidence for a hitherto unknown cost of fast growth, namely reduced cold stress resistance. Such relationships could be especially important under climate change. Against this background we here investigate the relationships between individual larval growth rate and adult heat as well as cold stress resistance, using eleven data sets from four different insect species (three butterfly species: Bicyclus anynana, Lycaena tityrus, Pieris napi; one Dipteran species: Protophormia terraenovae). Despite using different species (and partly different populations within species) and an array of experimental manipulations (e.g. different temperatures, photoperiods, feeding regimes, inbreeding levels), we were not able to provide any consistent evidence for trade-offs between fast growth and temperature stress resistance in these four insect species.status: publishe

Heritable responses to combined effects of heat stress and ivermectin in the yellow dung fly

In current times of global change, several sources of stress such as contaminants and high temperatures may act synergistically. The extent to which organisms persist in stressful conditions will depend on the fitness consequences of multiple simultaneously acting stressors and the genetic basis of compensatory genetic responses. Ivermectin is an antiparasitic drug used in livestock that is excreted in dung of treated cattle, causing severe negative consequences on non-target fauna. We evaluated the effect of a combination of heat stress and exposure to ivermectin in the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae). In a first experiment we investigated the effects of high rearing temperature on susceptibility to ivermectin, and in a second experiment we assayed flies from a latitudinal gradient to assess potential effects of local thermal adaptation on ivermectin sensitivity. The combination of heat and ivermectin synergistically reduced offspring survival, revealing severe effects of the two stressors when combined. However, latitudinal populations did not systematically vary in how ivermectin affected offspring survival, body size, development time, cold and heat tolerance. We also found very low narrow-sense heritability of ivermectin sensitivity, suggesting evolutionary constraints for responses to the combination of these stressors beyond immediate maternal or plastic effects. If the revealed patterns hold also for other invertebrates, the combination of increasing climate warming and ivermectin stress may thus have severe consequences for biodiversity. More generally, our study underlines the need for quantitative genetic analyses in understanding wildlife responses to interacting stressors that act synergistically and threat biodiversity

Replicated latitudinal clines in reproductive traits of European and North American yellow dung flies

Geographic variation in phenotypic traits is commonly correlated with spatial variation in the environment, e.g. seasonality and mean temperature, providing evidence that natural selection generates such patterns. In particular, both body size and egg size of ectothermic animals are commonly larger in northern climates, and temperature induces plastic responses in both traits. Size‐independent egg quality can also vary with latitude, though this is rarely investigated. For the widespread yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) we investigated whether there are latitudinal clines in reproductive traits (clutch size, egg size and egg composition), whether these clines are due to variation in body and/or egg size, and whether such clines replicate across independent experiments performed on different continents (North America and Europe). Egg size generally increased with latitude (especially in Europe), an effect largely explained by body size of the mother, while clutch size did not; overall reproductive effort thus increased with latitude. Both the absolute and relative (correcting for egg size) amount of egg protein increased with latitude, egg glycogen decreased with latitude, while latitudinal trends for egg lipids and total egg energy content were complex and non‐linear. Altitude sometimes showed relationships analogous to those of latitude (egg proteins and glycogen) but occasionally opposite (egg size), possibly because latitude and altitude are negatively related among populations of this cold‐adapted species. There was no evidence of a tradeoff between egg size and number across latitudinal populations; if anything, the relationship was positive. All traits, including body and egg size, varied with rearing temperature (12°C, 18°C, 24°C), generally following the temperature–size rule. Clines based on common garden rearing, thus reflecting genetic differentiation, were qualitatively but not always quantitatively consistent between continents, and were similar across rearing temperatures, suggesting they evolved due to natural selection, although the concrete selective mechanisms involved require further study