Influences of species, latitudes and methodologies on estimates of phenological response to global warming

New analyses are presented addressing the global impacts of recent climate change on phenology of plant and animal species. A meta‐analysis spanning 203 species was conducted on published datasets from the northern hemisphere. Phenological response was examined with respect to two factors: distribution of species across latitudes and taxonomic affiliation or functional grouping of target species. Amphibians had a significantly stronger shift toward earlier breeding than all other taxonomic/functional groups, advancing more than twice as fast as trees, birds and butterflies. In turn, butterfly emergence or migratory arrival showed three times stronger advancement than the first flowering of herbs, perhaps portending increasing asynchrony in insect–plant interactions. Response was significantly stronger at higher latitudes where warming has been stronger, but latitude explained < 4% of the variation. Despite expectation, latitude was not yet an important predictor of climate change impacts on phenology. The only two previously published estimates of the magnitude of global response are quite different: 2.3 and 5.1 days decade⁻¹ advancement. The scientific community has assumed this difference to be real and has attempted to explain it in terms of biologically relevant phenomena: specifically, differences in distribution of data across latitudes, taxa or time periods. Here, these and other possibilities are explored. All analyses indicate that the difference in estimated response is primarily due to differences between the studies in criteria for incorporating data. It is a clear and automatic consequence of the exclusion by one study of data on ‘stable’ (nonresponsive) species. Once this is accounted for, the two studies support each other, generating similar conclusions despite analyzing substantially nonoverlapping datasets. Analyses here on a new expanded dataset estimate an overall spring advancement across the northern hemisphere of 2.8 days decade⁻¹. This is the first quantitative analysis showing that data‐sampling methodologies significantly impact global (synthetic) estimates of magnitude of global warming response.     

Body temperature and territory selection by males of the speckled wood butterfly (Pararge aegeria): what makes a forest sunlit patch a rendezvous site?

1. Insects locate mobile resources like prey items or mates using either sit‐and‐wait (‘perching’) or active (‘patrolling’) searching strategies. The sit‐and‐wait strategy can be accompanied by defending and monopolising a site through territorial behaviour. 2. The present study focuses on the territorial perching behaviour in males of the speckled wood butterfly (Pararge aegeria L.). Recent studies suggested that the selection of territories (i.e. sunlit patches on the forest floor) is driven by structural characteristics of the site that affect male visual detection. However, given that adult butterflies are heliothermic organisms and that forests provide a diverse array of light environments, it seems likely that thermal aspects may also be used for territory selection. 3. We tested whether used and unused sunlit patches differed in thermal profile under field conditions in a Belgian woodland. We also used dummy butterflies to quantify variation in operative thoracic temperature and to calculate heating rates within (i.e. different vegetation structures) and between patches. 4. Sunlit patches occupied by a territorial male were larger, and were more frequently characterised by low vegetation structures compared with empty sunlit patches. It took longer to reach optimal thorax temperature (starting from a fixed suboptimal body temperature) in small patches compared with large patches. 5. We suggest that aspects of visual detection need to be combined with thermal aspects to fully understand territory selection in the speckled wood butterfly, as synergetic and/or trade‐off effects of ambient temperature, solar radiation, and canopy/vegetation structure may be involved.     

Host plant and competitor identity matter in genotype × genotype × environment interactions between vetch and pea aphids

1. Selection does not only operate in a genotype (G) × environment (E) context, but can also be modulated by the activities of organisms interacting with their environment (G × G × E). 2. The influences of aphid clonal identity and host plant (Vicia faba) intraspecific genetic variation on the performance of five genotypes of pea aphid (Acyrthosiphon pisum) were investigated – with and without interaction with a competing heterospecific clone of vetch aphid (Megoura viciae) – across three cultivars of V. faba. 3. Pea aphid performance in the presence of a competing vetch aphid clone (G × G × E) compared with the absence of competition (G × E) revealed strong context‐dependent, genotype‐specific shifts in performance, influenced by plant cultivar, competitor presence and their interaction. 4. The performance of vetch aphid in competition with each pea aphid clone was also compared. Here, competitor's genotype and abundance underlay a remarkably varied response by vetch aphid across interactions. 5. The study shows that aphid genotypes exhibit a varying degree of risk spreading, contingent on competitor identity and the patterns of aggregation across three plant cultivars. Owing to feedback loops between species activities and selective forces acting on them, our findings suggest that there are context‐dependent responses by competitors that are shaped via the interplay of the co‐occurring species and their biotic environment. 6. This work highlights the complexity of species interactions and the importance of investigating reciprocity between competition and intraspecific genetic variation. A better understanding of the eco‐evolutionary interactions between phloem‐feeding insects and their host plants can potentially be used to enhance crop protection and pest control.     

Male disguised females: costs and benefits of female‐limited dimorphism in a butterfly

1. In polymorphic species, two or more discrete phenotypes co‐occur simultaneously. Sex‐limited polymorphism is a particular case of polymorphism, in which several discrete morphs coexist within one of the two sexes only. Several hypotheses were proposed to explain the existence and the maintenance of sex‐limited polymorphism in insects: (i) the morphs have similar fitness, such as similar survival and expected fecundity, and their frequencies vary randomly (i.e. the null hypothesis); (ii) harassment by males is reduced towards the less common female morph, in this case andromorph females (i.e. the male mimicry and learned mate recognition hypotheses); (iii) morphs differ in predation risk (i.e. the predation hypothesis); or (iv) morphs differ in thermoregulation ability (i.e. the thermoregulation hypothesis). 2. Field observations and experiments were employed to compare the relative support of these hypotheses using dimorphic females of the bog fritillary butterfly. Differences were detected between morphs in survival, fecundity, harassment by males, predation pressure and thermal properties, thereby rejecting the null hypothesis. 3. The lifestyle of both morphs is associated with different costs and benefits, with advantages in daily survival and precocious emergence for the gynomorph females, and advantages in fecundity, predation and male harassment for the andromorph females. Besides, as the bog fritillary butterfly is protandrous (i.e. males emerge before females), the longer development of andromorph females puts them at risk of emerging when all the males are dead. The results raise the question as to which mechanisms control the ontogenetic pathways driving the production of the two morphs (i.e. genetic polymorphism or phenotypic plasticity).     

Tracing energy flow in stream food webs using stable isotopes of hydrogen

1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (δD) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in δD of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in δD in stream food webs in a forested catchment where variation in δ¹³C has been described previously. 3. Although algal δD varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67‰) from terrestrial carbon sources. Environmental conditions known to affect algal δ¹³C, such as water velocity and stream productivity did not greatly influence algal δD, and there was no evidence of seasonal variation. In contrast, algal δ¹³C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial δ¹³C in all streams with catchment areas larger than 10 km². 4. While knowledge of isotopic exchange with water and trophic fractionation of δD for aquatic consumers is limited, consistent source separation in streams suggests that δD may provide a complementary food web tracer to δ¹³C in aquatic food webs. Lack of significant seasonal or spatial variation in δD is a distinct advantage over δ¹³C for applications in many aquatic ecosystems.     

Absorption, Distribution, Metabolism and Leaching of [14C] ABA during Culture of Apple Embryos

Barthe, Ph. and Bulard, C. 1987. Absorption, distribution, metabolismand leaching of [¹⁴C] ABA during culture of apple embryos.—J.exp. Bot. 38: 1002–1011. It has been known for some time that dormant embryos, laid flaton damp filter-paper one cotyledon only being in direct contactwith it (C/2M mode of culture), exhibit unequal growth and greeningof their cotyledons. The aim of this work was to investigatewhether this particular mode of culture led to detectable differencesbetween the two cotyledons in the distribution and metabolismof [¹⁴C] abscisic acid (ABA). Two different approaches wereused, the material in both cases being dormant embryos of Pyrusmalus L. cv. Golden Delicious cultured at 23°C in darkness.In a first experiment, the embryos were cultured directly inthe C/2M mode and in the presence of 10^–2 mol m^–3[¹⁴C] ABA. In these conditions marked differences in the distributionof radioactivity between the lower (LC) and upper (UC) cotyledonappear after 24 h of culture. After 5 d, amounts of total radioactivitywere four times higher in LC than in UC, and the level of ABAwas three times higher. Metabolism was extremely active in LC,since certain metabolites were found in relative percentages(percentages with respect to the total radioactivity of thecotyledon) equivalent to (esters, glucosides), or even higher(dihydrophaseic acid, DPA) than those found in UC. It is suggestedthat this high level of metabolism in LC limits the availabilityof the transportable molecule, that is to say ABA. In a secondexperiment double culturing was carried out. The embryos werefirst cultured in the presence of 10^–2 mol m^–3 [¹⁴C]ABA in conditions which ensured equal distribution of ABA andits metabolites between the two cotyledons. After 5 d they weretransferred to an ABA-free medium and cultured in the C/2M mode.After 2 d and 5 d of culture, dissymmetry between the two cotyledonswas again noted; UC this time containing greater amounts ofradioactivity than LC. The differences, however, were less markedthan in the first experiment. This dissymmetry is due to leachingof a certain amount of radioactivity from LC, which is onlypartially compensated for by migration from UC. Key words: ¹⁴C-ABA distribution, leaching and metabolism, embryo culture, embryo dormancy