Environmental Effects on Temperature Stress Resistance in the Tropical Butterfly Bicyclus Anynana

BACKGROUND: The ability to withstand thermal stress is considered to be of crucial importance for individual fitness and species' survival. Thus, organisms need to employ effective mechanisms to ensure survival under stressful thermal conditions, among which phenotypic plasticity is considered a particularly quick and effective one. METHODOLOGY/PRINCIPAL FINDINGS: In a series of experiments we here investigate phenotypic adjustment in temperature stress resistance following environmental manipulations in the butterfly Bicyclus anynana. Cooler compared to warmer acclimation temperatures generally increased cold but decreased heat stress resistance and vice versa. In contrast, short-time hardening responses revealed more complex patterns, with, e.g., cold stress resistance being highest at intermediate hardening temperatures. Adult food stress had a negative effect on heat but not on cold stress resistance. Additionally, larval feeding treatment showed interactive effects with adult feeding for heat but not for cold stress resistance, indicating that nitrogenous larval resources may set an upper limit to performance under heat stress. In contrast to expectations, cold resistance slightly increased during the first eight days of adult life. Light cycle had marginal effects on temperature stress resistance only, with cold resistance tending to be higher during daytime and thus active periods. CONCLUSIONS/SIGNIFICANCE: Our results highlight that temperature-induced plasticity provides an effective tool to quickly and strongly modulate temperature stress resistance, and that such responses are readily reversible. However, resistance traits are not only affected by ambient temperature, but also by, e.g., food availability and age, making their measurement challenging. The latter effects are largely underexplored and deserve more future attention. Owing to their magnitude, plastic responses in thermal tolerance should be incorporated into models trying to forecast effects of global change on extant biodiversity

What You See Is What You Get? Exclusion Performances in Ravens and Keas

BACKGROUND:Among birds, corvids and parrots are prime candidates for advanced cognitive abilities. Still, hardly anything is known about cognitive similarities and dissimilarities between them. Recently, exclusion has gained increasing interest in comparative cognition. To select the correct option in an exclusion task, one option has to be rejected (or excluded) and the correct option may be inferred, which raises the possibility that causal understanding is involved. However, little is yet known about its evolutionary history, as only few species, and mainly mammals, have been studied. METHODOLOGY/PRINCIPAL FINDINGS:We tested ravens and keas in a choice task requiring the search for food in two differently shaped tubes. We provided the birds with partial information about the content of one of the two tubes and asked whether they could use this information to infer the location of the hidden food and adjust their searching behaviour accordingly. Additionally, this setup allowed us to investigate whether the birds would appreciate the impact of the shape of the tubes on the visibility of food. The keas chose the baited tube more often than the ravens. However, the ravens applied the more efficient strategy, choosing by exclusion more frequently than the keas. An additional experiment confirmed this, indicating that ravens and keas either differ in their cognitive skills or that they apply them differently. CONCLUSION:To our knowledge, this is the first study to demonstrate that corvids and parrots may perform differently in cognitive tasks, highlighting the potential impact of different selection pressures on the cognitive evolution of these large-brained birds

Thermal adaptation in insects: Effects of inbreeding, environment and selection

The ability to withstand thermal stress is considered to be of crucial importance for individual fitness and species’ survival. Thus, organisms need to employ effective mechanisms to ensure survival under stressful thermal conditions. Responses to environmental challenges may occur quickly through phenotypic plasticity or through genetic adaptation needing longer periods of time. Beside thermal stress, other environmental factors might have a similar impact on temperature stress resistance. We first investigated phenotypic adjustment in temperature stress resistance following different environmental manipulations in the butterfly Bicyclus anynana. We found that temperature-induced plasticity quickly and strongly modulated temperature stress resistance and that such responses are readily reversible. Short time hardening responses revealed more complex patterns, with, e.g., cold stress resistance being highest at intermediate hardening temperatures. However, we found resistance traits also to be affected by food availability, age and light cycle. We further investigated whether temperature stress resistance is affected by photoperiod in the fly Protophormia terraenovae. Indeed, variation in temperature stress resistance can be triggered by photoperiod (and temperature), with shorter day lengths inducing more cold- and longer day lengths more heat-tolerant phenotypes. We suggest that short-term, photoperiod-mediated changes in insect thermal tolerance represent a mechanism of adaptive seasonal plasticity. In addition to temperature stress, inbreeding may negatively affect an organism’s ability to cope with changing conditions. This may additively contribute to the extinction risk of small populations in the coming decades for which the frequency and intensity of extreme weather events is predicted to strongly increase. We investigated the effects of inbreeding on egg hatching success, development and temperature stress tolerance in the tropical butterfly Bicyclus anynana using three levels of inbreeding (outbred control, one and two full-sib matings). Even comparatively low levels of inbreeding yield negative consequences for reproduction and development under beneficial conditions. Inbreeding also reduced cold tolerance in adult butterflies, while heat tolerance remained unaffected. We therefore conclude that acute stress tolerance may not be generally impaired by inbreeding. Reduced genetic diversity as a consequence of inbreeding or drift may also interfere with a population’s evolutionary potential. We investigated the consequences of inbreeding on evolutionary potential (the ability to increase cold resistance) using artificial selection starting from three different levels of inbreeding (outbred control, one and two full-sib matings). Although a negative impact of genetic erosion (e.g. through inbreeding) on evolutionary potential is predicted by theory, empirical evidence for such effects seems to be exceedingly scarce. Our study showed a clear response to selection on cold stress resistance, which was smaller in inbred compared to outbred populations. Correlated responses to selection in 10 different life history and stress resistance traits were essentially absent. Inbreeding depression was still measurable in some traits after the course of selection. Traits more closely related to fitness showed a clear fitness rebound, suggesting a trait-specific impact of purging. Importantly, we here experimentally demonstrated that increased levels of inbreeding indeed reduced evolutionary potential, and therefore the ability to cope with environmental change. Finally we tested whether selection on increased cold tolerance in the adult stage increases cold resistance throughout ontogeny. A significant response to selection was found in one day-old butterflies (the age at which selection took place). Older adults showed a very similar though weaker response. Nevertheless, cold resistance did not increase in either egg, larval or pupal stage in the selection lines, but was even lower compared to control lines for eggs and young larvae. These findings suggest a cost of increased adult cold tolerance, with the latter presumably reducing resource availability for offspring provisioning and thereby stress tolerance during development. This thesis emphasized the importance of considering genetic as well as environmental effects together, as both may interactively challenge an individual’s ability to respond to changing conditions. In times of a human-induced loss and fragmentation of natural habitats reducing population size and thereby presumably reducing genetic diversity, plus increased temperature stress due to climate change, the long-term persistence of any given species or population will depend on this ability.Die Fähigkeit Temperaturstress zu wiederstehen gilt als äßerst wichtig für die Fitness eines Individuums oder das Überleben von Arten. Lebewesen müssen daher effektive Mechanismen entwickeln, um unter belastenden Temperaturbedingungen überleben zu können. Reaktionen auf sich ändernde Umweltbedingungen könnnen schnell durch phänotypische Plastizität oder langsame durch genetische Adaptation erfolgen. Neben Temperaturstress haben möglicherweise auch andere Umweltfaktoren einen Effekt auf die Temperaturstressresistenz. Wir erforschten zunächst phänotypische Anpassungen der Temperaturstressresistenz, ausgelöst durch unterschiedliche Manipulationen der Umwelt, bei dem Augenfalter Bicyclus anynana. Temperaturinduzierte Plastizität bewirkte eine schnelle und deutliche Änderung in der Temperaturstressresistenz, dieser Effekt ist reversibel. Kurzzeitige Abhärtung ergab komplexere Muster, so war die Kältestressresistenz beispielsweise am höchsten bei intermediären Temperaturen. Die Temperaturstressresistenz konnte auch durch Futtererhältlichkeit, Alter und Lichtzyklus beeinflußt werden. Des weiteren wurde der Einfluß der Photoperiode auf die Temperaturstressresistenz an der Fliege Protophormia terranovae erforscht. Variationen der Temperaturstressresistenz konnten durch Änderungen in der Photoperiode hervorgerufen werden, so bewirkten kürzere Tageslängen kälteresistentere und längere Tage hitzeresistentere Phänotypen. Wir schlagen vor, dass es sich hierbei um adaptive saisonale Plastizität handelt. Neben Temperaturstress hat möglicherweise auch Inzucht einen negativen Einfluss auf die Fähigkeit, mit sich ändernden Umweltbedingungen zurechtzukommen. Das könnte das Aussterberisiko kleiner Populationen erhöhen, insbesondere wenn Häufigkeit und Intensität extremer Wetterereignisse in Zukunft zunehmen sollen. Wir untersuchten den Einfluss von Inzucht auf den Schlupferfolg, die Entwicklung und die Temperaturstresstoleranz bei dem tropischen Augenfalter Bicyclus anynana indem wir drei verschiedene Inzuchtniveaus bildeten( Ausgekreuzt, nach 1 und nach 2 Geschwisterverpaarungen). Bereits diese vergleichsweise niedrigen Inzuchtniveaus hatten einen negativen Einfluss auf die Reproduktion und Entwicklung bei günstigen Umweltbedingungen. Inzucht reduzierte auch die Kältetoleranz bei adulten Schmetterlingen, während es keinen Einluss auf die Hitzetoleranz gab. Wir schließen daraus das Stresstoleranz nicht zwangsläufig durch Inzucht negativ beeinflusst wird. Verringerte genetische Diversität als Konsequenz von Inzucht oder Drift verringert möglicherweise auch das evolutionäre Potential einer Population. Wir erforschten die Auswirkungen von Inzucht auf das evolutionäre Potential (die Fähigkeit, Kältetoleranz zu erhöhen) mit Hilfe künstlicher Selektion beginnend von drei Inzuchtniveaus (ausgekreuzt, eine und zwei Geschwisterverpaarungen.) Obwohl ein negativer Einfluss genetischer Erosion (z.B. durch Inzucht) auf das evolutionäre Potential theoretisch vorhergesagt wird, sind empirische Nachweise bisher kaum vorhanden. Unsere Studie zeigt eine deutliche Raktion auf die Selektion, deren Effekt in den ingezüchteten Populationen kleiner war als in den ausgekreuzten Populationen. Korrelierte Reaktionen auf die Selektion untersucht in 10 verschiedenen Merkmalen der Lebensgeschichte konnten nicht gefunden werden. Eine Inzuchtdepression ließ sich in einigen untersuchten Merkmalen nach wie vor nachweisen. Merkmale, die bedeutender für die Fitness sind, zeigten dagegen eine deutliche Erholung von der Inzuchtdepression. Wir konnten mit diese Studie experimentell zeigen, das erhöhte Inzuchtniveaus das evolutionäre Potential reduzieren und damit auch die Fähigkeit, sich an ändernde Umweltbedingungen anzupassen. Zuletzt untersuchten wir, ob die durch Selektion erhöhte Kältetoleranz für alle Entwicklungsstadien gilt. Es gab eine positive signifikante Reaktion auf die Selektion bei Imagines, die ein Tag alt waren (das Alter, in dem die Selektion stattgefunden hatte). Ältere Individuen zeigten eine ähnliche, jedoch schwächere Reaktion. Die erhöhte Kälteresistenz ließ sich jedoch nicht bei Eiern, Raupen oder Puppen nachweisen und war sogar geringer in den Selektionslinien im Vergleich zu den Kontrollinien bei Eiern und jungen Raupen. Diese Ergebnisse deuten auf Kosten erhöhter Kältetoleranz im adulten Stadium hin, so dass vermutlich weniger Ressourcen für den Nachwuchs in frühen Stadien der Ontogenie bleiben. Diese Dissertation verdeutlicht, wie wichtig es ist, sowohl genetische als auch Umwelteffekt zusammen zu betrachten, da beide interaktiv die Fähigkeit eines Organismus herausfordern sich an ändernde Bedingungen anzupassen. In Zeiten von durch den Menschen verursachten Verlust und/oder der Verkleinerung von Habitaten, die die Populationsgrößen verkleinern und damit auch die genetische Diversität, sowie erhöhtem Temperaturstress aufgrund des Klimawandels, wird das langfristige Überleben von Arten von dieser Fähigkeit abhängen

selection

Selection on cold toleranc

reproductive traits

Fecundity, egg hatching succes

Data from: Does selection on increased cold tolerance in the adult stage confer resistance throughout development?

Artificial selection is a powerful approach to unravel constraints on genetic adaptation. While it has been frequently used to reveal genetic trade-offs among different fitness-related traits, only a few studies have targeted genetic correlations across developmental stages. Here we test whether selection on increased cold tolerance in the adult stage increases cold resistance throughout ontogeny in the butterfly Bicyclus anynana. We used lines selected for decreased chill-coma recovery time and according controls, which had originally been set up from three levels of inbreeding (outbred control, one or two full-sib matings). Four generations after having terminated selection, a significant response to selection was found in one day-old butterflies (the age at which selection took place). Older adults showed a very similar though weaker response. Nevertheless, cold resistance did not increase in either egg, larval or pupal stage in the selection lines, but was even lower compared to control lines for eggs and young larvae. These findings suggest a cost of increased adult cold tolerance, presumably reducing resource availability for offspring provisioning and thereby stress tolerance during development, which may substantially affect evolutionary trajectories

cold and heat stress

cold and heat tolerance after selectio

longevity and survival

longevity control, longevity after cold shock and survival after heat shoc

developmental traits

larval time, pupal time, pupal mass, growth rat

development stages

Survival of eggs, larvae and pupae after cold shocks and chill coma recovery times of adult