The influence of biological rhythms on host–parasite interactions

Biological rhythms, from circadian control of cellular processes to annual cycles in life history, are a main structural element of biology. Biological rhythms are considered adaptive because they enable organisms to partition activities to cope with, and take advantage of, predictable fluctuations in environmental conditions. A flourishing area of immunology is uncovering rhythms in the immune system of animals, including humans. Given the temporal structure of immunity, and rhythms in parasite activity and disease incidence, we propose that the intersection of chronobiology, disease ecology, and evolutionary biology holds the key to understanding host–parasite interactions. Here, we review host–parasite interactions while explicitly considering biological rhythms, and propose that rhythms: influence within-host infection dynamics and transmission between hosts, might account for diel and annual periodicity in host–parasite systems, and can lead to a host–parasite arms race in the temporal domain

My family and other animals: mixed broods of great and blue tits in the Loch Lomond woodlands

No abstract available

Seasonal timing in different environments: comparative studies in Stonechats

Vorstellung der Dissertation: Vögel müssen ihre jahreszeitlichen Aktivitäten präzise auf die saisonalen Bedingungen abstimmen, unter denen sie leben. Daher unterscheiden sich Populationen und nahe verwandte Arten häufig lokal in ihrem jahreszeitlichen Verhalten. Schwarzkehlchen (Saxicola torquata) sind wegen ihres riesigen nord-südlichen Brutareals eine Modellart für die Erforschung von saisonalem Verhalten und werden am Max-Planck-Institut für Ornithologie in Andechs seit etwa 25 Jahren untersucht. Um zu einem besseren Verständnis von Anpassungen an die zeitliche Umwelt zu gelangen, habe ich zentrale Ereignisse im Jahreszyklus von Schwarzkehlchen aus verschiedenen Herkunftsgebieten verglichen. Afrikanische Schwarzkehlchen aus Kenia, sibirische Schwarzkehlchen aus Kasachstan, sowie zentraleuropäische und irische Schwarzkehlchen wurden an unserem Institut in Oberbayern nachgezüchtet und gehalten. Langstreckenziehende sibirische Schwarzkehlchen stehen unter großem Zeitdruck, denn sie verbringen nur wenige Monate im Brutgebiet. Zentraleuropäische und irische Schwarzkehlchen ziehen über kurze Strecken und halten sich weit länger im Brutgebiet auf. Irische Schwarzkehlchen sind darüber hinaus Teilzieher, so dass nur ein Teil der Vögel zieht, während der Rest im Brutgebiet verbleibt. Populationsmitglieder unterscheiden sich also erheblich voneinander in ihrem Jahreszyklus. Afrikanische Schwarzkehlchen dagegen verbleiben ganzjährig in Paarterritorien. Schwarzkehlchen aus den von uns untersuchten Herkunftsgebieten müssen daher sehr unterschiedliche saisonale Aufgaben bewältigen und zeitlich einrichten. Der Vergleich ihrer Jahreszyklen soll einem besseren Verständnis davon dienen, inwieweit jahreszeitliches Verhalten programmiert bzw. modifizierbar ist, und inwieweit saisonale Aktivitäten miteinander verknüpft sind

Wild clocks: preface and glossary

No abstract available

Timing avian long-distance migration: from internal clock mechanisms to global flights

Migratory birds regularly perform impressive long-distance flights, which are timed relative to the anticipated environmental resources at destination areas that can be several thousand kilometres away. Timely migration requires diverse strategies and adaptations that involve an intricate interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarize the clock mechanisms that enable them to succeed. We examine the following challenges: departing in time for spring and autumn migration, in anticipation of future environmental conditions; using clocks on the move, for example for orientation, navigation and stopover; strategies of adhering to, or adjusting, the time programme while fitting their activities into an annual cycle; and keeping pace with a world of rapidly changing environments. We then elaborate these themes by case studies representing long-distance migrating birds with different annual movement patterns and associated adaptations of their circannual programmes. We discuss the current knowledge on how endogenous migration programmes interact with external information across the annual cycle, how components of annual cycle programmes encode topography and range expansions, and how fitness may be affected when mismatches between timing and environmental conditions occur. Lastly, we outline open questions and propose future research directions

Endogenous programs and flexibility in bird migration

Endogenous programs that regulate annual cycles have been shown for many taxa, including protists, arthropods, fish, mammals and birds. In migration biology, these programs are best known in songbirds. The majority of songbirds rely on a genetic program inherited from their parents that will guide them during their first solo-migration. The phenotypic components of the program are crucial for their individual fitness and survival, and include time components, direction, and distance. This program is constructed to both guide behavior and to regulate flexible responses to the environment at different stages of the annual cycle. The migration program is driven by a circannual rhythm, allowing for, and resetting, carry-over effects. With experience, the migration decisions of individual migrants may be based on information learnt on breeding sites, wintering sites, and en route. At the population level, substantial variation in route choice and timing of migration may be explained by inherited variation of program components, by interactions with environmental and social factors, and by individual learning. In this review we will explore the components of endogenous migration programs and discuss in what ways they can lead to flexibility and variation in migration behavior

Circannual rhythms anticipate the earth’s annual periodicity

Life on Earth has evolved in a periodic world, which in most environments cycles predictably between conditions that are favourable or unfavourable for an organism. Organisms use favourable seasons to reproduce and grow, and withdraw during unfavourable seasons. To deal with the predictable changes in their environments, all taxonomic groups have evolved genetically programmed timing mechanisms. These govern seasonal cycles in physiology and behaviour that optimise survival and reproductive success, and have been formally described as circannual rhythms. Experimentally, under conditions of constant day length and temperature, circannual rhythms of many species continue to be expressed, even throughout the life cycle, illustrating the fundamental endogenous control. Under natural conditions, they are usually entrained by seasonal time cues, notably photoperiod, to synchronise the biology to environmental periodicity. Here we review long-term timekeeping strategies from classical vertebrate models to invertebrate and unicell life histories. These circannual rhythms enable organisms to anticipate Earth’s periodicity

Integrated behavioural and stable isotope data reveal altered diet linked to low breeding success in urban-dwelling blue tits (Cyanistes caeruleus)

Animals often show reduced reproductive success in urban compared to adjacent natural areas. The lower availability and quality of natural food in cities is suggested as one key limiting factor. However, only few studies have provided conclusive support by simultaneously assessing food availability, diet and fitness. We consolidate this evidence by taking a holistic approach, comparing blue tits breeding in forest, suburban and urban areas. We (a) assessed arthropod availability, (b) investigated parental provisioning behaviour, (c) inferred diet through stable isotope analysis, and (d) measured reproductive success. At the urban site, we found a significant reduction in caterpillar availability, the main food source of blue tits, and consequently urban tits fed their offspring with fewer caterpillars than forest and suburban birds. Stable isotope analysis confirmed that diet in the urban area was fundamentally different than in the other sites. Reproductive success was lower in both urban and suburban sites compared to the forest site, and was positively associated with volume of provisioned caterpillars. Our findings provide strong integrative evidence that urban blue tit nestlings are not receiving a suitable diet, and this may be an important limiting factor for urban populations of this and potentially many other species

Baseline and stress-induced levels of corticosterone in male and female Afrotropical and European temperate stonechats during breeding

Background: Latitudinal variation in avian life histories falls along a slow-fast pace of life continuum: tropical species produce small clutches, but have a high survival probability, while in temperate species the opposite pattern is found. This study investigated whether differential investment into reproduction and survival of tropical and temperate species is paralleled by differences in the secretion of the vertebrate hormone corticosterone (CORT). Depending on circulating concentrations, CORT can both act as a metabolic (low to medium levels) and a stress hormone (high levels) and, thereby, influence reproductive decisions. Baseline and stress-induced CORT was measured across sequential stages of the breeding season in males and females of closely related taxa of stonechats (Saxicola spp) from a wide distribution area. We compared stonechats from 13 sites, representing Canary Islands, European temperate and East African tropical areas. Stonechats are highly seasonal breeders at all these sites, but vary between tropical and temperate regions with regard to reproductive investment and presumably also survival. Results: In accordance with life-history theory, during parental stages, post-capture (baseline) CORT was overall lower in tropical than in temperate stonechats. However, during mating stages, tropical males had elevated post-capture (baseline) CORT concentrations, which did not differ from those of temperate males. Female and male mates of a pair showed correlated levels of post-capture CORT when sampled after simulated territorial intrusions. In contrast to the hypothesis that species with low reproduction and high annual survival should be more risk-sensitive, tropical stonechats had lower stress-induced CORT concentrations than temperate stonechats. We also found relatively high post-capture (baseline) and stress-induced CORT concentrations, in slow-paced Canary Islands stonechats. Conclusions: Our data support and refine the view that baseline CORT facilitates energetically demanding activities in males and females and reflects investment into reproduction. Low parental workload was associated with lower post-capture (baseline) CORT as expected for a slow pace of life in tropical species. On a finer resolution, however, this tropical-temperate contrast did not generally hold. Post-capture (baseline) CORT was higher during mating stages in particular in tropical males, possibly to support the energetic needs of mate-guarding. Counter to predictions based on life history theory, our data do not confirm the hypothesis that long-lived tropical populations have higher stress-induced CORT concentrations than short-lived temperate populations. Instead, in the predator-rich tropical environments of African stonechats, a dampened stress response during parental stages may increase survival probabilities of young. Overall our data further support an association between life history and baseline CORT, but challenge the role of stress-induced CORT as a mediator of tropical-temperate variation in life history

Correlated patterns of genetic diversity and differentiation across an avian family

Comparative studies of closely related taxa can provide insights into the evolutionary forces that shape genome evolution and the prevalence of convergent molecular evolution. We investigated patterns of genetic diversity and differentiation in stonechats (genus Saxicola), a widely distributed avian species complex with phenotypic variation in plumage, morphology, and migratory behavior, to ask whether similar genomic regions have become differentiated in independent, but closely related, taxa. We used whole-genome pooled sequencing of 262 individuals from 5 taxa and found that levels of genetic diversity and divergence are strongly correlated among different stonechat taxa. We then asked if these patterns remain correlated at deeper evolutionary scales and found that homologous genomic regions have become differentiated in stonechats and the closely related Ficedula flycatchers. Such correlation across a range of evolutionary divergence and among phylogenetically independent comparisons suggests that similar processes may be driving the differentiation of these independently evolving lineages, which in turn may be the result of intrinsic properties of particular genomic regions (e.g., areas of low recombination). Consequently, studies employing genome scans to search for areas important for reproductive isolation or adaptation should account for corresponding regions of differentiation, as these regions may not necessarily represent speciation islands or evidence of local adaptation