Bird nests function to protect parents, eggs or offspring against fluctuations in the environment. In Blue Tits (Cyanistes caeruleus) producing first or replacement clutches, we examined relationships between nest height (a measure of nest size) and several parameters of breeding performance that are often quantified in long-term avian field studies. We artificially increased the cost of reproduction in randomly selected females by removing the whole first clutch and nest material after about 5 days of incubation. This experiment resulted in replacement nests. Experimentally increasing the range of breeding conditions across females, we expected to have more power to detect a positive correlation between nest height and breeding success. However, we found that nest height was not significantly related to any of the breeding traits investigated (clutch size, number of hatchlings, number of fledglings, hatching success, fledging success, chick mass), after controlling for factors frequently investigated in long-term monitoring programs and known to influence breeding performance (female age, year, clutch type as a proxy of egg-laying date). We conclude that the identification of the exact underlying mechanisms causing relationships between nest characteristics and breeding performance will require more experimental study and the exploitation of larger datasets, both within and across avian model systems.Zusammenfassung Vogelnester schützen Elternvögel, Eier oder Jungvögel vor Schwankungen in der Umwelt. Wir haben bei Blaumeisen (Cyanistes caeruleus), die Erst-oder Ersatzgelege produzierten, die Beziehungen zwischen Nesthöhe (einem Maß für Nestgröße) und mehreren Bruterfolgsparametern, die oftmals in Langzeitfeldstudien an Vögeln quantifiziert werden, untersucht. Wir haben für zufällig ausgewählte Weibchen die Kosten der Fortpflanzung experimentell erhöht, indem wir das gesamte Erstgelege sowie Nistmaterial nach etwa fünf Tagen Bebrütung entfernt haben. Dieses Experiment hatte Ersatznester zur Folge. Unsere Erwartung war, dass wir eine positive Korrelation zwischen Nesthöhe und Bruterfolg eher entdecken können, wenn wir die Brutbedingungen für Weibchen experimentell variabler machen. Wir fanden jedoch, dass die Nestgröße nicht signifikant mit irgendeinem der untersuchten Brutparameter (Gelegegröße, Anzahl geschlüpfter und ausgeflogener Jungvögel, Schlupf-und Ausfliegeerfolg, Körpermasse der Küken) zusammenhing, nachdem wir Faktoren, die in Langzeitstudien häufig untersucht werden und bekanntermaßen die Fortpflanzungleistung beeinflussen (Weibchenalter, Jahr, Gelegetyp als Maß für Legedatum), berücksichtigt hatten. Wir schlussfolgern, dass für die Ermittlung der genauen Mechanismen, die Zusammenhänge zwischen Nestmerkmalen und Fortpflanzungleistung verursachen, mehr experimentelle Untersuchungen und grö-ßere Datensätze benötigt werden, sowohl innerhalb als auch zwischen verschiedenen Vogel-Modellsystemen.

Phenological traits often show variation within and among natural populations of annual plants. Nevertheless, the adaptive value of post-anthesis traits is seldom tested. In this study, we estimated the adaptive values of pre- and post-anthesis traits in two stressful environments (water stress and interspecific competition), using the selfing annual species Arabidopsis thaliana. By estimating seed production and by performing laboratory natural selection (LNS), we assessed the strength and nature (directional, disruptive and stabilizing) of selection acting on phenological traits in A. thaliana under the two tested stress conditions, each with four intensities. Both the type of stress and its intensity affected the strength and nature of selection, as did genetic constraints among phenological traits. Under water stress, both experimental approaches demonstrated directional selection for a shorter life cycle, although bolting time imposes a genetic constraint on the length of the interval between bolting and anthesis. Under interspecific competition, results from the two experimental approaches showed discrepancies. Estimation of seed production predicted directional selection toward early pre-anthesis traits and long post-anthesis periods. In contrast, the LNS approach suggested neutrality for all phenological traits. This study opens questions on adaptation in complex natural environment where many selective pressures act simultaneously.

Demographic changes are known to leave footprints on genetic polymorphism. Together with the increased availability of large polymorphism data sets, coalescent-based methods allow inferring the past demography of populations from their present-day patterns of genetic diversity. Here, we analyzed both nuclear (20 noncoding regions) and mitochondrial (HVS-I) resequencing data to infer the demographic history of 66 African and Eurasian human populations presenting contrasting lifestyles (nomadic hunter-gatherers, nomadic herders, and sedentary farmers). This allowed us to investigate the relationship between lifestyle and demography and to address the long-standing debate about the chronology of demographic expansions and the Neolithic transition. In Africa, we inferred expansion events for farmers, but constant population sizes or contraction events for hunter-gatherers. In Eurasia, we inferred higher expansion rates for farmers than herders with HVS-I data, except in Central Asia and Korea. Although isolation and admixture processes could have impacted our demographic inferences, these processes alone seem unlikely to explain the contrasted demographic histories inferred in populations with different lifestyles. The small expansion rates or constant population sizes inferred for herders and hunter-gatherers may thus result from constraints linked to nomadism. However, autosomal data revealed contraction events for two sedentary populations in Eurasia, which may be caused by founder effects. Finally, the inferred expansions likely predated the emergence of agriculture and herding. This suggests that human populations could have started to expand in Paleolithic times, and that strong Paleolithic expansions in some populations may have ultimately favored their shift toward agriculture during the Neolithic.