Fitness consequences of northward dispersal as possible adaptation to climate change, using experimental translocation of a migratory passerine

Buffering and phenological mismatch: A change of perspective

The potential for climate change to disrupt phenology-mediated interactions in interaction networks has attracted considerable attention in recent decades. Frequently, studies emphasize the fragility of ephemeral seasonal interactions, and the risks posed by phenological asynchrony. Here, we argue that the fitness consequences of asynchrony in phenological interactions may often be more buffered than is typically acknowledged. We identify three main forms that buffering may take: (i) mechanisms that reduce asynchrony between consumer and resource; (ii) mechanisms that reduce the costs of being asynchronous; and (iii) mechanisms that dampen interannual variance in performance across higher organizational units. Using synchrony between the hatching of winter moth caterpillars and the leafing of their host-plants as a case study, we identify a wide variety of buffers that reduce the detrimental consequences of phenological asynchrony on caterpillar individuals, populations, and meta-populations. We follow this by drawing on examples across a breadth of taxa, and demonstrate that these buffering mechanisms may be quite general. We conclude by identifying key gaps in our knowledge of the fitness and demographic consequences of buffering, in the context of phenological mismatch. Buffering has the potential to substantially alter our understanding of the biotic impacts of future climate change-a greater recognition of the contribution of these mechanisms may reveal that many trophic interactions are surprisingly resilient, and also serve to shift research emphasis to those systems with fewer buffers and towards identifying the limits of those buffers.

Adaptation to climate change through dispersal and inherited timing in an avian migrant

Many organisms fail to adjust their phenology sufficiently to climate change. Studies have concentrated on adaptive responses within localities, but little is known about how latitudinal dispersal enhances evolutionary potential. Rapid adaptation is expected if dispersers from lower latitudes have improved synchrony to northern conditions, thereby gain fitness and introduce genotypes on which selection acts. Here we provide experimental evidence that dispersal in an avian migrant enables rapid evolutionary adaptation. We translocated Dutch female pied flycatchers (Ficedula hypoleuca) and eggs to Sweden, where breeding phenology is ~15 days later. Translocated females bred earlier, and their fitness was 2.5 times higher than local Swedish flycatchers. We show that between-population variation in timing traits is highly heritable, and hence immigration of southern genotypes promotes the necessary evolutionary response. We conclude that studies on adaptation to large-scale environmental change should not just focus on plasticity and evolution based on standing genetic variation but should also include phenotype-habitat matching through dispersal as a viable route to adjust.

Eco-Evolutionary Consequences of Dispersal Syndromes during Colonization in a Passerine Bird

AbstractIn most animal species, dispersing individuals possess phenotypic attributes that mitigate the costs of colonization and/or increase settlement success in new areas (dispersal syndromes). This phenotypic integration likely affects population dynamics and the direction of selection, but data are lacking for natural populations. Using an approach that combines population dynamics, quantitative genetics, and phenotypic selection analyses, we reveal the existence of dispersal syndromes in a pied flycatcher (Ficedula hypoleuca) population in the Netherlands: immigrants were larger, tended to have darker plumage, bred earlier, and produced larger clutches than local recruits, and some of these traits were genetically correlated. Over time, the phenotypic profile of the population gradually changed: each generation advanced arrival and breeding and exhibited longer wings as a result of direct and indirect selection on these correlated traits. Although phenotypic attributes of immigrants were favored by selection during the early phase of colonization, observed phenotypic changes were similar for immigrants and local recruits. We propose that immigrants facilitated initial population establishment but that temporal changes likely resulted from climate change-induced large-scale selection. This study highlights that newly established populations are of nonrandom composition and that phenotypic architecture affects evolutionary population trajectories.

Eating More and Fighting Less: Social Foraging Is a Potential Advantage for Successful Expansion of Bird Source Populations

Animals can expand distributions in response to climatic and environmental changes, but the potential expansive ability of a source population is rarely evaluated using designed experiments. Group foraging can increase survival in new environments, but it also increases intraspecific competition. The trade-off between benefit and conflict needs to be determined. The expanding Light-vented Bulbul Pycnonotus sinensis was used as a model to test mechanisms promoting successful expansion. Social foraging and its advantages were evaluated using lab-designed feeding trials. Consuming novel foods was compared between bulbuls and a sympatric, nonexpansive relative species, the finchbill Spizixos semitorques, from native areas at both solitary and social levels. Bulbuls increased their eating times when transferred from solitary to group, whereas social context did not affect finchbills. Bulbuls were significantly more likely to eat with their companions than finchbills when in a group. Thus, exploring food resources in a bulbul source population was facilitated by social context, indicating that social foraging is an important means by which birds successfully expand and respond to environmental changes. This research increases understanding of successful expansion mechanisms and will consequently help predict invasive potentials of alien species.

Unravelling the causes and consequences of dispersal syndromes in a wild passerine

Evidence accumulates that dispersal is correlated with individual behavioural phenotype (dispersal syndrome). The evolutionary causes and consequences of such covariation depend on the degree of plasticity versus inheritance of the traits, which requires challenging experiments to implement in mobile organisms. Here, we combine a forced dispersal experiment, natural colonization and longitudinal data to establish if dispersal and aggression levels are integrated and to test their adaptive nature in pied flycatchers (Ficedula hypoleuca). We found that (forced) dispersers behaved more aggressively in their first breeding year after dispersal and decreased their aggression in following years. Strength of dispersal syndrome and direction of fecundity selection on aggression in newly colonized areas varied between years. We propose that the net benefits of aggression for dispersers increase under harsh conditions (e.g. low food abundance). This hypothesis now warrants further testing. Overall, this study provides unprecedented experimental evidence that dispersal syndromes can be remodelled via adaptive plasticity depending on the individuals' local breeding experience and/or year-specific ecological conditions. It highlights the importance of individual behavioural variation in population dynamics.

Seasonal changes in predator community switch the direction of selection for prey defences

Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis. To understand such coexistence, we here report results from a field experiment where relative survival of artificial larvae, varying in conspicuousness, was estimated in natural bird communities over an entire season. This takes advantage of natural variation in the proportion of naive predators: naivety peaks when young birds have just fledged. We show that the relative benefit of warning signals and crypsis changes accordingly. When naive birds are rare (early and late in the season), conspicuous warning signals improve survival, but conspicuousness becomes a disadvantage near the fledging time of birds. Such temporal structuring of predator-prey relationships facilitates the coexistence of diverse antipredatory strategies and helps explain two patterns we found in a 688-species community of Lepidoterans: larval warning signals remain rare and occur disproportionately often in seasons when predators are educated.