The co-evolution of multiply-informed dispersal: information transfer across landscapes from neighbors and immigrants

Dispersal plays a key role in natural systems by shaping spatial population and evolutionary dynamics. Dispersal has been largely treated as a population process with little attention to individual decisions and the influence of information use on the fitness benefits of dispersal despite clear empirical evidence that dispersal behavior varies among individuals. While information on local density is common, more controversial is the notion that indirect information use can easily evolve. We used an individual-based model to ask under what conditions indirect information use in dispersal will evolve. We modeled indirect information provided by immigrant arrival into a population which should be linked to overall metapopulation density. We also modeled direct information use of density which directly impacts fitness. We show that immigrant-dependent dispersal evolves and does so even when density dependent information is available. Use of two sources of information also provides benefits at the metapopulation level by reducing extinction risk and prolonging the persistence of populations. Our results suggest that use of indirect information in dispersal can evolve under conservative conditions and thus could be widespread

Social network structure in wintering golden-crowned sparrows is not correlated with kinship

Stable social organization in a wide variety of organisms has been linked to kinship, which can minimize conflict due to the indirect fitness benefits from cooperating with relatives. In birds, kin selection has been mostly studied in the context of reproduction or in species that are social year round. Many birds however are migratory, and the role of kinship in the winter societies of these species is virtually unexplored. In a previous study, we discovered striking social complexity and stability in a wintering population of migratory golden-crowned sparrows (Zonotrichia atricapilla) – individuals repeatedly form close associations with the same social partners, including across multiple winters. Here, we test the possibility that kinship might be involved in these close and stable social affiliations. We examine the relationship between kinship and social structure for two of the consecutive wintering seasons from the previous study. We found no evidence that social structure was influenced by kinship. Relatedness between most pairs of individuals was at most that of first cousins (and mostly far lower). Genetic networks based on relatedness do not correspond to the social networks, and Mantel tests revealed no relationship between kinship and pairwise interaction frequency. Kinship also failed to predict social structure in more fine-grained analyses, including analyses of each sex separately (in the event that sex-biased migration might limit kin selection to one sex), and separate analyses for each social community. The complex winter societies of golden-crowned sparrows appear to be based on cooperative benefits unrelated to kin selection

Cooperative social clusters are not destroyed by dispersal in a ciliate

<p>Abstract</p> <p>Background</p> <p>The evolution of social cooperation is favored by aggregative behavior to facilitate stable social structure and proximity among kin. High dispersal rates reduce group stability and kin cohesion, so it is generally assumed that there is a fundamental trade-off between cooperation and dispersal. However, empirical tests of this relationship are rare. We tested this assumption experimentally using ten genetically isolated strains of a ciliate, <it>Tetrahymena thermophila</it>.</p> <p>Results</p> <p>The propensity for social aggregation was greater in strains with reduced cell quality and lower growth performance. While we found a trade-off between costly aggregation and local dispersal in phenotypic analyses, aggregative strains showed a dispersal polymorphism by producing either highly sedentary or long-distance dispersive cells, in contrast to less aggregative strains whose cells were monomorphic local dispersers.</p> <p>Conclusion</p> <p>High dispersal among aggregative strains may not destroy group stability in <it>T. thermophila </it>because the dispersal polymorphism allows social strains to more readily escape kin groups than less aggregative strains, yet still benefit from stable group membership among sedentary morphs. Such dispersal polymorphisms should be common in other social organisms, serving to alter the nature of the negative impact of dispersal on social evolution.</p

Loss of flockmates weakens winter site fidelity in golden-crowned sparrows (\u3ci\u3eZonotrichia atricapilla\u3c/i\u3e)

Animal social interactions have an intrinsic spatial basis as many of these interactions occur in spatial proximity. This presents a dilemma when determining causality: Do individuals interact socially because they happen to share space, or do they share space because they are socially linked? We present a method that uses demographic turnover events as a natural experiment to investigate the links between social associations and space use in the context of interannual winter site fidelity in a migratory bird. We previously found that golden-crowned sparrows (Zonotrichia atricapilla) show consistent flocking relationships across years, and that familiarity between individuals influences the dynamics of social competition over resources. Using long-term data on winter social and spatial behavior across 10 y, we show that i) sparrows exhibit interannual fidelity to winter home ranges on the scale of tens of meters and ii) the precision of interannual site fidelity increases with the number of winters spent, but iii) this fidelity is weakened when sparrows lose close flockmates from the previous year. Furthermore, the effect of flockmate loss on site fidelity was higher for birds that had returned in more than 2 winters, suggesting that social fidelity may play an increasingly important role on spatial behavior across the lifetime of this migratory bird. Our study provides evidence that social relationships can influence site fidelity, and shows the potential of long-term studies for disentangling the relationship between social and spatial behavior

Dispersal propensity in Tetrahymena thermophila ciliates - a reaction norm perspective

Dispersal and phenotypic plasticity are two main ways for species to deal with rapid changes of their environments. Understanding how genotypes (G), environments (E), and their interaction (genotype and environment; G × E) each affects dispersal propensity is therefore instrumental for predicting the ecological and evolutionary responses of species under global change. Here we used an actively dispersing ciliate to quantify the contributions of G, E, and G × E on dispersal propensity, exposing 44 different genotypes to three different environmental contexts (densities in isogenotype populations). Moreover, we assessed the condition dependence of dispersal, that is, whether dispersal is related to morphological, physiological, or behavioral traits. We found that genotypes showed marked differences in dispersal propensity and that dispersal is plastically adjusted to density, with the overall trend for genotypes to exhibit negative density-dependent dispersal. A small, but significant G × E interaction indicates genetic variability in plasticity and therefore some potential for dispersal plasticity to evolve. We also show evidence consistent with condition-dependent dispersal suggesting that genotypes also vary in how individual condition is linked to dispersal under different environmental contexts thereby generating complex dispersal behavior due to only three variables (genes, environment, and individual condition).12 page(s

Experimental confirmation that avian plumage traits function as multiple status signals in winter contests

Status signals are thought to reduce costs of overt conflict over resources by advertising social status or an individual’s ability to win contests. While most studies have focused on single badges of status, recent empirical work has shown that multiple status signals may exist. To provide robust evidence for multiple badges of status, an experimental manipulation is required to decouple signals from one another and from other traits linked to fighting ability. Such experimental evidence is lacking for most studies of multiple status signals to date. We previously found that two plumage traits in golden-crowned sparrows, Zonotrichia atricapilla, were correlated with social dominance in encounters between unfamiliar individuals. To confirm that each plumage patch functions as an independent status signal, we experimentally augmented the sizes of the gold crown patch and the black crown patch during encounters between unfamiliar individuals with similar premanipulation crown sizes. In nearly all cases, the individual with the artificially augmented gold or black crown was dominant during the trial and manipulations of each color were equally successful in conferring dominance. The relative differences in crown sizes between manipulated and unmanipulated individuals in a dyad and mismatches in crown sizes of the manipulated bird led to escalation in gold trials, but these same factors were not significant for black trials. This study provides unequivocal evidence for multiple status signals: both black and gold crown patches influence social status per se and they do so independently of the other crown patch