[Show abstract][Hide abstract] ABSTRACT: Distinguishing between interspecific and intraspecific coevolution as the selective driver of traits can be difficult in some taxa. A previous study of an avian obligate brood parasite, the black-headed duck, Heteronetta atricapilla, suggested that egg rejection by its two main hosts (two species of coot) is an incidental by-product of selection from conspecific brood parasitism within the hosts, not selection imposed by the interspecific parasite. However, although both species of coot can recognize and reject eggs of conspecific brood parasites, which closely resemble their own, they paradoxically also accept a moderate fraction of duck eggs (40–60%), which differ strikingly in shape and colour from their own eggs. Here we test the key assumption of the incidental by-product hypothesis that natural selection for egg recognition solely from conspecific brood parasitism can result in intermediate levels of rejection of nonmimetic eggs. We repeated the same egg rejection experiments conducted previously with the two Argentine hosts in a third closely related species that experiences only conspecific brood parasitism, the American coot, Fulica americana. These experiments yielded the same intermediate rejection rates for nonmimetic duck eggs. Our results confirm that selection from conspecific brood parasitism can lead to counterintuitive intermediate rejection rates of nonmimetic interspecific eggs and further support the suggestion that selection from antagonism within species can incidentally affect interactions between species.
[Show abstract][Hide abstract] ABSTRACT: 1.Multiple signals should be favored when the benefit of additional signals outweigh their costs. Despite increased attention on multiple-signaling systems, few studies have focused on signal architecture to understand the potential information content of multiple signals.2.To understand the patterns of signal plasticity and consistency over the lifetime of individuals we conducted a longitudinal study of multiple signals known to be under sexual selection in male lark buntings, Calamospiza melanocorys.3.Within years, we found extensive among-individual variation in all four plumage ornaments we measured. Surprisingly, there were few correlations among these signals, suggesting that individuals contain a mosaic of signals. Signals were only moderately repeatable across years, which indicates some signal plasticity or age related change. In some years, the direction of change in particular signals relative to the previous year was consistent for most individuals in the population, suggesting that broad scale ecological factors affected the ornament phenotype. Different ornaments were affected by different ecological or social factors because the population-wide shift in a given signal was independent of change in other signals.4.Our combined results suggest that different signals—including different components of the same color patch in some cases—provide diverse and independent information about the individual to signal receivers in the context of sexual selection.This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Western slave-making ants (Polyergus mexicanus) are obligate social parasites that raid heterospecific ant nests for “slave” workers. Slave-makers parasitize several Formica species, but each slave-making colony uses a single host species. Slave-makers are known to be aggressive towards conspecifics to the point of exclusion within their raiding territories, but we report a high density of slave-making colonies that coexist within each other’s raiding territories, often with little aggression. Variation in intraspecific competition for hosts may explain the variation in aggression among colonies, so we expected pairs of colonies that parasitize different hosts to be more mutually tolerant than those that parasitize the same host. We tested this prediction by measuring the area of territory overlap between pairs of slave-maker nests that use the same slave species compared to those that used two different slave species. Additionally, to identify nests that appear to be avoiding each other, we generated simulated raids by using the length of observed raids but in random directions and compared the resulting simulated area of territory overlap to the observed area of overlap.
Contrary to expectations, slave-making ant raiding territories share more area when neighbors use the same slave species than when they use different slave species. However, when considered in the context of the randomly generated raiding territories, there were no obvious differences in patterns of territory overlap between pairs of nests that used the same slaves compared to those that used different slaves. Interestingly, within both of these two groups (pairs of nests that have the same slave species and pairs of nests that do not) some individual pairs of nests’ raiding territories do show significant signs of avoidance while other pairs of nests show significantly more overlap than predicted by the random raiding simulation. Slave-making ant colonies appear to be sensitive to the existence of conspecific nests in some cases but it remains to be understood why some nests seem to respond to each other’s presence while others do not. Future work will examine the role of kinship, relative colony size, and the timing of raiding in shaping slave-making ant raiding territories.
[Show abstract][Hide abstract] ABSTRACT: Migratory birds often form flocks on their wintering grounds, but important details of social structure such as the patterns of association between individuals are virtually unknown. We analysed networks of co-membership in short-term flocks for wintering golden-crowned sparrows (Zonotrichia atricapilla) across three years and discovered social complexity unsuspected for migratory songbirds. The population was consistently clustered into distinct social communities within a relatively small area (~ 7 ha). Birds returned to the same community across years, with mortality and recruitment leading to some degree of turnover in membership. These spatiotemporal patterns were explained by the combination of space use and social preference - birds that flocked together in one year flocked together again in the subsequent year more often than were expected based on degrees of home range overlap. Our results suggest that a surprising level of social fidelity across years leads to repeatable patterns of social network structure in migratory populations.
[Show abstract][Hide abstract] ABSTRACT: Conspecific brood parasitism (CBP) occurs in various insects, fishes and birds, but it is disproportionately common in waterfowl (Anatidae). Studies of CBP in Anatids therefore have helped to develop a fundamental conceptual framework with which to explain this intriguing behaviour. Yom-Tov (1980) first drew attention to CBP, and Andersson and Eriksson (1982) also hinted at the fascinating behavioural, ecological and evolutionary aspects of CBP in waterfowl. Several reviews followed these early papers, but much has been learned more recently about CBP in waterfowl. Here we aim to review the traditional conceptual framework of CBP in waterfowl and to consider empirical studies that have attempted to test related hypotheses. The survey provided support for the hypotheses that CBP allows some females to reproduce when not otherwise possible, whereas other females use parasitic egg-laying as a way to enhance their fecundity. A recently developed framework that considers CBP as part of a flexible life-history strategy could provide a useful direction for future studies of CBP. A second aim of this review is to consider the use of cues by conspecific brood parasites seeking suitable places to lay eggs parasitically. Recent studies have revealed remarkable cognitive abilities in parasitic females, but the actual mechanisms remain unknown. Clearly, breeding females are sensitive to cues such as nest site security, patterns of previous nest use or success, clutch size, and perhaps even the degree of kinship between hosts and other parasites. Indeed, additional investigations of CBP are needed to provide a better understanding of the processes and patterns of this avian reproductive strategy.
[Show abstract][Hide abstract] ABSTRACT: 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 colour 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.
[Show abstract][Hide abstract] ABSTRACT: Parental food allocation in birds has long been a focal point for life history and parent-offspring conflict theories. In asynchronously hatching species, parents are thought to either adjust brood size through death of marginal offspring (brood reduction), or feed the disadvantaged chicks to reduce the competitive hierarchy (parental compensation). Here, we show that parent American coots (Fulica americana) practice both strategies by switching from brood reduction to compensation across time. Late-hatching chicks suffer higher mortality only for the first few days after hatching. Later, parents begin to exhibit parental aggression towards older chicks and each parent favours a single chick, both of which are typically the youngest of the surviving offspring. The late-hatched survivors can equal or exceed their older siblings in size prior to independence. A mixed allocation strategy allows parents to compensate for the costs of competitive hierarchies while gaining the benefits of hatching asynchrony.
[Show abstract][Hide abstract] ABSTRACT: Social selection influences the evolution of weapons, ornaments and behaviour in both males and females. Thus, social interactions in both sexual and non-sexual contexts can have a powerful influence on the evolution of traits that would otherwise appear to be detrimental to survival. Although clearly outlined by West-Eberhard in the early 1980s, the idea that social selection is a comprehensive framework for the study of ornaments and weapons has largely been ignored. In West-Eberhard's view, sexual selection is a form of social selection-a concept supported by several lines of evidence. Darwin's distinction between natural and sexual selection has been useful, but recent confusion about the limits of sexual selection suggests that some traits are not easily categorized as naturally or sexually selected. Because social selection theory has much to offer the current debates about both sexual selection and reproductive competition in females, it is sometimes viewed, narrowly, to be most useful when considering female roles. However, social selection theory encompasses much more than female reproductive competition. Our goal here was to provide that broader perspective.
Philosophical Transactions of The Royal Society B Biological Sciences 08/2012; 367(1600):2266-73. DOI:10.1098/rstb.2012.0012 · 6.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ornaments, weapons and aggressive behaviours may evolve in female animals by mate choice and intrasexual competition for mating opportunities-the standard forms of sexual selection in males. However, a growing body of evidence suggests that selection tends to operate in different ways in males and females, with female traits more often mediating competition for ecological resources, rather than mate acquisition. Two main solutions have been proposed to accommodate this disparity. One is to expand the concept of sexual selection to include all mechanisms related to fecundity; another is to adopt an alternative conceptual framework-the theory of social selection-in which sexual selection is one component of a more general form of selection resulting from all social interactions. In this study, we summarize the history of the debate about female ornaments and weapons, and discuss potential resolutions. We review the components of fitness driving ornamentation in a wide range of systems, and show that selection often falls outside the limits of traditional sexual selection theory, particularly in females. We conclude that the evolution of these traits in both sexes is best understood within the unifying framework of social selection.
Philosophical Transactions of The Royal Society B Biological Sciences 08/2012; 367(1600):2274-93. DOI:10.1098/rstb.2011.0280 · 6.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Conspecific brood parasites lay their eggs in the nests of other females in the same population, leading to a fascinating array of possible ‘games’ among parasites and their hosts (Davies 2000; Lyon & Eadie 2008). Almost 30 years ago, Andersson & Eriksson (1982) first suggested that perhaps this form of parasitism was not what it seemed--indeed, perhaps it was not parasitism at all!Andersson & Eriksson (1982) observed that conspecific brood parasitism (CBP) was disproportionally common in waterfowl (Anatidae), a group of birds for which natal philopatry is female-biased rather than the more usual avian pattern of male-biased natal philopatry. Accordingly, Andersson (1984) reasoned (and demonstrated in an elegantly simple model) that relatedness among females might facilitate the evolution of CBP--prodding us to reconsider it as a kin-selected and possibly cooperative breeding system rather than a parasitic interaction. The idea was much cited but rarely tested empirically until recently--a number of new studies, empowered with a battery of molecular techniques, have now put Andersson’s hypothesis to the test (Table 1). The results are tantalizing, but also somewhat conflicting. Several studies, focusing on waterfowl, have found clear evidence that hosts and parasites are often related (Andersson & Åhlund 2000; Roy Nielsen et al. 2006; Andersson & Waldeck 2007; Waldeck et al. 2008; Jaatinen et al. 2009; Tiedemann et al. 2011). However, this is not always the case (Semel & Sherman 2001; Anderholm et al. 2009; and see Pöysa 2004). In a new study reported in this issue of Molecular Ecology, Jaatinen et al. (2011a) provide yet another twist to this story that might explain not only why such variable results have been obtained, but also suggests that the games between parasites and their hosts--and the role of kinship in these games--may be even more complex than Andersson (1984) imagined. Indeed, the role of kinship in CBP may be very much one of relative degree!
[Show abstract][Hide abstract] ABSTRACT: Individualized markers that allow organisms to be identified without recapture are invaluable for studies of survival, movement, and behavior. Nape tags consisting of brass safety pins with unique combinations of two or three colored plastic beads were used to mark 5,868 American Coot (Fulica americana) chicks and 331 Ruddy Duck (Oxyura jamaicensis), 157 King Eider (Somateria spectabilis) and 664 White-winged Scoter (Melanitta fusca deglandi) ducklings. These markers allowed for documentation of parent-offspring interactions, post-hatching survival, brood movements and brood-mixing behaviors. Nape tags were inexpensive, easy to make, easy to observe with binoculars or spotting scopes and provided over 100 two-bead or 1,000 three-bead color combinations for individual identification. For coots, there was no evidence of color biases affecting parental care or offspring survival, although some colors (white, yellow) were easier to detect than others (brown). The only observed problem was marker loss, with tag loss rates reaching 20% near fledging age. Nape tags worked effectively on coots and ducklings and may be useful for other precocial waterbirds.
[Show abstract][Hide abstract] ABSTRACT: Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.
[Show abstract][Hide abstract] ABSTRACT: The reliability of information that animals use to make decisions has fitness consequences. Accordingly, selection should favor the evolution of strategies that enhance the reliability of information used in learning and decision making. For example, hosts of avian brood parasites should be selected to increase the reliability of the information they use to learn to recognize their own eggs and chicks. The American coot (Fulica americana), a conspecific brood parasite, uses cues learned from the first-hatched chicks of each brood to recognize and reject parasitic chicks. However, if parasitic eggs are among the first to hatch, recognition cues are confounded and parents then fail to distinguish parasitic chicks from their own chicks. Therefore, hosts could ensure correct chick recognition by delaying parasitic eggs from hatching until after the first host eggs. Here we demonstrate that discriminatory incubation, whereby coots specifically delay the hatching of parasitic eggs, improves the reliability of parasitic chick recognition. In effect, coots gain fitness benefits by enhancing the reliability of information they later use for learning. Our study shows that a positive interaction between two host adaptations in coots--egg recognition and chick recognition--increases the overall effectiveness of host defense.
Current biology: CB 03/2011; 21(6):515-9. DOI:10.1016/j.cub.2011.02.023 · 9.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Status signals are thought to reduce the potential costs of social con!ict over resources by advertising social status to other group members and reducing unnecessary contests between individuals of differing abilities. Nearly all studies of status signals to date have focused on single signalling traits, and most studies that have investigated multiple traits did not examine whether different traits are used in different contexts, as is required for them to function as multiple signals. We examined the role of gold and black crown patches of wintering golden-crowned sparrows, Zonotrichia atricapilla, in determining social dominance during experimentally staged encounters between unfamiliar individuals. Speci"cally, we determined whether variation in weakly correlated or uncorrelated traits (crown patch size and colour, body size) differentially affected the outcome of interactions involving avoidance versus aggression. Overall, crown patch size and colour were better predictors of dominance than were body size or sex. Several traits, including both crown features and morphological traits, predicted which individual avoided the other in dyadic interactions that did not escalate beyond avoidance. However, when dyads had similar gold crown patch sizes, the interaction was more likely to escalate, leading to aggression. In contrast to avoidance interactions, the outcomes of aggressive contests were largely predicted by variation in the colour of black crown patches. Taken together, our results show that gold and black crown features operate as multiple status signals that accommodate an escalated gradient of interactions and suggest that social status involves more complexity than can be accommodated by a single signal.
[Show abstract][Hide abstract] ABSTRACT: High levels of conspecific brood parasitism are found in a communally breeding bird, with implications for the evolutionary links between brood parasitism and communal breeding. It also uncovers a novel egg recognition mechanism hosts use to foil brood parasites.
Current biology: CB 11/2010; 20(21):R931-3. DOI:10.1016/j.cub.2010.09.056 · 9.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Avian brood parasites and their hosts provide model systems for investigating links between recognition, learning, and their fitness consequences. One major evolutionary puzzle has continued to capture the attention of naturalists for centuries: why do hosts of brood parasites generally fail to recognize parasitic offspring after they have hatched from the egg, even when the host and parasitic chicks differ to almost comic degrees? One prominent theory to explain this pattern proposes that the costs of mistakenly learning to recognize the wrong offspring make recognition maladaptive. Here we show that American coots, Fulica americana, can recognize and reject parasitic chicks in their brood by using learned cues, despite the fact that the hosts and the brood parasites are of the same species. A series of chick cross-fostering experiments confirm that coots use first-hatched chicks in a brood as referents to learn to recognize their own chicks and then discriminate against later-hatched parasitic chicks in the same brood. When experimentally provided with the wrong reference chicks, coots can be induced to discriminate against their own offspring, confirming that the learning errors proposed by theory can exist. However, learning based on hatching order is reliable in naturally parasitized coot nests because host eggs hatch predictably ahead of parasite eggs. Conversely, a lack of reliable information may help to explain why the evolution of chick recognition is not more common in hosts of most interspecific brood parasites.
[Show abstract][Hide abstract] ABSTRACT: Molecular techniques for identifying sex of birds utilize length differences between CHD-Z and CHD-W introns, but in some cases these methods can lead to sexing errors. Here we show that an additional W-specific primer can be used in conjunction with a pre-existing sexing primer pair to dramatically improve the reliability of molecular sexing methods. We illustrate the approach with American coots (Fulica americana), a species with CHD-Z polymorphism that could not be accurately sexed using traditional methods. We developed a reverse primer GWR2 designed to sit within the intron of the W chromosome and amplify a distinctively small DNA fragment that serves as a W-specific marker. Analysis of known-sex individuals indicates that this W-specific primer provides an efficient and reliable protocol to identify the sex of F. americana. The development of such sex-specific primers will likely increase the reliability of molecular sexing methods in other birds as well. Comparisons between CHD-Z alleles of coots and common moorhens (Gallinula chloropus) revealed that CHD-Z polymorphism evolved separately in these two closely related species. We discuss the implications of repeated evolution of CHD-Z polymorphisms among birds.