[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: 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. · 6.23 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. · 6.23 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: 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. · 10.99 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. · 10.99 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.
[Show abstract][Hide abstract] ABSTRACT: Conspecific brood parasitism (CBP), whereby females lay eggs in the nests of other conspecifics, occurs in over 200 species of birds. As an alternative tactic to typical nesting, CBP expands and enriches the classic avian clutch size problem. It is an integral component of a flexible life-history strategy and, consequently, many intriguing aspects of this behavior—adaptive benefits to parasites, host-parasite interactions, population and evolutionary dynamics—can be understood best from a life-history perspective. Because parasite fitness depends on hosts, yet parasitism potentially reduces host fitness, CBP offers a novel opportunity to explore conflicts of interest within species. The intersection of life-history evolution, conflicts of interest, and frequency-dependent fitness provides much scope for theoretical exploration, and recent models indicate a complex range of evolutionary dynamics is possible, including consequences of CBP for population dynamics and conservation. CBP may also be a macroevol...
[Show abstract][Hide abstract] ABSTRACT: Theory on the evolution of ornamental male traits by sexual selection assumes consistency in selection over time. Temporal variation in female choice could dampen sexual selection, but scant information exists on the degree to which individual female preferences are flexible. Here we show that in lark buntings sexual selection on male traits varied dramatically across years and, in some cases, exhibited reversals in the direction of selection for a single trait. We show that these shifts are probably because of flexibility in mate choice by individual females and that they parallel shifts in the male traits that predict female reproductive success in a given year. Plasticity in choice and concomitant reversals in mating patterns across time may weaken the strength of sexual selection and could maintain genetic variation underlying multiple sexual ornaments.
[Show abstract][Hide abstract] ABSTRACT: Competition over resources can lead to fights and injury, so many species have evolved badge-of-status signals to settle conflicts without resorting to overt aggression. Most studies of status signals have focused on a single trait, under the assumption that aggression is univariate and therefore multiple signals would be redundant. We examined the relationship between male–male social dominance and several plumage traits (wing patch size and colour, body colour and coverage of black feathers on the body or the rump) in lark buntings, Calamospiza melanocorys, using a combination of observation and experimental territorial intrusions. Large body size was correlated with elevated aggression in several assays. Our observational data suggest that some traits function as close-range badges of status, because males with a larger proportion of black feathers on the body and rump win escalated contests, whereas other traits function at longer distances, because males with larger wing patches experience fewer territorial intrusions. Experimental tests of social dominance further suggest that different male plumage traits convey different information: some traits were associated with physical aggression, whereas other traits were associated with the intensity of approach. Together, these results show that selection can favour multiple badges of status to accommodate different levels of escalation or context-dependent dominance interactions.
[Show abstract][Hide abstract] ABSTRACT: Hosts of avian brood parasites use a variety of defenses based on egg recognition to reduce the costs of parasitism; the most
important of which is rejecting the parasitic eggs. Two basic recognition mechanisms are possible: “true recognition”, whereby
hosts recognize their own eggs irrespective of their relative frequency in the clutch, and minority recognition (or “recognition
by discordancy”), whereby hosts respond to the minority egg type. The mechanism of recognition has been experimentally studied
in a handful of species parasitized by interspecific brood parasites, but the mechanism used in defenses against conspecific
brood parasitism is unknown. I experimentally determined the mechanism of egg recognition in American coots (Fulica americana), a species with high levels of conspecific brood parasitism, egg recognition, and rejection. I swapped eggs between pairs
of nests to alter frequencies of host and “parasite” eggs and then used two criteria for recognition: egg rejection and nonrandom
incubation positions in the clutch. Eight of 12 nests (66%) given equal frequencies of host and parasite eggs showed evidence
of true recognition. In contrast, only one of eight (12.5%) nests where host eggs were in the minority showed evidence of
recognition by discordancy. The nonrandom incubation positions of parasitic eggs indicates that birds sometimes recognize
parasitic eggs without rejecting them and provides a means of assessing recognition on a per nest basis in species with large
clutches. Adaptive recognition without rejection may also be an important evolutionary stepping stone to the evolution of
egg rejection in some taxa.
Behavioral Ecology and Sociobiology 12/2006; 61(3):455-463. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Autotomy, the voluntary shedding of limbs or other body parts in the face of predation, is a highly effective escape mechanism that has evolved independently in a variety of taxa. Crabs are unusual in that the limb that is typically sacrificed during autotomy, the anterior clawed cheliped, can also be used to ward off attack. During an encounter with a predator, an individual must thus decide between two mutually exclusive strategies: flight or fight. We used experimental predation encounters with two species of porcelain crabs (genus Petrolisthes) to examine the factors that influence the decision to flee versus fight and to determine the degree to which this decision is context-dependent. We found that autotomy was highly conditional. The characteristics that best predicted autotomy--smaller body size or female gender--also correlated with a lower escape rate by the alternative escape tactic, struggling and pinching the predator. Variation among individuals in the benefit of autotomy (relative to alternative tactics) appears to drive variation in propensity to autotomize. Porcelain crabs thus demonstrate adaptive flexibility, employing the costly strategy of autotomizing a limb as a last resort, only when their chance at success by struggling is low. Copyright 2005.
[Show abstract][Hide abstract] ABSTRACT: Reciprocal selection pressures often lead to close and adaptive matching of traits in coevolved species. A failure of one species to match the evolutionary trajectories of another is often attributed to evolutionary lags or to differing selection pressures across a geographic mosaic. Here we show that mismatches in adaptation of interacting species--an obligate brood parasitic duck and each of its two main hosts--are best explained by the evolutionary dynamics within the host species. Rejection of the brood parasite's eggs was common by both hosts, despite a lack of detectable cost of parasitism to the hosts. Egg rejection markedly reduced parasite fitness, but egg mimicry experiments revealed no phenotypic natural selection for more mimetic parasitic eggs. These paradoxical results were resolved by the discovery of intraspecific brood parasitism and conspecific egg rejection within the hosts themselves. The apparent arms race between species seems instead to be an incidental by-product of within-species conflict, with little recourse for evolutionary response by the parasite.