Why fight? Socially dominant jackdaws, Corvus monedula, have low fitness

Zoological Laboratory of the University of Groningen, Netherlands
Animal Behaviour (Impact Factor: 3.14). 10/2004; DOI: 10.1016/j.anbehav.2003.12.020
Source: OAI


Social dominance is intuitively assumed to be associated with higher fitness, because social dominance implies better access to resources. We found that, in a colony of jackdaws, the dominant males consistently produced fewer fledglings, which had lower chances of survival to 1 year of age. Laying date and clutch size were independent of dominance, but females that mated with dominant males were in poorer condition and laid smaller eggs. Parental survival was independent of social dominance, and the frequency of extrapair fertilizations in jackdaws is negligible. Dominance was a stable trait of individuals, and not a state that all individuals eventually attained. We conclude that, in this colony, dominant jackdaws had lower fitness. To our knowledge, this is the first example of such a pattern in a free-living species. We hypothesize that the high density of our colony resulted in high testosterone titres, which suppressed paternal care of mate and offspring to the extent that it outweighed the benefits of higher resource access.

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Available from: Simon Verhulst
    • "A prominent factor of intragroup cohesion in jackdaw colonies is the establishment of a dominance hierarchy. Socially dominant birds receive priority access to resources such as nesting sites and food (R ö ell 1978), and dominance also seems to play a role in jackdaws ' breeding success (Henderson and Hart 1995, Verhulst and Salomons 2004). In corvids, dominance rank is dependent on pair status: pair bonded individuals are in general more dominant than unpaired birds (R ö ell 1978, Haff er 1993, Braun and Bugnyar 2012; in females only: Wechsler 1988). "
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    ABSTRACT: Most birds rely on cooperation between pair partners for breeding. In long-term monogamous species, pair bonds are considered the basic units of social organization, albeit these birds often form foraging, roosting or breeding groups in which they repeatedly interact with numerous conspecifics. Focusing on jackdaws Corvus monedula, we here investigated 1) the interplay between pair bond and group dynamics in several social contexts and 2) how pair partners differ in individual effort of pair bond maintenance. Based on long-term data on free-flying birds, we quantified social interactions between group members within three positive contexts (spatial proximity, feeding and sociopositive interactions) for different periods of the year (non-breeding, pre-breeding, parental care). On the group level, we found that the number of interaction partners was highest in the spatial proximity context while in the feeding and sociopositive contexts the number of interaction partners was low and moderately low, respectively. Interactions were reciprocated within almost all contexts and periods. Investigating subgrouping within the flock, results showed that interactions were preferentially directed towards the respective pair partner compared to unmated adults. When determining pair partner effort, both sexes similarly invested most into mutual proximity during late winter, thereby refreshing their bond before the onset of breeding. Paired males fed their mates over the entire year at similar rates while paired females hardly fed their mates at all but engaged in sociopositive behaviors instead. We conclude that jackdaws actively seek out positive social ties to flock members (close proximity, sociopositive behavior), at certain times of the year. Thus, the group functions as a dynamic social unit, nested within are highly cooperative pair bonds. Both sexes invested into the bond with different social behaviors and different levels of effort, yet these are likely male and female proximate mechanisms aimed at maintaining and perpetuating the pair bond.
    No preview · Article · Nov 2014 · Journal of Avian Biology
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    • "But fast explorers might have to trade this off against the costs of heightened testosterone sensitivity, as is manifest during trade-offs with, for example, paternal effort (Ketterson et al. 1992, 1996). Individuals with high testosterone sensitivity could be worse fathers, since they are expected to desert at higher frequency and provide reduced rates of nestling feeding (Lynn et al. 2005) which consequently could decrease fitness (Verhulst & Salomons 2004; Duckworth 2006). "
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    ABSTRACT: Keywords: aggression behavioural syndrome great tit Parus major phytohaemagglutinin testosterone Individuals within species differ in their behavioural reactions to the environment. Consistent individual differences in these behaviours (personality traits) are often correlated and known to be under natural selection. These differences are frequently associated with variation in physiological traits, such as endocrine profiles. For example, variation in circulating testosterone levels is associated with variation in several personality traits and has been hypothesized to be a marker for personality in humans and rodents. The importance of testosterone in controlling both behavioural strategies and individual physiological differences suggests that direct selection on personality traits might cause pleiotropic selection on the physiological mechanisms underlying these traits. To test this hypothesis, we quantified levels of plasma testosterone levels and measured phytohaemagglutinin (PHA)-induced immune responses of male great tits, Parus major, in lines artificially selected for diverging levels of avian personality ('fast' and 'slow' exploratory behaviour). We found that testosterone levels were highly repeatable within individuals and fluctuated predictably over the season. Contrary to our expectations, 'slow' explorers had consistently higher levels of baseline testosterone and higher immune responses than 'fast' explorers. These results show that phenotypic selection for variation in personality traits corresponds to consistent differences in hormone profile and immune function, but that higher aggression levels do not need to be associated with higher baseline testosterone levels. Our results confirm that personality traits have evolved as a result of selection on both the underlying controlling physiological mechanisms and the phenotypic traits.
    Full-text · Article · Apr 2011 · Animal Behaviour
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    • "In organisms that might loosely be classified as displaying higher levels of 'sociality' (Costa & Fitzgerald, 2005), it is also common for dominant individuals to monopolize reproduction and receive benefits from subordinate helpers (Clutton- Brock et al., 2001). Thus, social dominance is generally viewed as being under positive selection, although empirical studies have highlighted that exceptions can and do occur (Ellis, 1995; Qvarnströ m & Forsgren, 1998; Verhulst & Salomons, 2004). A critical requirement for adaptive evolution is that trait variation within populations is, at least in part, caused by heritable differences among individuals. "
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    ABSTRACT: By determining access to limited resources, social dominance is often an important determinant of fitness. Thus, if heritable, standard theory predicts mean dominance should evolve. However, dominance is usually inferred from the tendency to win contests, and given one winner and one loser in any dyadic contest, the mean proportion won will always equal 0.5. Here, we argue that the apparent conflict between quantitative genetic theory and common sense is resolved by recognition of indirect genetic effects (IGEs). We estimate selection on, and genetic (co)variance structures for, social dominance, in a wild population of red deer Cervus elaphus, on the Scottish island of Rum. While dominance is heritable and positively correlated with lifetime fitness, contest outcomes depend as much on the genes carried by an opponent as on the genotype of a focal individual. We show how this dependency imposes an absolute evolutionary constraint on the phenotypic mean, thus reconciling theoretical predictions with common sense. More generally, we argue that IGEs likely provide a widespread but poorly recognized source of evolutionary constraint for traits influenced by competition.
    Full-text · Article · Feb 2011 · Journal of Evolutionary Biology
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