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Cotter S.C.,University of Cambridge | Topham E.,University of Cambridge | Price A.J.P.,University of Cambridge | Kilner R.M.,Center for Advanced Study
Ecology Letters | Year: 2010

Social immune systems comprise immune defences mounted by individuals for the benefit of others (sensuCotter & Kilner 2010a). Just as with other forms of immunity, mounting a social immune response is expected to be costly but so far these fitness costs are unknown. We measured the costs of social immunity in a sub-social burying beetle, a species in which two or more adults defend a carrion breeding resource for their young by smearing the flesh with antibacterial anal exudates. Our experiments on widowed females reveal that a bacterial challenge to the breeding resource upregulates the antibacterial activity of a female's exudates, and this subsequently reduces her lifetime reproductive success. We suggest that the costliness of social immunity is a source of evolutionary conflict between breeding adults on a carcass, and that the phoretic communities that the beetles transport between carrion may assist the beetle by offsetting these costs. © 2010 Blackwell Publishing Ltd/CNRS.

Moller A.P.,University Paris - Sud | Moller A.P.,Center for Advanced Study
Behavioral Ecology | Year: 2010

Urbanization and domestication share features in terms of characters that are favored by selection. These include loss of fear of humans, reduced corticosterone levels, prolonged breeding seasons, and several others. Here, I test the hypothesis that urbanization results from differential colonization of urban areas by species with heterogeneous levels of fear in the ancestral rural populations, followed by a reduction in variance in fear responses with a subsequent increase in diversity of fear responses as urban populations become adapted to the urban environment. Using information on variance in flight initiation distances (FIDs) when approached by a human, I show that rural populations of birds characterized by short mean flight distances and large variances in flight distances differentially colonized urban areas. As a consequence of this urban invasion, urban populations lost variation in FID. The variance in FID was initially larger in rural than in urban populations but eventually became larger in urban populations with time since urbanization. This secondary increase in variance in FID of urban populations was associated with an increase in population density of urban populations, suggesting that as birds became adapted to urban areas, they secondarily gained variance in behavioral flexibility.

Moller A.P.,University Paris - Sud | Moller A.P.,Center for Advanced Study
Behavioral Ecology | Year: 2010

Many animals have successfully adapted to human proximity, with dramatic increases in abundance as a consequence. Although such transitions imply a fitness advantage, the fitness benefits of associations between animals and humans have not been thoroughly investigated. In a comparative study of nest predation, I compared predation rates in 6874 nests of 11 species of birds with sympatric populations breeding indoors and outdoors. Mean nest predation rates were 23.5% outdoors, but only 1.0% indoors, because corvid nest predators never entered buildings. There was a negative correlation between nest predation rate and the proportion of individuals breeding indoors, implying that as species became more adapted to humans, and hence breeding indoors became more frequent, there was a significant decrease in nesting failure that translated into a difference in reproductive success due to reductions in nest predation. Finally, the difference in predation rate between outdoor and indoor nests was related to time since urbanization and number of generations since urbanization, implying that initially there was a large selection differential followed by reduced fitness differences between birds breeding outdoors and indoors due to gradual adaptation to human proximity by reproducing birds. With a high intensity of natural selection, these findings suggest that such adaptation to human proximity may only take a few hundred generations, as shown by several species that have only recently become associated with humans. © 2010 The Author.

Moller A.P.,University Paris - Sud | Moller A.P.,Center for Advanced Study
Journal of Evolutionary Biology | Year: 2010

Animals fleeing a potential predator can escape horizontally or vertically, although vertical flight is more expensive than horizontal flight. The ability to escape in three dimensions by flying animals has been hypothesized to result in greater survival and eventually slower senescence than in animals only fleeing in two dimensions. In a comparative study of flight initiation distance in 69 species of birds when approached by a human, I found that the amount of variance explained by flight initiation distance was more than four times as large for the horizontal than the vertical component of perch height when taking flight. The slope of the relationship between horizontal distance and flight initiation distance (horizontal slope) increased with increasing body mass across species, whereas the slope of the relationship between vertical distance and flight initiation distance (vertical slope) decreased with increasing body mass. Therefore, there was a negative relationship between horizontal and vertical slope, although this negative relationship was significantly less steep than expected for a perfect trade-off. The horizontal slope decreased with increasing density of the habitat from grassland over shrub to forest, whereas that was not the case for the vertical slope. Adult survival rate increased and rate of senescence (longevity adjusted for survival rate, body mass and sampling effort) decreased with increasing vertical, but not with horizontal slope, consistent with the prediction that vertical escape indeed provides a means of reducing the impact of predation. © 2010 The Author. Journal Compilation © 2010 European Society For Evolutionary Biology.

Cotter S.C.,University of Cambridge | Cotter S.C.,Queens University of Belfast | Ward R.J.S.,University of Cambridge | Kilner R.M.,University of Cambridge | Kilner R.M.,Center for Advanced Study
Functional Ecology | Year: 2011

How much should an individual invest in reproduction as it grows older? Answering this question involves determining whether individuals measure their age as the time left for future reproduction or as the rate of deterioration in their state. Theory suggests that in the former case individuals should increase their allocation of resources to reproduction as opportunities for future breeding dwindle, and terminally invest when they breed for the last time. In the latter case they should reduce their investment in reproduction with age, either through adaptive reproductive restraint or as a passive by-product of senescence. Here we present the results of experiments on female burying beetles, Nicrophorus vespilloides, in which we independently manipulated the perceived risk of death (by activating the immune system) and the extent of deterioration in state (by changing age of first reproduction and/or prior investment in reproduction). We found that the risk of death and state each independently influenced the extent of reproductive investment. Specifically, we found a state-dependent decline in reproductive investment as females grew older that could be attributed to both adaptive reproductive restraint and senescence. A perceived increase in the risk of death, induced by activation of the immune system, caused females to switch from a strategy of reproductive restraint to terminal investment. Nevertheless, absolute reproductive investment was lower in older females, indicating constraints of senescence. Our results show that a decline in reproductive investment with age does not necessarily constitute evidence of reproductive senescence but can also result from adaptive reproductive restraint. Our results further suggest that the extent of reproductive investment is dependent on several different intrinsic cues and that the particular blend of cues available at any given age can yield very different patterns of investment. Perhaps this explains why age-related reproductive investment patterns seen in nature are so diverse. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.

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