Evolution of cooperative breeding
Brouwer, LB, Richardson, DS and Komdeur, J (2012) Helpers at the nest improve late-life offspring performance: evidence from a long-term study and a cross-foster experiment. PLoS ONE, 6
Conditions during an individual’s rearing period can have far reaching consequences for its survival and reproduction later in life. Conditions typically vary due to variation in parental quality and/or the environment, but in cooperative breeders the presence of helpers adds an important component to this.
Determining the causal effect of helpers on offspring fitness is difficult, since high-quality breeders or territories are likely to produce high-quality offspring, but are also more likely to have helpers because of past reproductive success. This problem is best resolved by comparing the effect of both helping and non-helping subordinates on offspring fitness, however species in which both type of subordinates commonly occur are rare.
We used multi-state capture-recapture models on 20 years of data to investigate the effect of rearing conditions on survival and recruitment in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis), with both helping and non-helping subordinates. The number of helpers in the rearing territory, but not territory quality, group- or brood size, was positively associated with survival of offspring in their first year, and later in life. This was not a result of group size itself since the number of non-helpers was not associated with offspring survival. Furthermore, a nestling cross-foster experiment showed that the number of helpers on the pre-foster territory was not associated with offspring survival, indicating that offspring from territories with helpers do not differ in (genetic) quality.
Our results suggest that the presence of helpers not only increase survival of offspring in their first year of life, but also subsequent adult survival, and therefore have important fitness consequences later in life. This means that when calculating the fitness benefits of helping not only short-term but also the late-life benefits have to be taken into account to fully understand the evolution of cooperative breeding.
Barrett, ELB, Burke, T, Hammers, M, Komdeur, J and Richardson, DS (2013) Telomere length and dynamics predict mortality in a wild longitudinal study. Molecular Ecology. 22 (1) pp. 249-259
Explaining variation in life expectancy between individuals of the same age is fundamental to our understanding of population ecology and life history evolution. Variation in the length and rate of loss of the protective telomere chromosome caps has been linked to cellular lifespan. Yet, the extent to which telomere length and dynamics predict organismal lifespan in nature is still contentious.
Using longitudinal samples taken from a closed population of Acrocephalus sechellensis (Seychelles warblers) studied for over 20 years, we describe the first study into life-long adult telomere dynamics (1–17 years) and their relationship to mortality under natural conditions (n = 204 individuals). We show that telomeres shorten with increasing age and body mass, and that shorter telomeres and greater rates of telomere shortening predicted future mortality.
Our results provide the first clear and unambiguous evidence of a relationship between telomere length and mortality in the wild, and substantiate the prediction that telomere length and shortening rate can act as an indicator of biological age further to chronological age when exploring life history questions in natural conditions.
Personality and fitness
Edwards, HA, Winney, IS, Schroeder, J and Dugdale, HL (2013) Do rapid assays predict repeatability in labile (behavioural) traits? A reply to Biro. Animal Behaviour. 85 (3). pp. e1–e3
We discuss a recent letter by Biro on measuring personalities.
Behavioural traits may be conflated in an increasingly familiar environment.
Greater intervals between samples may minimize habituation to novelty.
Testing in novel environments reflects a comparable behavioural response in the wild.
Trade-off between number of individuals to the number of measurements per individual
Consequences of diversity at immune loci
Brouwer, L, Barr, I, Van De Pol, M, Burke, T, Komdeur, J and Richardson, DS (2010) MHC-dependent survival in a wild population: evidence for hidden genetic benefits gained through extra-pair fertilizations. Molecular Ecology, 19 (16). pp. 3444-3455
Females should prefer to be fertilized by males that increase the genetic quality of their offspring. In vertebrates, genes of the major histocompatibility complex (MHC) play a key role in the acquired immune response and have been shown to affect mating preferences.
They are therefore important candidates for the link between mate choice and indirect genetic benefits. Higher MHC diversity may be advantageous because this allows a wider range of pathogens to be detected and combated. Furthermore, individuals harbouring rare MHC alleles might better resist pathogen variants that have evolved to evade common MHC alleles.
In the Seychelles warbler, females paired with low MHC-diversity males elevate the MHC diversity of their offspring to levels comparable to the population mean by gaining extra-pair fertilizations. Here, we investigate whether increased MHC diversity results in higher life expectancy and whether there are any additional benefits of extra-pair fertilizations.
Our 10-year study found a positive association between MHC diversity and juvenile survival, but no additional survival advantage of extra-pair fertilizations. In addition, offspring with a specific allele (Ase-ua4) had a fivefold longer life expectancy than offspring without this allele. Consequently, the interacting effects of sexual selection and pathogen-mediated viability selection appear to be important for maintaining MHC variation in the Seychelles warbler.
Our study supports the prediction that MHC-dependent extra-pair fertilisations result in genetic benefits for offspring in natural populations. However, such genetic benefits might be hidden and not necessarily apparent in the widely used fitness comparison of extra- and within-pair offspring.
Genomics of translocated populations
Translocation – the movement of individuals to new areas – can reduce extinction risk of endangered species. However, a factor that will affect the success of translocations is the amount of genetic diversity that is ‘lost in translocation’. If translocated populations lose diversity at the ‘ecologically important’ genes, which form the targets for natural selection, they will be unable to adapt to changing environments. Lewis Spurgin will use novel genetic techniques to analyse, for the first time, the effects of translocations on diversity across the entire genome
Richardson, D.S., Bristol, R. and Shah, N.J. (2006) Translocation of Seychelles warbler Acrocephalus sechellensis to establish a new population on Denis Island, Seychelles. ConservationEvidence.com, 3. pp. 54-57
In May–June 2004, 58 adult Seychelles warblers Acrocephalus sechellensis were translocated to Denis Island. The first pairs started nest-building within three days of release. By August 2005, their numbers had increased to 75. Of the 35 breeding territory vacancies created by the translocation on the source island of Cousin, all but three were occupied within an average of 5.4 days, by sub-ordinate birds.