Components of fitness in the cooperatively breeding Seychelles warbler Acrocephalus sechellensis

Cooperative breeding is a social system in which group members care for offspring that are not their own. Individuals are selected to maximise their fitness, so why do some individuals help others to breed, rather than focusing on their own reproduction? Kin selection theory formulated how altruistic behaviour may evolve by natural selection; however, measuring fitness (the relative contribution of a genotype to the next generation) in natural systems remains problematic.

Quantifying fitness requires powerful genetic markers (to accurately assign parentage), and a closed wild population that is fully monitored (to accurately record survival, fecundity and life-history decisions over a lifetime). The Seychelles warbler, a facultative cooperative breeder endemic to the Seychelles, is an ideal species in which to investigate the fitness consequences of life-history decisions. This is because birds rarely move between islands and long-term observations are available providing life-time data on individuals.

From 1994 onwards, nearly all of the warblers on Cousin Island have been individually colour-ringed, blood-sampled and their status (helper, non-helper, dominant) identified in each breeding season until death. Using 30 microsatellite loci and a Bayesian programme, a genetic pedigree has been built which enables researchers to follow the decisions of individuals over their lifetimes and to relate these to the realised fitness benefits.

Realised fitness benefits are not only gained by dominants: subordinate females may gain direct fitness benefits through co-breeding, and males may gain paternity by breeding outside of their territory. Furthermore, birds may help rear offspring within a territory that are not their own, although not all birds do this. These characteristics allow the acts of delaying dispersal, delaying breeding and the decision to help to be statistically uncoupled.

The reasons underlying the variation in fitness obtained from different life-history strategies can then be stripped down to their environmental and genetic components. This enables investigation of whether cooperative breeding traits are heritable, which has been studied rarely, yet is vital to understanding how the traits evolved.

Personnel

Principal Investigator

Professor Terry Burke

email : t.a.burke@sheffield.ac.uk

Collaborators

Other Seychelles warbler projects

The genetic pedigree that is being built by this project both gains from and contributes to the other ongoing projects within the overall Seychelles warbler study program:

Janske van de Crommenacker
Stress and fitness in small bottlenecked populations of the tropical Seychelles warbler

  • PhD thesis (2006–2010) University of Groningen
  • Supervised by Prof. Jan Komdeur & Dr. David S Richardson
  • Supported by Nature Seychelles and NWO

Kim Hutchings
Parasites, MHC genes and fitness in the Seychelles warbler

  • PhD thesis (2005–2009) UEA / University of Groningen
  • Supervised by Prof. Jan Komdeur & Dr. David S Richardson

Martijn Hammers
Individual model based analysis of the causes of senescence in a wild living cooperative breeding vertebrate species

  • PhD thesis (2008–2012) University of Groningen
  • Supervised by Prof. Jan Komdeur & Dr. David S Richardson
  • Supported by Nature Seychelles and NWO

Jildou van de Woude
Physiological consequences of different life-history strategies in the Seychelles Warbler

  • PhD thesis (2008–2012) University of Groningen
  • Supervised by Prof. Jan Komdeur & Dr. David S Richardson
  • Supported by Nature Seychelles and NWO

Dr Emma Barrett
Telomeres as biomarkers of costs and quality in a wild population

  • NERC Postdoctoral research associate (2009–2012)

Selected publications

Brouwer, L., J. M. Tinbergen, C. Both, R. Bristol, D. S. Richardson, and J. Komdeur. 2009. Experimental evidence for density-dependent reproduction in a cooperatively breeding passerine. Ecology 90:729–741.

Eikenaar, C., J. Komdeur, and D. S. Richardson. 2008. Natal dispersal patterns are not associated with inbreeding avoidance in the Seychelles warbler. Journal of Evolutionary Biology 21:1106–1116.

Hadfield, J. D., D. S. Richardson, and T. Burke. 2006. Towards unbiased parentage assignment: combining genetic, behavioural and spatial data in a Bayesian framework. Molecular Ecology 15:3715–3730.

Komdeur, J., and D. S. Richardson. 2007. Molecular ecology reveals the hidden complexities of the Seychelles warbler. Advances in the Study of Behavior 37:147–187.

Richardson, D. S., J. Komdeur, and T. Burke. 2003. Avian behaviour: altruism and infidelity among warblers. Nature 422:580.

van de Crommenacker, J., D. S. Richardson, T. G. G. Groothuis, C. M. Eising, A. L. Dekker, and J. Komdeur. 2004. Testosterone, cuckoldry risk and extra-pair opportunities in the Seychelles warbler. Proceedings of the Royal Society B: Biological Sciences 271:1023–1031.