Evidence of inbreeding depression but not inbreeding avoidance in a natural house sparrow population

Authors

  • ANNA M. BILLING,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • ALINE M. LEE,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • SIGRUN SKJELSETH,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
    • Present address: The Norwegian Biodiversity Information Centre, Erling Skakkes gt. 47, NO-7491 Trondheim, Norway.

  • ÅSA A. BORG,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • MATTHEW C. HALE,

    1. Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
    Search for more papers by this author
    • Present address: Purdue University, Forestry and Natural Resources, 715 West State Street, West Lafayette, IN 47907-2061, USA.

  • JON SLATE,

    1. Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
    Search for more papers by this author
  • HENRIK PÄRN,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • THOR H. RINGSBY,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • BERNT-ERIK SÆTHER,

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author
  • HENRIK JENSEN

    1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
    Search for more papers by this author

Anna M. Billing, Fax: +47 73596100; E-mail: anna.billing@bio.ntnu.no

Abstract

Inbreeding is common in small and threatened populations and often has a negative effect on individual fitness and genetic diversity. Thus, inbreeding can be an important factor affecting the persistence of small populations. In this study, we investigated the effects of inbreeding on fitness in a small, wild population of house sparrows (Passer domesticus) on the island of Aldra, Norway. The population was founded in 1998 by four individuals (one female and three males). After the founder event, the adult population rapidly increased to about 30 individuals in 2001. At the same time, the mean inbreeding coefficient among adults increased from 0 to 0.04 by 2001 and thereafter fluctuated between 0.06 and 0.10, indicating a highly inbred population. We found a negative effect of inbreeding on lifetime reproductive success, which seemed to be mainly due to an effect of inbreeding on annual reproductive success. This resulted in selection against inbred females. However, the negative effect of inbreeding was less strong in males, suggesting that selection against inbred individuals is at least partly sex specific. To examine whether individuals avoided breeding with close relatives, we compared observed inbreeding and kinship coefficients in the population with those obtained from simulations of random mating. We found no significant differences between the two, indicating weak or absent inbreeding avoidance. We conclude that there was inbreeding depression in our population. Despite this, birds did not seem to actively avoid mating with close relatives, perhaps as a consequence of constraints on mating possibilities in such a small population.

Ancillary