Hybridization increases measures of innate and cell-mediated immunity in an endangered bird species

Journal of Animal Ecology (2006) 75, 559–564
doi: 10.1111/j.1365-2656.2006.01076.x

ABSTRACT

• 1. 

  Given the increasing threat of 'emerging infectious diseases' (EIDs), and the vulnerability of small inbred populations to such novel challenges (at least partly through compromised immunity), a degree of interspecific hybridization may improve the viability of endangered species by enriching depauperate gene pools.
• 2. 

  To investigate this hypothesis, we quantified indicators of the strength of both innate and cell-mediated immunity in wild populations of hybridizing parakeets on the Chatham Islands, New Zealand.
• 3. 

  We show that both measures of immune function are markedly higher in the cosmopolitan red-crowned parakeet Cyanoramphus novaezelandiae than in the island endemic Forbes' parakeet C. forbesi, as is to be expected when comparing relatively outbred vs. relatively inbred species.
• 4. 

  In addition, we show that both measures of immune function are higher in Forbes'× red-crowned parakeet hybrids than in the Forbes' parakeet. Even those individuals with few red-crowned characteristics, suggesting they are the products of matings between hybrids and Forbes' parakeets, have significantly higher measures of immune function.
• 5. 

  As at least one of the immune indicators measured correlates directly with both survivorship and the viability of small bird populations, this study reveals a potential management option for hybridizing species of conservation concern, where an increase in resilience to novel disease challenges could outweigh some loss of genetic integrity.