Inbreeding Depression in Incubation Behaviour
Published: 12 November 2014
It is well-known that inbreeding causes physical defects, but what about more subtle effects. We looked at the parenting ability of inbred zebra finches. Offspring of inbred parents may survive less well because of reduced parental care
Inbreeding can have incredibly detrimental impacts. For example in 1700 the first European Superpower, the Hapsburg dynasty of Spain came to a crashing end after over 200 years in power and ruling during the Golden Age in the history of Spain. That year, the last Hapsburg ruler, Charles II died aged 39. For 16 generations Hapsburgs married blood relatives to hold on to their wealth and power. Maybe not surprising Charles II had extensive physical, intellectual and emotional disabilities and was an ineffectual leader. He died childless and heirless and thus inbreeding killed off a mighty dynasty.
Yet Charles might have been lucky to be born at all given the long history of inbreeding in his family. Inbred individuals often produce fewer young because offspring die early as an embryo. That might be understandable when the parents are related and thus the offspring itself is inbred. But what if one of the parents is inbred and mates with an unrelated partner? The offspring is less inbred but still has a poorer survival than offspring from families with no inbreeding. Why is this? One hypothesis could be that inbred individuals are poorer parents. This is what we wanted to address with our study.
The first step was to produce inbred birds by pairing brother and sisters. These brother-sister pairs produced offspring as readily as pairs of unrelated birds. Inbred females produced from these brother-sister pairs were then paired up with unrelated males. We wanted to look at the care inbred females provided to her eggs, i.e. her incubation behaviour. The time inbred and control females spent incubating was observed using small nest cameras and we predicted that inbred females would spend less time incubating than control females. Indeed that was exactly what we found; inbred females spending 17% less time incubating than control females.
We then also wanted to test whether the reduction in parental care had consequences on embryo survival, i.e. hatching success of eggs. As inbreeding may not only affect the ability to incubate but also the ability to produce eggs, we cross-fostered control eggs into the nests of inbred females. The hatching success of control eggs incubated by inbred females was 8% lower than of non-inbred females although not statistically significant. Yet 8% difference in survival is a considerable effect and together with the additional potential effects of inbreeding on the ability to form high-quality eggs and raise the offspring, which in natural condition all act together, detrimental effects of inbreeding on parental care can lead to poorer breeding success and ultimately to a decline of a population. And the extinction of their dynasty is what the Spanish Hapsburg experienced. Maybe somewhat better fared the Egyptian Ptolemaic dynasty whose last active pharaoh of Ancient Egypt was Cleopatra. Although she was married to her brother, as was tradition in this dynasty, she was probably not the only Ptolemy to sensibly find fathers for their children outside their incestuous marriage; her children were from Julius Caesar and Mark Antony.
Pooley, E.L., Kennedy, M. & Nager, R.G. 2014. Maternal inbreeding reduces parental care in the zebra finch, Taeniopygia guttata. Animal Behaviour 97,153-163.
First published: 12 November 2014