Heritability and Genetic Correlations of Fear-Related Behaviour in Red Junglefowl–Possible Implications for Early Domestication

Abstract

Domesticated species differ from their wild ancestors in a number of traits, generally referred to as the domesticated phenotype. Reduced fear of humans is assumed to have been an early prerequisite for the successful domestication of virtually all species. We hypothesized that fear of humans is linked to other domestication related traits. For three generations, we selected Red Junglefowl (ancestors of domestic chickens) solely on the reaction in a standardized Fear of Human-test. In this, the birds were exposed for a gradually approaching human, and their behaviour was continuously scored. This generated three groups of animals, high (H), low (L) and intermediate (I) fearful birds. The birds in each generation were additionally tested in a battery of behaviour tests, measuring aspects of fearfulness, exploration, and sociality. The results demonstrate that the variation in fear response of Red Junglefowl towards humans has a significant genetic component and is genetically correlated to behavioural responses in other contexts, of which some are associated with fearfulness and others with exploration. Hence, selection of Red Junglefowl on low fear for humans can be expected to lead to a correlated change of other behavioural traits over generations. It is therefore likely that domestication may have caused an initial suite of behavioural modifications, even without selection on anything besides tameness.

Is evolution of domestication driven by tameness? A selective review with focus on chickens

“…Furthermore, there were several significant genetic correlations (rs) between the fear score and other behavioural traits recorded, with absolute values mostly ranging between 0.1< rs <0.6 (Agnvall et al, 2012). For example, activity and reactions in a social reinstatement test had significant genetic correlations with fear score.…”

“…There was a significant effect of selection group on the fear-ofhuman trait, and the heritability (h 2 ) was estimated to 0.17 (Agnvall et al, 2012).…”

“…These were reciprocally cross-bred for two generations, thereby producing the initial parental generation (P0), consisting of about 100 birds, on which our selection program started (Agnvall et al, 2012).…”

“…The behaviour was recorded throughout the test and used to form a fear score for each individual. Detailed information can be found in Agnvall et al (2012).…”

“…In subsequent generations, we selected the most fearful H-birds and the least fearful Lbirds as parents, and continued to randomly breed U-birds. More details can be found in Agnvall et al (2012).…”