For most dog breeders, behavior represents a major challenge. It is indeed one of the main fields of interest in terms of breeding. In a survey we made with French breeders a few years ago (Leroy et al. 2007), behavior was ranked as a breeding goal after morphology, but before health and work. Yet, although the influence of genes on behavioral traits, which are illustrated by the large behavioral differences between breeds, cannot be denied, those traits are also largely impacted by education and environment, which makes selection of those traits difficult.
A recent study (Hradecká et al. 2015) tried to make a reappraisal on the heritability of behavioral traits in dogs, i.e. of the proportion of behavior variation that can be attributed to genes. For this 1763 heritability estimations from 48 studies were gathered in a meta-analysis study, traits being classified into five categories: Environment interaction, herding, hunting, play and psychical characteristics. As showed in the following table, whatever the categories, heritabilities were found to be low, ranging between 9 and 15%. In other words, according to this study, depending on trait categories, around 9-15% of within breed observed variability could be explained by gene differences.
Heritability of traits for different categories according to Hradecká et al. (2015) meta-analysis
This low heritability has several consequences relative to breeding and welfare issues.
First, it underlines the importance of education. It is of course not a surprise, but when coming to behavior, breeders should rely more on their capacity at providing an environment optimal for the behavioral development of the puppies than to genetics.
Secondly, improving the behavior of a breed through selection is not going to be an easy task. Two shortcuts may, however, be considered. First, if the improvement of behavior of the breed is an absolute necessity, maybe the genes of interest can be found outside the breed. Heritabilities are, indeed, in general estimated within breeds, so they do not take into account differences across breeds. It may also be wondered if genomics could be of some help. Given the complexity of behavioral traits, it is expected that even the small proportion of variability which is genetic involves a large number of genes, possibly with small and indirect effects. Yet in the last years, several studies have been able to identify gene variants impacting behavior. Some examples:
- In Belgian Shepherd breed, Lit et al. (2013) identified a mutation in dopamine transporter gene, single copy carriers showing seizures, loss of responsiveness to environmental stimuli, episodic aggression, and hyper-vigilance.
- When considering disorders related to behavior, several genes have been identified to underlie some inherited forms of epilepsy (see Ekestedt et al. 2013).
- A recent comparative analysis between pointing and non-pointing dog breeds allowed researchers to identify two gene candidates that could contribute to pointing behavior in hunting dogs (Akkad et al. 2015).
- In German Shepherd Dogs, a Chinese study (Yang et al. 2015) has linked the genotypes for some olfactory receptors to the olfactory ability of those dogs.
Although interesting, it may be argued that some of these findings (e.g., for instance, the last one) do not directly relate to behavior. But actually, the behavior is connected to a wide range of morphological and physiological mechanisms, and it may be expected, for instance, that olfactory capacity impacts the environment interaction and hunting capacities of dogs. It is, however, important to underline that results should always be replicated and confirmed, especially if there are conflicting findings. Also, results may only be of interest or applicable to some breeds or populations. Nevertheless, it may be expected that in the next years, some gene test(s), more or less relevant, will be developed for selection on behavior. As for all other developments in diagnostic molecular genetics, the test(s), their validity, potential impact and application within breeding strategies will need to be carefully considered.
Akkad, D. A., Gerding, W. M., Gasser, R. B., & Epplen, J. T. (2015). Homozygosity mapping and sequencing identify two genes that might contribute to pointing behavior in hunting dogs. Canine Genetics and Epidemiology, 2(1), 1-13.
Ekenstedt, K. J., & Oberbauer, A. M. (2013). Inherited epilepsy in dogs. Topics in companion animal medicine, 28(2), 51-58.
Hradecká, L., Bartoš, L., Svobodová, I., & Sales, J. (2015). Heritability of behavioural traits in domestic dogs: A meta-analysis. Applied Animal Behaviour Science, 170, 1-13.
Leroy, G., Verrier, E., Wisner-Bourgeois, C., & Rognon, X. (2007). Breeding goals and breeding practices of French dog breeders: results from a large survey. Revue de Médecine Vétérinaire, 158(10), 496.
Lit, L., Belanger, J. M., Boehm, D., Lybarger, N., Haverbeke, A., Diederich, C., & Oberbauer, A. M. (2013). Characterization of a dopamine transporter polymorphism and behavior in Belgian Malinois. BMC genetics, 14(1), 45.