The German Shepherd is alert, docile, brave and has a strong character. The Golden Retriever is very sociable and makes a bad watchdog. These characteristics are mentioned by the Société centrale canine, which defines the standards for dog breeds in France. But a study published in Science in April 2022 questioned these natural dispositions, believing that a dog’s breed only partially predicts most of its behavior. A major new study published in Cell return to this topic.
Thousands of canids studied
“Selective breeding of domestic dogs has generated different breeds that are often optimized to perform specialized tasks, resumes the new study published on December 8, 2022 and carried out by researchers from the NIH (National Institutes of Health, USA), which benefits from very significant public funding, much more than in France. Despite the heritability of breed-typical behavioral traits, the identification of loci (precise locations of genes on a given chromosome, editor’s note) Causal studies have proven difficult due to the complexity of dog population structure“. In other words, it’s hard to know how certain specific behaviors are encoded in the genetic makeup of different breeds. But they are.
This work is based on genetic data from more than 4,000 domestic dogs (including 2,823 purebred dogs, 226 affected breeds), semi-wild and wild dogs. The researchers also collected the results of a questionnaire from a sample of owners of more than 46,000 purebred dogs. The C-BARQ, as it is called, is a 100-item behavioral assessment questionnaire.
10 main lines grouping closely related breeds
This is how the authors of this study discovered 10 large dog genetic lines and their behavioral correlates. In fact, each line corresponded, unconsciously, to a category of breeds (hunting, protection…), which means that sets of common genes are responsible for the behavior that these dogs share. And the questionnaire made it possible to refine these behavioral tendencies within the 10 lines. The results show, for example, that terriers have a natural tendency to hunt, which sheepdogs practically do not.
“Having established significant behavioral trends that correlated with large dog lineages, we then identified the genetic drivers of these behaviors by performing a genome-wide association study on the DNA samples.“, Emily Dutrow, lead author of the study, explains in a press release. Together with her colleagues, she has thus identified several genes associated with the specific behavior of certain breeds.
“This study shows that that there is intra- and inter-variation in behavioral traits, explain to Science and the Future Dr. Benoît Hédan, veterinarian and research engineer in the dog genetics team at the Rennes Institute of Genetics and Development (CNRS), who did not participate in the study. But some of these traits are enriched in groups of dog breeds. Genetic regions associated with this behavior have been identified here, some even found in wolves“.
It is directly in the dog’s ancestor that certain behaviors find their origin. Thousands of years of artificial selection have perpetuated them. “Unlike characteristics such as height, weight, type of coat, color, etc., which are due to the selection of a few mutations, according to this study, the selection of behavior was played out on many gene regions at the same time, and this selection has been enriched in strains of dogs that respond to a specific task. This results in dog lines sharing common ancestry and common job functions.“, continues Dr. Hédan.
Sheepdogs were particularly targeted by the study. Border Collies, for example, exhibit fascinating herding behavior associated with “unique engine diagrams“, according to the researchers’ expression. This complex faculty could find its origin in the wiring of their brain.
“Axon guidance is the biological process by which interaction networks between neurons are established, often during early brain development, explain to Science and the Future Doctors Ostrander and Dutrow, authors of the study. Attractive and repulsive signals control neural projections called axons, and the direction and goals of these projections are the basis for making connections within and between different parts of the brain. Neural circuits formed by such processes regulate behavior“.
A neuron connected to two others through its axon. Credits: AMANDINE WANERT / BSIP / BSIP via AFP
The study revealed that genetic variants at the level of the genes involved in the guidance of these famous axons were enriched (term that translates a particularly high frequency of genes involved in a particular biological pathway) in sheepdogs. The same phenomenon is found in genes linked to the development of brain areas involved in social cognition and responses to fear.
This study reveals how humans shaped the world’s most versatile pets“, the authors say. In addition, some of the genes associated with different dog lines may also be associated with genes involved in the behavior of other species, including humans.”The results of this study may show us how differences in the human genome can contribute to behavioral diversity in the same people.” notes Dr. Ostrander in an NIH statement.
A previous study of more measured dog breeds
This study is published only a few months after that of Science, who believed it dog breed stereotypes are largely unfounded. The latter stated that many behavioral traits can be inherited, but that race only partially predicts most behaviors. And sometimes not even at all. For this, its authors had sequenced the DNA of 2,155 purebred or crossbred dogs and had combined these results with the answers to a questionnaire sent to 18,385 dog owners.
“Genetics play a role in any individual dog’s personality, but breed does not effectively predict these traits.“, explained Elinor Karlsson, one of the authors of this work.What we have demonstrated is that the criteria for a golden retriever are its physical characteristics – the shape of its ears, the color and quality of its fur, its size. But not if he is loving“, she added.
The researchers had nevertheless found 11 loci associated with behavioral differences according to breed, including obedience, the ability to bring an object or even howl. In these cases, race played a role. But in total it explained only 9% of the behavioral variation. The explanation is that since the dog lives together with man, the latter has gradually chosen the same abilities of all animals. Today these behaviors would therefore all be more or less present in Canis lupus familiaris.
Shaping the brain, generation after generation
“Both studies involve extensive resources – thousands of DNA samples from dogs, sequencing those samples and collecting responses to questionnaires – and complex statistical analyses.“, remark Dr. Benoit Hedan. But they also have differences in the analyzed data and in the way it is processed. “In the new study, the genotypes (all the genetic characteristics of each examined dog, editor’s note) comes from different techniques, especially sequencing, and was not partially deduced as in the previous study. The questionnaires used are also different“, continues the French researcher.
The two studies nevertheless follow the same path: the dogs’ behavior is not determined within the same breed. If they are very similar physically, these dogs remain the fruit of different possible characters. However, the influence due to selection is exerted a little more on certain breeds.
“For races that share a selection for a specific task, man has selected many genetic regions involved, among other things, in the development of the brain, generation after generation.”, explains Dr. Hédan. This is how sheepdogs, and the border collie in particular, have become so remarkable.