People in Alaska served pacific salmon to their dogs 250–750 years ago. New protein research can advance researchers’ knowledge on the historical relationship with our best friends.
Some people find dog excrement disgusting, and others want to examine it closely.
One of these is archaeological scientist and PhD student Anne Kathrine Runge from the University of Copenhagen.
In fact, she is so fascinated by dog poop that she has investigated it thoroughly to determine what dogs ate in Alaska between 250 and 750 years ago.
The new proof-of-concept study shows that protein analysis provides opportunities to discover more about the diet of dogs centuries ago.
“The quest for more knowledge about our ancestors is also interesting because we can also explore our historical relationship to a person’s best friend. Did we eat the same things, or did we give the dogs leftovers from our own meals? Studying the proteins in dogs’ faeces enables us to ascertain this,” explains Anne Kathrine Runge.
The study has been published in Proceedings of the Royal Society B: Biological Sciences.
Extracted all the protein from dog palaeopoop
Anne Kathrine Runge and colleagues examined five samples of ancient dog excrement (palaeofaeces) from a pre-contact Yup’ik village in Alaska.
Even though the samples were all more than 250 years old, the archaeologists knew exactly what they had excavated. They also were certain about the human faeces they unearthed: they were so pungent that they had to be rapidly refrigerated.
Back in the laboratory, Anne Kathrine Runge extracted proteins from the dog poop to initially discover whether the small stools really came from dogs or were simply lumps of soil. She also wanted to determine what the dogs had eaten before they defecated on the floor of the house where the excrement was found.
The researchers then sequenced all the proteins in the samples and compared their findings with a database (Swiss-Prot) containing many types of proteins from animals, plants and humans.
This enabled Anne Kathrine Runge and colleagues to determine what the dogs had eaten.
“Our first goal was to determine whether we could find analysable proteins in the samples; we found proteins in four of the five samples collected,” says Anne Kathrine Runge.
Dogs ate salmon morning, noon and night
The samples contained proteins from the dogs themselves, and this confirmed that the poop really was from dogs and not from wolves, polar bears or humans.
Other material excavated indicated that the dogs were probably sled dogs, and the researchers found proteins derived from salmon muscle and bone tissue as well as roe and guts.
This suggests that the dogs were fed every bit of the salmon, including the guts, which humans probably did not eat.
“This provides insight into the relationship between people and dogs at the time. We have no written sources that can tell us how humans treated their dogs, and there have been conflicting suggestions that the dogs may have eaten the same food as people – or maybe completely different food. Maybe the people ate fish and their dogs ate marine mammals? The results show that both dogs and people ate salmon, but the dogs ate parts of the salmon that humans may not have eaten,” explains Anne Kathrine Runge.
Dogs ate different types of Pacific salmon centuries ago
Another interesting aspect of the discovery is that the Yup’ik people, who still live close to the Alaskan pre-contact village, still have dogs today. These dogs eat chum salmon, also known as dog salmon (Oncorhynchus keta).
Chum salmon does not have the same economic value as the other Pacific salmon species, and the local community says that the dogs have been fed this type of salmon for a long time.
Nevertheless, Anne Kathrine Runge’s research has shown that the dogs were fed a variety of types of salmon 250 to 750 years ago. Feeding them chum salmon exclusively is a recent development.
“Palaeoproteomic analyses of dog excrement sheds new light on how society has changed over several centuries,” says Anne Kathrine Runge.
Examining human faeces
The interim goal of the study was to confirm that knowledge can be obtained on the diet of ancient dogs.
The researchers’ next step is to determine whether they can obtain the same information from stool samples that are even older than those unearthed in Alaska – maybe even many millennia ago.
Anne Kathrine Runge would like to compare the findings from the dog poop with those from humans.
This will provide a definitive overview of whether ancient people ate the same food as their dogs or whether they reserved some types of food for humans, with dogs eating something else.
“Perhaps we can also go far back in time and determine what people ate or examine stool samples from locations where the DNA that researchers would otherwise examine rarely survives. We can also use our analytical method to examine whether people had disease-related proteins in their gut – such as proteins related to inflammatory bowel diseases. Palaeofaeces contain much information that we cannot obtain through archaeology or by studying DNA,” concludes Anne Kathrine Runge.