Dogs and Wolves: What’s the Difference?

Contributed by Nadia Irfan and Joseph Birchansky

This is a graphic representation of the phylogenetic tree showing relatedness between dogs and wolves as it compares to outgroup (less related) species which branches off to form new species earlier on in history. The images show structural similarity and differences between the three species as well.

This is a graphic representation of the phylogenetic tree showing relatedness between dogs and wolves as it compares to outgroup (less related) species which branches off to form new species earlier on in history. The images show structural similarity and differences between the three species as well.

Dogs are the classic American pet, but how much do you really know about them? Dogs’ behavior is quite similar to humans’. For instance, even puppies that haven’t interacted with humans show social and cognitive skills on par with human children. This is surprising, considering their closest relative in the wild is the wolf, which is known to be more aggressive and less compatible with people. Wolves raised by humans don’t develop the same mental and social skills that domesticated dogs do. In addition, dogs are less fearful and more playful than wolves. This divergence is due to artificial selection by humans over many generations, which has resulted in dogs with improved tameness and temperament, which were reinforced by a population bottleneck – a significant reduction in population size.

Ancestors with dog-like characteristics originate in the fossil record up to 33,000 years ago. It appears dogs were first domesticated about 16,000 years ago, which actually happened before the development of agriculture. They then completely diverged from wolves 14,000 years ago, and there is evidence suggesting that dogs emerged from a single species of ancestral wolf. This divergence occurred via bottlenecks, significant reductions in population size, in both species, which were especially pronounced in dogs, from 32,000 to less than 2,000 individuals – a 16-fold reduction – and less so in wolves, which only experienced a threefold reduction. It is unclear why this reduction in wolves occurred, but it happened before humans began intentionally hunting them.

It’s interesting that, with so many behavioral and physical differences, dogs and wolves actually have very similar genomes. What’s different is which genes are being expressed, including those involved with cognition, memory, growth, and social skills. These differences in gene expression are driven in large part by artificial selection. Humans also influenced the morphology of dogs, including coat color variation, reduced cranial volume, and smaller skeletal size. These changes in morphology could potentially be deleterious because a possible effect of artificial selection may be a reduction in purifying selection, which ordinarily eliminates characteristics that are unfavorable in the wild. Research shows that humans may also have selected for behavioral traits, and these traits may have been selected for even before morphological traits. Not only did humans select for behavioral traits but food, shelter, and water availability given to them by humans are specifically responsible for differences in hypothalamic gene expression – a region associated with behavior and intelligence.

As a result of these selective pressures dogs have evolved different pack mentalities than wolves. Whereas wolves have a pair-bonded family unit that collaborates in hunting and rearing babies, dogs are less inclined to stay with one mate, are less active in raising their young, and are more dependent on human-provided resources. Overall, dogs’ and wolves’ different social, behavioral, and physical characteristics reflect speciation and domestication.

Also see: Who Helped the Dogs Evolve?

For more information, please refer to the following sources:

Albert, F.W., et al. 2012. A Comparison of Brain Gene Expression Levels in
Domesticated and Wild Animals. PLOS Genetics 8:9.

Freedman, A.H., et al. 2014. Genome Sequencing Highlights the Dynamic Early
History of Dogs. PLOS Genetics 10:1.

Li, Y., et al. 2013. Artificial Selection on Brain-Expressed Genes during the
Domestication of Dog. Molecular Biology and Evolution 30:8. 1867-1876.

Marshall-Pescini, S., Viranyi, Z, & F. Range. 2015. The Effect of Domestication on
Inhibitory Control: Wolves and Dogs Compared. PLOS ONE 10:2.

Ramirez, O., et al. 2014. Analysis of structural diversity in wolf-like canids reveals
post-domestication variants. BMC Genomics 15:.

Saetre, P., et al. 2004. From wild wolf to domestic dog: gene expression changes in
the brain. Molecular Brain Research 126:2 198-206.

Zhang, H. & Chen, L. 2011. The complete mitochondrial genome of dhole Cuon alpinus:
phylogenetic analysis and dating evolutionary divergence within canidae. Molecular
Biology Reports 38. 1656

Don’t Trust Your Eyes: Sea Slug Speciation

Contributed by Ryan Martin, Rema Elmostafa, Valerie Linck, Andy Dong, Aneel Maini, Matt Morales

If it looks like a duck, and it quacks like a duck, well, it might not be a duck. This adage also applies to Doriopsilla areolata, a type of sea slug. In these cases we often want to use visible traits to identify species. However, many species look indistinguishably the same, while being distinct.  Species are acted on by evolutionary processes independently of other populations. For a new species to arise, a population of individuals must become isolated, then mutations and natural selection will allow this populations to diverge from the population from which it is isolated. If the populations come back together and cannot interbreed or their offspring often have lower fitness, then they can likely be considered a different species.

Doriopsilla areolata, also known as one type of sea slug, is found in many areas of the world such as Spain, South Africa, and the Caribbean (Goodheart & Valdes, 2012). Scientists originally thought that there was only one species of this sea slug but after research they have discovered that many other species exist.

Doriopsilla areolata

Doriopsilla areolata

In recent history there have been major technological advances that allowed evolutionary biologists to identify differences in their DNA. For sea slugs and other members of the Doriopsilla genus, researchers found several mutations and variations in rRNA sequences that were present only in members of the same species (Cortes et al. 2009). Researchers were also able to analyze parts of digestive and reproductive anatomy at a microscopic level, finding high variability between species, making it unlikely that they would interbreed (Hoover et al 2015).

Doriopsilla areolata is a species of sea slug that can be found in the area ranging from Southwest Africa to Spain, with one of the broadest geographic ranges (Goodheart et al, 2012). Doriopsilla miniata is a colorful species of sea slugs that is found along the Pacific region of Japan (Hirose 2014). Another species studied is Doriopsilla gemela which is a species of slug found on the north eastern coast of the pacific, and their sister species, D. albopunctata is found on the coast of southern California (Hoover 2015).


Not all populations are separate species, however. For example, since Doriopsilla does not travel long distances, it has been proposed that geographic separation would reliably lead to speciation (Goodheart & Valdes, 2012). However, in the case of the three D. areolata subspecies near the Caribbean, Africa, and the Mediterranean there was no significant genetic difference. Because of this, it is believed that the populations are interbreeding to a degree, and that the three groups, each called a subspecies, are actually one according to biological and genetic evidence.

These sea slugs are the perfect example of how speciation is more complex than what we see.

For added fun, see our creative comic which summarizes speciation in sea slugs below!

In the course of time, species that were once related can evolve and diverge from one another. This is the concept of speciation. Although speciation is marked by changes in color in the cartoon above, this is not always the case and different species may actually end up looking quite similar.

In the course of time, species that were once related can evolve and diverge from one another. This is the concept of speciation. Although speciation is marked by changes in color in the cartoon above, this is not always the case and different species may actually end up looking quite similar.

For more information, see:

Goodheart, Jessica, and Ángel Valdés. “Re-evaluation of the Doriopsilla Areolata Bergh, 1880 (Mollusca: Opisthobranchia) Subspecies Complex in the Eastern Atlantic Ocean and Its Relationship to South African Doriopsilla Miniata (Alder & Hancock, 1864) Based on Molecular Data.” Mar Biodiv Marine Biodiversity 43.2 (2012): 113-20. Web.

Hirose, Mamiko, Euichi Hirose, and Masato Kiyomoto. “Identification of Five Species of Dendrodoris (Mollusca: Nudibranchia) from Japan, Using DNA Barcode and Larval Characters.” Mar Biodiv Marine Biodiversity(2014).

Hoover, Craig, Tabitha Lindsay, Jeffrey H. R. Goddard, and Ángel Valdés. “Seeing Double: Pseudocryptic Diversity in the Doriopsilla Albopunctata-Doriopsilla Gemela Species Complex of the North-eastern Pacific.” Zoologica Scripta Zool Scr 44.6 (2015): 612-31. 

 Vonlanthen, P., D. Bittner, A. G. Hudson, K. A. Young, R. Müller, B. Lundsgaard-Hansen, D. Roy, S. Di Piazza, C. R. Largiader, and O. Seehausen. “Eutrophication Causes Speciation Reversal in Whitefish Adaptive Radiations.” Nature 482.7385 (2012): 357-62. 

Cortés, Jorge, and Ingo S. Wehrtmann. “Diversity of Marine Habitats of the Caribbean and Pacific of Costa Rica.” Marine Biodiversity of Costa Rica, Central America (2009): 1-45. Web.

Bertsch, Hans. “Nudibranch feeding biogeography: ecological network analysis of inter-and intra-provincial variations.” Thalassas 27.2 (2011): 155-168.

Helicobacter pylori and you.

Contributed by Thomas Partin and Austin Piccolo

Species do not live in a world separate from each other. Organisms interact with other organisms everyday, and over time adapt to each other accordingly. Often, the evolution of two species can become strongly linked to each other, for better or worse. Heliobacter pylori is a bacteria that thrives in the acidic conditions of the human stomach. It causes stomach ulcers and is strongly correlated with gastric cancer. As recently as the 1980’s, the idea of a bacteria being able to survive in the stomach’s harsh conditions and being responsible for this disease was so controversial that it took one doctor intentionally infecting himself to prove its role in stomach ulcers. That doctor later won the Nobel prize in medicine for his work.

H. pylori did not first start infecting humans in the 80’s though. H. pylori and humans have been living (and battling) together for millennia. The earliest humans also played host to H. pylori. One way this can be shown is a creative use of a phylogenetic tree. Scientists sampled many different strains of H. pylori, and used them to create an ancestral tree of the different strains. They then compared the tree they made to geographic locations of their samples. What they found was that lineages of H. pylori matched perfectly with the migration patterns of ancient humans as they moved out of Africa. Newer strains of H. pylori are found where humans migrated to most recently. The strains were carried and dispersed based on how early humans moved around the globe.

This intimate relation between H. pylori and humans provides a great opportunity to explore coevolution. Humans and H. pylori have been locked in an arms race for thousands of years. H. pylori colonization poses serious health consequences to the host, which creates a selective pressure for humans that can prevent H. pylori infection. Likewise, the human body is an incredibly hostile environment towards foreign invaders like H. pylori, which creates a strong selective environment for H. pylori cells that can overcome human defenses. There is evidence this selective pressure is so strong that H. pylori begins adapting specifically to the host after initial colonization. Although not an innate aspect of human biology, antibiotics are another human defense against H. pylori. Antibiotic use creates a selective pressure for H. pylori that is so strong that resistant strains can develop remarkably quickly after attempted treatment.

Please watch the below video to learn more!;

For further information see:

Linz, B., Ballouxm, F., Moodley, Y., Manica, A., Liu, H., Roumagnac, P., Falush, D., Stamer, C., Prugnolle, F., van der Mer, S.W., Yamaoka, Y., Graham, D.Y., Perez-Trallero, E., Wadstrom, T., Suerbaum, S., Achtman, M. 2007. An African origin for the intimate association between humans and Helicobacter pylori. Nature 445: 915-918

Gao, W., Cheng, H., Hu, F., Li, J., Wang, L., Yang, G., Xu, L., Zheng, X. 2010. The Evolution of Helicobacter pylori Antibiotics Resistance Over 10 Years in Beijing, China. Helicobacter. 15: 460-466.

Oh, J.D., Kling-Bäckhed, H., Giannakis, M., Xu, J., Fulton, R.S., Fulton, L.A., Cordum, H.S., Wang, C., Elliott, Glendoria., Edwards, J., Mardis, E.R., Engstrand, L.G., Gordon, J.I. 2006. The complete genome sequence of a chronic atrophic gastritis Helicobacter pylori strain: Evolution during disease progression. PNAS. 103: 9999-10004.

Blecker, U., Landers, S., Keppens, E., Vandenplas, Y. 1994. Evolution of Helicobacter pylori Positivity in Infants Born From Positive Mothers. Journal of Pediatric Gastroenterology and Nutrition. 19: 87-90

Kennemann, L., Didelot, X., Aebischer, T., Khun, S., Drescher, B., Droge, M., Reinhardt, R., Correa, P., Meyer, T.F., Josenhan, C., Falush, D., Suerbaum S. 2011. Helicobacter pylori genome evolution during human infection. PNAS. 108: 5033-5038.

Marshall, B.J., Warren, J.R. 1984. Unidentified curved bacilli in the stomach of patients with gastritis and peptic ulcers. The Lancet. 323: 1311-131.

Avasthi, T.S., Devi, S.H., Taylor, T.D., Kumar, N., Baddam, R., Kondo, S., Suzuki, Y., Lamouliatte, H., Mégraud, F., Ahmed, N. 2011. Genomes of Two Chronological Isolates (Helicobacter pylori 2017 and 2018) of the West African Helicobacter pylori Strain 908 Obtained from a Single Patient. Journal of Bacteriology. 193: 3385-3386.