Tag Archives: Evolution

Sea lampreys help scientists fill in gaps in our evolutionary history

A group of researchers at the University of British Columbia recently found that sea lampreys, an ancient species of jawless fish, appear to respond to stress much more differently than scientists originally thought.

Many species of lampreys are parasitic. Sea lampreys lack jaws and have suction-cup-like mouths that are lined with teeth, which they use to latch onto fish and suck their blood.
Source: Shutterstock.

The paper, which was published in General and Comparative Endocrinology in 2013, detailed a two-year-long experiment that culminated in some unexpected results. The researchers were attempting to determine whether previous assumptions about stress regulation in lampreys were true. By injecting lampreys with certain chemicals, called hormones, that are turned into “stress hormones” in other vertebrates, the researchers checked the lampreys’ blood levels for these “precursors” and for the stress hormone, cortisol, to see whether lampreys also turned each of these precursors into cortisol.

Click image to enlarge.
Simplified diagram of the classic stress response seen in many vertebrates.
Source: Jenny Labrie.

For years scientists had assumed that lampreys, like other fish, had a stress response that involved the same three types of hormones – corticotropin-releasing hormone (CRH), adrenocorticotropin (ACTH), and cortisol – that are seen in humans and other animals. These three hormones and their involvement in the stress pathway is discussed in the video below, as well as what is already thought to be true about the evolution of the stress pathway.

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The researchers found that, similar to other animals and to fish, lampreys do respond to CRH with increased levels of stress. CRH is a precursor to stress hormones in different species; in humans it is cortisol, which has been popularised over the past few decades as the concept of “stress” has received increasing amounts of attention – both from academia and the popular media. The lampreys injected with CRH displayed increases in their own type of cortisol, indicating that they were indeed experiencing stress in response, just as humans would.

Unexpectedly, the lampreys did not respond to several types of ACTH that they were injected with. In both humans and other fish, ACTH is the hormone that is released in response to CRH and eventually stimulates cortisol release, which causes classic signs of an activated stress response (e.g., increased heart rate).

What does this mean? Well, yes, scientists were once again mistaken; lampreys are not just like every other fish. But why should this matter? Who cares about this 505-million-year-old fish?

Click image to enlarge.
Source: Wikimedia Commons. Originally illustrated by Ernst Haeckel, and published in ‘Generelle Morphologie der Organismen’ (1866).

As it turns out, we all should. Contrary to popular opinion, scientists don’t know everything there is to know about human evolution, but we can fill in some of our knowledge gaps by studying lampreys. A better understanding of stress regulation in lampreys helps us better understand how this system has evolved since the time of these early vertebrates. Humans diverged from lampreys 500 million years ago, and we are related to them – as uncomfortable a thought that may be for some people. This link means that lampreys may be key to understanding the origins of biology in many higher vertebrates – including humans!

Perhaps for this reason alone it is worthwhile to strive to conserve lamprey species, and this research does also have implications for protection of certain lampreys, as discussed in the podcast below.

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Some have hailed the sea lamprey as an up-and-coming “evolutionary developmental model of choice.” Clearly, even blood-sucking parasites have their place in nature’s plan.

Text, video, and podcast by Jenny Labrie, Kelly Liu, Rubina Lo, and Kathy Tran.


Close, D.A.; Yun, S-S.; Roberts, B.W.; Didier, W.; Rai, S.; Johnson, N.S.; and Libants, S. (2013). Regulation of a putative corticosteroid, 17,21-dihydroxypregn-4-ene,3,20-one, in sea lamprey, Petromyzon marinus. General and Comparative Endocrinology, 196: 17-25.

Kimura, M. (1969). The rate of molecular evolution considered from the standpoint of population genetics. Proceedings of the National Academy of Sciences of the USA, 63(4): 1181-1188.

Nikitina, N.; Bronner-Fraser, M.; and Sauka-Spengler, T. (2009). The sea lamprey Petromyzon marinas: a model for evolutionary and developmental biology. In K. Behringer (Ed.), Emerging model organisms: a laboratory manual (pp. 405-421). Cold Spring Harbor, NY: CSHL Press.

Further reading

The hormone, cortisol

The sea lamprey and its cousin the Pacific lamprey

The stress response

Lampreys in the news

Scientists find genes linked to human neurological disorders in sea lamprey genome

Sea lampreys provide a unique solution to gene regulation

Lamprey research sheds light on nerve regeneration following spinal cord injury

Lampreys give clues to evolution of immune system

WE ARE THE EGG PEOPLE (Some brief notes on the evolution of live birth)

Here’s a strange thought: You, and all the people you know, were once microscopic bundles of cells, inside of another person’s body (in your case, your mother’s).  You may be all sorts of awesome now, but your life began extremely humbly – an elegant balance of symmetry, simplicity, and chaotic potential.  And it all started inside of an egg. You, like me, are an egg person. Deal with it.

Eggs are beautiful things. They are such an elegant solution to developing new life, that multiple taxa of animals have evolved to produce them, including fish, amphibians, birds, dinosaurs, reptiles and mammals.  For most fish and amphibians, the laying of eggs is the first step in the process of sexual reproduction.  The eggs are then fertilized by the male in water, where they remain until they develop and eventually hatch.

It’s a neat system, but not one that works very well for terrestrial (earth-living) animals like birds, reptiles and mammals. Developing embryos is a delicate business; they need to be kept moist, sheltered, at a relatively stable temperature, and with a steady supply of nutrients. These are all tall orders for any organism to maintain, let alone a defenseless embryo outside of water.

As it so happens, the safest place for many animals to grow their young is inside of their own bodies.

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Humans, as I’m sure you know, don’t lay eggs.  Instead, we retain our eggs, fertilize, and develop them internally; the type of egg we make defines us as Amniotes, along with reptiles and birds.  Amniotic animals have more complex eggs then fish and amphibians, as they have specialized membranes that grow out of the embryo, and preform multiple functions, including providing the growing fetus with nutrients.

Birds grow their eggs internally for a short period of time, then lay them, and then incubate (keep them warm while they develop).  Inside, the  bird embryos are supplied with nutrients from a yolk sac, which supports them as they grow.  Gas exchange also occurs through the membranes and pores of the shell (yes, eggs breathe!).

While many reptiles lay eggs, there are several species of snakes and lizards that give live birth; some snakes even have placentas.  Placentas are something that also define placental mammals – a group to which humans belong.

In placental animals, the membranes of the amniotic egg develop into the placenta and umbilical cord.  Considered in this way, a placenta is essentially a modified egg, and has many analogous features that can be compared to reptile and bird eggs (a couple of which are illustrated below).  Instead of a yolk sac, human fetuses get their nutrients from their mother’s body via the placenta and umbilical cord.

The placenta acts as a bridge between the mother’s body and the growing child’s – allowing the transport of nutrients, but also acting as a barricade against the mother’s immune system (which will naturally want to treat the baby as a hostile “foreign” life-form inside the mother).

There is considerable evidence that live birth has evolved hundreds times, within a diverse spectrum of animal forms – it is certainly not unique to mammals.  The earliest evidence for live birth dates back 380 million years, to the ancient armored fishes the placoderms.

This tells us something interesting about the nature of live birth from an evolutionary perspective – that the difference between live birthing-mammals and egg-laying mammals is not cut and dry (as nothing ever is in evolutionary biology).  Rather, the two methods of developing young have dozens of crossovers and grey areas, and in a more fundamental way, they are really the same thing. For nature, the egg has never truly gone out of style.

Text and illustrations by Sam MacKinnon, 2014



Power, M. L., Schulkin, J., & Project Muse University Press eBooks. (2012). The evolution of the human placenta. Baltimore: Johns Hopkins University Press.

Porous Science: How Does a Developing Chick Breathe Inside Its Egg? 2012 Scientific American.  Retrieved on 02/24/2014 from: http://www.scientificamerican.com/article/bring-science-home-chick-breathe-inside-shell/