Fish Fertilize Trees
When you think about relationships between organisms in nature, it is easy to think about the relationship between predator and prey (e.g. how the deer population would affect the population of wolves in a given area). There are various relationships that seem obvious to us, however, there are also some that may surprise us. Who would have though the salmon population would affect the growth of trees?
Figure 1 – Newly hatched Salmon alevin
Picture taken by the US department of Agriculture
Life cycle of Salmon
The life of a salmon begins in a freshwater river where a female’s nest of eggs is fertilized. The embryos in the egg develop throughout the winter and finally hatch in the spring and alevins emerge. The alevins (small fish that still have the yolk sack attached to them) remain hidden for a few months as they grow and develop into fry which then swim to the surface and begin to feed. Depending on the species, the fry may spend up to a year in their natal stream before starting their migration towards the sea. The salmon eventually travels downstream and can spend between one to seven years in the ocean eating and growing in size until they return back to their natal stream to procreate and die. In essence, the life cycle of the salmon is hatch, migrate, migrate back, spawn and die.
How does this affect the trees?
When salmon migrate back to their natal streams, they carry nitrogen and phosphates from the ocean in their bodies. When the salmon die (either naturally or when their carcass is discarded by bears in the forest), they release the nutrients that they carried up from the ocean into the soil. Dr. Tom Reimchen from the University of Victoria analyzed core tree samples and by working out the nutrient levels available to the tree over time, he found a direct correlation between the levels of nitrogen-15 available and the number fish. It has also been found that trees growing on the riverbanks can grow up to three times faster than those not growing on the riverbanks.
Who else does it affect?
Dr. Reimchen also found that up to 50% of nitrogen in insects comes from fish. It seems that not only the trees benefit from the abundance of nutrients provided by salmon, but so do various other organisms and hence, the presence of salmon in streams can increase biodiversity. The creatures that scavenge on the leftover salmon from the bears such as foxes, birds, and insects gain nitrogen from the salmon and are then in turn eaten by other predators in the forest which increases the available nitrogen in the forest.
What can we take away from this?
This shows that relationships between organisms may be more
complex than we previously thought and hence underlines the
importance of maintaining ecosystems as they are so as not to disturb them.
Sources and further reading:
Nps.gov. (2019). The Salmon Life Cycle - Olympic National Park (U.S. National Park Service). [online] Available at: https://www.nps.gov/olym/learn/nature/the-salmon-life-cycle.htm [Accessed 3 Jan. 2019].
Whitfield, J. (2001). Fish fertilize trees. [online] nature.com. Available at: https://www.nature.com/news/2001/011001/full/news011004-4.html [Accessed 3 Jan. 2019].
Wohlleben, P., 2017. The Secret Network of Nature. 1st ed. London: The Bodley Head.
Maya C. Lemaire
(Year 12 Student at Bangkok Patana School)
Figure 2 – Brown bear eating salmon, picture taken by Christoph Strässler
Foot Fetishes and Phantom Limbs
Foot fetish. These controversial words instill a myriad of different emotions from person to person and love them or hate them, there are people out there that have gone to prison for their obsessions.
Michael Wyatt, the “Toe Suck Fairy”, was arrested in 2012 and served time for a year for a series of assaults directed at women’s feet – now you may be wondering, what could possibly be so fascinating about feet that it drives someone to such extreme actions?
Neuroscientist Vilanayar S. Ramachandran approached the mystery of foot fetishes while studying phantom limb syndrome (the sensation that an amputated or missing limb is still attached) and discovered that podophilia (attraction to feet), may stem from a “neural crosstalk” between feet and genitals, as they occupy adjacent areas in the somatosensory homunculus.
As shown in the diagram (mapped out by Wilder Penfield), the feet are positioned right next to the genitals and due to a phenomenon called “spreading activation”, when the “foot” part of the brain is activated, the genital area may also be linked - therefore, sexual stimulation is then associated with the feet.
However other studies argue that the foot is not a source of somatic pleasure, but a visual pleasure and is therefore based on some form of a neural body map elsewhere in the brain, just not the S1.
So how is this related to phantom limbs?
In a horrific study conducted by Dr. Tim Pons, he severed the nerve endings of a monkey’s arm (leaving it paralyzed) and discovered that upon stimulating the somatosensory cortex associated with the face, the cells associated with the hand also fired.
Inspired by this, Ramachandran conducted his own experiment and found that stroking different parts of the face led to perceptions of being touched on different parts of the phantom limb for some amputees. This is where his theories on the “neural crosstalk” of feet and genitals come in.
He hypothesized that once the somatosensory cortex learns that a limb no longer works, the neurons correlating with that limb start to invade neighbouring areas (therefore foot and genital overlap is possible).
People began to come forward with confessions of feeling strange sensations in their phantom limbs and a few select conversations with an amputee working at Beth Israel Hospital and an engineer that had lost their leg below the knee appeared to support Ramachandran’s theory.
"Well, I feel a little embarrassed to tell you this . . . Doctor, every time I have sexual intercourse, I experience sensations in my phantom foot . . . I actually experience my orgasm in my foot. And therefore it's much bigger than it used to be because it's no longer confined to just my genitals."
In his acclaimed book “Phantoms in the Brain”, Ramachandran theorized that there was a link between the phenomenon of phantom limbs and neural plasticity (the ability of the brain to change throughout an individual's life) in the adult human brain. He showed that there indeed were changes in the somatosensory cortex of several amputees and that after the loss of the limb, sensory inputs no longer correlated to the exact same spot as before.
What does this mean?
There is still no official consensus on the cause of phantom limb pain and his theory on cortical reorganization, but if Ramachandran’s theories are indeed true, this could revolutionize how phantom limb pain is treated (as currently, there is still no concrete “cure” for it). Furthermore, solutions to many other life-threatening medical conditions such as stroke, cerebral palsy and traumatic brain injuries could be better developed with more research into cortical remapping and CIMT (constraint-induced movement therapy) already begins to utilize this.
Reuters U.S 2012 Arkansas Toe Sucking Fairy. [Online] [Accessed January 2019] Available from: https://www.reuters.com/article/us-usa-crime-toesucker/arkansas-toe-suck-fairy-jailed-for-one-year-idUSBRE86B02520120712
Google. 2019. Somatosensory homunculus. [Online] [Accessed January 2019] Available from: https://www.google.com/search?q=somatosensory+homunculus&safe=active&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiPhLyJ5vjfAhUBa94KHYEHAaEQ_AUIDigB&biw=1280&bih=596#imgrc=COYw6qY_dAXrNM:
Nih.gov 2014. The functional significance of cortical reorganisation and the parallel development of CI Therapy [Online] [Accessed January 2019] Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4072972/
McDermott, A. 2016. Constraint-Induced Movement Therapy - upper extremity. [Online] [Accessed January 2019] Available from: https://www.strokengine.ca/en/intervention/constraint-induced-movement-therapy-upper-extremity/
Year 12 student at Bangkok Patana School