#accessible science

Introduction

We talk about how species help one another, in this case, a plant and an animal doing things to help one another. This is what we call “Mutualism”. In figs, with figs and wasps, this has happened for an estimated 60 million years and is still happening to this day. Fig “fruits”, called syconia, are actually a bunch of flowers, surrounded by delicious fleshiness. Some of these flowers are sterile, meaning they won’t produce seeds. These are the ones that female wasps can use as nests for their egg, and will lay one egg per each of these tiny flowers. For the fig tree, it’s not realistic to make a lot of these sterile flowers, so why does it make them at all? Making a small sacrifice to get the wasps to keep coming back and pollinating its flowers is worth it to be able to pass along its offspring. With some trees, they will produce separate fruits or monoecious fruits so that there are male and female flowers all within the same fig “fruit”. Going back to the idea of “Mutualism”, the flowers being pollinated vs the amount of wasps being born is related to the lengths of the styles aka pollen tubes in the flowers. Only in the short-pollen-tube flowers or the sterile ones can the fig wasp lay her eggs.

Figure 1: Short vs long styled flowers and the wasp’s egg laying preference, art by @wildlifemajor in MS Paint.

While some wasps can lay their eggs in the long styled ones, they’re usual avoided. I’d be happy to go into some explanations for that at a later time. 

Basically it comes down to the fig wasps being unable to live long enough to lay eggs in all of the flowers and will go to the flowers at the tip of the fig sarconia first and fill up as many as possible. after that. This study looked at how weather changed the wasps lifespans and ability to lay eggs, and how the opening of the fig (the ostiole) closes after a wasp enters it. 

Results

Wasps have shorter lifespans in warmer and dryer conditions, meaning that they will be able to produce less babies. Depending on how many wasps can get into each fig fruit (sarconia) there will be more flowers pollinated because more wasps are getting in and moving around. In the winter, they saw an increase in flowers being laid in (galled flowers) and more wasps being born, presumably because of the lower temperatures. In winter if there were more wasps in one fig fruit than another, there were actually less babies made. 

Lower temperatures increase the amount of babies, but only when there is a small number of female wasps (ie just 1 per fig). When multiple female wasps are in the same fruit, they spend less time laying eggs. 

This next part is really exciting to me, because we learned in class that only one female wasp (foundress) is able to enter the fig before it closes. This is debunked in this study in “Figure 6: Ostiole closure in syconia with different numbers of simultaneously introduced foundresses.” here:

This is so exciting because it means the figs want to have more female wasps inside of them so they compete against one another producing less baby wasps and increasing the pollination chances of their own fruits so that the fig tree can reproduce. The fig will close more slowly depending on how many wasps have entered it in hopes more wasps will enter. 

Discussion

In winter there are less wasps pollinating the figs. Why? Maybe because there are more figs, or maybe because the wasps can’t find the figs because of bad weather. In many species of fig, we see the same thing happening with them closing entirely once a wasp has entered. Making sure the fig doesn’t get too many wasps babies instead of its own fruit being pollinated, could be one of the reasons why figs evolved to have their flowers covered by the fleshiness. The fig wants to have a lot of pollinators so the pollinators fight with one another and only lay so many eggs, but the figs get a lot of pollination out of it. 

So the article then gets really cool. It talks about how plants basically sweat from their leaves, or in this case the fig “fruit” to give the inside of the fig a constant temperature, the perfect place for wasp eggs to grow up! This process is called “transpiration”. This is important because the warmer temperature limits the amount of wasps born. Too many wasp babies? ROAST THEM. ROAST THEM ALL.

A final cool point is that the reason why fig wasps are so small, some of them you need a microscope to see, is because of how small the flowers (and ovules). Only the smallest of wasps will be able to reproduce.

Materials and Methods

The researchers collected wild fig fruit or syconia before the babies were born, cut them open, and counted the number of dead momma wasps inside them. 

They also did research on putting the adult wasps in isolated spaces with the figs measured the length of time for the fig opening (oscicle) to close. "After the introductions, syconia were bagged with organdy cloth to prevent attack by parasitic wasps that oviposit from outside the syconium.” It wasn’t really discussed, but these fig wasps are often vulnerable to being harmed by other parasitic wasps that dig into figs and lay their own eggs into the baby fig wasps that have just been born but we can go more another time. 

Experiments were repeated in Summer and Winter. 

Personal Afterthoughts

It was an interesting read.It definitely highlights the impact of climate change on pollinators. Even if they only discussed wasps as pollinators there is still connections to be made.

I still don’t know what triggers the oscicles to close. I don’t know if anyone does know, but the process begins to close after the first wasp enters. 

Something that stood out to me in this article, is the Materials and Methods were listed last on page 7. I disliked reading this article as the Results were jumbled together while also describing the methods on how they used the data. URRRGGG

Finally, I didn’t want to use the word in my summary for fear of being more confusing, but the author kept using the term “foundress” to refer to the wasp mommas, which means female founder, and I just think that is the best thing.

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Definitions:

Organism – a living thing

Organ – a part of an organism that performs a specific function e.g. heart, liver

Cells – the smallest unit of life, e.g. a red blood cell (erythrocyte), nerve cell

Stimuli – something that can be detected and causes an organism to react, e.g. light, heat

Anatomical – relating to the body

Introduction

Receptors are organs or cells that allow you to detect stimuli. For example, there are cone cells in your eye that allow you to detect light and ultimately see, and pain receptors in your skin that allow you to feel pain.

Receptors that are present all over the body and detect stimuli such as touch and pressure are known as somatosensory receptors. These can be difficult to count in many animals, but in the noses of moles these receptors are clustered into structures known as Eimer’s organs. They contain at least four different kinds of receptor allowing them to detect vibrations, light touch, pressure, information about shapes and edges, and pain. These organs are visible under a microscope, so can be counted.

The star-nosed mole has a nose with 22 appendages, sometimes called rays. The whole surface of these rays is covered with Eimer’s organs. Star-nosed moles on average have more and smaller Eimer’s organs than other moles. The fact they are smaller is actually beneficial as they have a greater tactile resolution, or in other words, can distinguish between smaller things.

The nose is comparable to the human hand in the distribution of the somatosensory receptors. From your palm to your finger tips you have an increasing number of somatosensory receptors. The rays of a star-nosed mole, from base to tip, show the same pattern. Where there are more Eimer’s organs, they are smaller, so they have a greater tactile resolution.

The shortest of the rays, number 11, is located bottom-middle and can be compared to the fovea of the eye. This is the part of the eye that gives the clearest vision, it is used in activities such as reading and driving. Similarly, ray 11 is thought to give a clearer tactile image than the other rays. Moles use it for tasks such as examining food before eating it, even if the food was detected by other rays. Ray 11 also has more brain power dedicated to it. Out of the total region of the brain dedicated to the star, a quarter of it is dedicated to ray 11. It’s interesting to note that there is no increased density of Eimer’s organs, so due to its shorter length, actually has less overall.

Eva K. Sawyer and Kenneth C. Catania set out to quantify the number of Eimer’s organs on the tips of the rays and determine if there was a difference between the number on ray 11 and the number on the other rays.

Materials and Methods

The animals used in this experiment were ones killed in a previous experiment. They had been killed via overdose of sodium pentobarbital, were treated in order to preserve cells and tissues, and stored for later use. The stars had been removed at least two months prior to this experiment taking place. Stars that were visibly injured were not used in the experiment and fifteen stars were used overall. All were from adults.

Whole star measurements were done by using a glass slide to gently squash the star flat and put on a lightbox.

There are two kinds of electron microscope, the one used in this experiment was SEM, or a scanning electron microscope. It works by firing a beam of electrons at a sample and creates a 3D image. To prepare the sample it was dehydrated in ethanol (the alcohol in alcoholic drinks) and coated in gold. It’s standard to prepare insulating samples with conductive transition metals such as gold.

The area and circularity were calculated from the pictures taken. Circularity is a measure from 0 to 1 of how circular a shape is, 1 being perfectly round. The micrographs from the SEM were used to measure surface area, density and eccentricity. Eccentricity was calculated by dividing the distance of the Eimer’s organ from the base by the total length of the ray then multiplied by 100. This gives a percentage of how far along the ray the Eimer’s organ is. This is useful because it allows a comparison between rays of different lengths.

The density was recorded in two ways, a heat map was produced to get an idea visually of how the data looked, and for statistical analysis each ray was split into 20 sections of different areas with the same number of Eimer’s organs in them. The density was then calculated by dividing the number of Eimer’s organs by the area.

Results

As you might expect, the bigger the individual, the bigger the star. And if ray 1 of an individual was larger, you could also expect the other rays to be larger. Ray 10 had the smallest surface area. The most circular ray was ray 1, then rays 10 and 11.  

Below is one of the density heat maps produced, red to blue corresponds to the highest to lowest density.

 For one of the stars tested, the largest Eimer’s organ was more than 26 times as large. The larger organs are near the base, and as shown in the heat map, are less dense. The smaller organs are near the tips and are more densely packed.

There was no difference between the density of Eimer’s organs on ray 11 compared to the other rays.

Discussion

These results, taken together with previous research, seems to suggest that the tips of the rays are especially important whereas behavioural and anatomical observations from past research suggest it is ray 11 that is important.

So why may ray 11 be so important despite having no increase in Eimer’s organ density? In part it can be explained by increased innervation, which simply means more nerves go to ray 11 than the other rays. Also, more of those nerves are myelinated. Myelin sheaths are a fatty, insulating layer that protects the nerves and allows impulses to travel more quickly. If each nerve is separate it allows for a greater resolution.

A mechanoreceptor is a type of receptor than detects pressure or distortions. Like in the star-nosed mole, the tips of an appendage often have the most mechanoreceptors. This pattern is found in many animals including platypus, crocodiles and several types of bird.

Why might this pattern be observed in the in star-nosed moles? It may be a structural rather than functional adaption; maybe for the Eimer’s organs to completely cover the surface of the ray and still allow movement, the size of the unit must be different at base and tip. Another suggestion is that instead of spatial resolution the tips are instead simply more sensitive. The difference between these is that a spatial resolution allows you to determine between two points whereas a greater sensitivity will allow you to detect smaller stimuli.

We’ve already highlighted some similarities between the human hand and the star of star-nosed moles, but to finish, we’ll note some differences. Humans and moles detect textures differently, while humans move their hands across a surface, mole rapidly probe surfaces. And moles have a greater density of nerve endings, up to 7,180 nerve endings per mm2 compared to only 525 in humans (in the cornea of the eye).

Notes

Introduction

Traditional computers are made with separate units for the memory and the processor - stuff is stored in one section and is dealt with in the other section. The processor for these computers goes through one command at a time in a sequence. It is just inefficient because transferring data from the memory to the processor takes a relatively long time.

Brains, on the other hand, process a lot of signals simultaneously. So if you build hardware that mimics the biological structure of the brain, you could process and analyse data in parallel just like the brain does! That is what a neural network aims to do. A network is just a collection of things that are all connected to each other and can communicate with each other. For example, the internet. A neural network is just a network which is based on how actual neurons in our actual brains are connected.

How do neurons work?

Neurons are cells in our nervous system that respond to sound, smell, touch, and sight. They can also send signals to control muscles, or they can just pass the signals from one neuron to the other. The important thing to note here is that towards their end is a structure called a synapse that allows them to transmit the signal onwards to other neurons or parts of the body. These are electrical signals, as neurons are electrically excitable and are said to ‘fire’ or activate or send a signal forward if a threshold voltage is exceeded. The oldest, (probably) simplest, and most used model to describe this behaviour of the neurons is given by the integrate-and-fire model. (This is not relevant enough to the paper to go into any detail, but if there are requests for it I’m happy to write about it at length!)

Since synapses allow neurons to send signals around, they are very important in any kind of learning or forming memories. A thing often talked about is the plasticity of synapses. As weird as that sounds, it just means that neurons can form new connections or strengthen old connections with each other when they are activated together. Like when you make a cup of coffee and you look at it and you smell it and you drink it, the neurons that code for the sight of coffee get activated at the same time as those that code for the smell and taste of coffee. In the words of a famous neuroscientist, ‘neurons that fire together wire together’.

What did they do?

The writers of this paper wanted to create a network with a brain-like structure and see if it was capable of fast and efficient data processing. To do this, they needed to make a network that mimicked both neurons and synapses. Recently, a new way of doing this has been developed and it’s super cool because it uses lasers to send signals instead of electricity! Networks developed this way are called optical neural networks.

To build the cell acting as a neuron, the authors of this paper used a material that can change between two states - it is opaque by default but becomes transparent when heated by a laser pulse. This is fascinating because in this setting the material behaves like a neuron! Like a neuron, the cell switches phases only above a threshold. When it is opaque, it absorbs all the signal and so represents a weak connection between the neurons. When it is transparent, it allows most of the signal to propagate and so represents a strong connection between the neurons. This is a working imitation of the integrate-and-fire model of the neuron and the plasticity of the synapse!

Once they could confirm that their model of the neural network really did behave like it was supposed to, they tested to see if this network could actually learn things like a human! They tested to see if it could learn to recognise the letter ‘A’ if it was told “this is the what the letter ‘A’ looks like” (supervised learning), and they also tested to see if it could just figure out what the letter ‘A’ looks like after handing it a couple of pictures of it (unsupervised learning).

But now that they were confident it can do both, how could such a network be scaled up to perform more complicated tasks? They took one system and connected it up in many layers by connecting the output signal of one layer to the input signal of the other. By processing each layer step by step, they found that this network could indeed take on more complicated tasks.

1. 8

2. a. 87; b. 160; c. 0.54