Evolution through bat's eyes

What the loss of colour is revealing about the process of evolution...
27 February 2019

Interview with 

Alexa Sadier, UCLA


Artibeus watsonii bat


Darwin did the hefty lifting when it came to explaining the broad basis of evolution, but now we need to understand at the level of the genetic machinery how this actually works across the species spectrum. Speaking with Chris Smith, UCLA's Alexa Sadier has been doing this by looking at the evolution of the visual systems of bats...

Alexa - We choose bats because bats are really really really diverse. You have a thousand four hundred species approximately, and they all look different in terms of shape, in terms of size, and in terms of colour vision as well. We have a huge difference in terms of that, also in bats. So that's why we choose bats, because of these diversity that can help us to then go broader about other species.

Chris - And what specifically were you asking off the bats? So how did you approach this?

Alexa - The methods, yeah. So first we need to go to the field we need to go where they are, to the tropics. For example Dominican Republic, Puerto Rico or Trinidad, because that's where they live. To catch bats, we put some mist nets - like a big volleyball net - between the trees in the forest and they fly in, and we put some traps in the caves as well. So now we have the bats. We were studying the eyes, so we took some eye samples to see the final protein that is used to see colours.

Chris - Now there's this saying - I know that you're from France but I'm sure the same thing exists there -there's this saying "as blind as a bat". But actually that's not true is it, because bats actually have quite good vision. We should probably really say things like "as blind as a rat", because bats can see quite well can't they?

Alexa - Yeah exactly. They see very well at night, and during the day they can see colours - only two - we can see three. So, yeah, that's something that people don't expect for sure.

Chris - But when you actually begin to probe into these visual pigments that the bats are using to endow them with their vision, what did you learn and how did that inform the overall sort of thesis of this work, which is trying to understand how they've evolved?

Alexa - So we had this idea before that maybe all bats can see two colours: so green and UV; and when we studied that we realised that a lot of bats can see both green and UVB, so they can distinguish colours during the daylight or dim light. But a lot of them can only see green light. So they are a kind of monochromatic, because they can't distinguish colours. What it showed us is one colour is lost in many bats; it just show that losing things it seems to be an important rule during the evolution of species, because you can think that you will gain new things but what we show here is, at the beginning it's likely that we had green and  UV vision in bats and that UV vision was lost independently, repeatedly in different species of bats.

Chris - Do they all lose that visual pigment via the same mechanism? Is it the loss of the gene? Because there are lots of different ways that you can lose something: the gene can go wrong; the process that turns the gene into the physical protein in the cell can go wrong. So there are a range of different ways of losing something. Are they all losing it the same way, or different ways? 

Alexa - So different ways. And that's one of the other main findings of the paper actually. Some of the bats have lost everything from the gene so they don't have a functional gene anymore. Some species have the gene, they have the RNA, but they have lost the protein; and some species are in-between: they have lost the final product, the protein, they have lost the RNA, but they still have a functional gene. So we believe that we are in different steps at the process of losing colour vision in these different species, and it's never done exactly in the same way.

Chris - So what are the implications of this? Obviously you've widened the repertoire of knowledge about this important groups of bats, but what does this tell us in terms of the bigger picture?

Alexa - So first we had this idea about these evolution by what we called parallel losses, which is losing things. But here it inform us how it works. And here we can see it can works at different levels: gene expression, going from the gene to the protein. That's very important because we when we had this idea about having rules to have evolution we really want to understand how it works. Now that we have that, we can apply this idea to many different protein, many different genes and many different other species.


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