Sparrows: changing with the times

With very few exceptions, wherever on Earth humans have set up home, sparrows have gone too, and this is a testimony to their incredible ability to adapt. And speaking with Chris Smith, evolutionary biologist Marty Martin from the University of South Florida, thinks it’s genetic plasticity that enables them to do this.

Marty - There are not too many species besides us, cockroaches, pigeons, a few species of rats and some mice that have so many successes in so many places and for about 20 years my group has been interested in trying to figure out why this species is able to do what so few other species seem able to do.

Chris - Can you tell us a bit about the origins of the humble sparrow? Where did it actually come from? How long has it been living alongside us?

Marty - It's been living with us for quite some time. Its origins, the oldest birds of which we have record, come from the Middle East. Many thousands of years ago it started to become quite popular in places where humans are active. There was some really nice work done in back in 2018 showing how the bird had managed to move out of the Middle East into Europe and as it moved its digestive capacity changed to be able to handle the diets it was more likely becoming exposed to. It's a granivorous species, it had always, you know, mostly focused on seeds and things. But as it became more commensal with human populations in Western Europe, it evolved to adjust to those populations.

Chris - Do we only find sparrows then where we find humans or do they actually live away from us under certain circumstances?

Marty - There are not too many places that we find sparrows without people anymore. But there are some exceptions that I find incredibly compelling. We have examples of sparrows living more than a mile underground brought there by miners and fed, you know, occasionally. So they're still in contact with people, but it's only when the miners are coming and going and bringing them food. And then there are some populations that are able to live in regions that are quite isolated from human populations. They tend to be favoring, scrubby sorts of habitats, mostly the edges of grasslands and such where their ancestors would have been. But by and large, the majority of populations now are living where people are.

Chris - And does that give us then a kind of model species to study to tell us how a species co-evolved with humans and adapts to humans? Can it tell us something about how we impact on nature but nature can mould itself around what we do?

Marty - It's becoming more and more popular as a model in that light. I should say that we wrote this paper for a special section on model organisms somewhat reluctantly because the idea of model to an evolutionary biologist, and I am one my PhD is evolutionary biology, it's always been a little bit of a difficult pill to swallow. But that said, this is a species that people have become interested in understanding how it has adjusted as we modify the environments by changing the habitats and sometimes adding more pollutants or pesticides or antibiotics or whatever it might be. There are more and more people interested in figuring out how the house sparrow deals with that as a proxy for how other, at least songbirds, would deal with that. But in a broader sense, it provides an opportunity for understanding two things. One that's more practical about as we change the planet, what types of habitats are wildlife most going to be able to occupy? And what are the mechanisms by which they do that? What has to evolve? What has to be adjusted behaviourally or physiologically for animals to thrive there? And that ends up being very interesting in a basic sense too, because those are ineffective mechanics of evolution. So how a population comes to get to new places, and maybe even ultimately how one species turns into two, has to do with the details by which individuals are moving and succeeding, breeding in new places.

Chris - What do we need to know about them, then? What do you think the big questions are for sparrows, but also birds more broadly that gets an evolutionary biologist like you interested?

Marty - My lab in particular works on something that I'm sure you know your audience has heard many times in the past, these molecular epigenetic mechanisms like DNA methylation. Without going into the details of how that works, for an animal to become bigger or smaller or faster or slower, that involves some level of gene expression and these little methylation marks, these methyl molecules sit on the DNA and influence how genes get expressed. What we're finding is this molecular epigenetic machinery is in a sense providing the species a plasticity that allows it to quickly adjust to new places. And that's compelling to me as an evolutionary biologist, again, because I'd like to know the details by which evolution proceeds, but I think it's really interesting too in the light of other species, especially when we think about how we're changing the climate, we're removing habitat and how will the species that are in those places adjust. Maybe there are some signatures in their genomes that'll help us to direct our management efforts. The sparrow being a guide for the conservation of native species is a pleasant thing to think about.

Chris: - Just sparrows that have the ability to do this or do all birds come with this enhanced ability to be genetically agile in this way and adapt in a more fluid way than say you or I could?

Marty - That's a great question, and in 10 years, I hope to have the answer for you. This field of, it's called ecological epigenetics, is a fairly young field. It's hard to do it in general, but it's especially difficult to do it with wild animals like sparrows for which we've only had a sequenced genome since 2017. It's to be expected that this process of DNA methylation exists in other species, but the propensity for species to use it differently maybe, you know, in the case of house sparrows, we think they have a lot of this stuff, what we call epigenetic potential, whether other species do is years of study yet to come.