Red and Grey Hybridisation

[KeenTeen17]

I recently got into a debate with the family about why do Greys and Red Squirrels not hybridise. I told them that they don't because due to the fact that the Grey is American and the Red is English native. Is this right or have there been recorded hybrids between the 2?

[thunder]

Well, they are in the same genus (Sciurus), but nobody has described a hybrid as far as I know. Perhaps the size difference is a problem.

henrya

[aeshna5]

I'm not aware of any hybrids, but the fact that one is American + the other European alone doesn't make hybridisation impossible; think of all the american Canada x European Greylag hybrids or problems with Ruddy x white-headed Ducks.

However geographical isolation is an evolutionary factor that leads to speciation.

[mbaldw]

I recently got into a debate with the family about why do Greys and Red Squirrels not hybridise.

I've never come across any records of hybrids between these two species, although -- as aeshna5 said -- the fact that one's American and the other is European in origin doesn't preclude hybridization. They certainly have the same number of chromosomes (2n = 40) and, although this is not the only necessary requisite, this does suggest that any hybrids could be fertile. Personally, I'm inclined to think that the reason they don't interbreed is probably related to the observation that the two species generally do not occur sympatrically (i.e. their ranges tend not to overlap, producing a form of geographical isolation). So, the opportunity to interbreed probably doesn't raise itself very often, if at all. Of course, even if their ranges did overlap, merely being in the the same place at the same time doesn't mean that you'd necessarily expect hybridization.

Cheers,
Marc.

[Gaina]

If red and grey ranges don't overlap, I'd be interested to know how the grey passes the parapoxy virus on to the reds.

I've just been reading a bit about the virus and it also occurs in sheep, goats cattle and New Zealand Red Deer.

[mbaldw]

If red and grey ranges don't overlap, I'd be interested to know how the grey passes the parapoxy virus on to the reds.

You're right, I should've worded my response more carefully - sorry about that! Just to clarify, I should've said that their home ranges generally don't overlap significantly, even though the species' distributions might. The populations may be directly adjacent and there may well be some range overlap at the periphery, especially where mutually accessible food is prolific. Nonetheless, I think it's fair to say that for the most part, the two species typically do not intermingle. Assuming that's correct, and given that squirrels tend to focus most of their activity within their core territory, even where there are neighbouring populations of Greys and Reds, the two species probably don't come into direct contact -- and hence don't have the opportunity to mate -- with one another very often (if at all these days, thanks to human intervention). Hence it seems to me that this is a possible reason for the lack of hybridization.

However, as you rightly point out, the fact that the two probably don't bump into each other with any degree of regularity doesn't mean that the two species would never come into contact with each other, or -- more likely, in my opinion -- use the same feeding stations. Additionally, most populations have their share of itinerant individuals, which may pass through the territory/home range of individuals of both species - if one such individual were infectious, this provides opportunity for the virus to spread. Anyway, itinerants aside, Greys have been observed to pilfer Red caches (suggesting they do sometimes enter into Red territories) and, although I've not heard of any recently, there are reports of Red and Greys feeding together. So, with this in mind, it makes sense that one of the leading theories of squirrel poxvirus transmission is that the two species may come into contact with the same contaminated feeders. Given that the virus is very resistant to dessication, it seems logical that the virus could also be passed to other hard surfaces that the two might also come into contact with (e.g. branches where stripping or scent-marking has taken place, or pilfered caches) and this may play a role in its epidemiology. As you point out, there are other species (e.g. some ruminants) that can carry the virus and they may play a role in aiding the spread of the disease within and between populations.

Cheers,
Marc.

[Rob_D]

Even if they were capable of hybridising, sexual selection might stop it happening in nature. Possibly Red's just don't fancy grey's and vice-versa. If that were true, and there were suitable mates of their own species around, they would never try to hybridise. I suspect that squirrel mating is abit more consensual than with ducks?

They certainly have been recorded as being close together - some research papers mentioning that they had been found curled up together in dreys - though they were obviously just good friends

[Gaina]

Originally Posted by mbaldw

You're right, I should've worded my response more carefully - sorry about that! Just to clarify, I should've said that their home ranges generally don't overlap significantly, even though the species' distributions might. The populations may be directly adjacent and there may well be some range overlap at the periphery, especially where mutually accessible food is prolific. Nonetheless, I think it's fair to say that for the most part, the two species typically do not intermingle. Assuming that's correct, and given that squirrels tend to focus most of their activity within their core territory, even where there are neighbouring populations of Greys and Reds, the two species probably don't come into direct contact -- and hence don't have the opportunity to mate -- with one another very often (if at all these days, thanks to human intervention). Hence it seems to me that this is a possible reason for the lack of hybridization.

However, as you rightly point out, the fact that the two probably don't bump into each other with any degree of regularity doesn't mean that the two species would never come into contact with each other, or -- more likely, in my opinion -- use the same feeding stations. Additionally, most populations have their share of itinerant individuals, which may pass through the territory/home range of individuals of both species - if one such individual were infectious, this provides opportunity for the virus to spread. Anyway, itinerants aside, Greys have been observed to pilfer Red caches (suggesting they do sometimes enter into Red territories) and, although I've not heard of any recently, there are reports of Red and Greys feeding together. So, with this in mind, it makes sense that one of the leading theories of squirrel poxvirus transmission is that the two species may come into contact with the same contaminated feeders. Given that the virus is very resistant to dessication, it seems logical that the virus could also be passed to other hard surfaces that the two might also come into contact with (e.g. branches where stripping or scent-marking has taken place, or pilfered caches) and this may play a role in its epidemiology. As you point out, there are other species (e.g. some ruminants) that can carry the virus and they may play a role in aiding the spread of the disease within and between populations.

Cheers,
Marc.

Thanks for the enlightenment, Marc .

[Paul mabbott]

Originally Posted by mbaldw

.......... They certainly have the same number of chromosomes (2n = 40) and, although this is not the only necessary requisite, this does suggest that any hybrids could be fertile.

It's feasible that they might mate and produce offspring but there is surely no chance that the offspring could be fertile. Can anyone think of an example of a mammal (or indeed, vertebrate) where interspecific hybrids were fertile? The sort of thing that happens in plants but very rarely in animals ....

[mbaldw]

No worries, Gaina - it's about time I started making some sense today! I blame the heat I think RobD has the clincher here - even if Red and Grey did come into contact with each other, if no amount of wine, chocolates and flowers (or possibly mast and mating chases in this case!) ignite a 'spark' between them, then nothing's going to happen!

Cheers,
Marc.