beaver,  literature,  wild boar

A mixed population

Today I taught an advanced undergraduate class on Ecosystem Management here at UmU and gave a lecture on reintroduction then led a discussion section. The discussion centered on Martin Goulding’s “Native or Alien? The Case of the Wild Boar in Britain,” which is one of the bright spots in the Invasive and Introduced Plants and Animals: Human Perceptions, Attitudes and Approaches to Management edited collection that I criticised in a previous post.

In our discussion, one of the students commented on how strange it was that the wild boar were seen as aliens and rejected when they were thought to be hybrid animals (wild boar crossed with domestic pig) but after genetic studies showed that continental wild boars were just as genetically mixed, the wild boars in England were native and more acceptable. I completely agree. After all, if it looks like a wild boar and acts like a wild boar, isn’t it close enough to be a wild boar? Maybe, maybe not.

I think with today’s advancing genetic science, conservation decisions are increasingly being made on genetic grounds. I recently read an article about the recommended source of beavers for reintroduction to Great Britain (Halley 2011 in Mammal Review). It turns out that the European beaver (Castor fiber) has been previously divided into 8 subspecies based on the remnant populations that survived to the 20th century. That means that the ones in Norway were classified as C. fiber fiber, the ones along the Elbe as C. fiber albucus, the ones along the Rhône as C. fiber galliae, etc. This was based on very small differences in cranial morphology. I can only think of phrenology here and the attempt to classify people into subspecies by their cranial morphology. It’s funny how the same idea in animal species has been allowed to persist without comment much longer.

Graphic from Halley 2011 showing the similarity of the genes of different beaver populations: (fi) Telemark, (ga) Rhône, (al) Elbe, (bi) Mongolia, (po) Ob, (tu) Yenesei, and (in) Pripet/Voronezh
Graphic from Halley 2011 showing the similarity of the genes of different beaver populations: (fi) Telemark, (ga) Rhône, (al) Elbe, (bi) Mongolia, (po) Ob, (tu) Yenesei, and (in) Pripet/Voronezh

Halley, on the contrary, points out that genetics divide the extant beaver population before the 20th century reintroduction into western and eastern evolutionarily significant units (ESUs). The remnant populations in Norway, Germany and France that survived to the 20th century are all closely related and have low genetic diversity because of the low population levels in the “founder” remnant populations. The eastern populations in Ukraine and Belarus and China are put into another group, although these are much less closely related to each other. This leaves a “hybrid” group with mixes of east and west.

So why does this genetic tree matter? In the IUCN Guidelines for Re-introductions from 1998, it states

the source population should ideally be closely related genetically to the original native stock and show similar ecological characteristics (morphology, physiology, behaviour, habitat preference) to the original sub-population.

Thus, when new reintroduction projects are undertaken, if they are to comply with the guideline, the beavers should be as closely related genetically as possible to the original population of the area.

The problem Halley identifies with this approach is genetic bottlenecks. The beavers in the western ESU all got down to very small populations, and thus may have lost genetic diversity. Reintroducing from a single stock would be “to reintroduce only a fragment of the genetic variability formerly present.” Thus, he advocates that a mixture of beavers from all three of the western refugia stock be used in reintroduction in Great Britain. He also points out that mixing in eastern individuals would maximize genetic diversity, even though such a decision would be contrary to the IUCN guidelines. Halley’s suggestion to bring in eastern stock was vehemently rejected in 2012 by Rosell et al. who argued that such mixing was clearly against the guidelines and should under no circumstances be taken forward.

Where does this leave the beaver in the UK? The trial reintroduction in Scotland includes only beaver from Norway. Perhaps if a full scale reintroduction is undertaken, beavers from the other western groups will be mixed in, but the eastern groups will likely be left out.

To me, dividing the European beaver into genetic groups that shouldn’t be mixed can be dangerous. It seems all too reminiscent of fears about racial mixing in general. While I understand being careful about reintroducing the “wrong” species — like bringing the North American beaver (Castor canadensis) to Europe where it shouldn’t be — eastern and western populations of Castor fiber are still the same species. If the argument is that these beavers shouldn’t interbreed because they are genetically not identical, then from a philosophical position the same should apply to different breeds of dogs or people from different ethic backgrounds — and we all know that such a position is absolutely unacceptable. If there are geographical boundaries that would have kept these populations clearly isolated forever (like what happens in island geographies), then it might be more reasonable to keep them apart, but that’s not the case here. Instead, beavers in the geographical middle of the range are “hybrids” between west and east. It goes to show that the populations regularly mixed in the past and will continue to do so. This mixing may be a critical part of the gene flow that has kept beavers healthy and competitive. Mixing is not the unnatural thing it’s been made out to be.

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