RAUK - Archived Forum - Pool Frog reintroduction

I've just heard about the latest plans regarding the pool frog. Reintroductions to Norfolk are planned for 2004, using Swedish stock. The site used may not be the site where the last native pool frogs were known.

There's some background on the pool frog on my site at:

http://www.darkwave.org.uk/~caleb/poolfrog.html

and on the HCT's site at:

http://www.hcontrst.f9.co.uk/noframes/animals/pool_frog.htm

The Biodiversity Action Plan is here:

http://www.ukbap.org.uk/asp/UKPlans.asp?UKListID=545

Have there been any actual peer-reviewed publications on this issue? Anything in, say, the Herpetological Journal?

I am intrigued as to how they reach the decision that Swedish frogs will be more related than from any other part of Europe. I am sure this would be on the same basis the other reintroductions are to take place. But I would like to see a cautious approach to this, with use of good monitoring before and after reintroduction. I think with everyone adding a new species to the reintroduction band wagon, maybe success on each project will be stretched.

Hi Tom,

The main papers supporting the theory that the Norfolk population was native appear to be

Buckley. J. (1986). Water frogs in Norfolk. Transactions of the Norfolk and Norwich Naturalists Society 27:199-211.

Snell, C. (1994). The pool frog: a neglected native? British Wildlife 6:1-4

(Source Beebee. T. and Griffiths. R. (2002) Amphibians and Reptiles, HarperCollinspublishers)

and the discovery by Chris Gleed-Owen of a single pool frog bone of historical origin. It certainly seems that the Norfolk population looked superficially like its Swedish relatives. I also assume that there is good biogeographical evidence supporting that the population was of Swedish origin.

Perhaps Chris can let us know about any progress on the genetic studies being carried out, or point us to the relevant papers.

I'm intrigued as to how it can be ruled out that the Norfolk population might have been introduced in earlier times by human activity, fascinating stuff.

Since the papers Gemma mentioned, Charles Snell and Trevor Beebee have done some DNA studies, as David said. I'm not sure where this has been published, but I was told that preliminary results showed that the Swedish, Norwegian and Norfolk populations were a distinct group, separated from all the others studied.

Julia Wycherley also did some bioacoustic work, comparing calls of pool frogs from various parts of their range, using some recordings of Norfolk frogs from the 1970s. I think these recordings are available from the British Library wildlife sound archives at:

http://www.bl.uk/collections/sound-archive/wild.html

Does sound quite fascinating how the story is being pieced together.

My own personal opinion is that the merit of reintroduction at the present time should be based very much on the current conservation status of the most closely related Swedish meta-populations as I share Toms reservations concerning the import of European stock.

If it is a case that they are under threat a range extension into a possible former isolate seems reasonable enough and also the knowledge gained in doing so might prove quite invaluable. (Such as the work done by the HCT with Natterjacks and the discovery that ephemeral scrapes were the key to successful reintroductions).

If it is a case that the Swedish populations are under no immediate threat I feel that caution would be prudent until such time that the true status of the former Norfolk population can be ascertained and agreed by all authorities to have been of native origin.

Here are some more recent papers supporting the native species status of the pool frog, which also explain a little bit about why the Swedish populations were chosen as a source for re-introductions:

Zeisset I, Beebee TJC (2001). Determination of biogeographical range: an application of molecular phylogeography to the European pool frog Rana lessonae. Proc.R.Soc.Lond B, 268, 933-938.

Wycherley J, Doran S, Beebee TJC (2002). Frog calls echo microsatellite phylogeography in the European pool frog (Rana lessonae). J. Zool. Lond 258, 479-484.

I think with those studies, plus Chris Gleed Owens find of two pool frog bones dating from between 880 to 1060 AD, we have shown that the pool frogs in all likelyhood were a native species in England.

Inga Zeisset

The following report has just been published by English Nature:

English Nature Research Reports Number 585: A population viability analysis for the reintroduction of the pool frog (Rana lessonae) in Britain. By Clair Williams and Richard A. Griffiths

It is available as a hard copy from our Enquiry Service (01733 455100 / 101 / 102) or to download as a PDF from:

http://www.english-nature.org.uk/pubs/publication/PDF/585.pdf

The reintroduction of the pool frog is currently in the final stages of preparation and further news will be posted at a later date.

Jim

I am one of those who are highly sceptical about the native status of the pool frog in Britain.

One area I am seeking clarification is the evidence for native status of the species in Norway, Sweden and Denmark. Together with any archeo/palaeontological evidence in those countries. 

The arguments put foward so far for native status, as summarised in the English Nature bibliography (report 480) are far from conclusive, and  seem to be based on a tiny number of bones (notoriously difficult to identify), and the fact that there are genetic similarities betwen British and Scaninavian populations. If the latter are non-native, where does it leave the English populations?

Regarding earlier comments made on these pages:

a)      Re. GemmaÆs posting (14 Feb. 2003). The similarity between the E. Anglian pool frogs and those of Norway and Sweden was not just superficial and more than one pool frog ilium bone was found. The closeness of external appearance (compared to the European mainland) and voice (see Wycherley et al. under Inga Zeisset's post given earlier) was remarkable.

b)      Regarding John Burton's posting it would be best to read:

Tegelstr÷m, H. & Sj÷gren-Gulve, P. (2004). Genetic differentiation

among northern European pool frog (Rana lessonae) populations.

Herpetological Journal 4: 187-193.

 The authors conclude that the diversity found in Sweden's pool frog populations indicate that they are a relict population rather than being descendants of an introduction, and that the Swedish, Norwegian and British frogs are part of a northern clade.

I am aware of the work quoted by Charles Snell, but none of it addresses some of the key issues. One is what is the origin of the numerous esculenta populations in Sweden? Another is why is it that lessonae does not occur in Denmark or on Bornholm, but apparently does occur in Sweden and Norway?  My original question is also unresolved, viz.: what is the archeological evidence for green frogs in Sweden? I am having difficulty trying to find anything even pre 1940.

The problem with some of the conclusions based purely on genetics (such as an ancient origin for Swedish populations), is that they fly in the face of common sense zoogeography. If we accept the genetic evidence at face value, then the zoogographical explantions need to be overhauled. We can't have it both ways.

I have also seen the mounting evidence since my original post in 2003 and am now aware of the established genetic similarites between what is know known as the northern clade populations.

I also share JA Burton's concerns over the highly fragmented distribution of the northern clade.

Something else that nags me personally, is why if originally native, pool frogs failed to establish themselves more widely in the UK and were only finally recorded in remnant populations in Norfolk? Is there any evidence of particularly specialised habitat requirements for the northern clade to explain this?

This is very useful indeed, and certainly helps. Is there any published references for all this data?

I am still very confused though. If there are populations of esculenta in Swecden, and esculenta is a hybrid, what is it a hybrid between, if the only other species present is lessonae.

And why are there no lessonae in Denmark? 

Re. John Burtons last posting:

The part of Denmark nearest to Sweden (Sjealland) holds triploid, self-fertile populations of the edible frog R. esculenta and Bornholm holds an edible frog û marsh frog complex.  The edible frogs in SW Sweden are, like the Danish population, self-fertile hybrids and do not require the presence of  the pool frog (R. lessonae) or marsh frog (R. ridibunda) to perpetuate themselves.

If Sweden was colonised naturally, the view that Denmark should also hold pool frog populations, is to assume that post-glacial colonisation was a simple matter of south to north migration and also to assume that the pool frog is a generalist (and not a specialist or relict species, as is the case with northern clade pool frogs) as far as habitat is concerned.

We (Snell, C., Tetteh, J., Evans I. H. (in press)) have proposed that, based on the genetic evidence, on reaching the Baltic there was an east to west migration route to Britain with East Anglia as the first area colonised (bear in mind that the S. North Sea was dry land at that point and there were thousands of glacially created ponds ideal for amphibia; the Norfolk pingos being a relict landscape from that time).

Answer (to some extent, hopefully) to GemmaÆs last posting:

The pool frog is far from being a generalist in its habitat preference; in my view also, the pool frog is, among the green frogs, to some extent a pioneer species.  That is to say, it is more cold tolerant and moves more quickly to colonise new ground after the retreat of ice.

Pool frogs, are a relict species in Britain and to remain successful over time, need a large metapopulation structure with many suitable, fairly sunny ponds as they originally had at the Norfolk site which was rich in permafrost-created, pingo pools.  Heavy shading around their breeding ponds is something they cannot tolerate on their range edge as they need high pond temperatures. Research in Sweden has demonstrated the metapopulation dynamics underpinning the turnover in sub-populations in this sort of landscape, and helps to explain why they have a restricted range. The increasing coverage of wild woods, which occurred about 9000 years ago, would probably have affected range penetration across Britain because of higher shading levels. This, and the later declines in average spring and summer temperatures which exacerbated breeding pond temperature problems, would likely have caused a great range reduction. Moreover, the many actions of man had a major impact - including agriculture and the great fen drainages which, starting in the
1600s, still continue today (in which I include modern day borehole water extraction). In fact an early pool frog report (Fowlmere Fen, Cambs in the mid 1800s) was sadly about extinction through fenland drainage. For these reasons it is impossible, at this point, to know with confidence the full extent of their post glacial range in Britain.
However, it should be noted that Chris Gleed-Owen's subfossil finds did include bones from Lincolnshire and Cambridgeshire and the population genetically tested was the Norfolk population which died out in the late 1990s.

The processes leading to the highly fragmented natures of relict populations are well documented. Current distributions are influenced by past colonisation routes; the habitat around them may have changed considerably (naturally or through human action); they manage to persist in few isolated locations with suitable habitat and climatic conditions.
In the case of the last East Anglian population of pool frogs, they were found in the ancient Norfolk pingos and Norfolk has Britain's sunniest and arguably most continental climate. Isolated native populations, particularly near range edges, are not unusual - the sand lizard and natterjack are good examples here in the UK (see also Jan Pr÷jts's post).