THE WOOD WHITE BUTTERFLIES IN IRELAND

In the1940s Williams investigated the taxonomy of the Wood White (Leptidea sinapis) in Ireland, mainly studying specimens from Cos Kildare and Dublin. He came to the conclusion that the species in Ireland was different from that found in Britain in relation to a number of fairly subtle markings. He proposed that the Irish butterfly should be raised to the rank of subspecies. Since then (1946) the Wood White in Ireland was been known as Leptidea sinapis sub-species juvernica.

Across Europe seven species of Leptidea (wood white) have now been identified: L. sinapis, L. reali, L. juvernica, L. amurensis, L. morsei, L. lactea and L. duponcheli. The latter four occur in the eastern part of Europe and are quite localised. But L. sinapis appears to be quite widespread on the continent as well as being in both Britain and Ireland. In the 1970s and 1980s Réali, and later Lorkovic, did further work involving dissections of “sinapis”. They concluded that sinapis was not a single species but was really two ‘cryptic’ species. Both species looked identical to the naked eye, did not interbreed and only on the dissection of their genitalia were they found to be separable. The new species was named Leptidea reali Réal’s Wood White after its initial discoverer.

About ten years ago, work by Brian Nelson, Maurice Hughes and Ken Bond showed that both species existed in Ireland with sinapis confined to the limestone pavements of Cos Clare and Galway , i.e. to areas with similar habitat to the Burren. Reali was found to exist elsewhere in Ireland and is often seen on roadsides, in abandoned quarries and locations which are sheltered, in the presence of one of its larval food plants. Both species have so far not been found flying together in Ireland although they have been found less than 10 km apart in a few instances. In addition, they appear to have very similar larval found plant preferences – mainly Meadow Vetchling and Common Bird’s-foot Trefoil. Britain’s only wood white species sinapis  is considered ‘threatened’.

This year, investigations by Spanish and Russian lepidopterists (Dincã and colleagues) have thrown further light on the identity and distributions of the wood whites across Europe, using techniques based on chromosome counts and DNA analysis. Their conclusions are that reali is not in fact a single species but is itself made up of two species now being named reali and juvernica. They are separate entities from sinapis. As, you will now probably have guessed, the species that occurs outside the ‘Burren’ in Ireland is now to be known as Leptidea juvernica,  the Cryptic Wood White or Bánóg choille dhuaithne. So William’s identification skills appear to have been quite exceptional.

The work of *Dincã and his colleagues suggests that 270,000 years ago the common ancestor of these three species split into two. One of these lines eventually evolved into L. juvernica. The other division split again about 120,000 years ago and became what we know today as L. sinapis and L. reali. 27,000 years ago L. sinapis expanded into the territory of L. juvernica. So is L. sinapis in Ireland an interloper that arrived late and since then conditions were never favourable enough to colonise the whole island, or has it more recently contracted in its range and retreated to the ‘Burren’?

* Vlad Dincã, Vladimir A. Lukhtanov, Gerard Talavera & Roger Vila. Unexpected layers of cryptic diversity in wood white Leptidea butteflies. Nature Communications 2:324 DOI: 10.1038/ncomms1329 (2011).