Almost all European species of Mediterranean origin have had their ice-age refugia in at least one of the three major European peninsulas of the Mediterranean area (i.e. Iberia, Italy and the Balkans; Figure 1), and most of the more widespread species had ice-age refugia in all the three of them 4569. In the majority of cases, the populations of these three peninsulas had no or only limited exchange of individuals and thus the populations of these disjuncted areas evolved independently often resulting in three major genetic groups, one for each of these peninsulas as shown for a large number of different animal and plant species 469. These structures were also found in butterflies, as in the chalk-hill blues Polyommatus coridon/hispana complex (Figure 2) 3233, the marbled whites Melanargia galathea/lachesis complex 34 and the adonis blue Polyommatus bellargus 35.

However, some cases became recently known in which no genetic differentiation among these three refugial centres were detected. Thus, the meadow brown Maniola jurtina only shows two major genetic lineages, one Atlantic-Mediterranean lineage and a Central-Eastern-Mediterranean one (Figure 3) 36. These allozyme data are supported by morphological data of the male genitalia and of the wings of both sexes 37. The eastern phylogenetic group most probably is due to considerable gene flow between the Adriatic- and the Pontic-Mediterranean centres during the last ice-age, whereas the Atlantic-Mediterranean area remained isolated. In an allozyme study of the common blue Polyommatus icarus over major parts of Europe no differentiation among the three major European refugial areas has been detected 38, thus supporting constant gene flow for this species on a European scale even during the last ice-age. As the common blue is recently distributed as far north as northern Scandinavia 39 and the arctic parts of Asia 40, a relatively wide European distribution even during glacial periods is feasible, thus making P. icarus not a typical Mediterranean species.

A sub-division of the large Mediterranean refugia, based on chorological analyses, was previously postulated e.g. by Reinig 41. These assumptions have recently been supported by genetic analyses, and a large number of taxa show a strong sub-structuring within the Mediterranean sub-centres such as the Maghreb, Iberia, peninsular Italy, the Balkans and Asia Minor.

The Atlantic-Mediterranean refugial area embraces Iberia and the major part of the Maghreb 2 and thus is divided into an African and a European part by the Strait of Gibraltar, and several examples of strongly differentiated taxa north and south of this sea barrier are known, especially in amphibians as in the genera Pleurodeles, Discoglossus, Alytes, Pelobates, Rana and Salamandra 42434445464748495051. This sea water barrier has permanently existed since the end of the Messinian Salinity Crisis about 5.33 Ma ago 52535455, and thus has strongly impeded the migration of sea water intolerant organisms like amphibians. Nevertheless, strongly differentiated genetic lineages on both sides of the Strait of Gibraltar are also known e.g. in the lizard Psammodromus algirus 56 and the butterfly sibling species complex M. galathea/lachesis 34.

In groups of organisms not being strongly restricted in their dispersal by sea (e.g. reptiles, butterflies) relatively recent (e.g. late Pleistocene) exchange of individuals is known, as in several snakes 5758, turtles 5960, tortoises 61, chameleons 62, butterflies 36, bark beetles 63, but also in the frog Hyla meridionalis 64. The more southern and thus warmer Maghreb more often represented the centre of origin 4757585960616264656667686970 than Iberia 56.

In many cases, the Maghreb populations show remarkable east-west differentiations as in the lizard P. algirus 56, the snake Malpolon monspessulanus 58 and the shrew Crocidura russula 70 most probably representing the frequent existence of eastern and western sub-centres of differentiation. In the turtle Mauremys leprosa, the two Maghreb lineages are separated by the Atlas Mts. in Morocco and Algeria with the southern lineage expanding from southern Morocco to the Mediterranean Sea in Tunisia 60. This distribution matches the Mauretanic-Mediterranean sub-centre postulated by de Lattin 2.

In Iberia, a strong genetic differentiation into a western and an eastern group is also known for a larger number of species as in the case of Pleurodeles newts 474866, Discoglossus frogs 50, the burnet moth Aglaope infausta 71, the lizards P. algirus 56 and perhaps Acanthodactylus erythrurus 72. Paleoclimatology shows that the climatically most favourable areas of Iberia were in disjunct areas in the southwestern and the southeastern parts of the peninsula 73. Therefore, it is most likely that xero-thermophilic species had two disjunct areas of glacial survival and differentiation in the Iberian Peninsula 71. However, several of these and other taxa evolved an even more complex genetic structure beyond this simple east-west split 4650516574757677787980.

Thus, the Iberian lizard species Lacerta schreiberi consists of four major genetic lineages, two coastal clades and two inland clades, most probably representing four disjunct areas of glacial survival in Iberia with only the northern coastal clade becoming expansive during the postglacial 74. Chioglossa lusitanica, an endemic salamander species of northwestern Iberia, has a none-expansive clade in central Portugal and an expansive clade in northern Portugal and northwestern Spain 8182. The western lineage of P. algirus is further divided into a southern and a northern sub-cluster 56. As much as six lineages are distinguished in the western Iberian endemic newt Lissotriton boscai, and three of these lineages are confined to southwestern Portugal 80. These structures strongly support the existence of several sub-refugia in Iberia along the Pleistocene often resulting in remarkable differentiations between genetic lineages.

The southwest of Portugal revealed to be of special importance as refugial area. This is further supported by the rather fine-grained genetic lineages of the cyprinid Squalius aradensis in the Algarve (southern Portugal) 78, and the extremely high haplotype diversity of M. leprosa in southern Portugal 60 underlining the long-term persistence of taxa in this part of Iberia. If postglacial northwards expansions occurred in one of these lineages within Iberia, remarkable genetic impoverishment is the frequently observed result 6063748182 as in other species on the continental scale (see below) 4.

The fire salamander Salamandra salamandra is also present in three lineages in Iberia, one endemic lineage in the south, another in central and northern Iberia, which is the predominant lineage of Europe, and a third one in a limited area in Cantabria that is identical with the one in the southernmost tip of Italy. The origin of the latter is still ambiguous, and the widespread lineage might have entered Iberia only in the postglacial 45. The Timarchia goettingensis complex shows a highly complex genetic structure in Iberia implying a series of vicariance events and differentiation centres for this beetle 7576.

The Adriatic-Mediterranean refugial area is represented by peninsular Italy 2. As the geographical diversity of this area and the total land mass is considerably less in peninsular Italy than in Iberia, the phylogeographical patterns are considerably simpler in the Adriatic- than in the Atlantic-Mediterranean region. Truly Mediterranean species like the bark beetle Tomicus destruens 63 and the Apennine yellow-bellied toad Bombina pachypus 83 only survived in relatively restricted areas of Calabria and Sicily, and only expanded to more northern regions of Italy when the climate warmed in the postglacial; hereby, they lost genetic diversity. Calabria is particularly rich in strongly differentiated lineages, e.g. four in the Italian wall lizard Podarcis sicula 84, two in S. salamandra 45 and two in B. pachypus 83. This underlines the great importance of this area as refugial region and its particular substructure. However, Sicily is not differentiated from Calabria in most cases reflecting the close geographic proximity with the peculiar exception of the hedgehog Erinaceus europaeus showing a remarkable genetic differentiation in Sicily 85.

Apart from differentiation centres in southern Italy, several species also show distinct lineages in the northern part of peninsular Italy, such as the lizard P. sicula 84, the grasshopper Chorthippus parallelus 86, the honey bee Apis mellifera 87, and the asp viper Vipera aspis 88, thus underlining the existence of additional allopatric differentiation centres in this region. In some cases different lineages expanding in Italy from the south and the north (the latter sometimes with their roots outside of Italy) have built up hybrid zones in Italy as in the case of the honey bee 87 and the bark beetle T. destruens 63.

The Pontic-Mediterranean refugial region sensu de Lattin 2 embraces the Balkan Peninsula, Asia Minor and the east coast of the Mediterranean as far south as Palestine. For this area even Reinig 41 suggested a number of sub-centres, a hypothesis which is strongly supported by recent genetic analyses in this region. Thus, often deep genetic splits between the Balkan Peninsula and Asia Minor support the long lasting biogeographic isolation of these two areas as e.g. detected in the hedgehog Erinaceus concolor 8589, the grasshopper C. parallelus 86, the bark beetle T. destruens 63 and most probably the badger Meles meles 90.

Several genetic data sets support Reinig's idea 41 of several sub-centres in the Balkan Peninsula. Thus, phylogeographic work on the pond turtle Emys orbicularis 59, the fire-bellied toad Bombina variegata 91, the hedgehog E. concolor 8589 and the slug Arion fuscus 30 all support an east-west split of the Balkan Peninsula with western Illyrian and eastern Aegean phylogroups. A similar situation was found in the marbled white M. galathea 92. The allozyme analysis of individuals from southeastern Europe support at least three centres of survival along the Mediterranean coasts of the Balkans: the Illyrian Coast, the Aegean Coast and the southwestern coast of the Black Sea. Whether these three centres of dispersal were linked to each other during the Würm ice-age or not is still unknown.

Old splits in the southern Balkan Peninsula even date back to the formation of the mid-Aegean trench (12 to 9 Ma ago) 93. This event has been reported to have acted as a major factor determining the biogeographical patterns of scorpions 9495 and reptiles 9697. In the scorpion Iurus dufoureius this vicariance is mirrored in a western group from the Peloponnisos to Crete island and an eastern clade from Karpathos island to southwestern Turkey 94. In other species, more complex genetic patterns evolved with localised endemic lineages especially in the long-term isolated islands of the southern Kyklades and Crete as in the scorpion Mesobuthus gibbosus 95, Podarcis lizards 9697 and land snails 9899.

The postglacial re-colonisation of Central and Northern Europe by Mediterranean species followed in general four paradigm patterns 5634: (i) the hedgehog (postglacial expansion from all three southern European differentiation centres) 100, (ii) the bear (expansion of the western and the eastern lineage, but trapping of the Adriatic-Mediterranean lineage by the Alps, nota bene that the expansion of the eastern lineage in the bear example is not from the Pontic-Mediterranean region but from an eastern continental differentiation centre) 101, (iii) the butterfly (expansion of the Adriatic- and the Pontic-Mediterranean lineages, but trapping of the Atlantic-Mediterranean lineage by the Pyrenees) 34 and (iv) the grasshopper (major expansion to Central Europe only from the Balkans and trapping of the Atlantic- and Adriatic-Mediterranean lineages by the Pyrenees and Alps, respectively) 86.

These paradigms are frequently repeated in many animal and plant species, thus the "hedgehog" paradigm e.g. in oaks Quercus ssp. 102, the silver fir Abies alba 103 and the house mouse Mus musculus 104, the "bear" in e.g. the shrews Sorex araneus 105106 and Crocidura suaveolens 9 and the water vole Arvicola terrestris 9 and the "grasshopper" e.g. in the black alder Alnus glutinosa 107, the common beech Fagus sylvatica 108 and the newt Triturus cristatus 109. Only three examples are actually known for the "butterfly" paradigm: the marbled whites M. galathea/lachesis complex 34, the chalk-hill blues P. coridon/hispana complex (Figure 2) 33 and, based on a small data set, the adonis blue P. bellargus 35. The latter paradigm might be a common phylogeographical structure for quickly expanding species, so that the Italian lineage might have expanded rapidly, passing westwards south of the Alps and afterwards expanding all over southern France, so that this space had been occupied when individuals of the Iberian lineage started to pass the Pyrenees. However, further examples are needed for this paradigm's support.

The Postglacial range changes had major impact on the genetic conditions of the affected species. Therefore, it is of major importance for the genetic texture whether a species is expanding phalanx like, stepping stone or leptokurtic 110.

In the first case, the species perform only weak genetic differentiation during the process of range expansion, often without loss of genetic diversity. Such structures are characteristic for species with wide ecological amplitudes and were also found in common butterfly species like in the green-veined white Pieris napi 111112, the common blue P. icarus 38, the small tortoiseshell Aglais urticae 113, the meadow brown M. jurtina 36 and the marbled white M. galathea 34. All these species do not show significant losses of their genetic diversity from their expansion centres towards their recent northern distribution border.

On the contrary, stepping stone and leptokurtic dispersal are responsible for the evolution of genetic patterns along the process of expansion often going along with the loss of genetic information during the processes of expansion, as shown for many animal and plant species 114115116117118119120121. Such a genetic structure is characteristic for species with specific habitat requirements so that no phalanx can expand, but only some few individuals reach so far unoccupied emerging habitats, as also known for the chalk-hill blue P. coridon. This species shows a linear loss of genetic diversity from the south to the north in its Pontic-Mediterranean lineage 122 and a stepwise loss of genetic diversity in the Adriatic-Mediterranean lineage (i.e. no loss of genetic diversity over larger distances as from southern France to northeastern France, and abrupt reduction of genetic diversity as a decrease of 10% of the number of alleles resulting from the passing through of the Burgundian Gate between the Vosges and the Jura Mts.) 123.

As a consequence of postglacial range expansion in the group of species of Mediterranean origin, a network of contact zones is spread over Europe (Figure 1). However, these contact zones between different genetic lineages are not randomly scattered over the continent, but show a systematic pattern. Thus, the mountain systems of the Pyrenees and Alps, often acting as dispersal barriers, represent two important areas where different biota met, but also three other regions of Europe show a high number of secondary contact zones between genetic lineages 569: (i) western Central Europe along the French-German border region and along the western Alps (Figure 3), (ii) eastern Central Europe along the eastern borders of Germany and through the eastern Alps and (iii) running east-west through central Scandinavia.

For butterflies, the meadow brown M. jurtina has a typical contact zone in western Central Europe where the Atlantic-Mediterranean lineage meet with the Central-Eastern-Mediterranean group (Figure 3), which is supported by two allozyme studies, the morphology of the male genitalia and three wing patterns 3637. Along the French-German border regions, no natural obstacles are separating these two lineages; apparently, these lineages have met in that area and the populations, once set up by one evolutionary lineage, remained mostly stable over time; however, some hybridisation in Belgium and the Netherlands is possible, based on the morphology of the male genitalia 37.

Evidence for the eastern Central European contact zone exists e.g. for two butterfly species. The two major genetic lineages of the chalk-hill blue P. coridon, based on allozyme analysis and wing patterns, meet in this region (Figure 2) 3233. Mostly all along this contact zone the natural conditions for the survival of this warm-loving species of calcareous grasslands 124125 limit its existence: an acid sandy area in northeastern Germany, acid cold mountains ranges along the Czech-German border region and the watersheds of the eastern Alps 32 so that this contact zone might partly be shaped by natural expansion obstacles too, but not so extreme as in the cases of the Alps and Pyrenees. The Czech-German border mountains also act as contact zone for the woodland ringlet Erebia medusa; these mountains apparently were reached by an eastern and a western lineage early in the postglacial (more details on the molecular biogeography of this continental species in the next chapter), but the high elevations of these mountains could only be colonised by the species some time after its arrival so that the main ridges mostly represent the contact zone between both lineages 126.