A Word about Cryptic Refugia

Dryas Octapetalus - Mountain Avens
namesake of the Young Dryas

Temperate species expanded and contracted with temperature fluxes during glacial cycles. Many cold-tolerant species that survived in northern cryptic refugia had larger distributions: the Arctic Fox (Alopex lagopus), the reindeer (Rangifer tarandus) the little white flower Dryas octapetala (pictured left) and dwarf birch (Betula nana). These species expanded during glacials and contracted during interglacials.   With impending global warming, their contracted distributions may well retreat into isolated cooler refugia just as the reverse is true for heat-loving plants.  Recent phylogeographic studies have given support to the existence of previously unknown, or cryptic, refugia during the LGM  Provan (2008)

        The Arctic Fox (Alopex lagopus)

Phylogeographic evidence indicates there was a major northern refugium for a variety of taxa in the area around the Carpathians, with divergent lineages in the region, many predating the LGM.

The existence of a Carpathian refugium characterized by mixed deciduous and coniferous woodland, often on milder south facing slopes is supported by the fossil record and palyncological studies.  Its role in the postglacial colonization of Northern and Western Europe has only become apparent with genetic analysis. 

The Carpathian Mountains  

The Carpathians were a cryptic refugium for Carpathians Regions of mixed coniferous and deciduous woodland as well as Microtus agrestis (field vole) Jaarola (2008), Clethriononys glareolus (bank vole), Kotlik (2006) Vipera berus (adder) Ursenbacher (2006), Triturus spp. (newts) Babik (2005)  Rana arvalis (moor frog).  

The Carpathians are a chain of mountains stretching in an arc from the Czech Republic, Slovakia, Poland, Hungary, Ukraine to Romania. The highest range is theTatras Mtns on the border of Poland and Slovakia.  

Northern North America ice-free regions in the Canadian high Arctic and between the Laurentide and Cordilleran ice sheets was a cryptic refugia for Dryas integrifolia (plant) Tremblay (1999), Ovis spp. (mountain sheep), Loehr (2006) Lagopus mutus (rock ptarmigan), Holder (2000) Dicrostonyx groenlandicus (collared lemming) Federov (2002) and Packera spp. (plants) Golden (2000) .

In the English Channel, the Hurd Deep, or surrounding trenches, which might have
persisted as ‘marine lakes’ were the cryptic refugia for Ascophyllum nodosum (seaweed), Olsen (2010)  Fucus serratus (seaweed) (Coyer, 2003) Palmaria palmata (seaweed) Provan (2005)

In the last few years,  many pieces of the European Cryptic Refugia puzzle have come from phylogeoraphic research by many dedicated scholars -  associating patterns of gene geneology with geographic distributions. 

Fish migrate south to warmer waters during the LGM

Archaeozoological finds  of marine and amphihaline fish remains from the Last Glacial Maximum (LGM)  show evidence of very different species ranges compared to the present.

An ecological niche model based on paleoclimatic reconstructions of sea surface temperatures and bathymetry have been used to effectively predict the spatial range of marine fish during the LGM. The results indicate that the ranges of marine fish species now in northwestern Europe were displaced significantly southwards from the modern distribution, challenging an existing paradigm of marine glacial refugia. 

The model presents strong evidence of an invasion of important fish through the Straits of Gibraltar in glacial times, where they were exploited by Palaeolithic populations around the western Mediterranean Sea. Kettle (2010)

The Megalodon Megaselachus megalodon was an enormous shark. It first appeared around 18 million years ago and was found in all oceans of the world from the Miocene until the Mid-Pleistocene.  It became extinct around 1.5 million years ago. It evolved from the Isurus during the Eocene (around 50 million years ago). The first true ancestor was the Carcharocles auriculatus, which was rather smaller. People used to see the Megalodon as ancestor of the modern white shark. It is however, more likely that the Megalodon belongs to a separate genus and is just a distant relative of the modern white shark.

Reconstructed megalodon skeleton 
on display at the Calvert Marine Museum
Solomon, Maryland, USA

This animal dominated the oceans and is regarded one of the largest and most powerful predators of all vertebrate animals to have ever lived. He could reach a length up to 18 metres, dilate its mouth about 2 metres with tail fins  over 4 metres in length and a dorsal fin could reach a length of 2 metres. He had a cosmopolitan distribution, which means that its habitat was spread throughout the entire world, in (almost) every ocean. 

The enormous triangular teeth, with a length of 15 cm (enamel + crown),that have been found, were first believed to be derived from snakes and dragons. It was discovered in 1667, they were in fact, shark teeth.   

Megalodon Tooth

Most fossils are teeth or vertebral columns. Fossils of Megaselachus megalodon have been found near St. Maria Island, the Azores. Avila (2012)

The Sabre-Toothed Salmon (Oncorhynchus rastrosus)
 first appeared near the coast of modern California, during the Miocene, disappearing during the Pleistocene. They travelled up the rivers from the sea to breed. This extinct fish was about 250-300 cm in length. Characteristic for this animal were its fangs, sticking out the tip of its snout. Besides these fangs, the fish had relatively little teeth, which suggests that it ate plankton.

For the eel, this refugium was probably on the Atlantic coasts of Portugal and Morocco.Kettle (2008)  The glacial refuge of the shad is unclear, but remains have been discovered on the upper Tagus River system at Aridos-1 from the Mindel-Riss interglacial approximately 300 ka BP  and  it is likely to have survived the glacial maximum around the Iberian Peninsula and northwest Africa. 

In Southern Spain, the boreal gadid species, haddock Melanogrammus aeglefinus) and pollock (Pollachius pollachius) have been reported for the Cueva de Nerja near Malaga dating to the LGM:  significant because these species are currently found in Northwest Europe, and the southernmost range for haddock and pollock is currently the Bay of Biscay and northern Portugal, respectively. Whitehead (1986)

The most recent analyses of the LGM deposits from the Cueva de Nerja have revealed that the northern gadids (including saithe Pollachius virens, cod Gadus morhua, and ling Molva molva) make up more than 30% of the identified fish remains and thus represented a significant presence among the  fish exploited by Paleolithic hunters with the exploitation of gadids continuing for an extended period of time after the LGM until the early Holocene as sea levels were returning to present levels and sea surface temperatures approached present values.

Atlantic Salmon (Salmo salar)

Among the most spectacular  species range shifts  have been reports of  of Atlantic salmon (Salmo salar) remains in archaeological sites from the Mediterranean drainage basins of France, Spain, and Italy dating from the LGM up to the early Holocene. Additional small art objects unambiguously depicting salmon have been located at the Grand Grotte de Bize on a Mediterranean drainage basin with reports from late Palaeolithic–early Mesolithic sites in France, Spain, and Italy) suggesting  the presence of resident salmon populations in the western Mediterranean Sea.  However recent genetic analysis has shown a mitochondrial DNA variation in Pleistocene and modern Atlantic salmon from the Iberian glacial refugium.

Consuegra (2002)

The current southernmost range of Atlantic salmon in Northwest Europe is Northern Portugal, which indicates that immigrant populations would have had to pass through the Straits of Gibraltar when temperatures in Southern Spain during the LGM were similar to  present day Northern Europe. However, the archaeozoological evidence is contested. Many  sites in southern France are in proximity to Atlantic drainage basins, and it is possible that the Atlantic salmon remains in the Mediterranean watersheds may have been transported as part of a seasonal migration of fishermen.

Europe: Trees or No Trees? A New Emerging Synthesis

The study of biodiversity during the Pleistocene offers many opportunities to assess the impacts of climate change.  

GOAT WILLOW (Salix Caprea) now believed to
have had wide boreal distribution during the LGM

Scientists are fascinated by distributions of European trees in the coldest stages of the last full glacial, especially at isolated locations where some species survived to influence their long-term ancestry and current distributions. For fauna and flora species, the location of their European refugium during the coldest glacial maximum remains a teasing puzzle.  

Emerging evidence from fossil proxies, paleoclimatic modelling and genetic research suggests the traditional paradigm of trees being restricted to S. Europe, especially the 3 southern peninsulas (Iberian, Balkan and Italian) is questionable.  

Evidence includes 151 carbon-14 dated and identified pieces of macrofossil charcoal wood from 40 sites in central and eastern Europe that suggest that during the last full glacial, there were populations of conifers with some deciduous trees growing much further north and east than previously believed.  

Plotted against a new high-resolution millennial time-scale for the interval ∼32–∼16 ka BP in Greenland our evidence shows that coniferous as well as some broadleaf trees were continuously present throughout those interstadial/stadial cycles for which there are adequate data.Willis (2004)

Southern vs. northern refugia hypotheses were investigated by estimating the potential LGM distributions of 7 boreal and 15 nemoral widespread European tree species using species distribution modelling. The models were calibrated using data for modern species distributions and climate and projected onto two LGM climate simulations for Europe. Five modelling variants were implemented.

Broadly consistent results were obtained irrespective of the climate simulation and modelling variant used. Results indicated that LGM climatic conditions suitable for boreal species existed across Central and Eastern Europe and into the Russian Plain. 

In contrast, suitable climatic conditions for nemoral tree species were largely restricted to the Mediterranean and Black Sea regions. Large proportions of these northern and southern regions would have been suitable for a number of boreal or boreal plus nemoral tree species, respectively.

Synthesis:  It is clear that the view of the LGM landscape in Europe as largely treeless, especially north of the Alps, needs to be revised. Trees were probably much more widespread during the LGM than hitherto thought, although patchily distributed at low densities due to low atmospheric CO₂ concentrations and high wind-speeds. 

The findings presented here help explain the occurrence of mammal assemblages with mixtures of forest, tundra and steppe species at many localities in southern Central and Eastern Europe during the LGM, as well as the phylogeographic evidence for the extra-Mediterranean persistence of many boreal species.
Svenning (2008)

Trembling Aspen - Populus Tremuloides propagates by root sprouts, to form enormous clone coloni of one single organism  - Utah's Pando Populus colony has the distinction of being both the oldest (80,000 years old) and heaviest living organism at 6 million kg. 

The northern refugia hypothesis is that trees were distributed much more widely in Europe during the LGM.  According to this hypothesis, trees occurred not only across Southern Europe, but also in the southern parts of Central Europe, a proposal is mainly based on evidence from pollen and plant macrofossil evidence but is also receiving support from phylogeographic studies of certain species (e.g. Silver Burch (Betula pendula and Betula pubescens), Trembling Aspen (Populus tremuloides, and willow (Salix caprea).  These species all show wide boreal pleistocene distributions.  

Betula Pendula -Tiver, Russia

The phylogeographic evidence for nemoral (woodland) tree species appears to be more consistent with the southern refugia hypothesis.

Survival for the non-boreal beech tree Fagus sylvatica  as far north as the Carpathians has been suggested. Late-glacial and post-glacial increases in the number of pollen sites where Fagus was locally present suggests that the area occupied by beech populations expanded exponentially from the glacial refugia for a duration of over 10,000 years, until about 3500 years before present.  Magri (2008)

Glacial refuge areas should be expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. Chloroplast DNA variation was studied in 22 widespread European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. Petit (2003)

Glacial Refugia were hot spots but not melting pots of genetic diversity .... genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugium.

Multispecies genetic divergence of each of the 25 European forests studied. Higher than average values in black circles, lower than average, white circles.  For all forests, divergence levels represented by connecting lines, with continous black lines indicating comparatively high divergence, dotted lines, intermediate divergence.  Altitude is indicated by grey shading (lightest gray 250-500 m with gray intensifying as altitude increases from 500-1000 and over 1000 m).  Past sea levels are indicated by black dotted lines Petit (2003)