Molecular evidence for glacial refugia of mountain plants in the European Alps

Many mountain ranges have been strongly glaciated during the Quaternary ice ages, and the locations of glacial refugia of mountain plants have been debated for a long time. A series of detailed molecular studies, investigating intraspecific genetic variation of mountain plants in the European Alps, now allows for a first synopsis. A comparison of the phylogeographic patterns with geological and palaeoenvironmental data demonstrates that glacial refugia were located along the southwestern, southern, eastern and northern border of the Alps. Additional glacial refugia were present in central Alpine areas, where high-elevation plants survived the last glaciation on ice-free mountain tops. The observed intraspecific phylogeographies suggest general patterns of glacial survival, which conform to well-known centres of Alpine species diversity and endemism. This implies that evolutionary or biogeographic processes induced by climatic fluctuations act on gene and species diversity in a similar way.     

Beyond the Mediterranean peninsulas: evidence of central European glacial refugia for a temperate forest mammal species, the bank vole (Clethrionomys glareolus)

This study details the phylogeographic pattern of the bank vole, Clethrionomys glareolus, a European rodent species strongly associated with forest habitat. We used sequences of 1011 base pairs of the mitochondrial DNA cytochrome b gene from 207 bank voles collected in 62 localities spread throughout its distribution area. Our results reveal the presence of three Mediterranean (Spanish, Italian and Balkan) and three continental (western, eastern and 'Ural') phylogroups. The endemic Mediterranean phylogroups did not contribute to the post-glacial recolonization of much of the Palaearctic range of species. Instead, the major part of this region was apparently recolonized by bank voles that survived in glacial refugia in central Europe. Moreover, our phylogeographic analyses also reveal differentiated populations of bank voles in the Ural mountains and elsewhere, which carry the mitochondrial DNA of another related vole species, the ruddy vole (Clethrionomys rutilus). In conclusion, this study demonstrates a complex phylogeographic history for a forest species in Europe which is sufficiently adaptable that, facing climate change, survives in relict southern and northern habitats. The high level of genetic diversity characterizing vole populations from parts of central Europe also highlights the importance of such regions as a source of intraspecific genetic biodiversity.     

Phylogeography of the Russian flying squirrel (Pteromys volans): implication of refugia theory in arboreal small mammal of Eurasia

A phylogeographical study of the Russian (Siberian) flying squirrel (Pteromys volans) was carried out using the complete mitochondrial (mt) cytochrome b gene sequences with special reference to the refugia theory for the arboreal traits of this species. We examined 31 specimens from 24 localities, resulting in 28 haplotypes. One breeding specimen with a unique haplotype from Hokkaido, Japan was included in the phylogenetic analysis. There were three mtDNA lineages: Hokkaido, Far Eastern, and northern Eurasia. Divergence data among lineages demonstrated that the Hokkaido group separated from the other groups during the Holsteinian interglacial. The phylogeographical pattern of P. volans is different from that previously reported for terrestrial rodents associated with treeless habitats. Unlike grasslands, forests decreased during glaciation and moved southward because of the cold and arid environmental conditions. The glacial refugia of P. volans would have been associated with forest dynamics in the Pleistocene.     

Phylogeographic analysis of the red seaweed Palmaria palmata reveals a Pleistocene marine glacial refugium in the English Channel

Phylogeography has provided a new approach to the analysis of the postglacial history of a wide range of taxa but, to date, little is known about the effect of glacial periods on the marine biota of Europe. We have utilized a combination of nuclear, plastid and mitochondrial genetic markers to study the biogeographic history of the red seaweed Palmaria palmata in the North Atlantic. Analysis of the nuclear rDNA operon (ITS1-5.8S-ITS2), the plastid 16S-trnI-trnA-23S-5S, rbcL-rbcS and rpl12-rps31-rpl9 regions and the mitochondrial cox2-3 spacer has revealed the existence of a previously unidentified marine refugium in the English Channel, along with possible secondary refugia off the southwest coast of Ireland and in northeast North America and/or Iceland. Coalescent and mismatch analyses date the expansion of European populations from approximately 128,000 BP and suggest a continued period of exponential growth since then. Consequently, we postulate that the penultimate (Saale) glacial maximum was the main event in shaping the biogeographic history of European P. palmata populations which persisted throughout the last (Weichselian) glacial maximum (c. 20,000 BP) in the Hurd Deep, an enigmatic trench in the English Channel.     

Production of microcystins in calcareous Mediterranean streams: The Alharabe River,Segura River basin in south-east Spain

The development of epilithic cyanobacteria communities in a Mediterranean calcareous stream in the province of Murcia (SE Spain) was studied during the course of one year in an attempt to clarify the environmental variables that influence the production of microcystins. The predominant cyanobacteria were species of Rivularia, which formed conspicuous colonies throughout the year. Seasonally, other species were abundant: Schizothrix fasciculata, Tolypothrix distorta and Phormidium splendidum. All the species collected produced microcystins to a varying degree (up to five varieties), while the benthic community as a whole produced concentrations as high as 20.45 mg m⁻². At the same time, the presence of microcystins dissolved in water was confirmed. Among environmental variables, air temperature and silicate content were positively and strongly correlated with total microcystins, while nitrite, nitrate, orthophosphate, calcium and flow were negatively correlated with them. Dissolved microcystins were negatively correlated with microcystin LR, P.A.R. and total phosphorus and positively with rainfall. The production of microcystin YR seems to be regulated by different factors from those regulating the other main varieties (microcystin LR and microcystin RR). The data obtained indicate that all the tested benthic cyanobacteria produced microcystins in this shallow calcareous stream, which may contribute to their predominance in the prevailing conditions. The accumulation of microcystins in mucilaginous colonies of other groups of algae poses new questions concerning the possible ecological function of these compounds and needs further study.     

Microdistribution of chironomids (Diptera: Chironomidae) in Alpine streams: an autoecological perspective

Chironomid communities from three glacial and three non-glacial high mountain streams in three Alpine river basins were analyzed (Conca, Niscli, Cornisello, NE Italy, 46°N, 10°E). Eighteen sampling reaches belonging to five stream types (kryal, subkryal, glacio-rhithral, kreno-rhithral, outlet) were investigated. At each reach, geomorphological, physical, chemical and biological data were collected. Field surveys were carried out during three periods per year from 1996 to 1998: immediately after spring snowmelt, in mid-summer and in early autumn. In all, 439 zoobenthos samples were collected from 5 to 10 microhabitats of 0.1m² in each reach and date using a standard pond net (mesh size of 250m). About 50% of individuals collected were chironomids (26673 specimens, 53 taxa), with densities ranging from 4 to 2652indm^–2. With few exceptions, they dominated as number of taxa and individuals in all reaches. Chironomid subfamilies Diamesinae and Orthocladiinae were most abundant, especially in glacial reaches, where Diamesa spp. constituted up to 100% of the total fauna. Chironomid distribution was analyzed in relation to 37 abiotic variables, referring to stream origin, hydrology, geomorphology, physics and chemistry. Diamesa steinboecki, D. latitarsis gr. A and Pseudokiefferiella parva were the taxa best associated with glacial conditions (i.e. high channel instability or presence of bedrock, high suspended solids and total phosphorous content, low conductivity and silica content, highly variable diel discharge and low mean temperature), while Pseudodiamesa branickii, Corynoneura spp., Eukiefferiella spp., Parorthocladius nudipennis, Tvetenia calvescens/bavarica, Thienemaniella spp. and Micropsectra atrofasciata were mostly associated with non-glacial conditions. Substratum particle size, water depth, current velocity, the presence of riffles/pools and of mosses/algae (Hydrurus foetidus) were the major factors affecting microdistribution of chironomids in the investigated streams.     

Diatom Communities and Water Quality Assessment in Mountain Rivers of the Upper Segre Basin (La Cerdanya,Oriental Pyrenees)

Epilithic diatoms of mountain rivers from the upper Segre catchment (Oriental Pyrenees) were studied in 1998, during three different seasons: March, July and September. Four rivers, the river Segre and its three most important tributaries, Duran, Molina and Querol, were sampled in upstream and downstream stretches. The diatom communities were comparable in all upstream stretches of these mountain rivers draining siliceous substrates. Dominant taxa were Achnanthidium subatomus, Diatoma mesodon, Encyonema cf. minutum, E. silesiacum, Fragilaria arcus, F. capucina, Gomphonema calcifugum, G. pumilum, Meridion circulare and Nitzschia pura. Changes in water quality in the downstream stretches lead to the appearance of pollution tolerant taxa, such as Eolimna minima, Gomphoneis minuta, Navicula gregaria, and Nitzschia inconspicua. As a result, the values obtained with the diatom water quality indices (IPS Specific Polluosensitivity Index, CEE and IBD Biological Diatom Index) decreased. The diatom community composition and the derived water quality values did not change in the upstream stretches over the year. In contrast, significant changes were observed in the downstream stretches with best water␣quality in July, during high flows due to melting snow, and worst values in September, during low␣discharge. The diatom indices, especially the IPS, showed a good performance in these mountain rivers.     

Microfaunal communities in three lowland rivers under differing flow regimes

Microfaunal samples were collected from within the channels of three rivers in north eastern Victoria, Australia (the Murray, Ovens and Broken Rivers) as a component of a study examining the effects of flow on the biota of lowland rivers in Australia. Samples were collected from the water column of the river channel and slackwaters and from the layer of water immediately above the bottom sediment of the slackwaters. There was no connectivity between the river channel and the floodplain wetlands for all three rivers during the sampling period. Substantial numbers of microfauna were resident in the slackwaters of all three rivers, with the greatest densities occurring close to the bottom sediment, with densities often exceeding 1000 animals l⁻¹ whereas in the plankton samples densities were usually less than 500 animals l⁻¹. The presence of large and diverse microfaunal communities and the lack of connectivity between the river channel and associated floodplain wetland indicate that these communities are capable of persisting and recruiting within riverine channel slackwaters.     

Conserving biodiversity under climate change: the rear edge matters

Modern climate change is producing poleward range shifts of numerous taxa, communities and ecosystems worldwide. The response of species to changing environments is likely to be determined largely by population responses at range margins. In contrast to the expanding edge, the low-latitude limit (rear edge) of species ranges remains understudied, and the critical importance of rear edge populations as long-term stores of species' genetic diversity and foci of speciation has been little acknowledged. We review recent findings from the fossil record, phylogeography and ecology to illustrate that rear edge populations are often disproportionately important for the survival and evolution of biota. Their ecological features, dynamics and conservation requirements differ from those of populations in other parts of the range, and some commonly recommended conservation practices might therefore be of little use or even counterproductive for rear edge populations.     

Life‐history variability of non‐native centrarchids in regulated river systems of the lower River Guadiana drainage (south‐west Iberian Peninsula)

Life‐history variability of two non‐native centrarchids, pumpkinseed Lepomis gibbosus and largemouth bass Micropterus salmoides, was evaluated in three stream stretches of the lower River Guadiana drainage (south‐west Iberian Peninsula) with different degrees of regulated flows. Abundance, condition and population structure differed among populations for both species, but invasion success was lower in the least regulated river. Lepomis gibbosus were abundant and had multiple age classes in the three river sites, whereas M. salmoides were less abundant and mainly represented by young‐of‐the‐year fish. Juvenile growth in L. gibbosus was similar in all three populations, though longevity was slightly greater in the population from the River Guadiana mainstream. Lepomis gibbosus exhibited a long reproductive season, but the duration of season, size at maturity and reproductive effort varied among populations. The life‐history differences found demonstrate the importance of species adaptation to local conditions which might favour their invasion success. Lepomis gibbosus were more adaptable and resilient to local conditions, whereas M. salmoides seemed dependent on reservoirs and large rivers for maintenance of riverine populations.