Synchronous timing of return to breeding sites in a long-distance migratory seabird with ocean-scale variation in migration schedules

BACKGROUND

Migratory birds generally have tightly scheduled annual cycles, in which delays can have carry-over effects on the timing of later events, ultimately impacting reproductive output. Whether temporal carry-over effects are more pronounced among migrations over larger distances, with tighter schedules, is a largely unexplored question.

METHODS

We tracked individual Arctic Skuas Stercorarius parasiticus, a long-distance migratory seabird, from eight breeding populations between Greenland and Siberia using light-level geolocators. We tested whether migration schedules among breeding populations differ as a function of their use of seven widely divergent wintering areas across the Atlantic Ocean, Mediterranean Sea and Indian Ocean.

RESULTS

Breeding at higher latitudes led not only to later reproduction and migration, but also faster spring migration and shorter time between return to the breeding area and clutch initiation. Wintering area was consistent within individuals among years; and more distant areas were associated with more time spent on migration and less time in the wintering areas. Skuas adjusted the period spent in the wintering area, regardless of migration distance, which buffered the variation in timing of autumn migration. Choice of wintering area had only minor effects on timing of return at the breeding area and timing of breeding and these effects were not consistent between breeding populations.

CONCLUSION

The lack of a consistent effect of wintering area on timing of return between breeding areas indicates that individuals synchronize their arrival with others in their population despite extensive individual differences in migration strategies.

Taking the beat of the Arctic: are lemming population cycles changing due to winter climate?

Reports of fading vole and lemming population cycles and persisting low populations in some parts of the Arctic have raised concerns about the spread of these fundamental changes to tundra food web dynamics. By compiling 24 unique time series of lemming population fluctuations across the circumpolar region, we show that virtually all populations displayed alternating periods of cyclic/non-cyclic fluctuations over the past four decades. Cyclic patterns were detected 55% of the time (n = 649 years pooled across sites) with a median periodicity of 3.7 years, and non-cyclic periods were not more frequent in recent years. Overall, there was an indication for a negative effect of warm spells occurring during the snow onset period of the preceding year on lemming abundance. However, winter duration or early winter climatic conditions did not differ on average between cyclic and non-cyclic periods. Analysis of the time series shows that there is presently no Arctic-wide collapse of lemming cycles, even though cycles have been sporadic at most sites during the last decades. Although non-stationary dynamics appears a common feature of lemming populations also in the past, continued warming in early winter may decrease the frequency of periodic irruptions with negative consequences for tundra ecosystems.

Behavioural responses of breeding arctic sandpipers to ground-surface temperature and primary productivity

Most birds incubate their eggs, which requires time and energy at the expense of other activities. Birds generally have two incubation strategies: biparental where both mates cooperate in incubating eggs, and uniparental where a single parent incubates. In harsh and unpredictable environments, incubation is challenging due to high energetic demands and variable resource availability. We studied the relationships between the incubation behaviour of sandpipers (genus Calidris) and two environmental variables: temperature and a proxy of primary productivity (i.e. NDVI). We investigated how these relationships vary between incubation strategies and across species among strategies. We also studied how the relationship between current temperature and incubation behaviour varies with previous day's temperature. We monitored the incubation behaviour of nine sandpiper species using thermologgers at 15 arctic sites between 2016 and 2019. We also used thermologgers to record the ground surface temperature at conspecific nest sites and extracted NDVI values from a remote sensing product. We found no relationship between either environmental variables and biparental incubation behaviour. Conversely, as ground-surface temperature increased, uniparental species decreased total duration of recesses (TDR) and mean duration of recesses (MDR), but increased number of recesses (NR). Moreover, small species showed stronger relationships with ground-surface temperature than large species. When all uniparental species were combined, an increase in NDVI was correlated with higher mean duration, total duration and number of recesses, but relationships varied widely across species. Finally, some uniparental species showed a lag effect with a higher nest attentiveness after a warm day while more recesses occurred after a cold day than was predicted based on current temperatures. We demonstrate the complex interplay between shorebird incubation strategies, incubation behaviour, and environmental conditions. Understanding how species respond to changes in their environment during incubation helps predict their future reproductive success.

Documenting lemming population change in the Arctic: Can we detect trends?

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective.

Correction to: Documenting lemming population change in the Arctic: Can we detect trends?

In the original published article, some of the symbols in figure 1A were modified incorrectly during the typesetting and publication process. The correct version of the figure is provided in this correction.

Persistence of arctic-alpine flora during 24,000 years of environmental change in the Polar Urals

Plants adapted to extreme conditions can be at high risk from climate change; arctic-alpine plants, in particular, could "run out of space" as they are out-competed by expansion of woody vegetation. Mountain regions could potentially provide safe sites for arctic-alpine plants in a warmer climate, but empirical evidence is fragmentary. Here we present a 24,000-year record of species persistence based on sedimentary ancient DNA (sedaDNA) from Lake Bolshoye Shchuchye (Polar Urals). We provide robust evidence of long-term persistence of arctic-alpine plants through large-magnitude climate changes but document a decline in their diversity during a past expansion of woody vegetation. Nevertheless, most of the plants that were present during the last glacial interval, including all of the arctic-alpines, are still found in the region today. This underlines the conservation significance of mountain landscapes via their provision of a range of habitats that confer resilience to climate change, particularly for arctic-alpine taxa.

Rough-legged buzzards, Arctic foxes and red foxes in a tundra ecosystem without rodents

Small rodents with multi-annual population cycles strongly influence the dynamics of food webs, and in particular predator-prey interactions, across most of the tundra biome. Rodents are however absent from some arctic islands, and studies on performance of arctic predators under such circumstances may be very instructive since rodent cycles have been predicted to collapse in a warming Arctic. Here we document for the first time how three normally rodent-dependent predator species-rough-legged buzzard, arctic fox and red fox - perform in a low-arctic ecosystem with no rodents. During six years (in 2006-2008 and 2011-2013) we studied diet and breeding performance of these predators in the rodent-free Kolguev Island in Arctic Russia. The rough-legged buzzards, previously known to be a small rodent specialist, have only during the last two decades become established on Kolguev Island. The buzzards successfully breed on the island at stable low density, but with high productivity based on goslings and willow ptarmigan as their main prey - altogether representing a novel ecological situation for this species. Breeding density of arctic fox varied from year to year, but with stable productivity based on mainly geese as prey. The density dynamic of the arctic fox appeared to be correlated with the date of spring arrival of the geese. Red foxes breed regularly on the island but in very low numbers that appear to have been unchanged over a long period - a situation that resemble what has been recently documented from Arctic America. Our study suggests that the three predators found breeding on Kolguev Island possess capacities for shifting to changing circumstances in low-arctic ecosystem as long as other small - medium sized terrestrial herbivores are present in good numbers.

Sources of variation in small rodent trophic niche: new insights from DNA metabarcoding and stable isotope analysis

Intraspecific competition for food is expected to increase the trophic niche width of consumers, defined here as their diet diversity, but this process has been little studied in herbivores. Population densities of small rodents fluctuate greatly, providing a good study model to evaluate effects of competition on trophic niche. We studied resource use in five arctic small rodent populations of four species combining DNA metabarcoding of stomach contents and stable isotope analysis (SIA). Our results suggest that for small rodents, the most pronounced effect of competition on trophic niche is due to increased use of secondary habitats and to habitat-specific diets, rather than an expansion of trophic niche in primary habitat. DNA metabarcoding and SIA provided complementary information about the composition and temporal variation of herbivore diets. Combing these two approaches requires caution, as the underlying processes causing observed patterns may differ between methodologies due to different spatiotemporal scales.

Bird communities of the arctic shrub tundra of Yamal: habitat specialists and generalists

Background

The ratio of habitat generalists to specialists in birds has been suggested as a good indicator of ecosystem changes due to e.g. climate change and other anthropogenic perturbations. Most studies focusing on this functional component of biodiversity originate, however, from temperate regions. The Eurasian Arctic tundra is currently experiencing an unprecedented combination of climate change, change in grazing pressure by domestic reindeer and growing human activity.

Methodology/Principal Findings

Here we monitored bird communities in a tundra landscape harbouring shrub and open habitats in order to analyse bird habitat relationships and quantify habitat specialization. We used ordination methods to analyse habitat associations and estimated the proportions of specialists in each of the main habitats. Correspondence Analysis identified three main bird communities, inhabiting upland, lowland and dense willow shrubs. We documented a stable structure of communities despite large multiannual variations of bird density (from 90 to 175 pairs/km²). Willow shrub thickets were a hotspot for bird density, but not for species richness. The thickets hosted many specialized species whose main distribution area was south of the tundra.

Conclusion/Significance

If current arctic changes result in a shrubification of the landscape as many studies suggested, we would expect an increase in the overall bird abundance together with an increase of local specialists, since they are associated with willow thickets. The majority of these species have a southern origin and their increase in abundance would represent a strengthening of the boreal component in the southern tundra, perhaps at the expense of species typical of the subarctic zone, which appear to be generalists within this zone.

The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better?

In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change with the availability of that habitat, resulting in a functional response in habitat use. Here, we investigate the relationship of two specialized herbivores, willow ptarmigan (Lagopus lagopus) and mountain hare (Lepus timidus), to willows (Salix spp.) in three regions of the shrub tundra zone-northern Norway, northern European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets represent a major structural element and are important for herbivores both as food and shelter. Habitat use was quantified using feces counts in a hierarchical spatial design and related to several measures of willow thicket configuration. We document a functional response in the use of willow thickets by ptarmigan, but not by hares. For hares, whose range extends into forested regions, occurrence increased overall with willow cover. The occurrence of willow ptarmigan showed a strong positive relationship to willow cover and a negative relationship to thicket fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be limited by reindeer browsing. In regions with higher cover, in contrast, such relationships were not observed. Differences in predator communities among the regions may contribute to the observed pattern, enhancing the need for cover where willow thickets are scarce. Such region-specific relationships reflecting regional characteristics of the ecosystem highlight the importance of large-scale investigations to understand the relationships of habitat availability and use, which is a critical issue considering that habitat availability changes quickly with climate change and human impact.

Intrapopulation variability shaping isotope discrimination and turnover: experimental evidence in arctic foxes

Background

Tissue-specific stable isotope signatures can provide insights into the trophic ecology of consumers and their roles in food webs. Two parameters are central for making valid inferences based on stable isotopes, isotopic discrimination (difference in isotopic ratio between consumer and its diet) and turnover time (renewal process of molecules in a given tissue usually measured when half of the tissue composition has changed). We investigated simultaneously the effects of age, sex, and diet types on the variation of discrimination and half-life in nitrogen and carbon stable isotopes (δ¹⁵N and δ¹³C, respectively) in five tissues (blood cells, plasma, muscle, liver, nail, and hair) of a top predator, the arctic fox Vulpes lagopus.

Methodology/Principal Findings

We fed 40 farmed foxes (equal numbers of adults and yearlings of both sexes) with diet capturing the range of resources used by their wild counterparts. We found that, for a single species, six tissues, and three diet types, the range of discrimination values can be almost as large as what is known at the scale of the whole mammalian or avian class. Discrimination varied depending on sex, age, tissue, and diet types, ranging from 0.3‰ to 5.3‰ (mean  = 2.6‰) for δ¹⁵N and from 0.2‰ to 2.9‰ (mean  = 0.9‰) for δ¹³C. We also found an impact of population structure on δ¹⁵N half-life in blood cells. Varying across individuals, δ¹⁵N half-life in plasma (6 to 10 days) was also shorter than for δ¹³C (14 to 22 days), though δ¹⁵N and δ¹³C half-lives are usually considered as equal.

Conclusion/Significance

Overall, our multi-factorial experiment revealed that at least six levels of isotopic variations could co-occur in the same population. Our experimental analysis provides a framework for quantifying multiple sources of variation in isotopic discrimination and half-life that needs to be taken into account when designing and analysing ecological field studies.

The importance of marine vs. human-induced subsidies in the maintenance of an expanding mesocarnivore in the arctic tundra

1. Most studies addressing the causes of the recent increases and expansions of mesopredators in many ecosystems have focused on the top-down, releasing effect of extinctions of large apex predators. However, in the case of the northward expansion of the red fox into the arctic tundra, a bottom-up effect of increased resource availability has been proposed, an effect that can counteract prey shortage in the low phase of the multi-annual rodent cycle. Resource subsidies both with marine and with terrestrial origins could potentially be involved. 2. During different phases of a multi-annual rodent cycle, we investigated the seasonal dynamics and spatial pattern of resource use by red foxes across a coast to inland low arctic tundra gradient, Varanger Peninsula, Norway. We employed two complementary methods of diet analyses: stomach contents and stable isotope analysis. 3. We found that inland red foxes primarily subsisted on reindeer carrions during the low phase of a small rodent population cycle. Lemmings became the most important food item towards the peak phase of the rodent cycle, despite being less abundant than sympatric voles. Isotopic signatures of tissue from both predator and prey also revealed that red foxes near the coast used marine-derived subsidies in the winter, but these allochthonous resources did not spillover to adult foxes living beyond 20-25 km from the coast. 4. Although more needs to be learned about the link between increasing primary productivity due to climatic warming and trophic dynamics in tundra ecosystems, we suggest that changes in reindeer management through a bottom-up effect, at least regionally, may have paved the way towards the establishment of a new mesopredator in the tundra biome.

Denning-area fidelity and mitochondrial DNA diversity of female polar bears (Ursus maritimus) in the Barents Sea

Polar bears ( Ursus maritimus Phipps, 1774) show fidelity to general denning areas in subsequent reproductive events. Studying the level and spatio-temporal scale of denning-area fidelity is critical to determine the adaptability of polar bears to climate change. We used mark–recapture data in conjunction with mitochondrial DNA (mtDNA) data to investigate the level of fidelity of polar bears from the Barents Sea population to five maternal denning areas. There was no differentiation in mtDNA haplotype frequencies between denning areas. The fidelity of females to denning areas is at a local geographic scale and small groups of neighboring females (3–13) shared similar haplotypes with higher probability than expected by chance. The transmission of denning-area fidelity is supported by the short distances (≤60.0 km) observed between capture locations of six (out of eight) denning mother–daughter pairs. Moreover, our results suggested that some females (3 out of 13) used different denning areas in subsequent denning events. This behavioral plasticity implies that females are likely to be able to change denning locations if unsuitable ice conditions prevent them from reaching their preferred denning areas. We consider this plasticity an important attribute of polar bears when facing climate change.

The mating system of polar bears: a genetic approach

Parentage analysis data for 583 individuals genotyped at 27 microsatellite loci were used to study the mating system of polar bears ( Ursus maritimus Phipps, 1774) in the Barents Sea area. We discriminated statistically between full and half-siblings identified through only one common parent. We document for the first time multiple paternity in polar bears. We demonstrated for both sexes low fidelity to mating partners over time. We did not detect any significant difference between the age distribution of adult males at capture and the age distribution of males siring cubs. This might indicate that the male’s age and size are less indicative of the reproductive success than previously thought. This is further supported by a rather long mean litter interval of 3.9 years for males siring several litters. The mating system of polar bears in the Barents Sea appears to be promiscuous, usually with a single successful father siring full siblings within a year, but with consecutive litters of a mother being fathered by different males. We discuss how population density, landscape characteristics, and adult sex ratio might influence the mating system of polar bears. This is of particular importance for management decisions such as, e.g., implementing sex ratios in hunting quotas.

Toward understanding the effect of top predators on ecosystems

To what extent top predators - carnivores at the top of food chains - drive or just respond to ecosystem dynamics is a central, but partially unresolved, question in ecology. In this report, we highlight how different research approaches employed in aquatic and terrestrial ecology may have a bearing on how the role of top predators in ecosystems is perceived.

Statistical analysis of amplified fragment length polymorphism data: a toolbox for molecular ecologists and evolutionists

Recently, the amplified fragment length polymorphism (AFLP) technique has gained a lot of popularity, and is now frequently applied to a wide variety of organisms. Technical specificities of the AFLP procedure have been well documented over the years, but there is on the contrary little or scattered information about the statistical analysis of AFLPs. In this review, we describe the various methods available to handle AFLP data, focusing on four research topics at the population or individual level of analysis: (i) assessment of genetic diversity; (ii) identification of population structure; (iii) identification of hybrid individuals; and (iv) detection of markers associated with phenotypes. Two kinds of analysis methods can be distinguished, depending on whether they are based on the direct study of band presences or absences in AFLP profiles ('band-based' methods), or on allelic frequencies estimated at each locus from these profiles ('allele frequency-based' methods). We investigate the characteristics and limitations of these statistical tools; finally, we appeal for a wider adoption of methodologies borrowed from other research fields, like for example those especially designed to deal with binary data.

Pleistocene colonization of afro-alpine 'sky islands' by the arctic-alpine Arabis alpina

The afro-alpine region comprises the high mountains of Ethiopia and tropical East Africa, which represent biological 'sky islands' with high level of endemism. However, some primarily arctic-alpine plants also occur in the afro-alpine mountains. It has been suggested that these plants are Tertiary relicts, but a recent worldwide study of Arabis alpina suggests that this species colonized the region twice during the Pleistocene. Here we investigate the detailed colonization history of A. alpina in the afro-alpine region based on chloroplast DNA sequences from 11 mountain systems. The results confirm the twice-into-Africa scenario. The Asian lineage is confined to the mountains closest to the Arabian Peninsula, on opposite sides of the Rift Valley (Simen Mts and Gara Muleta in Ethiopia), suggesting long-distance dispersal of this lineage. The African lineage is divided into two phylogeographic groups with distinct geographic distribution. The observed pattern is consistent with isolation of the African lineage in at least two interglacial refugia, located on separated highlands, followed by range expansion in cooler period(s), when the afro-alpine habitat extended further down the mountains. Several long-distance dispersal events, also across the Rift Valley, are suggested by single haplotypes observed outside the area occupied by the phylogeographic groups they belonged to.

[Orbital foreign bodies -- diagnostics, therapy and management]

BACKGROUND

Orbital foreign bodies constitute an interdisciplinary challenge, diagnosis being especially difficult because of inconspicuous entrance orifices. Indication for the removal of an orbital foreign body has always to be decided upon individually taking into account the benefits and risks resulting from an operation. The latter is particularly indicated if there are acute and chronic functional restrictions or inflammatory reactions either present or to be expected. The objective of our study was to produce systematic guidelines concerning the therapeutic procedure of dealing with orbital foreign bodies with a view to a benefit-risk assessment.

PATIENTS AND METHODS

Over the last ten years ten patients with an orbital foreign body were treated in our Department, four of them requiring acute attention. CTs were taken of all patients. Only in one case additional MRTs were produced. Eight out of ten patients underwent operation, of which seven resulted in a complete removal of the foreign body. In the case of two patients we decided against an operation after interdisciplinary consultation.

RESULTS

In our view the imaging--providing diagnostics by means of computer tomography is the most promising method for determining a foreign body in the orbit. Decision for an operative removal of a foreign body was invariably taken interdisciplinary in cooperation with an ophthalmologist. Surgical approach was chosen in accordance with the localisation of the foreign bodies. None of the patients suffered from a loss of vision or a restriction of functions as a result of the operation.

CONCLUSIONS

In the indication the foreign material is of essential importance. Orbital foreign bodies that have been present in the tissue for a longer time can be allowed to stay, unless loss of functions are progressive. Loss of vision always being a consequence of the initial trauma.

Verletzungen der ableitenden Tränenwege - primäre und sekundäre operative Versorgung

BACKGROUND

Canalicular lacerations can be the result of sharp or blunt trauma as well as burns of the facial region. The nasolacrimal duct may become obstructed as an after-effect of naso-orbital trauma.

MATERIAL AND METHODS

Main principles of surgical repair of the lacrimal system are reviewed with regard to the outcome of our own patients compared with the literature.

RESULTS

Success rates in the primary repair of traumatic injuries of canalicular system are about 70 to 82 %. 14 of 20 patients who were managed between 1976 and 1980 in our department were cured permanently. 55 of 272 secondary reconstructions of canalicular obstructions (1976 - 1997) were caused by trauma. Conjunctivodacryocystorhinostomy with polyethylene or silicone tubes (1978 - 1999, n = 37, 21 traumatic) had success rates of 61 % and 72 %, respectively. 11 (4.8 %) of 228 dacryocystorhinostomies (1991 - 2000) were necessary as a result of traumatic injuries and achieved a success rate of 87.5 %.

CONCLUSIONS

Canalicular lacerations need urgent primary repair with silicone intubation and special heed to the medial canthal tendon. The success rate of secondary reconstructions of traumatically caused tear-duct system obstructions depends on the microsurgical techniques that were used.

[The use of intracorneal rings in penetrating keratoplasty]

BACKGROUND

The visual rehabilitation after penetrating keratoplasty (PKP) is affected by postoperative corneal astigmatism. Up to now studies were focused on different trephine systems as well as the suture techniques. A new option for reducing postoperative corneal astigmatism could be the implantation of an intracorneal ring.

PATIENTS AND METHODS

Over a period of 2 years we implanted in 20 patients, who were suffering from keratoconus, Fuchs' dystrophy or bullous keratopathy, an 8-mm cobalt-molybdenum-titanium intracorneal ring in a prospective clinical trial. We used the guided trephine system (GTS) for preparation and a 10-0 nylon double running suture. The mean follow-up period was 16.2 months. A control group of 20 additional patients who underwent PKP was randomized. Topographic astigmatism as well as the spherical equivalent was evaluated after 1, 3, 6 and 12 months, respectively.

RESULTS

Although a lower topographic astigmatism in the intracorneal ring group was reached 12 months postoperatively (3.0 dptr., SD 1.2 versus 4.0 dptr., SD 1.8) no statistical significance was found. The spherical equivalent in that group was lower during the complete evaluation period with a hyperopization in both groups as well. We did not see any immunological reactions caused by the ring.

CONCLUSIONS

Whether the intracorneal ring could be a useful addition to PKP is not yet clear. Therefore more patients need to be enrolled and further studies established.

Genetic structure of Siberian lemmings (Lemmus sibiricus) in a continuous habitat: large patches rather than isolation by distance

In a continuous habitat, restricted dispersal and local genetic drift are likely to create a pattern of increasing genetic differentiation with distance. Here, we describe the genetic structure of Siberian lemming (Lemmus sibiricus) populations in a continuous tundra habitat on the western coast of the Taimyr Peninsula, in order to determine the spatial scale at which genetic differentiation and isolation by distance occur. Sampling was carried out at three different geographical scales: (1) a continuous 11 km transect; (2) localities 10-30 km apart; and (3) two localities at 300 and 600 km from the main study area. Two types of genetic markers were used: partial sequences of the mitochondrial DNA control region and four microsatellite loci. On this basis the study populations were genetically quite homogeneous within patches extending over 8 km or more. Contrary to theoretical predictions, no pattern of isolation by distance among patches could be identified. This observation was interpreted as representing populations in migration-drift disequilibrium after a recent major mixing event. The lack of concordance between mtDNA haplotype phylogeny and the geographical distribution of haplotypes supported this interpretation. Spatial autocorrelation among individual genotypes on a local scale was weak and observed only in females, indicating a considerable amount of mostly male-mediated gene flow. Average gene flow per generation was estimated to be in the range of several hundred metres.

Spatial structure of lemming populations (Dicrostonyx groenlandicus) fluctuating in density

The pattern and scale of the genetic structure of populations provides valuable information for the understanding of the spatial ecology of populations, including the spatial aspects of density fluctuations. In the present paper, the genetic structure of periodically fluctuating lemmings (Dicrostonyx groenlandicus) in the Canadian Arctic was analysed using mitochondrial DNA (mtDNA) control region sequences and four nuclear microsatellite loci. Low genetic variability was found in mtDNA, while microsatellite loci were highly variable in all localities, including localities on isolated small islands. For both genetic markers the genetic differentiation was clear among geographical regions but weaker among localities within regions. Such a pattern implies gene flow within regions. Based on theoretical calculations and population census data from a snap-trapping survey, we argue that the observed genetic variability on small islands and the low level of differentiation among these islands cannot be explained without invoking long distance dispersal of lemmings over the sea ice. Such dispersal is unlikely to occur only during population density peaks.

[Prognosis of conjunctivo-dacryocystorhinostomy. Modification with different implant materials]

BACKGROUND

In cases of total canalicular occlusion or the total absence of the lacrimal apparatus the functional restoration requires the repair of a newly created lacrimal system. The intraoperatively reestablisted lacrimal drainage from the conjunctival sac will be maintained by a plastic tube. Beside other criteria the influence of the used inserted materials polyethylene or silicone should be evaluated.

PATIENTS AND METHODS

From 9/1978 to 2/1999 we have been treated and consecutive documented 37 cases of conjunctivodacryocystorhinostomy and its modifications in 36 patients (1mal both eyes). The patients (22 men, 14 women) ranged in age from 9-76 years (mean age of 35.2 years). In a retrospective review results were compared for the following two groups based on the type of used plastic tube: group I: (n = 23); insertion of a polyethylene tube (from 1976-1990); group II: (n = 14) insertion of a silicone tube (from 1991-1998).

RESULTS

Causes of lacrimal drainage system obstruction were trauma (n = 21), malformation (n = 8), chronic inflammation (n = 5) and tumor (n = 2). The following different surgical techniques were performed: conjunctivodacryocystorhinostomy (cdr, n = 23), conjunctivodacryocystostomy (cd, n = 10) and conjunctivorhinostomy (cr, n = 4), (right eye: n = 21, left eye: n = 16). In group I 14 of 23 operations (61%) had successful functional results, in group II 10 of 14 operations (72%), respectively. The polyethylene tubes on the average were maintained for 15 months after surgery (4mal spontaneous removal) and the silicone tubes for 12 months, respectively (4mal spontaneous removal).

CONCLUSION

Traumatic disturbance and congenital defects of canaliculi and surrounding tissue require in the case of any symptoms the surgical reconstruction of the lacrimal pathway. With the introduction of the silicone tube the success rate could be further advanced.

Phylogeography and mitochondrial DNA (mtDNA) diversity in North American collared lemmings (Dicrostonyx groenlandicus)

Variation in the nucleotide sequence of the mitochondrial control region (250 bp) and the cytochrome b region (870 bp) was examined in collared lemmings (Dicrostonyx groenlandicus) from 19 localities in northern Alaska and the Canadian Arctic. The division of D. groenlandicus in two phylogeographical groups with limited divergence across the Mackenzie River is consistent with the separation of this species in more than one refugial area located to the northwest of the Laurentide ice sheet during the last glaciation. Populations of D.groenlandicus from formerly glaciated areas are no less variable than those in nonglaciated areas. Instead, the low intrapopulation and intraregional diversity estimates in D. groenlandicus are probably a result of regional bottleneck events due to range contractions during Holocene warming events. These results are consistent with findings previously reported on collared lemmings (D. torquatus) from the Eurasian Arctic.

Successful early streptokinase thrombolysis of aortocoronary vein grafts

Two patients recently underwent successful early thrombolytic recanalization of thrombosed saphenous vein coronary bypass grafts. This treatment strategy must be weighed against the potential risk of bleeding.