Mednyi Island Research Articles

Behavioral Island Syndrome and Its Ecological Drivers in the Mednyi Island Arctic Fox Population

Behavioral Island Syndrome and Its Ecological Drivers in the Mednyi Island Arctic Fox Population

GEOGRAPHIC VARIATIONS IN THE SHAPE OF THE UPPER TOOTHROW OF THE ARTCIC FOX (<i>VULPES LAGOPUS</i> L. 1758): EFFECTS OF ASYMMETRY AND ALLOMETRY

Geographic variations in the shape of the upper cheek toothrow were studied using geometric morphometrics. For this, 288 specimens from 19 localities (North America, Eurasia, and Pacific and Arctic islands) were employed. Monomorphism of the toothrow for mainland foxes, both from North America and Eurasia, as well as the foxes from Greenland and St. Lawrence Island was found. The Arctic foxes of four Pacific island populations, i.e. two from the Commander Islands and two from the Pribilof Islands, differ significantly from the mainland counterparts in toothrow shape. The Arctic foxes from the Mednyi Island, the Bering Island and the Pribilof Islands differ from each other by toothrow shape as well. The Mednyi Island Arctic foxes show the shortest toothrow, a wide hard palate, and the most massive teeth. On the contrary, the Pribilof Islands Arctic foxes are the most small-toothed. Allometry does not affect geographic variations in the shape of the Arctic fox toothrow. High-level fluctuating asymmetry is found in the Mednyi Island and St. George Island Arctic foxes. Most probably the high level of fluctuating asymmetry is conditioned by both the extremely low genetic diversity as the result of a dramatic numbers decline in the recent past and the strong impact of heavy metals as the result of a coastal diet. We suppose that the same reasons. i.e. low genetic diversity and coastal diet, could have determined the high level of fluctuating asymmetry of the Arctic fox toothrow on the St. George Island.

Behavioral island syndrome and its ecological drivers in the Mednyi Island Arctic fox

Reptiles, birds, and mammals inhabiting oceanic islands tend to change many ecological, behavioral, and genetic characteristics. These changes are referred to as the “island syndrome”. The behavioral components of these changes have been little studied so far. Based on a 40-year study of the biology of the Arctic fox (Vulpes lagopus) on the Mednyi Island, we show that the island Arctic foxes changed many behavioral characteristics compared to mainland foxes. They use smaller home ranges, travel shorter daily distances, and their dispersal distance from the natal territory is much smaller. An increase in the family size of the island Arctic foxes, together with a decrease in litter size, leads to an increase in parental and kin investment and increased cooperation between family members. At the same time, the island foxes, to a large extent, lost their fear of humans. These features are consistent with those found in other island populations. On the other hand, in contrast to other island populations, Mednyi Arctic foxes have increased territoriality, apparently in response to an increased risk of infanticide. Furthermore, Mednyi Arctic foxes expose sex-biased dispersal and maternal inheritance of home range, which are absent in the mainland foxes. The sex-biased dispersal can be considered a mechanism for avoiding inbreeding. Comparison with island fox (Urocyon littoralis) populations in the Channel Islands (Southern California) suggests that these traits have evolved under the influence of specific environmental drivers of the Mednyi Island: patchy and highly predictable resource distribution. The particular resource distribution led to the increased importance of another driver, social landscape, and a new behavioral metatrait of the Mednyi fox – increased conservatism in spatial, reproductive, and foraging behavior.

An Individual-Based Model of the Population Dynamics of the Arctic Fox (Vulpes lagopus semenovi) on Mednyi Island, Commander Islands, North Pacific

We have developed a spatially explicit individual-based model that imitates the population dynamics of the Arctic fox on Mednyi Island. In the Red Data Book of the Russian Federation, the Mednyi Arctic fox is listed as an endangered species. The model developed is based on data collected over 19 years of fieldwork. Annual marking of cubs in the study area allowed us to identify up to 80% of animals individually and to collect their life-history data. As a result, we identified the mortality rates of males and females of all age groups, the probabilities of breeding, litter sizes, the sex ratios of animals in different age groups, social structures, dispersion distances, and the patterns of making decisions in the selection of social partners and habitat patches. The model is spatially explicit, i.e., the heterogeneity of the habitat patches is defined in explicit form. The model works with a time step of one year. In simulations, demographic parameters such as population dynamics, population age structure, sex ratio in different age groups, and the structure and size of families conformed to the empirical data. An analysis of the model sensitivity to variations in mortality rates in different age groups showed that the sensitivity to shifts in cub mortality is much higher compared to adults of all age groups. Through increasing the cub mortality rate to 95% over a period of one to five years, we simulated the effect of the otodectic mange epizootic, which was observed in a real population of the Mednyi Arctic fox. The population recovery time after the end of the impact in the simulation was significantly longer compared to field data. We suggest that, in reality, with a low population size, the productivity of the population increases. This feedback that accelerates population recovery has not yet been introduced into the model. In conclusion, we discuss advantages of the individual-based modeling based on long-term field studies.

Sea star from the northwestern Pacific referred to as Henricia aspera Fisher and H. a. robusta Djakonov (Echinodermata, Echinasteridae) is amphiboreal H. oculata (Pennant)

The sea star Henricia oculata (Pennant, 1777) is a common species known from the northern Atlantic for more than two centuries. This species has never been reported from Russian coastline along the Arctic and northwestern Pacific. Here, we report its population from Bering Sea off Mednyi Island of Commander Islands archipelago. DNA barcode of H. oculata from Commander Islands, which is a fragment of mitochondrial 16S rRNA gene, is similar to the barcodes of the specimens from the northeastern Pacific and northern Atlantic. Moreover, all museum collections H. aspera from Russian waters of the Pacific belong to H. oculata because of their morphology. A form known as H. aspera robusta Djakonov, 1958 previously reported from Bering Sea to the Sea of Japan represents closely related lineage to H. oculata, therefore the name robusta Djakonov 1958 is likely a junior synonym of oculata Pennant, 1777 or its Pacific subspecies. In addition, I am recognizing the name H. aspera robusta Djakonov, 1949 as unavailable because its publication does not contain a description or definition that states in words the characters that are purposed to differentiate the taxon, as required by International Code of Zoological Nomenclature, therefore, the lectotype for H. aspera robusta Djakonov, 1958 has been designated. I found no differences between H. aspera and H. a. robusta specimens studied by A.M. Djakonov, who reported H. aspera from Russian waters of the northwestern Pacific. The neotype of Asterias oculata Pennant, 1777 is fixed in this publication.

Severe population bottleneck and cranial morphology change in the Mednyi Island subspecies of Arctic fox Vulpes lagopus (Carnivora: Canidae)

Abstract Arctic foxes, Vulpes lagopus living on Mednyi Island suffered a drastic decline in population size in the late 1970s due to an outbreak of mange epizootic. This dramatic fall in numbers rendered the subspecies endangered, and the concomitant loss of variability resulted in a population bottleneck. Here, we investigate whether differences in cranial morphology between Mednyi Island Arctic foxes and Bering Island Arctic foxes could be attributed to the severe population bottleneck suffered by the Mednyi population in the 1970s. We used morphometric traits as proxies for genetic data to provide estimates of FST. Results show higher FST estimates for the Mednyi population than for the Bering population, which we interpret as a bottleneck signature. FST results also indicate a pattern of divergence between the two populations consistent with random genetic drift. Bottleneck detection is critical for the interpretation of the demographic history of the endangered Mednyi Island Arctic fox, with consequences for conservation management.

Correlates between Feeding Ecology and Mercury Levels in Historical and Modern Arctic Foxes (Vulpes lagopus)

Changes in concentration of pollutants and pathogen distribution can vary among ecotypes (e.g. marine versus terrestrial food resources). This may have important implications for the animals that reside within them. We examined 1) canid pathogen presence in an endangered arctic fox (Vulpes lagopus) population and 2) relative total mercury (THg) level as a function of ecotype (‘coastal’ or ‘inland’) for arctic foxes to test whether the presence of pathogens or heavy metal concentration correlate with population health. The Bering Sea populations on Bering and Mednyi Islands were compared to Icelandic arctic fox populations with respect to inland and coastal ecotypes. Serological and DNA based pathogen screening techniques were used to examine arctic foxes for pathogens. THg was measured by atomic absorption spectrometry from hair samples of historical and modern collected arctic foxes and samples from their prey species (hair and internal organs). Presence of pathogens did not correlate with population decline from Mednyi Island. However, THg concentration correlated strongly with ecotype and was reflected in the THg concentrations detected in available food sources in each ecotype. The highest concentration of THg was found in ecotypes where foxes depended on marine vertebrates for food. Exclusively inland ecotypes had low THg concentrations. The results suggest that absolute exposure to heavy metals may be less important than the feeding ecology and feeding opportunities of top predators such as arctic foxes which may in turn influence population health and stability. A higher risk to wildlife of heavy metal exposure correlates with feeding strategies that rely primarily on a marine based diet.

Impact of historical founder effects and a recent bottleneck on MHC variability in Commander Arctic foxes (Vulpes lagopus).

Populations of Arctic foxes (Vulpes lagopus) have been isolated on two of the Commander Islands (Bering and Mednyi) from the circumpolar distributed mainland population since the Pleistocene. In 1970–1980, an epizootic outbreak of mange caused a severe population decline on Mednyi Island. Genes of the major histocompatibility complex (MHC) play a primary role in infectious disease resistance. The main objectives of our study were to compare contemporary variation of MHC class II in mainland and island Arctic foxes, and to document the effects of the isolation and the recent bottleneck on MHC polymorphism by analyzing samples from historical and contemporary Arctic foxes. In 184 individuals, we found 25 unique MHC class II DRB and DQB alleles, and identified evidence of balancing selection maintaining allelic lineages over time at both loci. Twenty different MHC alleles were observed in mainland foxes and eight in Bering Island foxes. The historical Mednyi population contained five alleles and all contemporary individuals were monomorphic at both DRB and DQB. Our data indicate that despite positive and diversifying selection leading to elevated rates of amino acid replacement in functionally important antigen-binding sites, below a certain population size, balancing selection may not be strong enough to maintain genetic diversity in functionally important genes. This may have important fitness consequences and might explain the high pathogen susceptibility in some island populations. This is the first study that compares MHC diversity before and after a bottleneck in a wild canid population using DNA from museum samples.

The food habits of arctic fox (Alopex lagopus semenovi) reproductive families on mednyi island (Commander Islands)

In total, 1406 samples of scat of 19 arctic fox families and 1755 prey remains collected near the dens of 32 families during the cub rearing period were analyzed. This is the first attempt to evaluate the food use in the population according to averaged data for a large number of families. After the population had passed through the bottleneck, the arctic fox diet changed considerably. Colonies of petrels—the northern fulmar Fulmarus glacialis rodgersii and the storm-petrels Oceanodroma furcata and O. leucorhoa—became the main food source, whereas the use of alternative resources (alcids, cormorants, marine invertebrates, and otarid rookery products) decreased considerably. The following factors are assumed to determine the arctic fox foraging strategy, i.e., the selectivity in food acquisition: (1) passing of the population through the bottleneck; (2) termination of anthropogenic influence due to the liquidation of human settlements on the island; (3) decrease in both the bird populations and abundance of marine invertebrates (sea urchins and mussels); and (4) stable low density of the current arctic fox population. A hypothetical scenario for formation of the foraging specialization in the island population is discussed.

Is alloparenting helpful for Mednyi Island arctic foxes, Alopex lagopus semenovi?

The Arctic Fox Alopex lagopus semenovi population on Mednyi Island is completely isolated and subsists largely by scavenging on seabird colonies, which have remained abundant and spatio-temporally predictable for many years. We compared population data at the beginning of 1976/1978 and some time after 1994-2005, finding an 85% decline in fox numbers due to disease, to assess the effect of population size on social structure. A total of 81 groups of known size and composition was observed during this 29-year period. Overall, helpers (usually non-lactating yearling females) occurred in 25.7% of groups, and in 32.4% of groups there were two or three lactating females. Female engagement in alloparental behaviour decreased, but not statistically significantly, after the decline in population density. Total food availability was apparently constant throughout the study period, and therefore, the amount available per individual was much higher later in the study. Both communally nursing females and helpers brought food and helped to guard the litter. However, the benefits of communal rearing were unclear. While cubs were left without guards significantly more rarely in the groups with an additional adult, the number of cubs weaned per lactating female was greater in groups with one (3.93 +/- 1.60), as opposed to two or three (3.06 +/- 0.92), lactating females. Survival of cubs to 1 year of age in the groups with two lactating females and/or with helpers was lower than that in the families with one lactating female without helpers (22.2% vs 32.2%). Fewer second-generation litters were born to foxes produced by composite families than to those produced by pairs. Reproductive adults producing by pairs had, on average, 1.23 (+/-1.72) second-generation litters. In groups that initially included additional adults, the average number of second-generation litters per reproductive female was 0.21 (+/-0.49) and 0.46 (+/-0.81) litters per male. Thus, according to three measures, increased group size had no apparent positive impact on reproductive success. The increased parental investment and enhanced guarding of the cubs in the larger families could be beneficial under conditions of high population density and a saturated biotope to which the island fox population was presumably adapted before the population crash in the late 1970s.

Genetic monomorphism of the second exon of the DRB1 gene in the major histocompatibility complex of the arctic fox of Mednyi Island (Alopex lagopus semenovi Ognev, 1931)

Genetic monomorphism of the second exon of the DRB1 gene in the major histocompatibility complex of the arctic fox of Mednyi Island (Alopex lagopus semenovi Ognev, 1931)

Genetic polymorphism of commander islands polar foxes Alopex lagopus semenovi Ognev, 1931 and Alopex lagopus beringiensis Merriam, 1902

The polymorphism of the mitochondrial DNA (mtDNA) control region sequence was examined in 30 polar foxes from Bering Island and 30 polar foxes from Mednyi Island. Seven haplotypes were revealed in polar foxes from Bering Island, and one, in polar foxes from Mednyi Island. The age of divergence of these populations (12 000 +/- 600 years) was calculated based on a fragment of the D-loop. In Bering polar foxes, the sequence nucleotide diversity (pi) was 0.003 (S.D. = 0.002), the haplotype diversity h in Bering polar foxes was 0.835 (S.D. = 0.037). The effective number of females n the Bering Island population was estimated as 105 animals.

‘Island syndrome’ in a population of Arctic foxes (Alopex lagopus) from Mednyi Island

AbstractComparative analysis of the biology of insular and mainland populations has demonstrated a number of differences in characteristics of insular populations, termed the ‘island syndrome’. A subspecies of Arctic fox on the Commander Islands (Alopex lagopus semenovi on Mednyi Island) has been isolated for an evolutionarily significant time in small territories at the periphery of the species' range. The number of foxes on Mednyi had been observed to be very high since the islands were discovered in 1741, but a drastic decline in population density in the late 1970s, owing to mange, has left the population low. The aim of the study was to determine whether the Mednyi Arctic fox population exhibited the features expected in an isolated insular population, such as difference in body size, increased population density, larger social groups, lower tendency to disperse and lower fertility, and whether any behavioural changes were evolutionarily reinforced or were a temporal response to current ecological factors on the island. Eight predictions were identified based on the island syndrome, of which the Mednyi Arctic foxes conformed to seven. We suggest a new prediction, namely that the tendency for increased sex dimorphism in dispersal may also be a distinguishing feature of insular populations. All the features displayed by the insular population on Mednyi – conservative use of space, increased tendency to form complex groups, decreased fertility and dispersal – seemed to be preserved regardless of the currently comparatively low populations. Thus, although foxes have been below carrying capacity for at least 10 generations, island syndrome characteristics have persisted.

Effects of food availability on dispersal and cub sex ratio in the Mednyi Arctic fox

Since the Pleistocene, Arctic foxes, Alopex lagopus, on Mednyi Island in the North Pacific have been isolated in a small area with rich food resources and no other terrestrial carnivores. This situation provides an unusually simple system within which the effect of food dispersion on demography and social organisation was examined. We studied the composition, location and dispersal of 67 Arctic fox groups and mapped their major food resources (seabird colonies) during 1994–2000 on Mednyi. We compared our observations with the predictions of models of sex-ratio determination. Our observations are most consistent with the predictions of Julliard's (2000) model, where mothers are expected to produce more offspring of the most dispersing sex in low-quality habitats, and more offspring of the most philopatric sex in high-quality habitats. The polygynous foxes on Mednyi Island lived where the principal food resources were patchily distributed (present on 11% of the shoreline), and cub survival to dispersal age or reproductive adult was higher in rich (25/45) than in poor (24/79) home ranges. Furthermore, dispersal was strongly sex-biased: most females (60%) remained on their natal ranges, whereas very few males (9%) did so. Significantly more female than male cubs (54 compared with 24) emerged from dens in resource rich ranges, whereas the sex ratio on poor ranges was approximately equal (51 females and 56 males). While our observations are also to some extent consistent with the local resource enhancement (LRE) hypothesis (which predicts a bias towards the sex most likely to cooperate with parents), this does not account for the observed spatial variability.

Macrogeographic genetic variability in the Gastropod Mollusk Littorina sitkana from the Northwest Pacific

Variation at four highly polymorphic allozyme loci (inorganic pyrophosphatase, peptidase, and two esterase loci) was examined in 25 settlements of the marine snail Littorina sitkana (Mollusca, Gastropoda). The sampling localities covered a wide part of the species range: from the Peter the Great Bay (the Sea of Japan) at the southwest to the Mednyi Island (Commander Islands) at the northeast. Like other littorines lacking the pelagic stage, L. sitkana was characterized by significant genetic differentiation (G(ST) for the pooled sample was 0.310). Cluster analysis and nonmetric multidimensional scaling conducted on a matrix of pairwise genetic distances between all of the settlements studied revealed four genetically different groups: southern Primorye, northern Prymorye, Sakhalin, and Kuril-Commanders. The population-genetic structure of the L. sitkana settlements is close to that described by the isolation-by-distance and stepping-stone models: the geographic and the genetic distances between the most settlements examined are distinctly correlated.

The Mednyi Arctic foxes: treating a population imperilled by disease

By the early 1990s only 90 individuals of the endangered Arctic fox subspecies Alopex lagopus semenovi, remained. These few survivors are confined to Mednyi Island, part of the Commander Islands chain. The formerly abundant population crashed in the mid-1970s and has never recovered from only 10–15 per cent of its former numbers. In 1983 the Mednyi Island foxes were listed in the Russian Red Data Book. Their demise coincided with the arrival of mange, introduced by seafaring trappers and caused by the mite Otodectes cynotis, which was associated with devastating cub mortality. In 1994, in a unique intervention, we sought to save the population by treating cubs with antiparasitic drugs. That summer, mortality was reduced. A census in 1995 suggested that over-winter survival was at least no worse, although it is too soon to judge whether this intervention can be a route to population recovery.