RAPD analysis of genetic variation and dispersal of the moss Bryum argenteum in Ross Island and Victoria Land, Antarctica

The Random Amplified Polymorphic DNA technique was used to assess the level of genetic diversity in Bryum argenteum from Ross Island and southern Victoria Land, Antarctica. Samples were collected from three separate transects, and from other geographically distinct populations within 150 km of Ross Island. Moss growth in two transects, sampled down small exposed meltstream channels at Cape Royds and Cape Chocolate, was very sparse with no other moss colonies found within 0.4 or 4 km, respectively. However, samples from these channels showed similar levels of genetic variation to those from a transect at Granite Harbour, where moss colonies were large, luxuriant and turf-like between boulders. In all transects, high levels of genetic diversity were apparent both within and between colonies, and some spatial relationships were observed down the length of the channels, with more extensive variation at the top than the bottom of two transects. Samples from other sites in the region showed varying but high levels of genetic diversity; overall, the majority showed some clustering according to site of collection, with short-distance dispersal of propagules by water and transmission between sites presumably by wind. The extensive genetic diversity observed appears mainly due to somatic mutation within colonies, with some contribution by immigration of propagules from elsewhere into established colonies. Accepted: 10 January 1999     

RAPD analysis of genetic variation and dispersal of the moss Bryum pseudotriquetrum from Southern Victoria Land, Antarctica

The RAPD technique (Random Amplified Polymorphic DNA) was used to assess the level of genetic diversity in Bryum pseudotriquetrum from Southern Victoria Land, Antarctica. Isolates were collected from two transects, and from several other geographically distinct populations within 150 km of Ross Island. Moss growth in one transect, sampled down a small exposed meltstream channel at Cape Chocolate, was very sparse with no other moss colonies found within several hundred meters. Isolates from this transect showed low levels of genetic variation, with many moss clumps appearing identical; these were probably dispersed by water along the channel. In another transect analysed from Granite Harbour, the moss colonies were large, luxuriant and protected by boulders. These isolates showed considerably higher levels of genetic variability than the Cape Chocolate samples, and both within- and between-clump variation was observed. Samples from other sites showed varying levels of genetic diversity. It appears from these results that the degree of protection from the harsh Antarctic environment can influence not only the type of moss growth, but also the level of genetic diversity. Evidence is presented for both short-distance dispersal by water and long-distance dispersal by wind. Received: 29 December 1997 / Accepted: 10 April 1998     

High levels of genetic variability in the moss Ceratodon purpureus from continental Antarctica, subantarctic Heard and Macquarie Islands, and Australasia

The random amplified polymorphic DNA (RAPD) technique, and DNA sequencing of the conserved nuclear ribosomal DNA internal transcribed spacer region (ITS1-5.8S-ITS2), have been used to assess levels of genetic diversity in the moss Ceratodon purpureus from several locations in Australasia, subantarctic Heard and Macquarie Islands, and continental Antarctica. Populations from Heard and Macquarie Islands and from Antarctica maintain high levels of genetic variation. Both within- and among-colony variation were observed at these locations. DNA sequence analysis showed that samples from the Ross Sea region of Antarctica were most closely related to colonies from Casey and Macquarie Island, and that one colony from Heard Island was most closely related to one from Europe. DNA sequence data separated two Australian populations from the Antarctic and subantarctic group on a dendrogram. Detailed RAPD analysis of a single colony from continental Antarctica demonstrated that mutation probably causes the high variability observed in this moss. DNA sequencing and RAPD analysis are complementary techniques for genetic investigation of Antarctic moss populations.Jenny Ninham was an integral part of this research team for several years. Unfortunately she did not live to see these results published.     

Genetic diversity in the moss Hennediella heimii in Miers Valley, southern Victoria Land, Antarctica

The moss Hennediella heimii constitutes a significant proportion of the terrestrial flora of East Antarctica, especially in the McMurdo Dry Valleys region of southern Victoria Land. This is the first investigation of the extent of genetic variation within a population of H. heimii. Random Amplified Polymorphic DNA has been used to study both genetic diversity and dispersal of this moss in Miers Valley, southern Victoria Land. The results showed that genetic variation does occur in H. heimii (possibly due to increased exposure to UV-B irradiation), even between shoots within single colonies, and that colonies collected from three transects along meltstreams within the valley constitute a single large population. However, comparison with samples of the same species from nearby valleys and sites up to 500 km distant showed that the Miers Valley population is distinct from these other populations. The results also indicate that wind plays a major role in dispersal of H. heimii in this region of Antarctica. Accepted: 2 September 1998     

Genetic variation in Antarctic populations of the moss Sarconeurum glaciale

Sixty-six isolates of the moss Sarconeurum glaciale were collected from sites in continental Antarctica at Ross Island, southern Victoria Land and the Vestfold Hills. Genetic variation within and among the populations was estimated using isozymes and random amplified polymorphic DNA (RAPD) technology. Isozyme results only reproducibly showed variation between the populations with one enzyme; RAPDs indicated significantly higher levels of genetic variability within and among the Vestfold Hills samples than in the Ross Sea region samples. A dendrogram produced from the RAPD bands suggested that the Ross Island and southern Victoria Land samples form one population, and those from the Vestfold Hills form a separate and more variable population, possibly resulting from separate colonisation events on the continent. Received: 15 March 1996 / Accepted: 1 May 1997     

Genetic diversity in the moss Pohlia nutans on geothermal ground of Mount Rittmann, Victoria Land, Antarctica

The only known population of the moss Pohlia nutans in continental Antarctica occurs on geothermally heated ground of volcanic Mt. Rittmann in northern Victoria Land. Colonisation by this bryophyte is due to peculiar environmental characteristics of the geothermal ground, because mosses do not normally grow in Antarctica at such elevations. Specimens from several moss patches within two sites of 80 m² total area were analysed genetically to determine whether they all originated from a single colonisation event, whether the population is genetically diverse, and whether the temperature range of geothermal ground (17-35°C under moss colonies) affects rates of mutation. Both the RAPD technique and DNA sequencing of the conserved nuclear ribosomal RNA 18S-26S ITS region were used to compare this extremely isolated population with specimens of P. nutans from elsewhere in Antarctica. Like the moss Campylopus pyriformis on volcanic Mt. Melbourne, the Pohlia population exhibits low levels of genetic diversity and appears to be derived from a single immigration event followed by vegetative growth, mutation and dispersal.     

Inter-island movements and population differentiation in a pelagic seabird

We used mark-resight data and amplified fragment length polymorphism (AFLP) markers to assess movements and gene flow between Central Pacific breeding colonies of the great frigatebird, Fregata minor. Of 715 adult frigatebirds marked on Tern Island and Johnston Atoll, 21.3% were resighted at other frigatebird colonies at least 582 km away. Mark-resight data indicated regular movement of males and females between Tern Island and Johnston Atoll (873 km apart), and less frequent movements to other islands; no birds marked on Tern or Johnston were seen on Christmas Island, but one was seen in the Philippines, 7627 km from where it was marked. Despite the regular occurrence of interisland movements, Bayesian analyses of AFLP data showed significant genetic differentiation between Tern Island and Johnston Atoll, and more pronounced differentiation between these two islands and the more distant Christmas Island. The AFLP profiles of three birds breeding on Tern Island fell within the profile-cluster typical for Christmas Island birds, both in a nonmetric multidimensional scaling analysis and in a population assignment test, suggesting dispersal events from Christmas Island to Tern Island. Several factors could explain the persistence of genetic structure despite frequent movements between colonies: many movements occurred during the nonbreeding season, many breeding-season movements did not involve mate-acquisition behaviours and individuals that do disperse may be selected against, as suggested by morphometric differences between colonies. The persistence of genetic structure among breeding colonies despite significant interisland movements suggests limits to the effectiveness of migration as a homogenizing force in this broadly distributed, extremely mobile species.     

RAPD profiling of genetic diversity in two populations of the moss Ceratodon purpureus in Victoria Land, Antarctica

Isolates of the moss Ceratodon purpureus were collected down a channel formed by a meltstream waterfall at Granite Harbour in Southern Victoria Land, Antarctica. The RAPD technique was used to analyse the extent of genetic variation within clumps, between clumps, and between this population and specimens of the same species from two other areas in Antarctica (one a few hundred metres away, the other at Edmonson Point, 300 km further north) and from Sydney, Australia. Genetic variation was detected within and among clumps, with some spatial structure to the population within the channel. Isolates from the nearby location were quite closely related, whereas those from Edmonson Point formed an outgroup on a phylogenetic tree of relatedness. Received: 10 June 1997 / Accepted: 30 September 1997     

Population structure and genetic diversity in four tropical tree species in Costa Rica

Despite intensified interest in conservation of tropical forests, knowledge of the population genetics of tropical forest trees remains limited. We used random amplified polymorphic DNA (RAPD) data to evaluate trends in genetic diversity and differentiation for four tropical tree species, Alchornea latifolia, Dendropanax arboreus, Inga thibaudiana and Protium glabrum . These species occur at contrasting population densities along an elevational gradient and we use RAPD and ecological data to examine natural levels of genetic diversity of each species, trends in genetic variability with population density and structure, genetic differentiation along the elevation gradient, and the relationship between genetic diversity and such factors as seed dispersal and pollination syndrome. At the distances we examined (plot distances ranging from 0.8 to 8.6 km) there was very little genetic structuring at any distance along the gradient. All four species exhibited levels of variation expected for spatial distribution, mating system and pollinator syndrome; greater than 96% of the genetic variation occurred within plots for Inga thibaudiana, Protium glabrum and Dendropanax arboreus. Alchornea latifolia only occurred in a single plot. The results of this study contribute to a growing database of genetic diversity data that can be utilized to make predictions about the effect of disturbance and subsequent reductions in population size on genetic variation and structure in tropical tree species.     

The phylogeography of Adelie penguin faecal flora

The gut of animals changes quickly from a totally sterile environment before birth to a numerous and highly diverse microbial community shortly after birth. However, few studies have examined the source of the bacteria colonizing the gut. We used a genetic based approach to investigate the distribution and acquisition of faecal microbial communities by Adelie penguins, Pygoscelis adeliae , breeding in the Ross Sea region of Antarctica by cloning a portion of the 16S rRNA gene and by automated ribosomal intergenic spacer analysis (ARISA). We hypothesized that bacteria were either acquired from the penguins' neighbours or inherited from their ancestors. Samples were collected from Adelie penguin breeding colonies at the north-western edge of the Ross Sea coast through to the southernmost Adelie penguin colonies on Ross Island. Most of the bacterial sequences we obtained were only distantly homologous with previously published sequences. Bacterial taxa appear to have a restricted distribution as the majority of 16S rRNA clones were isolated from only one or two hosts. Faecal bacterial community similarity was strongly negatively correlated with the genetic distance between hosts suggesting that bacterial communities are inherited. There was little support for a correlation between distance between collection sites and community similarity.     

Genetic structure of island populations of the endangered bat <Emphasis Type="Italic">Hipposideros turpis turpis</Emphasis>: implications for conservation

Efforts for the conservation of the endangered bat species Hipposideros turpis turpis in southern Japan are hampered by a lack of information about its biology and natural history and by the increasing effect of human activities. In an attempt to address some of the conservation challenges faced by this species, we studied the genetic structure and dispersal of intra- and interisland populations using six species-specific microsatellite markers. In particular, we sought to establish the relationship between island populations and to define effective management units for conservation. Pairwise co-ancestry index (F _ST) analysis, analysis of molecular variance, and Bayesian clustering suggested the presence of significant genetic differentiation between islands but little differentiation within them. The small Yonaguni Island population appeared to be not only geographically isolated, but also genetically isolated. This population is at the greatest risk of extinction, considering its size and low genetic variation. The larger populations on Iriomote and Ishigaki Islands are genetically related to each other to a greater degree and exhibit higher genetic variation than the Yonaguni Island population. This suggests that these two island populations should be included in a single management unit, while bats from Yonaguni Island should be managed independently and given higher priority for conservation. Actions such as defining vegetation corridors between colonies, as well as building gates at the entrance of the largest known colony, should be included in the conservation agenda of this still poorly known species.     

Identification of polymorphic microsatellite loci in the queenless,ponerine ant Diacamma ceylonense

Diacamma ceylonense is a queenless, ponerine ant whose colonies are headed by a single, mated, egg‐laying worker referred to as the gamergate. Thus, new colonies are a result of dispersal by wingless gamergates. This is expected to influence patterns of colony dispersal and spatial distribution of genetic variablity. In order to facilitate the study of population genetic structure we have identified six unique, polymorphic, microsatellite loci. We have used fluorescence tagged primers to detect polymorphism at these loci.     

Vagrant Subantarctic fur seal at Cape Shirreff,Livingston Island,Antarctica

A vagrant adult male Subantarctic fur seal Arctocephalus tropicalis was observed among Antarctic fur seals A. gazella at Cape Shirreff, Livingston Island, Antarctica, which is located to ~4,190 and ~5,939 km from the nearest breeding colonies of Subantarctic fur seals. Although the colony of origin of this animal and the reason for its movement outside its distribution range are unknown, this sighting shows the high dispersal capacity of this species and provides an insight into possible changes in its distribution. Although this vagrant was not observed with females Antarctic fur seal, news sightings in the future could result in viable hybrid, and introgressive hybridization could represent a threat for Cape Shirreff population recovery, if still the population way to go to recover to presailing levels.     

Multiple colonization and dispersal events hide the early origin and induce a lack of genetic structure of the moss Bryum argenteum in Antarctica

The dispersal routes of taxa with transoceanic disjunctions remain poorly understood, with the potential roles of Antarctica not yet demonstrated. Mosses are suitable organisms to test direct intra‐Antarctic dispersal, as major component of the extant Antarctic flora, with the cosmopolitan moss Bryum argenteum as ideal target species. We analyzed the genetic structure of B. argenteum to provide an evolutionary time frame for its radiation and shed light into its historical biogeography in the Antarctic region. We tested two alternative scenarios: (a) intra‐Antarctic panmixia and (b) intra‐Antarctic genetic differentiation. Furthermore, we tested for evidence of the existence of specific intra‐Antarctic dispersal routes. Sixty‐seven new samples (40 collected in Antarctica) were sequenced for ITS nrDNA and rps4 cpDNA regions, and phylogenetic trees of B. argenteum were constructed, with a focus on its Southern Hemisphere. Combining our new nrDNA dataset with previously published datasets, we estimated time‐calibrated phylogenies based on two different substitution rates (derived from angiosperms and bryophytes) along with ancestral area estimations. Minimum spanning network and pairwise genetic distances were also calculated. B. argenteum was potentially distributed across Africa and Antarctica soon after its origin. Its earliest intra‐Antarctic dispersal and diversification occurred during a warming period in the Pliocene. On the same timescale, a radiation took place involving a dispersal event from Antarctica to the sub‐Antarctic islands. A more recent event of dispersal and diversification within Antarctica occurred during a warm period in the Pleistocene, creating favorable conditions also for its colonization outside the Antarctic continent worldwide. We provide evidence supporting the hypothesis that contemporary populations of B. argenteum in Antarctica integrate a history of both multiple long‐range dispersal events and local persistence combined with in situ diversification. Our data support the hypothesis that B. argenteum has been characterized by strong connectivity within Antarctica, suggesting the existence of intra‐Antarctic dispersal routes.     

Deciphering translocations from relicts in Baranof Island mountain goats: is an endemic genetic lineage at risk?

Human-mediated movement of wildlife is a common practice in North America. Some translocations have occurred where local populations were thought to be extinct or simply not present. In Alaska’s Alexander Archipelago, mountain goats (Oreamnos americanus) were not considered indigenous and were introduced to Baranof Island in 1923. However, a range-wide survey using microsatellites and mitochondrial DNA revealed a distinct genetic subpopulation endemic to the island. In this study, we attempted to clarify the evolutionary history of the mountain goats on Baranof Island by examining sequence variation in the Y chromosome. We first screened five regions of the Y chromosome in a subset of mountain goats from across their native range. We detected a single polymorphic site in the SRY promoter, and subsequently sequenced this gene in 100 mountain goats. A unique Y chromosome polymorphism was restricted to Baranof Island and an area near Haines, Alaska, and not detected in the presumed source population. An island-to-mainland dispersal scenario from a cryptic refugial population during the retreat of the Cordilleran ice-sheet would account for this distribution. Overall, these data support the hypothesis that a glacial relict population of mountain goats was present on the island prior to introduction. Based on a combination of mitochondrial, microsatellite, and Y chromosome data, we recommend recognizing Baranof Island mountain goats as an evolutionary significant unit.     

Long-term isolation and recent range expansion from glacial refugia revealed for the endemic springtail Gomphiocephalus hodgsoni from Victoria Land,Antarctica

We examined the phylogeography of the endemic Antarctic collembolan Gomphiocephalus hodgsoni using allozymes and mitochondrial DNA (mtDNA; COI) to determine if potentially limited dispersal and long-term habitat fragmentation have promoted regional genetic differentiation. Allozyme analyses showed that differentiation among 21 populations within the Ross Dependency was high (FST = 0.55) with two main groups each representing a distinct geographical region: (1) Ross Island and Beaufort Island; and (2) all continental sites. Ross Island populations showed low levels of differentiation (FST = 0.05) and no correlation with geographical distance, suggesting their derivation from a single glacial refuge. By contrast, continental regions revealed moderate levels of differentiation (FST = 0.27) and a strong correlation with geographical distance, indicating a much older history with several refugia likely. Two sympatric allozyme genotypes were found at three continental sites from Taylor Valley and were congruent with two mtDNA haplotypes, implying nonrandom breeding groups. Although haplotype sharing between one Ross Island site (Cape Bird) and one continental site (Granite Harbour) was identified, the clades showed mostly fragmented allopatric distributions. The extensive Pleistocene glaciations, in conjunction with limited dispersal opportunities, appear to have promoted isolation and divergence among the fragmented habitats. Furthermore, the McMurdo Sound appears to be an effective isolating barrier to dispersal. However, we suggest that the unaided dispersal capacity of G. hodgsoni is unlikely to account for the limited mixing of haplotypes across the McMurdo Sound and recent human- or bird-mediated dispersal is highly probable.     

Inbreeding and population structure of the potato cyst nematode (Globodera pallida) in its native area (Peru)

The dispersal abilities and the population genetic structure of nematodes living in the soil are poorly known. In the present study, we have pursued these issues in the potato cyst nematode Globodera pallida, which parasitizes potato roots and is indigenous to South America. A hierarchical sampling regime was conducted in Peru to investigate gene flow on regional, field and plant scales. Multilocus genotypes of single individuals were obtained using eight polymorphic microsatellites markers. Large heterozygote deficiencies were observed at most loci. The limited active dispersal of larvae from their cyst, which favours mating between (half) siblings, could be responsible for this pattern. Within fields, as well as among fields within regions (even 35 km apart), low F(ST) values suggest extensive gene flow. Among fields within regions, only 1.5-4.4% genetic variability was observed. Passive dispersal of cysts by natural means (wind, running water, or wild animals) or by anthropogenic means (tillage, movement of infected seed tubers) is probably responsible for the results observed. Among regions, high F(ST) values were observed. Thus long-range dispersal (more than 320 km apart) is probably limited by major biogeographical barriers such as the mountains found in the Andean Cordillera. These results provide useful information for the management of resistant varieties, to slow down the emergence and spread of resistance-breaking pathotypes.     

Winter migration of rockhopper penguins (Eudyptes c. chrysocome) breeding in the Southwest Atlantic: is utilisation of different foraging areas reflected in opposing population trends?

Rockhopper penguins (Eudyptes chrysocome) breeding on Staten Island, Argentina, were satellite tracked in 2002 and 2003 during the onset of their winter migration. After their moult, the dispersal of 24 birds was monitored for a mean period of 50.0±40.3 days. Birds travelled at a mean velocity of 3.1±1.1 km/h. The mean minimum distance travelled was 1,640±1,425 km; the maximum distance to the colony was generally less than 1,000 km, although one bird travelled more than 2,000 km from the colony. The penguins dispersed over an area totalling about 1.3 million km2, ranging from 50 to 62°S and from 49°W in the Atlantic to 92°W in the Pacific, and covering polar, sub-polar and temperate waters in oceanic regions as well as shelf waters. Despite the very wide dispersal, both temporally and spatially, two important wintering grounds for rockhopper penguins from Staten Island could be identified, both located over shelf regions: one extended from Staten Island to the north along the coast of Tierra del Fuego up to the Magellan Strait; the other was located over the Burdwood Bank, an isolated extension of the Patagonian Shelf to the south of the Falkland Islands. The Drake Passage also appeared to be an important area for wintering penguins, although dispersal was far more widely spread. Comparison with data obtained during winter from rockhopper penguins originating from the Falkland Islands showed that the area off the coast of Tierra del Fuego was used more or less exclusively by birds from Staten Island, whereas the Burdwood Bank was shared with penguins coming from southern colonies in the Falkland Islands. The implications of these findings are discussed with regard to (a) opposing population trends of rockhopper penguins in the Southwest Atlantic, and (b) the urgent need to establish adequate conservation measures for species and habitat protection.     

High connectivity in a long-lived high-Arctic seabird,the ivory gull <Emphasis Type="Italic">Pagophila eburnea</Emphasis>

Species may cope with rapid habitat changes by distribution shifts or adaptation to new conditions. A common feature of these responses is that they depend on how the process of dispersal connects populations, both demographically and genetically. We analyzed the genetic structure of a near-threatened high-Arctic seabird, the ivory gull (Pagophila eburnea) in order to infer the connectivity among gull colonies. We analyzed 343 individuals sampled from 16 localities across the circumpolar breeding range of ivory gulls, from northern Russia to the Canadian Arctic. To explore the roles of natal and breeding dispersal, we developed a population genetic model to relate dispersal behavior to the observed genetic structure of worldwide ivory gull populations. Our key finding is the striking genetic homogeneity of ivory gulls across their entire distribution range. The lack of population genetic structure found among colonies, in tandem with independent evidence of movement among colonies, suggests that ongoing effective dispersal is occurring across the Arctic Region. Our results contradict the dispersal patterns generally observed in seabirds where species movement capabilities are often not indicative of dispersal patterns. Model predictions show how natal and breeding dispersal may combine to shape the genetic homogeneity among ivory gull colonies separated by up to 2800 km. Although field data will be key to determine the role of dispersal for the demography of local colonies and refine the respective impacts of natal versus breeding dispersal, conservation planning needs to consider ivory gulls as a genetically homogeneous, Arctic-wide metapopulation effectively connected through dispersal.     

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax