Genomic evidence of rapid,global-scale gene flow in a Sulfolobus species

Local populations of Sulfolobus islandicus diverge genetically with geographical separation, and this has been attributed to restricted transfer of propagules imposed by the unfavorable spatial distribution of acidic geothermal habitat. We tested the generality of genetic divergence with distance in Sulfolobus species by analyzing genomes of Sulfolobus acidocaldarius drawn from three populations separated by more than 8000 km. In sharp contrast to S. islandicus, the geographically diverse S. acidocaldarius genomes proved to be nearly identical. We could not link the difference in genome conservation between the two species to a corresponding difference in genome stability or ecological factors affecting propagule dispersal. The results provide the first evidence that genetic isolation of local populations does not result primarily from properties intrinsic to Sulfolobus and the severe discontinuity of its geothermal habitat, but varies with species, and thus may reflect biotic interactions that act after propagule dispersal.     

Fine-scale spatial patterns in bacterial community composition and function within freshwater ponds

The extent to which non-host-associated bacterial communities exhibit small-scale biogeographic patterns in their distribution remains unclear. Our investigation of biogeography in bacterial community composition and function compared samples collected across a smaller spatial scale than most previous studies conducted in freshwater. Using a grid-based sampling design, we abstracted 100+ samples located between 3.5 and 60 m apart within each of three alpine ponds. For every sample, variability in bacterial community composition was monitored using a DNA-fingerprinting methodology (automated ribosomal intergenic spacer analysis) whereas differences in bacterial community function (that is, carbon substrate utilisation patterns) were recorded from Biolog Ecoplates. The exact spatial position and dominant physicochemical conditions (for example, pH and temperature) were simultaneously recorded for each sample location. We assessed spatial differences in bacterial community composition and function within each pond and found that, on average, community composition or function differed significantly when comparing samples located >20 m apart within any pond. Variance partitioning revealed that purely spatial variation accounted for more of the observed variability in both bacterial community composition and function (range: 24–38% and 17–39%) than the combination of purely environmental variation and spatially structured environmental variation (range: 17–32% and 15–20%). Clear spatial patterns in bacterial community composition, but not function were observed within ponds. We therefore suggest that some of the observed variation in bacterial community composition is functionally ‘redundant''. We confirm that distinct bacterial communities are present across unexpectedly small spatial scales suggesting that populations separated by distances of >20 m may be dispersal limited, even within the highly continuous environment of lentic water.     

Phenotypic evolution of dispersal-enhancing traits in insular voles

Evolutionary theory predicts that in metapopulations subject to rapid extinction–recolonization dynamics, natural selection should favour evolution of traits that enhance dispersal and recolonization ability. Metapopulations of field voles (Microtus agrestis) on islands in the Stockholm archipelago, Sweden, are characterized by frequent local extinction and recolonization of subpopulations. Here, we show that voles on the islands were larger and had longer feet than expected for their body size, compared with voles from the mainland; that body size and size-specific foot length increased with increasing geographical isolation and distance from mainland; and that the differences in body size and size-specific foot length were genetically based. These findings provide rare evidence for relatively recent (less than 1000 years) and rapid (corresponding to 100–250 darwins) evolution of traits facilitating dispersal and recolonization in island metapopulations.     

Extremely reduced dispersal and gene flow in an island bird

The Réunion grey white-eye, Zosterops borbonicus, a passerine bird endemic to Réunion Island in the Mascarene archipelago, represents an extreme case of microgeographical plumage colour variation in birds, with four distinct colour forms occupying different parts of this small island (2512 km²). To understand whether such population differentiation may reflect low levels of dispersal and gene flow at a very small spatial scale, we examined population structure and gene flow by analysing variation at 11 microsatellite loci among four geographically close localities (<26 km apart) sampled within the distribution range of one of the colour forms, the brown-headed brown form. Our results revealed levels of genetic differentiation that are exceptionally high for birds at such a small spatial scale. This strong population structure appears to reflect low levels of historical and contemporary gene flow among populations, unless very close geographically (<10 km). Thus, we suggest that the Réunion grey white-eye shows an extremely reduced propensity to disperse, which is likely to be related to behavioural processes.     

The role of anthropogenic dispersal in shaping the distribution and genetic composition of a widespread North American tree species

Dispersal and colonization are among the most important ecological processes for species persistence as they allow species to track changing environmental conditions. During the last glacial maximum (LGM), many cold‐intolerant Northern Hemisphere plants retreated to southern glacial refugia. During subsequent warming periods, these species expanded their ranges northward. Interestingly, some tree species with limited seed dispersal migrated considerable distances after the LGM ~19,000 years before present (YBP). It has been hypothesized that indigenous peoples may have dispersed valued species, in some cases beyond the southern limits of the Laurentide Ice Sheet. To investigate this question, we employed a molecular genetics approach on a widespread North American understory tree species whose fruit was valued by indigenous peoples. Twenty putative anthropogenic (near pre‐Columbian habitations) and 62 wild populations of Asimina triloba (pawpaw), which produces the largest edible fruit of any North American tree, were genetically assayed with nine microsatellite loci. Putative anthropogenic populations were characterized by reduced genetic diversity and greater excess heterozygosity relative to wild populations. Anthropogenic populations in regions that were glaciated during the LGM had profiles consistent with founder effects and reduced gene flow, and shared rare alleles with wild populations hundreds of kilometers away (mean = 723 km). Some of the most compelling evidence for human‐mediated dispersal is that putative anthropogenic and wild populations sharing rare alleles were separated by significantly greater distances (mean = 695 km) than wild populations sharing rare alleles (mean = 607 km; p = .014). Collectively, the genetic data suggest that long‐distance dispersal played an important role in the distribution of pawpaw and is consistent with the hypothesized role of indigenous peoples.     

Between‐patch natal dispersal declines with increasing natal patch size and distance to other patches in the endangered Southern Dunlin Calidris alpina schinzii

Natal dispersal has profound consequences for populations through the movement of individuals and genes. Habitat fragmentation reduces structural connectivity by decreasing patch size and increasing isolation, but understanding of how this impacts dispersal and the functional connectivity of landscapes is limited because many studies are constrained by the size of the study areas or sample sizes to accurately capture natal dispersal. We quantified natal dispersal probability and natal dispersal distances in a small migratory shorebird, the Southern Dunlin Calidris alpina schinzii, with data from two extensively monitored endangered metapopulations breeding in Sweden and Finland. In both metapopulations philopatry was strong, with individuals returning to or close to their natal patches more often than expected by chance, consistent with the patchy distribution of their breeding habitat. Dispersal probabilities were lower and dispersal distances were shorter in Sweden. These results provide a plausible explanation for the observed inbreeding and population decline of the Swedish population. The differences between Sweden and Finland were explained by patch‐specific differences. Between‐patch dispersal decreased with increasing natal patch size and distance to other patches. Our results suggest that reduced connectivity reduces movements of the philopatric Dunlin, making it vulnerable to the effects of inbreeding. Increasing connectivity between patches should thus be one of the main goals when planning future management. This may be facilitated by creating a network of suitably sized patches (20–100 ha), no more than 20 km apart from each other, from existing active patches that may work as stepping stones for movement, and by increasing nest success and pre‐fledging survival in small patches.     

Oceanographic features and limited dispersal shape the population genetic structure of the vase sponge Ircinia campana in the Greater Caribbean

Understanding population genetic structure can help us to infer dispersal patterns, predict population resilience and design effective management strategies. For sessile species with limited dispersal, this is especially pertinent because genetic diversity and connectivity are key aspects of their resilience to environmental stressors. Here, we describe the population structure of Ircinia campana, a common Caribbean sponge subject to mass mortalities and disease. Microsatellites were used to genotype 440 individuals from 19 sites throughout the Greater Caribbean. We found strong genetic structure across the region, and significant isolation by distance across the Lesser Antilles, highlighting the influence of limited larval dispersal. We also observed spatial genetic structure patterns congruent with oceanography. This includes evidence of connectivity between sponges in the Florida Keys and the southeast coast of the United States (>700 km away) where the oceanographic environment is dominated by the strong Florida Current. Conversely, the population in southern Belize was strongly differentiated from all other sites, consistent with the presence of dispersal-limiting oceanographic features, including the Gulf of Honduras gyre. At smaller spatial scales (<100 km), sites showed heterogeneous patterns of low-level but significant genetic differentiation (chaotic genetic patchiness), indicative of temporal variability in recruitment or local selective pressures. Genetic diversity was similar across sites, but there was evidence of a genetic bottleneck at one site in Florida where past mass mortalities have occurred. These findings underscore the relationship between regional oceanography and weak larval dispersal in explaining population genetic patterns, and could inform conservation management of the species.Subject terms: Genetic variation, Ecology     

Intertidal estimates of sea urchin abundance reveal congruence in spatial structure for a guild of consumers

We hypothesized congruence in the spatial structure of abundance data sampled across multiple scales for an ecological guild of consumers that exploit similar nutritional and habitat resources. We tested this hypothesis on the spatial organization of abundance of an herbivorous guild of sea urchins. We also examined whether the amount of local along‐shore rocky habitat can explain the observed spatial patterns of abundance. Standardized estimates of abundance of four intertidal sea urchins—Diadema cf. savignyi, Echinometra mathaei, Parechinus angulosus, and Stomopneustes variolaris—were determined by six observers at 105 sites across 2,850 km of coast of South Africa. For each species and observer, wavelet analysis was used on abundance estimates, after controlling for potential biases, to examine their spatial structure. The relationship between local sea urchin abundance and the amount of upstream and downstream rocky habitat, as defined by the prevailing ocean current, was also investigated. All species exhibited robust structure at scales of 75–220 km, despite variability among observers. Less robust structure in the abundances of three species was detected at larger scales of 430–898 km. Abundance estimates of sympatric populations of two species (D. cf. savignyi and E. mathaei) were positively correlated with the amount of rocky habitat upstream of the site, suggesting that upstream populations act as larval sources across a wide range of scales. No relationship between abundance and habitat size was found for P. angulosus or S. variolaris. Within the range of scales examined, we found robust congruence in spatial structure in abundance at the lower, but not the larger, range of scales for all four species. The relationship between abundance and upstream habitat availability in two species suggests that larval supply from upstream populations was probably the mechanism linking habitat size and abundance.     

Fine-scale spatial genetic structure and gene dispersal in Silene latifolia

Plants are sessile organisms, often characterized by limited dispersal. Seeds and pollen are the critical stages for gene flow. Here we investigate spatial genetic structure, gene dispersal and the relative contribution of pollen vs seed in the movement of genes in a stable metapopulation of the white campion Silene latifolia within its native range. This short-lived perennial plant is dioecious, has gravity-dispersed seeds and moth-mediated pollination. Direct measures of pollen dispersal suggested that large populations receive more pollen than small isolated populations and that most gene flow occurs within tens of meters. However, these studies were performed in the newly colonized range (North America) where the specialist pollinator is absent. In the native range (Europe), gene dispersal could fall on a different spatial scale. We genotyped 258 individuals from large and small (15) subpopulations along a 60 km, elongated metapopulation in Europe using six highly variable microsatellite markers, two X-linked and four autosomal. We found substantial genetic differentiation among subpopulations (global F_ST=0.11) and a general pattern of isolation by distance over the whole sampled area. Spatial autocorrelation revealed high relatedness among neighboring individuals over hundreds of meters. Estimates of gene dispersal revealed gene flow at the scale of tens of meters (5–30 m), similar to the newly colonized range. Contrary to expectations, estimates of dispersal based on X and autosomal markers showed very similar ranges, suggesting similar levels of pollen and seed dispersal. This may be explained by stochastic events of extensive seed dispersal in this area and limited pollen dispersal.     

Do mountain hare populations cycle?

We investigated the occurrence and distribution of multi-annual cycles in abundance of mountain hare populations across a wide area of their range in northern Europe. We analysed 125 time-series of mountain hare abundance indexed from hunting bag records and questionnaire responses from Scotland, Sweden, Finland and Switzerland. We also reanalysed 17 previously published time-series based on hunting bag records and snow track indices from mountain hare populations in Scotland, Norway, Sweden, Finland, Russia and Italy. Autocorrelation analysis showed that 45% of mountain hare populations showed evidence of cycles, characterised by significant negative autocorrelations at half or the whole cycle period. The amplitude and periodicity of cycles varied between and within countries. Time-series in Scotland were characterised by high-amplitude weak cycles with a mean periodicity of nine years but with a range of 4–15 years. Norwegian and Swedish time-series revealed low amplitude weak cycles with a 3–7 year period. Finnish time-series showed low amplitude cycles with a 4–11 year period. Alpine time-series were predominantly non-cyclic, while the limited number of series from Russia showed high amplitude weak cycles with an 8–11 year period. The results reveal that mountain hare populations show a wide range of population dynamics with distinct regional differences in periodicity, amplitude and density dependent structure of cycles. These findings suggest that different factors may limit or regulate mountain hare populations in different regions of Europe thus supporting the results of recent field studies.     

Admixture and Gene Flow from Russia in the Recovering Northern European Brown Bear (Ursus arctos)

Large carnivores were persecuted to near extinction during the last centuries, but have now recovered in some countries. It has been proposed earlier that the recovery of the Northern European brown bear is supported by migration from Russia. We tested this hypothesis by obtaining for the first time continuous sampling of the whole Finnish bear population, which is located centrally between the Russian and Scandinavian bear populations. The Finnish population is assumed to experience high gene flow from Russian Karelia. If so, no or a low degree of genetic differentiation between Finnish and Russian bears could be expected. We have genotyped bears extensively from all over Finland using 12 validated microsatellite markers and compared their genetic composition to bears from Russian Karelia, Sweden, and Norway. Our fine masked investigation identified two overlapping genetic clusters structured by isolation-by-distance in Finland (pairwise F_ST = 0.025). One cluster included Russian bears, and migration analyses showed a high number of migrants from Russia into Finland, providing evidence of eastern gene flow as an important driver during recovery. In comparison, both clusters excluded bears from Sweden and Norway, and we found no migrants from Finland in either country, indicating that eastern gene flow was probably not important for the population recovery in Scandinavia. Our analyses on different spatial scales suggest a continuous bear population in Finland and Russian Karelia, separated from Scandinavia.     

Patterns of pollen dispersal in a small population of the Canarian endemic palm (Phoenix canariensis)

The genetic diversity of small populations is greatly influenced by local dispersal patterns and genetic connectivity among populations, with pollen dispersal being the major component of gene flow in many plants species. Patterns of pollen dispersal, mating system parameters and spatial genetic structure were investigated in a small isolated population of the emblematic palm Phoenix canariensis in Gran Canaria island (Canary Islands). All adult palms present in the study population (n=182), as well as 616 seeds collected from 22 female palms, were mapped and genotyped at 8 microsatellite loci. Mating system analysis revealed an average of 5.8 effective pollen donors (N_ep) per female. There was strong variation in correlated paternity rates across maternal progenies (ranging from null to 0.9) that could not be explained by the location and density of local males around focal females. Paternity analysis revealed a mean effective pollen dispersal distance of ∼71 m, with ∼70% of effective pollen originating from a distance of <75 m, and 90% from <200 m. A spatially explicit mating model indicated a leptokurtic pollen dispersal kernel, significant pollen immigration (12%) from external palm groves and a directional pollen dispersal pattern that seems consistent with local altitudinal air movement. No evidence of inbreeding or genetic diversity erosion was found, but spatial genetic structure was detected in the small palm population. Overall, the results suggest substantial pollen dispersal over the studied population, genetic connectivity among different palm groves and some resilience to neutral genetic erosion and subsequently to fragmentation.     

Longevity and migration distance differ between wild and hand-reared mallards Anas platyrhynchos in Northern Europe

The mallard Anas platyrhynchos is the world’s most widespread and numerous dabbling duck. It is also farmed and released to the wild by the millions each year, but the effects of this on wild populations remain little studied. By using historical national ringing–recovery data from Sweden and Finland, we here address three predictions based on previous studies: (1) longevity is higher in wild than in hand-reared mallards, (2) wild mallards migrate longer than hand-reared, and (3) migration distance in wild ducks surviving long enough to start fall migration has decreased over the last 50 years. Indeed, wild mallards lived longer than hand-reared (19 versus 9 months in Swedish birds and 13 versus 4 months in Finnish birds). Compared to wild mallards, a smaller proportion of hand-reared birds survived long enough to have the chance to enter the wild breeding population; less than 25 % of the Swedish birds and less than 10 % of the Finnish birds lived a year or longer. Wild birds migrated farther than hand-reared (mean distance in Swedish birds, 676 versus 523 km; in Finnish birds, 1,213 versus 157 km), a pattern caused by both shorter life span and lower migration speed in hand-reared birds. Mean migration distance in wild Swedish mallards was 787 km in 1947–1972 but 591 km in 1977–1993. This difference was not statistically significant, though, possibly due to the limited sample size and lack of data from the last two decades. In general, our study provides a conservative test of the predictions addressed, calling for more research about the consequences of restocking duck populations.     

Low levels of realized seed and pollen gene flow and strong spatial genetic structure in a small,isolated and fragmented population of the tropical tree Copaifera langsdorffii Desf

Over the past century, the Brazilian Atlantic forest has been reduced to small, isolated fragments of forest. Reproductive isolation theories predict a loss of genetic diversity and increases in inbreeding and spatial genetic structure (SGS) in such populations. We analysed eight microsatellite loci to investigate the pollen and seed dispersal patterns, genetic diversity, inbreeding and SGS of the tropical tree Copaifera langsdorffii in a small (4.8 ha), isolated population. All 112 adult trees and 128 seedlings found in the stand were sampled, mapped and genotyped. Seedlings had significantly lower levels of genetic diversity (A=16.5±0.45, mean±95% s.e.; H_e=0.838±0.006) than did adult trees (A=23.2±0.81; H_e=0.893±0.030). Parentage analysis did not indicate any seed immigration (m_seeds=0) and the pollen immigration rate was very low (m_pollen=0.047). The average distance of realized pollen dispersal within the stand was 94 m, with 81% of the pollen travelling <150 m. A significant negative correlation was found between the frequency and distance of pollen dispersal (r=−0.79, P<0.01), indicating that short-distance pollinations were more frequent. A significant SGS for both adults (∼50 m) and seedlings (∼20 m) was also found, indicating that most of the seeds were dispersed over short distances. The results suggested that the spatial isolation of populations by habitat fragmentation can restrict seed and pollen gene flow, increase SGS and affect the genetic diversity of future generations.     

Climate and habitat configuration limit range expansion and patterns of dispersal in a non‐native lizard

Invasive species are one of the main causes of biodiversity loss worldwide. As introduced, populations increase in abundance and geographical range, so does the potential for negative impacts on native communities. As such, there is a need to better understand the processes driving range expansion as species become established in recipient landscapes. Through an investigation into capacity for population growth and range expansion of introduced populations of a non‐native lizard (Podarcis muralis), we aimed to demonstrate how multi‐scale factors influence spatial spread, population growth, and invasion potential in introduced species. We collated location records of P. muralis presence in England, UK through data collected from field surveys and a citizen science campaign. We used these data as input for presence‐background models to predict areas of climate suitability at a national‐scale (5 km resolution), and fine‐scale habitat suitability at the local scale (2 m resolution). We then integrated local models into an individual‐based modeling platform to simulate population dynamics and forecast range expansion for 10 populations in heterogeneous landscapes. National‐scale models indicated climate suitability has restricted the species to the southern parts of the UK, primarily by a latitudinal cline in overwintering conditions. Patterns of population growth and range expansion were related to differences in local landscape configuration and heterogeneity. Growth curves suggest populations could be in the early stages of exponential growth. However, annual rates of range expansion are predicted to be low (5–16 m). We conclude that extensive nationwide range expansion through secondary introduction is likely to be restricted by currently unsuitable climate beyond southern regions of the UK. However, exponential growth of local populations in habitats providing transport pathways is likely to increase opportunities for regional expansion. The broad habitat niche of P. muralis, coupled with configuration of habitat patches in the landscape, allows populations to increase locally with minimal dispersal.     

Chemolithotrophic acetogenic H2/CO2 utilization in Italian rice field soil

Acetate oxidation in Italian rice field at 50 °C is achieved by uncultured syntrophic acetate oxidizers. As these bacteria are closely related to acetogens, they may potentially also be able to synthesize acetate chemolithoautotrophically. Labeling studies using exogenous H₂ (80%) and ¹³CO₂ (20%), indeed demonstrated production of acetate as almost exclusive primary product not only at 50 °C but also at 15 °C. Small amounts of formate, propionate and butyrate were also produced from ¹³CO₂. At 50 °C, acetate was first produced but later on consumed with formation of CH₄. Acetate was also produced in the absence of exogenous H₂ albeit to lower concentrations. The acetogenic bacteria and methanogenic archaea were targeted by stable isotope probing of ribosomal RNA (rRNA). Using quantitative PCR, ¹³C-labeled bacterial rRNA was detected after 20 days of incubation with ¹³CO₂. In the heavy fractions at 15 °C, terminal restriction fragment length polymorphism, cloning and sequencing of 16S rRNA showed that Clostridium cluster I and uncultured Peptococcaceae assimilated ¹³CO₂ in the presence and absence of exogenous H₂, respectively. A similar experiment showed that Thermoanaerobacteriaceae and Acidobacteriaceae were dominant in the ¹³C treatment at 50 °C. Assimilation of ¹³CO₂ into archaeal rRNA was detected at 15 °C and 50 °C, mostly into Methanocellales, Methanobacteriales and rice cluster III. Acetoclastic methanogenic archaea were not detected. The above results showed the potential for acetogenesis in the presence and absence of exogenous H₂ at both 15 °C and 50 °C. However, syntrophic acetate oxidizers seemed to be only active at 50 °C, while other bacterial groups were active at 15 °C.     

Geographical distribution of Allium oleraceum cytotypes in Finland and Sweden

Chromosome numbers from a total number of 226 populations of Allium oleraceum were determined in Finland, Sweden and seven other countries. Two different chromosome numbers or cytotypes were found, tetraploids (2n = 32) and pentaploids (2n = 40). In Finland, samples were collected for chromosome counts from a total of 190 populations, which fairly well covers the distribution area of the species in Finland. The majority of the populations of A. oleraceum in Finland contained only one of the two cytotypes. A clear pattern in the geographical distribution of the cytotypes could be distinguished. The pentaploid cytotype predominates in the Åland Islands and in the archipelago of Regio aboënsis. The tetraploid cytotype predominates on the mainland of the Regio aboënsis and along the coast of the Nylandia. In south Häme, all studied native populations were of the tetraploid cytotype. Of all the studied populations in Finland 43.7% were tetraploid and 51.6% pentaploid. A few mixed populations with both tetraploid and pentaploid plants occurring in the same population were also found (4.7%). The chromosome numbers of 19 populations of A. oleraceum from the southern part of Sweden were pentaploids, with the exception of one tetraploid population. It seems that the pentaploid cytotype is predominant in Sweden, but no conclusions about a geographical pattern between the two cytotypes could be drawn. Based on the occurrence of the cytotypes, it is suggested that the pentaploid cytotype might have spread to Finland from the Swedish east coast via the Åland Islands to Kaland on the Finnish west coast and along the coast of Nyland to the archipelagos of Kotka and Hamina in Karelia australis. The tetraploid populations in south Häme are clearly connected to Iron Age activity and to old inland trade routes, and may be of eastern origin.     

Genetic admixture despite ecological segregation in a North African sparrow hybrid zone (Aves,Passeriformes, Passer domesticus × Passer hispaniolensis)

Under different environmental conditions, hybridization between the same species might result in different patterns of genetic admixture. Particularly, species pairs with large distribution ranges and long evolutionary history may have experienced several independent hybridization events over time in different zones of overlap. In birds, the diverse hybrid populations of the house sparrow (Passer domesticus) and the Spanish sparrow (Passer hispaniolensis) provide a striking example. Throughout their range of sympatry, these two species do not regularly interbreed; however, a stabilized hybrid form (Passer italiae) exists on the Italian Peninsula and on several Mediterranean islands. The spatial distribution pattern on the Eurasian continent strongly contrasts the situation in North Africa, where house sparrows and Spanish sparrows occur in close vicinity of phenotypically intermediate populations across a broad mosaic hybrid zone. In this study, we investigate patterns of divergence and admixture among the two parental species, stabilized and nonstabilized hybrid populations in Italy and Algeria based on a mitochondrial marker, a sex chromosomal marker, and 12 microsatellite loci. In Algeria, despite strong spatial and temporal separation of urban early‐breeding house sparrows and hybrids and rural late‐breeding Spanish sparrows, we found strong genetic admixture of mitochondrial and nuclear markers across all study populations and phenotypes. That pattern of admixture in the North African hybrid zone is strikingly different from i) the Iberian area of sympatry where we observed only weak asymmetrical introgression of Spanish sparrow nuclear alleles into local house sparrow populations and ii) the very homogenous Italian sparrow population where the mitogenome of one parent (P. domesticus) and the Z‐chromosomal marker of the other parent (P. hispaniolensis) are fixed. The North African sparrow hybrids provide a further example of enhanced hybridization along with recent urbanization and anthropogenic land‐use changes in a mosaic landscape.     

Quantification of virus genes provides evidence for seed-bank populations of phycodnaviruses in Lake Ontario,Canada

Using quantitative PCR, the abundances of six phytoplankton viruses DNA polymerase (polB) gene fragments were estimated in water samples collected from Lake Ontario, Canada over 26 months. Four of the polB fragments were most related to marine prasinoviruses, while the other two were most closely related to cultivated chloroviruses. Two Prasinovirus-related genes reached peak abundances of >1000 copies ml⁻¹ and were considered ‘high abundance'', whereas the other two Prasinovirus-related genes peaked at abundances <1000 copies ml⁻¹ and were considered ‘low abundance''. Of the genes related to chloroviruses, one peaked at ca 1600 copies ml⁻¹, whereas the other reached only ca 300 copies ml⁻¹. Despite these differences in peak abundance, the abundances of all genes monitored were lowest during the late fall, winter and early spring; during these months the high abundance genes persisted at 100–1000 copies ml⁻¹ while the low abundance Prasinovirus- and Chlorovirus-related genes persisted at fewer than ca 100 copies ml⁻¹. Clone libraries of psbA genes from Lake Ontario revealed numerous Chlorella-like algae and two prasinophytes demonstrating the presence of candidate hosts for all types of viruses monitored. Our results corroborate recent metagenomic analyses that suggest that aquatic virus communities are composed of only a few abundant populations and many low abundance populations. Thus, we speculate that an ecologically important characteristic of phycodnavirus communities is seed-bank populations with members that can become numerically dominant when their host abundances reach appropriate levels.