Population genetics after fragmentation: the case of the endangered Spanish imperial eagle (Aquila adalberti)

Genetic diversity and structure of mongolian gazelle (Procapra gutturosa) populations in fragmented habitats

BACKGROUND

The Mongolian gazelle (Procapra gutturosa) population has shown a considerable range of contractions and local extinctions over the last century, owing to habitat fragmentation and poaching. A thorough understanding of the genetic diversity and structure of Mongolian gazelle populations in fragmented habitats is critical for planning effective conservation strategies.

RESULT

In this study, we used eight microsatellite loci and mitochondrial cytochrome b (Cytb) to compare the levels of genetic diversity and genetic structure of Mongolian gazelle populations in the Hulun Lake National Nature Reserve (HLH) with those in the China-Mongolia border area (BJ). The results showed that the nucleotide diversity and observed heterozygosity of the HLH population were lower than those of the BJ population. Moreover, the HLH and BJ populations showed genetic differentiation. We concluded that the HLH population had lower genetic diversity and a distinct genetic structure compared with the BJ population.

CONCLUSION

The genetic diversity of fragmented Mongolian gazelle populations, can be improved by protecting these populations while reinforcing their gene exchange with other populations. For example, attempts can be made to introduce new individuals with higher genetic diversity from other populations to reduce inbreeding.

Generation of raptor diversity in Europe: linking speciation with climate changes and the ability to migrate

Europe holds a rich community of diurnal birds of prey, and the highest proportion of transcontinental migratory raptorial species of any landmass. This study will test the hypotheses that the high diversification of the raptor assemblage in Europe is a recent event, that closely related species sharing the same trophic niches can only coexist in sympatry during the breeding period, when food availability is higher, and finally that migration is a function of size, with the smaller species in every trophic group moving further. A consensus molecular phylogeny for the 38 regular breeding species of raptors in Europe was obtained from BirdTree (www.birdtree.org). For the same species, a trophic niche cluster dendrogram was constructed. Size and migratory strategy were introduced in the resulting phylogeny, where trophic groups were also identified. Multispecific trophic groups tended to be composed of reciprocal sister species of different sizes, while monospecific groups (n = 3) were composed of highly specialized species. Many speciation events took place recently, during the glacial cycles of the Quaternary, and size divergence among competing species may be due to character displacement. Nowadays, the smaller species in every trophic group migrate to sub-Saharan Africa. This investigation illustrates how the rich assemblage of diurnal birds of prey in Europe, more diverse and more migratory than, for instance, the North American assemblage at equivalent latitudes, has emerged recently due to the multiplication of look-alike species with similar trophic ecologies, possibly in climate refugia during cold periods.

Contrasting patterns of genetic diversity and lack of population structure in the lesser spotted eagle Clanga pomarina (Aves: Accipitriformes) across its breeding range

Characterizing the genetic diversity and structure of populations is essential for understanding their evolutionary history and planning species conservation. The lesser spotted eagle (Clanga pomarina) is a large migratory raptor with a relatively small breeding range concentrated in Eastern Europe. We evaluated the level of genetic diversity and population structuring by estimating the length diversity of 23 microsatellite markers in 306 individuals and sequencing 473 nucleotides from the mitochondrial pseudo-control region in 265 individuals across the distribution range. The microsatellite data suggested shallow differentiation between geographical regions and moderate genetic diversity across the range; no recent population bottlenecks were detected. Mitochondrial diversity was relatively low; however, high values were recorded at the southern edge of the distribution range. This, in combination with the star-like distribution of mitochondrial haplotypes, suggests the expansion of the European population from a single (Balkan) refugium during the late Pleistocene or early Holocene after the glacial population bottleneck. However, the Caucasian population may have survived in a separate refugium. We conclude that the lack of clear population structuring and ongoing gene flow across Europe support the treatment of the geographically restricted global population of the lesser spotted eagle as a single evolutionary and conservation unit.

Genetic Diversity Analysis of Mitochondrial Cytb Gene, Phylogeny and Phylogeography of Protected Griffon Vulture (Gyps fulvus) from Serbia

Once a widespread and common species across the region of southeast Europe, the Griffon vulture is now confined to small and isolated populations across the Balkan Peninsula. The population from Serbia with 290 couples represents its biggest and most viable population that can serve as an important reservoir of genetic diversity from which the birds can be used for the region’s reintroduction or recolonization programs. To estimate the level of genetic diversity, the mitochondrial Cytb gene from 58 unrelated birds sampled during the marking in the nests was sequenced and compared to the homologous Griffon vulture sequences available in publicly accessible online databases. Phylogeographic analysis based on Cytb sequences showed that the most frequent haplotype is found in all Griffon vulture populations and that each population possesses private haplotypes. Our data suggest that the Griffon vulture population from Serbia should be used as a source population for restocking and reintroduction programs in the region. The observed genetic differentiation between the populations from the Iberian and Balkan Peninsulas suggest that the introduction of foreign birds from remote populations should be avoided and that birds from indigenous or neighboring populations, if available, should be used instead.

Common patterns in the molecular phylogeography of western palearctic birds: a comprehensive review

A plethora of studies have offered crucial insights in the phylogeographic status of Western Palearctic bird species. However, an overview integrating all this information and analyzing the combined results is still missing. In this study, we compiled all published peer-reviewed and grey literature available on the phylogeography of Western Palearctic bird species. Our literature review indicates a total number of 198 studies, with the overwhelming majority published as journal articles (n = 186). In total, these literature items offer information on 145 bird species. 85 of these species are characterized by low genetic differentiation, 46 species indicate genetic variation but no geographic structuring i.e. panmixia, while 14 species show geographically distinct lineages and haplotypes. Majority of bird species inhabiting the Western Palearctic display genetic admixture. The glaciation cycles in the past few million years were pivotal factors in shaping this situation: during warm periods many species expanded their distribution range to the north over wide areas of Eurasia; whereas, during ice ages most areas were no longer suitable and species retreated to refugia, where lineages mixed.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10336-021-01893-x.

Low genetic diversity and shallow population structure in the endangered vulture, Gyps coprotheres

Globally, vulture species are experiencing major population declines. The southern African Cape vulture (Gyps coprotheres) has undergone severe population collapse which has led to a listing of Endangered by the IUCN. Here, a comprehensive genetic survey of G. coprotheres is conducted using microsatellite markers. Analyses revealed an overall reduction in heterozygosity compared to other vulture species that occur in South Africa (Gypaetus barbatus, Necrosyrtes monachus, and Gyps africanus). Bayesian clustering analysis and principal coordinate analysis identified shallow, subtle population structuring across South Africa. This provides some support for regional natal philopatry in this species. Despite recent reductions in population size, a genetic bottleneck was not detected by the genetic data. The G. coprotheres, however, did show a significant deficiency of overall heterozygosity. This, coupled with the elevated levels of inbreeding and reduced effective population size, suggests that G. coprotheres is genetically depauperate. Given that genetic variation is considered a prerequisite for adaptation and population health, the low genetic diversity within G. coprotheres populations is of concern and has implications for the future management and conservation of this species.

High genetic diversity and low differentiation retained in the European fragmented and declining Greater Spotted Eagle (Clanga clanga) population

Characterising genetic diversity and structure of populations is essential for effective conservation of threatened species. The Greater Spotted Eagle (Clanga clanga), a large and globally vulnerable raptor, is extinct or in severe decline in most of its previous range in Europe. We assessed whether the remnants of European population are genetically impoverished, and isolated from each other. We evaluated levels of genetic diversity and population structuring by sequencing mitochondrial pseudo-control region and 10 introns from various nuclear genes, and estimated length diversity in 23 microsatellite markers. The European population has expanded since the late Pleistocene, and does not exhibit signs of a recent population bottleneck. The global genetic diversity in Europe was rather similar to that detected in other similar species. Microsatellites suggested shallow but significant differentiation between the four extant populations in Estonia, Poland, Belarus and Russia (Upper Volga region) populations, but introns and mtDNA showed that only the Estonian population differed from the others. Mitochondrial diversity was highest in the northernmost Estonian population, introns suggested lower diversity in Upper Volga, microsatellites indicated equal diversity among populations. A recent bottleneck was detected in Poland, which is consistent with the observed repopulation of the region. We conclude that significant gene flow and high genetic diversity are retained in the fragmented Greater Spotted Eagle populations; there is currently no need for genetic augmentation in Europe.

Analysis of the Genetic Diversity and Structure of the Grey-Faced Buzzard (Butastur indicus) in Japan, Based on mtDNA

The grey-faced buzzard (Butastur indicus) is a raptor that inhabits East Asia, including Japan. Because the number of individuals has decreased by 75% over the last 40 years, this species is classified as vulnerable (VU) in Japan. In the present study, wesought to reveal the genetic structure of the Japanese grey-faced buzzard population at several breeding sites, and to assess the levels of genetic diversity within the Japanese population. We sequenced 555 bp of the mitochondrial DNA of 96 individuals sampled during the breeding season at 18 sites, and 11 individuals sampled during the winter season at one site. In total, 21 variable sites were found in the control region, and we detected 26 haplotypes among the 107 individuals. Fukuoka represented the core breeding area for grey-faced buzzards, as half of all haplotypes were detected there. Four unique haplotypes were detected in the overwintering area. The results of the network and mismatch distribution analyses indicated that the grey-faced buzzard has not experienced a genetic bottleneck in the past, but did experience recent population expansion. In addition, comparisons with other raptors revealed rich genetic diversity in the grey-faced buzzard population. Our results indicate that conservation of both breeding and wintering areas is important for the protection of the grey-faced buzzard.

Reduction of Genetic Diversity of the Harpy Eagle in Brazilian Tropical Forests

Habitat loss and fragmentation intensify the effects of genetic drift and endogamy, reducing genetic variability of populations with serious consequences for wildlife conservation. The Harpy Eagle (Harpia harpyja) is a forest dwelling species that is considered near threatened and suffers from habitat loss in the forests of the Neotropical region. In this study, 72 historical and current samples were assessed using eight autosomal microsatellite markers to investigate the distribution of genetic diversity of the Harpy Eagle of the Amazonian and Atlantic forests in Brazil. The results showed that the genetic diversity of Harpy Eagle decreased in the regions where deforestation is intense in the southern Amazon and Atlantic Forest.

The road to opportunities: landscape change promotes body-size divergence in a highly mobile species

Landscape change provides a suitable framework for investigating population-level responses to novel ecological pressures. However, relatively little attention has been paid to examine the potential influence of landscape change on the geographic scale of population differentiation. Here, we tested for morphological differentiation of red-necked nightjars Caprimulgus ruficollis breeding in a managed property and a natural reserve situated less than 10 km apart. At both sites, we also estimated site fidelity over 5 years and quantified the potential foraging opportunities for nightjars. Breeding birds in the managed habitat were significantly larger in size—as indexed by keel length—than those in the natural one. However, there were no significant differences in wing or tail length. Immigration from neighboring areas was almost negligible and, furthermore, no individual (out of 1130 captures overall) exchanged habitats between years, indicating strong site fidelity. Food supply for nightjars was equally abundant in both habitats, but the availability of foraging sites was remarkably higher in the managed property. As a result, nightjars—particularly fledglings—in the latter habitat benefited from increased foraging opportunities in relation to those in the natural site. It seems likely that the fine-scale variation in nightjar morphology reflects a phenotypic response to unequal local conditions, since non-random dispersal or differential mortality had been determined not to be influential. High site fidelity appears to contribute to the maintenance of body-size differences between the two habitats. Results from this nightjar population highlight the potential of human-induced landscape change to promote population-level responses at exceedingly small geographic scales.

Development of microsatellite markers for Hyacinth macaw (Anodorhynchus hyacinthinus) and their cross-amplification in other parrot species

Background

Hyacinth macaw Anodorhynchus hyacinthinus is the largest parrot of the world and is considered vulnerable to extinction due to its habitat loss and illegal trade associated to the international pet market demand. Genetic studies on this species are still incipient to generate a consistent characterization of the population dynamics and to develop appropriate conservation strategies. In this sense, microsatellite markers may support the detection of a population genetic structure for this bird species. However, at this time, none Hyacinth macaw species-specific primers for microsatellite loci have been so far established. This study aimed to develop and characterize polymorphic microsatellite markers for A. hyacinthinus and to check for their cross-amplification in other parrot species.

Findings

Sequences containing repeated dinucleotide motifs were prospected and optimized from a genomic library that was enriched for microsatellites using magnetic beads. The analyses of 43–57 samples from wild individuals of three distinct Brazilian subpopulations led to the characterization of five polymorphic microsatellite loci. Allele richness per locus ranged from two to 12. Three loci exhibited observed heterozygosity values higher than 50 %, but the overall average value among all loci was close to 45 %. In addition, successful primer cross-amplification was verified in seven other investigated species of Neotropical parrots.

Conclusions

The newly developed markers have shown to be potentially useful for in situ and ex situ population studies to support future conservation actions of Hyacinth macaw and other parrots.

Being cosmopolitan: evolutionary history and phylogeography of a specialized raptor, the Osprey Pandion haliaetus

BACKGROUND

The Osprey (Pandion haliaetus) is one of only six bird species with an almost world-wide distribution. We aimed at clarifying its phylogeographic structure and elucidating its taxonomic status (as it is currently separated into four subspecies). We tested six biogeographical scenarios to explain how the species' distribution and differentiation took place in the past and how such a specialized raptor was able to colonize most of the globe.

RESULTS

Using two mitochondrial genes (cyt b and ND2), the Osprey appeared structured into four genetic groups representing quasi non-overlapping geographical regions. The group Indo-Australasia corresponds to the cristatus ssp, as well as the group Europe-Africa to the haliaetus ssp. In the Americas, we found a single lineage for both carolinensis and ridgwayi ssp, whereas in north-east Asia (Siberia and Japan), we discovered a fourth new lineage. The four lineages are well differentiated, contrasting with the low genetic variability observed within each clade. Historical demographic reconstructions suggested that three of the four lineages experienced stable trends or slight demographic increases. Molecular dating estimates the initial split between lineages at about 1.16 Ma ago, in the Early Pleistocene.

CONCLUSIONS

Our biogeographical inference suggests a pattern of colonization from the American continent towards the Old World. Populations of the Palearctic would represent the last outcomes of this colonization. At a global scale the Osprey complex may be composed of four different Evolutionary Significant Units, which should be treated as specific management units. Our study brought essential genetic clarifications, which have implications for conservation strategies in identifying distinct lineages across which birds should not be artificially moved through exchange/reintroduction schemes.

Genetic Signatures of Demographic Changes in an Avian Top Predator during the Last Century: Bottlenecks and Expansions of the Eurasian Eagle Owl in the Iberian Peninsula

The study of the demographic history of species can help to understand the negative impact of recent population declines in organisms of conservation concern. Here, we use neutral molecular markers to explore the genetic consequences of the recent population decline and posterior recovery of the Eurasian eagle owl (Bubo bubo) in the Iberian Peninsula. During the last century, the species was the object of extermination programs, suffering direct persecution by hunters until the 70's. Moreover, during the last decades the eagle owl was severely impacted by increased mortality due to electrocution and the decline of its main prey species, the European rabbit (Oryctolagus cuniculus). In recent times, the decrease of direct persecution and the implementation of some conservation schemes have allowed the species' demographic recovery. Yet, it remains unknown to which extent the past population decline and the later expansion have influenced the current species' pattern of genetic diversity. We used eight microsatellite markers to genotype 235 eagle owls from ten Spanish subpopulations and analyse the presence of genetic signatures attributable to the recent population fluctuations experienced by the species. We found moderate levels of differentiation among the studied subpopulations and Bayesian analyses revealed the existence of three genetic clusters that grouped subpopulations from central, south-western and south-eastern Spain. The observed genetic structure could have resulted from recent human-induced population fragmentation, a patchy distribution of prey populations and/or the philopatric behaviour and habitat selection of the species. We detected an old population bottleneck, which occurred approximately 10,000 years ago, and significant signatures of recent demographic expansions. However, we did not find genetic signatures for a recent bottleneck, which may indicate that population declines were not severe enough to leave detectable signals on the species genetic makeup or that such signals have been eroded by the rapid demographic recovery experienced by the species in recent years.

Demographic history, genetic structure and gene flow in a steppe-associated raptor species

Background

Environmental preferences and past climatic changes may determine the length of time during which a species range has contracted or expanded from refugia, thereby influencing levels of genetic diversification. Connectivity among populations of steppe-associated taxa might have been maximal during the long glacial periods, and interrupted only during the shorter interglacial phases, potentially resulting in low levels of genetic differentiation among populations. We investigated this hypothesis by exploring patterns of genetic diversity, past demography and gene flow in a raptor species characteristic of steppes, the Montagu's harrier (Circus pygargus), using mitochondrial DNA data from 13 breeding populations and two wintering populations.

Results

Consistent with our hypothesis, Montagu's harrier has relatively low genetic variation at the mitochondrial DNA. The highest levels of genetic diversity were found in coastal Spain, France and central Asia. These areas, which were open landscapes during the Holocene, may have acted as refugia when most of the European continent was covered by forests. We found significant genetic differentiation between two population groups, at the SW and NE parts of the species' range. Two events of past population growth were detected, and occurred ca. 7500-5500 and ca. 3500-1000 years BP in the SW and NE part of the range respectively. These events were likely associated with vegetation shifts caused by climate and human-induced changes during the Holocene.

Conclusions

The relative genetic homogeneity observed across populations of this steppe raptor may be explained by a short isolation time, relatively recent population expansions and a relaxed philopatry. We highlight the importance of considering the consequence of isolation and colonization processes in order to better understand the evolutionary history of steppe species.

Remote sensing analysis reveals habitat, dispersal corridors and expanded distribution for the Critically Endangered Cross River gorilla Gorilla gorilla diehli

Habitat loss and fragmentation are among the major threats to wildlife populations in tropical forests. Loss of habitat reduces the carrying capacity of the landscape and fragmentation disrupts biological processes and exposes wildlife populations to the effects of small population size, such as reduction of genetic diversity and increased impact of demographic stochasticity. The Critically Endangered Cross River gorilla Gorilla gorilla diehli is threatened in particular by habitat disturbance because its population is small and it lives in an area where high human population density results in intense exploitation of natural resources. We used remotely-sensed data to assess the extent and distribution of gorilla habitat in the Cross River region and delineated potential dispersal corridors. Our analysis revealed > 8,000 km2 of tropical forest in the study region, 2,500 km2 of which is in or adjacent to areas occupied by gorillas. We surveyed 12 areas of forest identified as potential gorilla habitat, 10 of which yielded new records of gorillas. The new records expand the known range of the Cross River gorilla by > 50%, and support genetic analyses that suggest greater connectivity of the population than previously assumed. These findings demonstrate that considerable connected forest habitat remains and that the area could potentially support a much larger gorilla population if anthropogenic pressures such as hunting could be reduced.

When conservation management becomes contraindicated: impact of food supplementation on health of endangered wildlife

Understanding the conditions that force the implementation of management actions and their efficiency is crucial for conservation of endangered species. Wildlife managers are widely and increasingly using food supplementation for such species because the potentially immediate benefits may translate into rapid conservation improvements. Supplementary feeding can also pose risks eventually promoting undesired, unexpected, subtle, or indirect, and often unnoticed, effects that are generally poorly understood. For two decades, intensive food supplementation has been used in attempting to improve the breeding productivity of the Spanish Imperial Eagle, Aquila adalberti, one of the most endangered birds of prey in the world. Here, we examined the impact of this intensive management action on nestling health, including contamination, immunodepression, and acquisition of disease agents derived from supplementation techniques and provisioned food. Contrary to management expectations, we found that fed individuals were often inadvertently "medicated" with pharmaceuticals (antibiotics and antiparasitics) contained in supplementary food (domestic rabbits). Individuals fed with medicated rabbits showed a depressed immune system and a high prevalence and richness of pathogens compared with those with no or safe supplementary feeding using non-medicated wild rabbits. A higher presence of antibiotics (fluoroquinolones) was found in sick as opposed to healthy individuals among eaglets with supplementary feeding, which points directly toward a causal effect of these drugs in disease and other health impairments. This study represents a telling example of well-meaning management strategies not based on sound scientific evidence becoming a "contraindicated" action with detrimental repercussions undermining possible beneficial effects by increasing the impact of stochastic factors on extinction risk of endangered wildlife.

It's not too late for the harpy eagle (Harpia harpyja): high levels of genetic diversity and differentiation can fuel conservation programs

Background

The harpy eagle (Harpia harpyja) is the largest Neotropical bird of prey and is threatened by human persecution and habitat loss and fragmentation. Current conservation strategies include local education, captive rearing and reintroduction, and protection or creation of trans-national habitat blocks and corridors. Baseline genetic data prior to reintroduction of captive-bred stock is essential for guiding such efforts but has not been gathered previously.

Methodology/Findings

We assessed levels of genetic diversity, population structure and demographic history for harpy eagles using samples collected throughout a large portion of their geographic distribution in Central America (n = 32) and South America (n = 31). Based on 417 bp of mitochondrial control region sequence data, relatively high levels of haplotype and nucleotide diversity were estimated for both Central and South America, although haplotype diversity was significantly higher for South America. Historical restriction of gene flow across the Andes (i.e. between our Central and South American subgroups) is supported by coalescent analyses, the haplotype network and significant F_ST values, however reciprocally monophyletic lineages do not correspond to geographical locations in maximum likelihood analyses. A sudden population expansion for South America is indicated by a mismatch distribution analysis, and further supported by significant (p<0.05) negative values of Fu and Li's D_F and F, and Fu's F_S. This expansion, estimated at approximately 60 000 years BP (99 000–36 000 years BP 95% CI), encompasses a transition from a warm and dry time period prior to 50 000 years BP to an interval of maximum precipitation (50 000–36 000 years BP). Notably, this time period precedes the climatic and habitat changes associated with the last glacial maximum. In contrast, a multimodal distribution of haplotypes was observed for Central America suggesting either population equilibrium or a recent decline.

Significance

High levels of mitochondrial genetic diversity in combination with genetic differentiation among subgroups within regions and between regions highlight the importance of local population conservation in order to preserve maximal levels of genetic diversity in this species. Evidence of historically restricted female-mediated gene flow is an important consideration for captive-breeding programs.

Genetic structure of the Imperial Eagle (Aquila heliaca) population in Slovakia

The distribution of the Imperial Eagle (Aquila heliaca) in the Carpathian Basin is not continuous, since western and eastern breeding pairs are separated by 150 km from each other in Slovakia, and 70 km in Hungary. In the present study our aim was to examine whether this geographical distance has resulted in any genetic separation between the Western and Eastern Slovak breeding groups. We have used 132 shed feathers and 128 blood samples collected in the fields geographically representing the whole of the Slovak breeding population, and included all juveniles ringed between 2004 and 2006. After successful DNA extractions we have determined the sex, microsatellite DNA-profiles and mtDNA control region haplotypes of the specimens. Data were integrated in a common Hungarian-Slovak "DNA-fingerprint" database, making identification of the same specimen possible when recaptured. Based on a subsample of the collected individuals, the genetic structure of the Slovak population was tested using ten microsatellite loci and mtDNA control region haplotypes, and marginally significant genetic differentiation was found between western and eastern subpopulations. These results suggest that, in spite of the large dispersal capacity of the species, a relatively small geographic distance can also decrease the exchange rate of individuals between subpopulations. As this result involves only samples from the northern part of the breeding area, major conclusions concerning genetic structure and gene flow of Imperial Eagles in the entire Carpathian Basin population cannot be drawn without sampling and analysing the southern subpopulations in Hungary.

Strong philopatry derived from capture-recapture records does not lead to fine-scale genetic differentiation in lesser kestrels

1. The integration of capture-recapture and molecular approaches can improve our understanding of the consequences of habitat fragmentation on population connectivity. Here we employed microsatellites to test dispersal hypotheses derived from intense and long-term ringing programmes of the lesser kestrel Falco naumanni in Western Europe. 2. Re-encounters of 1308 marked individuals in Spain have revealed that most first-time breeders settled within 10 km from their natal colony, with a negative association between dispersal and geographical distance. Although these findings would predict fine-scale spatial patterns of genetic differentiation, the genetic impact of rarely reported events concerning long-distance effective dispersal (> 100 km) is unknown. 3. First, we investigated a spatially structured and geographically isolated population located in north-eastern Spain, where capture-recapture records and genetic data could be appropriately compared over similar spatial and temporal scales. Spatial autocorrelation analyses (N = 174 nestlings from different broods) did not reveal either significant differences in average relatedness at any distance class nor decreased relatedness as a function of distance. At a broader spatial scale, Bayesian analysis of population structure (N = 432 nestlings) indicated panmixia across Western Europe. However, F(ST) comparisons between four geographically distinct populations indicated low but significant genetic differentiation. 4. Our genetic data would therefore challenge traditional assumptions associating philopatry with the emergence of fine-scale genetic structuring. This could be because even low levels of gene flow are enough to preclude the development of local genetic structure. Nevertheless, the analysis of a geographically isolated and small population from Southern France exemplifies a situation in which restricted dispersal has translated into weak but consistently significant genetic differentiation. 5. Relevant to conservation genetics and evolutionary biology, our results may lessen the genetic concerns derived from population fragmentation at relatively small geographical scales in species with apparently limited dispersal abilities, but raises concerns about increased genetic divergence in small and isolated demes.

Population fragmentation leads to isolation by distance but not genetic impoverishment in the philopatric Lesser Kestrel: a comparison with the widespread and sympatric Eurasian Kestrel

Population fragmentation is a widespread phenomenon usually associated with human activity. As a result of habitat transformation, the philopatric and steppe-specialist Lesser Kestrel Falco naumanni underwent a severe population decline during the last century that increased population fragmentation throughout its breeding range. In contrast, the ubiquitous Eurasian Kestrel Falco tinnunculus did not suffer such adverse effects, its breeding range still remaining rather continuous. Using microsatellites, we tested the effects of population fragmentation on large-scale spatial patterns of genetic differentiation and diversity by comparing these two sympatric and phylogenetically related species. Our results suggest that habitat fragmentation has increased genetic differentiation between Lesser Kestrel populations, following an isolation-by-distance pattern, while the population of Eurasian Kestrels is panmictic. Contrary to expectations, we did not detect significant evidence of reduced genetic variation or increased inbreeding in Lesser Kestrels. Although this study reports genetic differentiation in a species that has potential for long-distance dispersal but philopatry-limited gene flow, large enough effective population sizes and migration may have been sufficient to mitigate genetic depauperation. A serious reduction of genetic diversity in Lesser Kestrels would, therefore, only be expected after severe population bottlenecks following extreme geographic isolation.

Short-term transformation of matrix into hospitable habitat facilitates gene flow and mitigates fragmentation

Habitat fragmentation has major implications for demography and genetic structure of natural plant and animal populations as small and isolated populations are more prone to extinction. Therefore, many recent studies focus on spatial fragmentation. However, the temporal configuration of suitable habitat may also influence dispersal and gene flow in fragmented landscapes. We hypothesize that short-term switching of inhospitable matrix areas into suitable habitat can mitigate effects of spatial fragmentation in natural and seminatural ecosystems. To test our hypothesis, we investigated the hairy-footed gerbil (Gerbillurus paeba, Smith 1836), a ground-dwelling rodent, in fragmented Kalahari savannah areas. Here, rare events of high above mean annual rainfall suggest short-term matrix suitability. During the field survey in 'matrix' areas in the Kalahari (shrub encroachment by heavy grazing) we never observed the hairy-footed gerbil in years of average rainfall, but observed mass occurrences of this species during rare events of exceptionally high rainfall. In a second step, we developed an agent-based model simulating subpopulations in two neighbouring habitats and the separating matrix. Our mechanistic model reproduces the mass occurrences as observed in the field and thus suggests the possibly underlying processes. In particular, the temporary improvement in matrix quality allows reproduction in the matrix, thereby causing a substantial increase in population size. The model demonstrates further how the environmental trigger (rainfall) impacts genetic connectivity of two separated subpopulations. We identified seasonality as a driver of fragmentation but stochasticity leading to higher connectivity. We found that our concept of temporal fragmentation can be applied to numerous other fragmented populations in various ecological systems and provide examples from recent literature. We conclude that temporal aspects of fragmentation must be considered in both ecological research and conservation management.

Genetic evidence for a recent divergence and subsequent gene flow between Spanish and Eastern imperial eagles

BACKGROUND

Dating of population divergence is critical in understanding speciation and in evaluating the evolutionary significance of genetic lineages, upon which identification of conservation and management units should be based. In this study we used a multilocus approach and the Isolation-Migration model based on coalescence theory to estimate the time of divergence of the Spanish and Eastern imperial eagle sister species. This model enables estimation of population sizes at split, and inference of gene flow after divergence.

RESULTS

Our results indicate that divergence may have occurred during the Holocene or the late Pleistocene, much more recently than previously suspected. They also suggest a large population reduction at split, with an estimated effective population size several times smaller for the western population than for the eastern population. Asymmetrical gene flow after divergence, from the Eastern imperial eagle to the Spanish imperial eagle, was detected for the nuclear genome but not the mitochondrial genome. Male-mediated gene flow after divergence may explain this result, and the previously reported lower mitochondrial diversity but similar nuclear diversity in Spanish imperial eagles compared to the Eastern species.

CONCLUSION

Spanish and Eastern imperial eagles split from a common ancestor much more recently than previously thought, and asymmetrical gene flow occurred after divergence. Revision of the phylogenetic proximity of both species is warranted, with implications for conservation.