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1.
Endemic and endangered species are highly vulnerable to habitat perturbations and may be subject to variations in their population size. Management plan for these species is crucial to avoid population decline, loss of genetic variability, inbreeding and ultimately extinction. The sand lizard, Liolaemus lutzae, is endemic to a habitat of sandy coastal plain (restinga). Its geographical distribution extends for only 200 km stretch of the coast of Rio de Janeiro state, Brazil, one of South America’s most densely populated regions. Extensive development and degradation of the beaches where the species inhabits, have led to the species becoming critically endangered. We used mitochondrial DNA sequences and microsatellite loci to resolve patterns of population connectivity and genetic variation within the species in order to provide a platform for a species management plan. Our results indicate the existence of three main populations, separated from each other by the Guanabara Bay and by the Arraial do Cabo Peninsula. The low microsatellite genetic variation and heterozygosity witnessed in each of the three populations, together with high levels of inbreeding and low effective population sizes suggest that the species is in urgent need of intensive management. Based on the results of this study we propose strong measures to protect existing restinga fragments and the implementation of programmes of captive breeding and reintroduction of individuals from the heavily threatened regions to protected refugia. Such measures may be the only way of ensuring the continuity of the species.  相似文献   

2.
Oceanic island ecosystems harbour many endemic plant and animal species, which are often threatened because they have only a few small populations. Many factors contribute to the biological viability of such populations, such as demography and population dynamics, breeding system and pollination ecology, seed dispersal and genetic variation. In a collaborative project, all these factors were studied in the rare endemic, predominantly monoecious shrub Bencomia exstipulata Svent. (Rosaceae), which grows exclusively in the national parks of El Teide (Tenerife) and La Caldera de Taburiente (La Palma). Demography was monitored through annual censuses of individual plants in a natural and an augmented population on Tenerife. The breeding system and reproductive success were studied through bagging and pollination experiments, and insect visitation censuses. Seed dispersal by animals was assessed using cafetaria experiments. With matrix projection models and stochastic simulations, we show that the Tenerife population was demographically stable. This was largely explainable by the high survival of adult individuals. Despite frequent germination, successful seedling recruitment was very rare. Male and female flowers occurred in separate inflorescences within individuals, although some inflorescences were mixed and some shrubs were entirely male or female. Despite frequent visits by honeybees, the species is predominantly wind pollinated. Insect-proof bags reduced seed set by 12.5%, and pollen-proof bags by 44%. Large quantities of airborne pollen were detected on unbagged sticky microscope slides, this was 56% reduced by insect-proof and 96% by pollen-proof bags. Hence, some self-pollination also seems to occur. Cafetaria experiments showed that the local lizards (Gallotia galloti Oudart) readily eat the fruits and that the seeds pass through their intestines unharmed and germinable. Since other dispersal vectors are unknown, saurochory seems the most likely mode of dispersal. Our study strongly suggests that the population of B. exstipulata on Tenerife is viable, and that there are no significant threats associated with its breeding system, pollination or seed dispersal. To alleviate the natural extinction risk typical of narrow endemics, five main conservation measures are proposed.  相似文献   

3.
We use the information provided by 36 RAPD loci and 15 morphological traits to describe and construe the population differentiation in A. arbuscula, a Canarian endemic Asteraceae threatened with extinction that exhibits a disjunct distribution in the islands of Gran Canaria (var. schizogynophylla) and Lanzarote (var. arbuscula). Our evaluation of morphological characters and the extent of RAPD differentiation found sets the stage for a taxonomic restructuring to hoist both var. arbuscula and var. schizogynophylla to subspecies category. Our genetic results suggest that fragmentation and generally low population sizes are jeopardising the survival of this species through a predominance of stochastic processes in microevolutionary dynamics, especially in Gran Canaria, where subpopulations exhibit the lowest levels of genetic variation and gene flow. If, as most Asteraceae, these plants have a sporophytic self-incompatibility system, the scarce reproductive turnover observed in the much smaller subpopulations from Gran Canaria (ssp. schizogynophylla) is possibly more influenced by a deficiency of S-alleles (that would be provoking the unavailability of compatible mating types, and a cascade of deleterious effects associated with the Allee effect) than by a reduced pollinator visitation frequency. Based on the depauperated values of genetic parameters for this subspecies, urgent mixed subpopulation reinforcements and reintroductions (with specimens belonging to the same subspecies) seem advisable on the grounds that they might allow the isolated habitat remnants to retrieve from inbreeding through the introduction of a new stock of S-alleles and the subsequent production of genotypes that may have a higher selective value.  相似文献   

4.
Geographical isolation by oceanic barriers and climatic stability has been postulated as some of the main factors driving diversification within volcanic archipelagos. However, few studies have focused on the effect that catastrophic volcanic events have had on patterns of within‐island differentiation in geological time. This study employed data from the chloroplast (cpDNA haplotypes) and the nuclear (AFLPs) genomes to examine the patterns of genetic variation in Canarina canariensis, an iconic plant species associated with the endemic laurel forest of the Canary Islands. We found a strong geographical population structure, with a first divergence around 0.8 Ma that has Tenerife as its central axis and divides Canarian populations into eastern and western clades. Genetic diversity was greatest in the geologically stable ‘palaeo‐islands’ of Anaga, Teno and Roque del Conde; these areas were also inferred as the ancestral location of migrant alleles towards other disturbed areas within Tenerife or the nearby islands using a Bayesian approach to phylogeographical clustering. Oceanic barriers, in contrast, appear to have played a lesser role in structuring genetic variation, with intra‐island levels of genetic diversity larger than those between‐islands. We argue that volcanic eruptions and landslides after the merging of the palaeo‐islands 3.5 Ma played key roles in generating genetic boundaries within Tenerife, with the palaeo‐islands acting as refugia against extinction, and as cradles and sources of genetic diversity to other areas within the archipelago.  相似文献   

5.
Fagus grandifolia var. mexicana(Fagaceae) is a Mexican endemic tree, currently threatened with extinction. In order to assess the level and structure of genetic variation in four remaining populations, leaf samples were analysed using random amplified polymorphic DNA (RAPD) and cpDNA PCR-RFLP markers. A sample of the more widespread congener, F. grandifoliavar. grandifolia from the USA was also analysed for comparison. Thirty-three polymorphic RAPD bands were produced using 18 10-mer primers. AMOVA of RAPD data indicated significant (P < 0.002) population differentiation, with 15.6% of variation recorded between Mexican populations. PCR-RFLP analysis enabled three cpDNA haplotypes to be identified, denoted types A, B, and C. Types A and B were each restricted to an individual Mexican population, whereas Type C was fixed for two Mexican populations, and the population from the USA. Within-population genetic variation, quantified as percentage polymorphic bands, Shannon's Diversity Index and Nei's gene diversity measure, was found to be lower in Mexican populations than in that from the USA, and was positively related to population size. These results suggest that an unexpectedly high degree of genetic variation exists within Mexican beech, and this variation should be considered in developing the conservation strategy that is urgently required if extinction of this taxon is to be prevented.  相似文献   

6.
Genetic connectivity is a key factor for maintaining the persistence of populations in fragmented landscapes. In highly modified landscapes such us peri-urban areas, organisms’ dispersal among fragmented habitat patches can be reduced due to the surrounding matrix, leading to subsequent decreased gene flow and increased potential extinction risk in isolated sub-populations. However, few studies have compared within species how dispersal/gene flow varies between regions and among different forms of matrix that might be encountered. In the current study, we investigated gene flow and dispersal in an endangered marsupial, the southern brown bandicoot (Isoodon obesulus) in a heavily modified peri-urban landscape in South Australia, Australia. We used 14 microsatellite markers to genotype 254 individuals which were sampled from 15 sites. Analyses revealed significant genetic structure. Our analyses also indicated that dispersal was mostly limited to neighbouring sites. Comparisons of these results with analyses of a different population of the same species revealed that gene flow/dispersal was more limited in this peri-urban landscape than in a pine plantation landscape approximately 400 km to the south-east. These findings increase our understanding of how the nature of fragmentation can lead to profound differences in levels of genetic connectivity among populations of the same species.  相似文献   

7.
Polyploidy and hybridization are thought to have significant impacts on both the evolution and diversification of the genus Actinidia, but the structure and patterns of morphology and molecular diversity relating to ploidy variation of wild Actinidia plants remain much less understood. Here, we examine the distribution of morphological variation and ploidy levels along geographic and environmental variables of a large mixed-ploidy population of the A. chinensis species complex. We then characterize the extent of both genetic and epigenetic diversity and differentiation exhibited between individuals of different ploidy levels. Our results showed that while there are three ploidy levels in this population, hexaploids were constituted the majority (70.3%). Individuals with different ploidy levels were microgeographically structured in relation to elevation and extent of niche disturbance. The morphological characters examined revealed clear difference between diploids and hexaploids, however tetraploids exhibited intermediate forms. Both genetic and epigenetic diversity were high but the differentiation among cytotypes was weak, suggesting extensive gene flow and/or shared ancestral variation occurred in this population even across ploidy levels. Epigenetic variation was clearly correlated with changes in altitudes, a trend of continuous genetic variation and gradual increase of epigenomic heterogeneities of individuals was also observed. Our results show that complex interactions between the locally microgeographical environment, ploidy and gene flow impact A. chinensis genetic and epigenetic variation. We posit that an increase in ploidy does not broaden the species habitat range, but rather permits A. chinensis adaptation to specific niches.  相似文献   

8.
9.
Examining historical and contemporary processes underlying current patterns of genetic variation is key to reconstruct the evolutionary history of species and implement conservation measures promoting their long-term persistence. Combining phylogeographic and landscape genetic approaches can provide valuable insights, especially in regions harboring high levels of biodiversity that are currently threatened by climate and land cover changes, like southern Iberia. We used genetic (mtDNA and microsatellites) and spatial data (climate and land cover) to infer the evolutionary history and contemporary genetic connectivity in a short-range endemic salamander subspecies, Salamandra salamandra longirostris, using a combination of ecological niche modelling, phylogeographic, and landscape genetic analyses. Ecological-based analyses support a role of the Guadalquivir River Basin as a major vicariant agent in this taxon. The lower genetic diversity and greater differentiation of peripheral populations, together with analyses of climatically stable areas throughout time, suggest the persistence of a population in the central part of the current range since the Last Inter Glacial [LIG; ~?120,000–140,000 years BP], and a micro refugium in the eastern end of the range. Habitat heterogeneity plays a major role in shaping patterns of genetic differentiation in S. s. longirostris, with forests representing key areas for its long-term persistence under scenarios of environmental change. Our study stresses the importance of maintaining population genetic connectivity in low-dispersal organisms under rapidly changing environments, and will inform management plans for the long-term survival of this evolutionarily distinct Mediterranean endemic.  相似文献   

10.
The endemic Sardinian chalk hill blue butterfly, Polyommatus coridon gennargenti, is considered vulnerable to extinction because of its low genetic variation and restricted distribution. The species also has a fragmented distribution, which follows the patchy distribution pattern of its larval host-plant. A preliminary investigation of the population structure of P. coridon gennargenti was carried out on a small network of four local populations by means of capture–recapture methods. Estimated population sizes and movement rates among the four adjacent local populations suggest that this taxon has a metapopulation structure composed of loosely connected small local populations. Natural fragmentation, isolation, and traditional land use contribute to the vulnerability of P. coridon gennargenti to extinction. Low effective population sizes and restricted movement between habitat patches lead to inbreeding and an increased vulnerability to extinction of this island population.  相似文献   

11.
The Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis; MGRS) is endemic to the Pinaleño Mountains of Arizona at the southernmost extent of the species’ range. The MGRS was listed as federally endangered in 1987, and is currently at high risk of extinction due to declining population size and increasing threats. Here we present a genetic assessment of the MGRS using eight nuclear DNA microsatellite markers and a 472 bp fragment of the mitochondrial cytochrome b gene. We analyzed 34 MGRS individuals and an additional 66 red squirrels from the nearby White Mountains, Arizona (T. h. mogollonensis). Both nuclear and mitochondrial DNA analyses revealed an extreme reduction in measures of genetic diversity relative to conspecifics from the White Mountains, suggesting that the MGRS has either experienced multiple bottlenecks, or a single long-term bottleneck. Additionally, we found a high degree of relatedness (mean = 0.75 ± 0.18) between individual MGRS. Our study implies that the MGRS may lack the genetic variation required to respond to a changing environment. This is especially important considering this region of the southwest United States is expected to experience profound effects from global climate change. The reduced genetic variability together with the high relatedness coefficients should be taken into account when constructing a captive population to minimize loss of the remaining genetic variation.  相似文献   

12.
Invasive populations typically demonstrate genetic isolation which results in a loss of genetic diversity and a reduction in invasion success. This study focused on the genetic population of a successful invasive species of tarantula. Individuals were sampled in two mainland localities of the Yucatan Peninsula (Zoh-Laguna and Raudales), in addition to two island localities (El Cedral and Rancho Guadalupe on Cozumel Island). All populations present high genetic diversity (mean: He = 0.23, P = 99%), with significant differences between the Raudales and Rancho Guadalupe localities. The AMOVA analysis revealed a significant population structure (14.5% variation among populations), consistent with the gene differentiation coefficient (GST = 0.21), and spatial analysis of population structure. Our results suggested that the original introduced population did not suffer a loss of genetic diversity during establishment on the island, possibly a result of different biological conditions. Population structure analysis leads us to suggest that one island population is similar to the original genetic profile, whereas the genotypic profile of the other island population reflects recent introductions from the mainland. We identified a potential risk of extinction for one local mainland population, suggesting that this species may be a successful invader in a new environment but endangered in some parts of its natural area.  相似文献   

13.
Genetic diversity and temperature increases associated with global climate change are known to independently influence population growth and extinction risk. Whether increasing temperature may influence the effect of genetic diversity on population growth, however, is not known. We address this issue in the model protist system Tetrahymena thermophila. We test the hypothesis that at temperatures closer to the species’ thermal optimum (i.e., the temperature at which population growth is maximal, or T opt), genetic diversity should have a weaker effect on population growth compared to temperatures away from the thermal optimum. To do so, we grew populations of T. thermophila with varying levels of genetic diversity at increasingly warmer temperatures and quantified their intrinsic population growth rate, r. We found that genetic diversity increases population growth at cooler temperatures, but that as temperature increases, this effect weakens. We also show that a combination of changes in the amount of expressed genetic diversity (G) in r, plastic changes in population growth across temperatures (E), and strong G × E interactions underlie this temperature effect. Our results uncover important but largely overlooked temperature effects that have implications for the management of small populations with depauperate genetic stocks in an increasingly warming world.  相似文献   

14.
Theoretical work has shown that reduced phenotypic heterogeneity leads to population instability and can increase extinction potential, yet few examples exist of natural populations that illustrate how varying levels expressed diversity may influence population persistence, particularly during periods of stochastic environmental fluctuation. In this study, we assess levels of expressed variation and genetic diversity among demographically independent populations of tidewater goby (Eucyclogobius newberryi), show that reductions in both factors typically coincide, and describe how low levels of diversity contribute to the extinction risk of these isolated populations. We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals. Several study populations deviated from the natural pattern of year-round reproduction typical for the species, rendering those with severely truncated reproductive periods vulnerable to extinction in the event of environmental fluctuation. In contrast, demographically diverse populations are more likely to persist through such periods through the continuous presence of adults with broader physiological tolerance to abrupt salinity changes. Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics. These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.  相似文献   

15.
Eriogonum ovalifolium var. williamsiae (Steamboat buckwheat) is a narrow endemic subshrub, known from a single locality in Washoe County, Nevada. We examined genetic structure of the only known population by analyzing patterns of allozyme variation. Our results suggest that Steamboat buckwheat has high genetic variability, with levels of variation similar to that typical of a widespread species rather than a narrow endemic. Genotype frequencies suggest that mating is random. We detected no genetic subdivision of the population. Several clones spanning up to 67 cm were found, but we do not know if such clones are common. We used allozyme data to assess the genetic similarity of var. williamsiae to five other varieties of E. ovalifolium. All six varieties are very similar allozymically with var. williamsiae being the most similar to the widespread var. ovalifolium. Although var. williamsiae and var. ovalifolium are morphologically distinct, their genetic similarity warrants further study to determine whether or not they should be treated as separate taxa. Evidence of male sterility in var. williamsiae plus other data leads us to hypothesize that this taxon might be either a hybrid or undergoing cytoplasmic introgression. Information gathered from this study, in concert with ongoing work on the breeding system of Steamboat buckwheat, should be helpful in forming management strategies for this plant.  相似文献   

16.
The Old Kladruber horses arose in the 17th century as a breed used for ceremonial purposes. Currently, grey and black coat colour varieties exist as two sub-populations with different recent breeding history. As the population underwent historical bottlenecks and intensive inbreeding, loss of genetic variation is considered as the major threat. Therefore, genetic diversity in neutral and non-neutral molecular markers was examined in the current nucleus population. Fifty microsatellites, 13 single nucleotide polymorphisms (SNPs) in immunity-related genes, three mutations in coat colour genes and one major histocompatibility (MHC-DRA) gene were studied for assessing genetic diversity after 15 years of conservation. The results were compared to values obtained in a similar study 13 years ago. The extent of genetic diversity of the current population was comparable to other breeds, despite its small size and isolation. The comparison between 1997 and 2010 did not show differences in the extent of genetic diversity and no loss of allele richness and/or heterozygosity was observed. Genetic differences identified between the black and grey sub-populations observed 13 years ago persisted. Deviations from the Hardy–Weinberg equilibrium found in 19 microsatellite loci and in five SNP loci are probably due to selective breeding. No differences between neutral and immunity-related markers were found. No changes in the frequencies of markers associated with two diseases, melanoma and insect bite hypersensitivity, were observed, due probably to the short interval of time between comparisons. It, thus, seems that, despite its small size, previous bottlenecks and inbreeding, the molecular variation of Old Kladruber horses is comparable to other horse breeds and that the current breeding policy does not compromise genetic variation of this endangered population.  相似文献   

17.
Low genetic variation is often considered to contribute to the extinction of species when they reach small population sizes. In this study we examined the mitochondrial control region from museum specimens of the Heath Hen (Tympanuchus cupido cupido), which went extinct in 1932. Today, the closest living relatives of the Heath Hen, the Greater (T. c. pinnatus), Attwater’s (T. c. attwateri) and Lesser (T. pallidicinctus) Prairie-chicken, are declining throughout most of their range in Midwestern North America, and loss of genetic variation is a likely contributor to their decline. Here we show that 30 years prior to their extinction, Heath Hens had low levels of mitochondrial genetic variation when compared with contemporary populations of prairie-chickens. Furthermore, some current populations of Greater Prairie-chickens are isolated and losing genetic variation due to drift. We estimate that these populations will reach the low levels of genetic variation found in Heath Hens within the next 40 years. Genetic variation and fitness can be restored with translocation of individuals from other populations; however, we also show that choosing an appropriate source population for translocation can be difficult without knowledge of historic population bottlenecks and their effect on genetic structure.  相似文献   

18.
The finless porpoise (genus Neophocaena) is a poorly known cetacean of great conservation concern. Within its range, from western Pacific to northwestern Indian Ocean, there are currently two species recognized (N. asiaeorientalis and N. phocaenoides), thought to be reproductively isolated since last glacial maximum, with the only sympatric overlap zone in Taiwan Strait. However, the genetic variation across the genus’ distribution has not yet been extensively studied, especially in the Indian Ocean. We performed an exhaustive review of molecular data of the finless porpoise across its range. Neighbor-net networks analyses based on two mitochondrial loci (control region/CR and cytochrome b/cyt b) suggest that finless porpoises from the Indian and Pacific Ocean constitute two distinct clades, well-defined by fixed mutations at both loci. A molecular clock analyses indicate early split (CR: 13.1 Ma, cyt b: 12.9 Ma) between these two oceanic lineages, while spatial genetic analyses further suggest that in the Pacific the divergence was primarily due to the taxon from Japanese waters rather than inter-species divergence across the Taiwan Strait. As extinction risks can be substantially underestimated if threatened species are pooled together with non-threatened, especially in the absence of long-distance migration, we suggest that the present 2-species taxonomy of the genus Neophocaena should be given further examination, with concerted sampling effort in the Western Indian Ocean. More research effort and genomic information is needed before taxonomic revisions can be considered; such further studies are strongly recommended as they may affect the current status classification of the species constituting the genus Neophocaena. Most notably, the narrow-ridged finless porpoise off Japan merits urgent conservation attention.  相似文献   

19.
Marine species with high fecundities and mortalities in the early life stages can have low effective population sizes, making them vulnerable to declines in genetic diversity when they are commercially harvested. Here, we compare levels of microsatellite and mitochondrial sequence variation in the western rock lobster (Panulirus cygnus) over a 14-year period to test whether genetic variation is being maintained. Panulirus cygnus is a strong candidate for loss of genetic variation because it is a highly fecund species that is likely to experience high variance in reproductive success due to an extended larval planktonic stage. It also supports one of the largest and most economically important fisheries in Australia, with landings of between 8,000 and 14,500 tons (~70 % of the total legal-sized biomass) being harvested in some years. We found remarkably high levels of genetic variation in all samples and no evidence of a decline in genetic diversity over the time interval we studied. Furthermore, there was no evidence of a recent genetic bottleneck, and effective population size estimates based on single sample and temporal methods were infinitely large. Analysis of molecular variance indicated no significant population structure along 960 km of coastline or genetic differentiation among temporal samples. Our results support the view that P. cygnus is a single, panmictic population, and suggest genetic drift is not strong enough to reduce neutral genetic diversity in this species if current management practices and breeding stock sizes are maintained.  相似文献   

20.
Genetic variation plays a pivotal role in species viability and the maintenance of population genetic variation is a main focus of conservation biology. Threatened species often show reduced genetic variation compared to non-threatened species, and this is considered indicative of lowered evolutionary potential, compromised reproductive fitness, and elevated extinction risk. The southern purple-spotted gudgeon, Mogurnda adspersa, is a small freshwater fish with poor dispersal potential that was once common throughout the Murray–Darling Basin (MDB) and along the central east coast of Australia. Its numbers and distribution have shrunk dramatically in the MDB due to flow alteration, degradation of habitat, decreasing water quality, and introduction of alien species. We used microsatellite DNA markers to assess population structure and genetic variation at both large (i.e. across basin) and fine (i.e. within river catchments) spatial scales using a substantial sampling effort across the species range (n = 579 individuals; 35 localities). The results consistently indicated very low levels of genetic variation throughout, including along the east coast where the species is relatively common. At the broader scale, three highly differentiated groups of populations were found, concordant with previously reported genealogical distinctiveness. Hence we propose each group as a distinct Evolutionarily Significant Unit. We also inferred a minimum of 12 management units in M. adspersa, with no appreciable gene flow between them. Our study discloses findings relevant for both long- and short-term management, as it informs on the geographic context in which conservation priorities should be defined and specifies biological units for population monitoring and translocations.  相似文献   

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