Genetic consequences of an introduction-colonization process in an endangered butterfly species

From a theoretical point of view, the genetic consequences of foundation events are relatively well known but few field experimental data are available on this subject. At the beginning of the 1970s, a small number of Proclossiana eunomia females were released in a region where this glacial relict was absent. We report here the genetic aspects of the evolution of the populations generated by these translocations. Both enzyme electrophoresis and wing pattern morphometry disclosed a significant differentiation of the populations both with their mother population and within themselves. Field observations and enzyme data suggest a stepping-stone colonization process, but there is no significant isolation by distance at this stage of population establishment, as predicted by 32 model. Concerning phenotypic characters, there is a significant correlation between morphometric and geographical distances; this may be due to isolation by distance but the action of environmental gradients cannot be excluded. Our results show that this colonization, although induced with a low number of founders, was a success, despite a predicted loss of polymorphism.     

Coastal heathland succession influences butterfly community composition and threatens endangered butterfly species

Succession has a strong influence on species diversity and composition of semi-natural open terrestrial ecosystems. While several studies examined the effects of succession on butterflies in grassland and forest ecosystems, the response of heathland butterflies to succession had not been investigated so far. To address this issue we sampled butterfly abundance and environmental parameters on the Baltic island of Hiddensee (NE Germany) along a gradient of coastal heathland succession from grey dunes to birch forest. Our results provide evidence that succession of coastal heathland has a strong influence on butterfly diversity, abundance, and species composition. Thereby grass and tree encroachment present the main threats for heathland butterflies. Diversity and abundance of butterflies were highest in shrub-encroached heath directly followed by early stages of coastal heathland succession (dwarf-shrub heath, grey dune). Both observed threatened species (Hipparchia semele, Plebeius argus) were negatively affected by succession: abundance decreased with increasing vegetation density (both species) and grass cover (P. argus); consequently, the two later successional stages (shrub, birch forest) were not occupied. Our findings highlight the importance of the preservation of early stages of coastal heathland succession for endangered butterfly species. For coastal heathland management we therefore suggest to maintain early successional stages by sheep grazing, mowing or, in case of high nutrient contents, intensive techniques such as sod-cutting or choppering. To a lower extend shrub-encroached sites should also be present, which might be beneficial for overall species richness.     

Structure and genetic diversity of Ixora margaretae an endangered species

The dry forests of New Caledonia are an exceptional ecosystem because of their numerous endemic botanical species and their highly diversified fauna of insects, mollusks, reptiles and birds. Unfortunately, the area of the dry forests has been significantly reduced, mainly by human activities. Ecological, phenological and genetic analysis of Ixora margaretae, a symbolic species of the sclerophyll forest, has revealed contrasting traits among natural stands. The division of the natural range and then the separation of forest islands has greatly reduced the existing genetic variability of this species. The genetic diversity is strongly structured in genetic clusters which correspond well to specific ecotypes according to the environmental conditions and the forest types. Furthermore, genetic analysis of the reproductive and non-reproductive trees as well the half-sib families obtained by complete protection of mother trees has revealed substantial genetic drift which has resulted in increased loss of allelic variability. The total consumption of seeds by mainly rats confirms the observed absence of natural regeneration. All these results show that measures taken to protect the stands of dry forests will not be enough to maintain sufficient genetic variability of I. margaretae populations in the long term. Assisted regeneration with control of the increase in variability will be necessary to maintain the biodiversity of the species. The results obtained for I. margaretae must be confirmed with other symbolic species in order to take the necessary measures for the effective preservation of the dry forests in New Caledonia.     

Metapopulation structure and dynamics of an endangered butterfly

Recovery plans for endangered invertebrates will improve with a better understanding of population dynamics and structure. Some spatially distributed structures beyond the classic metapopulation, including highly integrated patchy populations and core-satellite, maybe better suited for the recovery of endangered populations. In this study we examined the population dynamics of the Karner blue butterfly, Lycaeides melissa samuelis (Nabokov) [Lepidoptera: Lycaenidae], which is federally endangered in the USA, at eleven sites at Fort McCoy, Wisconsin. Adult L. m. samuelis butterflies were surveyed approximately weekly at each site using a straight line transect method. We used autocorrelation and partial autocorrelation function to look for patterns in the population dynamic, and tested for density-dependent growth and weather factors as potential explanatory factors of the yearly variation. We found non-declining or stable Karner blue populations at all eleven sites at Fort McCoy, a long-term trend and an alternating generational cycle. The trend occurred at seven of the eleven sites and was synchronous, suggesting that Karner blue butterflies were not functioning as a classic metapopulation and maybe functioning as a patchy metapopulation. We also found density-dependent growth and a positive relationship between early summer precipitation and population growth from the spring to summer generation. We suggest that aiming to recover patchy metapopulations will reduce monitoring costs, simplify reserve design, and create more robust populations, which are more likely to persist into the future.     

Preferred habitat and effective population size drive landscape genetic patterns in an endangered species

Landscape genetics provides a framework for pinpointing environmental features that determine the important exchange of migrants among populations. These studies usually test the significance of environmental variables on gene flow, yet ignore one fundamental driver of genetic variation in small populations, effective population size, N_e. We combined both approaches in evaluating genetic connectivity of a threatened ungulate, woodland caribou. We used least-cost paths to calculate matrices of resistance distance for landscape variables (preferred habitat, anthropogenic features and predation risk) and population-pairwise harmonic means of N_e, and correlated them with genetic distances, F_ST and D_c. Results showed that spatial configuration of preferred habitat and N_e were the two best predictors of genetic relationships. Additionally, controlling for the effect of N_e increased the strength of correlations of environmental variables with genetic distance, highlighting the significant underlying effect of N_e in modulating genetic drift and perceived spatial connectivity. We therefore have provided empirical support to emphasize preventing increased habitat loss and promoting population growth to ensure metapopulation viability.     

Mammalian herbivores reveal marked genetic divergence among populations of an endangered plant species

Quantitative genetically based traits in dominant and keystone tree species can have extended effects on other biota and also on ecosystem processes. This has direct implications for managed plant systems, where choice of genetic stock in conservation or commercial plantings will affect the ecological and evolutionary trajectory of the associated biotic communities. Hence an understanding of genetic variation in quantitative traits, especially those that relate directly to fitness, should be incorporated into the management of species. In plants, quantitative traits such as foliar defences that mediate the complexity of biotic interactions (e.g. herbivory), may be key fitness traits to consider in the management of gene pools of species that are of high conservation value. In this paper we examine the interactions of an endangered eucalypt species, Eucalyptus morrisbyi and a marsupial herbivore, the common brushtail possum Trichosurus vulpecula. We investigate the genetic variability of resistance of plants sourced from two populations and genetic variability in foliage defences as key quantitative traits that may be essential for survival of this eucalypt species. Trichosurus vulpecula detect clear genetic divergence in the two E. morrisbyi populations as evidenced by their browsing preferences in the field. In addition, trees from the more susceptible population (Calverts Hill) suffered fitness consequences with lower flowering than trees from the more resistant population (Risdon Hills). Field feeding preferences were confirmed in captive feeding trials arguing differences were due to foliar attributes consistent with the genetic‐based differences observed in key chemical and physical foliage traits. Biotic interactions such as herbivory may affect populations of rare plant species. Results of this study highlight the need to understand the degree of genetic differentiation of resistance to herbivores and in the quantitative traits mediating these interactions in species of high conservation value, as these traits affect the adaptive potential of populations.     

Local genetic population structure in an endangered plant species, Silene tatarica (Caryophyllaceae)

Genetic substructuring in plant populations may evolve as a consequence of sampling events that occur when the population is founded or regenerated, or if gene dispersal by pollen and seeds is restricted within a population. Silene tatarica is an endangered, perennial plant species growing along periodically disturbed riverbanks in northern Finland. We investigated the mechanism behind the microspatial genetic structure of S. tatarica in four subpopulations using amplified fragment length polymorphism markers. Spatial autocorrelation revealed clear spatial genetic structure in each subpopulation, even though the pattern diminished in older subpopulations. Parentage analysis in an isolated island subpopulation indicated a very low level of selfing and avoidance of breeding between close relatives. The mean estimated pollen dispersal distance (24.10 m; SD = 10.5) was significantly longer and the mean seed dispersal distance (9.07 m; SD = 9.23) was considerably shorter than the mean distance between the individuals (19.20 m; SD = 13.80). The estimated indirect and direct estimates of neighbourhood sizes in this subpopulation were very similar, 32.1 and 37.6, respectively. Our results suggested that the local spatial genetic structure in S. tatarica was attributed merely to the isolation-by-distance process rather than founder effect, and despite free pollen movement across population, restricted seed dispersal maintains local genetic structure in this species.     

Nectar and hostplant scarcity limit populations of an endangered Oregon butterfly

As grassland habitats become degraded, declines in juvenile and adult food resources may limit populations of rare insects. Fender's blue butterfly (Icaricia icarioides fenderi), a species proposed for listing as endangered under the US Endangered Species Act, survives in remnants of upland prairie in western Oregon. We investigated the effects of limited larval hostplants and adult nectar sources on butterfly population size at four sites that encompass a range of resource densities. We used coarse and detailed estimates of resource abundance to test hypotheses relating resource quantity to population size. Coarse estimates of resources (percent cover of hostplant and density of nectar flowers) suggest that butterfly population size is not associated with resource availability. However, more detailed estimates of resources (density of hostplant leaves and quantity of nectar from native nectar sources) suggest that butterfly population size is strongly associated with resource availability. The results of this study suggest that restoring degraded habitat by augmenting adult and larval resources will play an important role in managing populations of this rare butterfly. Received: 20 June 1998 / Accepted: 25 November 1998     

Forest characteristics and population structure of Glyptostrobus pensilis,a globally endangered relict species of southeastern China

The Chinese water pine Glyptostrobus pensilis is the sole surviving species of the genus Glyptostrobus. It is endemic to southern China, central Vietnam, and eastern Laos, and today it is nearly extinct in the wild. Forest community characteristics and population structure of G. pensilis in China have remained un-known up to now. We investigated six swamp forest stands and analyzed their forest community characteristics (i.e. vertical stratification, species composition, and diversity) and population structure, including the frequency distribution of DBH (diameter at breast height) and age-classes as found in Fujian Province, southeastern China. The vertical stratifications of all the forest stands were rather simple. The remaining wild specimens ranged from roughly 15 to some 357 years for an average of ca. 85 years, with only a few individuals less than 20 years old. Compared with the stands and populations of G. pensilis in Vietnam, the taxonomic compositions of the stands in the two regions were different, except for the dominant species-G. pensilis. The Shannon-Wiener index showed the overstory of each stand had much lower diversity (0.26 on average) in Fujian Province than that (1.97 on average) in Vietnam, whereas the diversity indices were about the same (around 2.41) for the understories in the two regions. Furthermore, we discovered 18 G. pensilis seedlings at the study sites in Fujian Province. This discovery demonstrates that G. pensilis regeneration is extremely poor and its populations are declining, although these populations are rela-tively healthier than those in Vietnam.     

The great scallop: an endangered species

The great scallop is a highly valued marine species. It makes its home on rocky seabeds around the British Isles and has been heavily exploited. Fears that natural stocks are showing signs of over fishing are being remedied by strict enforcement of fisheries legislation and by the development of stock enhancement practices.     

Rapid loss of genetic variation in an endangered possum

The endangered mountain pygmy possum is the only Australian marsupial that hibernates under snow cover. Most of its alpine habitat was burnt by a rare fire in 2003, and habitat loss and disturbance have also occurred owing to ski resort development. Here we show that there has been a rapid loss of genetic variation following habitat loss associated with resort development, but no detectable loss of alleles or decrease in heterozygosity following the fire.     

Reproductive biology and spawning habitat supplementation of the relict darter, Etheostoma chienense, a federally endangered species

We investigated the reproductive biology of Etheostoma chienense in the Bayou du Chien drainage of western Kentucky. Etheostoma chienense is similar in its ecology and reproductive biology to other members of the E. squamiceps complex. However, E. chienense is opportunistic in its choice of egg deposition substrates, as nests were found on a variety of natural and anthropogenic items. Due to an apparent lack of suitable spawning substrates, we added half-cylindrical ceramic tiles to several stretches of stream to increase potential nest productivity. Egg-clutches attached to artificial substrates were twice the size of egg clutches attached to naturally occurring materials. Laboratory experiments were conducted to determine nest rock size and mate choice preferences. Both the size of the male and of the nest rock appeared to be important parameters to spawning females. The life history information gathered here has significant management implications. Artificial spawning substrates should be placed in appropriate microhabitats (i.e., shallow, low-flow reaches in headwaters). Nest cavity vertical height should be about 3.0 cm and tiles should be spaced at least 0.5 m apart. We feel the use of surrogates (e.g., E. oophlyax) to investigate other types of spawning cover, and restoration of riparian buffer zones among other actions, would particularly benefit recovery efforts for this endangered species.     

Allorecognition in the Tasmanian devil (Sarcophilus harrisii), an endangered marsupial species with limited genetic diversity

Tasmanian devils (Sarcophilus harrisii) are on the verge of extinction due to a transmissible cancer, devil facial tumour disease (DFTD). This tumour is an allograft that is transmitted between individuals without immune recognition of the tumour cells. The mechanism to explain this lack of immune recognition and acceptance is not well understood. It has been hypothesized that lack of genetic diversity at the Major Histocompatibility Complex (MHC) allowed the tumour cells to grow in genetically similar hosts without evoking an immune response to alloantigens. We conducted mixed lymphocyte reactions and skin grafts to measure functional MHC diversity in the Tasmanian devil population. The limited MHC diversity was sufficient to produce measurable mixed lymphocyte reactions. There was a wide range of responses, from low or no reaction to relatively strong responses. The highest responses occurred when lymphocytes from devils from the east of Tasmania were mixed with lymphocytes from devils from the west of Tasmania. All of the five successful skin allografts were rejected within 14 days after surgery, even though little or no MHC I and II mismatches were found. Extensive T-cell infiltration characterised the immune rejection. We conclude that Tasmanian devils are capable of allogeneic rejection. Consequently, a lack of functional allorecognition mechanisms in the devil population does not explain the transmission of a contagious cancer.     

Levels and patterns of genetic variation in the endangered species Abronia macrocarpa

Genetic variation was evaluated in the federally endangered species Abronia macrocarpa (large-fruited sand-verbena), an herbaceous perennial restricted to deep sandy soils and endemic to three counties of east-central Texas. Seven of the ten known populations were sampled and analyzed using starch gel electrophoresis of eight enzymes coded by 18 interpretable loci. Duplicate gene expression was observed for four loci, suggesting polyploid ancestry for the lineage that includes A. macrocarpa. Values for estimators of genetic polymorphism within populations (ranges: P = 38.9%-61.1%, A = 1.7-2.1, H = 0.122-0.279) exceeded average values for seed plants (P = 34.2%, A = 1.53, H = 0.113). Genotype proportions at most loci in most populations were in Hardy-Weinberg equilibrium, consistent with obligate outcrossing previously documented for this species; exceptions could be attributed to population substructure. Values of F(ST) tended to be high, ranging from 0.021 to 0.481 for individual loci (mean F(ST) = 0.272), indicating substantial divergence and limited gene flow among populations, despite their close geographic proximity. Pairwise values of Nei's genetic identity between populations ranged from 0.799 to 0.975 and tended to be influenced by geographic proximity of population pairs. Collectively, these data suggest a long history of isolation among populations that have not been subjected to bottlenecks. Isolation of A. macrocarpa populations apparently results from the disjunct occurrence of suitable habitat and perhaps has been accentuated by human disturbance.