Effect of temperature on spontaneous interneuron activity in grasshoppers Tettigonia cantans and Metrioptera roeselii (Orthoptera, Tettigoniidae)

Using electrophysiological methods, effects of temperature on rhythmic impulsation of spontaneously active neurons of thoracic ganglia was studied in grasshoppers Tettigonia cantans and Metrioptera roeselii. Several types of response to temperature changes were observed. Its elevation caused an increase or decrease of the discharge dispersion and a gradual, proportional or abrupt rise of the impulse rate. On decreasing temperature, the impulsation usually returned to its original state, although sometimes at different rate. In neurons whose impulse rate was close to that of pulse repetition rate in male advertisement calls, this dependence was preserved at temperature changes. On the whole, there is reason to believe that changes of temperature in CNS are accompanied not only by a simple change of the neuronal activity level, but also by a complex readjustment in the neuronal network functioning, which allow preserving optimal level of insect metabolic processes and adequate behavior.     

Dispersal in a metapopulation of the bush cricket, Metrioptera bicolor (Orthoptera: Tettigoniidae)

1. I present a stochastic simulation model that describes individual movements of Metrioptera bicolor Philippi in a heterogeneous landscape, consisting of patches of suitable habitat surrounded by a matrix of unprofitable habitats. Although the model is parameterized with information about daily movement behaviour, it can generate spatially explicit predictions about inter-patch dispersal rates for much longer periods, e.g. one generation.
2. Long-term dispersal experiments were conducted to evaluate model predictions. Patch-specific emigration rates and the total distance moved by individuals could be predicted with satisfactory precision. Because of the stochastic nature of the model, it failed to predict which recipient patches emigrating individuals actually chose in a particular situation.
3. Spatially explicit simulations of the movement model were made for the whole natural distribution area of M. bicolor . The results suggest that emigration rates are negatively correlated with patch size. Local populations occurring on small patches may be more prone to extinction than those on large patches, by losing more emigrants than are compensated for by immigration.     

Seasonal pattern in population dynamics and host plant use of non‐swarming Ruspolia differens Serville (Orthoptera: Tettigoniidae)

The edible Ruspolia differens (Serville) (Orthoptera: Tettigoniidae) is an important source of food in East Africa, but the seasonality of its population dynamics and host plant use are not fully understood. We studied seasonal patterns in the population density and relative frequency of developmental stages, sexes, colour morphs and host plants of the non‐swarming R. differens at two study sites in central Uganda over 15 months. Linear mixed models were used to study how precipitation and Enhanced Vegetation Index (EVI) predict population density and relative frequency of developmental stages, sexes, colour morphs and host plants. The results showed that all developmental stages of non‐swarming R. differens were found in the field throughout the year. The population densities of R. differens were high in wet seasons and low in dry seasons and were best predicted by the EVI of the previous month. The sex ratio of the non‐swarming R. differens populations was female biased. The proportion of males and green colour morphs increased during and after the rainy season. The use of host plants fluctuated seasonally so that during the greener seasons individuals used the more preferred host Panicum maximum more frequently. Overall, our work indicates that R. differens has a seasonal dynamic so that vegetation greenness can be used to forecast non‐swarming R. differens population densities. Our results also suggest that source populations for swarming individuals might have a local origin. This is important for the management of habitats for reproduction and conservation of viable populations of R. differens in East Africa.     

The influence of environmental factors on dormancy and duration of egg development in Metrioptera roeseli (Orthoptera: Tettigoniidae)

Summary Developing eggs of Metrioptera roeseli HGB. have an obligate embryonic diapause in stage 23 and a facultative initial diapause in stage 4. Initial diapause is lacking when the ovipositing females are kept at long day photoperiod (LD 16/8), but is induced at LD 14/10 and LD 8/16. When natural light conditions are given in the laboratory, the females mostly lay diapausing eggs from the end of August onwards. In eggs without initial diapause, a larger number of embryos reach a stage, in which the embryonic diapause can be broken by chilling, only at favorable temperature (4 weeks at 24°C or 8 at 18°C) and in contact with water before the first winter. Thus, some individuals of a given population of M. roeseli have an annual, others a biennial life cycle. The variability in the duration of egg development is due to a photoperiodically induced, facultative initial diapause and to a possible quiescence caused by insufficient temperature and/or moisture.     

Microsatellite diversity and population genetic structure of Squalidus argentatus (Cyprinidae) on the Island of Hainan and mainland China

Squalidus argentatus is a small-sized cyprinid fish and widely distributed in mainland China. A total of nine polymorphic microsatellite markers were employed to study 216 individuals collected from nine populations. The average number of alleles among nine populations was 8.0 with a range from 6.5 to 9.7. The mean observed (H_O) and expected (H_E) heterozygosity ranged from 0.56 to 0.68 and from 0.74 to 0.86, respectively. The analysis of molecular variance (AMOVA) showed that most genetic variation was maintained within individual component, rather than shaped according to geographical regions. Small but highly significant values of pairwise F_ST values were detected among nine populations. The genetic homoplasy and overfishing are supposed to be major factors responsible for the current genetic structure. This study can be not only helpful for sustainable management of genetic resources, but also valuable to demonstrate genetically how freshwater species is vulnerable to human activity.     

Assessment of genetic diversity and population structure of Bergenia stracheyi (Saxifragaceae) in the Western Himalaya (India)

Genetic diversity and population structure in Bergenia stracheyi, a threatened medicinal herb in the Western Himalaya of India was analysed using directed amplification of minisatellite DNA (DAMD) and inter simple sequence repeats (ISSR) markers. A total of 41 accessions of B. stracheyi representing three populations (Khillenmarg –KLM, Jalori Pass-JLP and Rohtang-RTG) were considered in the present study. The cumulative data analysis for 26 (10 DAMD + 16 ISSR) markers revealed 87.1% polymorphism. The maximum inter-population genetic distance was found between KLM and JLP, whereas the minimum genetic distance was found between RTG and JLP populations. The analysis of molecular variance (AMOVA) revealed maximum percentage of variation among individuals within populations (75%) than among the populations (25%). Clustering pattern of the three sample populations in STRUCTURE and PCoA analyses showed high genetic variation at population level. The present study revealed that distribution patterns, high altitudinal ranges, high habitat specificity, relatively high gene flow, small and isolated population size have shaped the current population structure of B. stracheyi in the Western Himalayan region. DAMD and ISSR markers have provided significant insights into characterization of B. stracheyi populations, and facilitate selection of appropriate accessions for further utilization in conservation and bioprospecting programmes.     

Variation in outcrossing rate and population genetic structure of Clarkia tembloriensis (Onagraceae)

Summary Outcrossing rate estimates for eight accessions of Clarkia tembloriensis indicate that this annual plant species has a wide interpopulational range of outcrossing rate ( ). Populations' t estimates were significantly correlated with observed heterozygosity and mean number of alleles per locus. Estimated fixation indices, , for most populations were very close to their expected values, F_eq, for a given Nei's gene diversity statistics showed that the group of outcrossing populations have more total genetic variation and less differentiation among populations than does the group of selfing populations. These results indicate that the breeding system of C. tembloriensis has had a strong influence on the amount and distribution of genetic variation within and among its populations.     

Strong intraspecific variation in genetic diversity and genetic differentiation in Daphnia magna: the effects of population turnover and population size

Theory predicts that genetic diversity and genetic differentiation may strongly vary among populations of the same species depending on population turnover and local population sizes. Yet, despite the importance of these predictions for evolutionary and conservation issues, empirical studies comparing high‐turnover and low‐turnover populations of the same species are scarce. In this study, we used Daphnia magna, a freshwater crustacean, as a model organism for such a comparison. In the southern/central part of its range, D. magna inhabits medium‐sized, stable ponds, whereas in the north, it occurs in small rock pools with strong population turnover. We found that these northern populations have a significantly lower genetic diversity and higher genetic differentiation compared to the southern/central populations. Total genetic diversity across populations was only about half and average within‐population diversity only about a third of that in southern/central populations. Moreover, an average southern population contains more genetic diversity than the whole metapopulation system in the north. We based our analyses both on silent sites and microsatellites. The similarity of our results despite the contrasting mutation rates of these markers suggests that the differences are caused by contemporary rather than by historical processes. Our findings show that variation in population turnover and population size may have a major impact on the genetic diversity and differentiation of populations, and hence may lead to differences in evolutionary processes like local adaptation, hybrid vigour and breeding system evolution in different parts of a species range.     

Development of new EST-derived SSRs in Salvia miltiorrhiza (Labiatae) in China and preliminary analysis of genetic diversity and population structure

Salvia miltiorrhiza, known as Dan-shen in China, is a well-known and important medicinal herb in Asia. Its root and rhizome has been used to treat cardiovascular diseases in China for centuries. Recently, it had been widely cultivated in China due to a rapid decline in wild resources. However, the germplasm resources of different cultivated regions are extremely variable. Here, new simple sequence repeats (SSRs) from expressed sequence tags (ESTs) were mined to analyze the frequency and distribution of SSRs, assess the validity of developed EST-SSR marker and identify new EST-SSR marker for the preparatory investigation of the population structure in cultivated S. miltiorrhiza. This study showed that 5160 unique ESTs were accumulated from database, 760 SSRs combined with 41 types of SSR motifs were mined. High polymorphism and transferability were presented in newly developed EST-SSR marker. It also showed that cultivated S. miltiorrhiza were mainly divided into three large groups. The results suggested that S. miltiorrhiza may has high abundance of SSRs in transcribed regions of genome and the developed EST-SSR marker may be useful for analysis of genetic diversity and population structure.     

Relationship between microspatial population genetic structure and habitat heterogeneity in Pomatias elegans (O.F. Müller 1774) (Caenogastropoda, Pomatiasidae)

In the present study the population genetic structure of the terrestrial snail Pomatias elegans was related to habitat structure on a microspatial scale. The genetic variability of 1607 individuals from 51 sampling sites in five different populations in Provence, France, was studied with an allozyme marker using population genetic methods, Mantel tests and spatial autocorrelation techniques were applied to different connectivity networks accounting for the structural features of the landscape. It is suggested that the population structure is, to a large extent, a function of the habitat quality, quantified as population density, and of the spatial arrangement of the habitat in the landscape and not of the geographical distance per se . In fragmented habitats, random genetic drift was the prevailing force for sampling sites separated by a few hundred meters.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 565–575.     

Production and structure in the early stages of vegetation development in the Lauwerszee-polder

Summary In this study on vegetation development in the newly enclosed polder of the former Lauwerszee-estuary, data are presented on a qualitative and quantitative analysis of the pioneer vegetation of five experimental areas over the first four years. The methods used and the background to the study are briefly outlined. Data are given on structure, in terms of density and biomass, involving the speciesSalicornia spp., Suaeda maritima, Atriplex hastata andSpartina × townsendii and on soil factors (carbonate, organic matter, texture, K, P, total N, mineral N, pH and salt). Pattern and process in the pioneer stages are discussed, especially the underlying changes in environmental conditions and the behaviour of species in relation to these conditions. Only the halophytes mentioned could cope with the conditions of high salinity. It was found that in the initial phase plant densities are determined by the available amount of seeds, while after three years the total number and biomass is limited by environmental factors, especially those affecting soil-fertility. Thanks are due to Prof. Dr. D. Bakker for his stimulating and continuous interest in all stages of the present study and to Dr. A. J. Gray for critical reading and correcting of the English text. The project was realized by financial support of the Netherlands Organisation for the Advancement of Pure Research (Z.W.O.).     

Fluctuating asymmetry, call structure and the risk of attack from phonotactic parasitoids in the bushcricket Sciarasaga quadrata (Orthoptera: Tettigoniidae)

The acoustically orienting parasitoid Homotrixa alleni (Diptera: Tachinidae) is a significant mortality factor of calling male Sciarasaga quadrata (Orthoptera: Tettigoniidae), with less than 10% of males escaping parasitism within the duration of the calling season. This study examined fluctuating asymmetry (FA) (small, random deviations from perfect symmetry) in five morphological traits in S. quadrata and its relation to the survival of calling males in the field. A significant relationship was demonstrated in only a single trait; across three consecutive field seasons and among each of the collections per season, parasitised males were shown to have significantly more asymmetric hind tibia than unparasitised males. Since the morphological development of males is complete prior to parasitoid attack, this relationship is not caused by the activities of the parasitoid. Further experimentation revealed that there was no relationship between the level of FA in the hind tibia and the success of parasitism, with males artificially parasitised in the laboratory showing no difference in FA from those where parasitism was unsuccessful. Instead, FA was shown to be negatively related to chirp length, an aspect of call structure that significantly affects the survival of calling males under parasitism risk in the field. We explore the possible reasons why more asymmetric males produce calls of shorter chirp length and hypothesise that the difference in hind tibia asymmetry seen between parasitised and unparasitised males in the field is related to host location in H. alleni rather than the inability of S. quadrata to defend itself against parasitoid attack. Received: 14 November 1997 / Accepted: 20 April 1998     

Comparison of distance matrices in studies of population structure and genetic microdifferentiation: quadratic assignment

Questions concerning the relative effects of various evolutionary forces in molding the genetic variability exhibited by groups of human populations have typically been investigated by comparing a variety of genetic and cultural/historical "distance" matrices. A major methodological difficulty has been the lack of formal testing procedures with which to assess the degree of confirmation or disconfirmation of an estimated measure of relationship between such matrices. In this paper, we examine a very flexible matrix combinatorial procedure which generates statistical significance levels for correlational measures of pattern similarity between distance matrices. A recent generalization of the basic procedure to the three-matrix case allows questions concerning which of two matrices best fits a third matrix to be formally tested. Applications of these hypothesis testing and inference procedures to two separate sets of genetic, geographic, and cultural distance matrices illustrates their potential for finally solving a long-standing problem in anthropological genetics.     

Main roads and land cover shaped the genetic structure of a Mediterranean island wild boar population

Patterns of genetic differentiation within and among animal populations might vary due to the simple effect of distance or landscape features hindering gene flow. An assessment of how landscape connectivity affects gene flow can help guide management, especially in fragmented landscapes. Our objective was to analyze population genetic structure and landscape genetics of the native wild boar (Sus scrofa meridionalis) population inhabiting the island of Sardinia (Italy), and test for the existence of Isolation‐by‐Distance (IBD), Isolation‐by‐Barrier (IBB), and Isolation‐by‐Resistance (IBR). A total of 393 Sardinian wild boar samples were analyzed using a set of 16 microsatellite loci. Signals of genetic introgression from introduced non‐native wild boars or from domestic pigs were revealed by a Bayesian cluster analysis including 250 reference individuals belonging to European wild populations and domestic breeds. After removal of introgressed individuals, genetic structure in the population was investigated by different statistical approaches, supporting a partition into five discrete subpopulations, corresponding to five geographic areas on the island: north‐west (NW), central west (CW), south‐west (SW), north‐central east (NCE), and south‐east (SE). To test the IBD, IBB, and IBR hypotheses, we optimized resistance surfaces using genetic algorithms and linear mixed‐effects models with a maximum likelihood population effects parameterization. Landscape genetics analyses revealed that genetic discontinuities between subpopulations can be explained by landscape elements, suggesting that main roads, urban settings, and intensively cultivated areas are hampering gene flow (and thus individual movements) within the Sardinian wild boar population. Our results reveal how human‐transformed landscapes can affect genetic connectivity even in a large‐sized and highly mobile mammal such as the wild boar, and provide crucial information to manage the spread of pathogens, including the African Swine Fever virus, endemic in Sardinia.     

Genetic structure of the forest herb Primula elatior in a changing landscape

To investigate whether changes in land use and associated forest patch turnover affected genetic diversity and structure of the forest herb Primula elatior, historical data on landscape changes were combined with a population genetic analysis using dominant amplified fragment length polymorphism markers. Based on nine topographic maps, landscape history was reconstructed and forest patches were assigned to two age classes: young (less than 35 years) and old (more than 35 years). The level of differentiation among Primula populations in recently established patches was compared with the level of differentiation among populations in older patches. Genetic diversity was independent of population size (P > 0.05). Most genetic variation was present within populations. Within-population diversity levels tended to be higher for populations located in older forests compared with those for populations located in young forests (Hj = 0.297 and 0.285, respectively). Total gene diversity was also higher for old than for young populations (Ht = 0.2987 and 0.2828, respectively). The global fixation index FST averaged over loci was low, but significant. Populations in older patches were significantly more differentiated from each other than were populations in recently established patches and they showed significant isolation by distance. In contrast, no significant correlations between pairwise geographical distance and FST were found for populations in recently established patches. The location of young and old populations in the studied system and altered gene flow because of increased population density and decreased inter-patch distances between extant populations may explain the observed lower genetic differentiation in the younger populations. This study exemplifies the importance of incorporating data on historical landscape changes in population genetic research at the landscape scale.     

Living in the city: resource availability, predation, and bird population dynamics in urban areas

This article explores factors that shape population structure in novel environments that have received scant theoretical attention: cities. Urban bird populations exhibit higher densities and lower diversity. Some work suggests this may result from lower predation pressure and more predictable and abundant resources. These factors may lead to populations with few winners and many losers regarding access to food, body condition, and reproductive success. We explore these hypotheses with an individual-energy-based competition model with two phenotypes of differing foraging ability. We show that low frequency resource fluctuations favor strong competitors and vice versa. We show that low predation skews equilibrium populations in favor of weak competitors and vice versa. Increasing the time between resource pulses can thus shift population structure from weak to strong competitor dominance. Given recent evidence for more constant resource input and lower predation in urban areas, the model helps understand observed urban bird population structure.     

Comparative population structure of three snook species (Teleostei: Centropomidae) from the eastern central Pacific

Three snook species, Centropomus viridis, Centropomus medius, and Centropomus robalito, from the eastern central Pacific, representing three of the four proposed phyletic lineages in the genus, were analyzed for genetic variability by means of allozyme and RAPD to evaluate the divergence between populations at different levels of dispersal ability and to evaluate the importance of barriers to dispersal in the population subdivision and genetic diversity. Levels of genetic diversity among species estimated by allozymes were similar and consistent with the observed levels of differentiation in marine fish species. Mean heterozygosity ranged from 0.089 for C. viridis to 0.10 for C. robalito. Genetic diversity for the snook species studied was slightly higher than the mean estimation reported in allozymes for 106 marine fish (0.055) and for anadromous fish species (0.043 to 0.057). Multilocus allele frequency homogeneity tests and population-subdivision estimates for both allozyme and RAPD markers revealed the existence of population structure in C. viridis and C. medius, in coincidence with geographic separation of samples, whereas no divergence was detected in C. robalito. This finding may be attributed to the greater population size of C. robalito, which originated by a recent population range expansion, and hence the potential for dispersal is mediated by larval drift. Fluctuations in population size and population range expansion are used to explain discrepancies between levels of genetic diversity and population structure in the studied species. Supplementary material to this paper is available in electronic format at