Population studies on an endemic troglobitic beetle: geographical patterns of genetic variation, gene flow and genetic structure compared with morphometric data

Highly specialized obligatory cave beetles endemic to the French Pyrenees offer an opportunity to investigate the relative importance of environmental conditions and ecological characteristics on the organization of genetic variability, to describe the genetic structure of populations, and to assess the extent of gene flow between local populations in relation to geologic structure. Twenty-three geographically close populations of the beetle Speonomus hydrophilus occurring both in caves (reduced fluctuations in many abiotic parameters) and under the deepest layer of soil in mountains (more exposed to climatic variations) were studied. Significant genetic differentiation at 17 allozyme loci was found among populations in close proximity, as well as among those from distant parts of range. On a larger scale, genetic differences among populations appear to result from low dispersal rates between populations. The spatial patterning observed suggests that allozyme frequencies are not responding to environmentally controlled selection. Substantial genetic divergence (F(ST) = 0.112) occurred throughout the range, with important variation in levels of genetic variability (H: 0.065-0.184) among populations. A significant level of substructuring has occurred among the populations with four major geographic areas of similarity indicated. The substructuring of the species into regions suggests an influence of paleoclimatic gradient and paleoenvironment on the population's genetic structure. Also, founder effect and reduced gene flow appear to have influenced populations in the southeastern portion of the range.     

Scree habitats: ecological function,species conservation and spatial-temporal variation in the arthropod community

<Abstract>

Earlier studies suggested that the Mesovoid Shallow Substratum (MSS), a subterranean network of voids immediately under the soil and scree horizon, might play an important role in the life cycle of some troglobitic species. No ecological studies have been conducted to test whether this terrestrial shallow subterranean habitat only plays an important role for a few subterranean or preferential species, or whether it is also important for the soil faunal structure and dynamics. We investigated the spatial and temporal patterns of the arthropod community in the MSS and sub-alpine scree and analysed the correlations with environmental variables. We identified 140 soil-dwelling, characteristic and troglobitic species that inhabited the MSS in different seasonal assemblages. Combined statistical analyses of the environmental factors and seasonal variation in arthropod abundance and biomass emphasized the importance of the MSS as an ecological microrefuge for many soil-dwelling species (including important predators and detritivores) which usually live in the adjacent forests or mountain pastures. Conservation plans for invertebrates should include the protection of the MSS.     

Variabilité génétique entre les populatiosn de Speonomus zophosinus

Genetic variability was examined in six troglobitic populations of Speonomus zophosinus which were limited to a very small geographical area. Results indicate a high genetic variation and a high degree of heterozygosity (H 0.43). The genetic variability observed between the populations reveals the existence of two genetically heterogeneous groups (one upstream, one downstream. There are significant differences in the frequency of the six alleles of the locus Est 3 found in these two groups.     

Population dynamics and density-dependent seasonal mortality indices of the tick Rhipicephalus appendiculatus in eastern and southern Africa

Abstract. Eight sets of previously published data on the seasonal abundance of the tick Rhipicephalus appendiculatus in Burundi, Uganda, Tanzania and Zimbabwe are analysed to yield seasonal mortality indices. Correlations between these indices and abiotic (climatic) and biotic (tick density) variables suggest that it is the stage from females to larvae that is most sensitive to adverse abiotic conditions, specifically low moisture availability. Mortality at the other stages of the tick's life cycle is strongly density-dependent. The precise nature of this density-dependence suggests that it may be caused by acquired resistance to ticks by cattle. Robust correlations between satellite-derived vegetation indices, climatic factors and mortality indices suggest that detailed climatic data, often unavailable, may be replaced by satellite data, now widely available, for use in modelling tick populations.     

Seasonality in Southern Hemisphere freshwater phytoplankton assemblages

Seasonal climatic cycles induce corresponding fluctuations in phytoplankton abundance and productivity at all latitudes, the magnitude of these fluctuations tending to increase with distance from the Equator. In equatorial regions seasonality is dependent on prevailing wind and rainfall patterns while annual temperature fluctuations exert increasing control over seasonal events at higher latitudes. The small annual temperature range of equatorial aquatic systems increases their sensitivity to localized climatic events which can bring about diel changes that exceed normal month-to-month variations. Long-term hydrological cycles with a periodicity greater than one year can also cause dramatic changes in equatorial and tropical aquatic systems leading to greater unpredictability.The factors regulating seasonal patterns of phytoplankton abundance and species composition in equatorial and low-latitude temperate regions of the Southern Hemisphere are examined and compared with similar features in the Northern Hemisphere. Despite the striking diversity of phytoplankton populations and the wide variety of habitats they occupy, seasonal succession follows a common sequence controlled, successively, by physical, chemical and biotic factors. This permits a high degree of predictability in the environmental conditions promoting growth of different taxa.Examination of Southern Hemisphere data indicates that, at class level, phytoplankton successional sequences in Southern Hemisphere aquatic systems are in agreement with the successional paradigm formulated for northern tropical and temperate latitudes. Diatoms characterize early successional episodes and these are followed by chlorophytes, and finally blue-green algae. Extreme habitat modification (e.g. hypertrophy, salinity) tends to lead to dominance of the habitat by a single taxon, often represented by a single species. Predictions of within-taxon species succession in phytoplankton assemblages are far less precise.     

Variations in oxygen consumption of Demidoff's bushbaby (Galago demidovii, lorisidae, primates) in captivity

Summary In captivity,Galago demidovii shows annual variations in oxygen consumption which are independent of daylength cycles. This rhythm is characterized by two periods during which metabolic and sexual activities are increased: a short period in November/December; and a longer period from March to June inclusive. These two periods alternate with periods of decreased metabolic rate, of which the most pronounced extends from July to September. Another point of interest is that the basal metabolism of captive Galagos is 17.5% above the value calculated from its body weight.The physiological cycle observed in captivity is synchronized with climatic variations in Makokou (Gaboon), from where the animals originated: higher metabolic and sexual activities are correlated with rainy seasons. This study suggests that an endogenous rhythm may exist inGalago demidovii.     

The first born,their dispersal,and vole cycles

Summary On the basis of some empirical data and the existing theory of vole cycles, a new hypothesis is proposed. It explains cyclicity as an effect of obligatory dispersal of the first seasonal cohort of young (Y1) from their natal (optimal) habitats into vacant (suboptimal) habitats. This behaviour could evolve, because it increases contribution of genetic lineages with dispersing Y1, to subsequent generation. It is assumed that the dispersal of Y1 is common among vole species, it does not change during consecutive phases of the cycle, and it does not vary between cyclic and non-cyclic populations. It results in multiannual cycles only under a certain set of spatial and climatic conditions, which are discussed in a paper. Otherwise it results in annual dynamics.     

Stress levels over time in the introduced ascidian Styela plicata: the effects of temperature and salinity variations on hsp70 gene expression

Species distribution, abundance, and long-term survival are determined by biotic and abiotic regimes. However, little is known about the importance of these factors in species range expansion. Styela plicata is a solitary ascidian introduced all over the world by ship fouling, including salt marsh habitats, where introduced populations must tolerate high seasonal variations in temperature and salinity. To determine the seasonal stress levels in a salt marsh population of S. plicata, we quantified heat shock protein (hsp70) gene expression using quantitative real-time PCR throughout a 2-year cycle. Results showed that hsp70 expression varied over time, with higher stress levels recorded in summer and winter. Periodic conditions of high temperatures, particularly when coupled with low salinities, increased hsp70 gene expression. Mortality events observed every year around June were concurrent with sharp increases in temperature (>6°C), indicating that drastic changes in abiotic factors may overwhelm the observed stress response mechanisms. Determining the ability of introduced species to cope with stress, and the thresholds above which these mechanisms fail, is fundamental to predict the potential expansion range of introduced species and design efficient containment plans.     

Seasonal variations of pollution biomarkers in two populations of Corbicula fluminea (Müller)

Seasonal variations of pollution biomarkers have been studied in two populations of Corbicula fluminea (Müller) for 2 years. Clams were collected from the Sanguinet lake and the Dronne river (Southwest France), sites characterised by water of excellent and passable quality, respectively. Biological parameters studied were enzymatic activity (catalase, propionylcholinesterase, glutathione S-transferase, NADPH-cytochrome c reductase and NADH-cytochrome c reductase activities) and indicators of physiological (protein, carbohydrate, lipid and ash contents, fresh and dry tissue weights, condition factor) and reproductive (amount of oocytes present in gonads and clams incubating larvae in gills) status. Environmental parameters (e.g. water temperature, chlorophyll a concentration) were also monitored. Effects of site, sampling date and season (from spring to winter) were studied, as well as relationships between abiotic and biotic factors. Finally, an index of variability was calculated for each biomarker. Catalase, propionylcholinesterase, NADH-cytochrome c reductase and lipids experienced the most pronounced seasonal fluctuations, whereas glutathione S-transferase, NADPH-cytochrome c reductase and proteins suffered less pronounced ones. For some parameters, results differed depending on the site. Most seasonal changes were related to the reproductive cycle and/or water temperature. Implications of such variations in the use of pollution biomarkers in environmental surveys are discussed.     

Occurrence and distribution of zoosporic organisms in water bodies from Brazilian Cerrado

Zoosporic organisms are commonly found in different aquatic ecosystems; however little is known about the influence of environmental factors and seasonal fluctuations on their occurrence and distribution. This study investigated patterns of abundance, frequency and diversity of these organisms and their relationship with some abiotic factors and seasonality in a cerrado remnant in Sao Paulo, Brazil. Water samples were collected at four dates in two areas of this remnant during the rainy and dry seasons, and 13 abiotic factors were analyzed. From 48 samples collected, 32 taxa were isolated with the multiple baiting technique. The community structure of the zoosporic organisms showed some changes in response to different spatial distribution and seasonal fluctuations, probably influenced by distinct abiotic characteristics of each area or climatic period. Still, the similarity between areas and seasons indicated by S?rensen index and diversity (richness, evenness, Shannon and Simpson indices) were high.     

Specific features of the life cycle of <Emphasis Type="Italic">Pterostichus melanarius</Emphasis> (Coleoptera,Carabidae) in mosaic floodplain meadows

Some features of the spatial and temporal distribution of Pterostichus melanarius (Illiger, 1798) in a mosaic of meadow floodplain landscape, as well as its habitat and interannual variations of its life cycle, are discussed. In the studied landscape, P. melanarius preferred flooded meadows of the medium and low levels that were residential for this species during three years of research. In most habitats, the annual life cycle was successively replaced by the facultative and then by the obligate biennial life cycle, primarily due to interannual variations in the hydrological and temperature regimes. The transformation of the life cycle and redistribution of individuals between adjacent habitats appear to determine the interannual fluctuations in the abundance of P. melanarius. The age heterogeneity of the local populations also contributes to maintaining the total abundance at a relatively stable level.     

Population Dynamics Inferred from Temporal Variation at Microsatellite Loci in the Selfing Snail Bulinus Truncatus

We analyzed short-term forces acting on the genetics of subdivided populations based on a temporal survey of the microsatellite variability in the hermaphrodite freshwater snail Bulinus truncatus. This species inhabits temporary habitats, has a short generation time and exhibits variable rates of selfing. We studied the variability over three sampling dates in 12 Sahelian populations (1161 individuals). Classical genetic parameters (estimators of H(o), H(e), f, selfing rate and Fst) showed limited change over time whereas important temporal changes of allelic frequencies were detected for 10 of the ponds studied. These variations are not easily explained by selection, sampling drift and genetic drift alone and may be due to periodic migration. Indeed the habitats occupied by the populations studied are subject to large temporal fluctuations owing to annual cycles of drought and flood. In such ponds our results support a demographic model of population expansions and contractions under which available habitats, after the rainy season, are colonized by individuals originating from a smaller number of refuges (areas that never dry out in the deepest parts of the ponds). In contrast, selfing appeared to be an important force affecting the genetic structure in permanent ponds.     

Genetic population structure in a troglobitic beetle (Speonomus zophosinus)

Genetic variation of five variable loci was analyzed for troglobitic beetles within and between populations along the Salat and Arac Rivers in the central Pyrenees; the patterns of variation are described. Significant genetic differentiation was found for Speonomus zophosinus from populations in close proximity (10 km), largely due to differences between two groups of three populations. F_ST values range from 0.004 (Phi) to 0.354 (Est-6). Within a region, populations on opposite banks are genetically similar. Within populations genotypic frequencies were not in Hardy-Weinberg equilibrium. For troglobitic species such as S. zophosinus, gene flow is a function of intrinsic (active movement and reproductive strategy) and extrinsic factors (geologic structure of the subterranean environment). It seems that natural selection has played little, if any, role in generating the observed gene frequency patterns. The patterns of variation are most reasonably explained as having resulted from genetic dirft occurring between two areas separated by an inhospitable habitat which acts as a dispersal barrier or limits gene flow.     

Primary Productivity and Precipitation-Use Efficiency in Temperate Grassland in the Loess Plateau of China

Clarifying spatial variations in aboveground net primary productivity (ANPP) and precipitation-use efficiency (PUE) of grasslands is critical for effective prediction of the response of terrestrial ecosystem carbon and water cycle to future climate change. Though the combination use of remote sensing products and in situ ANPP measurements, we quantified the effects of climatic [mean annual precipitation (MAP) and precipitation seasonal distribution (PSD)], biotic [leaf area index (LAI)] and abiotic [slope gradient, aspect, soil water storage (SWS) and other soil physical properties] factors on the spatial variations in ANPP and PUE across different grassland types (i.e., meadow steppe, typical steppe and desert steppe) in the Loess Plateau. Based on the study, ANPP increased exponentially with MAP for the entire temperate grassland; suggesting that PUE increased with increasing MAP. Also PSD had a significant effect on ANPP and PUE; where more even PSD favored higher ANPP and PUE. Then MAP, more than PSD, explained spatial variations in typical steppe and desert steppe. However, PSD was the dominant driving factor of spatial variations in ANPP of meadow steppe. This suggested that in terms of spatial variations in ANPP of meadow steppe, change in PSD due to climate change was more important than that in total annual precipitation. LAI explained 78% of spatial PUE in the entire Loess Plateau temperate grassland. As such, LAI was the primary driving factor of spatial variations in PUE. Although the effect of SWS on ANPP and PUE was significant, it was nonetheless less than that of precipitation and vegetation. We therefore concluded that changes in vegetation structure and consequently in LAI and/or altered pattern of seasonal distribution of rainfall due to global climate change could significantly influence ecosystem carbon and water cycle in temperate grasslands.     

Obligate annual and successive facultative diapause establish a bet‐hedging strategy of Rhagoletis cerasi (Diptera: Tephritidae) in seasonally unpredictable environments

To cope with temporal and spatial heterogeneity of habitats, herbivorous insects in the temperate zone usually enter diapause that facilitates synchronization of their life cycle with specific stages of host plants, such as fruit ripening. In the present study, we address those factors regulating dormancy responses as part of a ‘longer strategy’ to persist and thrive in temperate environments, focusing on Rhagoletis cerasi, a univoltine, oligophagous species, which overwinters as pupae and emerges when host fruits are available for oviposition at local scale. To ensure population survival and reproduction at habitats with ecological heterogeneity, R. cerasi has evolved a sophisticated diapause strategy based on a combination of local adaptation and diversified bet‐hedging strategies. Diapause duration is determined both by (i) the adaptive response to local host fruit phenology patterns (annual diapause) and (ii) the plastic responses to unpredictable inter‐annual (temporal) climatic variability that drives a proportion of the populations to extend dormancy by entering a second, successive, facultative cycle of prolonged diapause as part of a bet‐hedging strategy. Besides the dormant periods, post‐diapause development (which varies among populations) exerts ‘fine tune’ adjustments that assure synchronization and may correct possible errors. Adults emerging from pupae with prolonged diapause are larger in body size compared with counterparts emerging during the first year of diapause. However, female fecundity rates are reduced, followed by an extended post‐oviposition period, whereas adult longevity remains unaffected. Overall, it appears that R. cerasi populations are adapted to ecological conditions of local habitats and respond plastically to unpredictable environmental (climatic) conditions.     

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture-recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control.     

Inter-annual and inter-plot variations of wood biomass production as related to biotic and abiotic characteristics at a deciduous forest in complex terrain, Korea

This study aims to evaluate inter-annual and inter-plot variation of wood biomass production (WBP) and to investigate the relationships of the WBP variations with several biotic and abiotic characteristics at a deciduous forest in complex terrain, the Gwangneung Experimental Forest, Korea. Based on field survey in the plot-scale study area, WBP during 1991–2004 was estimated by a dendrochronological method. Our field data indicated that the inter-annual variation of WBP was closely related to the seasonal climate of both winter air temperature and spring precipitation. The inter-plot variation of WBP was highly associated with basal area, biomass, and frequency of Quercus spp. in the plots, and correlations of the inter-plot variation with the stand characteristics of the specific species were stronger than those with slope and soil water content. Our results suggest that the annual fluctuation of forest productivity is primarily governed by severe climate in a season of the year, and the spatial distribution of a dominant species largely represent plot variation in the productivity. Our findings contribute to an enhanced understanding of climatic effects on the annual variability of forest productivity and the spatial heterogeneity of the productivity, which are extensively concerned with forested ecosystems of Korea.     

Diurnal and seasonal profiles of melatonin in the liver and their correlates of ovarian functions under natural photo-thermal conditions in adult carp Catla catla

Present study aimed to demonstrate daily rhythm features of hepatic melatonin concentrations in relation to ovarian functions during four reproductive phases of an annual cycle by measuring the levels of melatonin, 17-β estradiol (E2), vitellogenin (Vg) and maturation inducing hormone (MIH) in the liver and/or serum of adult carp Catla catla. Melatonin titres in liver, irrespective of reproductive phase, underwent daily variations with a peak in early dark phase and nadir at midday. However, the acrophase (Ø) of serum melatonin varied from late night in preparatory phase to midnight in the remaining parts of annual cycle. Their amplitude was highest during post-spawning phase and lowest during spawning phase. Hepatic E2 levels showed daily peak at midday and seasonal peak during pre-spawning phase. Though levels of serum Vg proteins and MIH did not exhibit daily variations, underwent seasonal changes with the highest and lowest values during spawning and post-spawning phases respectively. Hepatic melatonin titres always displayed significant negative correlation with the levels of both E2 and Vg. In essence, our study presented the first data on the daily and seasonal rhythm features of hepatic melatonin in carp and underlined their temporal relationship with the functions of ovary in any fish species.     

Estimating the per‐capita contribution of habitats and pathways in a migratory network: a modelling approach

Every year, migratory species undertake seasonal movements along different pathways between discrete regions and habitats. The ability to assess the relative demographic contributions of these different habitats and pathways to the species’ overall population dynamics is critical for understanding the ecology of migratory species, and also has practical applications for management and conservation. Metrics for assessing habitat contributions have been well‐developed for metapopulations, but an equivalent metric is not currently available for migratory populations. Here, we develop a framework for estimating the demographic contributions of the discrete habitats and pathways used by migratory species throughout the annual cycle by estimating the per capita contribution of cohorts using these locations. Our framework accounts for seasonal movements between multiple breeding and non‐breeding habitats and for both resident and migratory cohorts. We illustrate our framework using a hypothetical migratory network of four habitats, which allows us to better understand how variations in habitat quality affect per capita contributions. Results indicate that per capita contributions for any habitat or pathway are dependent on habitat‐specific survival probabilities in all other areas used as part of the migratory circuit, and that contribution metrics are spatially linked (e.g. reduced survival in one habitat also decreases the contribution metric for other habitats). Our framework expands existing theory on the dynamics of spatiotemporally structured populations by developing a generalized approach to estimate the habitat‐ and pathway‐specific contributions of species migrating between multiple breeding and multiple non‐breeding habitats for a range of life histories or migratory strategies. Most importantly, it provides a means of prioritizing conservation efforts towards those migratory pathways and habitats that are most critical for the population viability of migratory species.     

Circadian rhythm of photosensitivity and the adaptation of reproductive function to the environment in two populations of Arvicanthis niloticus from Mali and Burkina Faso.

Previous studies have shown that there is a circadian rhythm of photosensitivity in different rodent species of the Sahel (Burkina Faso) and that, despite the low amplitude of seasonal variations in daylength, the photoperiod may control reproductive function. The present investigation of Arvicanthis niloticus provides additional support for this hypothesis. Populations of Arvicanthis niloticus from two regions at the same latitude 1000 km apart but with different climates were studied. Oursi, Burkina Faso, has an arid climate (annual rainfall 315 mm) and Kamalé, Mali has a wetter climate (annual rainfall 1114 mm). The circadian rhythm of photosensitivity had the same features in both populations, involving inhibition of testicular activity, but the photosensitive phase began 11 h 30 min after dawn in the population from Burkina Faso and 45 min later in that from Mali. Comparison of these results with the annual variation of daylength showed that the photoperiod inhibits the reproductive activity of A. niloticus from April to December in Burkina Faso and only from mid-May to mid-August in Mali. The population of Arvicanthis niloticus living in an environment with a large and seasonally stable food supply (Mali) thus has a longer reproductive period. This corroborates results from field studies on annual variations of population density.