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Mor
Buchshtav, 2007-2008 Genetic variation in Myrmeleon hyalinus population's across a climatic gradient |
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| A population is an ensemble of individuals which differ in their genetic background and phenotypic characters. Environmental influences on an organism can be manifested genetically, phenotypically or by a combination of both. Israel is situated in a transition zone between Mediterranean and desert climate, therefore can be used as a good model system to investigate how climatic gradients influence the genetic and phenotypic structure of populations. Pit-building antlions (Neuroptera: Myrmeleontidae) are holometabolous insects. They spend most of their life as larvae digging conical pits in sandy soils. Adults are short-lived and weak fliers. Because of their sedentary nature, their ability to buffer environmental conditions is restricted, suggesting that traces of local adaptations should be evident in different antlion populations along the steep climatic gradient characterizing Israel. For example, previous research on Myrmeleon hyalinus in which larvae were raised under varying climatic conditions indicated that there are substantial differences in body size and life history between desert and Mediterranean populations irrespective of the climatic treatment. This implies a population sub-structure. The goal of my research was to examine to what extent the genetic structure of M. hyalinus populations is consistent with their phenotypic structure. I hypothesized that there should be a substantial genetic differentiation between climatic regions and among populations. In order to test my hypothesis, I amplified three mitochondrial gene fragments: CO1, CO3 and 16S, in 122 samples pertaining to10 antlion populations (4 Mediterranean + 5 Arid + 1 hyper Arid populations). Mediterranean population showed higher genetic diversity than desert population. However, analysis of molecular variance indicated that most of the genetic variation (>95%) occurred within populations, implying that there is almost no genetic differentiation among different populations or regions. Clearly these findings are not consistent with previous phenotypic analyses indicating that the antlion population is not panmictic. The low genetic differentiation among antlion populations could be the result of a selective sweep, background selection, or recent population expansion (the 1st and 2nd are mutually exclusive). No traces of positive selection could be detected at the level of the entire protein sequence (ka/ks < 1) or the single amino acid contradictory to the selective sweep predictions. Linkage disequilibrium analysis indicated that less than 1% of the association among polymorphic sites was non-random, refuting expectations of selective sweep while supporting those of population expansion or background selection. Several tests of neutrality showed an excess of newly derived and rare haplotypes. Moreover, the unimodal curves of pairwise nucleotide site differences strongly suggested that a recant population expansion has occurred. Since these sandy habitats were created only recently, the most plausible explanation for the low genetic differentiation among antlion population is recent population expansion. Further analysis is required in order to achieve an unequivocal conclusion. | |
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Daphna Ben-Yehoshua, 2007-2008 Phenotypic variation and plasticity of flight morphology in Myrmeleon hyalinus as a function of climatic conditions |
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| Flight ability of flying insects can be subject to a strong selective pressure, as it is tightly linked to their fitness. Previous studies have shown that insects in colder climates tend to be of a larger body size and have a lower wing loading (ratio of body mass to wing area). This may be a means of compensation for the decrease in wing-beat frequency that occurs in cold temperatures and thereby lowers the lift power. My research aimed to examine how climatic conditions influence body size and the flight-related characters of antlion adults. As a model system I used the most abundant pit-building antlion in Israel, Myrmeleon hyalinus (Neuroptera: Myrmeleontidae). This species inhabits a wide range of sandy habitats in Israel from the northern part of the Mediterranean coast to the Arava valley. As temperatures for Mediterranean climate are generally lower than for desert climate, I hypothesized that: (1) individuals from Mediterranean populations will have a larger body size than individuals from desert populations; (2) wing loading will be lower among individuals from Mediterranean populations to compensate for the decrease in lift power associated with reduced temperature; and 3) Morphological variation will be mainly caused by response to environmental conditions (i.e., phenotypic plasticity) rather than by genetic fixation. This is owing to the sedentary nature characterizing most of the antlion's life span, restricting its ability to buffer environmental changes. The first two hypotheses concern the general patterns characterizing different antlion populations along Israel's climatic gradient, while the last relates to the transplant experiment described below. To test these hypotheses I conducted a classical transplant experiment. Specifically, I collected antlion larvae from both Mediterranean and desert populations along the south-to-north climatic gradient characterizing Israel, and randomly assigned them to one of two environmental chambers simulating Mediterranean and Desert climates. The larvae were raised in these environmental chambers for about one year and as soon as adults started to emerge I took the following measurements: body mass, length of head+thorax and lengths of the forewings and hindwings. As expected, my results indicated that body size increases, and wing loading decreases, along Israel's south-to-north climatic gradient. Furthermore, the results for the transplant experiment showed that body size was significantly larger for individuals raised under Mediterranean condition, regardless of their population-of-origin; however, no significant difference between treatments was shown for wing loading. I can therefore suggest that this increase in body size may be an adaptation to reduced flight ability in colder temperatures, and that body size appears to be subject to greater phenotypic plasticity than does wing loading. To this end, I suggest that combining field data with common garden or transplant experiment such as the one described above can largely improve our understanding of how different selective forces shape the phenotypic structure of populations in nature. | |
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Erez Barkae, 2007-2008 The effect of beetle movement pattern on their ability to disperse to neighboring patches |
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| Habitat fragmentation is considered to be a major factor affecting population dynamics. As a result, it can lead to a breakdown of continuous populations into isolated ones which in turn negatively influence their persistence in the landscape. Recent studies indicated that spatial heterogeneity substantially influences the way in which animals move. Movement collectively determines the spatial structure of populations. Consequently, information on movement is essential for developing a mechanistic understanding of spatial distribution and abundance of animals. My research aimed at 1) testing whether spatial heterogeneity affects the directionality levels in movement of darkling beetles (family: Tenebrionidae), and 2) evaluating the extent to which such changes in movement patterns of darkling beetles influence their ability to disperse into a neighboring patch. The research system is located in the Southern Judean Lowland of Israel, a fragmented landscape which consists of natural scrub patches surrounded by agricultural fields. As a model organism I used two species of ground dwelling beetles: Adesmia ulcerosa and Dailognatha crenatha. I followed the movement path of nearly 30 individuals of each species using numbered flags in the natural patches and agricultural fields surrounding them separately. Turning angles and step lengths were measured along each movement path. A spatially explicit-individual based simulation model was used to extrapolate the field data and to estimate the proportion of individuals that can potentially disperse into a neighboring patch under different scenarios manipulating patch size, degree of isolation and predation risk in the surrounding matrix. Analyzing the movement pattern of beetles in both the agricultural field and the natural patch indicated that A. ulcerosa and D. crenatha have a more directional movement pattern in the natural patch than in the agricultural field. Specifically, their turning angle distribution was significantly narrower in the natural patch. Step length distribution of both species in the agricultural field was skewed to the left indicating that their movement velocity in this habitat decreases substantially. Comparison of the turning angles between the two species showed that D. crenatha has a more directional movement in the agricultural fields than A. ulcerosa. Analyzing the results of the simulation model indicated that A. ulcerosa always has a higher probability to reach a neighboring patch than D. crenatha. My results are in accord with previous studies suggesting that in the absence of predation risk non directional movement can substantially improve the probability to disperse into a neighboring patch. However, when predation risk in the surrounding matrix is high, directional movement should be more advantageous since it can shorten the time spent in the hostile area. I thus expected that increased predation risk in the surrounding matrix should decrease the relative advantage of the less directional species A. ulcerosa over the more directional one D. crenatha. Surprisingly, this prediction was not supported by the simulations, probably because the velocity of D. crenatha is substantially slower than that of A. ulcerosa. Further investigation should focus on mark-recapture data over large spatial scale as well as on developing spatially realistic individual-based models. Finally, my study suggests that combining field data with simulation models can largely improve our understanding of how movement influences species distributional patterns. | |
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Inbal Atias, 2007-2008 Molecular phylogeny of darkling beetles (Tenebrionidae) |
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| Darkling beetles (Tenebrionidae) comprise one of the largest known beetle families (ca. 20,000 in the world, ca. 300 in Israel). Most of these flightless ground-dwelling beetles have a black color, they are common in various habitats, but are more abundant in desert or dry landscapes. Larval hatching, development and pupation occur underground, while the emerging adults are active aboveground. Adults are largely detritivorous feeding on available dead organic matter, which can also consume vegetal material and fungus. A substantial variation in body length exists among darkling beetle species in Israel, ranging from ~2 to 40 mm length. Like many other Coleopteran families, Tenebrionidae taxonomy is mainly based morphological characteristics. During the last two decades, taxonomy has been rapidly changing owing to the development of molecular tools which enabled to reevaluate the classical taxonomy. The aim of my research was to explore the molecular phylogeny of 22 common darkling beetle species in Israel and to examine to what extent it is consistent with their classical phylogeny. I hypothesized that inconsistencies between classical and molecular systematics should arise mainly at the genus level but not at the tribe or the sub-family levels. This is because finer scale morphological classifications are subject to more errors than coarser classifications. To test my hypothesis, I collected Tenebrionidae specimens from the Southern Judean Lowland of Israel, identified them to the species level, extracted their DNA and amplified a fragment of their 16S mitochondrial gene. I then used the sequence data of 22 identified darkling beetle species to construct their phylogeny. Surprisingly, the classical division into sub-families was only partially supported by the molecular data. Specifically, there was no clear distinction between the Tenebrioninae and Pimeliinae sub-families, although species of the former were distinctively clustered. Additionally, the Pimeliinae sub-family was substantially more diverse than the other sub-families. The clustering of species within tribes was largely supported by the molecular data. Similar patterns were observed when examining extended phylogenetic trees which included all available data on Tenebrionidae in the GeneBank. To conclude, my study emphasizes the importance of adopting different and complementary taxonomic tools for evaluating relationship between close taxa. Clearly, further research including more Tenebrionidae species as well as more variable mitochondrial and nuclear genes should be done to arrive at a better understanding of beetle taxonomy. | |
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Adi Arbiv, 2007-2008 Resource gradients as predictors of future growing conditions in plants |
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| The rate at which environmental factors change often varies between growing seasons. Throughout evolution, plants have developed mechanisms which can assist them to best utilize resources under variable conditions. Phenotypic plasticity is one of the strategies adopted by plants to cope with this type of temporal variability. Since developmental changes take time, mechanisms that can assist plants to estimate future growth conditions are expected to be selected for. The ability to sense environmental trends can enable plants to predict such changes, and correlate their phenotype accordingly, which in turn should increase their fitness. Absolute values of environmental factors may serve as good predictors for future conditions when the rate of environmental changes is consistent among growing seasons. But, if the environment demonstrates more complex temporal dynamics in resource availability, sensitivity to gradients is expected. I tested the hypothesis that plants are able to better preempt their future growth conditions by perceiving and responding to both the absolute levels and changes in resource availabilities. As a model system, I used Pisum sativum plants grown in a split-root choice experimental setup where different roots of the same plant experienced temporally dynamic and static nutrient regimes given via irrigation using a 20*20*20 fertilizer. The regimes were as follows: constant high (0.225g/l), constant low (0.025g/l), constant medium (0.125g/l), increasing and decreasing; producing in total 15 different treatment combinations. By focusing on resource availability, I was able to directly manipulate a specific environmental factor and to produce both increasing and decreasing trends. Additionally, the split-root set up enabled me to test the effects of environmental trends on habitat selection at the level of the individual plant. Two harvests were conducted: the first after 4.5 week's period – the point at which increasing/decreasing concentrations equaled, and the second at the end of the experiment - 9 weeks after the treatments were initiated. I found that P. sativum has the ability to develop roots according to nutrient gradients. This ability is manifested by allocating more resources to roots experiencing improving conditions, and fewer resources to roots experiencing deteriorating conditions, regardless of absolute levels. When comparing roots that were exposed to the increasing regime with roots exposed to decreasing regime, I found that in both harvests root mass of the former exceeded that of the latter. Note, that in the first harvest total fertilizer concentration was significantly lower for the increasing regime. Moreover, in both harvests, root mass of the increasing regime was always higher than that of all other regimes, and vice versa, roots experiencing decreasing regime were smaller in mass than roots of the other regimes (excluding constant low). Such sensitivity to resource gradients may assist plants to adaptively preempt future growth conditions. In both harvests, plants that were exposed to homogenous regimes in both roots, demonstrated similar root mass, with a non significant difference. To conclude, studies as the one described here may have important implications in agriculture, since they can serve as the basis for developing new and improved fertilization methods without unnecessary chemical overload. Additional research should also test whether sensitivity to trends exists for other limiting factors, such as water and light, in different types of plants. | |
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Dror Kapota, 2007-2008 Using mark-recapture study and theoretical modeling to investigate the dispersal ability of darkling beetles in the fragmented landscape of southern Judea lowland |
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| Dispersal is the process of movement from one patch to another, and is considered to influence a wide spectrum of ecological patterns and processes. In the human-induced fragmented landscape of the Southern Judea Lowland (SJL) in Israel, relatively small populations of flightless ground beetles occupy separate patches of natural area. The agricultural inter-patch area might form a partial dispersal barrier for these ground beetles. Slower rates of dispersal and gene-flow are hypothesized to affect the spatial, demographic and genetic processes of these local populations. My research aimed at evaluating the dispersal ability of these beetles in order to better understand their response to the progressive fragmentation process occurring in SJL. As a model system, I used two species of darkling beetles, Blaps cribarosa and Pimmelia mittrei, which co-occur in SJL. I hypothesized that the dispersal ability of beetles should be substantially constrained by the inter-patch matrix which might be more hostile than the natural patch. To test my hypothesis I estimated two major dispersal components: the probability of individual to leave the patch, and the fraction of individuals in the population that are able to move a sufficient distance in order to get into the nearest patch (~60m). To address this issue, I conducted an individual mark-recapture field study, in which a grid of 119 pitfall traps was established over a single patch (area size 2800 m3) surrounded by wheat field matrix. Each captured beetle was individually marked and released. The daily fraction of recaptured beetles, the time and distances they traveled, constitute the data set. Using the program MARK, I constructed a series of alternative likelihood functions which describe the probability of the specific data set to occur. These models differ in the time dependence of their parameters. A model selection procedure indicated that a time independence model best fitted the data. The apparent survival (i.e., φ = survival probability ´ the probability to stay in the patch) of individuals was estimated. Furthermore, I derived an analytical model describing the population demography during the course of the study. Using non-linear regression, I estimated the apparent survival. These two independent approaches for estimating dispersal components yielded similiar results for Blaps cribarosa (φ=0.989, range 0.676-0.999 and φ=1.00, range 0.905-1.00, for MARK and the analytical model, respectively) whereas Pimmelia mittrei estimations were slightly different (MARK: φ=0.915, range 0.798-0.967; analytical model: φ=1.00, range 0.864-1.00). A series of alternative displacement kernels was fitted to the cumulative distributions of distances traveled by beetles, by a model selection procedure. A fat tailed model best fitted the data, suggesting a probable long distance travel. The fraction of individuals that are able to move the inter-patch distance at one activity night, was estimated (0.005, range 0.002-0.011). The quantitative results suggest that darkling beetles dispersal is a plausible event in the study area. Among the studied population (estimated size of ~700, Jolly-Seber method), 7 individuals in average, are predicted to leave a patch per activity night, and 3-4 individuals in average, are predicted to be able to move the distance to the next patch. Such a flow between sub-populations is assumed to contradict to some level, process as genetic drift and inbreeding, local and global extinctions. Nevertheless, fragmentation is an on-going process. The western part of the region for example, is much more fragmented, with smaller and more distant patches. Dispersal abilities thus, might change among populations which inhabit different areas of the region, and therefore should be evaluated specifically. | |
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Boaz Golan, 2007-2008 The effect of sand depth, feeding regime, density and body mass on the foraging behavior of a pit-building ant-lion |
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| Pit building ant-lions are small sit-and-wait arthropod predators, which dig conical pits in sandy soils. In such trap building predators, foraging effort is reflected in the amount of energy invested in trap construction and maintenance. The decision of a sit-and-wait predator to relocate is analogous to the decision of an active predator to leave the current patch and search for a more profitable one. Sit-and-wait predators use the rate of prey arrival to estimate the profitability of their location, but since ant-lions can lower their metabolism and resist starvation, they should decide whether such relocation is energetically worthwhile. If the food shortage is due to a bad season, it is better to stay in place, whereas if the shortage is owing to a bad location it is better to relocate. I studied how biotic (conspecific density and feeding regime) and a-biotic (sand depth) factors affect pit diameter and depth of Myrmeleon hyalinus larvae while taking into account their body mass. My study consisted of three complementary experiments. In the 1st experiment, I manipulated conspecific density and sand depth. Since sand throwing and interference increase with crowding, I predicted that pit dimensions should decrease with density. I also predicted that pit dimensions should be positively correlated with sand depth due to the physical properties of the sand and the strong positive dependence of pit diameter on pit depth. In the 2nd experiment, I provided each ant-lion prey items of different sizes, and documented the change in pit diameter. I hypothesized that as prey size increases, pit diameter should increase to a lesser extent owing to increased satiation. In the 3rd experiment I fed the neighbor of a focal individual and documented the changes in the behavior of the focal individual. I expected that an ant-lion whose neighbor was fed should relocate more often or increase pit diameter as a response to its apparently inferior spatial location. In the 1st experiment, pit depth and pit diameter were positively correlated, there was also a positive correlation between sand depth and pit size, and there was a negative correlation between density and pit size. Since all ant-lions belonged to the 3rd instar stage, there was no significant correlation between body mass and pit size. In the 2nd experiment, pit diameter increased significantly as a function of the larval body size, at a decelerating rate. Furthermore, the increase in pit diameter after feeding was negatively correlated with the size of the prey item provided. When no prey was provided, there was almost no increase in pit diameter. In the 3rd experiment, no relationships were detected between the feeding of the neighbor and the behavior of the focal individual. My study supported the sand depth and conspecific density predictions, suggesting that interference competition and physical constraints largely influence ant-lion foraging behavior and capture success. Ant-lions, which have no information about the quality of their location, invested no further effort in enlarging their pits. Moreover, receiving large amounts of prey satiated the ant-lions to the extent that there was no need to further invest in pit enlargement. Pit dimensions were increased only when small or medium-sized prey was provided, indicating on the good quality of the ant-lion current location, without being yet satiated. Ant-lions in the 3rd experiment did not respond to the feeding of their neighbor, and neither increased pit size nor increased relocation rate. It is possible that ant-lions are not capable of acquiring data from their neighbors or cannot use it for their benefit. It is also possible that distances between ant-lions were too large or that the experiment duration was too short. In conclusion, pit dimensions are flexible and may be modified as a function of at least the several biotic and a-biotic factors as was illustrated in this study. | |
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Hagai
Guterman, 2005-2006 |
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Flowers
are the plant's tools for sexual reproduction and as such they usually
grow above ground, where cross pollination occurs. Nonetheless, over the
course of evolution plants with underground flowers have evolved. This
phenomenon of growing aerial and subterranean flowers on the same plant is
called amphicarpy. An amphicarpic plant diverts its reproductive energy
into both kinds of seeds but this ratio of investment is not necessarily
fixed. This rare phenomenon of multiple reproductive strategies in a
single individual can give amphicarpic plants a competitive advantage
across a wide range of environmental conditions. The aim of this study is
to investigate the effect seed type and environmental signals on the way
Emex spinosa divert its reproductive energy into aerial and subterranean
seeds. |
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Asaf
Sadeh, 2005-2006 |
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Amphicarpy
is a rare trait displayed mostly by annual plants, where two types of
flowers are produced on each individual: aerial flowers that generally
cross-pollinate and develop into aerial achenes (AA) for long range
dispersal, and subterranean flowers that generally self-pollinate and
develop into subterranean achenes (SA) for germination in situ. In
E. spinosa, AA are smaller and morphologically adapted to dispersal by
thorns, while SA are much bigger, lack thorns, are never shed from the
mother plant, and produce seedlings that are more competitive during the
first four weeks after germination compared to AA. It has been shown that
AA production responds to environmental conditions. Such plasticity
enables the amphicarpic species to adapt to unpredictable, disturbed and
stressful environments, as a generalist weed. No study has been published
that examines environmental effect on the ratio of investment in AA/SA
(here termed ‘amphycarpic ratio’). This study aims at determining E.
spinosa response, expressed by amphycarpic ratio, to two environmental
factors, intra-specific density (ISD) and nutrient availability (NA).
Furthermore, we test for variability in amphycarpic ratio response to the
above factors between different natural populations of E. spinosa, from
localities characterized by distinctively different environmental
conditions. Such measurements would enable us to compare the reaction
norms and to estimate to what extent amphycarpic ratio is plastic. |
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Reut
Loria, 2004-2005 |
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Predation
often operates as a strong selection force shaping animal behavior and
morphology. Prey experiencing predation pressure should trade-off the risk
of being killed by the predator against the fitness gain of staying active
(e.g., foraging). Predators adopt different foraging modes, ranging from
active to passive hunting tactics. The combined effect of predator
foraging mode and habitat domain (i.e., narrow vs. broad) determines the
prey's response to predation risk. Antlion species adopt two distinct
foraging modes: sit & wait predators which utilize pits constructed in
the ground (e.g., Myrmeleon hyalines) and sit & pursue
predators (e.g., Synclisis baetica) which ambush their prey above
the ground. We investigated the response of these two antlion species to
predation risk by predators that differ in their foraging modes, Lycosidae
(sit & pursue) and Anthia sexmaculata (active predator), as a
function of sand depth which can affect the ability of antlions to
construct pits and to evade predators. We hypothesized that antlions
should respond adaptively to the presence of predators (particularly
predators adopting an active mode) by reducing their activity (movement
propensity, movement distance and pit construction), and that constraining
this response by providing a shallow-sand microhabitat should result in
increased antlion activity. We found that S. baetica movement
propensity decreased with the presence of predator and with sand depth. M.
hyalines movement propensity and pit construction decreased with sand
depth, but was unaffected by the presence of predator. In both species,
the average movement distance (only among relocating individuals) on deep
sand was significantly lower than that on shallow sand. In M. hyalines
there was a significant interaction between predation and sand depth
treatments. Specifically, the presence of predator had a negative effect
on movement distance in the deep sand treatment, but not in the shallow
sand treatment. It is important to note that all relocating individuals in
the shallow sand treatment shifted to the deep sand microhabitat. In
conclusion, M. hyalines (sit & wait), is influenced mainly by
sand depth, while S. baetica (sit & pursue), responded to both
treatments. Therefore, pit construction might be an effective way to
reduce predation risk for M. hyalines. |
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Yael
Hollender, 2004-2005 |
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The
spatial distribution of pit constructing antlion larvae may change across
scales of observation and can be affected by different biotic and abiotic
factors. One of the most abundant pit constructing antlion species in |
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Olga
Sapoznikov, 2004-2005 |
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Antlions
(Myrmeleontidae: Neuroptera) comprise an important and highly diverse
insect group in the sandy habitats of |
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Lavut
Anna, 2004-2005 |
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Antlions
(Myrmeleontidae) comprise the most diverse group within the order of
Neuroptera. There are about 2000 antlion species worldwide of which 90
species inhabit the fauna of |