bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetic, structural, and stratigraphic constraints on transverse fault kinematics during basin inversion: The Pamplona Fault (Pyrenees, north Spain)
Authors: Larrasoaña Juan Cruz , Parés Josep María , Millán Héctor , del Valle Joaquín , Pueyo Emilio Luis
Published: December 2003

The Pamplona Fault in the Pyrenees is a major transverse structure that has been classically interpreted as a strike‐slip fault. However, lack of consensus concerning the sense of movement casts doubt on its actual kinematics and, as a consequence, its role in the Cenozoic evolution of the Pyrenees remains controversial. In order to assess its kinematics, we have conducted a paleomagnetic, structural, and stratigraphic study focused on the Mesozoic and Tertiary sedimentary rocks that outcrop around the southern segment of the fault. Restoration of balanced cross sections allows us to examine the present‐day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during Mesozoic rifting episodes in the Bay of Biscay and Pyrenean domains. Paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during Tertiary inversion of the Pyrenees. The lack of tectonic rotations and revaluation of previous hypotheses argues against a strike‐slip movement of the fault. We propose a new model in which the Pamplona Fault is treated as a large‐scale “hanging wall drop” fault whose kinematics was determined by variations in the geometry and thickness of Mesozoic sequences on both sides of the fault. These variations influenced the geometry of the thrust sheet developed during Tertiary compression. We are unaware of any other transverse fault that has been interpreted in this fashion; thus the Pamplona Fault serves as a case study for the evolution of transverse faults involved in basin inversion processes.
Parameterizing the effect of a wind shelter on evaporation from small water bodies
Authors: Hipsey Matthew R. , Sivapalan Murugesu
Published: December 2003

The potential use of windbreaks to reduce evaporation from small agricultural reservoirs motivated the development of a simple evaporation model that includes the effect of wind shelters. The shelter effect is parameterized by averaging the integral of the horizontal velocity deficit curve over the length of the water body. This parameterization, termed the “shelter index,” ranges between 0 and 1, representing no shelter to complete shelter, respectively. The results of a two‐dimensional aerodynamic model that solves the disturbed flow field and evolving microclimate over the water body guided the development of a Dalton‐type evaporation model, modified to include the shelter parameterization. The modified Dalton expression summarized the results of the aerodynamic model to a high degree of accuracy (R2 = 0.988). Because the shelter parameterization requires knowledge of the horizontal velocity profile, an approximation of the shelter index that can easily be estimated from physical windbreak characteristics (height, porosity) is presented. In addition, a simple approximation based exclusively on upwind meteorological information is presented for estimation of surface humidity. The evaporation model using the approximations for the shelter index and surface humidity showed excellent agreement (R2 = 0.875) with measured evaporation data from a variety of small wind‐sheltered water bodies at two sites in the agricultural districts of Western Australia. The evaporation model and approximations have the advantage of requiring only routinely available meteorological information and information on windbreak physical characteristics that can be estimated a priori. It is therefore an excellent design tool for water resource managers to evaluate the efficiency of a wind shelter in reducing evaporation or for coupling with hydrodynamic models.
A process typology of regional floods
Authors: Merz R. , Blöschl G.
Published: December 2003

We propose a framework for identifying types of causative mechanisms of floods. The types are long‐rain floods, short‐rain floods, flash floods, rain‐on‐snow floods, and snowmelt floods. We adopt a catchment perspective, i.e., the focus is on the catchment state and the atmospheric inputs rather than on atmospheric circulation patterns. We use a combination of a number of process indicators, including the timing of the floods, storm duration, rainfall depths, snowmelt, catchment state, runoff response dynamics, and spatial coherence. On the basis of these indicators and diagnostic regional plots we identify the process types of 11,518 maximum annual flood peaks in 490 Austrian catchments. Forty‐three percent of the flood peaks are long‐rain floods, only 3% are snowmelt floods, and the relative contribution of the types changes with the flood magnitude. There are pronounced spatial patterns in the frequency of flood type occurrence. For example, rain‐on‐snow floods most commonly occur in northern Austria. Runoff coefficients tend to increase with rainfall depth for long‐rain floods but are less dependent of rainfall depth and exhibit much larger scatter for flash floods. All types exhibit seasonal patterns, both in terms of flood magnitudes and catchment altitudes of flood occurrence. The coefficient of variation (CV) of the flood samples stratified by process type decreases with catchment area for most process types with the exception of flash floods for which CV increases with catchment area.
Heat flow and flexure at subduction zones
Authors: Stein Carol A.
Published: December 2003

It is often suggested that heat flow in the incoming plate at subduction zones is lower than expected for crust of that age due to increased hydrothermal circulation from flexure (extending about 300 km seaward of the trench) and faulting (observed starting about 50–75 seaward of the trench). Testing this suggestion using global heat flow data shows no significant difference between heat flow near the trench and the global means for the same age crust. However, on average, heat flow in the overriding plate is about 60% of that in the incoming plate.
Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone
Authors: Calvert Andrew J. , Fisher Michael A. , Ramachandran Kumar , Tréhu Anne M.
Published: December 2003

Seismic reflection profiles shot across the Cascadia forearc show that a 5–15 km thick band of reflections, previously interpreted as a lower crustal shear zone above the subducting Juan de Fuca plate, extends into the upper mantle of the North American plate, reaching depths of at least 50 km. In the extreme western corner of the mantle wedge, these reflectors occur in rocks with P wave velocities of 6750–7000 ms−1. Elsewhere, the forearc mantle, which is probably partially serpentinized, exhibits velocities of approximately 7500 ms−1. The rocks with velocities of 6750–7000 ms−1 are anomalous with respect to the surrounding mantle, and may represent either: (1) locally high mantle serpentinization, (2) oceanic crust trapped by backstepping of the subduction zone, or (3) rocks from the lower continental crust that have been transported into the uppermost mantle by subduction erosion. The association of subparallel seismic reflectors with these anomalously low velocities favours the tectonic emplacement of crustal rocks.
Using anticyclonicity to determine the position of the Southern Hemisphere westerlies: Implications for the LGM
Authors: Wardle Richard
Published: December 2003

The possible meridional displacement of southern hemisphere westerlies under a different climate regime is examined by studying the characteristics of surface anticyclones. An atmospheric general circulation model is used to simulate the climates of the present day and the Last Glacial Maximum. A vortex‐tracking scheme, applied to the model data, determines the characteristics of southern hemisphere anticyclones. The statistics of anticyclone system density and system strength suggest the glacial epoch had surface westerlies that were displaced poleward over much of the hemisphere during both the summer and winter seasons. The largest displacement occurred in the Australian region during austral winter. The anticyclones also reflect different atmospheric circulations in the past winter climate. These are a weaker tropical circulation and more intense mid‐latitude eddy activity. The simulation results are compared to paleo reconstructions and the consequences of potentially important ocean forcing are highlighted.
Current tectonics of northern Cascadia from a decade of GPS measurements
Authors: Mazzotti Stéphane , Dragert Herb , Henton Joseph , Schmidt Michael , Hyndman Roy , James Thomas , Lu Yuan , Craymer Michael
Published: December 2003

Global Positioning System (GPS) measurements to study regional deformation were initiated in northern Cascadia in the late 1980s and early 1990s. On the basis of a decade of GPS data, we derive a crustal velocity field for NW Washington‐SW British Columbia. The permanent and campaign GPS velocities are defined with respect to North America in the ITRF2000 reference frame. Velocity uncertainties are estimated using a model of time series noise spectra. This new velocity field is the basis for interpretation of the tectonics of the northern Cascadia subduction system. GPS velocities are interpreted in terms of interseismic loading of the megathrust using different coupling models. Our data confirm that the upper part of the megathrust is nearly fully locked. An exponential model for the downdip transition zone gives slightly better agreement with the data compared to the common linear transition. The landward decrease of forearc strain loading is smaller than predicted by any of the current subduction interseismic models. This could be a consequence of a small (0–3 mm/yr) long‐term motion of the southern Vancouver Island forearc, with respect to North America, or of a concentration of interseismic strain across the elastically weaker Cascadia volcanic arc. In northern Vancouver Island, our velocity field supports the existence of an independent Explorer microplate currently underthrusting underneath North America, at least up to Brooks Peninsula. Further north, GPS velocities indicate transient and/or permanent deformation of northernmost Vancouver Island related to the interaction with the Explorer microplate and possibly with the Queen Charlotte transform margin.
On the optical thickness in the UV range: Analysis of the ground‐based data taken at Belsk, Poland
Authors: Jarosławski Janusz , Krzyścin Janusz W. , Puchalski Sylwester , Sobolewski Piotr
Published: December 2003

The longest time series of UV‐B and short wavelength of UV‐A aerosol optical depth has been constructed for the period 1992–2002 using the direct Sun irradiances obtained during standard calculations of total ozone by the Brewer spectrophotometer at Belsk (51°84N, 20°78E), Poland. The long‐term variations appear to be trendless with only small year‐to‐year variations. The statistical analysis of the 1‐day change of aerosol optical depth in the UV range shows that in 30% of cases the scale of the aerosol change is important for the next day UV index forecast. In the analysis of dependence of the aerosol optical depth on wavelength we combine the CIMEL Sun photometer and the Brewer spectrophotometer optical depth data. The Ångström's exponent is calculated for the pairs of wavelengths in the visible, UV‐A, and UV‐A/UV‐B ranges. It is found that Ångström's exponent decreases for the shorter wavelength pair, and it is possible that in the UV‐B/UV‐A range the exponent is actually negative, yielding an increase of aerosol optical depth with wavelength. The Mie code simulations corroborate the hypothesis of possible negative values for the Ångström's exponent in the UV‐B/UV‐A range.
Neoproterozoic “snowball Earth”: Dynamic sea ice over a quiescent ocean
Authors: Lewis Jeffrey P. , Weaver Andrew J. , Johnston Stephen T. , Eby M.
Published: December 2003

Low‐latitude sea level glacial deposits suggest the existence of “snowball Earth” conditions in the Neoproterozoic. Previous modeling studies have offered conflicting support for the snowball hypothesis. We use a climate model of intermediate complexity, including an ocean GCM and a sophisticated thermodynamic/dynamic sea ice component, to conduct a suite of experiments with different orbital/paleogeographical configurations, wind‐forcing, and atmospheric CO2 levels. We show that depending on the orbital configuration and paleogeography, snowball conditions prevail even with atmospheric CO2 levels up to 1800 ppmv. Overall, our modeling paradigm is consistent with the original snowball hypothesis in which an ice covered ocean surrounds a largely snow and ice‐free barren land, with some coastal regions permitting the growth of thick glaciers.
A simplified land data assimilation scheme and its application to soil moisture experiments in 2002 (SMEX02)
Authors: Pathmathevan Mahadevan , Koike Toshio , Li Xin , Fujii Hideyuki
Published: December 2003

The influences of vegetation and its spatial and temporal heterogeneity on the detection of soil moisture can be significant and may limit the applicability of satellite passive microwave sensors. Sensitivity analysis of an applied soil moisture algorithm using ground‐based measurements can show where problems can arise and how they may be circumvented. This paper investigates a method of retrieving a one‐dimensional soil moisture profile and the surface and canopy temperature, under the influence of different vegetations and dynamics, by integrating numerical models and passive microwave, visible, and near‐infrared measurements via a novel application of data assimilation. The land surface scheme (LSS), which is at the heart of the present land data assimilation scheme (LDAS), is a biophysically based model (simplified biosphere model 2: SiB2) of soil, vegetative and atmospheric interactions. The ground‐based microwave radiometer (GBMR) measurements, gathered over the soil moisture experiments in 2002 (SMEX02) in Iowa, were assimilated into the LSS via a radiative transfer model (RTM) using LDAS. Compared to open loop simulations, the results of LDAS are in better agreement with observations.
A nonparametric model for stochastic generation of daily rainfall amounts
Authors: Harrold Timothy I. , Sharma Ashish , Sheather Simon J.
Published: December 2003

This paper presents a model for stochastic generation of rainfall amounts on wet days that is nonparametric, accommodates seasonality, and reproduces important distributional and dependence properties of observed rainfall. The model uses kernel density estimation techniques, which minimize the assumptions that are made about the underlying probability density, and representation of seasonal variations is achieved through the use of a moving window approach. Four different classes of rainfall amount are considered and categorized according to the number of adjacent wet days, and the model is conditioned on the rainfall amount on the previous day. The proposed model can emulate the day‐to‐day features that exist in the historical rainfall record, including the lag 1 correlation structure of rainfall amounts. We link this model with long sequences of rainfall occurrence generated by the model ofHarrold et al.[2003], which is designed to reproduce the longer‐term variability of the observed record. The approach is applied to daily rainfall from Sydney, Australia, and the performance of the approach is demonstrated by presentation of model results at daily, seasonal, annual, and interannual timescales.
Aggression and RHP in the Northern Swordtail Fish, Xiphophorus cortezi: The Relationship Between Size and Contest Dynamics in Male–Male Competition
Authors: Moretz Jason A.
Published: December 2003

Current theory predicts that contest outcome, as well as decisions on whether to initiate a contest, escalate during a contest or retreat are decided by asymmetries in resource holding potential (RHP) and/or expected payoffs between contestants. In this investigation, dyadic contests were staged between male swordtail fish (Xiphophorus cortezi) where individuals were paired based on cumulative fight records and were ranked at the end of the trials in order to approximate RHP. Size was the only asymmetry that I did not attempt to control for and as a result, I was able to determine the relationships between size, contest initiation, escalation and outcome. Individuals changed their contest initiation strategy based on their size relative to that of their opponents, and contrary to predictions, the smaller of the two males in each contest was more likely to initiate the conflict than was the larger male. However, the larger of the two males was more likely to win and standard length proved to be a moderate predictor of an individual's final rank. Regardless of size, initiators fared poorly, winning only 31% of the contests. In instances where the smaller males won the contests, they were no more likely to initiate the encounter than was the larger male. However, when small males did win, fights lasted longer, suggesting that in some cases smaller males may be able to outlast their opponents.
The Occurrence and Context of the Shaking Signal in Honey Bees (Apis mellifera) Exploiting Natural Food Sources
Authors: Biesmeijer Jacobus C.
Published: December 2003

This study reports on the occurrence of the shaking signal during a honey bee forager's life‐time while it visits natural food sources. Experienced foragers and dance followers accounted for more than 93% of the shaking signals. Foraging success triggered shaking directly, during the next return to the hive, and indirectly, on the morning of the next day. Shaking occurred most often after the first foraging successes of the day and frequently following the first foraging success after a spell of bad weather. These findings confirm several hypotheses that predict that individual foraging success underlies colony‐level patterns in shaking activity. Some results do not fit the previously suggested messages of the shaking signal. Therefore, I propose that the shaking signal has the very broad message: ‘reassess your current activity’. This message can explain the wide range of contexts that trigger shaking while it acknowledges that the meaning of the signal depends entirely on the context of the recipient.
Diversity and ecology of saxicolous vegetation mats on inselbergs in the Brazilian Atlantic rainforest
Authors: POREMBSKI STEFAN , MARTINELLI GUSTAVO , OHLEMÜLLER RALF , BARTHLOTT WILHELM
Published: December 2003

Inselbergs occur as mostly dome‐shaped rock outcrops in all climatic and vegetational zones of the tropics. Consisting of Precambrian granites and gneisses, they form ancient and stable landscape elements. Due to harsh edaphic and microclimatic conditions, the vegetation of inselbergs differs markedly from those of the surroundings. Monocotyledonous mats form one of the most characteristic communities of this ecosystem. The floristic composition of this community was studied on six inselbergs located in the Brazilian Atlantic rainforest. Dominating are Bromeliaceae (Alcantarea, Encholirium), Velloziaceae (Vellozia), Cactaceae (Coleocephalocereus) and the Cyperaceae Trilepis. The alpha diversity of the mats was relatively uniform among the six outcrops. However, beta diversity varied considerably between the different sites. Beta diversity was highest at the most speciose locality indicating a high degree of stochasticity in colonization. In contrast to the low diversity mats on West African inselbergs, the Brazilian rock outcrops bear a floristically more diverse mat community rich in endemics. Thus the edaphically controlled inselberg vegetation reflects the outstanding diversity of the Mata Atlaântica. Possibly the high species richness of mats on East Brazilian inselbergs is a consequence of a large species‐pool. The processes that regulate regional and local diversity in the Mata Atlaântica are not fully clear. It is assumed that historical (i.e. long‐term stability) and biotic (i.e. evolutionary interchange of taxa between canopies and rock outcrops followed by differentiation of local populations) conditions have promoted high rates of speciation and their coexistence in isolated habitats. A danger to the unique vegetation of East Brazilian inselbergs is the establishment of invasive weeds.
The distribution of mammal body masses
Authors: BLACKBURN TIM , GASTON KEVIN
Published: December 2003

How the diversity of organisms relates to their body sizes has long been a question of interest to biologists, an interest that has grown as data have become available from an increasing number of taxa at ever larger spatial scales. Here, we examine the form of this relationship for a large proportion of the global placental mammal fauna. In common with other large‐scale assemblages, the frequency distribution of mammal body masses is strongly right‐skewed, even after logarithmic transformation. The modal body mass is slightly lower than predicted by a recent energetic fitness model, but the exact modal value depends on the taxonomic inclusivity of the analyses. Moreover, threatened species are larger bodied than expected by chance, suggesting that extinct species may also have been so. Therefore, the loss of large‐bodied species from the global mammalian fauna could potentially have lowered the mode of the distribution. However, this loss must be balanced against evidence that most mammal species for which body mass data were not available for our analyses are small‐bodied, which may in turn raise the apparent mode of the distribution. Clearly, tests of explanations for patterns in body size frequency distributions will be complicated by the fact that present‐day distributions may be significantly biased by species that are missing from them.
Body size, dispersal ability and compositional disharmony: the carnivore‐dominated fauna of the Kuril Islands
Authors: HOEKSTRA HOPI , FAGAN WILLIAM
Published: December 2003

As part of the International Kuril Island Project, we collected data on the distribution patterns of native terrestrial, non‐volant mammals inhabiting the Kuril archipelago in the northwest Pacific. The Kurils have a complex physical geography, featuring both landbridge and oceanic islands in which small mammal‐occupied islands are near mainlands, whereas larger islands are more isolated. This geography, in combination with the Kurils’ cold climate, causes the mammalian fauna to deviate from traditional island biogeographic patterns. We examined these patterns and the mechanisms influencing them using both nestedness analyses and measures of compositional disharmony. We found, as island isolation increases, carnivores constitute an increasing fraction of the mammalian fauna. We suggest that this intriguing pattern of carnivore dominance occurs because species’ dispersal abilities increase with increasing body size in the Kurils’ cold climate. Substantial energy reserves and cold tolerance of large‐bodied carnivores may have been a major factor in determining mam‐ malian colonization patterns, patterns which are perhaps indicative of the complex manners in which challenging climates impact mammalian community assemblages.
Unexpected patterns of genetic structuring among locations but not colour morphs inAcropora nasuta(Cnidaria; Scleractinia)
Authors: Mackenzie J. B. , Munday P. L. , Willis B. L. , Miller D. J. , Van Oppen M. J. H.
Published: December 2003

Symbiotic relationships have contributed greatly to the evolution and maintenance of biological diversity. On the Great Barrier Reef, species of obligate coral‐dwelling fishes (genusGobiodon) coexist by selectively recruiting to colonies ofAcropora nasutathat differ in branch‐tip colour. In this study, we investigate genetic variability among sympatric populations of two colour morphs ofA. nasuta(‘blue‐tip’ and ‘brown‐tip’) living in symbiosis with two fish species,Gobiodon histrioandG. quinquestrigatus,respectively, to determine whether gobies are selecting between intraspecific colour polymorphisms or cryptic coral species. We also examine genetic differentiation among coral populations containing both these colour morphs that are separated by metres between local sites, tens of kilometres across the continental shelf and hundreds of kilometres along the Great Barrier Reef. We use three nuclear DNA loci, two of which we present here for the first time forAcropora. No significant genetic differentiation was detected between sympatric colour morphs at these three loci. Hence, symbiotic gobies are selecting among colour morphs ofA. nasuta, rather than cryptic species. Significant genetic geographical structuring was observed among populations, independent of colour, at regional (i.e. latitudinal separation by < 500 km) and cross‐shelf (< 50 km) scales, alongside relative homogeneity between local populations on within reef scales (< 5 km). This contrasts with the reported absence of large‐scale genetic structuring inA. valida, which is a member of the same species group asA. nasuta. Apparent differences in biogeographical structuring between species within theA. nasutagroup emphasize the need for comparative sampling across both spatial (i.e. within reefs, between reefs and between regions) and taxonomic scales (i.e. within and between closely related species).
Circum Black Sea phylogeography of Barbus freshwater fishes: divergence in the Pontic glacial refugium
Authors: Kotlík P. , Bogutskaya N. G. , Ekmekçi F. G.
Published: December 2003

We used DNA sequence variation at the mitochondrial cytochrome b gene (1141 bp) to assess the phylogeography of Barbus fishes in the Black Sea region. Our aim was to test whether the recent (≈ 22 000–7500 years ago) freshwater phase of the Black Sea was a conduit for gene flow among freshwater fishes that today are found in streams entering the saltwater Black Sea. Deep phylogeographical breaks suggestive of allopatric divergence were observed between four regional groups of populations. Coalescent simulation used to distinguish between this and an alternative scenario that the phylogeographical structure was due to random lineage sorting showed that the contemporary populations were unlikely (P < 0.001) to have been founded by a single ancestral population. Divergences between the lineages (0.86–2.54%) were dated to the Middle to Late Pleistocene using distances and a molecular clock corrected for superimposed substitutions. Taken together, this evidence suggests that multiple refugial populations survived over several later glaciations in the vicinity of the Black Sea. This Pontic refugium served as the primary source for the postglacial expansion throughout Europe as far as the Atlantic basin. However, only one of the phylogeographical lineages contributed to this dispersion, whereas the others remain restricted to the Black Sea region and followed independent evolutionary trajectories.
Phylogeographical history of the spongeCrambe crambe(Porifera, Poecilosclerida): range expansion and recent invasion of the Macaronesian islands from the Mediterranean Sea
Authors: Duran S. , Giribet G. , Turon X.
Published: December 2003

We studied sequence variation in the nuclear ribosomal internal transcribed spacers (ITS‐1 and ITS‐2) in 111 individuals from 11 populations/localities of the spongeCrambe crambeacross the core species range in the western Mediterranean Sea and Atlantic Ocean. We report the first confirmed instance of intragenomic variation in sponges. Phylogeographical, nested clade and population genetic analyses were used to elucidate the species’ evolutionary history. The study revealed highly structured populations affected by restricted gene flow and isolation‐by‐distance. A contiguous range expansion in the whole distribution area of the sponge was inferred. Phylogenetic analyses indicate a recent origin of most sequence types that could be explained by a recent origin of the species or a by recent bottleneck event in the studied area. A recent expansion of the distribution range to the Macaronesian region from the Mediterranean Sea was also detected, suggesting thatC. crambewas recently introduced from the Mediterranean Sea to the Atlantic Ocean via human‐mediated transport, and that the pattern observed is not the result of a natural biogeographical relationship between these zones.
Population genetic structure of the sugar beet cyst nematode Heterodera schachtii: a gonochoristic and amphimictic species with highly inbred but weakly differentiated populations
Authors: Plantard O. , Porte C.
Published: December 2003

The sugar beet cyst nematode Heterodera schachtii is a soil‐dwelling phytoparasitic nematode that feeds on beet roots. It is an important pest in most sugar beet growing areas, and better knowledge of its genetic variability is an important step to preserve the durability of resistant sugar beet varieties. The population genetic structure of this species in northern France was studied using five microsatellite markers. A hierarchical sampling design was used to investigate spatial structuring at the scale of the region, the field and the plant. Multilocus genotypes were obtained for single individual second‐stage larvae, using only one individual per cyst in order to avoid the analysis of closely allied individuals (larvae from the same cyst share at least the same mother). A consistent trend of heterozygote deficit at all loci was observed at all spatial scales. Heterozygote deficit at the level of individual plants argues against its generation through a Wahlund effect. Inbreeding could be due to very limited active dispersal of larvae in the soil, favouring mating between siblings, such as larvae emerging from the same cyst. Such behaviour could have important consequences for the evolution of virulence in increasing the production of homozygous virulent individuals. Moreover, an analysis of molecular variance (amova) reveals that only 1.6% of the genetic variability is observed among regions, 3.7% among fields of the same region and 94.6% within fields. The very low level of genetic differentiation among fields is also indicated by low values of FST (≤ 0.105) even for fields 150 km apart. We suggest that long‐distance gene flows occur due to passive transport of cysts by human activities, water or wind. As such mechanisms of gene flow would involve cysts and not larvae, the strong signals of inbreeding observed at the local scale should not be disrupted. To our knowledge, this study constitutes the first investigation of the genetic structure of a phytoparasitic nematode based on neutral codominant genetic markers scored in single individuals.
Mitochondrial DNA variation in North American populations of Daphnia obtusa: continentalism or cryptic endemism?
Authors: Penton E. H. , Hebert P. D. N. , Crease T. J.
Published: December 2003

The morphological stasis of many freshwater crustaceans has resulted in the prior delineation of cosmopolitan species and has been explained by their capacity for long‐distance dispersal. This study examines the phylogeography of Daphnia obtusa, a cladoceran thought to be widespread in North America. However, sequence variation of the mitochondrial cytochrome c oxidase subunit I gene indicates that this taxon is composed of two morphologically cryptic species, designated D. obtusa NA1 and NA2. NA2 is restricted to the east, whereas NA1 is broadly distributed across the United States, and is subdivided into four phylogroups that show weak genetic differentiation over broad geographical areas, which likely reflects recent long‐distance dispersal. The current distributions of the four phylogroups in NA1 can be explained by recent range expansion from different refugia following the last Pleistocene glacial advance. Interestingly, the mitochondrial phylogroups identified in this study do not correspond to lineages detected in a previous allozyme analysis. However, the latter groups are associated with a habitat shift suggesting that natural selection may have played a role in their divergence. The results of this and previous studies illustrate the complicated biogeographical history of freshwater cladocerans.
Extensive sharing of chloroplast haplotypes among European birches indicates hybridization among Betula pendula, B. pubescens and B. nana
Authors: Palme A. E. , Su Q. , Palsson S. , Lascoux M.
Published: December 2003

Extensive sharing of chloroplast haplotypes among the silver birch, Betula pendula Roth., the downy birch, B. pubescens Ehrh., and the dwarf birch, B. nana L., was discovered using polymerase chain reaction–restriction fragment length polymporphism markers. The geographical component of the genetic variation was stronger than the species component: the species were not significantly different while 11% of the variation could be attributed to differentiation between the two main regions studied, Scandinavia and western Russia. All haplotypes occurring in more than 2% of the individuals were shared among the species and the introgression ratios were quite large: 0.79 between B. pubescens and B. pendula and 0.67 between B. pubescens and B. nana. The data also indicate that B. pendula individuals are more similar to sympatric B. pubescens than to B. pendula individuals from nearby forests. However, this trend is not as pronounced when B. pubescens is considered, suggesting that introgression is not symmetrical. The haplotype sharing among the three Betula species is most likely caused by hybridization and subsequent cytoplasmic introgression.
Speciation of Iberian diving beetles in Pleistocene refugia (Coleoptera, Dytiscidae)
Authors: Ribera Ignacio , Vogler Alfried P.
Published: December 2003

The Mediterranean basin is an area of high diversity and endemicity, but the age and origin of its fauna are still largely unknown. Here we use species‐level phylogenies based on ≈ 1300 base pairs of the genes 16S rRNA and cytochrome oxidase I to establish the relationships of 27 of the 34 endemic Iberian species of diving beetles in the family Dytiscidae, and to investigate their level of divergence. Using a molecular clock approach, 18–19 of these species were estimated to be of Pleistocene origin, with four to six of them from the Late Pleistocene (≈ 100 000 years). A second, lower speciation frequency peak was assigned to Late Miocene or Early Pliocene. Analysis of the distributional ranges showed that endemic species placed in the tip nodes of the trees are significantly more likely to be allopatric with their sisters than endemic species at lower node levels. Allopatric sister species are also significantly younger than sympatric clades, in agreement with an allopatric mode of speciation and limited subsequent range movement. These results strongly suggest that for some taxa Iberian populations were isolated during the Pleistocene long enough to speciate, and apparently did not expand their ranges to recolonize areas north of the Pyrenees. This is in contradiction to observations from fossil beetles in areas further north, which document large range movements associated with the Pleistocene glacial cycles hypothesized to suppress population isolation and allopatric speciation.
Significant reproductive skew in the facultatively polygynous antPheidole pallidula
Authors: Fournier D. , Aron S. , Keller L.
Published: December 2003

Reproductive skew — the extent to which reproduction is unevenly shared between individuals in a social group — varies greatly between and within animal species. In this study, we investigated how queens share parentage in polygynous (multiple queen) colonies of the Mediterranean antPheidole pallidula. We used highly polymorphic microsatellites markers to determine parentage of gynes (new queens), males and workers inP. pallidulafield colonies. The comparison of the genotypes of young and adult workers revealed a very low queen turnover (less than 2%). The first main finding of the study of reproductive skew in these colonies was that there was a significant departure from equal contribution of queens to gyne, male and worker production. Reproductive skew was greater for male production than for queen and worker production. There was no relationship between the magnitude of the reproductive skew and the number of reproductive queens per colony, their relatedness and the overall colony productivity, some of the factors predicted to influence the extent of reproductive skew. Finally, our study revealed for the first time a trade‐off in the relative contribution of nestmate queens to gyne and worker production. The queens contributing more to gyne production contributed significantly less to worker production.
Amplified fragment length polymorphism versus random amplified polymorphic DNA markers: clonal diversity in Saxifraga cernua
Authors: Kjølner S. , Såstad S. M. , Taberlet P. , Brochmann C.
Published: December 2003

Random amplified polymorphic DNA (RAPD) markers are sensitive to changes in reaction conditions and may express polymorphisms of nongenetic origin. Taxa with variable chromosome numbers are particularly challenging cases, as differences in DNA content may also influence marker reproducibility. We addressed these problems by comparing RAPD and amplified fragment length polymorphism (AFLP) analyses of clonal identity and relationships in a chromosomally variable arctic plant, the polyploid Saxifraga cernua, which has been thought to be monoclonal over large geographical distances. Fifty‐seven plants from four Greenland populations were analysed using a conservative scoring approach. In total, 26 AFLP and 32 RAPD multilocus phenotypes (putative clones) were identified, of which 21 were identical and each of the remaining five AFLP clones was split into two to three very similar RAPD clones. This minor difference can be explained by sampling error and stochastic variation. The pattern observed in Greenland corroborates our previous results from Svalbard, suggesting that rare sexual events in S. cernua are sufficient to maintain high levels of clonal diversity even at small spatial scales. We conclude that although AFLP analysis is superior in terms of efficiency, RAPDs may still be used as reliable markers in small low‐tech laboratories.
Consequences of unequal population size, asymmetric gene flow and sex‐biased dispersal on population structure in brook charr (Salvelinus fontinalis)
Authors: Fraser Dylan J. , Lippé Catherine , Bernatchez Louis
Published: December 2003

Unravelling relationships between dispersal and population structure requires considering the impacts of assumption violations of indirect gene flow models in a given system. We combined temporal, individual and coalescent‐based analyses of microsatellite DNA variation to explore the general hypothesis that unequal effective population size (Ne), asymmetric gene flow (m) and nonrandom (sex‐biased) individual dispersal had an important effect on spatiotemporal population structuring in lake‐dwelling brook charr (Salvelinus fontinalis). This integrative examination shed light on the dichotomous structuring observed between an outlet and three tributary‐spawning populations and their potential for adaptive divergence. It revealed further that finer tributary population structuring incongruent with drainage structure has been shaped by asymmetric m from one population with a large Ne towards two populations of smaller Ne. Gene flow among the tributaries was also mediated mainly by male‐biased dispersal. However, longer distance dispersal from tributaries to the outflow was female‐biased. Spatially dependent sex‐biased dispersal may have contributed therefore to gene flow at different levels of population structuring. Our results demonstrate how dispersal and population structure may interrelate to produce spatial variation in intraspecific diversity, and are therefore relevant for conservation programmes seeking to define conservation units or predict recolonization rates of extirpated populations.
Mitochondrial control region diversity of the houbara bustard Chlamydotis undulata complex and genetic structure along the Atlantic seaboard of North Africa
Authors: Idaghdour Youssef , Broderick Damien , Korrida Amal , Chbel Faiza
Published: December 2003

The houbara bustard, Chlamydotis undulata, is a declining cryptic desert bird whose range extends from North Africa to Central Asia. Three subspecies are currently recognized by geographical distribution and morphology: C.u.fuertaventurae, C.u.undulata and C.u.macqueenii. We have sequenced 854 bp of mitochondrial control region from 73 birds to describe their population genetic structure with a particular sampling focus on the connectivity between C.u.fuertaventurae and C.u.undulata along the Atlantic seaboard of North Africa. Nucleotide and haplotypic diversity varied among the subspecies being highest in C.u.undulata, lowest in C.u.fuertaventurae and intermediate in C.u.macqueenii. C.u.fuertaventurae and C.u.undulata are paraphyletic and an average nucleotide divergence of 2.08% splits the later from C.u.macqueenii. We estimate that C.u.fuertaventurae and C.u.undulata split from C.u.macqueenii approximately 430 000 years ago. C.u.fuertaventurae and C.u.undulata are weakly differentiated (FST = 0.27, Nm = 1.3), indicative of a recent shared history. Archaeological evidence indicates that houbara bustards have been present on the Canary Islands for 130–170 000 years. However, our genetic data point to a more recent separation of C.u.fuertaventurae and C.u.undulata at around 20–25 000 years. Concordant archaeological, climatic opportunities for colonization and genetic data point to a scenario of: (i) initial colonization of the Canary Islands about 130 000 years ago; (ii) a period of secondary contact 19–30 000 years ago homogenizing any pre‐existing genetic structure followed by; (iii) a period of relative isolation that persists today.
Genetic consequences of Pleistocene glaciations for the tundra vole (Microtus oeconomus) in Beringia
Authors: Galbreath Kurt E. , Cook Joseph A.
Published: December 2003

Repeated glacial events during the Pleistocene fragmented and displaced populations throughout the northern continents. Different models of the effects of these climate‐driven events predict distinct phylogeographic and population genetic outcomes for high‐latitude faunas. The role of glaciations in (i) promoting intraspecific genetic differentiation and (ii) influencing genetic diversity was tested within a phylogeographic framework using the rodent Microtus oeconomus. The spatial focus for the study was Beringia, which spans eastern Siberia and northwestern North America, and was a continental crossroads and potential high arctic refugium during glaciations. Variation in mitochondrial DNA (cytochrome b and control region; 214 individuals) and nuclear DNA (ALDH1 intron; 63 individuals) was investigated across the Beringian region. Close genetic relationships among populations on either side of the Bering Strait are consistent with a history of periodic land connections between North America and Asia. A genetic discontinuity observed in western Beringia between members of a Central Asian clade and a Beringian clade is geographically congruent with glacial advances and with phylogeographic discontinuities identified in other organisms. Divergent island populations in southern Alaska were probably initially isolated by glacial vicariance, but subsequent differentiation has resulted from insularity. Tests of the genetic effects of postglacial colonization were largely consistent with expansion accompanied by founder effect bottlenecking, which yields reduced diversity in populations from recently deglaciated areas. Evidence that populations in the Beringian clade share a history of expansion from a low‐diversity ancestral population suggests that Beringia was colonized by a small founder population from central Asia, which subsequently expanded in isolation.
Phenotypic Plasticity and Repeatability in the Mating Signals of Enchenopa Treehoppers, with Implications for Reduced Gene Flow among Host‐Shifted Populations
Authors: Sattman Danielle A. , Cocroft Reginald B.
Published: December 2003

Mate signaling systems, because of their role in assortative mating, have often been implicated in the origins of evolutionary independence between lineages. We investigated three sources of phenotypic plasticity in mating signals with potential relevance to assortative mating in a species in the Enchenopa binotata complex of treehoppers. This group has been a model for speciation in sympatry through shifts to novel host plants. Host shifts result in partial reproductive isolation in Enchenopa binotata because of their effects on life history timing, but interbreeding is still possible if there is dispersal and some overlap of mating periods. Courtship in these plant‐feeding insects is mediated by plant‐borne vibrational signals. We asked whether variation in male mate signaling behavior is influenced by plant substrate, age, or size, each of which may play a role in interactions among host‐shifted populations. Males produced fewer, shorter signals when on non‐hosts than when on hosts. However, there were no effects of age or size on signal variation. Significant repeatability of some signal features (carrier frequency and the number of signals produced in a signaling bout) is consistent with the presence of genetic variation and thus the potential to respond to selection. Our results suggest that plasticity in mate signaling systems, and in particular in male mate searching behavior on hosts and non‐hosts, may have the potential to reduce interbreeding between populations that use different species of host plant.
Seaweeds, latitudinal diversity patterns, and Rapoport's Rule
Authors: SANTELICES BERNABÉ , MARQUET PABLO
Published: December 2003

We analysed the geographic distribution of 645 species of marine benthic algae along the Atlantic coast of Europe and Pacific coast of temperate South America to test for the existence of an association between geographic range size and latitude (Rapoport's Rule) and for three key components of the explanations offered for it. We found that species in high diversity areas are characterized by small geographic ranges and by low specific growth rates as compared to species with large geographic ranges, thus supporting the Rapoport‐rescue hypothesis. However, the pattern is not related to species’ tolerances, to abiotic conditions or to climatic variability. Further, the inverse latitudinal diversity pattern shown by the marine algal flora of temperate Pacific South America, and the opposite patterns shown by tropical and subantarctic species within this flora, stressed that small geographic ranges are linked to high diversity areas in general, and not only in relation to the pole to tropic species diversity gradient.
Estimating regional plant biodiversity with GIS modelling
Authors: IVERSON LOUIS , PRASAD ANANTHA
Published: December 2003

In this study, we analysed a statewide species database together with a county‐level geographic information system (GIS) to build a model based on well‐surveyed areas to estimate species richness in less surveyed counties. The Illinois Plant Information Network (ILPIN), a species‐based database on all the vascular flora of Illinois, contains county distributions (totalling nearly 90,000) for each taxon and information on the taxonomy, ecology, biology, and ecodistribution. We compiled a statewide database with 112 variables on climate, landuse (current and historic), landscape pattern, soils and human population. We used a subset of this database to build a regression model for assessing native plant species richness for thirty‐three botanically well‐surveyed counties in Illinois. The best model was then used to predict the richness of the remaining sixty‐nine less botanically surveyed counties. The model involved GIS (Arc/Info) and statistics (S‐PLUS), including spatial statistics (S+SpatialStats). The resultant model had anR2of 0.80 and used the following variables: percentage of the county in cropland, the percentage with soils somewhat limiting for agriculture, the percentage of urban land, and the average size of farms. Although this particular model is not transferable to other locations without validation, the methodology shown here should be useful in estimating species richness patterns across regions where botanical sampling is heterogeneous.