bluuebunny/crossref_metadata_2025 huggingface dataset:
Preoperative plasma concentrations of vascular endothelial growth factor and matrix metalloproteinase 9 are associated with stage progression in papillary thyroid cancer
Authors: Lin Shih Y. , Wang Ya Y. , Sheu Wayne H.‐H.
Published: June 2003

objective Vascular endothelial growth factor (VEGF), a potent angiogenic peptide, and matrix metalloproteinase 9 (MMP‐9), a proteolytic enzyme, are found to be abundantly expressed in several types of cancer and correlate with tumour progression. In this study, we investigated the relationship between preoperative plasma VEGF, MMP‐9 levels and disease stages in papillary thyroid cancer.

design Plasma samples were consecutively collected from 30 patients with papillary thyroid cancer preoperatively (seven males and 23 females with a mean age of 45 ± 16 years) and control plasmas obtained from 30 patients with benign goitre (seven males and 23 females with a mean age of 44 ± 18 years) and 23 healthy persons (four males and 19 females with a mean age 44 ± 15 years). Plasma VEGF and MMP‐9 concentrations were determined by enzyme‐linked immunosorbent assay. Cancer progression was staged by the TNM classification of the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC).

results In thyroid cancer patients, the plasma VEGF and MMP‐9 values were higher than those in controls (51·8 ± 11·5 ng/l vs. 27·0 ± 0·8 ng/l; 72·3 ± 23·3 µg/l vs. 22·1 ± 3·0 µg/l, respectively; P < 0·05), and those in benign goitre (51·8 ± 11·5 ng/l vs. 39·7 ± 8·8 ng/l; 72·3 ± 23·3 µg/l vs. 23·0 ± 2·2 µg/l, respectively; P < 0·05). But, there was no difference of plasma VEGF and MMP‐9 between patients with goitre and normal subjects. A comparison of VEGF and MMP‐9 levels in patients at each cancer stage and in patients with benign nodule found that plasma VEGF and MMP‐9 values in TNM stages III and IV, but not stage I or II, were significantly elevated (P < 0·05). When cancer patients were grouped according to clinopathological features, the plasma VEGF and MMP‐9 concentrations were both significantly elevated in patients with large tumour size (P < 0·01), lymph node involvement (P < 0·01), extrathyroidal invasion (P < 0·05), distant metastasis (P < 0·05) or advanced stages (P < 0·01).

conclusion Our study demonstrated that circulating VEGF and MMP‐9 levels correlated with progression of papillary thyroid cancer, suggesting plasma VEGF and MMP‐9 may serve as preoperative adjuvant markers for assessing disease activity in papillary thyroid cancer. However, they should not be used as a diagnostic tool for differentiating malignant from benign thyroid disorders.
Cortisol and the metabolic syndrome in South Asians
Authors: Ward Alexandra M. V. , Fall Caroline H. D. , Stein Claudia E. , Kumaran K. , Veena S. R. , Wood Peter J. , Syddall Holly E. , Phillips David I. W.
Published: June 2003

objective The cardiovascular risk factors which comprise the metabolic syndrome are associated with increased hypothalamic–pituitary–adrenal axis (HPAA) activity in some Caucasian populations. South Asians have high rates of cardiovascular disease and its risk factors. We have investigated the relationships between HPAA activity, adiposity and the metabolic syndrome in a South Asian population.

design Cross‐sectional cohort study.

participants A total of 509 men and women born at the Holdsworth Memorial Hospital, Mysore, South India between 1934 and 1954 and still living in the area.

measurements Fasting 09·00 h cortisol and corticosteroid‐binding globulin. The cohort had previously been investigated for features of the metabolic syndrome.

results At 09·00 h, cortisol concentration was strongly associated with systolic and diastolic blood pressure (r = 0·25 and r = 0·24, respectively; P < 0·001), fasting glucose concentration (r = 0·26; P < 0·001), insulin resistance (r = 0·20; P < 0·001) and fasting triglyceride concentration (r = 0·17; P < 0·001). In general, higher cortisol concentrations added to the effect of adiposity in increasing cardiovascular risk factors, but there was evidence of an interaction between cortisol and adiposity in determining fasting glucose concentration (P = 0·045) and insulin resistance (P = 0·006).

conclusions Associations between 09·00 h cortisol concentration and cardiovascular risk factors in this South Asian cohort were stronger than those previously shown in Caucasian populations, despite similar mean cortisol concentrations, and were amplified by adiposity. This suggests that increased glucocorticoid action may contribute to ethnic differences in the prevalence of the metabolic syndrome, particularly among men and women with a higher body mass index.
Demonstration of progesterone receptor‐mediated gonadotrophin suppression in the human male
Authors: Brady B.M. , Anderson R.A. , Kinniburgh D. , Baird D.T.
Published: June 2003

objective Synthetic gestogens in combination with testosterone have potential as a male hormonal contraceptive, predominantly acting by augmenting suppression of gonadotrophin secretion. Little is known, however, of the effects of gestogens in the male. Gestogens have affinity for both androgen and progesterone receptors but the relative contribution of action at these two receptors in gonadotrophin suppression remains unclear. In this study the effects of progesterone, with no significant androgen‐receptor affinity are compared to desogestrel, a synthetic gestogen with relatively low affinity for the androgen receptor, on gonadotrophin secretion in normal men.

design Subjects received either 50 mg progesterone intramuscularly (i.m.) or 300 µg desogestrel orally daily for 7 days. Frequent blood sampling over 12 h was undertaken before and after drug administration. GnRH [100 µg intravenously (i.v.)] was administered 2 h before the end of the frequent sampling period.

subjects Twenty healthy men were randomly allocated to the two treatment groups.

results Both progesterone and desogestrel administration resulted in decreases in the concentration of both LH and FSH secretion, as well as testosterone. Analysis of the pulsatile nature of LH secretion indicated that both treatments reduced LH pulse amplitude, and that progesterone reduced LH pulse frequency. Progesterone, but not desogestrel, treatment also reduced the increase in LH secretion in response to GnRH.

conclusions The effects of progesterone were at least as marked as those of a maximally effective dose of desogestrel. As progesterone has negligible affinity for the androgen receptor, these results are compatible with the suppressive effects of synthetic 19‐norgestogens on gonadotrophin secretion in the male being mediated via the progesterone receptor, with its androgenicity contributing minimally to gonadotrophin suppression.
Population genetics of the endangered Knysna seahorse, Hippocampus capensis
Authors: Teske P. R. , Cherry M. I. , Matthee C. A.
Published: June 2003

The evolutionary history of the endangered Knysna seahorse, Hippocampus capensis, and the extent of gene flow among its three known populations, were investigated using 138 mitochondrial DNA control region sequences. Similarly high levels of genetic diversity were found in two of the populations (Knysna and Keurbooms Estuaries), whereas diversity in the third population (Swartvlei Estuary) was lower. Although most haplotypes are shared between at least two populations, based on the haplotype frequency distributions the three assemblages constitute distinct management units. The extant population structure of H. capensis suggests that the Knysna seahorse originated in the large Knysna Estuary. The presence of seahorses in the two smaller estuaries is either the result of a vicariance event at the beginning of the present interglacial period, colonization of the estuaries via the sea, or a combination of the two.
Determinants of intracolonial relatedness inPogonomyrmex rugosus(Hymenoptera; Formicidae): mating frequency and brood raids
Authors: Gadau J. , Strehl C.‐P. , Oettler J. , Hölldobler B.
Published: June 2003

The genusPogonomyrmexis one of three ant genera with aneffective mating frequency(me) > 2.0. We developed microsatellites to determinemeforP. rugosusbecause mating frequency ofP. rugosuswas known only from observational data which do not allow an estimate ofme. We genotyped 474 workers from 20 colonies for two microsatellite loci. Observed mating frequencies ranged from 3 to 12 andmeforP. rugosuswas 4.71. Observed patriline frequencies were significantly different from the expected patriline frequencies generated with a simulated data set under the assumption of equal patriline representation. The available mating frequency data and phylogenetic information of the genusPogonomyrmexsuggest that multiple mating is the ancestral state in the North AmericanPogonomyrmex sensu stricto. EstablishedP. rugosuscolonies raid and destroy smaller conspecific colonies. During these raids ant workers were observed carrying pupae and larvae from the raided colony into the nest of the raiding colony. However, it was not clear whether raided brood emerged in the raiding colony and were subsequently recruited into the work force (intraspecific slavery) or were used as food (predation). Our analyses indicate 6 of 14 field colonies contained foreignP. rugosusworkers (43%). The range of the intracolonial frequency of foreign workers collected directly from the nest entrance was between 4 and 28%.
Hybridization andRorippa austriaca(Brassicaceae) invasion in Germany
Authors: Bleeker W.
Published: June 2003

Introgressive hybridization between the invasiveRorippa austriacaand the nativeR. sylvestrisin Germany has been studied using chloroplast DNA (trnL intron) and amplified fragment length polymorphism. Three hybrid zones between the invasive and native species were located in the Ruhr Valley (Mülheim) and at the River Main near Würzburg (Randersacker, Winterhausen). In each hybrid zone hybridization was indicated by additivity of region‐specific amplified fragment length polymorphism markers proving independent hybridization events. The hybrids were either morphologically intermediate (R. × armoracioides) or were close toR. sylvestris. ThetrnL intron ofR. austriacais characterized by a species‐specific deletion. This diagnostic chloroplast marker ofR. austriacawas detected in three individuals ofR. sylvestrisproviding evidence for introgression of the invasive chloroplast into the native species. Bidirectional introgression ofR. austriacamarkers intoR. sylvestrisand ofR. sylvestrismarkers intoR. austriacawas detected in the amplified fragment length polymorphism analysis. Some of the invasiveR. austriacapopulations showed high within‐population variation. A possible association among introgression, within‐population variation and invasion success is discussed. The morphologically intermediate hybridR. × armoracioidesis currently spreading in northern Germany. It forms large populations without its parent speciesR. austriacaandR. sylvestris. It is concluded that hybridization between invasiveR. austriacaand nativeR. sylvestrismay lead to the evolution of a new invasive speciesR. × armoracioides.
Wolbachiaand genetic variability in the birdnest blowflyProtocalliphora sialia
Authors: Baudry E. , Bartos J. , Emerson K. , Whitworth T. , Werren J. H.
Published: June 2003

Wolbachiaare widespread cytoplasmically inherited bacteria that induce various reproductive alterations in host arthropods, including cytoplasmic incompatibility (CI), an incompatibility between sperm and egg that typically results in embryonic death. CI has been invoked as a possible mechanism for reproductive isolation and speciation in arthropods, by restricting gene flow and promoting maintenance (and evolution) of genetic divergence between populations. Here we investigate patterns ofWolbachiainfection and nuclear and mitochondrial differentiation in geographical populations of the birdnest blowflyProtocalliphora sialia. Blowflies in western North America are infected with two A‐groupWolbachia, with some individuals singly and others doubly infected. Individuals in eastern North America mostly show single infections with a B‐groupWolbachia.Populations in the Midwest are polymorphic for infections and show A‐ or B‐group infection. There is a low level of mitochondrial divergence and perfect concordance of mitochondrial haplotype with infection type, suggesting that twoWolbachia‐associated selective sweeps of the mitochondrion have occurred in this species. Amplified fragment length polymorphism analysis of nuclear genetic variation shows genetic differentiation between the eastern–Midwestern and western populations. Both Midwestern and eastern flies infected with A‐Wolbachiashow eastern nuclear genetic profiles. Current results therefore suggest thatWolbachiahas not acted as a major barrier to gene flow between western and eastern–Midwestern populations, although some genetic differentiation between A‐Wolbachiainfected and B‐Wolbachiainfected individuals in eastern–Midwestern populations cannot be ruled out.
AFLP utility for population assignment studies: analytical investigation and empirical comparison with microsatellites
Authors: Campbell David , Duchesne Pierre , Bernatchez Louis
Published: June 2003

Individual‐based population assignment tests have thus far mainly relied on the use of microsatellite loci. However, the logistic difficulty of screening large numbers of loci required to reach sufficient statistical power hampers the usefulness of microsatellites in situations of weak population structuring. Amplified fragment length polymorphisms (AFLP) represents an alternative for overcoming this logistical issue as the technique allows the user to characterize a much larger number of loci with a comparable analytical effort. In this study, an assignment test based on maximum likelihood for dominant markers was used to investigate the potential usefulness of AFLP for population assignment. We also compared assignment success achieved with AFLP with that obtained using microsatellites in a case study of low population differentiation involving whitefish (Coregonus clupeaformis) sympatric ecotypes. The analytical investigation showed that the minimum number of AFLP loci required to reach an assignment success of 95% stood within values that are easily achievable in many situations. This also showed how assignment success varied according to the number of AFLP loci used, their absolute frequency and their frequency differential and sampling errors, as well as the number of putative source populations. The case study showed that given a comparable analytical effort in the laboratory, AFLP were much more efficient than the microsatellite loci in discriminating the source of an individual among putative populations. AFLP resulted in higher assignment success at all levels of stringency and the log‐likelihood differences between populations obtained with AFLP for each individual were much larger than those obtained with microsatellites. These results indicate that research involving individual‐based population assignment methods should benefit importantly from the use of AFLP markers, especially in systems characterized by weak population structuring.
Parentage assignment detects frequent and large‐scale dispersal in water voles
Authors: Telfer S. , Piertney S. B. , Dallas J. F. , Stewart W. A. , Marshall F. , Gow J. L. , Lambin X.
Published: June 2003

Estimating the rate and scale of dispersal is essential for predicting the dynamics of fragmented populations, yet empirical estimates are typically imprecise and often negatively biased. We maximized detection of dispersal events between small, subdivided populations of water voles (Arvicola terrestris) using a novel method that combined direct capture–mark–recapture with microsatellite genotyping to identify parents and offspring in different populations and hence infer dispersal. We validated the method using individuals known from trapping data to have dispersed between populations. Local populations were linked by high rates of juvenile dispersal but much lower levels of adult dispersal. In the spring breeding population, 19% of females and 33% of males had left their natal population of the previous year. The average interpopulation dispersal distance was 1.8 km (range 0.3–5.2 km). Overall, patterns of dispersal fitted a negative exponential function. Information from genotyping increased the estimated rate and scale of dispersal by three‐ and twofold, respectively, and hence represents a powerful tool to provide more realistic estimates of dispersal parameters.
Fine‐scale genetic structure of two carabid species with contrasted levels of habitat specialization
Authors: Brouat C. , Sennedot F. , Audiot P. , Leblois R. , Rasplus J.‐Y.
Published: June 2003

Using microsatellite markers, we compared the genetic structure of populations of two carabid species, one described as a generalist (commonly found in forest and in open habitats) and the other known as a forest specialist. Both species were sampled in the same forest plots, which were separated from each other by either open or forested areas. At the local scale considered (13.6 km separating the most distant plots), genetic differentiation was substantial for both species studied, but populations of the forest specialist Carabus punctatoauratus appeared to be more spatially structured than those of C. nemoralis. Isolation by distance analyses showed that nonforested areas are partial barriers to gene flow for both species studied, although more clearly for the forest specialist. Between and within forests, dispersal capacity of the generalist C. nemoralis was shown to be higher than that of the specialist C. punctatoauratus.
The evolution of extreme shell shape variation in the land snailAinohelix editha: a phylogeny and hybrid zone analysis
Authors: Teshima Hiroaki , Davison Angus , Kuwahara Yasuhiro , Yokoyama Jun , Chiba Satoshi , Fukuda Tatsuya , Ogimura Hideo , Kawata Masakado
Published: June 2003

Ainohelix edithafrom Hokkaido, Japan, exhibit great geographical variation in their shell morphology. In particular,A. edithain two quite separate locations, Shimamaki and Samani, are striking because they are extremely flat and have a sharp keel, whereas at adjacent sites the shells are globular or depressed‐globular. We used mitochondrial 16S rRNA and nuclear ITS‐2 sequences to infer a phylogeny among 47 snails from 29 locations. Snails from the two keeled‐flat populations clustered separately in the phylogeny, suggesting that this unusual shell form could have evolved independently. A morphological analysis of shells collected along a transect between keeled‐flat and globular snail sites showed a cline for shell shape and the angle of the keel. Two different mtDNA lineages were found across the transect, with a cline for an ITS‐2 single nucleotide polymorphism. Together, the results may suggest a lack of reproductive isolation between keeled‐flat and globular snails, with possible introgression by hybridization.
Latitudinal divergence of common frog (Rana temporaria) life history traits by natural selection: evidence from a comparison of molecular and quantitative genetic data
Authors: Palo J. U. , O'Hara R. B. , Laugen A. T. , Laurila A. , Primmer C. R. , Merilä J.
Published: June 2003

The relative roles of natural selection and direct environmental induction, as well as of natural selection and genetic drift, in creating clinal latitudinal variation in quantitative traits have seldom been assessed in vertebrates. To address these issues, we compared molecular and quantitative genetic differentiation between six common frog (Rana temporaria) populations along an approximately 1600 km long latitudinal gradient across Scandinavia. The degree of population differentiation (QST ≈ 0.81) in three heritable quantitative traits (age and size at metamorphosis, growth rate) exceeded that in eight (neutral) microsatellite loci (FST = 0.24). Isolation by distance was clear for both neutral markers and quantitative traits, but considerably stronger for one of the three quantitative traits than for neutral markers.QSTestimates obtained using animals subjected to different rearing conditions (temperature and food treatments) revealed some environmental dependency in patterns of population divergence in quantitative traits, but in general, these effects were weak in comparison to overall patterns. Pairwise comparisons ofFSTandQSTestimates across populations and treatments revealed that the degree of quantitative trait differentiation was not generally predictable from knowledge of that in molecular markers. In fact, both positive and negative correlations were observed depending on conditions where the quantitative genetic variability had been measured. All in all, the results suggest a very high degree of genetic subdivision both in neutral marker genes and genes coding quantitative traits across a relatively recently (< 9000 years) colonized environmental gradient. In particular, they give evidence for natural selection being the primary agent behind the observed latitudinal differentiation in quantitative traits.
Population size estimation in Yellowstone wolves with error‐prone noninvasive microsatellite genotypes
Authors: Creel Scott , Spong Goran , Sands Jennifer L. , Rotella Jay , Zeigle Janet , Joe Lawrence , Murphy Kerry M. , Smith Douglas
Published: June 2003

Determining population sizes can be difficult, but is essential for conservation. By counting distinct microsatellite genotypes, DNA from noninvasive samples (hair, faeces) allows estimation of population size. Problems arise because genotypes from noninvasive samples are error‐prone, but genotyping errors can be reduced by multiple polymerase chain reaction (PCR). For faecal genotypes from wolves in Yellowstone National Park, error rates varied substantially among samples, often above the ‘worst‐case threshold’ suggested by simulation. Consequently, a substantial proportion of multilocus genotypes held one or more errors, despite multiple PCR. These genotyping errors created several genotypes per individual and caused overestimation (up to 5.5‐fold) of population size. We propose a ‘matching approach’ to eliminate this overestimation bias.
Bimodal run distribution in a northern population of sockeye salmon (Oncorhynchus nerka): life history and genetic analysis on a temporal scale
Authors: Fillatre E. K. , Etherton P. , Heath D. D.
Published: June 2003

Life history variation and genetic differentiation were analysed in sockeye salmon in Klukshu River, Yukon Canada over 7 years (1994–2000). Sockeye salmon return to the Klukshu River in two distinct runs, with a small ‘early run’ in June–August, and a larger ‘late run’ in August–September. A maximum likelihood test for clusters indicated that the return frequency distribution was bimodal in all the years analysed. Life history differences (fork length, sex ratio, age at maturity, fresh‐ and saltwater residency times) were found between the early and late runs; however, inconsistent patterns suggest that environmental effects outweigh, or strongly interact with, genetic effects for the life history characters evaluated. Analysis of variation at eight microsatellite loci showed that the early and late runs are genetically differentiated in all years examined (exact test).FSTestimates between runs within years were significantly greater than zero (range: 0.018–0.041) for all years except one (0.004). The genetic variance explained by early vs. late runs (2.27%) was twice the variance among years (1.16%) based on analysis of molecular variance. Our neighbour‐joining tree showed early and late runs generally clustering separately, indicating higher gene flow among the early or late run fish across years relative to between‐run gene flow. Two years did not fit the general clustering pattern; although the early and late runs in 1995 and 2000 were genetically differentiated, they clustered separately from the rest of the groups. We cannot offer a definitive explanation for these anomalies; however, an analysis of possible cryptic population structure in early and late runs indicated that at least a few fish strayed between the runs in each year, and the highest rate of mixing was in 1995 and 2000. Our data indicate that the runs are at least partially reproductively isolated as a result of temporal and/or spatial isolating mechanisms. Such reproductive isolation has important implications for conservation and management of the Klukshu sockeye salmon, and make them an evolutionarily interesting group because of parallels with incipient speciation.
The role of environment in shaping the genetic diversity of the subalpine mosquito, Aedes rusticus (Diptera, Culicidae)
Authors: David J. P. , Huber K. , Failloux A. B. , Rey D. , Meyran J. C.
Published: June 2003

The relative involvement of larval dietary tolerance to the leaf‐litter toxic polyphenols in shaping population genetic structure of the subalpine mosquito Aedes rusticus was examined. This was compared with other parameters such as geographical range, type of vegetation surrounding the breeding site, and occurrence of annual larvicidal treatments. Population genetic structure was analysed at 10 presumed neutral polymorphic isoenzyme loci. Toxicological comparisons involved standard bioassays performed on larvae fed on toxic decomposed leaf litter. Significant overall genetic differentiation was observed among the 22 studied populations and within the five defined geographical groups. Analysis of molecular variance revealed an absence of relation between genetic and environmental parameters, genetic variance being essentially found within populations. This suggested that the larval dietary tolerance to the toxic leaf litter and the other studied parameters poorly influence population genetic structure. The local adaptation of subalpine mosquito populations to the surrounding vegetation thus appears as a labile trait. Such a dynamic adaptation is also suggested by the correlation between geographical and toxicological distances and the correlation between dietary tolerance to the leaf‐litter toxic polyphenols and annual larvicidal treatments.
Genetic identification of two sibling species ofLutzomyia longipalpis(Diptera: Psychodidae) that produce distinct male sex pheromones in Sobral, Ceará State, Brazil
Authors: Maingon R. D. C. , Ward R. D. , Hamilton J. G. C. , Noyes H. A. , Souza N. , Kemp S. J. , Watts P. C.
Published: June 2003

Lutzomyia longipalpis, the main sandfly vector for New World visceral leishmaniasis is a complex of an as yet undefined number of sibling species. At present, there is no consensus on the status (single species vs. species complex) of Brazilian populations. We applied five microsatellite loci to test the hypothesis thatL. longipalpisoccurs as two sympatric cryptic species in Sobral, Ceará State, Brazil as predicted by male sex pheromone chemotypes described previously for field specimens from this site [S‐9‐methyl‐germacrene‐B(9MGB) and a cembrene compound]. Abdominal spot morphology corresponds with pheromone type at this locality (9MGB in ‘1 spot’ males and cembrene in ‘2 spot’ males). Genotype data from 190 wild‐caughtL. longipalpisspecimens collected in October 1999 and April 2001 were used to estimate genetic differentiation between the two sex pheromone populations and sampling dates. No significant (P > 0.05) genetic differences were found between the 1999 and 2001 9MGB samples (θ = 0.018;RST = −0.005), and genetic differentiation was low between the cembrene collections (θ = 0.037,P < 0.05;RST = −0.043,P > 0.05). By contrast, highly divergent allelic frequencies (largely at two microsatellite loci) corresponded to significant (P > 0.05) genetic differentiation (θ = 0.221;RST = 0.215) for all comparisons between samples with different pheromones. When pheromone samples were pooled across sample date, genetic differentiation was high (θ = 0.229;P < 0.001;Nem = 0.84). The allele frequency distribution at each of the five microsatellite loci was similar for males and females from the two collection years. Two of these loci showed highly divergent allele frequencies in the two sex pheromone populations. This was reflected in the highly significant genetic differentiation obtained from the male genotypes, between populations producing different pheromones (θ = 0.229–0.268;P < 0.0001 for the 2001 and θ = 0.254–0.558;P < 0.0001 for the 1999 collections, respectively). Similar results were obtained when the females, assigned to a pheromone type, were included in the analysis. Both a Bayesian analysis of the data set and a population assignment test provided strong evidence for two distinct populations corresponding to pheromone type. Given its genotype, the probability of assigning a 9MGB male to the original 9MGB population was 100% once the two years’ collections were pooled. For cembrene‐producing ‘2 spot’ males this probability although still high, was lower than for 9MGB males, at 86%. This microsatellite data together with previously reported reproductive isolation between the two Sobral populations confirm that premating barriers are important in speciation ofL. longipalpis.
The use of nuclear and mitochondrial single nucleotide polymorphisms to identify cryptic species
Authors: Belfiore N. M. , Hoffman F. G. , Baker R. J. , Dewoody J. A.
Published: June 2003

There is growing interest in the use of single nucleotide polymorphisms for evolutionary and population genetics. We tested the efficacy of one of the available single nucleotide polymorphism techniques, single‐base extension, in distinguishing four cryptic species of Microtus. Sequence data were available for these species at nuclear and mitochondrial loci and their identity could be independently confirmed using karyotypes. We found that the development and optimization of single nucleotide polymorphisms required extensive effort, and that the method accurately identified the correct nucleotide at single nucleotide polymorphism sites ≈ 90% of the time at the conserved nuclear locus. Correct identification rates were much lower at the highly variable mitochondrial locus.
The phylogeography of dusky dolphins (Lagenorhynchus obscurus): a critical examination of network methods and rooting procedures
Authors: Cassens I. , Van Waerebeek K. , Best P. B. , Crespo E. A. , Reyes J. , Milinkovitch M. C.
Published: June 2003

We investigated the phylogeography and evolutionary history of dusky dolphins (Lagenorhynchus obscurus) using DNA sequences of the full mitochondrial cytochromebgene in 124 individuals from the putative stocks off Peru, Argentina and Southwest Africa. While genetic differentiation within oceans is surprisingly low, there is no evidence for recent female gene flow between Atlantic and Pacific waters. Highest genetic variability in terms of sequence divergence and number of haplotypes is found in the Atlantic. Our analyses also indicate that the eastern South Pacific dusky dolphins stock should be considered a separate management unit. Given the high level of mortality experienced by the Peruvian dusky dolphin in local fishery activities, these findings have important implications for an objective management of the species. Furthermore, we analysed our mitochondrial sequence data with several widely used network estimation and rooting methods. The resulting intraspecific gene genealogies and rooting inferences exhibited substantial differences, underlying the limitations of some algorithms. Given that scientific hypotheses and management decisions depend strongly on inferred tree or network topologies, there is a clear need for a systematic comparative analysis of available methods. Finally, the present study indicates that (i) the dusky and the Pacific white‐sided dolphins are sister species and (ii) not only the Westwind Drift hypothesis but also other models of dispersion are compatible with the current geographical distribution of dusky dolphins.
Molecular evidence for deep phylogenetic divergence in Mandrillus sphinx
Authors: Telfer P. T. , Souquière S. , Clifford S. L. , Abernethy K. A. , Bruford M. W. , Disotell T. R. , Sterner K. N. , Roques P. , Marx P. A. , Wickings E. J.
Published: June 2003

Mandrills (Mandrillus sphinx) are forest primates indigenous to western central Africa. Phylogenetic analysis of 267 base pairs (bp) of the cytochrome b gene from 53 mandrills of known and 17 of unknown provenance revealed two phylogeographical groups, with haplotypes differentiated by 2.6% comprising seven synonymous transitions. The distribution of the haplotypes suggests that the Ogooué River, Gabon, which bisects their range, separates mandrill populations in Cameroon and northern Gabon from those in southern Gabon. The haplotype distribution is also concordant with that of two known mandrill simian immunodeficiency viruses, suggesting that these two mandrill phylogroups have followed different evolutionary trajectories since separation.
The demographic history of the New Zealand short‐tailed bat Mystacina tuberculata inferred from modified control region sequences
Authors: Lloyd Brian D.
Published: June 2003

Short‐tailed bats Mystacina tuberculata were widespread throughout the forest that dominated prehuman New Zealand, but extensive deforestation has restricted them to scattered populations in forest fragments. In a previous study, the species’ intraspecific phylogeny was investigated using multiple mitochondrial gene sequences. Six phylogroups were identified with estimated divergences of 0.93–0.68 Ma. In the current study, the phylogeographical structure and demographic history of the phylogroups were investigated using control region sequences modified by removing homoplasic sites. Phylogeographical structure in the North Island was generally consistent with an isolation‐by‐distance dispersal model. Coalescent‐based analyses (i.e. mismatch distributions, skyline plots, lineage dispersal analysis and nested clade analysis) indicated that the three phylogroups found in central and southern North Island expanded before the last glacial maximum, presumably during interstadials when Nothofagus forest was most extensive. Genetic structure within a central North Island hybrid zone was consistent with range expansion from separate refugia following reforestation after catastrophic volcanic eruptions. Phylogeographical structure in the South Island was consistent with southern populations originating during rapid southward range expansion from refugia in northern South Island following postglacial reforestation of the South Island 10–9 kya.
Nuclear markers, mitochondrial DNA and male secondary sexual traits variation in a newt hybrid zone (Triturus vulgaris × T. montandoni)
Authors: Babik W. , Szymura J. M. , Rafiński J.
Published: June 2003

The smooth and the Montandon's newts (Triturus vulgarisandT. montandoni) are genetically similar sister species with highly divergent male secondary sexual traits involved in complex courtship behaviour. Their parapatric ranges overlap at moderate elevations in the Carpathian Mountains where they hybridize readily. Here we present a detailed study of genetic and morphological variation in populations from the area of sympatry. Analysis of variation at seven nuclear markers, mtDNA and male sexual secondary traits was complemented with an ecological survey of breeding sites characteristics. Extensive hybridization was revealed with back‐cross individuals similar to either parental species predominating among hybrids. The hybrid zone exhibited a mosaic pattern: the genetic composition of the populations was correlated only weakly with their geographical position. No association with habitat type was found. Departures from Hardy–Weinberg proportions, significant linkage disequilibria and bimodal distribution of genotypes suggest strongly that assortative mating is an important factor shaping the genetic composition of hybrid populations. The pattern of cytonuclear disequilibria did not indicate much asymmetry in interspecific matings. Changes in the frequency of nuclear markers were highly concordant, whereas mtDNA showed much wider bidirectional introgression with 14% excess ofT. montandonihaplotype. We argue that the mosaic structure of the newt hybrid zone results mainly from stochastic processes related to extinction and recolonization. Microgeographical differences in mtDNA introgression are explained by historical range shifts. Since morphologically intermediate males were underrepresented when compared to hybrid males identified by genetic markers, sexual selection acting against the morphological intermediates is implied. We discuss the implications of these findings in the context of reinforcement of prezygotic isolation in newts.
The role of plant species in biomass production and response to elevated CO2and N
Authors: Craine Joseph M. , Reich Peter B. , David Tilman G. , Ellsworth David , Fargione Joseph , Knops Johannes , Naeem Shahid
Published: June 2003

In an experiment that factorially manipulated plant diversity, CO2, and N, we quantified the effects of the presence of species on assemblage biomass over 10 time points distributed over 5 years. Thirteen of the 16 species planted had statistically significant effects on aboveground and/or belowground biomass. Species differed dramatically in their effects on biomass without any relationship between aboveground and below‐ground effects. Temporal complementarity among species in their effects seasonally, successionally, and in response to a dry summer maintained the diversity–biomass relationships over time and may be the cause behind higher diversity plots having less variation in biomass over time. The response of plant biomass to elevated N, but not CO2, was at times entirely dependent on the presence of a single species.
The population consequences of natural enemy enhancement, and implications for conservation biological control
Authors: Kean John , Wratten Steve , Tylianakis Jason , Barlow Nigel
Published: June 2003

We explore models for the management of invertebrate pests by enhancing the efficacy or local abundance of existing natural enemies. Different aspects of natural enemy biology had different effects on prey density. Enhancement of enemy search rate or prey conversion efficiency showed the greatest potential for reducing prey density, while maximum consumption rate by predators, and parasitoid fecundity, had less effect. The effect on prey density of increased natural enemy longevity depended on its interaction with other parameters. The degree of manipulation needed to achieve a given reduction in prey populations was largely determined by the enemy's potential reproductive rate. Spatial ‘‘attraction’’ of enemies to a target site had an almost linear effect on local prey density. We conclude that successful conservation biological control benefits from a directed approach, targeting the most important aspects of natural enemy ecology, and that there is considerable potential for further research in this area.
Food web complexity and higher‐level ecosystem services
Authors: Montoya José M. , Rodríguez Miguel A. , Hawkins Bradford A.
Published: June 2003

Studies mostly focused on communities of primary producers have shown that species richness provides and promotes fundamental ecosystem services. However, we know very little about the factors influencing ecosystem services provided by higher trophic levels in natural food webs. Here we present evidence that differences in food web structure and the richness of herbivores in 19 plant‐herbivore‐parasitoid food webs influence the service supplied by natural enemies, namely, the parasitism rates on hosts. Specifically, we find that parasitoids function better in simple food webs than in complex ones, a result relevant to biological control practice. More generally, we show that species richnessper seonly contributes partially to the understanding of higher‐level ecosystem services in multitrophic communities, and that changes in food web complexity should also be taken into account when predicting the effects of human‐driven disturbances in natural communities.
Bacterial diversity patterns along a gradient of primary productivity
Authors: Claire Horner‐Devine M. , Leibold Mathew A. , Smith Val H. , Bohannan Brendan J. M.
Published: June 2003

Primary productivity is a key determinant of biodiversity patterns in plants and animals but has not previously been shown to affect bacterial diversity. We examined the relationship between productivity and bacterial richness in aquatic mesocosms designed to mimic small ponds. We observed that productivity could influence the composition and richness of bacterial communities. We showed that, even within the same system, different bacterial taxonomic groups could exhibit different responses to changes in productivity. The richness of members of the Cytophaga‐Flavobacteria‐Bacteroides group exhibited a significant hump‐shaped relationship with productivity, as is often observed for plant and animal richness in aquatic systems. In contrast, we observed a significant U‐shaped relationship between richness and productivity for α‐proteobacteria and no discernable relationship for β‐proteobacteria. We show, for the first time, that bacterial diversity varies along a gradient of primary productivity and thus make an important step towards understanding processes responsible for the maintenance of bacterial biodiversity.
Size‐dependent species richness: trends within plant communities and across latitude
Authors: Niklas Karl J. , Midgley Jeremy J. , Rand Richard H.
Published: June 2003

We examine how species richness and species‐specific plant density (number of species and number of individuals per species, respectively) vary within community size frequency distributions and across latitude. Communities from Asia, Africa, Europe, and North, Central and South America were studied (60°4′N–41°4′S latitude) using the Gentry data base. Log–log linear stem size (diameter) frequency distributions were constructed for each community and the species richness and species‐specific plant density within each size class were determined for each frequency distribution. Species richness in the smallest stem size class correlated with the Y‐intercepts (β‐values) of the regression curves describing each log–log linear size distributions. Two extreme community types were identified (designated as type A and type B). Type A communities had steep size distributions (i.e. large β‐values), log–log linear species‐richness size distributions, low species‐specific plant density distributions, and a small size class (2–4 cm) containing the majority of all species but rarely conspecifics of the dominant tree species. Type B communities had shallow size distributions (i.e. small β‐values), more or less uniform (and low) size class species‐ richness and species‐specific density distributions and size‐dominant species resident in the smallest size class. Type A communities were absent in the higher latitudes but increased in number towards the equator, i.e. in the smallest size class, species richness increased (and species‐specific density decreased) towards the tropics. Based on our survey of type A and type B communities (and their intermediates), species richness evinces size‐dependent and latitudinal trends, i.e. species richness increased with decreasing body size and most species increasingly reside in the smallest plant size class towards the tropics. Across all latitudes, a trade‐off exists between the number of species and the number of individuals per species residing in the smaller size classes.
Grazer diversity effects on ecosystem functioning in seagrass beds
Authors: Emmett Duffy J. , Paul Richardson J. , Canuel Elizabeth A.
Published: June 2003

High plant species richness can enhance primary production, animal diversity, and invasion resistance. Yet theory predicts that plant and herbivore diversity, which often covary in nature, should have countervailing effects on ecosystem properties. Supporting this, we show in a seagrass system that increasing grazer diversity reduced both algal biomass and total community diversity, and facilitated dominance of a grazer‐resistant invertebrate. In parallel with previous plant results, however, grazer diversity enhanced secondary production, a critical determinant of fish yield. Although sampling explained some diversity effects, only the most diverse grazer assemblage maximized multiple ecosystem properties simultaneously, producing a distinct ecosystem state. Importantly, ecosystem responses at high grazer diversity often differed in magnitude and sign from those predicted from summed impacts of individual species. Thus, complex interactions, often opposing plant diversity effects, arose as emergent consequences of changing consumer diversity, advising caution in extrapolating conclusions from plant diversity experiments to food webs.
Habitat loss and connectivity of reserve networks in probability approaches to reserve design
Authors: Cabeza Mar
Published: June 2003

Quantitative methods for the design of reserve networks often select over‐dispersed reserves, and consequently a number of species extinctions can be expected in such reserves, especially if unprotected surrounding habitat is lost. A novel approach that deals with this problem is presented by considering factors such as habitat quality and spatial configuration of reserves during the selection process. Species‐specific effects of habitat loss and fragmentation, together with habitat composition, are taken into account when computing species probabilities of local occurrence. Sites are then chosen to represent all species with a given target probability. The method is applied to a dataset of butterflies and moths from the Creuddyn Peninsula, North Wales, UK, which includes species with various responses to habitat quality and configuration. The results show that the resulting level of reserve clustering will depend on the number of species for which the spatial configuration plays an important role (at the scale under consideration), and on the pattern and amount of habitat loss that is expected to follow around the reserves. The method represents a step towards taking better into account species persistence when selecting reserve networks in a changing world.
The adaptive response of a natural microbial population to carbon‐ and nitrogen‐limitation
Authors: Goddard Matthew R. , Bradford Mark A.
Published: June 2003

The majority of experiments investigating the population and community level consequences of altered carbon and nitrogen availability implicitly assume a fixed range of ability to obtain and process these nutrients. This may be fair when considering long‐lived organisms, however, short‐lived organisms (e.g. microbes) will pass through many more generations in the same time period providing scope for evolutionary adaptation. Using isolates of a natural fungal population we demonstrate significant adaptation to carbon‐limitation, but not to nitrogen‐limitation, over a modest number of generations. However, adaptation comes at a cost: those adapted to carbon‐limitation are significantly worse competitors for limited nitrogen when compared with their ancestors. The potential for adaptation (and correlated cost) we demonstrate with our model system highlights the need to consider evolutionary adaptation when interpreting responses of populations, communities and ecosystems to treatments that manipulate, either directly or indirectly, resource availability.
Male age, germline mutations and the benefits of polyandry
Authors: Radwan Jacek
Published: June 2003

The number of de novo mutations in the germline can be expected to increase with age in males, therefore females might decrease mutation load in their progeny by avoiding mating with older males. Here, I propose that female polyandry can be more effective in decreasing the risk of genetic disorders in progeny than pre‐copulatory mate choice, particularly if sperm competitiveness declines more steeply with age than other traits affecting chances of males to mate. If faster ageing of spermatogenic tissue causes older males to transfer inadequate numbers of functional sperm, polyandry would also benefit females directly.