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At least 865 records · Page 48Linked to original sources
PubMed2001

Partitioning of food resources amongst 18 abundant benthic carnivorous fish species in marine waters on the lower west coast of Australia.

The volumetric contributions made by prey and plant material to the diets of 4 elasmobranch and 14 teleost species, collected seasonally by trawling from waters along ca. 200 km of the lower west coast of Australia, have been compared. These benthic carnivores, which were all abundant and collectively contributed 83% to the total number of fish caught, represented nine families (Urolophidae, Scorpaenidae, Triglidae, Platycephalidae, Sillaginidae, Carangidae, Gerreidae, Mullidae and Pempherididae). Some species were numerous in both shallow (5-15 m) and deeper (20-35 m) waters and in both northern and southern regions, whereas others were largely confined to one of these water depths or regions. Comparisons between the diets of the different species, which utilised data collected from individuals throughout the study area, demonstrated that the dietary composition of any given species was almost invariably significantly different from that of every other species. This partly reflected the fact that, while errant polychaetes, gammarid amphipods and tanaids were ingested by all species, their contributions to the diets of the different species varied. Furthermore, echinoderms contributed to the diets of just nine species, and this was substantial only in the case of two sillaginid species, while teleosts were never consumed by six species and only made a marked contribution to the diets of the single species of platycephalid. The diet of each species underwent size-related changes, reflecting a shift from the consumption by smaller fish of prey such as amphipods, mysids and copepods, to the ingestion by larger fish of prey such as polychaetes, carid decapods, isopods and small teleosts. The interspecific and intraspecific differences in dietary compositions would spread the food resources amongst and within species, thereby reducing the potential for competition for those resources within the fish community. Non-metric multi-dimensional scaling (MDS) ordination plots emphasised that the dietary compositions of species within each family possessed some obvious similarities, reflecting similarities in body and mouth morphology and feeding behaviour. However, the extent to which the dietary compositions of the different families were similar or different was often not related to the phylogenetic relationships amongst those families. Furthermore, while differences in mouth size and morphology could sometimes be used to account for differences amongst the diets of the full suite of species, this was not always the case. Thus, the ways in which species feed and use their ancillary feeding structures were also employed to help elucidate the basis for variations in diets.

Journal Article↗
PubMed2000

Interspecific Competition, Environmental Gradients, Gene Flow, and the Coevolution of Species' Borders.

Darwin viewed species range limits as chiefly determined by an interplay between the abiotic environment and interspecific interactions. Haldane argued that species' ranges could be set intraspecifically when gene flow from a species' populous center overwhelms local adaptation at the periphery. Recently, Kirkpatrick and Barton have modeled Haldane's process with a quantitative genetic model that combines density-dependent local population growth with dispersal and gene flow across a linear environmental gradient in optimum phenotype. To address Darwin's ideas, we have extended the Kirkpatrick and Barton model to include interspecific competition and the frequency-dependent selection that it generates, as well as stabilizing selection on a quantitative character. Our model includes local population growth, movements over space, natural selection, and gene flow. It simultaneously addresses the evolution of character displacement and species borders. It reproduces the Kirkpatrick and Barton single-species result that limited ranges can be produced with sufficiently steep environmental gradients and strong dispersal. Further, in the absence of environmental gradients or barriers to dispersal, interspecific competition will not limit species ranges at evolutionary equilibrium. However, interspecific competition can interact with environmental gradients and gene flow to generate limited ranges with much less extreme gradient and dispersal parameters than in the single-species case. Species display character displacement in sympatry, yet the reduction in competition that results from this displacement does not necessarily allow the two species to become sympatric everywhere. When species meet, competition reduces population densities in the region of overlap, which, in turn, intensifies the asymmetry in gene flow from center to margin. This reduces the ability of each species to adapt to local physical conditions at their range limits. If environmental gradients are monotonic but not linear, the transition zone between species at coevolutionary equilibrium occurs where the environmental gradient is steepest. If productivity gradients are also introduced into the model, then patterns similar to Rapoport's rule emerge. Interacting species respond to climate change, as it affects the optimal phenotype over space, by a combination of range shifts and local evolution in mean phenotype, while solitary species respond solely by range shifts. Finally, we compare empirical estimates for intrinsic growth rates and diffusion coefficients for several species to those needed by the single-species model to produce a stable limited range. These empirical values are generally insufficient to produce limited ranges in the model suggesting a role for interspecific interactions.

Journal Article↗
PubMed2006

Leaf and wood carbon isotope ratios, specific leaf areas and wood growth of Eucalyptus species across a rainfall gradient in Australia.

Leaves and samples of recent wood of Eucalyptus species were collected along a rainfall gradient parallel to the coast of Western Australia between Perth in the north and Walpole in the south and along a southwest to northeast transect from Walpole in southwestern Australia, to near Mount Olga in central Australia. The collection included 65 species of Eucalyptus sampled at 73 sites and many of the species were collected at several sites along the rainfall gradient. Specific leaf area (SLA) and isotopic ratio of 13C to 12C (delta 13C) of leaves that grew in 2002, and tree ring growth and delta 13C of individual cell layers of the wood were measured. Rainfall data were obtained from the Australian Bureau of Meteorology for 29 locations that represented one or a few closely located collection sites. Site-averaged data and species-specific values of delta 13C decreased with decreasing annual rainfall between 1200 and 300 mm at a rate of 1.63 per thousand per 1000 mm decrease in rainfall. Responses became variable in the low rainfall region (< 300 mm), with some species showing decreasing delta 13C with rainfall, whereas delta 13C increased or remained constant in other species. The range of delta 13C values in the low rainfall region was as large as the range observed at sites receiving > 300 mm of annual rainfall. Specific leaf area varied between 2 and 6 m2 kg(-1) and tended to increase with decreasing annual rainfall in some species, but not all, whereas delta 13C decreased with SLA. The relationship between delta 13C and SLA was highly species and soil-type specific. Leaf-area-based nitrogen (N) content varied between 2 and almost 6 g m(-2) and decreased with rainfall. Thus, thicker leaves were associated with higher N content and this compensated for the effect of drought on delta 13C. Nitrogen content was also related to soil type and species identity. Based on a linear mixed model, statistical analysis of the whole data set showed that 27% of the variation in delta 13C was associated with changes in SLA, 16% with soil type and only 1% with rainfall. Additionally, 21% was associated with species identity. For a subset of sites with > 300 mm rainfall, 43% of the variation was explained by SLA, 13% by soil type and only 3% by rainfall. The species effect decreased to 9% because there were fewer species in the subset of sites. The small effect of rainfall on delta 13C was further supported by a path analysis that yielded a standardized path coefficient of 0.38 for the effect of rainfall on SLA and -0.50 for the effect of SLA on delta 13C, but an insignificantly low standardized path coefficient of -0.05 for the direct effect of rainfall on delta 13C. Thus, in contrast to our hypothesis that delta 13C decreases with rainfall independent of soil type and species, we detected no statistically significant relationship between rainfall and delta 13C in leaves of trees growing at sites receiving < 300 mm of rainfall annually. Rainfall affected delta 13C indirectly through soil type (a surrogate for water-holding capacity) across the rainfall gradient. Annual tree rings are not clearly visible in evergreen Eucalyptus species, even in the seasonally cool climate of SW Australia. Generally, visible density transitions in the wood are related not to a strict annual cycle but to periods of growth associated mainly with rainfall. The relationship between delta 13C of leaves and the width of these stem increments was not statistically significant. Analysis of stem growth periods showed that delta 13C in wood responded to rainfall events, but carbohydrate storage and reallocation also affected the isotopic signature. Although delta 13C in wood of any one species varied over a range of 2 to 4 per thousand, there was a general relationship between delta 13C of the leaves and the annual range of delta 13C in wood. We conclude that species-specific traits are important in understanding the response of Eucalyptus to rainfall and that the diversity of the genus may reflect its response to the large climatic gradient in Australia and to the large annual and interannual variations in rainfall at any one location.

Australia↗
PubMed1996

The Drosophila montium subgroup species. Phylogenetic relationships based on mitochondrial DNA analysis.

Mitochondrial DNA (mtDNA) restriction site maps for three Drosophila montium subgroup species of the melanogaster species group, inhabiting Indian and Afrotropical montium subgroup territories, were established. Taking into account previous mtDNA data concerning six oriental montium species, a phylogeny was established using distance-matrix and parsimony methods. Both genetic diversity and mtDNA size variations were found to be very narrow, suggesting close phylogenetic relationships among all montium species studied. The phylogenetic trees that were constructed revealed three main lineages for the montium subgroup species studied: one consisting of the Afrotropical species Drosophila seguyi, which is placed distantly from the other species, one comprising the north-oriental (Palearctic) species, and one comprising the southwestern (south-oriental, Australasian, Indian, and Afrotropical) species. The combination of the mtDNA data presented here with data from other species belonging to the melanogaster and obscura subgroups revealed two major clusters: melanogaster and obscura. The melanogaster cluster is further divided into two compact lineages, comprising the montium subgroup species and the melanogaster complex species; the species of the other complex of the melanogaster subgroup, yakuba, disperse among the obscura species. The above grouping is in agreement with the mtDNA size variations of the species. Overall, among all subgroups studied, the species of the montium subgroup seem to be the most closely related.

Animals↗
PubMed2006

Seasonal variations in plant species effects on soil N and P dynamics.

It is well established that plant species influence ecosystem processes, but we have little ability to predict which vegetation changes will alter ecosystems, or how the effects of a given species might vary seasonally. We established monocultures of eight plant species in a California grassland in order to determine the plant traits that account for species impacts on nitrogen and phosphorus cycling. Plant species differed in their effects on net N mineralization and nitrification rates, and the patterns of species differences varied seasonally. Soil PO4- and microbial P were more strongly affected by slope position than by species. Although most studies focus on litter chemistry as the main determinant of plant species effects on nutrient cycling, this study showed that plant species affected biogeochemical cycling through many traits, including direct traits (litter chemistry and biomass, live-tissue chemistry and biomass) and indirect traits (plant modification of soil bioavailable C and soil microclimate). In fact, species significantly altered N and P cycling even without litter inputs. It became particularly critical to consider the effects of these multiple traits in order to account for seasonal changes in plant species effects on ecosystems. For example, species effects on potential rates of net N mineralization were most strongly influenced by soil bioavailable C in the fall and by litter chemistry in the winter and spring. Under field conditions, species effects on soil microclimate influenced rates of mineralization and nitrification, with species effects on soil temperature being critical in the fall and species effects on soil moisture being important in the dry spring. Overall, this study clearly demonstrated that in order to gain a mechanistic, predictive understanding of plant species effects on ecosystems, it is critical to look beyond plant litter chemistry and to incorporate the effects of multiple plant traits on ecosystems.

Nitrogen↗
PubMed2004

Experimental small-scale grassland fragmentation alters competitive interactions among ant species.

Different species may respond differently to habitat fragmentation. Theory predicts that abundant generalist species should be less affected by fragmentation than specialist species. In ant communities, the most abundant species is often behaviourally dominant. Thus, habitat fragmentation could alter competitive interactions between the dominant ant species and the other species. We tested this hypothesis in a long-term grassland fragmentation experiment. Fragments of different size (20.25 and 2.25 m(2)) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots were situated in adjacent undisturbed grassland. Ant density and species composition were assessed 3 and 6 years after initiation of the experimental fragmentation. The effect of the dominant ant species on the resource use of the other species was examined at natural sugar resources (aphids and extrafloral nectaries) and at artificial sugar baits. Lasius paralienus was the most abundant ant species (72% of nests) in the grasslands examined. Species richness and forager density in the other species decreased with increasing density of L. paralienus in fragments but not in control plots. The overall forager density of the other species was positively related to their habitat niche overlap with L. paralienus. The density of foragers of the other species at sugar resources was not affected by L. paralienus forager density. The experimental fragmentation resulted in an increase in natural sugar resources in fragments. This may have reduced the intensity of interspecific competition for sugar resources. Our study shows that the grassland fragmentation altered interactions between the dominant L. paralienus and the other ant species.

Analysis of Variance↗
PubMed2006

The consequence of species loss on ecosystem nitrogen cycling depends on community compensation.

Repercussions of species loss on ecosystem processes depend on the effects of the lost species as well as the compensatory responses of the remaining species in the community. We experimentally removed two co-dominant plant species and added a 15N tracer in alpine tundra to compare how species' functional differences influence community structure and N cycling. For both of the species, production compensated for the biomass removed by the second year. However, the responses of the remaining species depended on which species was removed. These differences in compensation influenced how species loss impacted ecosystem processes. After the removal of one of the co-dominant species, Acomastylis rossii, there were few changes in the relative abundance of the remaining species, and differences in functioning could be predicted based on effects associated with the removed species. In contrast, the removal of the other co-dominant, Deschampsia caespitosa, was associated with subsequent changes in community structure (species relative abundances and diversity) and impacts on ecosystem properties (microbial biomass N, dissolved organic N, and N uptake of subordinate species). Variation in compensation may contribute to the resulting effects on ecosystem functioning, with the potential to buffer or accelerate the effects of species loss.

Analysis of Variance↗
PubMed2001

Evolution of calls and auditory tuning in the Physalaemus pustulosus species group.

In species within the Physalaemus pustulosus species group, male frogs produce a whine-like advertisement call consisting of a frequency sweep typically descending from 1,000 to 400 Hz (depending on the species). One species, Physalaemus pustulosus, the túngara frog, has evolved a second call syllable, the chuck, which males place after their whine. Most energy in the chuck is above 1,500 Hz and peaks at 2,400 Hz. We investigated whether the evolution of this new call component in P. pustulosus coincided with evolution of auditory tuning. We used multiunit electrophysiological recordings of auditory-evoked activity in the midbrain to characterize auditory tuning in Physalaemus pustulosus, four other Physalaemus species within the P. pustulosus clade, and three additional, closely related Physalaemus species as outgroups. All eight species had similar sensitivity profiles, with a broad area of enhanced sensitivity from 100 to 1,100 Hz, which we presume represents amphibian papilla (AP) tuning, and a second, narrower area of enhanced sensitivity centered above 2,100 Hz, which we presume represents basilar papilla (BP) tuning. For all species, the whine stimulates the AP. The P. pustulosus chuck stimulates the BP. The frequency with greatest AP sensitivity differed significantly among species. Although in all cases the AP peak lay within the frequency sweep of the whine, phylogenetically corrected correlations revealed no significant relationships between AP tuning and any spectral feature of the whine. BP tuning was similar among all species, with mean BP best excitatory frequencies (BEFs) around 2,100-2,200 Hz, with the exception of P. pustulatus, with a mean BP BEF of 2,549 Hz. Physalaemus pustulosus, the only investigated species that produces a call component stimulating the BP, had a BP BEF that was not significantly different from any of the species within its clade except P. pustulatus, or from any of the outgroup species. A phylogenetic reconstruction of ancestral BP tuning confirms that the only point of evolutionary change in BP tuning is in the line of descent leading to P. pustulatus, not in the line leading to P. pustulosus despite this being the species using the BP for communication. The results indicate that BP tuning around 2,200 Hz is a conserved trait in the Physalaemus pustulosus species group and that no evolution of BP tuning accompanied the subsequent evolution of the call component (the chuck) that stimulates it. This supports the sensory exploitation idea, which posits that signals evolve to match preexisting features of receiver systems.

Animals↗
PubMed2002

Comparison of pulsed-field gel electrophoresis (PFGE) and two different polymerase chain reactions (PCRs) for species identification of Borrelia burgdorferi sensu lato strains.

The purpose of the present study was to compare the findings of three different molecular-biological methods for Borrelia burgdorferi sensu lato species identification: (i) large DNA fragments pattern obtained with Mlul restriction endonuclease and separated with pulsed-field gel electrophoresis (PFGE); (ii) polymerase chain reaction (PCR), the region inside the 16S rRNA gene multiplied with species-specific primers; and (iii) PCR, the interspace region between the 5S and 23S rRNA genes amplified, the PCR product restricted with Msel restriction endonuclease and fragments separated in polyacrylamide gel. Forty-eight Borrelia strains isolated from diverse clinical materials and two tick strains were analyzed. Each of the 50 isolates analyzed by PFGE was found to be a single species: 30 B. afzelii, 14 B. garinii, and 6 B. burgdorferi sensu stricto. PCR amplification of 16S rRNA with species-specific primers revealed a single species in 41/50 samples and in nine samples two species were detected. PCR of the 5S-23S interspace region restricted with MseI restriction endonuclease detected a single species in 48/50 samples and a mixture of two species was found in 2/50 samples. In all cases where a single species was identified using PCR the species was in accordance with the PFGE result, and in all cases where a mixture of two species was identified by PCR one of the species was the same as that detected by PFGE. Using a criterion of complete concordance of the results a significant difference in species identification was found when PFGE and the 16S rRNA PCR were compared (p = 0.0026), but not between 5S-23S interspace PCR and PFGE (p = 0.4949) or between 16S rRNA and 5S-23S interspace PCRs (p = 0.0552). PCR assays were faster and easier to perform than PFGE for Borrelia species identification, however PFGE remains a standard procedure for analyzing isolates and demonstrating heterogeneity within species.

Animals↗
PubMed2005

Relationships between local and regional species richness in flea communities of small mammalian hosts: saturation and spatial scale.

The number of species coexisting in a community may be regulated by local factors (e.g., competitive interactions), or by regional processes (e.g., dispersal from a regional species pool). The relative importance of local and regional processes can be inferred from the shape of the relationship between local and regional species richness. We investigated this relationship in communities of fleas parasitic on small mammals at two spatial scales: between the richness of fleas on individual hosts (infracommunities) and that of fleas on host populations (component communities), and between the richness of component communities and that of the entire regional species pool. We tested linearity (proportional sampling) versus curvilinearity with an asymptote (species saturation) by plotting "local" against "regional" species richness of fleas either among host species or within host species among populations. At the two spatial scales, we found consistent curvilinear relationships between species richness of the more "local" communities and richness of the more "regional" communities. This was true across all host species in the data set and for geographic subsets, even after controlling for the influence of sampling effort on estimates of species richness, and that of host phylogeny in interspecific analyses. We also tested for density compensation in species-poor communities. There was no strong evidence for density compensation at the infracommunity level, although its existence at the component community level appeared likely. Our results suggest that identical patterns in local-versus-regional species richness observed on two different spatial scales arise via different mechanisms: infracommunities appear saturated with flea species most likely because of local processes, such as host immune defenses, whereas component communities are saturated with species through interspecific competition, possibly among larval stages.

Animals↗
PubMed2003

Does flood tolerance explain tree species distribution in tropical seasonally flooded habitats?

In the tropics, seasonally flooded forests (SFF) harbor fewer tree species than terra firme (i.e. non-flooded) forests. The low species diversity of tropical flooded forests has been ascribed to the paucity of species with adaptations to tolerate flooding. To test the hypothesis that flooding is the only factor restricting most species from SFF, we compared plant morphological and physiological responses to flooding in 2-month old seedlings of 6 species common to SFF and 12 species common to terra firme forests. Although flooding impaired growth, total biomass, maximum root length and stomatal conductance in most species, responses varied greatly and were species-specific. For example, after 90 days, flooding reduced leaf area growth by 10-50% in all species, except in Tabebuia, a common species from non-flooded habitats. Similarly, flooding had a 5-45% negative effect on total biomass for all species, except in 1 SFF and 1 terra firme species both of which had more biomass under flooding. A principal component analysis, using the above responses to flooding, provided no evidence that SFF and terra firme species differed in their responses to flooding. Flooding also caused reductions in root growth for most species. Rooting depth and root: shoot ratios were significantly less affected by flooding in SFF than in terra firme species. Although flood tolerance is critical for survival in flooded habitats, we hypothesize that responses to post-flooding events such as drought might be equally important in seasonal habitats. Therefore, we suggest that the ability to grow roots under anoxia might be critical in predicting success in inundated habitats that also experience a strong dry season.

Adaptation, Physiological↗
PubMed2005

Fire regenerative syndromes of forest woody species across fire and climatic gradients.

Community resilience after fire is determined by species' ability to regenerate through two main mechanisms growth of new sprouts (resprouter species) and germination from surviving seed banks or from seeds arriving from neighbouring populations (seeder species). Both the mechanisms are present in Mediterranean communities. The occurrence of both the types in a community depends on fire history and the bio-geographical history determining the available species pool. Regenerative traits also covary with other functional attributes associated with resource acquisition and stress tolerance. As post-fire regenerative responses can be related to various ecological factors other than fire, we tested the hypothesis of a different proportional representation of post-fire regenerative syndromes in forest woody species along a climatic gradient in Catalonia (NE Spain) ranging from Mediterranean to temperate-boreal climates. Specifically, we expected seeder species to become less common with colder and moister conditions while resprouters would not be so influenced by the climatic gradient. We also tested the hypothesis of change in the relative abundance of regenerative syndromes in relation to recent fire history. We analysed a large database obtained from extensive forestry surveys and remote sensing fire records. After correction for spatial autocorrelation, we found an increase in the proportion of seeder species under more Mediterranean conditions and a decrease in fire-sensitive species (with no efficient mechanisms of post-fire recovery) in moister conditions. Resprouter species were similarly present across the whole gradient. A similar pattern was observed after excluding recently burnt plots. Therefore, post-fire regenerative syndromes segregate along the climatic gradient. Recent fires reduced the occurrence of fire-sensitive species and increased the proportion of seeder species. No significant effect was observed on resprouter species. Fire has a sorting effect, shaping the occurrence of species with different regenerative traits. Overall, fire seems to explain better the variability of the proportion of fire-sensitive species and climate the variability of seeder species. In addition, other factors (forestry practices and the covariation between regenerative and functional attributes) are likely to contribute to the regional pattern of regenerative syndromes.

Climate↗
PubMed1985

The molecular species of phosphatidic acid, diacylglycerol and phosphatidylcholine synthesized from sn-glycerol 3-phosphate in rat lung microsomes.

The species pattern of phosphatidic acid, diacylglycerol and phosphatidylcholine synthesized from [14C]glycerol 3-phosphate was measured using a newly developed HPLC technique yielding 13 molecular species. A direct comparison of these species patterns presupposes determination of the lipolytic activity of lung microsomes. The lipolytic activity was quantitatively determined by measuring the changes of the endogenous concentration of diacylglycerol, triacylglycerol and free fatty acids. The species pattern of endogenous diacylglycerol measured in the time-course of lipolysis did not show any changes up to an incubation period of 20 min, suggesting that the lipolytic activity showed only a very low selectivity for individual substrate species. Diisopropylfluorophosphate (5 mumol/mg microsomal protein) strongly decreased the lipolytic activities as well as the microsomal phosphatidate phosphohydrolase activity, as measured by means of exogenous phosphatidic acid, and also the generation of phosphatidic acid from [14C]glycerol 3-phosphate. In lung microsomes, labeled phosphatidic acid and diacylglycerols were synthesized from the endogenous free fatty acids and sn-[14C]glycerol 3-phosphate, which had previously been added. By addition of CDPcholine to the prelabeled microsomes the synthesis of phosphatidylcholine was measured. After hydrolysis of phosphatidic acid and phosphatidylcholine with cytoplasmatic phosphatidate phosphohydrolase or phospholipase C, respectively, the de novo synthesized species patterns of these two lipids and of the diacylglycerol were determined. Comparison of the species pattern of de novo synthesized phosphatidic acid with that of diacylglycerol largely showed the same distribution of radioactivity among the individual species, except that the relative proportion of label was higher in the 16:0/16:0 and 16:0/18:0 species of phosphatidic acid and lower in the 16:0/20:4 and 18:0/20:4 species than in the corresponding species of diacylglycerol. The species pattern of de novo-synthesized diacylglycerol showed no differences from that of the phosphatidylcholine synthesized from it. From this result we concluded that the cholinephosphotransferase of lung microsomes is nonselective for individual species of the diacylglycerol substrate. The 16:0/18:1 and 16:0/18:2 species of phosphatidic acid, diacylglycerol and phosphatidylcholine showed a higher synthesis rate than their 18:0 counterparts, whereas the 16:0 or 18:0 analogues of species containing 20:4 and 22:6 fatty acids showed nearly the same synthesis rates.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed2001

Phylogeny of the European species of the genus Pellia (Hepaticae; Metzgeriales) based on the molecular data from nuclear tRNA(Leu)(CAA) intergenic sequences.

Species of the genus Pellia are similar to such an extent that their proper recognition based on morphological and anatomical features is difficult. To solve this problem isozyme methods were developed. As a result of these studies new cryptic species were recognized and new hypotheses concerning phylogenetic relationship in Pellia were formed. To examine hypotheses derived from isozyme data we decided to study species of the genus Pellia at the DNA level. Total DNA from all Polish Pellia species was isolated. The taxonomic and phylogenetic relationships in Pellia were examined using intergenic spacer sequences between nuclear tRNA(Leu) genes organised in tandem arrays. PCR (polymerase chain reaction) amplification of tRNA(Leu) gene spacers produced fragments of different sizes in all species and their restriction analysis showed species-specific patterns. PCR products were cloned and sequenced. Nucleotide sequence data were used for phylogenetic reconstruction. Sequence analysis confirmed previous results based on isozyme studies that P. endiviifolia- species A and species B as well as P. epiphylla- species S and species N (having different isozyme multilocus genotypes) are separate sibling species. Our results also confirmed the allopolyploid character of the only polyploid species in Pellia, P. borealis which was formed by hybridization of P. epiphylla- species N and P. epiphylla- species S cryptic species.

DNA, Intergenic↗
PubMed2002

Genetic, ecological, and behavioural divergence between two sibling snapping shrimp species (Crustacea: Decapoda: Alpheus).

Examination of genetic and ecological relationships within sibling species complexes can provide insights into species diversity and speciation processes. Alpheus angulatus and A. armillatus, two snapping shrimp species with overlapping ranges in the north-western Atlantic, are similar in morphology, exploit similar ecological niches and appear to represent recently diverged sibling species. We examined phylogenetic and ecological relationships between these two species with: (i) sequence data from two mitochondrial genes (16S rRNA and COI); (ii) data on potential differences in microhabitat distribution for A. armillatus and A. angulatus; and (iii) data from laboratory experiments on the level of reproductive isolation between the two species. DNA sequence data suggest A. armillatus and A. angulatus are sister species that diverged subsequent to the close of the Isthmus of Panama, and that haplotype diversity is lower in A. armillatus than in A. angulatus. Both species are distantly related to A. heterochaelis and A. estuariensis, two species with which A. angulatus shares some similarities in coloration. Ecological data on the distribution of A. angulatus and A. armillatus from two locations revealed differences in distribution of the two species between habitat patches, with each patch dominated by one or the other species. However, there was no apparent difference in distribution of the two species within habitat patches with respect to microhabitat location. Ecological data also revealed that heterospecific individuals often occur in close proximity (i.e. within metres or centimetres) where sympatric. Behavioural data indicated that these species are reproductively isolated, which is consistent with speciation in transient allopatry followed by post-divergence secondary contact. Our data further resolve taxonomic confusion between the sibling species, A. armillatus and A. angulatus, and suggest that sympatry in areas of range overlap and exploitation of similar ecological niches by these two recently diverged species have selected for high levels of behavioural incompatibility.

Animals↗
PubMed2002

[Genetic divergence of Far Eastern dace species belonging to the genus Tribolodon (Pisces, Cyprinidae) and closely related taxa].

Based on a biochemical-genetic approach, heterozygosity and divergence of structural genes of 30 enzyme loci were analyzed in six dace species. In addition, intra- and interspecific divergence of gene expression was analyzed based on a sample of 12 to 15 loci. Mean heterozygosities per individual varied as follows: Tribolodon species, Hobs = 0.007 +/- 0.007 and Hexp = 0.007 +/- 0.007; T. ezoe, Hobs = 0.045 +/- 0.016 and Hexp = 0.067 +/- 0.029. Several variants of genetic distances were estimated. Standard Nei's distances (DN) varied from 0.145 to 0.284 in four dace species studied. As related to Tribolodon dace species, the following genetic distances were obtained for two members of other genera: Pseudaspius leptocephalus, DN = 0.269; Leuciscus waleckii, DN = 0.769. Based on the distance matrices, different clustering algorithms were realized. The main feature shared by different dendrograms was a separate position of the cluster joining Far-Eastern dace species, to which P. leptocephalus and L. waleckii are successively added. Among the species studied, the proportion of loci similar by expression (E) varied from 87 to 100%. The greatest difference was found between anadromous and nonanadromous ecotypes of T. hakonensis, E = 67%. The following conclusions can be made: (1) Four studied species of the genus Tribolodon are rather well genetically differentiated. Diagnostic loci are available. (2) A nominal dace species, T. species, should be considered the fourth isolated species of this genus, which is confirmed by its recent zoological acceptance of this species. (3) The origin and divergence of dace species belonging to the genus Tribolodon are relatively late (1 to 3 Myr ago) historical events. (4) Taxonomically, the genus Tribolodon belong to the tribe Pseudaspinini together with P. leptocephalus, which is confirmed by genetic data. (5) Data on heterozygosity and the divergence of structural and regulatory elements of genome, along with the proposed scheme of speciation types, suggest the following speciation modes for the species studied: for four species, adaptive divergence and for two species, genetic transformation.

Animals↗
PubMed1984

Cytogenetic studies of some species complexes of Anopheles in Thailand and Southeast Asia.

Recent studies on cytogenetics, behavioral, geographical and distinct morphological characters on adult, pupal and larval stages have revealed that "balabacensis" is a species complex. Anopheles dirus the mainland species, is distributed widely in Thailand and is renowned for its role as primary vector of human malarial parasites. Further, evidence from cytogenetic and taxonomic studies suggests that "An. dirus" is a species complex comprising at least four distinct species provisionally designated: dirus A, B, C and D. These cryptic species are distinguishable only partially morphologically, but can be separated on the basis of metaphase chromosomes using the Giemsa and Hoechst 33258 staining techniques. Apparently, these siblings show distinct patterns of geographic distribution in Thailand and Peninsular Malaysia. The recognition of dirus as a complex of species in Thailand and Peninsular Malaysia requires a re-evaluation of the role that the individual members of this complex have in the transmission of malaria parasites in this region. Cytological analysis of gene rearrangements in ovarian polytene chromosomes has shown that An. maculatus is a sibling-species complex consisting of at least four species in Thailand provisionally designated: maculatus A, B, C and G. These siblings are sympatric in some populations. Furthermore, species B is so highly polymorphic for chromosome rearrangements that four geographic forms can be recognized. It is not known whether these four forms are subspecies or yet further species within the species B complex. These sibling-species must be differentiated in order to understand any differential capabilities in their transmission of human malaria parasites. Anopheles nivipes was elevated from synonymy under An. philippinensis to full species status by Reid, a decision recently confirmed by cross mating experiments. The Thailand Malaria Division does not differentiate these two species and only identifies An. philippinensis, yet, An. nivipes is by far the most common of the two species in Thailand. Furthermore, preliminary surveys of the ovarian polytene chromosomes of several widely separated populations of An. nivipes in Thailand have revealed at least two distinct chromosomal types of nivipes based on fixed inversions on the X chromosomes.

Animals↗
PubMed1994

Effect of dietary N-3 fatty acids upon the phospholipid molecular species of the monkey retina.

PURPOSE: To characterize the molecular species composition of ethanolamine glycerophospholipids (EGP) in the primate retina and to examine the effects of different dietary fats, the authors fed rhesus monkeys diets containing widely ranging amounts of n-3 fatty acids. METHODS: From birth, infant monkeys were fed either a control soybean oil diet, containing 8% of total fatty acids as 18:3 (n-3), or a safflower oil-based n-3 fatty acid deficient diet containing < 0.4% 18:3 (n-3). A subset of the n-3 deficient group was later repleted with 1.6% ethyl docosahexaenoate, 22:6 (n-3), starting at 10 months of age. Tissues were taken from all monkeys upon termination at 21 to 51 months of age. The diacyl, alkenylacyl, and alkylacyl EGPs were quantitated by high-pressure liquid chromatography (HPLC). RESULTS: Twenty-eight molecular species were identified in the retina of control monkeys. Ether phospholipids comprised 36% of the retinal ethanolamine glycerophospholipids. Species containing polyunsaturated fatty acids in both the sn-1 and sn-2 positions (dipolyenes) were present only in the diacyl subclass and comprised 16% of the total species. Species having n-3 fatty acids in the sn-2 position contributed 59%, 36%, and 70% of total species in the diacyl, alkenylacyl, and alkylacyl subclasses, respectively. In the molecular species of the n-3 fatty acid deficient monkeys, the major change was the loss of most of the 18:0-22:6(n-3) species and its partial replacement with 18:0-22:5(n-6). In contrast, the species 18:1-22:6(n-3) decreased only slightly, from 6.2% to 4.8% of total diacyl species. Although the total concentration of dipolyenes (15% to 20% of the total species) was not affected by diet, their fatty acid compositions were changed drastically. The dipolyene species 22:6(n-3)-22:6(n-3) nearly disappeared in the n-3 deficient monkeys. Concomitantly, two new species, 22:5(n-6)-22:6(n-3) and 22:5(n-6)-22:5(n-6), appeared at 2.6% and 2.0%, respectively. Deficient monkeys given the ethyl ester of 22:6(n-3) in the diet recovered to a near-normal molecular species composition, except in the ether lipids, in which 16:0-20:4 remained low. CONCLUSION: Diets of differing n-3 fatty acid content had profound qualitative and quantitative effects on the molecular species of retinal phospholipids, and the replacement of 22:6(n-3) by 22:5(n-6) in the retinas of n-3 deficient monkeys was asymmetric and functionally incomplete.

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