Geographical distribution of two haplotypes of chloroplast DNA in four oak species (<Emphasis Type="Italic">Quercus</Emphasis>) in Japan

Chloroplast DNA polymorphism in four oak species (Quercus serrata, Q. mongolica var. crispula, Q. dentata and Q. aliena) was studied using collections from a total of 127 localities in Japan and South Korea on the basis of five intergenic spacers (trnD-trnT, trnT-trnL, rps14-psaB, trnS-trnT and trnQ-trnS). Although no variation existed in sequences among the four species, a single nucleotide (T/C) substitution in the trnQ-trnS intergenic spacer was found in all the four species, resulting in two haplotypes (T- and C-type). Phylogenetic analyses of the four species and related species showed that the C-type is derived and even likely of monophyletic origin, while the T-type is ancestral. Geographically, the T-type is widespread from South Korea to Japan, whereas the C-type is restricted to eastern Japan with rare exceptions. Eastern Japan approximately coincides with the distribution range of the boreal conifer forest during the last glacial maximum. Overall evidence suggests that the mutation from T- to C-type occurred in an individual of one of the four oak species and then was transferred to all the species by hybridization in eastern Japan, and that the Kanto District provided individuals with the C-type with a refugium during the last glacial maximum.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Growth and competition between seedlings of an invasive plantation tree, <Emphasis Type="Italic">Acacia mangium,</Emphasis> and those of a native Borneo heath-forest species, <Emphasis Type="Italic">Melastoma beccarianum</Emphasis>

An introduced plantation tree species, Acacia mangium Willd., is becoming invasive in the Brunei region of Borneo. To examine its invasive potential, a greenhouse, additive series experiment (target–neighbour) involving seedlings of A. mangium and those of a common native heath-forest (kerangas), Melastoma beccarianum Cogn. was carried out under low and high light regimes in intra- and interspecific combinations over a 6-month period. Significant variations in growth parameters (other than biomass allocation patterns) existed amongst seedlings from different treatments. A major part of this variation in growth could be attributed to the main factors of target species, neighbour species, and competition (seedling density). For the growth variables examined, the target–species response was not consistent across light regimes. Under high light conditions, Acacia was the better competitor; the Lotka-Volterra competition coefficient effect of Melastoma on Acacia was lower (=0.30) than the effect of Acacia on Melastoma (=0.54). However, the reverse occurred under low light conditions with Melastoma gaining the upper hand (=1.45 and =0.44). These results show that light (and hence disturbance) can strongly influence the pattern and intensity of both intra- and interspecific competition between invasive and local flora species. Relatively intact forest is unlikely to be invaded by Acacia trees (as they are poor competitors under this scenario). On the other hand, the Acacia trees can easily invade disturbed forests, especially those prone to recurring drought and fire, and over time convert the habitats to nearly monospecific stands, as is presently being observed in Brunei.     

Salinity-temperature tolerance of two closely related triclad species,Dugesia lugubris and D. polychroa (Turbellaria), in relation to their distribution in The Netherlands

The tolerance of adult specimens of Dugesia lugubris and D. polychroa for 13 different chlorinities ranging from 15.0–3.8 and for two temperatures, viz. 4 and 23 °C, was tested.At chlorinities of 7.5 and lower, the survival time of both species was considerably longer than at higher chlorinities (a few hours at 7.5, one to several days at 6.6 and lower concentrations). It is assumed that this is determined by the osmoregulatory capacity of the planarians.It was found that at low chlorinities combined with a high temperature D. polychroa survived longer than D. lugubris, while at the same chlorinities the opposite was true for a low temperature. The effect of temperature on survival at low chlorinities was more drastic for D. lugubris than for D. polychroa.The results correlate with data on the distribution of both species in The Netherlands. Outside areas with an average chlorinity below 2 the two species were rarely found.     

A new species of Crepidostomum (Allocreadiidae: Digenea) from northeastern Finland,with comments on its possible origin

Crepidostomum wikgreni n. sp. is described from the gall-bladder and intestine of the whitefish Coregonus acronius in Lake Yli-Kitka in NE Finland. It is morphologically similar to Crepidostomum farionis, with which it occurs sympatrically and sometimes concurrently; but it differs in that the eggs are much larger, i.e. 96±6.5 m mean-length, as opposed to 71±4.7 m mean-length for C. farionis in the same host and locality.It is suggested that the new species has arisen from C. farionis after deglaciation and since c. 8,400 BP, at which time the waters of the Lake Kitka System were isolated from those in the rest of Finland and flowed eastwards into the White Sea Basin. The isolation of the White Sea Basin appears to have been maintained by watersheds running north-south close to the Fenno-Soviet border and east-west through central Karelia. It is further suggested that C. farionis currently occurring in Lake Yli-Kitka is a recent re-introduction brought about by the translocation of fish-stocks.     

ÜBER DIE URSACHEN DER UNTERSCHIEDLICHEN RESISTENZ VON VICIA FABA L. GEGENÜBER DER BOHNENBLATTLAUS,APHIS (DORALIS) FABAE SCOP

Zusammenfassung Fruchtbarkeit und Wachstum von vier auf Ackerbohnen (Vicia faba) lebenden Aphiden-Arten (Aphis fabae, A. craccivora, Acyrthosiphon pisum, Megoura viciae) werden von den Sorten Schlanstedter und Rastatter in gegensätzlicher Weise gefördert bzw. gehemmt. Post-infektionelle Resistenzeffekte treten daher einerseits bei Rastatter gegen A. fabae, andererseits aber bei Schlanstedter Ackerbohnen gegen Erbsen- und Wickenläuse auf, während sich A. craccivora auf beiden etwa gleich gut entwickelt.

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Summary Aphis fabae, Aphis craccivora, Acyrthosiphon pisum, and Megoura vicae (abbreviated Af, Ac, Ap and Mv, respectively) were allowed to develop under similar uncaged conditions on Rastatter (R) and Schlanstedter (S) field beans. Large, sometimes contradictory, differences in the fecundities and weights attained by adult apterous virginoparae on these plants were recoreded and ascribed to postinfestation resistance effects.Ap, which feed only on leaves, and Mv, which feed exclusively on internodes, weigh significantly more (17–18%) on R than on S. In contrast, Af, which feed on various plant parts, are 61% heavier on the leaves and 33% heavier on the stems of S than on the corresponding parts of R.However, Ac, which have a distribution on the plants similar to that of Af, are somewhat heavier (12%) on R-leaves and on S-stems than on the corresponding plant parts of the other variety. Such differences are greatly diminished if the aphids are reared on excised leaves and stems immersed in water. In this case growth of the aphids on excised parts of the resistant varieties (on which they previously grew poorly) closely approaches that on the intact satisfactory varieties (on which they grew well). Only small (Af, Ac) or no (Ap, Mv) improvement in growth results when the aphids are reared on excised parts of the satisfactory variety. Thus, the weights of apterous adults of Ap on excised S-leaves were only 17% greater than on intact S-leaves, whereas they were similar on excised and intact R-leaves. For Af, adult weights were 81% greater on excised R-leaves, 51% greater on excised S-leaves, and only 19% or no greater on excised R- and S-stems, respectively, than those on the corresponding intact plant parts.The possibility is discussed that these contradictory effects result from a mobilization and increase of proteinaceous constituents in the excised plant parts. Whereas the nutrition and growth of aphids on the resistant variety may thus become optimal, such an increase above an already optimal nutrient level on the satisfactory variety would not increase growth beyond the limit already achieved by a species. It is further deduced that postinfestational resistance to aphids of field beans depends on the nutrient value of the sap available to the aphids. However, since the nutritional demands of different aphid species may also differ, it is unlikely that a single plant species will be resistant to aphids in general.

     

Chromosomal polymorphism and small karyotypic differentiation in a group of Ctenomys species from Central Argentina (Rodentia: Octodontidae)

Cytogenetic analysis was performed in six nominal taxa of the genus Ctenomys with a diploid number of 2n=47/48. The studied species were: C. australis (2n=48, FN=76); C. mendocinus (2n=47/48, FN=68/75/76); C. porteousi (2n=47/48, FN=71/72/73); C. azarae (2n=47, FN=71); C. sp. (chasiquensis) (2n=47/48); and C. talarum (2n=48, FN=80). The first three species shared the whole complement, C. talarum shares with them 19 arms from a total of 43 (44%). In all species analyzed constitutive heterochromatin was detected in most short arms, and in several centromeres. Polymorphisms for several pairs involving the heterochromatic short arms together with a complex polymorphism of pair A1 were found in C. azarae, C. sp., C. mendocinus and C. porteousi. Intraindividual variation found in one specimen of C. porteousi involving heterochromatic arms is discussed.These results lead us to propose the inclusion of all species except C. talarum, within a complex called the mendocinus-group. A new case of conservatism for chromosomal number in the genus Ctenomys is found in this group.     

Diversity,metabolic types and δ13C carbon isotope ratios in the grass flora of Namibia in relation to growth form,precipitation and habitat conditions

The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in ¹³C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the ¹³C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest ¹³C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower ¹³C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative ¹³C values than PCK species and ¹³C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, ¹³C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.     

Ontogeny of the thymus in an antarctic teleost,Harpagifer sp. (Notothenioidei: Perciformes)

Summary The development of the thymus was examined in different stages of Harpagifer sp. from Signy Island (South Orkney Islands; 60°43S, 45°38W). The thymus was typical, both in position and structural development, of that observed in warmer-water teleosts. The infiltration of the thymic epithelia was not observed until 4 weeks post-hatch. Full development of the lymphoid organs was not achieved until the juvenile stage. Although an increased infiltration of the thymus, by sub-epithelial connective tissues and epithelial mucous cells, occurred in the juvenile and adult stages, there was no evidence of an advanced stage of thymic regression or involution in the adult Harpagifer. Thus a suppressive influence of the low temperature environment, on the onset and degree of thymic development and involution, was indicated in this species.The signy Island population of Harpagifer has been given the species name H. antarcticus (Prof. J.C. Hureau; personal communication)     

Spatial and temporal distribution of carbon isotopes in soil organic matter at the Dinghushan Biosphere Reserve, South China

The spatial and temporal distribution of carbon isotopes (¹³C, ¹⁴C) in soil organic matter (SOM) were studied based on SOM content, SOM ¹⁴C and SOM ¹³C of thinly layered soil samples for six soil profiles with different elevations at the Dinghushan Biosphere Reserve (DHSBR), South China. The results indicate that variations of SOM ¹³C with depth of the soil profiles at different elevations are controlled by soil development, and correlate well with SOM composition in terms of SOM compartments with different turnover rates, and SOM turnover processes at the DHSBR. The effect of carbon isotope fractionation was obvious during transformation of organic matter (OM) from plant debris to SOM in topsoil and SOM turnover processes after the topsoil was buried, which resulted in great increments of OM ¹³C, respectively. Increments of SOM ¹³C of topsoil from ¹³C of plant debris were controlled by SOM turnover rates. Both topsoil SOM ¹³C and plant debris ¹³C increase with elevation, indicating regular changes in vegetation species and composition with elevation, which is consistent with the vertical distribution of vegetation at the DHSBR. The six soil profiles at different elevations had similar characteristics in variations of SOM ¹³C with depth, alterations of SOM contents with depth and that SOM ¹⁴C apparent ages increasing with depth, respectively. These are presumably attributed to the regular distribution of different SOM compartments with depth because of their regular turnover during soil development. Depth with the maximal SOM ¹³C value is different in mechanism and magnitude with penetrating depth of ¹⁴C produced by nuclear explosion into atmosphere from 1952 to 1962, and both indicate controls of topography and vegetation on the distribution of SOM carbon isotopes with depth. Elevation exerts indirect controls on the spatial and temporal distribution of SOM carbon isotopes of the studied mountainous soil profiles at the DHSBR. This study shows that mountainous soil profiles at different elevations and with distinctive aboveground vegetation are presumably ideal sites for studies on soil carbon dynamics in different climatic-vegetation zones.     

Genetic interrelationships of proteolyticClostridium botulinum types A,B, and F and other members of theClostridium botulinum complex as revealed by small-subunit rRNA gene sequences

The phylogenetic interrelationships of members of theClostridium botulinum complex of species was investigated by direct sequencing of their 16S rRNA genes. Comparative analysis of the 16S rRNA sequences demonstrated the presence of four phylogenetically distinct lineages corresponding to: i) proteolyticC. botulinum types A, B, and F, andC. sporogenes, ii) saccharolytic types B, E and F, iii) types C and D andC. novyi type A, and iv) type G andC. subterminale. The phylogenetic groupings obtained from the 16S rRNA were in complete agreement with the four divisions recognised within the species complex on the basis of phenotypic criteria.     

Acidiphilium aminolytica sp. nov.: An acidophilic chemoorganotrophic bacterium isolated from acidic mineral environment

Acidiphilium aminolytica is proposed for a species of the genusAcidiphilium. Acidiphilium aminolytica can be phenotypically differentiated from all other species of the genusAcidiphilium. The seven strains of this species that have been studied are Gram-negative, aerobic, mesophilic, non-sporeforming, motile, and rod-shaped bacteria. They grow between pH 3.0 and 6.0, but not at pH 6.5. They yield positive results in tests for hippuric acid hydrolysis, catalase and urease production. Oxidase, esculin hydrolysis, and -galactosidase tests are negative. They can used-glucose,d-galactose, inositol, sorbitol,l-lysine,l-glutamate,l-arginine, -alanine,dl-4-aminobutyrate,dl-5-aminovalerate, sperimine, or diaminobutane as a sole carbon source, but cannot use elemental sulfur and ferrous iron as an energy source. The DNA base composition is 58.7–59.2 G+C mol%. The major isoprenoid quinone is ubiquinone with ten isoprene unit (Q-10). The major fatty acid is the C_18:1 fatty acid. Two ornithine amide lipids, the C_18:1 fatty acid esters of -N-3-hydroxystearylornithyltaurine and -N-3-hydroxystearylornithine, are detected as the polar aminolipid. DNA relatedness between this species and the other species ofAcidiphilium, the generaAcidomonas, andAcidobacterium was 29 to 2%. These results indicate, that this new species should be placed in the genusAcidiphilium. The type strain (strain 101) ofA. aminolytica is JCM 8796.     

Laboratory studies on the feeding habits,reproduction and development of three phytoseiid species,Typhlodromus pomi,Phytoseius macropilis andAmblyseius finlandicus (Acari: Phytoseiidae), occurring on abandoned apple trees in Ontario,Canada

Laboratory studies on predation, reproduction and development were conducted on three phytoseiid species,Typhlodromus pomi (Parrott),Phytoseius macropilis (Banks) andAmblyseius finlandicus (Oudemans). These species were dominant phytoseiid mites on the abandoned apple trees with which ecological experiments were carried out in southern Ontario, Canada. Throught the studies, a rust mite species (Diptacus gigantorhynchus sp. complex), a single consistent prey in the orchard, was used as food. Results showed that the three predators developed well with the rust mites as food, and thatA. finlandicus developed most rapidly and had the highest predation rate. However, this species showed a poor tolerance to low prey densities. These observations suggest that this species is a predacious species and the other two species were more or less general feeders. All species showed the same pre-mating behaviour (Amblyseius-Typhlodromus type), but they exhibited a variety of mating and oviposition behaviours.     

The sea anemone genus Actinostola Verrill 1883: variability and utility of traditional taxonomic features, and a re-description of Actinostola chilensis McMurrich 1904

Species of the genus Actinostola are known for high variability of features. Anatomy, histology and cnidae of type specimens of five species from South America and Antarctica originally described as members of Actinostola and one species of Stomphia were compared to specimens of Actinostola chilensis collected during this study. None of these traditionally used features clearly distinguish the examined Actinostola species. I therefore propose new distinctive taxonomic features, including in vivo and in situ data. I provide an emended diagnosis of the genus Actinostola and a revised list of its species. I accept the synonymy of A. excelsa, A. pergamentacea and A. intermedia with A. crassicornis, and reject the synonymy of A. chilensis with A. crassicornis and A. intermedia. I re-describe A. chilensis in detail, including in situ information. Specimens of A. chilensis inhabit exposed positions of rocky substrate from 22 m depth down in south Chilean fjords between Puerto Montt (41°3535S, 72°53W) and Puyuhuapi (44°3136S; 72°326W); the most conspicuous features are its relatively large size, bright-orange colour, smooth, tough column and numerous and clearly entacmaeic tentacles.Electronic Supplementary Material  Supplementary material is available in the online version of this article at The publisher regrets that during copy-editing of this article the names of the authors of species were styled incorrectly. Therefore, it was decided to publish this erratum which, due to the nature of the paper, contains the whole original article, but now with the names of species authors styled correctly.The online version of the original article can be found at     

Genetic Distance in Housekeeping Genes Between <Emphasis Type="Italic">Plasmodium falciparum</Emphasis> and <Emphasis Type="Italic">Plasmodium reichenowi</Emphasis> and Within <Emphasis Type="Italic">P. falciparum</Emphasis>

The time to the most recent common ancestor of the extant populations of Plasmodium falciparum is controversial. The controversy primarily stems from the limited availability of sequences from Plasmodium reichenowi, a chimpanzee malaria parasite closely related to P. falciparum. Since the rate of nucleotide substitution differs in different loci and DNA regions, the estimation of genetic distance between P. falciparum and P. reichenowi should be performed using orthologous sequences that are evolving neutrally. Here, we obtained full-length sequences of two housekeeping genes, sarcoplasmic and endoplasmic reticulum Ca²⁺-ATPase (serca) and lactate dehydrogenase (ldh), from 11 isolates of P. falciparum and 1 isolate of P. reichenowi and estimate the interspecific genetic distance (divergence) between the two species and intraspecific genetic distance (polymorphism) within P. falciparum. Interspecific distance and intraspecific distance at synonymous sites of interspecies-conserved regions of serca and ldh were 0.0672±0.0088 and 0.0011±0.0007, respectively, using the Nei and Gojobori method. Based on the ratio of interspecific distance to intraspecific distance, the time to the most recent common ancestor of P. falciparum was estimated to be (8.30±5.40) × 10⁴ and (11.62±7.56) × 10⁴ years ago, assuming the divergence time of the two parasite species to be 5 and 7 million years ago, respectively.This article contains an online supplementary table.Reviewing Editor: Dr. Martin Kreitman     

Population genetics of <Emphasis Type="Italic">Collisella subrugosa</Emphasis> (Patellogastropoda: Acmaeidae): evidence of two scales of population structure

Marine invertebrate populations usually show high levels of genetic variability that has frequently been associated with spatial and temporal environmental heterogeneity. One of the most heterogeneous marine environments is the intertidal zone, the habitat of Collisella subrugosa, the most widespread and abundant Brazilian limpet. C. subrugosa has planktonic larvae that can disperse over long distances, what can promote gene flow among shores, working against interpopulational differentiation. In this study we investigated the genetic variability and populational substructure of C. subrugosa through analysis of 24 allozyme loci in 14 samples (590 individuals) collected along 2,700 km of the Brazilian coast. The genetic variability was high ( and ), as expected for intertidal species. Genetic differentiation among samples was low (F _ST = 0.03) what may reflect intensive gene flow associated with larval dispersal. However, we detected an isolation-by-distance pattern of population substructure in one sampled region. High levels of heterozygote deficiency were also observed for many loci in each sample. Alternative hypothesis are discussed, and the “breeding groups” is suggested to explain these pattern, indicating the main cause as environmental heterogeneity.     

<Emphasis Type="Italic">Atactorhynchus duranguensis</Emphasis> n. sp. (Acanthocephala: Atactorhynchinae) from <Emphasis Type="Italic">Cyprinodon meeki</Emphasis> (Pisces: Cyprinodontidae) near Durango,Mexico

Atactorhynchus duranguensisn. sp. (Acanthocephala: Atactorhynchinae) is described from the intestine of Cyprinodon meeki Miller, an endemic freshwater fish from a far-inland locality of Mexico. Diagnostic features include: body small, stout, ventrally curved; small cylindrical proboscis armed with 16 alternating vertical rows of four or five hooks; anterior two or three hooks conspicuous, stout and larger than other hooks, and have large, rod-shaped roots with a markedly and abruptly enlarged base; three posterior hooks of each row are smaller and rootless; single-walled proboscis receptacle; lemnisci equal in length, elongate and robust; and cement gland syncytial, larger than testis. The new species is smaller than A. verecundus Chandler, 1935, the only previously described species in the genus. The shape of the proboscis of the new species is strikingly different from that of A. verecundus, which is widest at the apex. Likewise, the greatest width of the trunk of the new species is in about the middle, differing from that of A. verecundus where the trunk is widest posteriorly. The new species also can be distinguished from A. verecundus because of its much smaller hook lengths and slightly smaller proboscis. In addition, the proportion of large apical proboscis hooks in relation to the small basal hooks is different: the basal hooks of A. verecundus are about half the size of the anterior hooks and but only about a quarter of the size in A. duranguensis. Unlike A. verecundus, the base of the roots are markedly and abruptly enlarged in the new species. Finally, the eggs of the new species are smaller (23–27 × 8–10 m) than those of A. verecundus (27–30 × 12–13 m).     

<Emphasis Type="Italic">Fusarium</Emphasis> species of the <Emphasis Type="Italic">Gibberella fujikuroi</Emphasis> complex and fumonisin contamination of pearl millet and corn in Georgia,USA

This study was designed to identify and compare the Fusarium species of the Gibberella fujikuroi complex on pearl millet (Pennisetum glaucum (L.) R. Br) and corn (Zea mays L.) crops grown in southern Georgia, and to determine their influence on potential fumonisin production. Pearl millet and corn samples were collected in Georgia in 1996, 1997 and 1998. Three percent of the pearl millet seeds had fungi similar to the Fusarium species of the G. fujikuroi species complex. One hundred and nineteen representative isolates visually similar to the G. fujikuroi species complex from pearl millet were paired with mating population A (Fusarium verticillioides (Sacc.) Nirenberg), mating population D (F. proliferatum (Matsushima) Nirenberg) and mating population F (F. thapsinum (Klittich, Leslie, Nelson and Marasas) tester strains. Successful crosses were obtained with 50.4%, 10.1% and 0.0% of these isolates with the A, D and F tester strains, while 39.5 of the isolates did not form perithecia with any tester strains. Two of the typical infertile isolates were characterized by DNA sequence comparisons and were identified as Fusarium pseudonygamai (Nirenberg and ODonnell), which is the first known isolation of this species in the United States. Based on the pattern of cross-compatibility, conidiogenesis, colony characteristics and media pigmentation, a majority of the infertile isolates belong to this species. Fumonisins FB₁ and FB₂ were not detected in any of the 81 pearl millet samples analyzed. The species of the G. fujikuroi species complex were dominant in corn and were isolated from 84%, 74% and 65% of the seed in 1996, 1997 and 1998, respectively. Representative species of the G. fujikuroi species complex were isolated from 1996 to 1998 Georgia corn survey (162, 104 and 111 isolates, respectively) and tested for mating compatibility. The incidence of isolates belonging to mating population A (F. verticillioides) ranged from 70.2% to 89.5%. Corn survey samples were assayed for fumonisins, and 63% to 91% of the 1996, 1997 and 1998 samples were contaminated. The total amount of fumonisins in the corn samples ranged from 0.6 to 33.3 g/g.     

Species pairs of north temperate freshwater fishes: Evolution,taxonomy, and conservation

Many fish species contain morphologically, ecologically and geneticallydistinct populations that are sympatric during at least some portion oftheir life cycle. Such reproductively isolated populations act asdistinct biological species, but are identified by a common Latinbinomial. These species pairs are particularly common in freshwaterfish families such as Salmonidae, Gasterosteidae and Osmeridae and aretypically associated with postglacial lakes in north temperateenvironments. The nature of the divergences between sympatric species,factors contributing to reproductive isolation, and modes of evolutionare reviewed with particular emphasis on benthic and limnetic pairs ofthreespine sticklebacks, Gasterosteus aculeatus, and anadromous(sockeye salmon) and nonanadromous (kokanee) pairs of Oncorhynchusnerka. Phylogenetic analyses typically indicate that divergencesbetween members of replicate pairs have occurred independently and,hence, particular phenotypes are not monophyletic. Consequently,taxonomic resolution of such species complexes is a vexing problem foradherents to our traditional Linnaean classification system. Sympatricspecies pairs represent a significant component of the biodiversity oftemperate freshwater ecosystems which may be underestimated because oursystem of formal taxonomy tends to obscure diversity encompassed byspecies pairs. Conservation of such systems should be recognized as apriority without formal taxonomic designation of members of speciespairs because taxonomic resolution will likely continue to proveextremely difficult when employing traditional hierarchies andprocedures.     

Population differentiation in Collinsia verna Nuttal (Scrophulariaceae): a multifaceted approach

Three species of Collinsia (commonly called Blue-eyed Mary, Innocence, Chinese Houses) including 12 populations of C. verna were examined for genetic variability and differentiation using three investigative techniques: enzyme electrophoresis, chiasma frequencies, and morphological measurements. Analysis of isozyme data showed higher heterozygosity was maintained in the C. verna populations (previously reported to be self pollinating) than in C. heterophylla and C. tinctoria, which are outcrossers. C. heterophylla and C. tinctoria were separated by a significant genetic distance from each other and especially from C. verna. Within C. verna isozyme, morphological, and chiasma frequency analyses separated the populations into subsets showing some geographical trends, possibly influenced by water dispersal of seeds. High genetic variability was maintained and differentiation has occured in the C. verna populations. The explanation may lie in a combination of factors associated with the heterozygosity paradox including microgeographical influence and inappropriate mating system classification.     

Branchinecta belki n. sp. (Branchiopoda: Anostraca), a new fairy shrimp from Mexico,hybridizing withB. packardi Pearse under laboratory conditions

A new fairy shrimp,Branchinecta belki n.sp., endemic to the south of Coahuila state is described and figured. A total of nine species of phyllopods, including the new species, occur in ponds in the type area.The laboratory hybridization ofB. belki andB. packardi through no-choice mating tests in reciprocal crosses is discussed. A mixture of characteristics of parental species is present in male F1 and F2 hybrids. This may provide a biological tool, or search image (sensu Wiman, 1979a), for detecting male hybrids, should such exist, between theBranchinecta species of this study in nature. In addition to the reported interspecific hybridizations inStreptocephalus (Wiman, 1979a & 1979b) and inArtemia (Bowenet al., 1985) under laboratory conditions, the new evidence inBranchinecta suggests that absence of efficient premating mechanisms may be common in Anostraca.