Genetic variation and differentiation of the two river sculpins,Cottus nozawae andC. amblystomopsis,deduced from allozyme and restriction enzyme-digested mtDNA fragment length polymorphism analyses

Genetic differentiation of the two sibling species,Cottus nozawae andC. amblystomopsis, from the northern part of Japan (Hokkaido Island and the Tohoku District) was investigated using allozyme variations and restriction fragment length polymorphisms of mitochondrial DNA. Although the two species are morphologically very similar, previously being thought to be a single species, they have different life-cycles;C. nozawae has a fluvial life-cycle with a small number of large-sized eggs, whereasC. amblystomopsis is an amphidromous species with a large number of small-sized eggs. Four populations ofC. amblystomopsis from Hokkaido Island and 24 populations ofC. nozawae (22 from Hokkaido Island and 2 from the Tohoku District) were sampled and examined Intrapopulational differentiation in the two species was measured by examining several indexes, including proportion of polymorphic loci (P), mean heterozygosity (H) and nucleotide diversity (π). All measurements were higher in theC. amblystomopsis populations, suggesting that intrapopulational variation inC. nozawae was less than inC. amblystomopsis and reflecting the difference in effective population sizes between them. Cluster analyses were performed using the UPGMA method, based on the data matrices of genetic distance (D) and the net nucleotide difference (δ) between populations. TheC. nozawae andC. amblystomopsis populations from Hokkaido Island composed a large cluster (Hokkaido group), while theC. nozawae populations from the Tohoku District composed a different cluster (Tohoku group). Bootstrap probabilities deduced from 1000 bootstrap replications for presence or absence of restriction sites showed that the mtDNA haplotypes detected within the Tohoku Group occurred in 99.9% of the bootstrap replicates outside the mtDNA haplotypes of the Hokkaido group, while those within the Hokkaido group occurred in 3.5–64.9% of bootstrap replicates. Consequently, the Hokkaido populations of the two species (Hokkaido group) were genetically close to each other, whileC. nozawae from the Tohoku District (Tohoku group) were distant from the Hokkaido group. These results suggest that the ancestral populations of the two species on Hokkaido Island shared the same gene pool, even after becoming geographically isolated from the ancestral population ofC. nozawae in the Tohoku District by the formation of the Tsugaru Straits.     

Thermal changes in the gastric evacuation rate of the freshwater sculpin Cottus nozawae Snyder

We experimentally measured thermal changes in the gastric evacuation rate (GER) of the freshwater sculpin Cottus nozawae Snyder under three water temperature regimes (2°, 7°, and 12°C). Laboratory experiments showed that the GER was accelerated with increasing water temperature. This result suggests that the daily food rations of fish are more likely to be underestimated at higher water temperatures if estimation is simply based on the stomach content weight alone. By comparing the GER for various fish species from subfrigid to temperate streams, we found a general pattern that the GER increases with water temperature, regardless of taxonomic group or foraging mode. However, the reaction norms of the GER against water temperature showed considerable interspecific variation. This means that stomach content weight is not comparable as a simple measure for determining the daily rations among fish species when water temperature regimes are different. To consider the temperature-dependent pattern of such a physiological phenomenon is important in understanding the feeding ecology of fishes and their roles in material cycles through food webs in aquatic ecosystems.     

Genetic studies on reference strains of mutans streptococci

Twenty four reference strains (serotype a-h) belonging to the mutans group of streptococci were compared for DNA fragment patterns of rDNA after treatment with Hind III. It was shown that Streptococcus cricetus (serotype a), S. rattus (serotype b), and S. downei (serotype h) reveals comparatively homogeneous patterns while S. mutans (serotype c, e and f) exhibits differences between the different serotypes as well as within single serotypes. S. sobrinus had an intermediary diversity. These data support the previous findings that S. mutans is heterogeneous at the serological, biochemical and genetical level.     

A correction for allele frequency estimates derived from isofemale lines

Isofemale lines are commonly used inDrosophila and other genera for the purpose of assaying genetic variation. Isofemale lines can be kept in the laboratory for many generations before genetic work is carried out, and permit the confirmation of newly discovered alleles. A problem not realized by many workers is that the commonly used estimate of allele frequency from these lines is biased. This estimation bias occurs at all times after the first laboratory generation, regardless of whether single individuals or pooled samples are used in each well of an electrophoretic gel. This bias can potentially affect the estimation of population genetic parameters, and in the case of rare allele analysis it can cause gross overestimates of gene flow. This paper provides a correction for allele frequency estimates derived from isofemale lines for any time after the lines are established in the laboratory. When pooled samples are used, this estimator performs better than the standard estimator at all times after the first generation. The estimator is also insensitive to multiple inseminations. After the lines have drifted oneN _e generations, multiple inseminations actually make the new estimator perform better than it does in singly inseminated females. Simulations show that estimates made using either estimator after the lines have drifted to fixation have a much greater error associated with their use than do those estimates made earlier in time using the correction. In general it is better to use corrected estimates of gene frequency soon after lines are established than to use uncorrected estimates made after the first laboratory generation. This work was supported by an NSERC fellowship to A.D.L.     

Description of juvenile development ofArtediellus neyelovi (cottidae) from off Usujiri, southern Hokkaido, Japan

Juveniles ofArtediellus neyelovi are described on the basis of 24 specimens (8.3–23.6 mm SL) from Hokkaido, Japan. All medial and paired fins were completely developed in all specimens. The smallest specimen (8.3 mm SL) had a slender elongated suborbital stay similar to that of adults. Specimens 8.3–10.1 mm SL had 4 preopercular spines, cirri absent on the head and body, except a very small supraorbital cirrus, and sensory canals comprising open grooves restricted to the head surface. Specimens 14.1–20.0 mm SL had complete cephalic sensory canals, and the 2nd and 3rd preopercular spines reduced. Specimens 20.8–23.6 mm SL had a nearly complete lateral line canal and exhibited most specific diagnostic characters except some cephalic cirri. The anterior 3 neural arches on both sides were separate at 8.3 mm SL, but had become fused (except for the anteriormost) at 14.3 mm SL. The anteriormost arch was not fused in an adult, 71.3 mm SL. Some juveniles had very reduced bony plates under the skin anterodorsally on the body, which were not present in adults.     

Similarities and relationships among populations of the bulb onion as estimated by nuclear RFLPs

Random nuclear restriction fragment length polymorphisms (RFLPs) were used to assess similarities and relationships among open-pollinated (OP) populations of the cultivated bulb onion (Allium cepa). Seventeen OP populations and 2 inbreds of contrasting daylength response [termed by convention as long (LD) and short (SD) day], 1 shallot (A. cepa var. ascalonicum), and one cultivar of bunching onion (Allium fistulosum) were examined with 104 cDNA clones and two to four restriction enzymes. Sixty (58%) clones detected at least 1 polymorphic fragment scorable among the OP populations and were used for analyses. The average number of polymorphic fragments per polymorphic probe-enzyme combination was 1.9, reflecting that numerous monomorphic fragments were usually present. Similarities were estimated as the proportion of polymorphic fragments shared by 2 populations. Average similarity values among LD, among SD, and between LD and SD OP populations were 0.79, 0.67, and 0.68, respectively. Relationships among the OP populations were estimated by parsimony, cluster analysis of similarities using the unweighted-pair-group method (UPGMA), and multivariate analysis using principle components. Parsimony analysis generated a strict consensus tree that grouped all but 1 LD onion with unresolved relationships to the SD OP populations. The UPGMA analysis placed together the LD storage OP populations. Principal component analysis grouped all but 2 LD onions; the other OP populations were dispersed. The results suggest that LD and SD onions do not represent distinct germ plasm, but that LD storage onions represent a derived group selected for production at higher latitudes. If it is assumed that the sampled populations are representative of all onion OP populations, the lower similarities among SD OP populations indicate that their collection and maintenance in germ plasm collections is important for the preservation of genetic diversity.     

Aplopsora corni sp. nov. onCornus controversa from Hokkaido,Japan

Aplopsora corni sp. nov. is proposed for a rust fungus whose uredinial and basidial stage occurs onCornus controversa (Cornaceae) in Hokkaido. This new species is separated by its larger urediniospores and probasidia from the morphologically closely relatedA. nyssae onNyssa aquatica andN. sylvatica (Cornaceae) distributed in southern North America.     

Temperature preferences and oxygen consumption of three species of sculpin (Cottus) from the Pit River drainage,California

Synopsis I examined the temperature preferences and routine metabolic rates of Pit sculpin, Cottius pitensis, marbled sculpin, C. klamathensis macrops, and rough sculpin, C. asperrimus, of the Pit River drainage of California to determine if the distributional patterns of these species can be explained on the basis of physiological or behavioral responses to temperature. The routine metabolic rates of these species did not increase significantly between 10 and 15°C, indicating an area of thermal compensation. Metabolic rates then rapidly increased between 15 and 20°C (Q₁₀ values>4.0) followed by little increase between 20 and 25°C (Q₁₀ values >2.0), indicating another area of thermal compensation. The final temperature preferenda of Pit, marbled and rough sculpin were 11.2, 12.1 and 13.5°C, respectively. Marbled and rough sculpin appear to be more stenothermal than Pit sculpin. At acclimation temperatures of 10, 15 and 20°C the acute preferred temperatures of marbled and rough sculpin ranged from 11.1 to 14.7° C and 13.3 to 14.4°C, respectively. Values for Pit sculpin ranged from 9.9 to 16.4°C at acclimation temperatures of 10, 15 and 20°C. The distributions of marbled and rough sculpin are consistent with their behavioral and metabolic responses to temperature. The widespread distribution of Pit sculpin is consistent with its greater tolerance of high temperatures and eurythermal behavior, but the absence of Pit sculpin from habitats dominated by marbled and rough sculpin is not consistent with a temperature related explanation.     

Seasonal variations and balanced polymorphisms in the reproductive potential of temperate D. Melanogaster populations

Flies from the first generation of isofemale lines of D. melanogaster founded by wild flies collected in spring, summer and autumn in two French populations have been studied for 4 successive years. Cyclical seasonal variations occur in various genetically determined characteristics involved in reproductive potential.The number of ovarioles of the females and female capacity to control oviposition are subject to variation consisting of an increase in frequency of genotypes controlling large number of ovarioles and strong oviposition blocking control in spring and autumn samples. The opposed genotypes (low number of ovarioles and weaker blocking of oviposition control) are favored in summer generations.This balancing selection, induced by temperature variations, modifies temporarily the genetic equilibrium of the population. This enhances the frequency of better adapted genotypes when conditions become less favorable.

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Résumé L'étude pendant 4 ans de lignées isofemelles, fondées par des mouches capturées dans la nature, au printemps, en été et en automne, dans deux population françaises de D. melanogaster, a mis en évidence des variations saisonnières cycliques portant sur différents caractères liés au potentiel reproducteur. Les individus observés appartenaient à la première génération de laboratoire, élévée en conditions standard; les fluctuations observées correspondaient donc à des variations d'ordre génétique.Le nombre d'ovarioles des femelles et leur capacité à controler leur ponte en présence d'un substrat peu favorable sont soumis à ce type de variations cycliques. Il consiste en une augmentation de la fréquence de certains phénotypes (nombre d'ovarioles élevé et forte capacité de blocage de l'oviposition) au printemps et en automne, tandis que les génotypes opposés (faible nombre d'ovarioles et faible capacité de blocage) sont favorisés pendant les générations estivales.Ces variations correspondent à une sélection balancée induite par les fluctuations de la température. Elles conduisent à une modification temporaire de l'équilibre génétique de la population et à un accroissement de la fréquence des génotypes considérés comme mieux adaptés au climat tempéré, lorsque les conditions environnementales deviennent moins favorables.

     

Reproductive capacity of triploid loaches obtained from Hokkaido Island, Japan

Reproductive capacity was investigated in naturally occurring triploid individuals of the loach Misgurnus anguillicaudatus collected from Memanbetsu Town, Abashiri County, Hokkaido Island, Japan. These triploids have been considered to appear by accidental incorporation of the haploid sperm genome from normal diploid into unreduced diploid eggs from the clonal lineage that usually reproduces unisexually. By fertilization with sperm from the normal male, one triploid female gave many inviable aneuploid (2.1–2.7n) and very few tetraploid progeny, whereas the other produced both diploid and triploid progeny. The results suggest that at least four different types of eggs can be formed in triploid females in this locality. In contrast, no progeny hatched when eggs of the normal female were fertilized with sperm or sperm-like cells obtained from triploid males. These gametes exhibited inactive or no motility after adding ambient water. They had larger head sizes than those of normal haploid sperm and had a short or no tail. Although their ploidy was triploid or hexaploid, a small number of haploid cells were detected in the semen by flow cytometry. Thus, triploid males were generally sterile, but they have a little potential for producing very few haploid sperm.     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.     

Multi-scale spatial pattern of recruitment in the barnacles Semibalanus cariosus at fishing ports on the Kameda peninsula, southern Hokkaido, Japan

The potential causes of the variable nature of recruitment of marine organisms can be inferred from the scales over which they vary. Sampling for recruits of Semibalanus cariosus on the intertidal concrete tetrapods at 21 fishing ports along the Kameda Peninsula, southern Hokkaido, Japan, was conducted at the end of the recruitment season in 1994 at three spatial scales: at each fishing port, separated by several km; at two sites at each fishing port, separated by several hundred m; and on three blocks at each site, separated by 1–2 m. At all spatial scales, recruitment intensity was independent of adult densities. Recruitment densities significantly varied within all spatial-scales, however, 85.6% of the total variances was estimated to be due to variation among ports. Such km-scale variation of recruitment intensities coincided with the hydrographic pattern of the direction of coastal current.     

A molecular genetic linkage map of mouse chromosome 19, including thelpr,Ly-44, andTdt genes

The mouselpr gene, which is an autosomal recessive gene causing autoimmune disease with features of human systemic lupus erythematosus and eventually death from severe immune-complex glomerulonephritis, has been mapped on chromosome 19. To determine its exact chromosomal location, a three-point backcross was carried out by mating (MRL/MpJ-lpr/lpr × MOL-MIT)F₁ × MRL/MpJ-lpr/lpr using the genesLy-44 (lymphocyte differentiation antigen-44) andTdt (terminal deoxynucleotidyl transferase) as markers. The following order of genes is proposed, with the distances between genes given in parentheses: centromere-Ly-44 (19.3 cM)-lpr (6.1 cM)-Tdt-telomere. TheLy-44 ^a andTdt ^a alleles are found in all laboratory strains and in the wild Western European subspecies,domesticus andbrevirostris. In contrast, theLy-44 ^b andTdt ^b alleles are found in some Asian subspecies, Chinese mice of wild origin,yamashinai andmolossinus. Furthermore the thirdTdt allele,Tdt ^c , is detected incastaneus.Some of the data in this study were previously presented at the 4th Mouse Gene Mapping Workshop, Annapolis, Maryland, in November 1990.     

Genetic diversity of six populations of Atractomorpha sinensis and Atractomorpha peregrina in Shanxi Province, China

Ten enzymes (AAT, CK, G3PDH, HEX, IDH, LDH, MDH, ME, PGI, PGM) were examined using horizontal starch gel electrophoresis to estimate the levels of genetic variation within and among six natural populations of two grasshopper species Atractomorpha sinensis and A. peregrina from Shanxi, China. The collecting sites were geographically distant from each other from south to north: Quwo district, Linfen city; Xiangyuan county, Changzhi; Jinyuan district, Taiyuan city; Yuanping county, Xinzhou city and Fanshi county of Xinzhou.A. sinensis showed 43 alleles at 16 loci but A. peregrine showed 39 alleles at 15 loci (Idh-1 was deficient). The zymograms showed that some common alleles were shared at several loci in these two species (Aat-1-b, Aat-2-b, G3pdh-a, Ck-1-b and Ldh-b). However, Hex-1-a, Hex-2-a, Hex-3-a, Idh-2-b, Mdh-2-b, Mdh-1-f, Pgi-b, Pgm-b had common alles in A. sinensis and Hex-1-b, Hex-2-b, Hex-3-b, Idh-2-a, Mdh-2-a, Mdh-1-d, Pgi-a, Pgm-c were of high frequency in A. peregrine instead. Most of the observed genotype frequencies were found to significantly deviate from the Hardy-Weinberg expectations in both species. A tendency of clinal distribution of allele frequency was observed at three loci. The frequency of the moderately migrating allele Me-c (0.318–0.740) in A. peregrina, Hex-1-a (0.800–1.000) and Ldh-b (0.487–0.750) in A. sinensis demonstrated increased frequency from north to south. Such tendency suggests that the allele frequency in these three loci may be correlated with the species’ geographic distributions. A. sinensis showed higher genetic diversity than A. peregrina as indicated by higher mean number of alleles per locus (A = 1.9–2.3 in A. sinensis and 1.7–2.2 in A. peregrina), percentage of polymorphic loci (56.3%–68.8% in A. sinensis and 43.8%–56.3% in A. peregrina), and the observed heterozygosities (H _o = 0.072–0.096 in A. sinensis and 0.70–0.107 in A. peregrina). The observed heterozygosities of the six populations were all noticeably lower than the Hardy-Weinberg expectations, mostly due to heterozygote deficiency in the populations of both species. The overall mean F _ST were small (F _ST = 0.045, P > 0.05 in A. sinensis populations and 0.087, P > 0.05 in A. peregrina populations). Nei’s genetic identity (I) estimates indicate low intraspecific (>0.95) but higher interspecific (0.377–0.447) genetic diversity. The cluster analysis based on modified Roger’s genetic distance (D) showed that the two species were divided into two branches. Both species are of limited dispersal capacity and a moderate geographical barrier might significantly restrict the gene exchange among populations, resulting in accumulation of local genetic differentiations. The A. sinensis populations used in this study were separated from each other by 155.2 to 271.4 km and the A. peregrina populations were separated from each other by 78.8 to 174.9 km with observable physical barriers. The allozyme data showed only minimal genetic differentiation at population level, most likely as a result of gene exchange. It is reasoned that natural factors and human agricultural activities might have facilitated migration and dispersal for the two species. __________ Translated from Acta Ecologica Sinica, 2005, 25(10): 2574–2481 [译自: 生态学报]     

Comparison of DNA restriction fragment length polymorphisms of Nostoc strains in and from cycads

DNA was prepared from cyanobacteria freshly isolated from coralloid roots of natural populations of five cycad species: Ceratozamia mexicana mexicana (Mexico), C. mexicana robusta (Mexico), Dioon spinulosum (Mexico), Zamia furfuraceae (Mexico) and Z. skinneri (Costa Rica). Using the Southern blot technique and cloned Anabaena PCC 7120 nifK and glnA genes as probes, restriction fragment length polymorphisms of these cyanobacterial symbionts were compared. The five cyanobacterial preparations showed differences in the sizes of their DNA fragments hybridizing with both probes, indicating that different cyanobacterial species and/or strains were in the symbiotic associations. On the other hand, a similar comparison of cyanobacteria freshly collected from a single Encephalartos altensteinii coralloid root and from three independently subcultured isolates from the same coralloid root revealed that these were likely to be one and the same organism. Moreover, the complexity of restriction patterns shows that a mixture of Nostoc strains can associate with a single cycad species although a single cyanobacterial strain can predominate in the root of a single cycad plant. Thus, a wide range of Nostoc strains appear to associate with the coralloid roots of cycads.Non-standard abbreviations bp base pairs - kbp kilobase pairs - RFLP's restriction fragment length polymorphisms     

Genetic variation in natural and laboratory populations of the marsupial Sminthopsis crassicaudata

Gel electrophoresis of blood proteins has detected allelic variation at five loci (TRF, PGD, SOD, ADA, GPI) in a laboratory colony of the dasyurid marsupial Sminthopsis crassicaudata. Family data show no significant departures from Mendelian expectations. Analysis of blood from wild-caught progenitors of the colony revealed significant differences in gene frequency between groups of animals captured from different parts of southern and central Australia and showed that there are two major population clusters. These interpopulation differences are particularly marked at the TRF locus and indicate that the river Murray is a barrier for this species.This project was supported by a grant from the Australian Research Grants Scheme.     

Comparing the frequencies of restriction fragment length polymorphisms for dystrophin gene in Chinese with those from Japanese and Caucasian populations

The restriction fragment length polymorphisms distribution and frequency of dystrophin gene in Chinese were studied by using 14 subclones of the entire 14kb cDNA for the dystrophin as hybridization probes. Allelic fragments were detected in hybridization patterns of PvuⅡ/la, Taq Ⅰ/2b-3, Taq Ⅰ/5b-7, and Xba Ⅰ/10. Among them, the allelic fragments (26kb and 3.8kb) in PvuⅡ/2b-3 pattern and the allelic fragments (10.0kb and 8.4kb) in Taq Ⅰ/5b-7 patterns had never been reported previously. Compared with the data from Caucasians and Japanese, it indicated that there was a significant difference (P<0.01) of the allelic fragment frequency in Taq Ⅰ/2b-3 and Xba Ⅰ/10 patterns between Chinese and Caucasians. The frequencies of allelic fragments A2 (5.6kb) in Taq Ⅰ/8 and A2 (10.Tkb) in EcoR Ⅴ/9 were high in Caucasians, yet had not been detected in Chinese, the differences were also highly significant. But in Chinese and Caucasians, the B1B2 allelic frequencies in Taq Ⅰ/5b-7 are the same. As to the frequency of the allelic fragments A1A2 and B1B2 in Pvu Ⅱ/la, there was no significant difference between Chinese and Japanese.     

Genetic Diversity and Genetic Structure of an Endangered Species, Trillium tschonoskii

The genetic diversity and genetic structure of Trillium tschonoskii (Maxim) were investigated using amplified fragment length polymorphism markers. Eight primer combinations were carried out on 105 different individuals sampled from seven populations. Of the 619 discernible DNA fragments generated, 169 (27.3%) were polymorphic. The percentage of polymorphic bands within populations ranged from 4.52 to 10.50. Genetic diversity (H_E) within populations ranged from 0.0130 to 0.0379, averaging 0.0536 at the species level. Genetic differentiation among populations was detected based on Nei's genetic diversity analysis (53.03%) and analysis of molecular variance (AMOVA) (52.43%). AMOVA indicated significant genetic differentiation among populations (52.43% of the variance) and within populations (47.57% of the variance) (p < 0.0002). Gene flow was low (0.4429) among populations. Species breeding system and limited gene flow among populations are plausible reasons for the high genetic differentiation observed for this species. We propose an appropriate strategy for conserving the genetic resources of T. tschonoskii in China.     

A Test for Genetic Exchange in Mixed Infections of Leishmania major in the Sand Fly Phlebotomus papatasi

We tested if genetic exchange was observable between two strains of Leishmania major (Trypanosomatidae) during mixed infection of the sand fly Phlebotomus papatasi. Previous studies suggested that genetic exchange may occur in natural populations of Leishmania at a low frequency, but experimental crosses examining small numbers of progeny (<60) did not reveal hybrid parasites. Accordingly, a strategy was devised to increase the number of progeny that could be screened by 100-fold. Clonal derivatives from two strains that were infective to flies and contained numerous restriction fragment length polymorphisms were characterized and selected for resistance to methotrexate or tunicamycin by gene amplification. A successfully mixed infection of P. papatasi was obtained, and a method was developed for directly plating promastigotes from the gut contents of infected flies onto selective media. Twenty-five hundred independent progeny were scored for the presence of both drug resistance markers. No hybrid parasites were observed, indicating that the frequency of genetic exchange in this cross must be less than 4 times 10^-4. The lines and methods established in this work may prove useful in future studies of the mechanism and frequency of gene exchange in Leishmania.