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PubMed2001

Courtship song genes and speciation in sand flies.

Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae: Phlebotominae) is a vector of visceral leishmaniasis in the Americas and it might represent a complex of sibling species. Reproductive isolation between closely related species often involves differences in courtship behaviour. cacophony (cac) and period (per) are two Drosophila genes that control features of the "lovesong" males produce during courtship that has been implicated in the sexual isolation between closely related species. We are using gene fragments from L. longipalpis' homologues of these two genes to study the speciation process in this putative species complex.

Animals↗
PubMed2006

Mixed swarms of the molecular M and S forms of Anopheles gambiae (Diptera: Culicidae) in sympatric area from Burkina Faso.

The M and S molecular forms of Anopheles gambiae sensu stricto Giles are thought to be reproductively isolated through premating barriers. However, the exact mechanisms of recognition of conspecific partners are unknown. Because mating in An. gambiae occurs in swarms, one might expect swarming behavior between the M and S forms to be different and that this probably reduces the risk of contact between males and females of the different forms in areas where they are sympatric. We report the occurrence of four mixed swarms, containing males of M and S forms, out of a total of 26 swarms sampled in Soumousso, a typical savannah village of Burkina Faso, West Africa. However, the frequency of mixed swarms was lower than that expected by chance. This observation suggests partial segregation between the swarms of the molecular forms, which may contribute to their isolation. Because the frequency of mixed swarms seems too high to explain the low frequency of cross-mating and hybrids, we suggest that mate recognition in a swarm is more important than swarm segregation.

Animals↗
PubMed2006

Shared microsatellite loci in Glossina morsitans sensu lato (Diptera: Glossinidae).

Estimation of allelic frequencies at three microsatellite loci among 20 populations of Glossina morsitans morsitans Westwood, Glossina morsitans submorsitans Newstead, and Glossina morsitans centralis Machado indicated only two of 99 alleles were shared between three subspecies and 18 between any two subspecies; 81 alleles were unshared. The conserved flanking regions of each locus were completely shared. Genetic differentiation among subspecies, based on allele size, was RST = 0.87, close to the theoretic maximum value. All evidence suggests longstanding and complete reproductive isolation in nature among the sibling species. They should be elevated to specific rank.

Alleles↗
PubMed2001

Gene flow between natural and domestic populations of Lutzomyia longipalpis (Diptera: Psychodidae) in a restricted focus of American visceral leishmaniasis in Venezuela.

The epidemiology of the visceral leishmaniasis in the Americas is associated with both a natural and a domestic cycle. The existence of reproductively isolated populations of Lutzomyia longipalpis (Lutz & Neiva), and the scarcity of records of this species from natural habitats in areas where it has been associated with domestic habitats indicated that natural populations could be genetically distinct from domestic ones. Therefore, we compared the genetic structure and estimated the gene flow between L. longipalpis from domestic and peridomestic habitat and from an adjacent undisturbed natural environment along a 1.2-km transect. The analyses were performed on electrophoretic data from eight isozyme loci. The absence of fixed differences in the diagnostic loci Ak and Hk indicated that all specimens belonged to one of the two cryptic species identified in Venezuela. The average number of alleles per locus ranged from 2.0 to 2.9 and the average heterozygosity ranged from 7.8 to 13.4%. No differences were detected in the genetic structure of this species from domestic or peridomestic habitats and those trapped as far as 1.2 km from human dwellings. Nm, estimated from Wright's Fst, indicated that at least 208 individuals per generation migrated between the peridomestic habitat and a 1.2-km distant point to maintain the observed similarities in allelic frequencies. This high rate of gene flow indicated that this species has high migration rates between domestic and natural environments, and has the potential to transport for Leishmania from natural to domestic environments.

Adenylate Kinase↗
PubMed2003

The Chagas vector, Triatoma dimidiata (Hemiptera: Reduviidae), is panmictic within and among adjacent villages in Guatemala.

Trypanosoma cruzi, the hemoflagellate parasite and cause of Chagas disease in Latin America, is carried by Triatomine vectors, principally Triatoma dimidiata and Rhodnius prolixus in Central America. To assist control efforts and to understand the epidemiology of the disease in Guatemala, the population genetics of T. dimidiata was analyzed among three houses within a village and two adjacent villages in Guatemala. Eleven Randomly Amplified Polymorphic DNA-polymerase chain reaction (RAPD-PCR) primers were screened and three used to amplify bands, 29 of which were scored, from T. dimidiata DNA of approximately 50 bugs per house from three houses within a village and from 66 and 33 bugs, respectively, from adjacent villages. Results show very small genetic distances among the three T. dimidiata subpopulations from the houses (D = 0.013-0.022) and the two villages (D = 0.0199). The amount of differentiation among houses (fixation index, F(ST)) was also very small, F(ST) = 0.025 among the houses and the two villages F(ST) = 0.019. These fixation indices give an average number of mating migrants per generation (Nm) of 9.7 (among houses) and 12 (among villages). Average heterozygosity (H) appears to be high, ranging from H = 0.299-0.325 among the houses and H = 0.273 among the villages. The low genetic distance and fixation indices, and high heterozygosity suggest that the subpopulations in the houses and in the adjacent villages are not reproductively isolated but are in fact, one large panmictic population. Therefore the geographic coverage necessary for effective control must include, at least, the area encompassing adjacent villages.

Animals↗
PubMed2004

Characterization of Wolbachia infections and interspecific crosses of Aedes (Stegomyia) polynesiensis and Ae. (Stegomyia) riversi (Diptera: Culicidae).

Prior studies have identified a complicated pattern of interspecific hybridization between members of the Aedes (Stegomyia) scutellaris (Walker) mosquito group, which includes medically important vectors of bancroftian filariasis and dengue. Here, we report that two members of the group, Aedes polynesiensis Marks and Aedes riversi Bohart & Ingram, are both infected with intracellular Wolbachia bacteria. Sequencing of the Wolbachia wsp gene demonstrates that the infections differ from each other and from Wolbachia infections previously reported in mosquitoes. Aedes polynesiensis is the first mosquito identified with a wMel Wolbachia type. Intraspecific crosses of infected and aposymbiotic lines generated via antibiotic treatment show that the Wolbachia infections in both species cause high levels of cytoplasmic incompatibility. Interspecific crosses show that the two species are reproductively isolated. However, repeating the interspecific crosses with aposymbiotic mosquito strains demonstrates that the Wolbachia infections play a role in preventing hybrid offspring. We discuss Wolbachia infections in relation to better defining the evolutionary relationships and causes of speciation within the group, understanding the basis for the observed east-to-west gradient in filarial refractoriness, and developing novel genetic control measures.

Aedes↗
PubMed2002

Morphological comparison among Drosophila lini and its two new sibling species (Diptera: Drosophilidae).

Morphological differences are investigated using several culture strains of three sibling species collected from Taiwan and Guangdong in China and Pyinoolwin and Yangon in Myanmar. Careful examination of male terminalia reveals distinguishable differences in the paramere and the aedeagal basal process among the three species. In addition, a number of quantitative characters are compared. Kruskal-Wallis tests with Bonferroni correction, which are carried out separately for each sex, detect significant differences in 15 characters, of which two are male-specific, among the three species. Canonical discriminant analysis using these characters reveals that the three species can be distinguished from each other with high confidence for both sexes. The results clearly show the presence of three good species, Drosophila (Sophophora) lini Bock & Wheeler, 1972 and its two new siblings. The new species are described as Drosophila (Sophophora) ohnishii sp. nov. from Pyinoolwin and Drosophila (Sophophora) ogumai sp. nov. from Yangon. The morphological differentiation among the three sibling species does not coincide with the degree of reproductive isolation (based on a previous study). The premating isolation pattern suggests two possibilities that premating isolation has been evolved or reinforced in sympatric populations between D. ohnishii and D. lini and between D. ohnishii and D. ogumai or that it has evolved in a very restricted local population of D. ohnishii, possibly by a few mutations.

Animals↗
PubMed2003

Occurrence of two types of Hynobius naevius in Northern Kyushu, Japan (Amphibia: Urodela).

A survey to examine genetic variation among Hynobius naevius from four localities of Fukuoka Pref., northern Kyushu, Japan, resulted in the detection of two, sympatric, genetic types (A and B) that are clearly different in the allelic frequencies of four loci (ACOH-A, ACOH-B, ADH-A, and SOD-A) in each locality. Morphological investigations between the two genetic types also proved that they are clearly discriminated; the type A is about 75 mm in SVL, lacks mottling pattern on bluish purple dorsum, and possesses relatively short vomerine teeth series, while the type B is about 60 mm in SVL, and has light mottling on reddish purple ground color. These results strongly suggest that reproductive isolation occurs between these two types, and that they could be regarded as separate species. Populations from Toyota-cho, western Honshu, and Yabe-machi, central Kyushu, both close to Fukuoka Pref., were very similar to the types A and B, respectively. From these results, we consider that two evolutionary lineages that first evolved allopatrically in western Honshu and southern Kyushu secondarily contacted and became sympatric in the region of northern Kyushu.

Analysis of Variance↗
PubMed2004

Molecular evidence of the existence of two sibling species within the echinothurioid echinoid Asthenosoma ijimai from Japanese waters.

The echinoid, Asthenosoma ijimai belonging to the order Echinothurioida from Japanese waters shows the geographical variation in morphological and ecological characters. The echinothurioid from Ryukyu Islands in southern Japan is cleary different from that of Sagami Bay and Suruga Bay in the middle part of Japan at non-molecular level. Their phylogenetic and taxonomic relationships were studied at the molecular level by allozyme analysis. The results demonstrated that the two echinothurioids from Ryukyu Islands and Sagami Bay do not share gene pools with each other, and they were fixed for different alleles at five genetic loci (Mdh, G6pd, Po, Alk-3 and Est-7) in a total of 23 enzyme genetic loci scored. This indicates no gene flow between the two echinothurioids, and is a molecular evidence for that they are reproductively isolated and genetically distinct species. The Nei's genetic distance (D=0.181) between the two were significantly higher than those between conspecific local populations, and comparable to those between closely related species in many other animals containing echinoderms. The present molecular data are well consistent with the non-molecular evidence from morphology, developmental biology and ecology. Putting these data together, we propose that the two echinothurioids should be classified as two sibling species of the genus Asthenosoma and would like to give the following scientific names: the echinothurioid species from Sagami Bay is Asthenosoma ijimai and that from Ryukyu Islands is A. ijimai R.

Animals↗
PubMed2004

Genetic structure of korean wild populations of the Medaka Oryzias latipes inferred from allozymic variation.

Previous allozymic studies have revealed that Korean wild populations of Oryzias latipes have differentiated regionally, and are composed of two distinct groups, the East Korean Population and the China-West Korean Population. Recently, mitochondrial DNA (mtDNA) sequencing and restriction fragment length polymorphism (RFLP) analyses have confirmed these two groups, and shown that the distribution ranges of the two groups overlap in western Korea. In order to describe the detailed distributions of the two groups and the gene flow between them, genotypes of 13 allozymic loci were determined in 444 specimens from 96 localities in Korea. The two major groups were supported by remarkable allele frequency differences at six diagnostic loci: ACP*, AMY*, CK-A*, LDH-A*, PGM* and TF*. Individuals with the typical "eastern" genotype were mainly distributed in eastern and southern areas. In contrast, fish with the "western" genotype were predominant in the western area, and were further divided into two subgroups (the Han River and Geum River Subpopulations) by unique alleles at the ADH* locus. In the western coast, two distinct (eastern and western) genotypes were distributed in a mosaic fashion. This distribution pattern was identical to those from mtDNA analyses. Although the distribution patterns of the alleles at three loci (GPI-A*, LDH-C* and SOD*) showed introgressive conditions between the two groups, each population was nearly fixed as either the eastern or western genotype at all six diagnostic loci despite the proximity among samples. Therefore, it is suggested that some reproductive isolation mechanisms exist between the two groups in natural habitats.

Animals↗
PubMed2004

Differences in the rDNA-bearing chromosome divide the Asian-Pacific and Atlantic species of Crassostrea (Bivalvia, Mollusca).

Karyotype and chromosomal location of the major ribosomal RNA genes (rDNA) were studied using fluorescence in situ hybridization (FISH) in five species of CRASSOSTREA: three Asian-Pacific species (C. gigas, C. plicatula, and C. ariakensis) and two Atlantic species (C. virginica and C. rhizophorae). FISH probes were made by PCR amplification of the intergenic transcribed spacer between the 18S and 5.8S rRNA genes, and labeled with digoxigenin-11-dUTP. All five species had a haploid number of 10 chromosomes. The Atlantic species had 1-2 submetacentric chromosomes, while the three Pacific species had none. FISH with metaphase chromosomes detected a single telomeric locus for rDNA in all five species without any variation. In all three Pacific species, rDNA was located on the long arm of Chromosome 10 (10q)--the smallest chromosome. In the two Atlantic species, rDNA was located on the short arm of Chromosome 2 (2p)--the second longest chromosome. A review of other studies reveals the same distribution of NOR sites (putative rDNA loci) in three other species: on 10q in C. sikamea and C. angulata from the Pacific Ocean and on 2p in C. gasar from the western Atlantic. All data support the conclusion that differences in size and shape of the rDNA-bearing chromosome represent a major divide between Asian-Pacific and Atlantic species of CRASSOSTREA: This finding suggests that chromosomal divergence can occur under seemingly conserved karyotypes and may play a role in reproductive isolation and speciation.

Animals↗
PubMed2005

Gamete compatibility and sperm competition affect paternity and hybridization between sympatric Asterias sea stars.

Gamete interactions may strongly influence speciation and hybridization in sympatric broadcast-spawning marine invertebrates. We examined the role of gamete compatibility in species integrity using cross-fertilization studies between sympatric Asterias sea stars from a secondary contact zone in the northwest Atlantic. In crosses between single males and single females, gametes of both species were compatible and produced viable, fertile hybrid offspring, but with considerable variation in the receptivity of eggs to heterospecific sperm. Differential compatibility of heterospecific gametes was detected in sperm competition studies in which we used a nuclear DNA marker to assign paternity to larval offspring. Several families showed conspecific sperm precedence in A. forbesi eggs, and one family showed competitive superiority of A. forbesi sperm fertilizing A. rubens eggs. Gametic interactions are an important component of prezygotic reproductive isolation in sympatric Asterias. The interaction between gametes of these closely related sea stars is consistent with the function of gamete recognition systems that are known to mediate fertilization success and speciation in other marine invertebrates.

Animals↗
PubMed2000

Molecular and behavioral analysis of sex-linked courtship song variation in a natural population of Drosophila melanogaster.

Genes controlling the "lovesong" in Drosophila are particularly interesting under a evolutionary point of view as they could be involved in the reproductive isolation between closely related species and, as a consequence, in the speciation process. We carried out a survey of sex-linked molecular and behavioral courtship song variation in 27 lines derived from a natural population of Drosophila melanogaster in Italy. We sequenced a 983 bp fragment of cacophony(cac), a calcium channel gene controlling aspects of the courtship song. The same region was also sequenced in a D. simulans strain. Only 5 non-coding sites were polymorphic among the D. melanogaster lines, and no amino acid substitutions were found between the two species. Statistical tests applied to the data did not reveal any significant deviations from a neutral model. Using the same lines we also carried out an analysis of three different song parameters which are known to be affected by the cac(S) song mutation: interpulse-interval (IPI), pulse amplitude (PA) and cycles per pulse (CPP). We found significant differences among the lines in IPI and PA, and for the latter a significant association with one of the polymorphic sites of cac.

Analysis of Variance↗
PubMed1999

Breeding structure of the sand fly Lutzomyia longipalpis (Lutz & Neiva) in Brazil.

Eleven populations of Lutzomyia longipalpis (Lutz & Neiva), the sand fly vector of Leishmania chagasi, from different areas of Brazil were analyzed for genetic variation at 16 enzyme loci. In this region, the prevalence of visceral leishmaniasis (VL) caused by L. chagasi is spotty and reproductive isolation among populations of Lu. longipalpis has been reported. It is thought that morphologically similar cryptic species with varying vectorial capacity may be responsible for the discontinuous distribution of VL. The aim was to study the genetic structure of populations within this region and to identify demes that may represent sibling species. Genotypic frequencies within populations were in close compliance to Hardy-Weinberg expectations, suggesting there are no sympatric species among these 11 populations. Levels of genetic distance between pairs of populations were very low (< 0.03), consistent with local populations within a single sand fly species. When genotypic frequency data for all populations were pooled, 9 of the 13 polymorphic loci deviated from Hardy-Weinberg expectations, indicating some degree of genetic substructuring. Estimates of effective migration rates (N(e)m) among all populations were low, 2.73, suggesting that gene flow is restricted among populations, which is probably the reason for the observed genetic substructuring.

Alleles↗
PubMed1999

The status of Clarkia australis (Onagraceae).

Clarkia australis and C. virgata grow on the western slope of the central Sierra Nevada of California. Clarkia australis was established to accommodate populations of C. virgata from south of the Tuolumne River that could not be successfully hybridized to populations north of the river. Although the species is maintained in the new Jepson Manual, its validity has been questioned because only two populations were originally tested, and they had no useful morphological traits that distinguished them from C. virgata. We report here the results of a large program of interpopulation hybridizations that show that C. australis is distinct and that its reproductive isolation from C. virgata is complete and absolute and reflects a compatibility block that apparently causes abortion of hybrid seeds in early development. Both species include populations north and south of the Tuolumne River and, in general, those of C. australis occupy higher elevations. Morphologically, the species are extremely similar though the mean values of several dimensions of the petals are different. However, significant variation among their populations has the consequence that, at present, the only certain way to assign particular populations to species is to test their compatibility with previously tested populations.

Journal Article↗
PubMed1999

STR polymorphisms in the population of the island of Hvar.

The aim of this study is to analyze short tandem repeat (STR) variation using data on 9 loci (D3S1358, VWA, FGA, THO1, TPOX, CSF1PO, D5S818, D13S317, D7S820) from the subpopulations of 6 villages on the island of Hvar, Croatia. The STR data help us to analyze the genetic structure of Hvar. The analysis of STR data in this study indicated genetic homogeneity among the village subpopulations on Hvar and the lack of the so-called east-west dichotomy, which had been indicated by some previous multidisciplinary anthropological studies. The observed value of GST (0.030) is most probably a consequence of high STR mutation rates, which produce a high level of within-group (village) diversity relative to total diversity of the population. The validity of STR markers in assessing genetic structure of small populations and especially in determining the relationships among closely related and reproductively isolated groups remains to be further evaluated.

Chi-Square Distribution↗
PubMed1998

The distribution and inversion polymorphism of chromosomally recognized taxa of the Anopheles gambiae complex in Mali, West Africa.

Data from polytene chromosome studies on the Anopheles gambiae complex in Mali were reviewed. The banding pattern was successfully scored in 17,705 specimens from 76 sampling sites representing the main ecological strata of the country. Two members of the complex, namely An. arabiensis and An. gambiae, were found widespread and frequently sympatric, with the latter prevalent in most localities. Population genetic analysis of the inversion polymorphisms indicated the existence of panmictic conditions for An. arabiensis only, whereas the parallel study of An. gambiae supported its splitting into at least three reproductive units, characterized by different 2R chromosome arrangements, designated Bamako, Mopti and Savanna. The chromosomal evidence was consistent with the hypothesis of complete reproductive isolation between Bamako and Mopti. Partial isolation between these two taxa and Savanna was suggested by the scoring of hypothetical hybrid 2R heterokaryotypes in various samples, but the actual hybrid origin of these specimens was not confirmed. Different patterns of geographical and seasonal distribution were shown as follows. An. arabiensis prevails in arid savannas (Sahel and Northern Sudan savanna) out of the flooded or irrigated zones; it is able to withstand the most arid conditions of Saharan localities and its breeding might extend throughout the dry season. An. gambiae Savanna and Bamako prevail in relatively humid savannas (Southern Sudan savanna) and their breeding generally occurs only during the rainy season. The Savanna taxon was almost absent in flooded or irrigated zones and in riverine localities; the Bamako taxon is distributed along the upper river Niger and its tributaries. An. gambiae Mopti extends its range in all ecological zones present in Mali including the Sahel and predesertic areas, showing high relative frequencies up to absolute dominance in flooded or irrigated areas; its breeding is highly successful also during the dry season. Rainfall at the sampling sites was found to correlate positively with the frequency of Savanna and negatively with the frequency of Mopti. The remarkable ecological flexibility of the latter was found associated with wide seasonal and geographical variations in its 2R inversion polymorphism bc/u. Higher frequencies of the bc arrangement were recorded both in the Southern localities during the dry season and in the Northern more arid localities during the rainy season. The absence or scarcity of An. arabiensis and An. gambiae Savanna in most flooded or irrigated zones suggests their competitive exclusion by An. gambiae Mopti.

Animals↗
PubMed2000

[Genetic structure of species community of macromycetes of the genus Leccinum Gray (Basidiomycetes, Boletaceae) of the right-bank Poles'ye].

The biochemical gene marking of the macromycete community of the genus Leccinum revealed nine reproductively isolated genetically differentiated forms instead of 2-5 forms traditionally recognized in Poles'ye. From 20 to 85% of the loci studied were found to have genetic distinctions and the degree of genetic variation did not always correlate with the morphological features of the forms identified. The variation of the locus number was found to be an important differentiating factor characteristic for this genus. In the group of L. scabrum s. I., every second locus was duplicated, whereas multiple isozymes were absent in L. aurantiacum s. I. The extremely high level of allozyme variation in macromycetes was found. The equilibrium between the expected and observed genotypes in the fruit body samples was established and discussed. It was the evidence of the fact that a panmictic model can be applied to the mushrooms of this genus, and that each fruit body is an individual organism.

Basidiomycota↗