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Reproduction and genetic variation in clam shrimps (Crustacea, Branchiopoda, Conchostraca)
No full textSamples of the three clam shrimp species. Eoleptestheria ticinensis and Leptestheria dahalacensis (Leptestheriidae) and Limnadia lenticularis were collected in north Italian rice paddies in Emilia and Lombardy. Sex-ratio analysis revealed that in the two species of Leptestheriidae, males are more frequent than females, whereas L. lenticularis has an all-female constitution. Allozyme analysis showed a low degree of genetic variation, the values of polymorphism parameters being very similar to those found for other Branchiopoda. In the Leptestheriidae it was generally found that genotypic frequencies conform to Hardy-Weinberg expectations, demonstrating a high outcrossing rate. No clear-cut relationship between the excess of males and cytological and genetic observations could be established, since neither sex chromosomes nor sex-linked genes were found. Nevertheless, male predominance could overcome the morphodynamic constraints that clam shrimps face during fertilization. The all-female constitution of the two populations of L. lenticularis and the hatching of unisexual progeny from virgin females suggest that they reproduce by obligate parthenogenesis; the almost complete lack of heterozygous genotypes at all the analyzed loci allows us to discard the previous hypothesis of automixis. Further analyses should be undertaken to fully clarify the sex-determination mechanisms operating in these clam shrimps, as was previously done in Eulimnadia texana
Molecular taxonomy and phylogeny of the 'living fossil' lineages Triops and Lepidurus (Branchiopoda: Notostraca)
No full textEuropean Triops cancriformis and Lepidurus apus were analysed for 12S and 16S mitochondrial genes and compared to North American and Japanese taxa. There are no cryptic species among European T. cancriformis populations, which are highly homogeneous in comparison to conspecific Japanese samples. T. cancriformis differs from congeneric taxa all over its range, which can be explained by its antiquity. In contrast, the parapatric subspecies L. apus apus and L. apus lubbocki are morphologically conserved and differ substantially at the mtDNA level. The genetic distance values between them are of the same order of magnitude as those observed between American Lepidurus species. Their subspecific status therefore requires further analysis. L. apus apus is more closely related to a L. arcticus sample from Iceland than to L. apus lubbocki. It is also related to a Canadian L. couesii population. Further analyses of populations from the whole range of L. arcticus and the European range of L. couesii are needed to understand the relationships among these notostracan taxa. When considering the two genera, it is clear that Lepidurus is a well supported monophyletic unit, while Triops is polyphyletic, embodying very divergent taxa
Chromosome analysis of Eoleptestheria ticinensis and Leptestheria dahalacensis (Branchiopoda, Spinicaudata)
No full textChromosome analysis of Italian populations of Spinicaudata, Eoleptestheria ticinensis and Leptestheria dahalacensis (Leptestheriidae), shows 2n = 10 chromosomes, like as the other Spinicaudata, Limnadia lenticularis (Limnadiidae). Some male meiotic metaphase I with 2 univalents probably suggest a male heterogamy as evidenced in Anostraca. Haploid chromosome number of Spinicaudata appears very similar with those of well investigated Notostraca genus and comparable with those of Anostraca and Cladocera ones
Molecular taxonomy and phylogeny of Italian Lepidurus taxa (Branchiopoda: Notostraca)
No full textNotostraca taxonomy is controversial, mainly owing to the high intraspecific variability of morphological characters; other complexity factors are represented by the consistent rate of reproductive variation. We undertook the molecular analyses of Italian Lepidurus taxa through the characterization of 12S, 16S and COI mitochondrial genes in new L. apus demes and in the L. couesii populations recently discovered in Southern Italy. For L. apus, the analysis of a wider data set (both in terms of molecular markers and of analysed populations) confirms the previously suggested specific rank of differentiation between its so far recognized subspecies, the Italian L. apus lubbocki and the European L. apus apus. The Italian L. couesii samples pertain to a well-defined taxonomic entity, strictly related to Canadian L. couesii. In 12S dendrograms, this taxon strongly diverges from the other North American Lepidurus species, but the relationships among nearctic taxa are unresolved. On the other hand, a high affinity between Italian/Canadian L. couesii and the circumpolar species L. arcticus is scored and a possible descent from a common ancestor is hypothesized. © 2009 Unione Zoologica Italiana
Mitochondrial and nuclear DNA variability in the living fossil Triops cancriformis (Bosc, 1801) (Crustacea, Branchiopoda, Notostraca)
No full textThe living fossil Triops cancriformis comprises bisexual (either gonochoric or hermaphroditic) and unisexual populations. Genetic surveys have recently revealed a general trend of low differentiation of 12S and 16S mitochondrial genes. We, therefore, surveyed further mitochondrial (COI gene and control region) and nuclear markers (dinucleotide microsatellites) to assess the genetic variability and to establish any relationship with the different reproductive modes found in European populations. The mitochondrial analyses confirmed the pattern of low variability. Hence, the low mitochondrial genetic variability appears as a common feature of the genus Triops. The microsatellite analysis found that Italian populations are monomorphic or exhibit little polymorphism, while other European samples display a higher degree of polymorphism and private alleles. Spanish, Austrian and Italian populations show patterns of Hardy-Weinberg disequilibrium that could be explained by the mode of reproduction, or by a higher frequency of null alleles in these populations. The low diversity and differentiation among Italian populations lead us to question the Monopolization Hypothesis. One microsatellite locus appears to be sex-linked, with heterozygotes detected only in males and hermaphrodites. © 2008 Nature Publishing Group All rights reserved
Characterization of dinucleotide microsatellite loci in the living fossil tadpole shrimp Triops cancriformis (Crustacea Branchiopoda Notostrace)
No full textFive dinucleotide markers were obtained from a microsatellite genomic library of the tadpole shrimp Triops cancriformis. The number of alleles at each locus was low (maximum three alleles) but all loci were polymorphic. The presence of null alleles could not be disregarded. Heterozygosity levels were indicative of self ing in the studied populations whose real sexuality will be further tested using these markers
Primo ritrovamento di Lepidurus couesii Packard, 1875 in Italia
No full textIl notostraco nordamericano Lepidurus couesii è stato ritrovato per la prima volta in Italia. I dettagli morfologici sono stati forniti anche al SEM
Genetic variability in European Leptestheria dahalacensis (Rüppel, 1837) (Crustacea, Branchiopoda, Spinicaudata)
No full textThe genetic variability of the gonochoric Leptestheria dahalacensis (Rüppel, 1837) was studied through the analysis of mitochondrial and nuclear (microsatellite loci) markers in eight Italian and two Central European populations. Mitochondrial data exhibited a low variability, as only six mitotypes were scored: five in Italy and one for both Central European samples, with a very low number of substitutions. All analysed microsatellite loci were variable, with 3-5 alleles per locus and 1-4 alleles per population. All populations were at the Hardy-Weinberg equilibrium, with the exceptions of two samples for locus ldAC-16, due to heterozygote excess, and of four populations for locus ldAC-11, probably linked to the presence of null alleles. A substantial population structuring was found between Central European and Italian samples for both utilized markers. This observation may be explained by isolation by distance and/or recent isolation events. On the other hand, the absence of a clear inter-pond variability in Italian sample comparisons may be ascribed to high dispersal ability in the short range. © 2007 Springer Science+Business Media B.V
Androdioecy inferred in the clam shrimp Eulimnadia agassizii (Spinicaudata: Limnadiidae)
No full textAndrodioecy (mixtures of males and hermaphrodites) is a rare mating system in both the plant and animal kingdoms. Androdioecy has been described in three branchiopod species, and is best known from the clam shrimp Eulimnadia texana Packard. Herein we describe sex ratio, genetic and histological evidence from the clam shrimp Eulimnadia agassizii Packard that suggest androdioecy is also found in this species. The E. agassizii population sampled had all-females, and when these females were isolated and allowed to produce eggs, those eggs yielded 100% female offspring in 15 out of 15 cases. Additionally, the originally isolated females proved to be completely homozygous at each of the six allozyme loci scored. The offspring from these isolated females also proved to be homozygous for the same alleles as their parent. Tissue sectioning of the gonad found that the "females" actually produced testicular tissue in the posterior portion of the gonad. Taken together, these data are entirely consistent with those of the androdioecious E. texana, and thus indicate that E. agassizii is also an androdioecious species, bringing the total number of branchiopod species with this form of reproduction to four
Chromosomes in sexual populations of notostracan and con-chostracan taxa (crustacea, branchiopoda)
No full textBranchiopods reproductive mechanisms range from gonochorism to unisexuality, passing through an-drodioecy. In order to contribute to still lacking or controversial basic knowledges, we analyzed the karyotype of the main Italian taxa: the Notostracan living fossils Triops cancriformis (parthenogenetic) and Lepidurus apus lubbocki (bisexual), and the Conchostracan Eoleptestheria ticinensis (bisexual). Also one male obtained from a supposedly hermaphroditic Austrian population of T. cancriformis was checked. In T. cancriformis a diploid number of 12 chromosomes is observed in both females and male; this is in line with previous results on other Italian populations, but contrasts with observations on European samples. The richness of normal meiotic pictures indicates that the male specimen is able to produce sperms. L. apus lubbocki shows a diploid number of 10 chromosomes; in male specimens the mispairings during meiosis I could explain the haploid number of 6 chromosomes obtained from diakinetic plates in Palestinian samples of the same subspecies found in literature. Irregular meiotic divisions also highlight the ultrastructurally observed abortive spermatogenesis. Finally, in the presently analyzed population of E. ticinensis, the adult females show 10 chromosomes as diploid number, while males present 10 or 11 elements; in the nauplii, chromosome numbers range from 8 to 12, differing among unrelated individuals, between nauplii produced by the same female and even within the same nauplius. B elements are taken into account. © 2005 Taylor & Francis Group, LLC
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