Michele Cesari

Polymerase chain reaction amplification of the Bag320 satellite family reveals the ancestral library and past gene conversion events in Bacillus rossius (Insecta Phasmatodea).

Polymerase chain reaction amplifications of genomic DNA in 17 individuals of bisexual and parthenogenetic populations of three subspecies of Bacillus rossius (Insecta Phasmatodea) revealed that the species still harbours the whole variability of the ancestral Bag320 satellite family, since monomers of all non-hybrid Bacillus taxa plus private sequences occur in it. Bag320 monomers had not been rescued as a major satellite component in B. rossius, but possibly represent the remnant of a set of diverging sequences present in the Bacillus ancestor. Following the library hypothesis, these monomer variants have been differently amplified along the evolutionary pathways leading to present taxa in agreement with the mitochondrial phylogeny of the genus. The putative converted tracts observed are explained as the results of past gene conversion events.

Molecular taxonomy and phylogeny of the ‘living fossil’ lineages Triops and Lepidurus (Branchiopoda: Notostraca)

Mantovani B. Cesari M. & Scanabissi F. (2004). Molecular taxonomy and phylogeny of the ‘living fossil’ lineages Triops and Lepidurus (Branchiopoda: Notostraca). —Zoologica Scripta, 33, 367–374.

ANDRODIOECY INFERRED IN THE CLAM SHRIMP EULIMNADIA AGASSIZII (SPINICAUDATA: LIMNADIIDAE)

Abstract Androdioecy (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.

Mitochondrial and nuclear DNA variability in the living fossil Triops cancriformis (Bosc, 1801) (Crustacea, Branchiopoda, Notostraca).

The 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.

Production of intersexes and the evolution of androdioecy in the clam shrimp Eulimnadia texana (Crustacea, Branchiopoda, Spinicaudata)

Summary The production of low numbers of offspring that exhibit a mixture of male and female traits (termed “intersexes”) is commonly reported for crustaceans. The production of intersexes has been ascribed to both genetic and non-genetic (e.g., parasitic infections and environmental pollutants) causes. Herein we report on two observed types of intersexes in the clam shrimp Eulimnadia texana: (1) a “morphological” intersex, possessing secondary male characteristics (e.g., claspers) and an eggproducing gonad, and (2) a “gonadal” intersex, possessing primarily male traits (e.g., male secondary sexual characters and male gamete production) but also producing low levels of abortive female gametes. We propose that these intersexes are likely the products of low frequencies of crossing over between the sex determining chromosomes that result in the array of observed mixed sexual phenotypes. Additionally, we suggest that the low-level production of intersexes, combined with the ephemeral nature of the habitats occupied by these shrimp, may explain the preponderance of androdioecy (mixtures of males and hermaphrodites) found in these clam shrimp, and possibly branchiopods more generally.

Genetic variability in European Leptestheria dahalacensis (Ruppel, 1837) (Crustacea, Branchiopoda, Spinicaudata)

The 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.

Molecular taxonomy and phylogeny of Italian Lepidurus taxa (Branchiopoda: Notostraca)

Notostraca 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.

Chromosomes in sexual populations of Notostracan and Con- chostracan taxa (Crustacea, Branchiopoda)

Abstract Branchiopods 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.