Mario Benazzi

Ginogenesi in tricladi di acqua dolce

ZusammenfassungBei der Rasse G von Dugesia benazzii von Sardinien hat das Spermatozoon nur die Funktion der Entwicklungserregung, da die Amphimixis nicht erfolgt und der männliche Vorkern wie ein Eichtungskörper eliminiert wird.Das Ei entwickelt sich allein mit der weiblichen Chromosomengarnitur (Gynogenese), und das erklärt die vom Autor an dieser Planarie festgestellte mütterliche Vererbung.Auch bei den italienischen Rassen von Polycelis rigra erfolgt die Entwicklung durch Gynogenese nach den genetischen Untersuchungen des Autors und den cytologischen von N. G. Lepori.

A robertsonian translocation in the fresh-water triclad Dugesia lugubris: karyometric analysis and evolutionary inferences

Biotype E of Dugesia lugubris has a haploid complement of 4, comprising 3 acrocentrics of different length and a short chromosome; biotype F has a haploid complement of 3, with a long metacentric, an acrocentric and a short chromosome. A karyometrical analysis has shown that the metacentric chromosome of biotype F derived from a centric fusion between the acrocentrics 1 and 3 of biotype E. — The evolutionary meaning of this centric fusion is discussed.

Feulgen-DNA Content and C-Banding of Robertsonian Transformed Karyotypes in Dugesia Lugubris

SUMMARYIn the planarian species, Dugesia lugubris, two biotypes are found: E (2n = 8, n = 4) and F (2n = 6, n = 3); on the basis of karyometric studies it has been hypothesized that the second was derived from the first through a Robert-sonian mechanism of centric fusion. The quantitative cytochemical data reported here confirm the hypothesis of karyotype evolution, since there are no significant differences between the DNA content of the nucleus in the two biotypes. The regenerative blastemas of both biotypes contain a number of cellular populations with a variable Feulgen-DNA content; these correspond to successive doublings of the 2C diploid content. In addition, metaphase plates with multistranded chromosomes have been found. A difference between the chromosome C-banding in the two biotypes has also been observed.

Considerations on the neoblasts of planarians on the basis of certain karyological evidence

The problem of the sexual differentiation of the neoblasts of planarians is approached on the basis of karyological evidence assembled by the author and by his collaborators. In the polyploid and pseudogamic biotypes of Dugesia benazzii, D. lugubris and Polycelis nigra, the transformation of the neoblasts into oogonia or spermatogonia is accompanied by variations in the chromosome set. These variations may be considered to be dependent upon the gradient of sexuality — that is, of the territorial influences that determine the evolution in a female or a male direction. Significant evidence is also inferred from the chromosome cycle of hybrids between amphigonic diploid biotypes and polyploid biotypes. A new direction of research, based on the comparison between anterior and posterior regenerated segments of experimental polyploids with variable chromosome sets aims at establishing possible regional differences in the set of the neoblasts.

Feulgen-DNA amounts and karyotype lengths of three planarian species of the genusDugesia

Genome sizes of the planariansD. lugubris (2n=8),D. polychroa (2n=8) andD. benazzii (2n=16) were evaluated on metaphase plates by measuring both the Feulgen-DNA contents and the karyotype lengths. In the three species, genome sizes are significantly different; this finding rules out the possibility of a karyotype evolution through simple chromosome rearrangements betweenD. lugubris andD. polychroa. A different Feulgen-DNA content per unit length of karyotype in the three species studied was also found, which suggests that DNA could be differently packed along metaphase chromosomes.

Sulla ibridazione fra Triturus helveticus e TV. vulgaris

Summary A female of Triturus helveticus mated to males of T. vulgaris meridionnlis laid during two years (1955 and 1956) 301 eggs, 34 of which fertilized. These last ones developed normally and produced vigorous larvae, which grew up to sexual maturity. The phenotype of the Ft hybrids is intermediate between the parental species; the sex-ratio is normal. Spermatogenesis in hybrid males shows strong abnormalities, e. g.: failure of true first metaphase stages and great abundance of meta-anaphases; number of bivalents always lower than normal (12), some chromosomes remaining as univalents; chiasma-frequency of the bivalents very low. However, sperms can be produced, although in scarcer number as compared with the pure species. Fertility of the Ft hybrids seems reduced, but further researches are needed.

Occurrence of a sexual population of Dugesia (Girardia) tigrina, a freshwater planarian native to America, in a lake of southern Italy

Abstract Dugesia (Girardia) tigrina, a freshwater planarian native to America and able to reproduce either sexually or by fission, has been casually introduced into Europe and various other areas of the world. In most cases, the immigrant specimens are fissiparous and, exceptionally, sexual. One sexual population, collected from the Lake of Monticchio in Southern Italy, is here described together with biogeographycal and karyological data.

Dugesia brigantii n.sp., a freshwater planarian found in an Italian cave

Abstract A new freshwater planarian from Liguria, Italy, belonging to the Dugesia gonocephala group, is described. The species is characterized by a parenchymatic adenodactyl laterally fused with the penis papilla. The taxonomic position of this new species within the Dugesia gonocephala group is discussed.

Considerazioni sulla cvoluzione cromosomica negli animali

Summary The A. analyzed the main aspects of chromosomal evolution in animals, trying to combine them with the general problems of preformationism and epigenesis, Having considered the fundamental modalities of the karyotype transformations and discussed the evolutional significance of polyploidy, the A. emphesized the evolution of sex-chromosome mechanisms. Although recognizing that some aspects of karyotype transformations might he interpreted as attributable to orthogenesis or genetic predetermination, the A. believes, however, that chromosome evolution is basically cpigcnctic.

New investigations on the reproductive biology of Planaria torva (Müller)

A new study on the reproductive biology ofPlanaria torva has evidenced a peculiar mechanism of cocoon hatching, which differs from that of other freshwater planarians. In fact, in this species, cocoon fragmentation is not complete so that some juveniles may remain in the cocoon. The fertility of iteroparousP. torva is discussed.RiassuntoIn unaNota del 1994 Benazzi di-mostro anzitutto chePlanaria torva appartiene alle specie che si riproducono ripetutamente, cosiddetteiteroparous. Partendo da una coppia ottenuta mediante divisione trasversale di un singolo individuo, egli ot-tenne un alto numéro di bozzoli, 1a maggioranza dei quali, tuttavia, si rivelò sterile ed i rimanenti con un basso numéro di nati (da 1 a 2). Usufruendo di 15 esemplari rimasti dalla précédente coltura, abbiamo ripreso 1e ricerche sulla biologia riproduttiva di questa specie, evidenziando un peculiare meccanismo di apertura del bozzolo: esso infatti non si frammenta completamente, come awiene di norma nelle planarie d’acqua dolce, per cui alcuni nati possono rimanervi dentro. Le nuove ricerche hanno permesso di stabilire la effettiva fertilità della specie.