Bruno Battaglia

Krill evolution and the Antarctic ocean currents : Evidence of vicariant speciation as inferred by molecular data

The phylogenetic relationships of the Antarctic krill Euphausia superba, the key species in the Antarctic food web, and other Antarctic and sub-Antarctic cuphausiids have been investigated using the 16S ribosomal mitochondrial gene. The phylogenetic reconstructions indicated that the Antarctic species form a monophyletic clade separated by the non-Antarctic species. The results revealed a large genetic divergence between the Antarctic (E. superba and E. crystallorophias) and sub-Antarctic species (E. vallentini). The time of separation between these species, estimated from the molecular data, is around 20 million years ago, which is comparable with the geological time of the formation of a circum-Antarctic water circulation and the Antarctic Polar Frontal Zone. The euphausiid molecular phylogeny therefore represents evidence for vicariant speciation.

Glucosephosphate isomerase and fitness : effects of temperature on genotype dependent mortality and enzyme activity in two species of the genus Gammarus (Crustacea : Amphipoda)

KRIMBAS, C. B. 1964a. The genetics ofD. subobscura populations. I. Inversion polymorphism in populations of Southern Greece. Evolution 18:541-552. ---. I964b. The genetics of D. subobscura populations. II. Inversion polymorphism in a population from Holland. Z. Vererbungsi. 95:125-128. ---. 1967. The genetics of D. subobscura populations. III. Inversion polymorphism and climatic factors. Mol. Gen. Genetics 99:133-150. KRIMBAS, C. B., AND M. LoUKAS. 1980. The inversion polymorphism ofD. subobscura. Evol. BioI. 12:163234. LATORRE, A., A. MOYA, AND F. J. AYALA. 1986. Evolution of mitochrondrial DNA in D. subobscura. Proc. Natl. Acad. Sci. USA 83:8649-8653. MALOGOLOVKIN-COHEN, CH., AND D. SPERLICH. 1981. The effect of isolation and marginality on the inversion polymorphism of D. subobscura in Israel. Rev. Bras. Genet. 2:213-230. MESTRES, F., G. PEGUEROLES, A. PREvOSTI, AND L. SERRA. 1980. Colonization of America by D. subobscura: Lethal genes and the problem of the 0, inversion. Evolution 44: 1823-1836. PINSKER, W., AND I. BOHM. 1989. Allozyme divergence between different gene arrangements in D. subobscura. J. Evol. BioI. 2:353-363. PREVOSTI, A., M. P. GARCiA, L. SERRA, M. AGUADE, G. RIBo, AND E. SAGARRA. 1983. Association between allelic isozyme alleles and chromosomal arrangements in European populations and Chilean colonizers of Drosophila subobscura. Isozymes 10: 171-191. PREVOSTI, A., G. RIBO, L. SERRA, M. AGUADE, J. BALANA, M. MONCLUS, AND F. MESTRES. 1988. Colonization ofAmerica by Drosophila subobscura: Experiment in natural populations that supports the adaptive role of chromosomal-inversion polymorphism. Proc. Natl. Acad. Sci. USA 85:5597-5600. PREVOSTI, A., L. SERRA, M. AGUADE, G. RIBO, F. MESTRES, J. BALANA, AND M. MONCLUS. 1989. Colonization and establishment of the Palearctic

Studies on differential fitness of PGI genotypes with regard to temperature in Gammarus insensibilis (Crustacea: Amphipoda)

This paper deals with an experimental study of survival, combined with estimates of biochemical activity, of different genotypes at the PGI (phosphoglucose isomerase) locus in Gammarus insensibilis, in relation to temperature. Samples were collected in the lagoon of Venice during 1987. No mortality occurred at 10°C whereas at 27°C, where mortality reached the value of 50%, heterozygotes exhibited significantly higher survival than homozygotes. Experiments conducted in order to evaluate the PGI biochemical activity of homo- and heterozygote genotypes at three different temperatures (4°, 20° and 37°C) showed in all genotypes an increased activity from 4° to 20°C and a fall of activity from 20° to 37°C. Heterozygotes exhibited higher activity at all temperatures tested. The difference between homo- and heterozygotes became more obvious at 37°C. Our results suggest that in G. insensibilis the PGI locus, as already shown in other organisms, may be subject to selection and that the heterozygous genotypes possess superior fitness. The biochemical bases of the observed differences between genotypes are briefly discussed.

Datibiologici rtguardanti ľArtemia delle saline italiane

Biological data (chromosomic number, repetitive DNA, mode of reproduction, genetic barrier, parameters of productivity, biogeography) of six ItalianArtemia populations have been presented. The data have been discussed in order to allow comparisons with foreign strains that may be introduced.Artemiae living outside saltworks have not been considered.RiassuntoIn questa Nota vengono riferiti per la prima volta i dati biologici (numero cromosomico, DNA ripetitivo, modo di riproduzione, barriera genetica, parametri legati alia produttività) di sei popolazioni diArtemia che vivono nelle saline italiane (di cui si danno anche i dati topografici) allo scopo di permettere confronti con altro materiale estraneo che possa essere introdotto. Non vengono considerate le artemie viventi fuori dalle saline.In questa Nota vengono riferiti per la prima volta i dati biologici (numero cromosomico, DNA ripetitivo, modo di riproduzione, barriera genetica, parametri legati alia produttivita) di sei popolazioni diArtemia che vivono nelle saline italiane (di cui si danno anche i dati topografici) allo scopo di permettere confronti con altro materiale estraneo che possa essere introdotto. Non vengono considerate le artemie viventi fuori dalle saline.

Ricerche sulla determinazione del sesso nel Copepode Tisbe gracilis (T. Scott)

Summary In the Copepod Tisbe gracilis sex-ratio is highly variable in the different families. The results of experiments of inbreeding, outbreeding, selection towards increase of males and towards increase of females, arc reported in the present paper. Inbreeding leads to an increase of males, outbreeding to an increase of females. Selection, when carried out under inbreeding, is effective only in the direction towards males. Some preliminary results show that selection, when carried out without inbreeding, is effective in bolli directions. Crosses between inbred lines previously selected towards increase of males for some generations are followed by an increase in the number of females, though not so high as that observed in the experiments of outbreeding. The above results suggest that selection has operated upon a system of polygenes controlling sexuality. In Tisbe gracilis, beside the action of specific multiple factors for maleness and femaleness, also the factor « degree of heterozygosity » plays an...

A study of enzyme polymorphism in the Antarctic amphipod Paramoera walkeri Stebbing

SummaryStudies concerning the evaluation of the genetic structure and the mechanisms of genetic adapation to the Antarctic environment were carried out on two population samples (A and B) of the amphipod Paramoera walkeri Stebbing collected in two different areas of the Terranova Bay during the Italian Antarctic Expedition 1987/1988. The analyses of the level of genetic variability were conducted on starch gel. The electrophoretic results on the twenty two loci examined reveal a very low amount of genetic polymorphism in both populations with an average observed heterozygosity of 0.6% in population A and 0.7% in population B. The two populations can be considered part of a single breeding unit on the basis of the Student test for paired observations since the differences in single-locus heterozygosity for seven polymorphic loci are not significant (P>0.70). A possible explanation of the observed low genetic polymorphism is discussed in terms of genetic adaptation, as suggested by some results obtained in studies on enzyme activity carried out at the level of the PGI locus.

Environmental Factors, Genetic Differentiation, and Adaptive Strategies in Marine Animals

Recent advances in oceanographic research have revealed an impressive spatial and temporal heterogeneity in a number of biotic and abiotic features at different scales. However, the possibility of bringing physical and biological observations in the marine realm into harmony is often precluded by the inadequacy of methods for a correct determination of marine species, particularly at the level of secondary producers. Laboratory and field investigations show that many taxonomic entities, previously considered as “good” species, are instead clusters of reproductively isolated sibling species, or species in statu nascendi among which gene-flow may be reduced. Certain physical conditions play an active role in creating barriers to gene-flow. Populations of the same species from different geographic and/or ecological origin may exhibit genetic differentiation affecting a broad spectrum of characters. Some of these inherited differences are adaptive and maintained by natural selection. Similar genetic changes may be induced also by the impact of man on the environment. The relevance of both long term and short term effects on recruitment is briefly discussed.

Polimorfismi enzimatici in copepodi del genere Acartia delta laguna di Venezia

In the framework of a study on the relationships between the ecological features of estuarine environments, the population dynamics and the genetic structure of the species which inhabit them, the populations of the following two planctonic Copepods from the lagoon of Venice were studied:Acartia clausi Giesbrecht andAcartia margalefi Alcaraz. Twelve isozymes (16 loci) of the first species and nine (12 loci) of the second were analyzed, by means of electroforetic methods, in samples of the inner and outer lagoon and from the adjacent sea. The mean genetic variability appears very similar in the two species;A. clausi shows a value of observed heterozigosity between 0,07 and 0,08,A. margalefi between 0,07 and 0,09. The data obtained suggest forA. clausi the condition typical for a single large population, whereasA. margalefi appears splitted in slightly-diversified, relatively isolated, subpopulations. The possible causes of such diversification are briefly discussed.RiassuntoNello studio dellie relazioni intercorrenti tra le caratteristiche ecologiche degli ambienti estuarini, la struttura genetica e la dinamica di popolazioni delle specie che li abitano, sono state prese in esame due specie di Copepodi planctonici presenti nella laguna di Venezia:Acartia clausi Giesbrecht eAcartia margalefi Alcaraz. Con tecniche elettroforetiche sono stati analizzati 12 sistemi enzimatici (16 loci) délia prima e 9 (12 loci) délia seconda in alcuni campioni provenienti da diverse zone della laguna e del mare prospiciente. La variabilità genetica media stimata è molto simile nelle due specie:A. clausi mostra un valore di eterozigosi media compreso tra 0,07 e 0,08 a seconda del campione. InA. margalefi le variazioni risultano comprese tra 0,07 e 0,09. I dati ottenuti suggeriscono, perA. clausi, l’esistenza di un’unica popolazione che occupa un vasto areale, mentreA. margalefi si presenta frazionata in subpopolazioni diversiricate e relativamente isolate tra di loro. Le possibili cause di tale diversificazione vengono brevemente discusse.

Polimorfismo e superiorità degli eterozigoti nel copepode Tisbe reticulata

Summary The results of various crosses have shown that the colour patterns of the Copepod Tisbe reticulata living in the Lagoon of Venice is due to a series of at least three allelomorphs at the same locus, two of which dominant over a common recessive. The Same two allelomorphs do not exhibit dominance when occurring together; consequently this heterozygote is phenotypically detectable. There is some evidence that, under laboratory conditions, this heterozygote is more viable than both the respective homozygotes. Balanced polimorphism in Tisbe seems to play a role, together with other mechanisms described in previous papers on the subject, in the maintenance of genetical variability in this species.

Processes of Differentiation Between Mediterranean Populations of the Super-Species Tisbe clodiensis Battaglia and Fava (1968) (Copepoda)

Evolutionary research deals mainly with the mechanisms that promote the formation of new species. This is not only because speciation is viewed as the central event of the whole evolutionary process, but also because it is the step which, under certain conditions, is more amenable to experiment.