E. De Matthaeis

Bottleneck effects and the depression of genetic variability in hatchery stocks of Penaeus japonicus (Crustacea, Decapoda)

Aquaculture of Penaeus japonicus is developing in Italy at a production level. Genetic analysis of the founder stock and five subsequent hatchery generations revealed a constant reduction in levels of allozyme polymorphism. Average heterozygosity decreased from 0.102 to 0.039. The magnitude of the reduction in heterozygosity was much higher than expected from the numbers of breeders placed into spawning tanks at each reproductive cycle. We estimated, under the assumption of neutrality, that the effective number of parents contributing to each broodstock might have been as low as four, although the number of shrimp pairs held in spawning tanks varied from 50 to 300 after an initial bottleneck occurred in the first generation. This discrepancy may be explained as the combined effect of some common farming practices and it points out the importance of a careful check of the number of spawners actually contributing to each reproductive cycle.

Speciation, genetic divergence and palaeogeography in the hormogastridae

Abstract The genus Hormogaster includes a few species of earthworms, whose disjunct areas of distribution are of great interest. Three of them— H. redii , H. pretiosa and H. samnitica —occur in the region of the old granitic shield of Western Europe, and their distribution seems related to some geological events which can be dated with confidence. Sardinian H. pretiosa has a morphology only slightly different from the population found in Northeastern Catalonia and both differ to some extent from that of Roussillon (southwest France). The samples of H. redii are more uniform as also are those of H. samnitica . The electrophoretic analysis of the gene-enzyme systems reveals a wide molecular divergence between the Sardinian and both the Pyrenean populations of H. pretiosa , and an unsuspected similar divergence between the latter populations (only 60 km apart): such values suggest splitting of the morphospecies into three sibling species. The more widespread H. redii shows a lesser variability between its populations, even those separated by the sea. The genetic divergence between the populations of Hormogaster is tentatively correlated to geological events. The genetic divergence of the genus Xana from Hormogaster has also been studied.

GENETIC VARIABILITY AND DIVERGENCE IN CAVE POPULATIONS OF TROGLOPHILUS CAVICOLA AND T. ANDREINII (ORTHOPTERA, RHAPHIDOPHORIDAE)

This paper reports initial data on genetic variability and genetic divergence in five populations of two cave dwelling orthopterans, genus Troglophilus. Most of the present literature concerning electrophoretic variation of cavernicoles reports low levels of genetic variability, e.g., cave populations of fishes (Avise and Selander, 1972), millipedes (Laing et al., 1976a), leiodid beetles (Laing et al., 1976b) and spiders (Johnston and Carmody, 1977). However several recent reports (Sbordoni et al., 1976a, 1978, 1979, 1980a, 1980b; Giuseffi et al., 1978; Dickson et al., 1979; Sbordoni, 1980) and additional unpublished data from our own genetical analyses on different cavernicolous animals, indicate that troglophilic and troglobitic populations of aquatic and terrestrial invertebrates subjected to long term cave isolation may display levels of genetic variability comparable to, or even higher than, the levels observed in non-cave invertebrates (Powell, 1975; Selander, 1976). As far as cave crickets (Rhaphidophoridae) are concerned, Cockley et al. (1977) report low variability in the camelback cave cricket Ceuthophilus gracilipes from Pennsylvania, with heterozygosity values ranging, in different populations, from 0.020 to 0.033. In contrast to these results our preliminary data on Dolichopoda geniculata (Cobolli Sbordoni et al., 1974; Sbordoni et al., 1976b) and a further extensive study of 23 populations belonging to five species of Dolichopoda from Central Italy indicate a fairly high degree of variability, with levels of heterozygosity ranging from 0.113 to 0.280 (Sbordoni et al., unpubl.). Mediterranean Troglophilus cave crickets are similar to American Ceuthophilus. Both are Rhaphidophoridae and even if not closely related (Hubbell and Norton, 1978), occupy parallel niches in the two continents, most of the species being adapted to the twilight zones of caves, feeding on living arthropods, guano and chlorophyllan plants, sometimes outside caves (Remy, 1931; Vandel, 1964). The range of the genus Troglophilus extends from Anatolia to Lombardy including Greece, Yugoslavia and Austria. In Italy this genus shows a disjunct distribution: two species, T. cavicola (Kollar) and T. neglectus Krauss, are limited to limestone areas along the foothills of the Alps in northern Italy, from Friuli west to pre-alpine Lombardy, namely the Lake Como region, where marginal parthenogenetic populations of T. cavicola occur (Capra, 1951; Baccetti, 1961). A third species, T. andreinii Capra, is present in Apulia where two subspecies have been identified: T. andreinii andreinii, which is widespread in caves of northwestern Apulia, and T. andreinii hydruntinus La Greca, confined to the southern edge of the Salentine Peninsula (Baccetti and Capra, 1969). We investigated the patterns of genetic variability in five Troglophilus populations, two belonging to T. cavicola from northern Italy, and three belonging to T. andreinii from Apulia. We attempted to evaluate 1) levels of heterozygosity in Troglophilus to compare them with both Ceuthophilus and Dolichopoda and 2) the degree of genetic divergence between populations and species. The populations

Variation of genetic and behavioural traits in the sandhopper Talitrus saltator (Crustacea Amphipoda) along a dynamic sand beach

In an attempt to unravel the possible relationships among coastal stability, genetic variability and orientation behaviour in the sandhopper Talitrus saltator, we have screened four subpopulations of this species. Sandhoppers along 3 km of a dynamic sand beach were studied for orientation performance (i.e. adherence to the seaward theoretical escape direction (TED)) and sequence variation for a fragment of the mitochondrial (mt) gene encoding for the cytochrome oxidase subunit I (COI). The sampling sites differed in the stability of the shoreline (from severely eroded to accreting). Analysis of molecular variance (AMOVA) revealed significant subdivisions among the four locations. The subpopulation sampled at the most eroded point showed no haplotype diversity and had the highest scatter in orientation. Genetic diversity increased with decreasing erosion. Orientation performances were best where the beach is in dynamic equilibrium, and were progressively more scattered at the accreting points. Multiple linear regression analyses demonstrated that the variables and factors that affected orientation significantly were daytime, global solar radiation, sex of individuals and haplotype diversity. Environmental factors are likely to influence sandhopper behaviour on a short and medium time scale (i.e. from single individual life span to a few generations). The data also suggest that temporal stability of the shoreline has a positive effect on the genetic variability of the resident sandhopper populations.

Genetic variability and divergence between populations and species of Nesticus cave spiders

Genetic variability and divergence at 21 enzyme loci were studied in and between Italian populations of the cave spiders Nesticus eremita (13 populations), N. menozzii and N. sbordonii (one population each). The three species differ with respect to the degree of specialization to cave life, dispersion ability, isolation of populations, abundancy, extent of the distribution area, and range from the troglophilic and widespread N. eremita to the troglobitic N. sbordonii, endemic to a single cave in the Central Appennines.Heterozygosity ranges from 0.05 to 0.15 in N. eremita populations and appears to be largely controlled by the occurrence and the extent of gene flow among populations. The relatively low polymorphism levels of N. menozzii (H=0.081) and N. sbordonii (H=0.106) are also associated with reduced gene flow and small population sizes.Genetic distances between N. eremita populations vary considerably and are strictly related to the geographical distances involved, again indicating a major role of gene flow in determining the patterns of genetic differentiation between populations. This view is strongly supported by the results of a principal component analysis applied to the gene-frequency data. Estimates of genetic divergence between species suggest that the major cladogenetic events leading to complete separation of these three Nesticus species occurred in the Middle-late Pliocene.

Genetic variability and divergence between cave dwelling populations of Typhlocirolana from majorca and sicily

The genus Typhlocirolana includes six species discontinuously distributed in underground freshwater systems throughout southern Mediterranean coasts. The recent discovery of a Sicilian population of Typhlocirolana morphologically close to T. moraguesi from the Balearic Islands raised two issues: the taxonomic status of the Sicilian population and the evolutionary history leading to the present distribution of Typhlocirolana species which are thought to descend from a Cirolana-like marine ancestor. Electrophoretic analysis of eighteen gene loci encoding for enzymes and other proteins revealed a consistently high value of genetic distance (D=0.815) between the Sicilian sample and the two Majorcan population samples, strongly suggesting their status as separate species. Both genetic distance data and the low levels of heterozygosity detected in all samples suggest a relatively recent age for the Typhlocirolana species so far examined. Results from this study support the hypothesis by Stock according to which Typhlocirolana, as well as other ‘thalassoid’ hypogean Crustaceans, colonized ground-waters in connection with the sedimentary cycles of the Mediterranean coastal lines during the Upper Miocene or Lower Pliocene.

Biochemical systematics and evolutionary relationships in the Trichoniscus pusillus complex (Crustacea, Isopoda, Oniscidea)

In order to clarify taxonomic and phylogenetic relationships among Trichoniscus pusillus (Isopoda, Oniscidea) populations, allozyme variation was studied by means of starch gel electrophoresis. The genetic structure of several populations belonging to different subspecies (diploid bisexual, triploid parthenogenetic; epigean, troglophilic and troglobitic) was assessed by investigating 10 enzymatic systems corresponding to 15 putative loci. F-statistics and clustering analysis indicated a high degree of genetic differentiation, corresponding to low levels of gene flow among populations, both epigean and hypogean, still considered to be conspecific. Estimates of divergence times calculated from genetic distance data suggest that the pattern of differentiation and the colonization of cave environments may be related to the palaeoclimatic change of the Messinian and Plio-Pleistocene glaciations.

Genotoxicity biomarkers in the amphipod Gammarus elvirae exposed in vivo to mercury and lead, and basal levels of DNA damage in two cell types

ABSTRACT The present work deals with the application of genotoxicity biomarkers by means of the Comet assay in haemocytes and spermatozoa of the crustacean Gammarus elvirae exposed in vivo to heavy metals. Furthermore, a basal levels (BLs) study of DNA damage in the two cell types considered for two different gammarids species, G. elvirae and Echinogammarus veneris, was carried out. It is important to identify factors that influence the outcome of the assay in order to obtain reliable and reproducible results usable for risk assessment purposes. Our results highlight that the Italian legal limits for Hg and Pb, respectively, 0.5 and 50 µg/L, are inadequate for establishing safety thresholds in the aquatic environment. Furthermore, the freshwater invertebrate G. elvirae, used for the first time to measure the effect of genotoxicants, is a good candidate for evaluating the genotoxicity damage induced by heavy metals. Our results concerning spermatozoa show excessively variable responses and high BLs.

The name of a model species: the case of Orchestia cavimana (Crustacea: Amhipoda: Talitridae)

Abstract The species commonly known as Orchestia cavimana belonging to the Talitridae family (Amphipoda) has been used as crustacean model species. Here, we point out that this talitrid amphipod species is related to species in the genus Orchestia but now falls under what is described as Cryptorchestia garbinii, which is a different species from the nominal species Cryptorchestia cavimana endemic to the Island of Cyprus. It is therefore important that future basic research and applied studies involving this model organism refer to it as C. garbinii. Its old assignment O. cavimana, or even C. cavimana, as still reported in the National Center for Biotechnology Information (NCBI) GenBank and in recent papers, may lead to confusion.

Genetic Divergence in Populations of Dinocras Cephalotes (Curtis, 1827) from Three Different Catchments in Central Italy (Plecoptera, Perlidae)

We studied the genetic structure of Dinocras cephalotes (Curtis, 1827) in Central Italy, by means of starch-gel electrophoresis. Eleven populations from three different rivers (Aniene, Nera, Velino) were analysed. 21 enzymes were screened, yelding data for 27 presumptive loci. Genetic interpopulation distances (D; Nei, 1978) were relatively low, ranging from D=0.000 to D=0.052. These results show little differentiation among the populations and agree to some extent with the data coming from other genetic studies of Plecoptera. Nevertheless genetic distances among some contiguous subpopulations of each river seem fairly high for taxa spatially contiguous (D max=0.052).