M. Mattoccia

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.

Orientation behaviour and heterozygosity of sandhopper populations in relation to stability of beach environments

Felicita Scapini,’ Marcello Buiatti,’ Elvira De Matthaeis’ and Marco Mattoccia3 ‘Dipartimento di Biologia animale e Genetica, Universitri, via Romana 17, 50125 Firenze, Italy *Dipartimento di Biologia animale e dell’Uomo, Universitti “La Sapienza”, viale dell’Universitci 32, 00185 Roma, Italy 3Dipartimento di Biologia, Tor Vergata, II Universitd di Roma, via 0. Raimondo, 00173 Roma, Italy Key words: Amphipoda; behaviour; orientation; heterozygosity. Introduction The talitrid amphipod Talitrus saltator (Montagu) is a common inhabitant of sandy beaches, where it lives its whole life cycle, avoiding both the arid environment inland and submersion in sea water. Orientation towards the sea is critical for fitness, because good orientation is needed to avoid death by dehydration. During the night sandhoppers from Mediterranean populations migrate inland to feed, during the day they remain burrowed in moist sand at the water’s edge (Scapini et al., 1992). Orientation for zonal recovery occurs mainly by following a sun compass (see Pardi and Ercolini, 1986 for a review). This is of high survival value since these amphipods are not protected against dehydration by morphological structure and the narrow strip of moist sand at water’s edge is subjected to periodic and aperiodic shifting due to tides and storms. It has been shown that the sun compass is genetically determined. Differences among natural populations along the Italian Tyrrhenian and Adriatic shores are related to the orientation of the seashores where they live (Pardi, 1960; Pardi and Scapini, 1983; Scapini et al., 1985; Scapini and Buitatti, 1985; Scapini and Fasinella, 1990). However, the orientation tendency seems to be the result of a non-additive continuous interplay between individual learning and plasticity on one hand, and genetic variation on the population level on the other. It is through both processes that populations adapt to rapid environmental changes (Scapini et al., 1988; Ugolini and Scapini, 1988). Orientation, therefore, being a genetically determined character connected to fitness, for which the relative contributions of genetic and learning components 43

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.

Geographic variation in Talitrus saltator (Crustacea, Amphipoda): biochemical evidence

Allozyme variation of 30 populations of the amphipod Talitrus saltator collected from different localities of Atlantic and Mediterranean coasts was studied. A remarkable genetic differentiation was revealed among diverse geographic groups. Three main groups were highlighted showing values of genetic distance (average D = 0.4) frequently reported for interspecific comparisons. The estimates of gene flow calculated from the Fst values are reported. The pattern of genetic divergence between the different geographic groups is discussed taking into account the dispersal capacity of T. saltator, the pattern of the surface currents in the Mediterranean basin and the Pleistocene climatic fluctuations in the Mediterranean.