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Accumuli di conchiglie suggeriscono l’esistenza di predatori terrestri del bivalve alloctono Corbicula fluminea nel canale di Quarantoli (bassa pianura modenese)
No full textAccumuli di conchiglie del bivalve alloctono invasivo Corbicula fluminea sono stati rinvenuti in un sito lungo il canale di Quarantoli, nei pressi di Mirandola (MO). Le caratteristiche degli accumuli, costituiti solo da valve separate, prive di legamento e con danni minimi, suggeriscono che essi siano il prodotto della predazione di un mammifero terrestre, probabilmente il ratto (Rattus norvegicus).Heaps of shells of the invasive alien bivalve Corbicula fluminea were found at a site along the Quarantoli canal, near Mirandola (Po Plain, Italy). The characteristics of the heaps made up only of separated valves, lacking the ligament and almost intact, suggest than they may be the remains of predation by a terrestrial mammal, perhaps the rat (Rattus norvegicus)
Ciclo biologico, life history, demografia e cariologia di due popolazioni di Dinophilus gyrociliatus (Polychaeta: Dinophilidae).
No full textL’attività di ricerca ha riguardato in primo luogo l’analisi degli effetti della temperatura sulla life history e la demografia di due popolazioni geograficamente distanti del polichete interstiziale marino Dinophilus gyrociliatus considerato come organismo modello di specie iteropara semicontinua. Inoltre, è stato affrontato lo studio della cariologia di questa specie. E’ risultato che la temperatura influenza tutte le fasi del ciclo biologico e la riproduzione di questa specie in misura differente nelle due popolazioni considerate, anche se non tutte le differenze osservate appaiono imputabili ad un adattamento alle condizioni locali. Anche la sopravvivenza e la fecondità risentono della temperatura e ciò determina importanti conseguenze a livello demografico. La sopravvivenza giovanile, l’età alla maturità e la fecondità durante i primi eventi riproduttivi appaiono essere i fattori maggiormente responsabili della fitness delle popolazioni in tutte le condizioni testate. La ricerca ha inoltre evidenziato che la temperatura e l’età della madre possono influenzare la sex ratio della discendenza. Tuttavia il cariotipo femminile di D. gyrociliatus è risultato essere costituito da 2n=24 cromosomi mentre quello maschile presenta solo 2n=23, correggendo la precedente stima di 2n=32-31 fornita da altri Autori . E’ stato perciò confermato che il controllo della sex ratio della discendenza è progamico e dipende da fattori ambientali, mentre la determinazione sessuale del singolo zigote è cromosomica singamica di tipo XX-X0. E’ stato ipotizzato che le peculiari caratteristiche della life history e il complesso sistema di determinazione sessuale, che permette di allocare quasi tutte le risorse riproduttive nella discendenza di sesso femminile, abbiano contribuito al successo di D. gyrociliatus nella colonizzazione di ambienti imprevedibili come gli habitat portuali
Distribution and ecology of the genus Ophryotrocha (Polychaeta : Dorvilleidae) in Italian harbors and lagoons
No full textA series of field studies were conducted from March 1999 to October 2001 to investigate the distribution of the genus Ophryotrocha in Italian harbors and lagoons. In the localities examined to date, six species belonging to the genus Ophryotrocha have been found. In particular, O. japonica has been recorded for the first time along European and Mediterranean coastlines. There are considerable differences in the spatial and temporal distribution of these species. The species most commonly found were O. labronica and O. japonica. O. puerilis seems to be confined to the Ligurian and Tyrrhenian coastlines, while O. hartmanni, O. macrovifera and O. robusta are less widespread than the other species. O. labronica and O. japonica colonize brackish lagoons as well as harbor environments. Its wide distribution and some features of its biological cycle suggest that O. japonica may have been introduced as a result of maritime traffic and/or aquaculture. The consequences of seasonality on population dynamic and the links between environmental instability and life history features in some Ophryotrocha species are discussed.A series of field studies were conducted from March 1999 to October 2001 to investigate the distribution of the genus Ophrytrocha in Italian harbors and lagoons. In the localities examined to date, six species belonging to the genus Ophryotrocha have been found. In particular, O. japonica has been recorded for the first time along European and Mediterranean coastlines. There are considerable differences in the spatial and temporal distribution of these species. The species most commonly found were O. labronica and O. japonica. O. puerilis seems to be confined to the Ligurian and Tyrrhenian coastlines, while O. hartmanni, O. macrovifera and O. robusta are less widespread than the other species. O. labronica and O. japonica colonize brackish lagoons as well as harbor environments. Its wide distribution and some features of its biological cycle suggest that O. japonica may have been introduced as a result of maritime traffic and/or aquaculture. The consequences of seasonality on population dynamic and the links between environmental instability and life history features in some Ophryotrocha species are discussed
Effects of temperature on two Mediterranean populations of Dinophilus gyrociliatus (Polychaeta : Dinophilidae) II. Effects on demographic parameters
No full textThe effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus, the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts. Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 degreesC in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 degreesC is counter-balanced by the early attainment of sexual maturity induced at 30 degreesC. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus. (C) 2003 Elsevier Science B.V. All rights reserved
Relationship between body size and population growth rate in two opportunistic polychaetes.
No full textThe relationship between body size and population growth rate λ has been studied in two species of opportunistic polychaetes, Dinophilus gyrociliatus and Ophryotrocha labronica, which colonize harbour environments. These species exhibit a semi-continuous iteroparous reproductive strategy, are phylogenetically closely-related but differ in body size and in some aspects of their sexuality. Ophryotrocha labronica is about 4 mm in body length, displays only slight sexual dimorphism and its sex ratio is biased towards the female sex in the ratio 2:1. Dinophilus gyrociliatus is about 1 mm in length, the males are extremely small and the sex ratio is strongly biased (3:1) in favour of the females. In spite of the considerable differences in all traits of their life histories and in many demographic parameters, the growth rates of the two populations are very similar. The analyses carried out have shown that the rapid attainment of sexual maturity of D. gyrociliatus gives it an advantage that offsets the greater fecundity of O. labronica. It is very likely that the reproductive peculiarities of D. gyrociliatus help to raise the population growth rates. The ‘saving’ on the male sex achieved both by the shift of the sex ratio in favour of the females and by the reduction in the males' body size would appear to enable D. gyrociliatus to grow at the same rate as O. labronica, a larger and more fecund species
Effect of temperature on demography of Ophryotrocha labronica (Polychaeta, Dorvilleidae)
No full textA laboratory experiment was performed to evaluate the temperature-induced variation in the life history traits of Ophryotrocha labronica (Polychaeta). In this species age and size at maturity, survival and fecundity are affected by temperature. In particular in O. labronica, low temperatures cause a considerable delay in the attainment of sexual maturity, a reduced number of spawnings and longer intervals between one spawning and the next; fecundity is therefore lower and the animals generally live longer. At high temperatures, the animals mature rapidly, spawn very frequently and at shorter intervals; fecundity is high, even though the animals have a much shorter life span. Temperature determines the age-specific fecundity and survival patterns and hence the demographic characteristics of O. labronica; both the net reproductive rate R-0 and the population growth rate X vary in accordance with the temperature, thus demonstrating the importance of environmental factors in determining not only the reproductive characteristics of the individual animal but also the fitness of the populations as a whole
Effetto della dieta sulle life tables di Dinophilus gyrociliatus (Polychaeta: Dinophilidae)
No full textThe diet influences the rate of natural increase in Dinophilus gyrociliatus. two laboratory experiments were performed: the first with animals just collected from the field and the second in 1998 with animals reared in laboratory and fed with spinach or tetramin since 1996. the values of r are 1.21 and 1.50 respectively for spinach and tetramin in 1996; about 50 generations later in 1998 values increase to 1.29 and 2.66 respectively for spinach and tetrami
Differenze nella life history di tre popolazioni di Ophryotrocha japonica (Polychaeta: Dorvilleidae).
No full textThis paper examines the life history and demography of three populations of Ophryotrocha japonica an alien species that for until 2001 had only been reported in harbour environments along the Asian and American coasts of the Pacific. The populations analysed came from the Italian harbors of Leghorn and Ravenna and from the brackish Mar Piccolo of Taranto. The three strains are inter-fertile both with one another and with their Pacific counterparts. Notwithstanding among populations were found morphological, reproductive and demographic differences. In Leghorn and Taranto populations there is a sort of sexual dimorphism based on body size that is not present in the Ravenna strain. The most important differences concern the reproductive characteristics. Indeed, fecundity, eggs size and reproductive investment varies greatly between populations. The differences in the life history determine very important consequences for the demography and fitness of the populations, and may depend on the species’ adaptation to different environment or may be the result of independent introduction from different localities or at different times
Prime stime della longevità del verme di fuoco Hermodice carunculata (Annelida) dedotte grazie al contributo dei fotografi subacquei alla scienza partecipata
No full textLife history and demography of three populations of Ophryotrocha japonica (Polychaeta : Dorvilleidae)
Full text linkThis paper examines the life history and demography of 3 populations of the polychaete Ophryotrocha japonica, an alien species that until 2001 had only been reported in harbour environments along the Asian and American coasts of the Pacific. The populations analysed came from the Italian harbours of Leghorn and Ravenna, and from the brackish Mar Piccolo of Taranto. The 3 strains are inter-fertile, both with one another and with their Pacific counterparts, but were nevertheless found to have morphological, reproductive and demographic differences. In the Leghorn and Taranto populations there is a sort of sexual dimorphism based on body size that is not present in the Ravenna strain, while the most important differences concern their reproductive characteristics, with great variations being observed in their respective fecundity, egg size and reproductive investment. The differences in life history have very important consequences for the demography and fitness of each population. In particular, morphometric, reproductive and demographic characteristics set the Leghorn population apart from the other 2; it reaches sexual maturity more rapidly, lives longer, is decidedly larger and its population growth rate lambda is 2.26 wk(-1). The Ravenna and Taranto populations appear to be more alike; their eggs are the same size, they are equally fecund, make a similar reproductive investment and have lambda-values of 1.82 and 1.83 wk(-1), respectively. The marked differences observed among the 3 populations may depend on the species' adaptation to different environmental situations, but could also be the result of independent introductions from different localities or at different times
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