1,721,046 research outputs found
GROWTH-RATES OF PERINEREIS-RULLIERI (POLYCHAETA, NEREIDIDAE) UNDER DIFFERENT CONDITIONS OF TEMPERATURE AND DIET
No full textThe effects of temperature and diet on growth rates of the nereidid polychaete Perinereis rullieri have been investigated under controlled laboratory conditions from the beginning of larval feeding. Growth rate was evaluated under three diets (filamentous green algae, nauplii of Artemia salina, and Tetramin MikroMin dry fish-food), and three temperatures (15-degrees-C, 21-degrees-C, and 27-degrees-C). Growth rate was influenced both by diet and temperature. Diet appears the main factor strongly modifying the growth pattern
INFLUENCE OF TEMPERATURE AND DIET ON SURVIVAL OF PERINEREIS-RULLIERI PILATO (POLYCHAETA, NEREIDIDAE)
No full textThe effects of temperature and diet on survival of Perinereis rullieri have been investigated under controlled laboratory conditions, from the beginning of larval feeding to adult stage. Survival rate was evaluated under three diets (green algae, nauplii of Artemia salina and Tetramin MikroMin dry fish-food) and three temperatures (15-degrees-C, 21-degrees-C and 27-degrees-C). Survival was influenced both by the composition and size of the food source. Temperature did not significantly affect survival
Fecundity and reproductive effort in Ophryotrocha labronica (Polychaeta : Dorvilleidae)
No full textReproductive effort in terms of fecundity and energy allocation was studied in Ophryotrocha labronica La Greca and Bacci, 1962 a small, semicontinuous iteroparous species. In O. labronica fecundity is more or less constant throughout life, and the total fecundity of the 64 couples examined in this experiment only declined by 12% from the first to the last spawning. No linear relationship was found between fecundity and body size. The energy content of germinal and somatic tissues was determined by differential scanning calorimeter. The reproductive effort and a reproductive index based on the fifth spawning were evaluated to compare the patterns of energy allocation of a semicontinuous iteroparous species with semelparous and annual iteroparous species. The reproductive index ranged from 0.20 to 0.77, with an average of 0.480. The average reproductive effort was 0.840, ranging from 0.60 to 0.96. These figures highlight the enormous amount of energy that O. labronica allocates to reproductive tissues
Effects of diet and laboratory rearing on demography of Dinophilus gyrociliatus (Polychaeta : Dinophilidae)
No full textLife table response experiments were performed to evaluate the demographic consequences of: (1) the dietary regimes and (2) the length of laboratory rearing in strains of Dinophilus gyrociliatus, a small infaunal polychaete. The first experiment was performed using animals recently collected from the natural environment and fed either on spinach or on Tetramin (artificial fish food with high caloric content). Starting from this original group, two distinct laboratory strains were established: the first raised only with spinach, the second only with Tetramin. In the first experiment, the group fed on Tetramin exhibited greater population growth rate (lambda), shorter generation time (T) and reduced expectation of life (e(0)) with respect to the animals fed on spinach. The second experiment took place 2 years later to evaluate the difference in life history traits between these two laboratory strains. In the case of the group fed on Tetramin, population parameters exhibited marked variations; in fact, lambda and the net reproductive rate (R-0) were significantly higher and T and e(0) were shorter than the corresponding parameters observed in the first experiment. Conversely, the demographic variations induced by laboratory rearing on a spinach diet were limited to a reduction in the expectation of life. The decomposition analysis showed that the reduction in generation time and the increase in fecundity occurring during the first 4 weeks of life accounted for nearly all the differences in lambda. During the long breeding period at constant temperature, photoperiod and salinity, a continuous selection of the most precocious and fecund individuals may have taken place as a consequence of the abundance of resources and the lack of predation
Effects of temperature on two Mediterranean populations of Dinophilus gyrociliatus (Polychaeta : Dinophilidae) I. Effects on life history and sex ratio
No full textThe effects of temperature on the life history characteristics of two populations of the polychaete Dinophilus gyrociliatus, one from Ravenna (northern Adriatic Sea) and the other from Genoa (Ligurian Sea), were investigated. The temperatures tested (6, 12, 18, 24 and 30 degreesC) cover a wider range than those prevailing in the natural environment. In the populations studied there are broad differences in timing of development and reproduction. At 6 degreesC, the adults of both populations survive for a long time but they are unable to reproduce. At 12 degreesC, only the animals from Ravenna manage to reproduce. At the higher temperatures (18, 24 and 30 degreesC), the development of the animals belonging to the Genoa strain is faster than that of the Ravenna strain. The duration of the various phases of the biological cycle is very similar in both populations, but that from Ravenna exhibits greater tolerance of low temperatures, slower development rate and lower development threshold temperature than does the Genoa population. Temperature and geographical origin also have strong effects on reproductive characteristics. The highest fecundity values were observed at 12 degreesC in the Ravenna strain, the lowest at 30 degreesC in both groups. At 18 degreesC, the Genoa population is more fecund than the Ravenna one, while the situation is reversed at 12 degreesC. The smallest ovigerous capsules are produced at 30 degreesC, the biggest at 12 degreesC, and the Genoa females produce larger capsules than do the females from Ravenna, except at 12 degreesC. The size of both male and female eggs varies in relation to temperature, the smallest female eggs generally being laid at the higher temperatures. At all the temperatures tested, the sex ratio of the Ravenna population is higher than that of the Genoa population. In the Ravenna strain, temperature has no effect on the sex ratio, while in the Genoa strain the sex ratio at 24 degreesC is lower than at 18 and 30 degreesC. Comparison of the two populations at the same temperature reveals considerable differences in the characteristics of their respective life histories and sex ratios. It is very likely that the extreme selectivity of the harbor environments has favored the fragmentation of the species into differentiated populations that have adapted to the conditions prevailing in the different localities. (C) 2003 Elsevier Science B.V. All rights reserved
Life history and demography of three populations of Ophryotrocha japonica (Polychaeta : Dorvilleidae)
Get PDFThis 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
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
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
Survival and growth rate of Perinereis rullieri (Polychaeta, Nereididae) under different salinities and diets
No full textThe effects of salinity and diet on survival and growth rate of the nereidid polychaete Perinereis rullieri have been investigated under controlled laboratory conditions. The experiment began from nec nectochaetes at 5-6 setigerous segments to exclude the high mortality occurring immediately after hatching. The tested salinities were 10 - 20 - 30 and 40 parts per thousand that slightly exceed those recorded in the natural environment during larval emergence. The larvae were fed with Tetramin MicroMin dry fish food and Tetramin MicroMin added with freeze-dried lyophilised Ulva rigida to test the possible antistress effect of vitamins C and E, in which the alga is rich. The experimental results highlight the influence of salinity on survival and growth race of P. rullieri. Enrichment with alga does not significantly affect survivorship and growth rates under all experimental conditions
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
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