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  • Author or Editor: Fernando Mantelatto x
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Abstract

The present study characterised the fecundity of the hermit crab Pagurus brevidactylus as well as the influence of shell type and size on fecundity using the morphometric relationship. Ovigerous females were collected monthly from January to December 1999 in the infra-littoral region of Anchieta Island, using scuba-diving methods. Only the ovigerous females with eggs in the early phase of development were selected for the fecundity analysis. The number of eggs carried by individuals of several sizes (SL, shield length), condition of development, and egg size were determined. A high percentage (77.0%) of ovigerous females with eggs in the early phase of development were captured, with a low frequency (9.2%) of females with eggs in the final stage of development. A total of 157 females with recently produced eggs were analysed. Individual fecundity ranged from 27 (SL = 1.25 mm) to 1075 eggs (SL = 3.19 mm) and mean fecundity was 158 ± 119 eggs. The number of eggs produced during spring was significantly higher than those produced in the other seasons of the year. Considering the two shells most occupied by P. brevidactylus (C. atratum and M. nodulosa), the highest fecundity was observed for ovigerous females occupying M. nodulosa ones, showing that shell type can influence the reproductive potential of ovigerous females. The reproductive aspects of P. brevidactylus were related to the shell species occupied and to strategies developed to compensate for interspecific competition, i.e., continuous reproductive effort and early maturity.

In: Animal Biology

Abstract

Population genetic studies on marine taxa, specifically in the field of phylogeography, have revealed distinct levels of genetic differentiation in widely distributed species, even though they present long planktonic larval development. A set of factors have been identified as acting on gene flow between marine populations, including physical or physiological barriers, isolation by distance, larval behaviour, and geological and demographic events. In this way, the aim of this study was to analyse the genetic variability among populations of the crab species Sesarma rectum Randall, 1840 along the western Atlantic in order to check the levels of genetic diversity and differentiation among populations. To achieve this purpose, mtDNA cytochrome-c oxidase subunit I (COI) (DNA-barcode marker) data were used to compute a haplotype network and a Bayesian analysis for genetic differentiation, to calculate an Analysis of Molecular Variance (AMOVA), and haplotype and nucleotide diversities. Neutrality tests (Tajima’s D and Fu’s Fs) were accessed, as well as pairwise mismatch distribution under the sudden expansion model. We found sharing of haplotypes among populations of S. rectum along its range of distribution and no significant indication for restricted gene flow between populations separately over 6000 km, supporting the hypothesis of a high dispersive capacity, and/or the absence of strong selective gradients along the distribution. Nevertheless, some results indicated population structure suggesting the presence of two genetic sources (i.e., groups or lineages), probably interpreted as a result of a very recent bottleneck effect due to habitat losses, followed by the beginning of a population expansion.

In: Studies on Decapoda and Copepoda in Memory of Michael Türkay

Abstract

Population genetic studies on marine taxa, specifically in the field of phylogeography, have revealed distinct levels of genetic differentiation in widely distributed species, even though they present long planktonic larval development. A set of factors have been identified as acting on gene flow between marine populations, including physical or physiological barriers, isolation by distance, larval behaviour, and geological and demographic events. In this way, the aim of this study was to analyse the genetic variability among populations of the crab species Sesarma rectum Randall, 1840 along the western Atlantic in order to check the levels of genetic diversity and differentiation among populations. To achieve this purpose, mtDNA cytochrome-c oxidase subunit I (COI) (DNA-barcode marker) data were used to compute a haplotype network and a Bayesian analysis for genetic differentiation, to calculate an Analysis of Molecular Variance (AMOVA), and haplotype and nucleotide diversities. Neutrality tests (Tajima’s D and Fu’s Fs) were accessed, as well as pairwise mismatch distribution under the sudden expansion model. We found sharing of haplotypes among populations of S. rectum along its range of distribution and no significant indication for restricted gene flow between populations separately over 6000 km, supporting the hypothesis of a high dispersive capacity, and/or the absence of strong selective gradients along the distribution. Nevertheless, some results indicated population structure suggesting the presence of two genetic sources (i.e., groups or lineages), probably interpreted as a result of a very recent bottleneck effect due to habitat losses, followed by the beginning of a population expansion.

In: Studies on Decapoda and Copepoda in Memory of Michael Türkay

Abstract

Hermit crabs of the species Pagurus criniticornis (Dana, 1852) parasitized by the poorly known colonial rhizocephalan Peltogasterella socialis (Müller, 1863), were collected in the infralittoral rocky/sandy area of Anchieta Island (São Paulo), Brazil. We report the presence and pattern of occurrence of this rhizocephalan in the P. criniticornis population. The hermit crabs were obtained monthly during 1999 by two people using SCUBA methods. A total of 992 hermit crabs were captured and examined for rhizocephalans. The studied population showed non-normal size distribution and only 2.11% of the sample specimens carried externae of P. socialis. The parasite occurrence was seasonal and varied with host size. Some signs of feminization were observed on P. criniticornis pleopods (elongation of the endopod and reduction of the exopod of pleopods for males and reduction in the size of endopods for females). This is the first report on this parasite/host relationship for this South American host species. This is the first record of P. socialis (Müller, 1863) subsequent to the species' description, and possible occurrence of the parasite on hermit crabs in the Bahamas is also reported.

In: Animal Biology

Abstract

Among marine invertebrates, the overall biomass invested in egg production varies widely within populations, which can result from the interaction of endogenous and exogenous factors. Species that have constant reproduction throughout the year can be good models to study the influence of environmental factors on reproductive processes. We conducted a seasonal comparison of egg production in the intertidal snapping shrimp Alpheus nuttingi, which shows a continuous reproductive pattern, to examine the hypothesis that differences in egg production are driven by environmental conditions and population features. This population showed an uncommon strategy, characterized by females that produce eggs of varying sizes within their clutches, with reduced egg volume when the number of eggs is higher (Spring-Summer). In these seasons, higher temperatures and greater food availability may allow the production of more eggs compared to the Autumn-Winter seasons. Compared to other alpheid shrimps, this population produces small eggs, but in larger numbers. Despite the higher fecundity, the reproductive output is relatively low, this production being supported by the large size of females from the southern Atlantic region. Our findings showed that the egg production of A. nuttingi was greatly influenced by environmental factors. Therefore, this shrimp, and probably other decapods that possess continuous reproduction, adopt different reproductive strategies during the year.

In: Animal Biology