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Life history of the talitrid amphipod Macarorchestia remyi (Schellenberg, 1950) on a Tyrrhenian sandy beach, Italy
No full textIn this study, we analysed the life cycle and some aspects of the reproductive biology of the talitrid amphipod Macarorchestia remyi (Schellenberg, 1950) on a sandy beach in central Italy (Tyrrhenian Sea). The species is strongly associated with rotting wood carried by the sea. The animals were sampled once a month by hand over 1 year (May 2006-April 2007) and a total of 3,484 individuals were collected. Results showed the occurrence of intersexes in addition to males and females (n = 268) and a sex ratio always in favour of females. Breeding peaked twice during the year and the number of eggs in the ventral brood chamber ranged from 3 to 19. Linear regression analysis showed a positive correlation between total length of ovigerous females and the number of eggs they carried. The mean length of both mature males and mature females was 6 mm, while the maximum length was 13 mm. The presence of two cohorts during the year was also identified. Our results suggest that, despite the ephemeral habitats where the species lives, the population is stable over time and its life cycle does not differ in relation to other talitrid species that live on beaches
Supralittoral amphipod abundances across habitats on Mediterranean temperate beaches
No full textCommunity complexity and abiotic conditions are key components of environmental heterogeneity that affect the abundance and distribution of species. In this study we evaluated how environmental conditions affect abundances of supralittoral amphipods (Talitridae) in four habitats (sandy beach, rivermouth, wrack and lakeshore), along the Italian peninsula in the Mediterranean Sea. All samplings covered a 12 month period, and used the same sampling methodology thereby enabling comparison of abundances and species composition and richness. Four species (Talitrus saltator (Montagu, 1808), Orchestia gammarellus (Pallas, 1766), O. montagui Audouin 1826, O. cf. cavimana Heller 1865) were collected in the different habitats, but most species were found or were abundant in only one of the four habitats. Abundances of talitrids (numbers per sampling hour) differed significantly among the habitats with highest abundances found in the wrack and on the riverbank in proximity to an estuary, and lowest abundances observed on four sandy beach sites. Environmental conditions (temperature, moisture, substrate penetrability) differed among the habitats and were associated with some of the among-site variability in abundances. Our findings demonstrate that talitrids thrive better in some supralittoral habitats than others, and that some habitats could be considered to be "hotspots" of talitrid ecology and biodiversity.Community complexity and abiotic conditions are key components of environmental heterogeneity that affect the abundance and distribution of species. In this study we evaluated how environmental conditions affect abundances of supralittoral amphipods (Talitridae) in four habitats (sandy beach, rivermouth, wrack and lakeshore), along the Italian peninsula in the Mediterranean Sea. All samplings covered a 12 month period, and used the same sampling methodology thereby enabling comparison of abundances and species composition and richness. Four species (Talitrus saltator (Montagu, 1808), Orchestia gammarellus (Pallas, 1766), O. montagui Audouin 1826, O. cf. cavimana Heller 1865) were collected in the different habitats, but most species were found or were abundant in only one of the four habitats. Abundances of talitrids (numbers per sampling hour) differed significantly among the habitats with highest abundances found in the wrack and on the riverbank in proximity to an estuary, and lowe
Life history and temporal distribution of Orchestia sp. cf. cavimana (Amphipoda, Talitridae) on a lake shore in central Italy
No full textThe life history of the amphipod Orchestia sp. cf. cavimana (Heller, 1865) was studied throughout the course of a year with monthly samplings and the use of pitfall traps along the shores of Lake Albano in central Italy. The data thus obtained showed two peaks in abundance (the first in June and the second in October) and a minimum capture frequency in February. Egg-bearing females were recorded in spring and late summer, whilst recruitment occurred from spring to autumn, with maximum in June and October. The data collected also indicated the presence of a positive correlation between the abundance of talitrids and both temperature and sediment moisture. Morphological analysis enabled the identification of four different cohorts (with a lifespan of the species of approximately 12-15 months) all four of which remained distinguishable throughout the course of the year. It, moreover, enabled sex determination in individuals of 5 or more millimetres. The subsequent distribution indicated that, when significant, the sex ratio was female biased and that maximum size was greater in males. In particular, maximum sizes were recorded in spring for both males and females and were of 17.5 and 13.0 mm, respectively. Furthermore, the total body length recorded for egg-bearing females was positively correlated with the number of eggs in their brood pouch. (C) 2009 Elsevier GmbH. All rights reserved
Morphology and histology of the gut system of Macaorchestia remyi (Schellenberg, 1950) (Amphipoda, Talitridae)
No full textMorphology and histology of the mouthparts and gut system of Macarorchestia remyi (Schellenberg, 1950) (Amphipoda, Talitridae
No full textMacarorchestia remyi lives in beached logs, where it makes its tunnels by eating the wood. Hence, this wood-feeding species has a peculiar diet compared with other Mediterranean talitrid amphipods. We carried out a morphological analysis of its mouthparts and a mainly histological investigation (transverse sections) of its gut regions (foregut, midgut and hindgut). The ectodermal foregut and hindgut regions are typically lined with cuticle, finely elaborated into various structures. Near the distal end of the oesophagus are the lateralia, provided with two rows of setae and several stout spines. The primary filter, including two parallel channels, is located ventrally in the first region of the foregut, while the secondary filter lies ventrally in the posterior foregut chamber, composed on each side of two longitudinal channels covered by densely arranged parallel setae. In the hindgut, the lining folded cuticle of the cylindrical epithelium shows unspecialized spines. In the endodermal midgut, the fine materials extracted from the upper foregut chambers through the filter systems are conveyed from the ventral channels to two pairs of ventrally located hepatopancreatic tubules; all these lobes, surrounding the midgut and partially the hindgut, are characterized by large vacuolated cells in their proximal regions. The midgut caeca includes the paired tubular pyloric caeca lateral to the secondary filter and a single caecum dorsal to the midgut. Two posterior caeca, originating in the distal part of the midgut, are located dorsolaterally and partially surround the hindgut. Finally, we observed layers of peritrophic membranes in the lumen of the midgut. In summary, the molar surface morphology appears to agree with the trend previously hypothesized for talitrid taxa with an increasing landward habitat and shifting toward a typical terrestrial diet. However, our data suggest that M. remyi, despite its particular feeding preference, shows no major differences in the main gut structures from other talitroid species. This relatively uniform morphology can be considered close to the ground pattern of the gammaridean amphipods, probably representing the early stage of Amphipoda evolutio
Temporal Population Genetics and COI Phylogeography of the Sandhopper Macarorchestia remyi (Schellenberg, 1950) (Amphipoda, Talitridae)
No full textIn this study we assessed levels of genetic divergence and variability in 208 individuals of the supralittoral sandhopper Macarorchestia remyi, a species strictly associated with rotted wood stranded on sand beaches, by analyzing sequence polymorphisms in a fragment of the mitochondrial DNA (mtDNA) gene coding cytochrome oxidase subunit I (COI). The geographical distribution and ecology of the species are poorly known. The study includes 1 Tyrrhenian and 2 Adriatic populations sampled along the Italian peninsula plus a single individual found on Corfu Is. (Greece). The Tyrrhenian population was sampled monthly for 1 yr. Genetic data revealed a deep phylogeographic break between the Tyrrhenian and Adriatic populations with no shared haplotypes. The single individual collected on Corfu Is. carried the most common haplotype found in the Tyrrhenian population. A mismatch analysis could not reject the hypothesis of a sudden demographic expansion in almost all but 2 monthly samples. When compared to previous genetic data centered on a variety of Mediterranean talitrids, our results place M. remyi among those species with profound intraspecific divergence (sandhoppers) and dissimilar from beachfleas, which generally display little population genetic structuring
Figure 2 in Further morphological and molecular studies of driftwood hoppers (Crustacea: Amphipoda: Talitridae) from Mediterraneanłnorth-east Atlantic coastlines
No full textFigure 2. Scatterplots and fitted regression lines for: (A) A2 PL on TBL for the unknown taxon from the Swale, UK (★) and juvenile O. mediterranea from the Medway estuary, UK (A). (B) ED on TBL for the unknown taxon from the Swale, UK (★) and juvenile O. mediterranea from the Medway estuary, UK (A).Published as part of <i>Pavesi, Laura, Wildish, Dave J., Gasson, Peter, Lowe, Miranda & Ketmaier, Valerio, 2014, Further morphological and molecular studies of driftwood hoppers (Crustacea: Amphipoda: Talitridae) from Mediterraneanłnorth-east Atlantic coastlines, pp. 1047-1071 in Journal of Natural History 49 (17)</i> on page 1057, DOI: 10.1080/00222933.2014.974708, <a href="http://zenodo.org/record/4005843">http://zenodo.org/record/4005843</a>
Figure 4 in Further morphological and molecular studies of driftwood hoppers (Crustacea: Amphipoda: Talitridae) from Mediterraneanłnorth-east Atlantic coastlines
No full textFigure 4. Bayesian estimate of the evolutionary relationships among the talitrid species included in the study based on the COI partition. Numbers at nodes are posterior probabilities; divergence time (myr) ± standard deviation (SD) is reported at each node. Taxa are labelled following the codes in Table 1. Species delimitations obtained with the ABGD method are shown next to the tree.Published as part of <i>Pavesi, Laura, Wildish, Dave J., Gasson, Peter, Lowe, Miranda & Ketmaier, Valerio, 2014, Further morphological and molecular studies of driftwood hoppers (Crustacea: Amphipoda: Talitridae) from Mediterraneanłnorth-east Atlantic coastlines, pp. 1047-1071 in Journal of Natural History 49 (17)</i> on page 1064, DOI: 10.1080/00222933.2014.974708, <a href="http://zenodo.org/record/4005843">http://zenodo.org/record/4005843</a>
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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