1,720,967 research outputs found
Microgeographic genetic variation of populations of Idotea chelipes (Crustacea: Isopoda) in lagoons of the southern English coast
No full textAllozyme variability was examined using starch-gel electrophoresis between sub-populations of Idotea chelipes over a small geographic distance (approx. 104 km), in lagoons within the Solent area (Fort Gilkicker Moat; Ashlett Pond)and at one site in Dorset (the Fleet Lagoon). Genetic identity values indicate that all three populations are conspecific (I = 0.967 to 0.995), and mean heterozygosity per locus for all three populations was 8%. Significant levels of genetic differentiation (mean F sub(ST) = 0.119***; p< 0.001) were detected over this small spatial scale, but this mainly resulted from the slow esterase locus (mean F sub(ST) (no esterase) = 0.072***; p< 0.001). Genetic differentiation was moderate given the low geographic distances between populations with only one to two migrants per deme per generation (N sub(e)m(F sub(ST)) = 1.85) from the Fleet to Gilkicker. There was no significant deviation from the genotypes expected under the Hardy-Weinberg equilibrium despite an overall slight excess of heterozygotes (mean F sub(IS) = -0.01). Pairwise F sub(ST) values indicated that there was limited genetically effective migration between the sampled lagoons. This genetic differentiation may have been promoted by the presence of the Southampton Water and Solent estuarine system that may act as a physical barrier to gene flow for this species. The previous use of the esterase (ET2)locus as a sub-specific biochemical marker for Idotea chelipes is placed in doubt by this study. Original Abstract: La variabilite enzymatique de trois populations lagunaires daIdotea chelipes est examinee sur gel daelectrophorese daamidon a faible echelle spatiale (environ 104 km). Les trois populations font partie de la meme espece (I = 0,967 a 0,995) et laheterozygotie moyenne observee est de 8 %. Des valeurs de differenciation genetique significatives sont observees (F sub(ST)= 0,119***; p< 0,001) bien que resultant principalement de laesterase lente (F sub(ST)(sans esterase) = 0,072*** ; p< 0,001). Etant donnee la faible distance geographique separant les populations, le niveau de differenciation genetique reste modere avec un a deux migrants par deme par generation (Nem(F sub(ST)) = 1,85). En depit daun faible exces en heterozygote (F sub(IS) = -0,01), aucune deviation par rapport a laequilibre de Hardy-Weinberg naest observee. Les valeurs de differenciation genetique entre paires de populations indiquent que les echanges entre lagunes sont limites et que cette differenciation aurait pu etre accentuee par la presence du systeme estuarien oSolento qui jouerait le role de barriere au flux genique pour cette espece. Daautre part, lautilisation prealable de laesterase lente (ET2) comme marqueur subspecifique du complexe Idotea chelipes est placee en doute dans la presente etude
Composition and temporal distribution of cirripede larvae in Southampton Water, England, with particular reference to the secondary production of Elminius modestus
No full textSouthampton Water, an estuary on the south coast of England, has been the focus of a number of studies to determine the seasonality and productivity of its pelagic community. Although recognized as important in previous studies, the meroplankton component and, in particular, the cirripedes have been largely ignored, though they rank second to the Copepoda in abundance. In order to estimate the contribution of barnacle larvae to the pelagic community, 42 quantitative zooplankton samples were collected from a fixed station within the estuary during a period of 19 months (from 12 January 2001 until 16 July 2002). As expected, barnacles were the second most abundant group averaging 13% of the total population, and accounting for up to 60% on some occasions. Eight barnacle species were identified: Elminius modestus, Balanus improvisus, Balanus crenatus, Semibalanus balanoides, Verruca stroemia, Chthamalus stellatus, Sacculina carcini, and Peltogaster paguri. Of these E. modestus was the most abundant and frequent, dominating the Cirripedia fraction throughout the year, but being outnumbered by B. crenatus from February to May. Secondary production was calculated for E. modestus and mean daily rates of 0.077 mg C m?3 d?1 (28.08 mg C m?3 yr?1) were found
Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru
No full textGonzáles, Paúl, Montesinos-Tubée, Daniel B., Watson, John M., Cano, Asunción, Trinidad, Huber, Navarro, Eduardo, Jans, Harry, Sheader, Martin, Ballard, Harvey E., Flores, Ana R. (2022): Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru. Phytotaxa 571 (1): 52-64, DOI: 10.11646/phytotaxa.571.1.
Population structure of Abyssorchomene abyssorum () (Amphipoda: Lysianassoidea), a scavenging amphipod from the Mid-Atlantic Ridge in the vicinity of the Charlie-Gibbs Fracture Zone
No full textThis study focussed on the common and ubiquitous scavenging amphipod Abyssorchomene abyssorum collected from a section of the Mid-Atlantic Ridge with one pair of sampling areas at 49°N and the other at 54°N, north and south of the Charlie Gibbs Fracture Zone (CGFZ) and east and west of the ridge, at a water depth of 2500 m. Baited-trap samples of necrophagous amphipods were collected during three research expeditions on the RRS James Cook in 2007, 2009, and 2010, allowing for direct comparisons to be made amongst populations of A. abyssorum at the four sample areas. Random subsamples of 200 individuals from nine trap samples were sexed, dissected, and measured.
Males, females, and juveniles were found in all samples but no ovigerous females were identified. The finding of sexually mature mid-sized females, variability of oocyte size with body size, and presence of mature females with ‘empty’ ovaries, suggest that A. abyssorum is capable of having multiple broods in a lifetime. This reproductive strategy is beneficial to a scavenging organism living under a variable and unpredictable nutrient regime, allowing for a rapid reproductive response to advantageous conditions. Females north and south of the CGFZ fall into distinct cohorts with different distributional parameters. The total body lengths of female cohorts south of the CGFZ were consistently larger than those in the north. This is likely due to increased nutrient availability at the southern sampling areas.
Males were significantly smaller than females and possessed longer, more articulate antennae. Longer antennae are thought to facilitate mate-searching by males. Estimates of the maximum brood size ranged from 36–78 offspring with actual brood size expected to be at the lower end of this scale. This places the estimated brood size of A. abyssorum in a similar range to that of other scavenging amphipods of comparable size. The juvenile:non-juvenile ratio differed north and south of the CGFZ with significantly more juveniles in the north. Possible reasons for this difference are discussed
Megafauna from sublittoral to abyssal depths along the Mid-Atlantic Ridge south of Iceland
No full text101 species were identified from 102 biological samples obtained between 225 and 2600 m depth on the Reykjanes Ridge, extending the biogeographic records for several species. Multivariate analysis of between-sample species similarity reveals a two-zone bathymetric faunal distribution with the transition at 8001000 m. A hydrographic survey of the ridge axis suggests that this faunal zonation is influenced by the water mass structure. Despite the limitations of a sampling programme not designed a priori tot biological sampling, the recovery and preservation of the samples and the insight that they provide serves to reinforce that every effort should be made to capitalise on the opportunities for obtaining samples afforded by non- biological sampling programmes.</p
Infection with cerebral metacercariae of microphallid trematode parasites reduces reproductive output in the gammarid amphipod Gammarus insensibilis (Stock 1966) in UK saline lagoons
No full textAbstractSaline lagoons are priority habitats in the United Kingdom supporting several protected specialist species. One specialist, the amphipod Gammarus insensibilis, is infected with behaviour-altering microphallid trematodes such as Microphallus papillorobustus. In saline lagoons around the coast of England (Gilkicker and Lymington–Keyhaven on the Hampshire coast and Moulton Marsh in Lincolnshire) there is variation in the prevalence of this parasite in the gammarid populations (0 at Salterns in the Lymington–Keyhaven lagoon system to 98% at Gilkicker). Infection intensity ranged from 0 to 20 metacercariae in individual amphipods. Higher infection intensity can alter the shape of the amphipod's head. Under experimental conditions respiration rate is significantly reduced in infected animals and reproductive output (expressed as early stage embryos mg g dry weight−1) is significantly lower in infected females. It is important to consider the role of host–parasite interactions in order to understand the ecology of specialist lagoon species such as G. insensibilis and their lagoon habitats.<br/
FIGURE 5. Viola longibracteolata. A. Habit. B in Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru
No full textFIGURE 5. Viola longibracteolata. A. Habit. B. Top view of flower, showing inner lower petals and reverse of upper petals. C. Side view of flower showing abaxial surface of superior and lateral petals. D. Top view of flower, showing inner petals. Photos by E. Navarro.Published as part of Gonzáles, Paúl, Montesinos-Tubée, Daniel B., Watson, John M., Cano, Asunción, Trinidad, Huber, Navarro, Eduardo, Jans, Harry, Sheader, Martin, Ballard, Harvey E. & Flores, Ana R., 2022, Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru, pp. 52-64 in Phytotaxa 571 (1) on page 61, DOI: 10.11646/phytotaxa.571.1.4, http://zenodo.org/record/727046
FIGURE 4. Viola longibracteolata. A in Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru
No full textFIGURE 4. Viola longibracteolata. A. Leaf from centre of rosette (adaxial view). B. Leaf from centre of rosette (abaxial view). C. Leaf from outer circumference of rosette (adaxial view). D. Leaf from outer circumference of rosette (abaxial view). E. Bracteole. F. Upper sepal. G. Superior petals. H. Lateral petals. I. Inferior petal. J. Gynoecium with apical style crest. K. Inferior stamen, showing connective scale and nectar spur. L. Capsule. M. Seed (side view).Published as part of Gonzáles, Paúl, Montesinos-Tubée, Daniel B., Watson, John M., Cano, Asunción, Trinidad, Huber, Navarro, Eduardo, Jans, Harry, Sheader, Martin, Ballard, Harvey E. & Flores, Ana R., 2022, Viola ornata and Viola longibracteolata (Violaceae, subgen. Neoandinium), two rare, new rosulate species from southern Peru, pp. 52-64 in Phytotaxa 571 (1) on page 60, DOI: 10.11646/phytotaxa.571.1.4, http://zenodo.org/record/727046
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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