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New hypogean cyclopoid copepods (Crustacea) from the Yucatan Peninsula, Mexico
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Four previously unknown hypogean species of cyclopoid copepods were collected in cenotes and wells of the Yucatan Peninsula, Mexico. Diacyclops chakan sp. n. and D. puuc sp. n. differ from their congeners in combining 3-segmented swimming legs, 11-segmented antennules, and legs 1-4 endopodite segment 2 all with 2 setae. Species of Diacyclops rarely occur in tropical regions, and the Diacyclops described here are only the second and third species recorded from Mexico. The benthic D. puuc was found in the large underground reservoir of a cenote. Diacyclops chakan was encountered in such large open subterranean water basins, but more frequently and abundantly in wells. The two Mesocyclops species, M. chaci sp. n. and M. yutsil sp. n., most closely resemble their epigean benthic congener M. reidae Petkovski, but are modified by loss of some body ornament and attenuation of swimming legs and mouthparts. Mesocyclops chaci sp. n. occupies crevicular spaces (wells and small caverns). The second species, M. yutsil sp. n., with more pronounced attenuation of legs, has a planktonic life in large subterranean water volumes. The extremely attenuated appendages of both species distinguish them from all other Mesocyclops, and resemble those of the hypogean Kieferiella delamarei Lescher-Moutoué. These three species are considered as a species-flock which have radiated as specialists within a highly dynamic geomorphological environment.
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Cuticular linings and remodelisation processes in Crambe Crambe (Demospongiae: Poecilosclerida)
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The common Mediterranean sublittoral sponge Crambe crambe goes through a resting, non-feeding period with cellular restructuring which may have biological and ecological significance. This red encrusting sponge reproduces in summer and larvae released during July-August. After reproduction, from the end of August until the end of October, some specimens appeared covered with a glassy cuticle, obliterating the ostia and oscula. No water pumping and, hence, no feeding occurs during this stage. At the end of October and during November some specimens displayed a strongly hispid surface, with spicules retaining entangled debris. This hispid form is interpreted as an intermediate stage between the resting phase and the active period. SEM examination of the surface during the non-feeding period confirmed the absence of inhalant orifices and the presence of an acellular cuticle markedly different from the glycocalyx layer associated with the pinacoderm of active specimens. In some individuals, micro-organisms were found adhering to the outer side of the cuticle which were absent from the surface of active specimens. In TEM, the cuticle appeared as a complex 2.5-3μm thick structure made up of three layers: a proximal dense layer (0.06-0.12μm), an intermediate amorphous layer (0.15-0.3μm), and an outer granular layer also of variable thickness (more than 2μm) which progressively disintegrated. Collagen debris appeared between the proximal and intermediate layers. The zone beneath this triple-layered cuticle was either completely devoid of cells or showed scarce degenerating cellular components (mainly from pinacocytes and spherulous cells), and sparse collagen fibrils. The choanosome appeared rather disorganised, with most choanocyte chambers disintegrated, with abundant phagocytosing archeocytes, sclerocytes, spherulous cells, degenerated cells and cell debris. Later in the season the cuticle appeared broken in many places. It was cast off and a new pinacoderm with ostia developed below; filtering activity of the sponges resumed. Spicules, previously protected by the cuticle, were uncovered, giving rise to a hispid phase. Subsequently the emergent spicules were cast off and smoothness of the sponge surface was restored. These changes in sponge cell structure and activity may be explained as reorganisation processes after reproduction, but other causes, such as adverse water temperature, may have similar effects.
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Growth and regeneration rates of the calcareous skeleton of the Caribbean coralline sponge Ceratoporella nicholsoni: A long term survey
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The growth rate of the aragonitic skeleton of the Caribbean 'sclerosponge' Ceratoporella nicholsoni has been studied by in situ staining of specimens with calcein in a reef tunnel, 28m depth, near Discovery Bay, Jamaica. Experiments were performed up to five times from 1984 to 1997 on a population of 10 specimens ranging from 10-20cm maximum diameter. In each experiment small skeletal samples were removed from the periphery of sponges, and specimens were left in place for further studies on growth and regeneration. Perpendicular sections, ground to a thickness of about 10μm, were photographed by fluorescence microscopy. Annual skeletal growth rates were calculated from measurements of the linear extension between calcein stained lines along growth axes. Data indicate that although average annual growth rates remained in the same range for different periods (214.6±54.5-233.3±33.0μm yr -1), significant differences occurred from one individual to another within the same period. The annual growth rate of a given individual also varied significantly in time (191.1±30.0-269.9±37.0μm yr -1). A second population of smaller individuals, measured after a single period of one year, revealed a strikingly lower average annual growth rate (124.4±35.0μm yr -1). Regeneration of the skeleton of injured specimens was also characterised by an initial slower growth rate. Nevertheless, after the first year, it was comparable to normal growth, and exceeded it slightly thereafter. This first long term study of Ceratoporella provides important information on the variability in growth rates, with implications on the use of sclerosponges as paleoenvironmental proxies.
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Two new living species of Loxotaphrus (Gastropoda: Cancellariidae: Plesiotritoninae) from Queensland, Australia and Mozambique, East Africa
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Until now, the only living species assigned. to the cancellariid genus Loxotaphrus Harris, 1897 was the West African species L. deshayesii (Duval, 1841). Two new living species are described here, L. limpusi n. sp., from the Swain Reefs, Queensland, and L. rosadoi n. sp., from off southern Mozambique. L. limpusi most closely resembles the type species of the genus, L. variciferus (Tate, 1888) (Miocene, southern Australia). Although L. rosadoi resembles L. variciferus and L. limpusi more closely than it does L. deshayesii, it differs from all other species, assigned to Loxotaphrus in having weak sculpture, apart from the prominent, sharp nodules around the peripheral keel.
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Zonation and structuring factors of meiofauna communities in a tropical seagrass bed (Gazi Bay, Kenya)
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This study deals with the relation between tropical meiofauna and environmental variables by comparing the 'benthic' (i.e. in the bare sediment adjacent to seagrass plants) and the 'epiphytic' (i.e. in samples including seagrass plants) meiofauna associated with five seagrass species from the high intertidal to the high subtidal zone in Gazi Bay (Kenya), Ordination and variance analysis revealed three distinct 'benthic' and two 'epiphytic' meiofauna assemblages. These assemblages corresponded entirely with those identified for the seagrass species: a high intertidal pioneer association (Halophila ovalis/Halodule wrightii), an intertidal climax assemblage (Thalassia hemprichii) and a high subtidal pioneer association (Halophila stipulacea/ Syringodium isoetifolium). These data support the hypothesis that meiofaunal communities correspond to the characteristic zonation of the seagrass vegetation in Gazi Bay. In beds of the pioneer seagrass species, the close relationship between sediment characteristics and both 'benthic' and 'epiphytic' meiofauna communities suggests that these pioneer communities were mainly driven by physical factors. The 'benthic' communities adjacent to the climax seagrass species T. hemprichii were more structured by biogenic factors, e.g. \% TOM, chlorophyll a and c, fucoxanthin, habitat complexity and growth form of the seagrass species. For its associated 'epiphytic' meiofauna the latter conclusion was even more striking. These data corroborate the importance of physical factors in disturbed environments (intertidal zone, near pioneer seagrasses) and of biotic factors in more stable conditions (subtidal zone, near climax seagrasses). © 2001 Elsevier Science B.V.
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Morphological deformities in Chironomus riparius meigen larvae after exposure to cadmium over several generations
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In order to test the potential of chironomid deformities for biomonitoring, induction of morphological deformities in Chironomus riparius larvae was assessed after chronic exposure (static with renewal) of eggs and subsequent instars to sublethal nominal cadmium concentrations of 0, 3 (NOEC), 9 (intermediate) and 27 (chronic LC'50) μg Cd 1-1 during 7 to 10 generations. Deformities which could be associated with an indirect or direct cadmium effect were split medial mentum teeth (more frequent in 9 and 27 μg Cd 1-1) and premandible deformities (especially in 3 μg Cd 1-1). The control contained more larvae with additional teeth in mentum and mandible than the metal-exposed conditions. In the 9 μg Cd 1-1 condition the frequencies of larvae with split medial mentum teeth increased in the last four generations, to reach 40\%. The unpredictability of fluctuations of deformity frequencies over the generations was associated with parental effects and experimental manipulation. The deformity percentages correlated positively with the mortalities and could be related to the induction of tolerance to cadmium, as was concluded on the basis of life cycle analysis in a previous paper. This experiment demonstrated a concentration-response relationship between deformities and sublethal levels of cadmium. However, the observed generation fluctuations caution for (1) the use of single-generation experiments for defining ecotoxicological threshold values, and (2) experimentally induced genetical drift in multi-generation experiments.
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Echiuropus bekmanae n.sp. (Crustacea, Amphipoda, Carinogammaridae) from Lake Baikal, retrieved by a new deep-water sampling device
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Lake Baikal is well known for its exceptional diversity of gammarid amphipods, with 95\% of endemics from its 270 described species representing about 20\% of the world freshwater fauna. Echiuropus (Asprogammarus) bekmanae n.sp. was collected by an 'autonomous trap system', a sampling device thoroughly described here. Although not necrophagous itself, this new species was found in two baited trap samples (at 750 and more than 1600 m) from 1995 and 1996. This rather small (13 mm) deep water species is the eighth species of the subgenus Asprogammarus, of the Baikal endemic genus Echiuropus. Diagnoses of the subgenus and the closer species are given.
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Lake level fluctuations synchronize genetic divergences of cichlid fishes in African Lakes
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Water level fluctuations are important modulators of speciation processes in tropical lakes, in that they temporarily form or break down barriers to gene flow among adjacent populations and/or incipient species. Time estimates of the most recent major lowstands of the three African Great Lakes are thus crucial to infer the relative timescales of explosive speciation events in cichlid species flocks. Our approach combines geological evidence with genetic divergence data of cichlid fishes from the three Great East African Lakes derived from the fastest-evolving mtDNA segment. Thereby, we show for each of the three lakes that individuals sampled from several populations which are currently isolated by long geographic distances and/or deep water form clusters of equally closely related haplotypes. The distribution of identical or equally closely related haplotypes in a lake basin allows delineation of the extent of lake level fluctuations. Our data suggest that the same climatic phenomenon synchronized the onset of genetic divergence of lineages in all three species flocks, such that their most recent evolutionary history seems to be linked to the same external modulators of adaptive radiation. A calibration of the molecular clock of the control region was elaborated by gauging the age of the Lake Malawi species flock through the divergence among the utaka-cichlid and the mbuna-cichlid lineages to minimally 570,000 years and maximally 1 Myr. This suggests that the low-lake-level period which established the observed patterns of genetic relatedness dates back less than 57,000 years, probably even to 17,000-12,400 years ago, when Lake Victoria dried up and Lakes Malawi and Tanganyika were also low. A rapid rise of all three lakes about 11,000 years ago established the large-scale population subdivisions observed today. Over that period of time, a multitude of species originated in Lakes Malawi and Victoria with an impressive degree of morphological and ecological differentiation, whereas the Tanganyikan taxa that were exposed to the same habitat changes hardly diverged ecologically and morphologically. Our findings also show that patterns of genetic divergences of stenotopic organisms provide valuable feedback on geological and sedimentological time estimates for lake level changes.
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Microsatellite data reveals weak population substructuring in Copadichromis sp. `virginalis kajose', a demersal cichlid from Lake Malawi, Africa
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Small but significant differences were found in allele frequencies among five populations (overall F ST estimate (θ)=0.004, P=0.006; overall R ST estimate (RHO)=0.019, P<0.00001) of the demersal cichlid Copadichromis sp. `virginalis kajose', collected from five locations in Lake Malawi. Pairwise F ST estimates revealed significant differences between the most southerly population (Cape Maclear), and the three most northerly populations (Mbamba Bay, Metangula and Chilola). Pairwise R ST estimates also revealed significant differences between some populations, but no geographical pattern was discernible. There was no evidence of isolation by distance using either the shortest straight-line distance between samples, or the distance around the shoreline following a 50 m depth contour. F ST, estimates were considerably lower than found in previous studies on the mbuna (rock-dwelling species), but higher than those found in a study of three pelagic cichlid species from Lake Malawi. Substructuring in C. sp. `virginalis kajose' appears to be on a similar scale to the Atlantic cod. © 2001 The Fisheries Society of the British Isles.
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Restoration of tropical peat swamp rotifer communities after perturbation: An experimental study of recovery of rotifers from the resting egg bank
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In order to assess the recovery potential of tropical freshwater communities after disturbance, we performed an experimental study on the effects of exposure conditions and durations of storage on hatching of rotifer resting eggs in sediment. Well-mixed surface sediment samples from Mai Khao peat swamp on Phuket Island, Thailand, were stored under three conditions (cold -4°C & dark: CD; ambient -32-42°C & dark: AD; and ambient & daylight conditions: AL), for different periods of time (1, 2, 4, 6, 12, 18 and 24 months). The number of species hatching from the sediment was significantly affected by treatment for both short- (1-6 months) and long-term (6-20 months) exposure. Significant effects of short- and long-term exposure within treatments were also present. Both factors interacted significantly. Regarding numbers of specimens hatching, no short-term effects of differences in treatment condition were found, but increasing the duration did have an effect. Significant effects of treatment occurred after 6 months, in addition to prolonged effects of duration. Again, both factors interacted significantly. These experiments indicate that exposure time has a strong impact on the viability of resting eggs, whereas, an effect of exposure condition appears only after 6 months. So, recovery of rotifer communities from resident sediment egg banks in disturbed peat swamps can only be effectively attained when restoration occurs within a relatively short period after perturbation. © Springer 2005.
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