Effects of multi-year droughts on fish assemblages of seasonally drying Mediterranean streams

1. This study analysed changes occurring in Mediterranean stream fish assemblages over a sequence of dry years followed by a generally wet period (1991–98). Variations in assemblage attributes were quantified at the basin and stream reach scales, and related to variables reflecting the occurrence of unusually dry or wet conditions. 2. Assemblage variability increased along with the resolution of analysis, with little changes in species richness, composition and rank abundances, but significant variation in individual species abundances. Fluctuations in relative abundances were significantly affected by variables reflecting the severity of summer droughts and the occurrence of rainy springs. These patterns were evident at the basin scale, while variability at individual stream reaches tended to be higher and less related to rainfall patterns. 3. At least three response guilds to rainfall variation could be identified: two of the four abundant and widespread species (chub and loach) declined following dry years, whereas the two other core species (nase and eel) declined after rainy spring; one scarce native species (stickleback) increased in dry years. 4. Except at the two most upstream reaches, the assemblages tended to recover quickly to previous configuration after the changes occurring during the sequence of dry years. 5. Temporal variability of local assemblages was concordant among reaches but did not follow any consistent spatial pattern. Instead, spatial patterns in assemblage attributes changed over time in response to environmental variability, with a tendency for a disruption of upstream–downstream gradients following dry years. 6. Results supported the view that present‐day droughts cause relatively small and transient changes to Mediterranean stream fish assemblages. However, longer and more severe droughts expected under altered future climates, may result in declines or local extinctions of the most sensitive species and their potential replacement by more resistant species. Changing drought regimes thus need to be duly considered in the development of conservation strategies for Mediterranean stream fish.     

Quantification of gender specific thermal sensory and pain threshold before and after laser needle stimulation]

Quantitative thermal sensory and pain threshold testing (QST) was performed in 29 adult healthy volunteers (mean age 24.2 +/- 2.7 years; range: 18-29 years; 20 females, 9 males) using the Thermal Sensory Analyser TSA-II (Medoc Advanced Medical Systems, Ramat Yishai, Israel, and Minneapolis, Minnesota, USA) before and after laser needle acupuncture and placebo stimulation, respectively. Significant (p < or = 0,001; t-test) gender-specific differences were seen on cold pain threshold analysis. No significant changes in parameters of thermal sensory and pain thresholds were found before and after laser needle or placebo stimulation at acupuncture points for acute pain. However, a trend towards change in the median value of cold pain sensation after laser needle stimulation (p = 0.479; paired t-test; n.s.) was seen within the group of healthy females. The influence of stimulation of acupuncture points for chronic pain on the various parameters needs to be clarified in future studies.     

A profile of fertilization in mammals

Fertilization is defined as the process of union of two gametes, eggs and sperm. When mammalian eggs and sperm come into contact in the female oviduct, a series of steps is set in motion that can lead to fertilization and ultimately to development of new individuals. The pathway begins with species-specific binding of sperm to eggs and ends a relatively short time later with fusion of a single sperm with each egg. Although this process has been investigated extensively, only recently have the molecular components of egg and sperm that participate in the mammalian fertilization pathway been identified. Some of these components may participate in gamete adhesion and exocytosis, whereas others may be involved in gamete fusion. Here we describe selected aspects of mammalian fertilization and address some of the latest experimental evidence that bears on this important area of research.     

Zea ribosomal repeat evolution and substitution patterns

Zea and Tripsacum nuclear ribosomal internal transcribed spacer (ITS) sequences were used to evaluate patterns of concerted evolution, rates of substitutions, patterns of methylation-induced deamination, and structural constraints of the ITS. ITS pseudogenes were identified by their phylogenetic position, differences in nucleotide composition, extensive deamination at ancestral methylation sites, and substitutions resulting in low-stability secondary RNA structures. Selection was important in shaping the kinds of polymorphisms and substitutions observed in the ITS. ITS substitution rates were significantly different among the Zea taxa. Deamination of cytosines at methylation sites was a potent mutation source, but selection appeared to maintain high methylation site density throughout the ribosomal repeat except for the gene promoter. Nucleotide divergence statistics identified selectively constrained regions at the 5' ends of the ITS1 and ITS2.      

Reproductive barriers between two sympatric beetle species specialized on different host plants

Knowledge on interspecific pre‐ and post‐zygotic isolation mechanisms provides insights into speciation patterns. Using crosses (F₁ and backcrosses) of two closely related flea beetles species, Altica fragariae and A. viridicyanea, specialized on different hosts in sympatry, we measured: (a) the type of reproductive isolation and (b) the inheritance mode of preference and host‐specific performance, using a joint‐scaling test. Each species preferred almost exclusively its host plant, creating strong prezygotic isolation between them, and suggesting that speciation may occur at least partly in sympatry. Reproductive isolation was intrinsic between females of A. fragariae and either A. viridicyanea or F₁ males, whereas the other crosses showed ecologically dependent reproductive isolation, suggesting ecological speciation. The genetic basis of preference and performance was at least partially independent, and several loci coded for preference, which limits the possibility of sympatric speciation. Hence, both ecological and intrinsic factors may contribute to speciation between these species.     

Mass ivermectin treatment for Onchocerciasis: Lack of evidence for collateral impact on transmission of Wuchereria bancrofti in areas of co-endemicity

There has long been interest in determining if mass ivermectin administration for onchocerciasis has 'unknowingly' interrupted lymphatic filariasis (LF) transmission where the endemicity of the two diseases' overlaps. We studied 11 communities in central Nigeria entomologically for LF by performing mosquito dissections on Anopheline LF vectors. Six of the communities studied were located within an onchocerciasis treatment zone, and five were located outside of that zone. Communities inside the treatment zone had been offered ivermectin treatment for two-five years, with a mean coverage of 81% of the eligible population (range 58–95%). We found 4.9% of mosquitoes were infected with any larval stage of W. bancrofti in the head or thorax in 362 dissections in the untreated villages compared to 4.7% infected in 549 dissections in the ivermectin treated villages (Mantel-Haenszel ChiSquare 0.02, P = 0.9). We concluded that ivermectin annual therapy for onchocerciasis has not interrupted transmission of Wuchereria bancrofti (the causative agent of LF in Nigeria).     

Isometric force development, isotonic shortening, and elasticity measurements from Ca(2+)-activated ventricular muscle of the guinea pig

Isometric tension and isotonic shortening were measured at constant levels of calcium activation of varying magnitude in mechanically disrupted EGTA-treated ventricular bundles from guinea pigs. The results were as follows: (a) The effect of creatine phosphate (CP) on peak tension and rate of shortening saturated at a CP concentration more than 10 mM; below that level tension was increased and shortening velocity decreased. We interpreted this to mean that CP above 10 mM was sufficient to buffer MgATP(2-) intracellularly. (b) The activated bundles exhibited an exponential stress-strain relationship and the series elastic properties did not vary appreciably with degree of activation or creatine phosphate level. (c) At a muscle length 20 percent beyond just taut, peak tension increased with Ca(2+) concentration over the range slightly below 10(-6) to slightly above 10(-4)M. (d) By releasing the muscle length-active tension curves were constructed. Force declined to 20 percent peak tension with a decrease in muscle length (after the recoil) of only 11 percent at 10(-4)M Ca(2+) and 6 percent at 4x10(-6)M Ca(2+). (e) The rate of shortening after a release was greater at lower loads. At identical loads (relative to maximum force at a given Ca(2+) level), velocity at a given time after the release was less at lower Ca(2+) concentrations; at 10 M(-5), velocity was 72 percent of that at 10(-4)M, and at 4x10(-6)M, active shortening was usually delayed and was 40 percent of the velocity at 10(-4) M. Thus, under the conditions of these experiments, both velocity and peak tension depend on the level of Ca(2+) activation over a similar range of Ca(2+) concentration.     

Life mode of in situ Conularia in a Middle Devonian epibole

Abstract: Exceptionally abundant specimens of Conularia aff. desiderata Hall occur in multiple marine obrution deposits, in a single sixth‐order parasequence composed of argillaceous and silty very fine sandstone, in the Otsego Member of the Mount Marion Formation (Middle Devonian, Givetian) in eastern New York State, USA. Associated fossils consist mostly of rhynchonelliform brachiopods but also include bivalve molluscs, orthoconic nautiloids, linguliform brachiopods and gastropods. Many of the brachiopods, bivalve molluscs and conulariids have been buried in situ. Conulariids buried in situ are oriented with their aperture facing obliquely upward and with their long axis inclined at up to 87 degree to bedding. Most specimens are solitary, but some occur in V‐like pairs or in radial clusters consisting of three specimens, with the component specimens being about equally long or (less frequently) substantially different in length. The compacted apical end of Conularia buried in situ generally rests upon argillaceous sandstone. With one possible exception, none of the examined specimens terminates in a schott (apical wall), and internal schotts appear to be absent. The apical ends of specimens in V‐like pairs and radial clusters show no direct evidence of interconnection of their periderms. The apical, middle or apertural region of some inclined specimens abuts or is in close lateral proximity to a recumbent conulariid or to one or more spiriferid brachiopods, some of which have been buried in their original life orientation. The azimuthal bearings of Conularia and nautiloid long axes and the directions in which conulariids open are nonrandom, with conulariids being preferentially aligned between 350 and 50 degree and with their apertural end facing north‐east, and nautiloids being preferentially aligned between 30 and 70 degree. Otsego Member Conularia were erect or semi‐erect, epifaunal or partially infaunal animals, the apical end of which rested upon very fine bottom sediment. The origin of V‐like pairs and radial clusters remains enigmatic, but it is probable that production of schotts was not a regular feature of this animal’s life history. Finally, conulariids and associated fauna were occasionally smothered by distal storm deposits, under the influence of relatively weak bottom currents.