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.     

Quantitative Trait Loci (QTL) Study Identifies Novel Genomic Regions Associated to Chiari-Like Malformation in Griffon Bruxellois Dogs

Chiari-like malformation (CM) is a developmental abnormality of the craniocervical junction that is common in the Griffon Bruxellois (GB) breed with an estimated prevalence of 65%. This disease is characterized by overcrowding of the neural parenchyma at the craniocervical junction and disturbance of cerebrospinal fluid (CSF) flow. The most common clinical sign is pain either as a direct consequence of CM or neuropathic pain as a consequence of secondary syringomyelia. The etiology of CM remains unknown but genetic factors play an important role. To investigate the genetic complexity of the disease, a quantitative trait locus (QTL) approach was adopted. A total of 14 quantitative skull and atlas measurements were taken and were tested for association to CM. Six traits were found to be associated to CM and were subjected to a whole-genome association study using the Illumina canine high density bead chip in 74 GB dogs (50 affected and 24 controls). Linear and mixed regression analyses identified associated single nucleotide polymorphisms (SNPs) on 5 Canis Familiaris Autosomes (CFAs): CFA2, CFA9, CFA12, CFA14 and CFA24. A reconstructed haplotype of 0.53 Mb on CFA2 strongly associated to the height of the cranial fossa (diameter F) and an haplotype of 2.5 Mb on CFA14 associated to both the height of the rostral part of the caudal cranial fossa (AE) and the height of the brain (FG) were significantly associated to CM after 10 000 permutations strengthening their candidacy for this disease (P = 0.0421, P = 0.0094 respectively). The CFA2 QTL harbours the Sall-1 gene which is an excellent candidate since its orthologue in humans is mutated in Townes-Brocks syndrome which has previously been associated to Chiari malformation I. Our study demonstrates the implication of multiple traits in the etiology of CM and has successfully identified two new QTL associated to CM and a potential candidate gene.     

Recovery patterns in electroencephalographic global field power during maximal isometric force production

In previous work, cortical activity decreased with fatigue following novel movements or small muscle group actions. These muscle actions, however, do not appear related to the cortical activity seen with biologically relevant and highly trained movement patterns (i.e., ingrained patterns). The cortical recovery response to ingrained patterns-and how it differs with altered load, speed, or volume - is unknown. The purpose of this balanced, within-group study was to investigate differences in cortical activity 24 hours after physically distinct variations of a highly trained squat exercise (n = 7, minimum 4 years resistance training experience). Four resistance protocols were chosen: rate of force development (PWR, 6 × 3 squat jumps at 30% of 1 repetition maximum [1RM]); magnitude of force development (FOR, 6 × 3 squat at 95% of 1RM); volume of force development (VOL, 6 × 10 squat at 80% of their 1RM); and control (CTRL, 6 sets unracking an empty bar). Twenty-four hours later, subjects performed a peak isometric squat while electroencephalographic and biochemical markers of exertion and fatigue were obtained. Global field power detected the quantity of activity superficial to motor regions. Waveforms of activity throughout the isometric squats were obtained and grand averages calculated to produce quantitative depictions of cortical activity. Significance was P ≤ 0.05. Peak isometric squat force was not statistically different 24 hours postexercise (Force [N]: PWR: 2828.79 ± 461.17; FOR: 2887.64 ± 453.09; VOL: 2910.17 ± 625.81; CTRL 2768.53 ± 374.85). Subjects produced similar and characteristic cortical activity patterns during isometric squats despite varying indices of fatigue. Differences were observed based upon the use or nonuse of aerobic endurance exercise in their training program. Patterns of activity in data seem to have emerged based on differences in training preference. Global Field Power (uV) during the isometric squat for PWR was 26.98 ± 14.64; FOR 24.06 ± 19.05; VOL 23.05 ± 13.37; and CTRL 15.78 ± 8.11. Previous research suggests that cortical activity decreases with physical activity; however, despite substantial endocrine, perceptual, and biomechanical differences between protocols, cortical activity was not decreased below control during the performance of a maximal isometric squat 24 hours after various exercise protocols.     

Validity of the Myotest® in measuring force and power production in the squat and bench press

The purpose of this study was to verify the concurrent validity of a bar-mounted Myotest? instrument in measuring the force and power production in the squat and bench press exercises when compared to the gold standard of a computerized linear transducer and force platform system. Fifty-four men (bench press: 39-171 kg; squat: 75-221 kg) and 43 women (bench press: 18-80 kg; squat: 30-115 kg) (age range 18-30 years) performed a 1 repetition maximum (1RM) strength test in bench press and squat exercises. Power testing consisted of the jump squat and the bench throw at 30% of each subject's 1RM. During each measurement, both the Myotest? instrument and the Celesco linear transducer of the directly interfaced BMS system (Ballistic Measurement System [BMS] Innervations Inc, Fitness Technology force plate, Skye, South Australia, Australia) were mounted to the weight bar. A strong, positive correlation (r) between the Myotest and BMS systems and a high correlation of determination (R2) was demonstrated for bench throw force (r = 0.95, p < 0.05) (R2 = 0.92); bench throw power (r = 0.96, p < 0.05) (R2 = 0.93); squat jump force (r = 0.98, p < 0.05) (R2 = 0.97); and squat jump power (r = 0.91, p < 0.05) (R2 = 0.82). In conclusion, when fixed on the bar in the vertical axis, the Myotest is a valid field instrument for measuring force and power in commonly used exercise movements.     

Phylogenetic analysis of Micrathena and Chaetacis spiders (Araneae: Araneidae) reveals multiple origins of extreme sexual size dimorphism and long abdominal spines

The phylogenetic relationships amongst the New World spiny orb‐weaving spiders Micrathena and Chaetacis were assessed through parsimony and Bayesian analyses of morphological characters. A total of 146 characters was scored for ten outgroup taxa and 37 Micrathena and four Chaetacis species. The results indicate that Chaetacis nests within Micrathena and we propose Chaetacis as a junior synonym of Micrathena. Twelve subgeneric species groups of Micrathena are recognized and diagnosed. Species with extremely long spines evolved at least eight times in the genus and we suggest that this may be related to antipredator defences. Micrathena is primitively sexually monomorphic and extreme sexual size dimorphism has arisen at least six times in the genus. Most of these events are because of enlargement of the female in relation to the ancestral size, although in two cases sexual dimorphism was attained through male reduction, adding more data to the ‘giant females’ vs. ‘dwarf males’ controversy. The genus is probably of South American origin and has repeatedly invaded Central and North America. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 14–53.     

Gradients in stream fish assemblages across a Mediterranean landscape: contributions of environmental factors and spatial structure

1. Despite wide recognition that fish assemblages are influenced by factors operating over a range of spatial scales, little effort has been devoted to quantifying large‐scale variation and the multiscale dependencies of assemblage patterns and processes. This is particularly true for Mediterranean streams, where seasonally predictable drying‐up may lead to a strong association between assemblage attributes and large‐scale factors affecting the distribution of population sources and extinction likelihood. 2. The contribution of large‐scale factors to stream fish assemblage variation was quantified across a Mediterranean landscape, in south‐west Portugal. Fish abundance and species composition were estimated at 166 sites across third‐ to sixth‐order streams, in March–July 1998. Variance partitioning by redundancy analyses was used to analyse assemblage variation against three sets of predictor variables: environmental (catchment position, and geomorphic and hydrological factors), large‐scale spatial trends and neighbourhood effects. 3. Environmental variables and spatial trends accounted for 34.6% of the assemblage variation across the entire region, and for 36.6 and 57.8% within the two largest catchments (Mira and Seixe). Neighbourhood effects were analysed at the catchment scale, increasing the explained variation to 56.1% (Mira) and 70.7% (Seixe). 4. A prevailing environmental gradient was reflected in an increase in the abundance of all species and size‐classes in relation to catchment position, with more fish present in larger streams and in downstream reaches. Variables describing geomorphic and hydrological settings were less important in explaining assemblage variation. 5. Spatial trends always accounted for the smallest fraction of assemblage variation, and they were probably associated with historical barriers to fish dispersal. The strong neighbourhood effects may be related to spatially autocorrelated habitat conditions, but they are also a likely consequence of fish emigration/extinction and colonisation processes. 6. These results emphasise that a substantial proportion of fish assemblage variation in Mediterranean streams may be explained by large‐scale factors, irrespective of microhabitats and local biotic interactions. It is suggested that this pattern results to a large extent from the seasonal drying‐up, with the summer shortage of surface water limiting fish occurrence in headwaters, and consequently the key core areas for fish concentrating in larger streams and tributaries adjacent to large streams because of neighbourhood effects.     

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.     

Susceptibility to visceral leishmaniasis in the domestic dog is associated with MHC class II polymorphism

Zoonotic visceral leishmaniasis (VL) is a disease of dogs, humans and other animals caused by the intracellular macrophage parasite Leishmania infantum. We examined the relationship between DLA class II alleles ( DRB1, DQA1, DQB1) and the course of infection in a cohort of Brazilian mongrel dogs exposed to natural L. infantum infection. DLA alleles were typed by sequence-based typing. DLA-DRB1 genotype was significantly associated with levels of anti- Leishmania IgG and parasite status assessed by PCR. Dogs with DLA-DRB1*01502 had higher levels of specific IgG and an increased risk of being parasite positive compared with dogs without this allele, controlling for other alleles and significant variables. No significant associations were seen for DLA-DQA1 or DLA-DQB1 alleles. These results suggest that the DLA-DRB1 locus plays a role in determining susceptibility to canine VL. As the domestic dog is the main reservoir for human infection, the identification of genetic factors influencing canine resistance or susceptibility to VL may provide insights into the immunology and potential control through vaccination of VL.