Multiple environmental stressors confine the ecological niche of the rotifer Cephalodella acidophila

Summary

• 1 The planktonic food web in extremely acidic mining lakes is restricted to a few species that are either acidophilic or acidotolerant. Common metazoans inhabiting acidic mining lakes with a pH below 3 include rotifers in the genera Cephalodella and Elosa.
• 2 The life history response of Cephalodella acidophila to three environmental key factors, pH (2, 3.5, 5.0 and 7.0), temperature (10, 17.5 and 25 °C) and food concentration (10 000, 35 000 and 50 000 algal cells per mL), was investigated in a full factorial design using life‐table experiments.
• 3 The effect of each of the three environmental variables investigated on the rotifer life cycle parameters (life span, fecundity and population growth rate) differed. C. acidophila is a stenoecious species with a pH optimum in the range 3–4 and a comparably high food threshold. Combining the laboratory results with field data, we conclude that C. acidophila is severely growth limited in its natural habitat. However, low pH alone is not harmful as long as temperatures are moderate to warm and food is abundant.
• 4 The population of C. acidophila in the field is maintained mainly due to release from competitors and predators.

     

Pollination by ants: consequences of the quantitative effects on a mutualistic system

Summary We have analysed the importance of worker ants (Proformica longiseta, Formicidae) as pollinators of a mass-flowering woody plant (Hormathophylla spinosa, Cruciferae) in the high-mountain area of the Sierra Nevada (southern Spain). We have quantified the abundance and foraging behavior of P. longiseta in comparison with winged flower visitors. We have also examined, by means of selective exclusion experiments, the role of ants as true pollinators, comparing them with the winged flower visitors. A total of 39 species belonging to 18 families visited the flowers of H. spinosa. All the visitors were winged insects, except P. longiseta, a species which alone made up more than 80% of the total number of insects found on the flowers. All pollinators of H. spinosa had similar foraging patterns, with 98% of total movements made between flowers within the same plant. Ants always made contact with the plant reproductive organs when foraging for nectar, and transferred large numbers of pollen grains. However, pollen exposed to ants for brief periods exhibited reduced percentage of germination. P. longiseta is both the most abundant and spatio-temporally predictable flower visitor of H. spinosa. These characteristics, weighted by their flower visitation rate, make worker ants the pollinator that maintains the strongest mutualistic interaction with H. spinosa. The exclusion experiments show that workers behave as true pollinators, since they contribute to increase the number of viable seeds produced by H. spinosa. The key factor of this interaction is mainly the great density of workers throughout the flowering period. In short, the H. spinosa-P. longiseta mutualistic interaction mainly depends on its high probability of occurrence.     

Making red squirrels more visible: the use of baited visual counts to monitor populations

Understanding changes in the distribution and abundance of the red squirrel Sciurus vulgaris in Europe, as a result of the spread of the introduced North American grey squirrel Sciurus carolinensis, is vital to planning and implementing red squirrel conservation measures. We studied the effectiveness of a variation on a common method of monitoring squirrels, standardised visual counts that made use of a diffuse baiting approach to increase their detectability. Significantly more sightings of squirrels occurred on baited than on unbaited visual transect lines in trials with the assistance of volunteers, and we recommend the use of baits in future studies.     

Cl‐ homeostasis in includer and excluder citrus rootstocks: transport mechanisms and identification of candidate genes

To reveal specific Cl^‐ transport activities in the symplastic pathway, uptake, long‐distance transport and distribution of Cl^‐ have been investigated in the citrus rootstocks Carrizo citrange (CC, Cl^‐ includer) and Cleopatra mandarin (CM, Cl^‐ excluder). Using an external concentration of 4.5 mm Cl^‐, both species actively transported Cl^‐ to levels that exceeded the critical requirement concentration by one and two orders of magnitude in the excluder and the includer rootstocks, respectively. Both CC and CM modulated Cl^‐ influx according to the availability of the nutrient as uptake capacity was induced by Cl^‐ starvation, but inhibited after Cl^‐ resupply. Net Cl^‐ uptake was higher in the includer CC, an observation that correlated with a lower root‐to‐shoot transport capacity in the excluder CM. The patterns of tissue Cl^‐ accumulation indicated that chloride exclusion in the salt‐tolerant rootstock CM was caused by a reduced net Cl^‐ loading into the root xylem. Genes CcCCC1, CcSLAH1 and CcICln1 putatively involved in the regulation of chloride transport were isolated and their expression analysed in response to both changes in the nutritional status of Cl^‐ and salt stress. The previously uncharacterized ICln gene exhibited a strong repression to Cl^‐ application in the excluder rootstock, suggesting a role in regulating Cl^‐ homeostasis in plants.     

Cascading trophic effects in pampean shallow lakes: results of a mesocosm experiment using two coexisting fish species with different feeding strategies

Planktivorous fish, both visual predators and filter feeders, enhance eutrophication processes in lakes. In pampean shallow lakes several planktivorous species may coexist but often two species dominate: silverside (Odontesthes bonariensis), a visual planktivorous fish when young adult, and sabalito (Cyphocharax voga), an omnivorous filter feeder. To assess the relative strength of the cascading trophic effects of the two species, a mesocosm experiment was conducted using different proportions of both species as treatments. Differences were found in water transparency, phytoplankton biomass, crustacean abundance, individual size and biomass. Our results suggest that visual predators intensify eutrophication effects more strongly than filter feeders do.     

A 5.8 kb deletion removing the entire MNX1 gene in a Norwegian family with Currarino syndrome

Currarino syndrome (CS) is a clinically variable disorder characterized by anorectal, sacral and presacral anomalies. It is associated with loss-of-function mutations in the motor neuron and pancreas homeobox 1 (MNX1) gene. Inheritance is autosomal dominant, expression variable and penetrance incomplete. We describe a Norwegian family with typical CS in which a heterozygous deletion removes the entire MNX1 gene but no other known genes. We also report MNX1 mutations in three other Norwegian families and confirm that the GCC₁₂ repeat (c.373_375[12]) is a normal allelic variant. This work underscores the importance of dosage analysis of MNX1 when Sanger sequencing is negative.     

Survival strategies of Dalbulus maidis during maize off‐season in Brazil

Despite the importance of Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) as a vector of maize‐stunting pathogens, it is not understood how this leafhopper survives the maize off‐season in regions where overwintering hosts do not occur. We investigated migration and the use of alternate hosts as possible survival mechanisms for D. maidis during maize off‐season in Brazil. Dalbulus maidis populations were monitored with yellow sticky cards for 16–29 months in Anastácio (Mato Grosso do Sul State), in two farms with perennial pastures (Pasture1 and Pasture2), where maize had not been planted for >5 years, in a subsistence farm >20 km distant, where maize was annually planted (spring) (Maize1), and in Piracicaba (São Paulo State), where maize was grown year round (Maize2). RAPD‐PCR analysis of leafhoppers sampled on maize in two plots (Maize1 and Pasture1) at 15–20 and 110–120 days after germination was performed. Dalbulus maidis was trapped in the maize plots of all areas, but not in weedy or woody vegetation adjacent to the plots. Higher numbers were trapped throughout the year in Piracicaba, where maize was continuously grown under irrigation, and in the subsistence farm of Anastácio, where volunteer maize plants were available for long periods in the maize off‐season. In Anastácio farms, some population peaks were recorded in the absence of maize from midwinter to early spring, especially after soil plowing. RAPD‐PCR analysis showed that D. maidis populations sampled were genetically similar. Our data suggest that D. maidis uses a mixed strategy to survive the over‐season period in Brazil, in which part of the population overwinters locally on volunteer maize plants or nearby irrigated maize crops, whereas the other individuals migrate to colonize new maize crops in distant areas or regions. We hypothesize that immigrant D. maidis uses the contrast between plowed and vegetated soil as a visual cue for locating new maize crops.