The Contractile Vacuole in Amoeba proteus: Temperature Effects

The influence of temperature on the various aspects of the contractile vacuole cycle of Amoeba proteus has been established. In the upper temperature range (20, 25 and 30 C) an increase in temperature results in shorter vacuolar cycles with greater systolic (final) volumes. The systole is rapid and always complete. At 35 C the vacuole shows the effect of heat stress, cycles are irregular in volume and duration with only partial systoles. In the lower temperature range (15, 10 and 5 C), a new phenomenon has been observed, the plateau. Instead of undergoing systole, after reaching a certain critical volume the vacuole abruptly ceases to grow in size and remains in a state of pause for a well defined period of time, ending at a comparatively slow but complete systole. The duration of this plateau as well as its inception and termination seem quite precisely controlled. Its effect, a decrease in the fluid output by the vacuole, is such as to adjust vacuolar output to near constant Q₁₀ kinetics over our temperature range. This is correlated with a single straight line fit in an Arrhenius plot. Available data do not permit a complete explanation of the nature of the plateau. It could represent a steady state between 2 opposing phenomena: active fluid influx into the vacuole and osmotic losses from the vacuole into the relatively hypertonic cytoplasm.     

Aboveground herbivory affects indirect defences of brassicaceous plants against the root feeder Delia radicum Linnaeus: laboratory and field evidence

1. Belowground herbivory has recently been shown to disrupt the host location behaviour of aboveground parasitoids and thereby impact plants indirect defences. Reverse interactions, on the other hand, have received little attention so far. 2. Lab and field studies were conducted to examine whether the presence of the leaf herbivore Pieris brassicae Linnaeus on brassicaceous plants influences the response of Trybliographa rapae Westwood, a specialist parasitoid of the root feeder Delia radicum Linnaeus. 3. The present results show that the attraction of the parasitoid towards host‐infested plants disappeared when these plants were also infested by P. brassicae. This absence of attraction was observed both when the complete odour blend or only undamaged leaves from damaged plants were offered, emphasising the role of systemically induced volatiles for host location in T. rapae. 4. Furthermore, the field study revealed that parasitism levels dropped from 30% on root‐infested plants to 4% on double‐infested plants. 5. The present study is the first to confirm that reduced attraction to host‐infested plants as a result of simultaneous attack by below‐ and aboveground herbivores translates into lower levels of parasitism in the field.     

Molecular and chemical characters to evaluate species status of two cuckoo bumblebees: Bombus barbutellus and Bombus maxillosus (Hymenoptera,Apidae, Bombini)

Many methods, based on morphological, molecular or chemical characters, have been used to address the question of species taxonomic status. Integrative taxonomy aims to define stronger supported taxonomic hypotheses by considering complementary datasets from different characters. By following an integrative approach, the present study includes molecular, chemical and morphological criteria to establish the taxonomic status of two rare and doubtful cuckoo bumblebee taxa: Bombus (Psithyrus) barbutellus and Bombus (Psithyrus) maxillosus. These two sympatric taxa are discriminated by few morphological criteria (mainly wing darkness and hair length). We used these morphological character diagnoses to establish an a priori status of our samples (23 specimens). We developed a combined molecular dataset from one nuclear gene, elongation factor 1α (EF‐1α), and one mitochondrial gene, cytochrome c oxidase subunit I (COI), spanning 1623 bp, and a chemical dataset of sexual marking pheromones (73 compounds). The molecular data were subjected to maximum‐likelihood and Bayesian phylogenetic inference under partitioned model and maximum parsimony. The chemical data were analysed by clustering and the two‐group k‐means method to test divergences between the two species. The resulting phylogenetic trees show no consistent divergence between the two taxa. Moreover, we found no divergence in the sexual marking pheromones in the clustering and two‐group k‐means analyses. These converging results support the conspecificity of both taxa. Nonetheless, our determinations using the traditional morphological criteria separated our samples into two taxa. We conclude that the morphological criteria seem to relate to intraspecific variations: B. maxillosus is regarded as a syn.n. of B. barbutellus.     

Isolation and identification of 21 microsatellite loci in the Copper redhorse (Moxostoma hubbsi; Catostomidae) and their variability in other catostomids

Catostomidae represent an important family of freshwater fishes mainly distributed in North America, but also found in Eurasia. This paper describes the development of microsatellite DNA markers for a highly threatened member of this family, the Copper redhorse (Moxostoma hubbsi), as well as cross‐catostomids amplifications. 168 tetra‐nucleotide loci were screened to develop 21 polymorphic markers, with an average number of 8.5 alleles per locus and observed heterozygosity ranging between 0.52 and 1.00. Successful amplification was obtained for 12 other members of the family at between seven to 19 loci, with between two to 18 loci being polymorphic per species.     

The functional significance of aperture form in gastropods

Aperture form of marine prosobranch gastropods has evolved under the influence of a number of different selective forces, including: generation of shell form; protection from predation; accommodation of the foot during clamping behavior: and accommodation of water currents in and out of the mantle cavity. Aperture form correlates positively with foot shape in most gastropods and foot shape, in turn, correlates moderately well with substrate preference. Almost all gastropods that have non-round apertures elongate the aperture parallel to the foot so that water currenth tend to flow anteriorly to posteriorly. Fresh-water pulmonates have responded to somewhat different stresses. They exhibit clamping behavior and thus show correspondence between foot shape and aperture shape. They show less apertural strengthening as crab (or crayfish) predation is less of a factor and presumably because calcium carbonate is less available. They also lack anterior-posterior apertural elongation due to the absence of water currents through their mantle cavity. Due to the absence of mantle cavity water currents and clamping behavior, terrestrial gastropods do not show the apertural modifications associated with these two factors. In addition. few adaptations of apertural form are present to resist predation. Instead, many of the apertural modifications of terrestrial pulmonates seem to be concer-ned with the problems of water loss during estivation.