Heterophylly in Ranunculus flabellaris: The Effect of Abscisic Acid on Leaf Anatomy

Ranunculus flabellaris Raf., the yellow water crowfoot, exhibitsstriking heterophylly between submerged and terrestrial leaves.Leaves produced under water are highly divided with numerousnarrow lobes and deep sinuses, whereas terrestrial leaves havefew broad lobes and shallow sinuses. When plants are submergedin a 25 µM solution of ABA, the typical transition fromterrestrial to submerged leaves is completely suppressed and,instead, terrestrial-like leaves are produced. Image analysistechniques show that, in addition to this modification of leafmorphology, leaves produced under ABA treatment possess surfaceand internal features characteristic of terrestrial leaf anatomy.This study provides evidence that the environmental factorsthat influence the morphological and anatomical expression ofheterophylly may act through endogenous ABA. Ranunculus flabellaris, yellow water crowfoot, ABA, heterophylly, leaf anatomy     

Whole-body mechanics and kinematics of terrestrial locomotion in the Elegant-crested Tinamou Eudromia elegans

Whereas humans and certain birds experience an abrupt change in locomotor dynamics when shifting from walks to runs, a smooth walk–run transition characterizes many ground-dwelling birds. This study defines the biomechanical distinction between walks and runs in the Elegant-crested Tinamou Eudromia elegans using ground reaction forces. Three birds were filmed at 250 Hz from a lateral view as they moved over a force plate built into a trackway. Centre of mass mechanics and kinematic variables were analysed in 81 steady-speed trials that represented a speed range from 0.66 to 2.78 m/s. E. elegans undergoes two speed-related changes in locomotor mechanics. The first is a shift from walking strides that utilize vaulting mechanics to low-speed runs that exhibit bouncing mechanics; this transition occurs at Froude numbers between 0.4 and 0.6. Such low-speed runs exhibit duty factors exceeding 0.5 and, hence, lack an aerial phase between steps. The second transition, from grounded running to aerial running, occurs when duty factors decrease below 0.5. Grounded running in birds may enhance vision by stabilizing visual stimuli over the retina. The eventual incorporation of an aerial phase during running enables increased locomotor speeds primarily through longer stride lengths.     

Life history plasticity of Nemoura trispinosa (Plecoptera: Nemouridae) along a permanent-temporary water habitat gradient

1. The life history of the small herbivorous stonefly Nemoura trispinosa Claassen was studied in a variety of small springs in southern Ontario, Canada. Nymphs generally were able to tolerate a wide range of environmental conditions and were found in 78% of habitats sampled, although population densities differed markedly. 2. Life-cycle patterns varied from a univoltine, slow seasonal type to a univoltine, fast seasonal type with extended egg development. In one, highly stable, spring the life cycle was semivoltine. Inter-year variation was studied for 5 years in one spring and was found to be low relative to among-spring variation. 3. Differences in the life history traits of N. trispinosa populations from our spring series were most probably an expression of phenotypic plasticity rather than of genetic differentiation. 4. Maximum annual water temperature was the factor most influential on nymphal growth rate (non-linear relationship), whereas range in generation time was related to the degree of habitat permanence.     

Mini-exon Gene Sequences Define Six Groups within the Genus Crithidia

ABSTRACT. To develop molecular markers for lower trypanosmatids, we have examined the mini-exon gene repeats of 17 isolates that were classified as Crithidia by traditional methods. Representative repeats were amplified by polymerase chain reaction and the amplification products were cloned and used as hybridization probes against genomic DNA. Six hybridization groups of Crithidia were defined on the basis of the DNA blotting experiments. The three endosymbiont-bearing species ( C. deanei, C. desouzai and C. oncopelti ) and C. acanthocephali each belonged to single-member hybridization groups, while the C. fasciculata group contained additional named and undesignated species. The Crithidia lucilae thermophila probe hybridized to multiple undesignated isolates. The DNA sequence of the cloned products revealed that the specificity of the hybridization probes was due to substantial differences in the intron and the non-transcribed spacer regions. These data indicate substantial heterogeneity within the mini-exon gene locus of the taxon Crithidia .     

Isolation of polymorphic microsatellite markers in the sub‐Saharan tree,Acacia (Senegalia) mellifera (Fabaceae: Mimosoideae)

We isolated 11 polymorphic microsatellite markers from Acacia mellifera, a savannah woodland tree in sub‐Saharan Africa and southern Arabia. The loci were screened for polymorphism using 48 Kenyan individuals. Allelic diversity ranged from three to 19 per locus and the polymorphic information content varied from 0.287 to 0.893. These loci will be useful in studies of genetic structure, gene flow and breeding systems.     

Influence of simulated climate change and eutrophication on three‐spined stickleback populations: a large scale mesocosm experiment

1. Shallow lakes and their ectothermic inhabitants are particularly vulnerable to the effects of climatic warming. These impacts are likely to depend on nutrient loading, especially if the combination of warming and eutrophication leads to severe hypoxia. 2. To investigate effects of realistic warming and nutrient loading on a fish species with high tolerance of warming and hypoxia, we observed population changes and timing of reproduction of three‐spined sticklebacks in 24 outdoor shallow freshwater ecosystems with combinations of temperature (ambient and ambient +4 °C) and three nutrient treatments over 16 months. 3. Warming reduced stickleback population biomass by 60% (population size by 76%) and nutrient‐addition reduced biomass by about 80% (population size 95%). Nutrients and warming together resulted in extinction of the stickleback populations. These losses were mainly attributed to the increased likelihood of severe hypoxia in heated and nutrient‐addition mesocosms. 4. Warming of nutrient‐rich waters can thus have dire consequences for freshwater ectotherm populations. The loss even of a hardy fish suggests a precarious future for many less tolerant species in such eutrophic systems under current climate change predictions.