Challenges of metamorphosis in invertebrate hosts: maintaining parasite resistance across life‐history stages

1. Insects lack the acquired immune system of vertebrates, but there is some evidence that insect immunity can be primed against an encountered pathogen to mitigate the intensity of future infections within a life stage. 2. Many invertebrates have multiple life‐history stages separated by complete metamorphosis, but different life stages can often be infected by the same pathogens, and the potential loss of immune priming during metamorphosis could therefore have detrimental effects on the host. Evidence that invertebrate immune priming can persist through metamorphosis is still missing, and consequently it is unclear how host–parasite interactions change across different life‐history stages in the context of infection history. 3. By experimentally manipulating the infection history of the flour beetle Tribolium confusum, we show that intestinal gregarine parasite infections during the larval stage reduced parasite load in adults, demonstrating that a host‐controlled mechanism for parasite resistance can persist through complete metamorphosis in insects. 4. Infections reduced larval developmental rates and increased host mortality but only during the crucial metamorphic stage, indicating that parasites impact multiple life stages. In general, our results demonstrate that invertebrates can show surprisingly robust immune priming despite dramatic physiological changes and protect hosts across completely different life‐history stages.     

Adaptation to host plants may prevent rapid insect responses to climate change

We must consider the role of multitrophic interactions when examining species' responses to climate change. Many plant species, particularly trees, are limited in their ability to shift their geographic ranges quickly under climate change. Consequently, for herbivorous insects, geographic mosaics of host plant specialization could prohibit range shifts and adaptation when insects become separated from suitable host plants. In this study, we examined larval growth and survival of an oak specialist butterfly (Erynnis propertius) on different oaks (Quercus spp.) that occur across its range to determine if individuals can switch host plants if they move into new areas under climate change. Individuals from Oregon and northern California, USA that feed on Q. garryana and Q. kelloggii in the field experienced increased mortality on Q. agrifolia, a southern species with low nutrient content. In contrast, populations from southern California that normally feed on Q. agrifolia performed well on Q. agrifolia and Q. garryana and poorly on the northern, high elevation Q. kelloggii. Therefore, colonization of southern E. propertius in higher elevations and some northern locales may be prohibited under climate change but latitudinal shifts to Q. garryana may be possible. Where shifts are precluded due to maladaptation to hosts, populations may not accrue warm‐adapted genotypes. Our study suggests that, when interacting species experience asynchronous range shifts, historical local adaptation may preclude populations from colonizing new locales under climate change.     

A feeling for the micro-organism: structure on a small scale. Biofilms on plant roots

Biofilms are structured communities of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface; they have clinical, industrial and environmental impacts. Biofilms that are established by bacteria on plants are found on the surfaces of roots, leaves, seeds and internal vascular tissues where the microbes live in commensal, mutualistic or parasitic/pathogenic associations with their host. The study of the structure of plant-associated biofilms has been considerably helped by the development of techniques using fluorescent markers coupled with confocal scanning laser microscopy as well as scanning electron microscopy. We review several of these techniques as well as some of the research that has dealt with plant-associated biofilms. Our investigations focus on biofilm formation in the early stages of the Rhizobium –legume symbiosis, in which Gram-negative rhizobia provide fixed nitrogen to a host legume, and in return, the legume provides carbon-containing molecules. Because root colonization is an important early step in the establishment of the nitrogen-fixing symbiosis, we looked at Sinorhizobium meliloti attachment and biofilm establishment on the roots of its legume hosts, Medicago sativa L. and Melilotus alba Desr. We also examined biofilm formation by Rhizobium leguminosarum bv. viciae on the roots of Arabidopsis thaliana (L.) Heynh., a non-legume and non-host. Our ultimate goal is to characterize the rhizobial genes involved in aggregation and attachment to roots because several of these appear to be shared in biofilm formation and rhizobial entry of legume root cells.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 79–88.     

Immunochemical Characteristics of Isoperoxidases from Two Environmentally-induced Flax Genotrophs (Linum usitatissimum L.)

The homology between the acidic isoperoxidases from two environmentally-inducedflax genotrophs, L and S, was examined with antisera raisedagainst purified isozymes from S stem tissue. Peroxidases S1,S2 and S4 were found to be immunologically indistinguishablefrom their counterparts L1, L2 and L4 based on results fromimmunodiffusion, immunoinhibition and immunoprecipitation experiments.Corresponding isozymes from S and L, despite displaying differencesin apparent molecular weight, were shown to have identical plvalues. These results support our view that post-translationalmodification of the carbohydrate moiety of the isoperoxidasesfrom L and S is responsible for their differences on polyacrylamidegel electrophoresis. The affinity of the antisera toward threehorseradish peroxidases was also studied and the presence ofthree antigenically distinct groups of peroxidases in plantsis suggested. Key words: Flax peroxidase, horseradish peroxidase, isoperoxidases, homology     

Flagellar Membrane and Paraxial Rod Proteins of Leishmania: Characterization Employing Monoclonal Antibodies

Flagella-specific proteins of Leishmania have been identified employing the monoclonal antibody technique. Six monoclonal antibodies recognized 3 different proteins. A doublet of protein of Mr 69,000 and 74,000 Da identified by monoclonal antibodies F-3, F-4 and F-6 is continuously distributed along the flagellum by immunofluorescence. Immunocytochemical electron microscopic studies localize these molecules to the paraxial rod of the flagellum. A single protein of Mr 13,200 Da is recognized by monoclonal antibodies F-1, F-2 and F-5. The distribution of the Mr 13,200 protein appears irregular, occurring in localized patches along the length of the flagellum, especially at the flagellar tip. Immunocytochemical electron microscopic experiments show that the Mr 13,200 molecule is associated with the membrane of the flagellum. Indirect immunofluorescence experiments demonstrated these monoclonal antibodies cross-reacted with members of the Kinetoplastida family ( Endotrypanum, Trypanosoma, Leishmania ) suggesting that these molecules may be evolutionarily conserved.     

High Frequency Responsiveness in Rodents at the Level of the Inferior Colliculus

PREVIOUS work on the cochlear microphonic (CM) response of three species of rodents showed a second peak of sensitivity coinciding in frequency with the ultrasound emitted in each species¹. It was indicated that the microphonic response did not necessarily represent hearing, but Sewell's² finding that Apodemus can hear the ultrasonic cries of its young makes an investigation into the neural response to ultrasound seem necessary. The gross inferior collicular (IC) response of the same three species, Apodemus sylvaticus Linnaeus, Clethrionomys glareolus Schreber and Meriones shawi Rozet, has now been studied together with the CM response of the same individuals.     

Endogenous Sugar Levels and Their Effects on Root Formation and Petiole Yellowing of Detached Mustard Cotyledons

Detached cotyledons of Sinapis alba rooted readily in water in petri dishes in the light. The addition of (6 × 10^?2M) galactose, mannose or 2-deoxy-D-glucose to the culture medium proved toxic to cotyledon growth. Of the other sugars tested that were not toxic, sucrose was the most inhibitory to root formation and increased petiolar yellowing to the greatest extent. Glucose was more inhibitory than fructose which in turn increased petiolar yellowing more than methyl-D-glucose. Sucrose, glucose, or fructose at 6 × 10^?2M in the culture medium gave rise to very substantial increases in the cotyledon petiole of reducing sugar and starch with smaller increases in sucrose. Methyl-D-glucose had much less effect on internal sugar levels. It was found that the higher the internal level of glucose the more rapid the rate and final extent of petiolar yellowing. In general, the degree of petiolar yellowing was inversely related to the ability of the cotyledon to root. Methyl-D-glucose differed from the other sugars in that it delayed and reduced root formation but had very little effect on petiolar yellowing.     

Larval aestivation and direct development as alternative strategies in the speckled wood butterfly, Pararge aegeria, in Sweden

ABSTRACT.

• 1 Sweden has two disjunct populations of the speckled wood butterfly, Pararge aegeria L. The southern population has two generations per year but the central Swedish population is univoltine. When rearing larvae from central Sweden under normal photoperiodic conditions but at temperatures slightly above the ambient, 42% of the larvae developed directly and produced a second generation of adults the same summer. The egg—larval development time of the directly developing individuals was about 40 days, whereas that of the individuals developing along the univoltine pathway was about 100 days.
• 2 Larvae of the central Swedish population normally aestivate during part of the summer even though abundant food is available. In the closely related Lasiommata petropolitana F., which is the only Swedish satyrid that overwinters in the pupal stage besides P.aegeria, larvae do not aestivate, indicating that there does not seem to be any obligatory association between pupal hibernation and larval aestivation.
• 3 Development rates of aestivating and directly developing P.aegeria are equal up to the third larval instar. During the third and fourth instars, however, the development rate of aestivating individuals is retarded and females also have an additional fifth instar.
• 4 Since the central Swedish P.aegeria have the capacity to develop directly, and the southern Swedish ones have the capacity to aestivate, the evidence indicates that the outcome of the cost/benefit balance of univoltine versus bivoltine development differs between the two areas.

     

Conjugation Involving Dividing Cells of Tetrahymena thermophila

Feulgen-stained preparations of mixtures of starved Tetrahymena thermophila cells of complementary mating types have revealed an atypical form of conjugation involving cells which have completed the nuclear events of cell division, but have not undergone cytokinesis. Both micronuclei in the dividing cells are induced to undergo meiosis, but in 21 of 23 cases, the anterior micronucleus was activated 1st, suggesting that the meiotic inducer is synthesized near the mating junction and diffuses posteriad. Despite the induction of two micronuclei, “triad” conjugants appear to regulate nuclear events so as to produce a normal outcome.