EFFECTS OF A HAEMATOPHAGOUS MITE ON THE BARN SWALLOW (HIRUNDO RUSTICA): A TEST OF THE HAMILTON AND ZUK HYPOTHESIS

I tested three assumptions of the Hamilton and Zuk hypothesis (1982), which suggests that the extravagant male plumage of many bird species allows females to choose mates that are resistant to the parasites exploiting the host population at a given time. By choosing such males as mates, females will rear offspring carrying the genes for resistance. I tested three necessary conditions for the Hamilton and Zuk model: (1) whether parasites affect the fitness of their hosts; (2) whether there is heritable variation in parasite resistance, and (3) whether the expression of the sexual ornament varies with parasite burden. The haematophagous mite Ornithonyssus bursa (Macronyssidae, Gamasida) sucks blood from their Barn Swallow (Hirundo rustica) hosts. Experimental manipulation of mite loads and partial cross-fostering experiments on Barn Swallows, where half of the nestlings in the brood were exchanged with nestlings from another nest, shows that parasite burdens and origin, but not rearing conditions, of Bam Swallow nestlings, affected their adult tarsus length and maximum body weight shortly before fledging. Mite loads of adult Barn Swallows at spring arrival were more similar to mite loads of their own offspring, whether reared in their own or in foster nests inoculated with mites, than to loads of foster offspring. Parent Barn Swallows with long tail ornaments had offspring with smaller mite loads in the partial cross-fostering experiments. The amount of increase in male tail ornaments from one year to another was negatively related to experimentally manipulated mite loads of Barn Swallow nests during the preceding breeding season. In conclusion, the three assumptions of the hypothesis were supported by the experimental tests.     

Conservative resource utilization in the common blue butterfly–evidence for low costs of accepting absent host plants?

We studied host plant preference of the common blue butterfly, Polyommatus icarus , and larval performance on two different host plants, Oxytropis campestris and Lotus corniculatus . The study species is a small lycaenid butterfly believed to be relatively sedentary. The study populations originated from two different and widely separated geographical areas. In one area both hosts are naturally occurring, with O. campestris being most abundant at the study sites, in the other area only one of the host plants, L. corniculatus , is present. There was no difference in oviposition preference or larval performance between populations from the two different areas. Hence, P. icarus from sites dominated by O. campestris has not evolved a higher preference for or better performance on this host plant. More surprisingly, P. icarus from the area were O. campestris is completely absent has retained not only good larval performance on this host plant but also high female preference for it. This conservatism at a large geographical scale is seen even though there seems to be genetic variation present in both populations, at least for preference but perhaps also for performance. We suggest that such lack of variation in resource utilization between populations may be evidence for weak selection against "preferences" for plants that are rare or absent. A combination of other constraining factors may also contribute to some degree, especially stepping-stone gene flow between populations.     

Tumor necrosis factor-alpha converting enzyme is processed by proprotein-convertases to its mature form which is degraded upon phorbol ester stimulation.

Tumor necrosis factor-alpha converting enzyme (TACE or ADAM17) is a member of the ADAM (a disintegrin and metalloproteinase) family of type I membrane proteins and mediates the ectodomain shedding of various membrane-anchored signaling and adhesion proteins. TACE is synthesized as an inactive zymogen, which is subsequently proteolytically processed to the catalytically active form. We have identified the proprotein-convertases PC7 and furin to be involved in maturation of TACE. This maturation is negatively influenced by the phorbol ester phorbol-12-myristate-13-acetate (PMA), which decreases the cellular amount of the mature form of TACE in PMA-treated HEK293 and SH-SY5Y cells. Furthermore, we found that stimulation of protein kinase C or protein kinase A signaling pathways did not influence long-term degradation of mature TACE. Interestingly, PMA treatment of furin-deficient LoVo cells did not affect the degradation of mature TACE. By examination of furin reconstituted LoVo cells we were able to exclude the possibility that PMA modulates furin activity. Moreover, the PMA dependent decrease of the mature enzyme form is specific for TACE, as the amount of mature ADAM10 was unaffected in PMA-treated HEK293 and SH-SY5Y cells. Our results indicate that the activation of TACE by the proprotein-convertases PC7 and furin is very similar to the maturation of ADAM10 although there is a significant difference in the cellular stability of the mature enzyme forms after phorbol ester treatment.     

Long-distance migration: evolution and determinants

Long‐distance migration has evolved in many organisms moving through different media and using various modes of locomotion and transport. Migration continues to evolve or become suppressed as shown by ongoing dynamic and rapid changes of migration patterns. This great evolutionary flexibility may seem surprising for such a complex attribute as migration. Even if migration in most cases has evolved basically as a strategy to maximise fitness in a seasonal environment, its occurrence and extent depend on a multitude of factors. We give a brief overview of different factors (e.g. physical, geographical, historical, ecological) likely to facilitate and/or constrain the evolution of long‐distance migration and discuss how they are likely to affect migration. The basic driving forces for migration are ecological and biogeographic factors like seasonality, spatiotemporal distributions of resources, habitats, predation and competition. The benefit of increased resource availability will be balanced by costs associated with the migratory process in terms of time (incl. losses of prior occupancy advantages), energy and mortality (incl. increased exposure to parasites). Furthermore, migration requires genetic instructions (allowing substantial room for learning in some of the traits) about timing, duration and distance of migration as well as about behavioural and physiological adaptations (fuelling, organ flexibility, locomotion, use of environmental transport etc) and control of orientation and navigation. To what degree these costs and requirements put constraints on migration often depends on body size according to different scaling relationships. From this exposé it is clear that research on migration warrants a multitude of techniques and approaches for a complete as possible understanding of a very complex evolutionary syndrome. In addition, we also present examples of migratory distances in a variety of taxons. In recent years new techniques, especially satellite radio telemetry, provide new information of unprecedented accuracy about journeys of individual animals, allowing re‐evaluation of migration, locomotion and navigation theories.     

Spatial and Temporal Distribution of Song in the Yellowhammer Emberiza citrinella

The temporal and spatial distribution of song was studied in a population of yellowhammers Emberiza citrinella. Song was most frequent during the breeding season, and within the breeding season during the fertile period of both first, second, and replacement clutches. Song activity peaked at sunrise and sunset. During the fertile period most singing took place in the central parts of the territory. Song post heights peaked during the fertile period, and more song posts lacked foliage at that time. Intrusions by male conspecifics peaked in the fertile period and in territories where males sang relatively little. Song activity and mate guarding were strongly positively correlated. Song volume was loud and song was thus apparently used in long-distance communication. These observations are in accordance with a male deterrence hypothesis, suggesting that males sing to deter neighbouring males from trespassing during the fertile period of their mate. A female attraction hypothesis, suggesting that males sing to attract neighbouring females and thereby obtain extra-pair copulations, and a female reproduction hypothesis, suggesting that males sing to start the female reproductive cycle, were partly supported by observations.     

Behavioral responses of a sex-role reversed pipefish to a gradient of perceived predation risk

Conspicuous behaviors such as courtship and mating often makeanimals susceptible to predation. When perceiving themselvesat an elevated level of risk, animals frequently reduce conspicuousbehaviors in tradeoff for a decrease in probability of beingpreyed upon. In the present study, we used two experiments toexamine the effect of perceived predation risk from cod (Gadusmorhud) on nonreproductive and reproductive behaviors in thesex-role reversed pipefish (Syngnathus typhle). In the firstexperiment, no differences due to predation risk were detectedin the nonreproductive behaviors of either males or females.In the second experiment, predation risk had significant effectson reproductive behaviors. Pipefish were allowed to court andcopulate at four different predation levels. We created predationlevels differing in perceived predation risk by controllingthe number of sensory modes through which pipefish could detectthe presence of a cod. As predation risk increased, pipefishcopulated and courted less frequently, swam alone (displayedand searched for conspecifics) less often, and waited longerbefore commencing courtship. These changes in behavior minimizedthe amount of time spent above the eelgrass and presumably reducedconspicuousness to visual predators. Pipefish also copulatedafter a smaller amount of courtship as predation risk increased,indicating that they may trade information concerning mate qualityfor a reduction in predation risk. No differences were foundin any response variable between males and females. The roleof operational sex ratios and intersexual competition in determiningwhich sex assumes greater costs in mate acquisition is questioned.     

In Situ Microdialysis for Monitoring of Extracellular Glutathione Levels in Normal, Ischemic and Post-Ischemic Skeletal Muscle

Microdialysis probes were inserted into the tibialis anterior muscle and into the femoral vein of anaesthetised Sprague-Dawley rats for monitoring of reduced (GSH) and oxidized (GSSG) extracellular glutathione. The dialysates were analysed using HPLC. The levels of GSH and GSSG were high immediately after implantation in the skeletal muscle and declined to steady state levels after 90 minutes into the same range as that found in the venous dialysate. Total ischemia was induced two hours after implantation of the dialysis probe after steady state levels had been reached. The extracellular levels of GSH increased during total ischemia and had doubled at the end of the ischemic period compared to preischemic values. During the following initial 30 minutes of reperfusion the levels increased further to four-fold the preischemic levels. The levels of GSSG also increased (100%) during the initial 30 minutes of reperfusion. The extracellular GSH levels remained elevated for 1 hour of reperfusion, but the GSSG levels returned to preischemic levels. The results indicate that intermittent hypoxia or anoxia in muscle tissue through hypoperfusion or ischemia decreases intracellular GSH stores by leakage, reducing the intracellular antioxidative capacity and increasing the risk for oxidative reperfusion injury upon final normalization of tissue blood supply.     

Characterization of a newin vitro model for studies of reepithelialization in human partial thickness wounds

Summary Reepithelialization of artificial partial thickness wounds made in biopsies of human skin was determined after 3, 5, or 7 d of incubation, submerged or elevated to the air-liquid interface. The biopsies were reepithelialized within 5–7 d, with a more complete epidermal healing in wounds exposed to air. Both types of wounds showed similar time-course in deposition of basement membrane components, as detected by immunofluorescence labeling. Laminin and collagen type VII were deposited underneath the migrating tips, whereas collagen type IV was detected after reepithelialization. Markers of terminal differentiation showed a pattern close to normal in the air-liquid incubated wounds after reepithelialization. Involucrin was detected in the suprabasal regions of the migrating epidermis and thereafter in the upper half of neo-epidermis in the air-liquid incubated wound. Filaggrin could not be detected in the submerged wounds at any time during healing, whereas wounds exposed to air showed a well-differentiated epidermis by Day 7. Tritiated thymidine-incorporation indicated proliferation of epidermal and dermal cells during reepithelialization and a maintained viability, as shown by cultivation of endothelial- and fibroblast-like cells obtained from the dermis 7 d after wounding. Reepithelialization in this humanin vitro model is supported by a matrix close to normal with the possibility of extracellular influences and cell-cell interactions and, in addition, the technique is simple and reproducible. Therefore, we suggest this model for studies of regeneration in culture and as a complement toin vivo studies on epidermal healing.