In this study we analyze the participation of the PKC1-MAPK cell integrity pathway in cellular responses to oxidative stress in Saccharomyces cerevisiae. Evidence is presented demonstrating that only Pkc1 and the upstream elements of the cell integrity pathway are essential for cell survival upon treatment with two oxidizing agents, diamide and hydrogen peroxide. Mtl1 is characterized for the first time as a cell-wall sensor of oxidative stress. We also show that the actin cytoskeleton is a cellular target for oxidative stress. Both diamide and hydrogen peroxide provoke a marked depolarization of the actin cytoskeleton, being Mtl1, Rom2 and Pkc1 functions all required to restore the correct actin organization. Diamide induces the formation of disulfide bonds in newly secreted cell-wall proteins. This mainly provokes structural changes in the cell outer layer, which activate the PKC1-MAPK pathway and hence the protein kinase Slt2. Our results led us to the conclusion that Pkc1 activity is required to overcome the effects of oxidative stress by: (i) enhancing the machinery required to repair the altered cell wall and (ii) restoring actin cytoskeleton polarity by promoting actin cable formation.

The TOR (target of rapamycin) pathway controls cell growth in response to nutrient availability in eukaryotic cells. Inactivation of TOR function by rapamycin or nutrient exhaustion is accompanied by triggering various cellular mechanisms aimed at overcoming the nutrient stress. Here we report that in Saccharomyces cerevisiae the protein kinase C (PKC)-mediated mitogen-activated protein kinase pathway is regulated by TOR function because upon specific Tor1 and Tor2 inhibition by rapamycin, Mpk1 is activated rapidly in a process mediated by Sit4 and Tap42. Osmotic stabilization of the plasma membrane prevents both Mpk1 activation by rapamycin and the growth defect that occurs upon the simultaneous absence of Tor1 and Mpk1 function, suggesting that, at least partially, TOR inhibition is sensed by the PKC pathway at the cell envelope. This process involves activation of cell surface sensors, Rom2, and downstream elements of the mitogenactivated protein kinase cascade. Rapamycin also induces depolarization of the actin cytoskeleton through the TOR proteins, Sit4 and Tap42, in an osmotically suppressible manner. Finally, we show that entry into stationary phase, a physiological situation of nutrient depletion, also leads to the activation of the PKC pathway, and we provide further evidence demonstrating that Mpk1 is essential for viability once cells enter G 0 .

An important pattern in host-parasite assemblages is a higher intensity of parasites in juveniles than in adults, but the reasons for these differences remain obscure. Three non-mutually exclusive hypotheses have been proposed: (1) heavily parasitized juveniles die before being recruited into the adult population ('selection' hypothesis); (2) the development of an acquired immunity by the host in front of the parasite reduces the intensity of the parasite in adult hosts ('immunity' hypothesis); and (3) differences in behavior makes adults less exposed to the parasite than juveniles ('vector exposure' hypothesis). Having rejected the 'vector exposure' hypothesis in a previous study, here we tested the 'selection' and 'immunity' hypotheses in feral pigeons (Columba livia) infected by the blood parasite Haemoproteus columbae. In agreement with the 'selection' hypothesis, young (but not adult) pigeons that were highly parasitized had a lower probability of surviving until adulthood, independent of their body condition. However, selection was not strong enough to account for the observed differences in parasite intensity between age-classes, and after selection parasite intensity of survivors still remained 85% higher in juveniles than in adults. In contrast, the 'immunity' hypothesis offered a greater explanatory power. The intensity of blood parasites in young pigeons, but not in adults, decreased over time so dramatically that by the time they had become adults their intensities were indistinguishable from that typically seen in adults. Therefore, while selection against highly parasitized juveniles can contribute to some extent to a reduction in parasitism seen in the adult population, age-specific blood parasitism in feral pigeons is best explained as a transitory phase just before the host develops an effective immune response.

Prevalence and intensity of blood parasites are known to vary in space within a same species, yet the causes underlying such variation are poorly known. Theoretically, blood parasites variation can be attributed to differences to exposure to parasite vectors and/or to differences in host susceptibility. Here, we show that prevalence of Haemoproteus columbae in feral pigeons Columba livia varied among five near‐by populations (range 15%‐100%), paralleled by variation in the abundance of its main vector, the louse flies Pseudolynchia canariensis. Geographic variation in intensity of blood parasites did not covary with abundance of vectors. Within populations, older individuals had a higher probability of being parasitized than younger ones, whereas younger birds, when infected, suffered higher intensities. Furthermore, we found no evidence of sex‐related differences neither in prevalence nor in intensity of blood parasite infections. To demonstrate that geographical variation in prevalence was actually due to differences in vector exposure, we conducted two experiments based on translocation of unparasitized pigeons from a vector‐free area to an area where both the parasite and vector were abundant. With the first experiment, we demonstrated that unparasitized pigeons were not resistant to the parasite because when transmission was possible pigeons became parasitized in a few months. With the second experiment, in which half of the pigeons were prevented from contacts with the vector, we ruled out the posibility that pigeons we considered as unparasitized would have suffered from latent infections. Therefore, both observational and experimental evidence supports the view that vector abundance is the major factor influencing the spatial variation in prevalence of H. columbae in pigeons.

Eighty-five Eurasian badgers, Meles meles (Linnaeus, 1758), from four mainland biogeographic Spanish areas were analysed for helminths. Seventeen helminth species were found: Brachylaima sp., Euparyphium melis and Euryhelmis squamula (Trematoda), Atriotaenia incisa and Mesocestoides sp. (Cestoda) and Aelurostrongylus pridhami, Angiostrongylus vasorum, Aonchotheca putorii, Crenosoma melesi, Mastophorus muris, Molineus patens, Pearsonema plica, Physaloptera sibirica, Strongyloides sp., Trichinella sp., Uncinaria criniformis and Vigisospirura potekhina hugoti (Nematoda). In the Mediterranean area, Aonchotheca putorii, M. patens, Strongyloides sp., and U. criniformis were more prevalent in the occidental part, whereas Atriotaenia incisa and Mesocestoides sp. cestodes showed higher values on the continental slope. Metastrongyloid species (Aelurostrongylus pridhami, Angiostrongylus vasorum and Crenosoma melesi) were only detected in the occidental Mediterranean area. In contrast, spirurid species (Mastophorus muris and Vigisospirura potekhina hugoti) were almost restricted to the continental Mediterranean area. Helminthological differences between areas may result from the badger diet, abiotic factors and biocenosis present in each biogeographic area.

Anthropogenic drivers and global warming are altering the occurrence of infectious marine diseases, some of which produce mass mortalities with considerable ecosystemic and economic costs. The Mediterranean Sea is considered a laboratory to examine global processes, and the fan mussel Pinna nobilis a sentinel species within it. Since September 2016, fan mussels suffer a die-off, very likely provoked by the protozoan Haplosporidium pinnae. Population dynamic surveys, rescue programmes, larvae collector installation and protection of infected adults from predators, have increased knowledge about the factors conditioning the spread of the die-off; previous model simulations indicate that water temperature and salinity seem to be related to the manifestation of the disease, which at the end are strongly influenced by climate change and anthropogenic actions. The absence of natural recruitment implies that fan mussel populations are not recovering, but the survival of populations living in paralic environments provides an opportunity to study the disease and its conditioning factors. The present situation is proposed as an example of what is to come in the global context of climate change and poses several questions: are we the witnesses of the potential extinction of a sentinel species? Can we avoid the potential extinction of this species by applying active measures, and which measures will be more effective? How many other more overlooked species might experience a massive and unnoticed die-off before it is too late to implement any preservation action? For the extinction of community structure species will provoke unpredicted ecological cascade effects with global implications.

This paper presents the first extensive data on the helminth community of the wood mouse Apodemus sylvaticus in a coastal sand dune area in Portugal. The 557 hosts analysed in this study were trapped seasonally between autumn 2002 and summer 2005 across 6 habitat types. Twelve helminth species were detected among which, Taenia parva larvae, Angiostrongylus dujardini, Heligmosomoides polygyrus, Syphacia stroma and S. frederici constitute the component species, accounting for 98.7% of all worms. H. polygyrus was the most prevalent helminth parasite. Species richness varied according to habitat and season. The highest species richness was found in sand dunes during winter whereas the lowest was detected along lake margins also during the winter. Some differences in prevalence and mean intensity values were found in relation to year (T. parva larvae and H. polygyrus), habitat (A. dujardini), season (T. parva larvae, H. polygyrus, A. dujardini and S. stroma) and host sex (T. parva larvae and S. stroma). These differences are discussed both in view of the host's biology and habitat characteristics.

Ultrastructure of spermiogenesis and the main characters of the mature spermatozoon of Troglotrema acutum are described by means of transmission electron microscopy. Specimens were obtained from the nasolacrimal sinuses of an American mink (Mustela vison). Spermiogenesis in T. acutum follows the general pattern of digeneans. The zone of differentiation is a conical-shaped area bordered by cortical microtubules and delimited at its base by a ring of arched membranes. This area contains 2 centrioles associated with striated rootlets and an intercentriolar body between them. The centrioles develop 2 free flagella that grow ortogonally to the median cytoplasmic process. The posterior flagellar rotation and proximodistal fusion of the free flagella with the median cytoplasmic process originate the spermatozoon. The mature spermatozoon of T. acutum is characterized by the presence of 2 axonemes of different lengths presenting the 9+'1' trepaxonematan pattern, 2 bundles of parallel cortical microtubules, 2 mitochondria, a nucleus, and granules of glycogen. These ultrastructural characters are compared with other digenean species previously studied and the importance of different spermatological features is discussed.