RESUMEN

Food chain length provides key information on the flow of nutrients and energy in ecosystems. Variation in food chain length has primarily been explained by environmental drivers such as ecosystem size and productivity. Most insights are obtained from theory or aquatic systems, but the importance of these drivers remains largely untested in terrestrial systems. We exploited red wood ant nests markedly differing in size as natural experiments to quantify the drivers of trophic structure and food chain length of their symbiont arthropod communities. Using stable isotopes, we explored the variation in the trophic positions of four symbiont species with the trophic position of the top predator as a proxy for food chain length of the symbiont community. Nest size did not affect food chain length, nor trophic distance between the symbionts. Instead, food chain length and the trophic positions of the symbionts were strongly affected by the host's foraging decisions. When the host diet shifted from predominantly herbivorous to more predacious, the trophic position of the symbionts and food chain length strongly increased. We show for the first time that a food web can be structured by biotic interactions with an engineering species rather than by abiotic environmental variables.

Asunto(s)

RESUMEN

BACKGROUND: Host range is a fundamental trait to understand the ecological and evolutionary dynamics of symbionts. Increasing host specificity is expected to be accompanied with specialization in different symbiont traits. We tested this specificity-specialization association in a large group of 16 ant-associated silverfish species by linking their level of host specificity to their degree of behavioural integration into the colony and to their accuracy of chemically imitating the host's recognition system, i.e. the cuticular hydrocarbon (CHC) profile. RESULTS: As expected, facultative associates and host generalists (targeting multiple unrelated ants) tend to avoid the host, whereas host-specialists (typically restricted to Messor ants) were bolder, approached the host and allowed inspection. Generalists and host specialists regularly followed a host worker, unlike the other silverfish. Host aggression was extremely high toward non-ant-associated silverfish and modest to low in ant-associated groups. Surprisingly, the degree of chemical deception was not linked to host specificity as most silverfish, including facultative ant associates, imitated the host's CHC profile. Messor specialists retained the same CHC profile as the host after moulting, in contrast to a host generalist, suggesting an active production of the cues (chemical mimicry). Host generalist and facultative associates flexibly copied the highly different CHC profiles of alternative host species, pointing at passive acquisition (chemical camouflage) of the host's odour. CONCLUSIONS: Overall, we found that behaviour that seems to facilitate the integration in the host colony was more pronounced in host specialist silverfish. Chemical deception, however, was employed by all ant-associated species, irrespective of their degree of host specificity.

RESUMEN

BACKGROUND: Species interactions may affect spatial dynamics when the movement of one species is determined by the presence of another one. The most direct species-dependence of dispersal is vectored, usually cross-kingdom, movement of immobile parasites, diseases or seeds by mobile animals. Joint movements of species should, however, not be vectored by definition, as even mobile species are predicted to move together when they are tightly connected in symbiont communities. METHODS: We studied concerted movements in a diverse and heterogeneous community of arthropods (myrmecophiles) associated with red wood ants. We questioned whether joint-movement strategies eventually determine and speed-up community succession. RESULTS: We recorded an astonishingly high number of obligate myrmecophiles outside red wood ant nests. They preferentially co-moved with the host ants as the highest densities were found in locations with the highest density of foraging red wood ants, such as along the network of ant trails. These observations suggest that myrmecophiles resort to the host to move away from the nest, and this to a much higher extent than hitherto anticipated. Interestingly, functional groups of symbionts displayed different dispersal kernels, with predatory myrmecophiles moving more frequently and further from the nest than detritivorous myrmecophiles. We discovered that myrmecophile diversity was lower in newly founded nests than in mature red wood ant nests. Most myrmecophiles, however, were able to colonize new nests fast suggesting that the heterogeneity in mobility does not affect community assembly. CONCLUSIONS: We show that co-movement is not restricted to tight parasitic, or cross-kingdom interactions. Movement in social insect symbiont communities may be heterogeneous and functional group-dependent, but clearly affected by host movement. Ultimately, this co-movement leads to directional movement and allows a fast colonisation of new patches, but not in a predictable way. This study highlights the importance of spatial dynamics of local and regional networks in symbiont metacommunities, of which those of symbionts of social insects are prime examples.

RESUMEN

Indirect interactions occur when a species affects another species by altering the density (density-mediated interactions) or influencing traits (trait-mediated interactions) of a third species. We studied variation in these two types of indirect interactions in a network of red wood ants and symbiotic arthropods living in their nests. We tested whether the ant workers indirectly affected survival of a symbiotic prey species (Cyphoderus albinus) by changing the density and/or traits of three symbiotic predators, i.e., Mastigusa arietina, Thyreosthenius biovatus and Stenus aterrimus, provoking, respectively, low, medium and high ant aggression. An ant nest is highly heterogeneous in ant worker density and the number of aggressive interactions towards symbionts increases with worker density. We, therefore, hypothesized that varying ant density could indirectly impact prey-predator interactions of the associated symbiont community. Ants caused trait-mediated indirect effects in all three prey-predator interactions, by affecting the prey capture rate of the symbiotic predators at different worker densities. Prey capture rate of the highly and moderately aggressed spider predators M. arietina and T. biovatus decreased with ant density, whereas the prey capture rate of the weakly aggressed beetle predator S. aterrimus increased. Ants also induced density-mediated indirect interactions as high worker densities decreased the survival rate of the two predatory spider species. These results demonstrate for the first time that a host can indirectly mediate the trophic interactions between associated symbionts. In addition, we show that a single host can induce opposing indirect effects depending on its degree of aggression towards the symbionts.

Asunto(s)

RESUMEN

BACKGROUND: There is a paucity of treatment options for bipolar depression. The use of triiodothyronine (T3) has been suggested as adjunctive treatment. METHODS: A search on Medline, Limo and ScienceDirect was performed using the search terms bipolar disorder, bipolar depression, treatment resistant, treatment refractory, thyroid hormones, triiodothyronine, T3, acceleration and augmentation. RESULTS: We retrieved three open studies, one comparative study, two double blind and one retrospective chart review. The three open studies observed improvement in respectively 56%, 75% and 79% of patients, the retrospective chart review noted improvement in 89% of cases and the mirror design showed improvement in 66%. In the comparative study T3 performed significantly better than placebo. The only randomized double blind study could not prove any substantial difference between T3 and placebo. LIMITATIONS: Available studies are scarce and flawed. All have (very) low number of subjects: overall, only 353 subjects and only 194 of which in prospective trials. In only two of the prospective trials bipolar patients were analyzed separately. Comparing the studies is hampered by a high variability in assessment tools, baseline medication and degree of treatment-resistance. CONCLUSIONS: The few available studies are small and flawed. They do show promising results. We found many clues suggesting that T3 could augment and accelerate treatment response not only with antidepressants, but also with lithium and perhaps with other treatment options, that it might protect against rapid cycling bipolar disorder, as well as against relapse during the first few years of treatment.

Asunto(s)

RESUMEN

INTRODUCTION: The treatment of pseudomyxoma peritonei (PMPs) and appendiceal mucocele (AM) has changed radically. To assess the contribution of preoperative imaging to the treatment strategy and choice of approach, a surgeon and a radiologist different from the initial radiologist examined the files of all patients treated for PMP or AM in four facilities in one district from January 1, 1996, through December 31, 2008. PATIENTS AND METHODS: The study included 27 patients (20 men and seven women, mean age: 63+/-13 years). Eleven patients had an intact AM, seven synchronous PMP (malignant appendiceal lesion in two of seven), six metachronous PMP (five with peritoneal mucinous carcinomatosis and one with diffuse peritoneal adenomucinosis) and three a ruptured AM but not PMP. The incidence of mucin-secreting tumors observed (27 cases in 12 years in a region of 500 000 inhabitants) corresponds to a prevalence of approximately five cases per year per million inhabitants. Acute clinical pictures (7/27) were significantly more frequent for the malignant forms (5/7) (p<0,02). RESULTS AND DISCUSSION: The overall sensitivity of computed tomography (CT) for all the criteria studied was 93%. The predictive value for AM rupture of visualization of thick calcifications was 100%. On the other hand, rupture never occurred when the CT showed an AM under pressure, with thin walls and septa. The predictive value for PMP of "scalloping" was 100%. The diagnostic accuracy of the initial reading was 25/27 for the imaging overall and 25/25 for the CT. Preoperative visualization of the exact size of the intact AM or of diagnostic information about ruptured AM and PMP helped to select an appropriate approach in 25 of 27 cases.

Asunto(s)

Asunto(s)

Asunto(s)