The worm’s eye view of community ecology

The study of parasites in the context of community level organization, either as parasites embedded within host communities, or as parasite communities themselves, is now quite prevalent in parasitology and ecology today. However, this was not always the case. In terms of publications, there was almost no consideration of parasite interactions at the community level for most of the first half of the last century. Papers in The Journal of Parasitology by Clark Read (1951) and John Holmes (1961) were the defining contributions to the beginning of the field, and the ideas elaborated by these two parasitologists still inspire current debates on parasite community structure today. There are several probable explanations for why investigation of parasite communities was not popular during the early part of the century. Most likely, it was related to funding sources, and the strong biomedical rubric that has guided parasitological studies for most of the last century. The intensity of focus on treatment and control of parasites of medical and veterinary importance often resulted in indifference to the natural and evolutionary histories of the parasites. Fortunately, this situation has changed, and there has been an exponential growth of ideas based on ecological and evolutionary theory, especially since the beginning of this century. We are now entering into areas of inquiry that the early investigators probably never dreamed of. For example, it was only in 1997 that “Food webs: A plea for parasites” by Marcogliese and Cone (1997)made eloquent arguments for why parasites should be included in studies of food webs and ecosystems. This paper was an explicit call to action for community-minded parasitologists, and it ignited a huge transformation in the way ecologists and evolutionary biologists began to look at parasites in nature. Studies on the roles of parasites in food webs, an area that was almost totally ignored by ecologists for eight decades, are now fairly common (Sukhdeo, 2012)

Host Centrality in Food Web Networks Determines Parasite Diversity

Background: Parasites significantly alter topological metrics describing food web structure, yet few studies have explored the relationship between food web topology and parasite diversity. Methods/Principal Findings: This study uses quantitative metrics describing network structure to investigate the relationship between the topology of the host food web and parasite diversity. Food webs were constructed for four restored brackish marshes that vary in species diversity, time post restoration and levels of parasitism. Our results show that the topology of the food web in each brackish marsh is highly nested, with clusters of generalists forming a distinct modular structure. The most consistent predictors of parasite diversity within a host were: trophic generality, and eigenvector centrality. These metrics indicate that parasites preferentially colonise host species that are highly connected, and within modules of tightly interacting species in the food web network. Conclusions/Significance: These results suggest that highly connected free-living species within the food web may represent stable trophic relationships that allow for the persistence of complex parasite life cycles. Our data demonstrate that the structure of host food webs can have a significant effect on the establishment of parasites, and on the potential fo

β-Catenin Signaling Increases during Melanoma Progression and Promotes Tumor Cell Survival and Chemoresistance

Beta-catenin plays an important role in embryogenesis and carcinogenesis by controlling either cadherin-mediated cell adhesion or transcriptional activation of target gene expression. In many types of cancers nuclear translocation of beta-catenin has been observed. Our data indicate that during melanoma progression an increased dependency on the transcriptional function of beta-catenin takes place. Blockade of beta-catenin in metastatic melanoma cell lines efficiently induces apoptosis, inhibits proliferation, migration and invasion in monolayer and 3-dimensional skin reconstructs and decreases chemoresistance. In addition, subcutaneous melanoma growth in SCID mice was almost completely inhibited by an inducible beta-catenin knockdown. In contrast, the survival of benign melanocytes and primary melanoma cell lines was less affected by beta-catenin depletion. However, enhanced expression of beta-catenin in primary melanoma cell lines increased invasive capacity in vitro and tumor growth in the SCID mouse model. These data suggest that beta-catenin is an essential survival factor for metastatic melanoma cells, whereas it is dispensable for the survival of benign melanocytes and primary, non-invasive melanoma cells. Furthermore, beta-catenin increases tumorigenicity of primary melanoma cell lines. The differential requirements for beta-catenin signaling in aggressive melanoma versus benign melanocytic cells make beta-catenin a possible new target in melanoma therapy