From visit to emergence: Interactions between mycophagous Drosophilidae (Insecta, Diptera) and macroscopic fungi (Basidiomycota) and their patterns in ecological networks

ABSTRACT Ecological interactions are diverse, variable across space and time and not always well understood. The use of interaction network analysis has become a tool that promotes a deeper understanding on ecological and evolutionary processes. The interaction between insects and fungi is an interesting research model, helping to understand colonization dynamics and species specialization in spatially aggregated and ephemeral resources. Here, we describe the interactions between Drosophilidae species and the fungal basidiocarps in a subtropical forest in Brazil. Flies were collected when were visiting basidiocarps and then the basidiocarps themselves were also collected to obtain the emerging flies whose larvae fed on the fungi. We observed 31 species of drosophilids interacting with basidiocarps of 23 fungi species. An ecological network analysis was performed for the drosophilids breeding on basidiocarps and for those visiting them as adults. We found a specialized breeding network, with stronger interactions involving Hirtodrosophila and Auricularia and Zygothrica bilineata and a Marasmius species. Our results indicate the generalist habit of most Zygothrica species. The visitation network was highly specialized. Despite being well represented in the sampling, most Zygothrica species did not emerge from any fungal species. This study advances the knowledge on patterns of Drosophilid-fungi interactions and provides insights into their drivers.

The IRM cell adhesion molecules Hibris, Kin of irre and Roughest control egg morphology by modulating ovarian muscle contraction in Drosophila.

The Irre Cell Recognition Module (IRM) is an evolutionarily conserved group of transmembrane glycoproteins required for cell-cell recognition and adhesion in metazoan development. In Drosophila melanogaster ovaries, four members of this group - Roughest (Rst), Kin of irre (Kirre), Hibris (Hbs) and Sticks and stones (Sns) - play important roles in germ cell encapsulation and muscle sheath organization during early pupal stages, as well as in the progression to late oogenesis in the adult. Females carrying some of the mutant rst alleles are viable but sterile, and previous work from our laboratory had identified defects in the organization of the peritoneal and epithelial muscle sheaths of these mutants that could underlie their sterile phenotype. In this study, besides further characterizing the sterility phenotype associated with rst mutants, we investigated the role of the IRM molecules Rst, Kirre and Hbs in maintaining the functionality of the ovarian muscle sheaths. We found that knocking down any of the three genes in these structures, either individually or in double heterozygous combinations, not only decreases contraction frequency but also irregularly increases contraction amplitude. Furthermore, these alterations can significantly impact the morphology of eggs laid by IRM-depleted females demonstrating a hitherto unknown role of IRM molecules in egg morphogenesis.

Expression of Hbs, Kirre, and Rst during Drosophila ovarian development.

The Irre cell-recognition module (IRM) is a group of evolutionarily conserved and structurally related transmembrane glycoproteins of the immunoglobulin superfamily. In Drosophila melanogaster, it comprises the products of the genes roughest (rst; also known as irreC-rst), kin-of-irre (kirre; also known as duf), sticks-and-stones (sns), and hibris (hbs). In this model organism, the behavior of this group of proteins as a partly redundant functional unit mediating selective cell recognition was demonstrated in a variety of developmental contexts, but their possible involvement in ovarian development and oogenesis has not been investigated, notwithstanding the fact that some rst mutant alleles are also female sterile. Here, we show that IRM genes are dynamically and, to some extent, coordinately transcribed in both pupal and adult ovaries. Additionally, the spatial distribution of Hbs, Kirre, and Rst proteins indicates that they perform cooperative, although largely nonredundant, functions. Finally, phenotypical characterization of three different female sterile rst alleles uncovered two temporally separated and functionally distinct requirements for this locus in ovarian development: one in pupa, essential for the organization of peritoneal and epithelial sheaths that maintain the structural integrity of the adult organ and another, in mature ovarioles, needed for the progression of oogenesis beyond stage 10.

Transcriptional cross-regulation of Irre Cell Recognition Module (IRM) members in the Drosophila pupal retina.

Cell adhesion molecules play a central role in morphogenesis, as they mediate the complex range of interactions between different cell types that result in their arrangement in multicellular organs and tissues. How their coordinated dynamic expression in space and time - an essential requirement for their function - is regulated at the genomic and transcriptional levels constitutes an important, albeit still little understood question. The Irre Cell Recognition Module (IRM) is a highly conserved phylogenetically group of structurally related single pass transmembrane glycoproteins belonging to the immunoglobulin superfamily that in Drosophila melanogaster are encoded by the genes roughest (rst), kin-of-irre (kirre), sticks-and-stones (sns) and hibris (hbs). Their cooperative and often partly redundant action are crucial to major developmental processes such axonal pathfinding, myoblast fusion and patterning of the pupal retina. In this latter system rst and kirre display a tightly regulated complementary transcriptional pattern so that lowering rst mRNA levels leads to a concomitant increase in kirre mRNA concentration. Here we investigated whether other IRM components are similarly co-regulated and the extent changes in their mRNA levels affect each other as well as their collective function in retinal patterning. Our results demonstrate that silencing any of the four IRM genes in 24% APF retinae changes the levels all other group members although only kirre and hbs mRNA levels are increased. Furthermore, expression, in a rst null background, of truncated versions of rst cDNA in which the portion encoding the intracellular domain has been partially or completely removed not only can still induce changes in mRNA levels of other IRM members but also result in Kirre mislocalization. Taken together, our data point to the presence of a highly precise and fine-tuned control mechanism coordinating IRM expression that may be crucial to the functional redundancy shown by its components during the patterning of the pupal retina.

Diversity of Drosophilidae (Insecta, Diptera) in the Restinga forest of southern Brazil

Abstract Although members of Drosophilidae are frequently the topic of ecological studies in Brazil, few have explored Restinga or, until only recently, Pampa biome environments. This study proposes to describe the diversity and temporal variation of the Drosophilidae assemblage from a Restinga forest of Rio Grande do Sul, Brazil. We performed monthly collections from February 2013 to January 2014 using yeasted banana-baited traps. A total of 25,093 individuals of 46 species were sampled. Drosophila simulans and the D. willistoni subgroup were the dominant taxa; D. polymorpha, D. immigrans, D. paraguayensis and Zygothrica orbitalis were of intermediate abundance, and the other 40 species were rare. Based on sampling effort estimators, our collections were sufficient. Jaccard and Morisita indices evaluated using ANOSIM reveal little similarity in the composition of samples across months. Canonical correspondence analysis shows that the variables of maximum and minimum temperature are the main factors responsible for differentiation of the species composition of the assemblage throughout the year, whereby collections in the coldest periods (July, August and September) are those with a more differentiated composition. In these months, the dominance of D. simulans and the D. willistoni subgroup decreases while increased abundance of the D. tripunctata group (as D. paraguayensis) and Z. orbitalis occurs. In comparison to other studies carried out in environments in southernmost Brazil, we observed a similar pattern of fluctuation in abundance over the year, with a higher abundance of dominant species in warmer months and population sizes decreasing in colder months.