Abstracts (first author)

Talk 

Variation in disease epidemics across colonies

Author(s): Schmid-Hempel P, Schmid-Hempel R

Summary:

Colonies of social insects are paradigmatic study subjects for how diseases spread in social groups. Infections are typically acquired naturally from an external source and passed on to the colony members whilst the colony grows and develops through its normal cycle. Here, we report on the spread of an infectious pathogen, the trypanosome Crithidia bombi inside colonies of its host, Bombus terrestris. We show how extensive variation leads to very different outcomes across groups; furthermore, we demonstrate how the parasite population changes genetically as the epidemics unfolds. The data will be embedded in a more general conceptual framework.



Abstracts (coauthor)

Summary:

The red flour beetle, Tribolium castaneum, secretes quinones that control the microbial flora in the surrounding environment. These secretions act as an external immune defense that provides protection against pathogens. At high concentrations, however, these secretions are harmful to the host itself, and selection may thus have optimized the level of expression under natural conditions. Here we show that the expression of external immunity responded to selection during experimental evolution within a few generations. At the same time, one component of internal immune defense (phenoloxidase activity) was compromised in beetles selected for either high or low external defenses. Protection against a natural pathogen was lacking in flour obtained from beetle lines selected for low amounts of secretions. Altogether, this suggests that external and internal immune defenses work together efficiently under natural conditions, while every manipulation on the side of external immune defense comes with costs to the internal immune defense.

Summary:

Social living offers many benefits, but comes with a greater risk of infection, especially when the groups are genetically homogenous, as in some social insects. Surprisingly, the first social insect genome, the honeybee, revealed a reduced immune system. Honeybees, like many other highly social insects mate multiply, producing a genetically diverse and complex colony for parasites to invade. Bumblebees, however, mate singly thereby producing dense colonies of highly related sisters. The bumblebee Bombus terrestris is commonly infected with a trypanosome gut parasite Crithidia bombi. Different genotypes of bumblebees are susceptible to different clones of parasite, but the factors that produce this complex pattern of host-parasite matching remain elusive. We took a transcriptomic approach to understand how bumblebees respond to this parasite and whether host-parasite matching is driven by gene expression differences. We find exceptionally high variation in gene expression upon infection despite the low genetic diversity among sisters. This variation among individuals may be especially important in producing an immunologically diverse population, buffering the colony from parasite spread. We also find that different host genotypes down-regulate the same genes but up-regulate distinct suites of genes upon infection. This pattern suggests a core shared signal of infection, but a unique suite of up-regulated genes. We also find that clones of this parasite alter expression of their hosts differently. Highly infectious clones down regulate important immunological genes such as antimicrobial peptides but colonies differ in the scale of this effect. Host-parasite specificity may be generated by these specific patterns of expression. We discuss how parasites may manipulate host immune responses for their own gain and how variation among workers may contribute to the sustainability of highly related insect societies in a parasite rich world.

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
Close