Marine Ökologie

Global changes in a pipefish trematode system

PhD student Susanne Landis, PI Olivia Roth

Global change may result in local coevolutionary hot and cold spots that disrupt species interaction and evolutionary stable strategies. Close species interactions like the arms-race of hosts and parasites may in particular be affected by environmental variation. I want to investigate how global change will alter specific host - parasite interactions. As first step we simulated a summer heat wave to investigate how a changing environment affects the interaction between the broad-nosed pipefish (Syngnathus typhle) as a host and its digenean trematode parasite (Cryptocotyle lingua). In a fully reciprocal laboratory infection experiment, pipefish from three different coastal locations were exposed to sympatric and allopatric trematode cercariae. In order to examine whether an extreme climatic event disrupts patterns of locally adapted host-parasite combinations we measured the parasite’s transmission success as well as the host’s adaptive and innate immune defence under control and heat wave conditions. Independent of temperature, sympatric cercariae were always more successful than allopatric ones, indicating that parasites are locally adapted to their hosts.

Hosts suffered from heat stress as suggested by fewer cells of the adaptive immune system (lymphocytes) compared to the same groups that were kept at 18°C.  However, the proportion of the innate immune cells (monocytes) was higher in the 18°C water. Contrary to our expectations, no interaction between host immune defence, parasite infectivity and temperature stress were found, nor did the pattern of local adaptation change due to increased water temperature. Thus, in this host-parasite interaction, the sympatric parasite keeps ahead of the coevolutionary dynamics across sites, even under increasing temperatures as expected under marine global warming.

 

Global change and evolutionary genetics of parasite resistance in coastal ecosystems

Project led by Dr. M. Wegner

How global change and increasing physical stress interact with emerging marine diseases is largely unexplored in coastal ecosystems. Evolutionary consequences for such altered interactions between hosts and bacterial pathogens are even less known. Therefore, I will focus on ubiquitous bacterial pathogens (genus Vibrio) that can infect several host species from different key groups (bivalves and fish) within the Wadden sea ecosystem. Established model species, Pacific oysters and marine sticklebacks, will be studied in closer detail because their projected selective responses to rising temperatures point in opposite directions. By exploring the effects and evolutionary trajectories of bacterial pathogens and the genetic architecture of resistance in corresponding hosts, potential consequences of global change and bacterial disease for the ecosystem as a whole can be derived. The goals of the proposed research are to: (i) characterize the symbiont fauna of both host species/groups and identify pathogenic bacteria shared by both hosts, (ii) determine changes in their pathogenicity under global change scenarios, (iii) assess the impact of environmental change on quantitative genetic parameters (G matrices of immune and life history traits) as well as selection on candidate immune genes to quantify genotype x environment (GxE) interactions, and (iv) monitor the evolutionary trajectory of bacterial pathogenicity experimentally evolved on different hosts and different environmental conditions (GxGxE interactions). The fundamental aspect of extending single species GxE interaction to multiple species (GxGxE) explores the evolutionary consequences of parasitism in an ecosystem currently facing global change.