Fitness and eco-physiological response of a chytrid fungal parasite infecting planktonic cyanobacteria to thermal and host genotype variation

Abstract

Understanding how individual parasite traits contribute to overall fitness, and how they are modulated by both external and host environment, is crucial for predicting disease outcome. Fungal (chytrid) parasites of phytoplankton are important yet poorly studied pathogens with the potential to modulate the abundance and composition of phytoplankton communities and to drive their evolution. Here, we studied life-history traits of a chytrid parasite infecting the planktonic, bloom-forming cyanobacterium Planktothrix spp. under host genotype and thermal variation. When expressing parasite fitness in terms of transmission success, disease outcome was largely modulated by temperature alone. Yet, a closer examination of individual parasite traits linked to different infection phases, such as (i) the establishment of the infection (i.e. intensity of infection) and (ii) the exploitation of host resources (i.e. size of reproductive structures and propagules), revealed differential host genotype and temperature × host genotype modulation, respectively. This illustrates how parasite fitness results from the interplay of individual parasite traits that are differentially controlled by host and external environment, and stresses the importance of combining multiple traits to gain insights into underlying infection mechanisms.

Comparison of sterol and fatty acid profiles of chytrids and their hosts reveals trophic upgrading of nutritionally inadequate phytoplankton by fungal parasites

“…We attribute differences in carbon contents between the two chytrid species used in our experiment to differences in the size of zoospores. Zoospores size has been shown to be a flexible parasite trait that varies with host genotype (Agha et al 2018). As expected, zoospores of both chytrid species were rich in lipids, presenting a large lipid globule, a characteristic morphological feature of chytrids (Powell et al, 2015;Van den Wyngaert et al, 2018).…”

“…Zoospores size has been shown to be a flexible parasite trait that varies with host genotype (Agha et al . ). As expected, zoospores of both chytrid species were rich in lipids, presenting a large lipid globule, a characteristic morphological feature of chytrids (Powell et al ., ; Van den Wyngaert et al ., ).…”

Fungi in aquatic ecosystems

“…REF. 203 ), fatty acids 17 , stable isotopes or labelled FISH 177,[204][205][206][207] . Thus, it is about time to overcome the insufficient sampling and exploration of natural and artificial aquatic environments to understand the spatial and temporal distribution as well as the dynamics of aquatic fungi.…”

Adaptation of a Chytrid Parasite to Its Cyanobacterial Host Is Hampered by Host Intraspecific Diversity

“…All sample identities were blinded before analysis, except those from the initial fitness tests. Three different parasite traits were investigated: prevalence of infection, intensity of infection, and size of mature/empty sporangia after methods described in Agha et al ( 2018 ). In brief, prevalence of infection was determined from daily collected samples as the proportion of infected filaments after screening 200 filaments per sample.…”

“…Secondly, intensity of infection was scored to assess the ability of the parasite to find and successfully adhere to the host and, thereby, evade its barrier defenses. Lastly, the size of mature fungal reproductive structures (i.e., sporangia) was recorded as a proxy of parasite per capita reproductive output (i.e., greater sporangial sizes arguably imply more zoospores being released upon maturation) that negatively correlates with the intensity of infection (Agha et al, 2018 ).…”