Thermal ecology shapes disease outcomes of entomopathogenic fungi infecting warm-adapted insects

• Published in: Journal of invertebrate pathology 2024-06, Vol.204, p.108106-108106, Article 108106
• Main Authors: Slowik, Anna R., Hesketh, Helen, Sait, Steven M., De Fine Licht, Henrik H.
• Format: Article
• Language: English
• Subjects: Entomopathogenic fungi (EPF); Metarhizium; Tenebrio molitor; Thermal ecology; Thermal Mismatch Hypothesis (TMH); Thermal performance curves; Thermal profiles; Virulence
• ISSN: 0022-2011; 1096-0805
• DOI: 10.1016/j.jip.2024.108106

[Display omitted] •The thermal environment can determine the outcome of host-pathogen interactions.•Two species of entomopathogenic fungi share thermal growth optima with hosts.•Here we show that virulence varies with temperature and differ between fungal species.•Important to consider pathogen ecological niche when predicting thermal virulence. The thermal environment is a critical determinant of outcomes in host-pathogen interactions, yet the complexities of this relationship remain underexplored in many ecological systems. We examined the Thermal Mismatch Hypothesis (TMH) by measuring phenotypic variation in individual thermal performance profiles using a model system of two species of entomopathogenic fungi (EPF) that differ in their ecological niche, Metarhizium brunneum and M. flavoviride, and a warm-adapted model host, the mealworm Tenebrio molitor. We conducted experiments across ecologically relevant temperatures to determine the thermal performance curves for growth and virulence, measured as % survival, identify critical thresholds for these measures, and elucidate interactive host-pathogen effects. Both EPF species and the host exhibited a shared growth optima at 28 °C, while the host’s growth response was moderated in sublethal pathogen infections that depended on fungus identity and temperature. However, variances in virulence patterns were different between pathogens. The fungus M. brunneum exhibited a broader optimal temperature range (23–28 °C) for virulence than M. flavoviride, which displayed a multiphasic virulence-temperature relationship with distinct peaks at 18 and 28 °C. Contrary to predictions of the TMH, both EPF displayed peak virulence at the host's optimal temperature (28 °C). The thermal profile for M. brunneum aligned more closely with that of T. molitor than that for M. flavoviride. Moreover, the individual thermal profile of M. flavoviride closely paralleled its virulence thermal profile, whereas the virulence thermal profile of M. brunneum did not track with its individual thermal performance. This suggests an indirect, midrange (23 °C) effect, where M. brunneum virulence exceeded growth. These findings suggest that the evolutionary histories and ecological adaptations of these EPF species have produced distinct thermal niches during the host interaction. This study contributes to our understanding of thermal ecology in host-pathogen interactions, underpinning the ecological and evolutionary factors that shape infection o