associations when generalizing. While engineered vectors typically show reductions
of pathogen infection or transmission, variation in phenotypes, infection costs, and
transmission rates have been observed, which can arise from any of the interacting
participants (Ross et al. 2017; Ross et al. 2019b). But since higher temperatures and
heat shocks generally suppress both the strength of manipulative phenotypes and the
transmission efficiency (Corbin et al. 2017), warming may limit the ability to drive
pathogen-suppressing symbionts into vector populations, especially in tropical
regions where these diseases cause the most harm. Studies investigating the effects
of temperature on pathogen blocking strains are limited, but one study has shown
that the loss or retention of the driving mechanism (CI) under field conditions
depended on symbiont strain (Ross et al. 2019a). Hence, identifying microbial
strains that are robust to warmer temperatures will be important to the successful
deployment of symbiont-mediated disease suppression as heat waves and everincreasing mean temperatures may work to erode their efficacy.
In natural systems, the effects of warm temperatures on anti-pathogen traits and
manipulative phenotypes may generally limit the spread of Wolbachia into warmer
regions and at warmer times of the year. Wolbachia infection frequencies are highly
variable in natural populations, but generally appear to be more common in cooler,
temperate regions (Woodhams et al. 2020; Sazama et al. 2019; Charlesworth et al.
2019). Another widespread reproductive manipulator, Cardinium, in contrast, shows
positive correlations with surface temperature, including in Culicoides biting midges
that are important disease vectors (Morag et al. 2012; Charlesworth et al. 2019).
However, specific strains appear to perform better under cooler conditions. In the
parasitoid, Encarsia suzannae, warmer temperatures reduced Cardinium densities
and the strength of CI, while cooler temperatures strengthened CI even though
symbiont densities were also reduced (Doremus et al. 2019).
In total, these studies show that temperature has large effects on the phenotypes of
facultative symbionts. Given the importance of these animals as medical vectors and
agricultural pests, it is critical to understand how GCC will impact these symbioses.
Early results indicate that thermal stress is likely to generally reduce the strength of
symbiont-conferred phenotypes, which may impact host fitness, abundance, and
distributions across diverse systems, with effects that reverberate through food
webs. On the hopeful side, facultative symbiont genomes encode diverse bioactive
factors, and climate variables may select for resilience-conferring phenotypes. The
presence of these factors on mobile elements, including bacteriophages, indicates
their potential to be shared within and among symbiont lineages (Touchon et al.
2017; Lynn-Bell et al. 2019). The further ability of the symbionts to move horizontally among host lineages creates opportunities for the widespread transfer of
climate-mitigating traits across this hyper-diverse group (Oliver et al. 2010).
16 Symbiosis in a Rapidly Changing World
277
of pathogen infection or transmission, variation in phenotypes, infection costs, and
transmission rates have been observed, which can arise from any of the interacting
participants (Ross et al. 2017; Ross et al. 2019b). But since higher temperatures and
heat shocks generally suppress both the strength of manipulative phenotypes and the
transmission efficiency (Corbin et al. 2017), warming may limit the ability to drive
pathogen-suppressing symbionts into vector populations, especially in tropical
regions where these diseases cause the most harm. Studies investigating the effects
of temperature on pathogen blocking strains are limited, but one study has shown
that the loss or retention of the driving mechanism (CI) under field conditions
depended on symbiont strain (Ross et al. 2019a). Hence, identifying microbial
strains that are robust to warmer temperatures will be important to the successful
deployment of symbiont-mediated disease suppression as heat waves and everincreasing mean temperatures may work to erode their efficacy.
In natural systems, the effects of warm temperatures on anti-pathogen traits and
manipulative phenotypes may generally limit the spread of Wolbachia into warmer
regions and at warmer times of the year. Wolbachia infection frequencies are highly
variable in natural populations, but generally appear to be more common in cooler,
temperate regions (Woodhams et al. 2020; Sazama et al. 2019; Charlesworth et al.
2019). Another widespread reproductive manipulator, Cardinium, in contrast, shows
positive correlations with surface temperature, including in Culicoides biting midges
that are important disease vectors (Morag et al. 2012; Charlesworth et al. 2019).
However, specific strains appear to perform better under cooler conditions. In the
parasitoid, Encarsia suzannae, warmer temperatures reduced Cardinium densities
and the strength of CI, while cooler temperatures strengthened CI even though
symbiont densities were also reduced (Doremus et al. 2019).
In total, these studies show that temperature has large effects on the phenotypes of
facultative symbionts. Given the importance of these animals as medical vectors and
agricultural pests, it is critical to understand how GCC will impact these symbioses.
Early results indicate that thermal stress is likely to generally reduce the strength of
symbiont-conferred phenotypes, which may impact host fitness, abundance, and
distributions across diverse systems, with effects that reverberate through food
webs. On the hopeful side, facultative symbiont genomes encode diverse bioactive
factors, and climate variables may select for resilience-conferring phenotypes. The
presence of these factors on mobile elements, including bacteriophages, indicates
their potential to be shared within and among symbiont lineages (Touchon et al.
2017; Lynn-Bell et al. 2019). The further ability of the symbionts to move horizontally among host lineages creates opportunities for the widespread transfer of
climate-mitigating traits across this hyper-diverse group (Oliver et al. 2010).
16 Symbiosis in a Rapidly Changing World
277