Influence of experimental warming and shading on host–parasitoid synchrony

Abstract

As the climate warms, many species are showing altered phenology patterns, potentially disrupting synchrony between interacting species. Recent studies have documented disrupted synchrony in plant-herbivore and predator-prey interactions. However, studies investigating climate-related asynchrony in host-parasitoid interactions and exploring the relative responses of interacting hosts and parasitoids to climate change are lacking. This is an important gap in knowledge given the ubiquity of insect parasitoids and their importance in influencing the abundance and dynamics of their hosts. In the threatened marsh fritillary butterfly Euphydryas aurinia (Lepidoptera: Nymphalidae) and its specialized parasitoid, Cotesia bignellii (Hymenoptera: Braconidae) phenological synchrony (and consequently population fluctuations) are thought to be weather-dependent. To assess the likely influence of climate and microenvironment change on synchrony between E. aurinia and C. bignellii, we experimentally manipulated the exposure of sensitive-stage host larvae and parasitoid pupae to temperature (ambient or elevated) and shading (shaded or unshaded) regimes. We also analysed a 20-year population dynamic dataset from the United Kingdom for E. aurinia to investigate whether population variations could be explained by interannual variations in the thermal and sunshine environment. Development times were affected significantly by the experimental temperature and shading treatments for E. aurinia but not for C. bignellii. However, the contrasting responses were insufficient to significantly affect host availability for parasitoids. In the field, thermal and sunshine conditions did not influence population fluctuations, and population variations across a large (UK-wide) scale were uncorrelated. Changes to the thermal and sunshine environment of the magnitude investigated in our experiment and within the range experienced by wild E. aurinia populations over the last 20-years thus seem unlikely to cause breakdown in host-parasitoid synchrony. We suggest that experiments investigating the mechanistic responses of interacting species to environmental change are needed to support the analysis and interpretation of observational data on species' phenology.

Large‐scale migration synchrony between parasitoids and their host

“…However, there were times when aphids were present but parasitoids did not respond and vice versa (Fig. 2 a,b) which might be expected in noisy systems (Ekbom et al, 1992;Klapwijk et al, 2010). We explored whether daily temperatures were a potential mechanism that would explain observed relationships between parasitoids, aphids, and temperature over the whole datasets for both Rothamsted and Writtle.…”

“…Although temperature could affect the timing of parasitoid emergence, especially in early spring (van Nouhuys & Lei, 2004;Hance et al, 2007;Klapwijk et al, 2010), temperature does not directly explain the migration synchrony between parasitoids and their host. It is more likely that both host and parasitoids are responding to the effects of crop senescence that causes aphids to leave the crop owing to a reduced feeding potential and parasitoids to migrate because they are responding to a change in crop quality through a change in the density of the host (Schellhorn et al, 2014).…”

Effects of climate warming on host–parasitoid interactions

“…Under low ambient temperature conditions (cool, sunny weather in early spring) this generates high levels of phenological asynchrony (a temporal refuge), with a large fraction of hosts no longer susceptible by the time that adult parasitoids emerge. However, at higher ambient temperatures the relative gain in development speed from basking is lowered, increasing host-parasitoid synchrony and allowing adult parasitoids to emerge during periods when large numbers of susceptible hosts are available (Van Nouhuys & Lei, 2004;Klapwijk et al ., 2010). Although interacting species such as these could in theory become increasingly synchronised as the climate warms, experimental data on the interaction between Euphydryas aurinia and Cotesia bignellii suggest that realistic levels of climate change do not greatly alter the degree of synchronisation (Klapwijk et al ., 2010).…”

“…However, at higher ambient temperatures the relative gain in development speed from basking is lowered, increasing host-parasitoid synchrony and allowing adult parasitoids to emerge during periods when large numbers of susceptible hosts are available (Van Nouhuys & Lei, 2004;Klapwijk et al ., 2010). Although interacting species such as these could in theory become increasingly synchronised as the climate warms, experimental data on the interaction between Euphydryas aurinia and Cotesia bignellii suggest that realistic levels of climate change do not greatly alter the degree of synchronisation (Klapwijk et al ., 2010). This occurs in part because parasitoid development times appear to have a higher variance than those of their hosts, ensuring host-parasitoid temporal overlap even when mean emergence and susceptibility times differ considerably (Klapwijk et al ., 2010).…”

“…Although interacting species such as these could in theory become increasingly synchronised as the climate warms, experimental data on the interaction between Euphydryas aurinia and Cotesia bignellii suggest that realistic levels of climate change do not greatly alter the degree of synchronisation (Klapwijk et al ., 2010). This occurs in part because parasitoid development times appear to have a higher variance than those of their hosts, ensuring host-parasitoid temporal overlap even when mean emergence and susceptibility times differ considerably (Klapwijk et al ., 2010). This may be an adaptive strategy to reduce levels of asynchrony, and it would be interesting to investigate whether it is a general phenomenon in host-parasitoid interactions.…”