Study system
Insects and their parasitoids are an excellent system for studying effects of climate change on species interactions (Hance et al.2007; Jeffs & Lewis 2013). The strength of host-parasitoid interactions are predicted to be particularly sensitive to phenological shifts and global warming due to 1) age-related vulnerability of host to successful parasitism and 2) high thermal sensitivity given their obligate ties to host thermal performance (Tuda & Shimada 1995; Hance et al.2007). Furthermore, the duration of host vulnerability and degree of phenological synchrony have been suggested to influence local stability within host-parasitoid systems. Stable host-parasitoid interactions require that not all hosts have been parasitized, so some degree of asynchrony may be adaptive (Singer & Parmesan 2010). Thus, precise timing is critical for these tightly co-evolved interactions and any shift in the optimal temporal overlap is hypothesized to have significant effects on long-term persistence (Tuda & Shimada 1995).
We used a native Drosophila -parasitoid system from the seasonal tropical forests of North Queensland, Australia. Two species ofDrosophila , D. sulfurigaster and D. birchii , were collected from the field in March 2018 and maintained at the Czech Academy of Sciences (CAS) as a collection of isofemale lines (Shipped to the Czech Republic under permit no. PWS2016-AU-002018 from Australian Government, Department of the Environment). These species coexist across elevational gradients that span 900m at Kirrama (S18° 12.676’ E145° 47.530’) and Paluma (S19° 00.386’ E146° 12.732’) mountain ranges in Queensland, and are attacked by a shared suite of parasitoid wasp species (Jeffset al. 2021). Individuals used in this experiment were collected as eggs from mass bred population cages, which originated from eight isofemale lines from each fly species respectively.
We used two hymenopteran parasitoid species, collected from the same tropical Australian locations: Asobara sp.1 (Braconidae: Alysiinae; strain KHB from site Kirrama, elevation 900m, reference voucher no. USNMENT01557097, reference sequence BOLD process ID: DROP043-21, and Ganaspis sp.1 (Figitidae: Eucolinae; strain 69B from site Kirrama, elevation 900, reference voucher no. USNMENT01557100, USNMENT01557297 reference sequence BOLD process ID:DROP164-21) (Lueet al. 2021). These species await description by taxonomists but are precisely identified above so that this study can be linked to species names once available. Each parasitoid species specializes on larval stages of Drosophila and are known to successfully attackD. birchii and D. sulfurigaster . All parasitoids were maintained on D. melanogaster , so no parasitoid used in this experiment had prior experience with D. sulfurigaster or D. birchii , and thus no acquired oviposition preference.