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Contributed Talk

Session: : Population Dynamics And Regulation 2

COS 157-4 - Cryptic viruses have the potential to alter population dynamics in well-studied species

Wednesday, August 9, 2023
8:45 AM – 9:00 AM PDT
Location: D138
Abstract:

Background: Population fluctuations are common in nature, especially in species with high intrinsic growth rates. Ecologists seek to explain population dynamics as a function of observable environmental factors, but this approach often falls short. Recent advances in molecular ecology have revealed the ubiquity of pathogens in nature, and it is possible that previously cryptic pathogens play a significant role in unexplained population dynamics.

Goal: In this study, we took a vital-rate approach to investigate the potential for a cryptic virus to cause population decline in the Baltimore checkerspot butterfly (Euphydryas phaeton). Checkerspots are known to exhibit boom and bust dynamics, and recently a virus of the Buckeye butterfly (Junonia coenia densovirus (JcDNV)) was discovered to be endemic in many Baltimore checkerspot populations.

Methods: In spring 2021 and 2022 we established 45 individually caged host plants (Plantago lanceolata) in a field enclosure on Tufts campus, and topically applied JcDNV across a range of treatment levels. We placed six post-diapause late-4th instar larvae on each plant, and tracked survival to adulthood. We monitored the fecundity of each surviving female, and the early instar survival of their offspring on non-infected plants. In addition, after re-treating host plants we introduced non-infected early instar larvae and monitored their survival to diapause.

Results: We found that post-diapause survival to adulthood sharply declined in high-virus treatments in 2021, and sharply declined across all treatment levels in 2022. Fecundity and offspring survival did not differ between control females and females surviving larval viral exposure. Surprisingly, there was no reduction in survival to diapause in early-instar larva on virus-treated plants.

Conclusions: Despite the lack of demographic effects in other life-stages, the impact of viral exposure on post-diapause survival was enough to cause a 90% decline in estimated population growth rates. Cross-year differences in dose-response points to the role that weather conditions may play in disease outcomes, and overall these results suggest that JcDNV can cause density-dependent population decline in E. phaeton. Previously cryptic viruses can strongly influence insect populations, and their potential to influence eco-evolutionary dynamics through demographic processes is largely unexplored.