Carryover effects of thermal conditions on tick survival, behavior, and simulated detectability

Authors: MARSHALL, DANIEL - Washington State University; Poh, Karen; OWN, JEB - Washington State University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2025
Publication Date: 10/2/2025
Citation: Marshall, D.S., Poh, K.C., Own, J.P. 2025. Carryover effects of thermal conditions on tick survival, behavior, and simulated detectability. Ecology and Evolution. 15(10). Article e72252. https://doi.org/10.1002/ece3.72252.
DOI: https://doi.org/10.1002/ece3.72252

Interpretive Summary: Carryover effects may manifest as a result of previous exposure to environmental conditions, thereby impacting subsequent tick behavior and mortality. For the lone star tick, Amblyomma americanum, exposure to warm and cool conditions had significant effects on the behavior and mortality of the tick. Ticks exposed to cool temperatures for approximately four weeks had lower mortality and had steady movement activity, while those exposed to elevated temperatures had heightened levels of movement temporarily, but also increased mortality. During simulations of tick movement that incorporated these activity and mortality data, our models showed that ticks exposed to warm temperatures are more likely to be trapped (or "detected") due to increased movement, but then elevated mortality will reduce the chances of detection over time. Ticks exposed to cooler temperatures may have consistent activity before abundance declines due to mortality. These findings have real-world applications that could influence dynamics involved in tick-host interactions and pathogen transmission. Ticks exposed to warm conditions could initially be more likely to contact hosts and transmit pathogens. Several weeks later, those ticks will be more likely to die, decreasing the number of host-seeking ticks and lowering the likelihood of tick-host contact and pathogen transmission. After cool weather, tick activity would remain relatively consistent for at least a month with abundance declining more slowly than ticks exposed to warm temperatures. During this time, likelihood of tick-host contact is not elevated. Overall, these results provide evidence of carryover effects in A. americanum due to temperature exposures, which could have implications for tick-host interactions and tick-borne pathogen transmission. These results could also improve surveillance efforts by accounting for weather conditions over recent preceding weeks to improve estimations for true tick hazard in a given area.

Technical Abstract: Environmental history of an organism influences its fitness and ultimately population dynamics through carryover effects. Carryover effects have received some attention in the field of vector-borne disease ecology, but are understudied in the context of ticks and tick-borne pathogen transmission where they may influence tick-host contact, pathogen transmission, and tick surveillance. We investigated how recent thermal history affects mortality and activity of Amblyomma americanum, an emerging vector of human and animal pathogens. Following laboratory experiments, we used our data to simulate tick detection in nature during a one-month period following exposure to warm and cool conditions. Ticks exposed to warm conditions for four weeks exhibited increased mortality and heightened activity levels (as measured by time spent moving and distance moved in 24 hours) that declined over time. Ticks with cool thermal histories had lower mortality and maintained steady activity levels. Our model showed that short-term warm conditions temporarily elevate tick detection due to increased movement which is followed by reduced detection driven by elevated mortality. Cool conditions produce similarly declining detection rates due to mortality, but are not influenced by tick movement. These findings demonstrate short-term carryover effects in A. americanum and have implications for disease ecology by influencing tick-host contact and pathogen transmission and for public health by impacting tick surveillance accuracy and tick-borne pathogen risk.