Diapause and bet‐hedging strategies in insects: a meta‐analysis of reaction norm shapes

Abstract

Many organisms escape from lethal climatological conditions by entering a resistant resting stage called diapause, which needs to be optimally timed with seasonal change. As climate change exerts selection pressure on phenology, the evolution of mean diapause timing, but also of phenotypic plasticity and bet‐hedging strategies is expected. The potential of the latter strategy as a means of coping with environmental unpredictability has received little attention in the climate change literature. Populations should be adapted to spatial variation in local conditions; contemporary patterns of phenological strategies across a geographic range may hence provide information about their evolvability. We thus extracted 458 diapause reaction norms from 60 studies. First, we correlated mean diapause timing with mean winter onset. Then we partitioned the reaction norm variance into a temporal component (phenotypic plasticity) and among‐offspring variance (diversified bet‐hedging) and correlated this variance composition with variability of winter onset. Mean diapause timing correlated reasonably well with mean winter onset, except for populations at high latitudes, which apparently failed to track early onsets. Variance among offspring was, however, limited and correlated only weakly with environmental variability, indicating little scope for bet‐hedging. The apparent lack of phenological bet‐hedging strategies may pose a risk in a less predictable climate, but we also highlight the need for more data on alternative strategies.

Shifts in population density centers of a hibernating mammal driven by conflicting effects of climate change and disease

“…These values equate to diapause beginning for some species in early August and ending by early November for essentially all summer‐active insect species. This fits well with recorded dates of diapause onset (Joschinski & Bonte, 2021). The critical photoperiod of diapause onset is also shifting over time, likely in response to a changing climate (Bradshaw & Holzapfel, 2001).…”

“…This fits well with recorded dates of diapause onset (Joschinski & Bonte, 2021). The critical photoperiod of diapause onset is also shifting over time, likely in response to a changing climate (Bradshaw & Holzapfel, 2001).…”

“…We used a range of critical photoperiods to represent differences in diapause timing in different potential prey eaten by foraging bats. In the south study area, we set critical photoperiods to a range between 12 and 14.2 h. Critical photoperiod in insects increases by approximately 10 min for each latitudinal degree (Joschinski & Bonte, 2021), so we added 0.167 h to these values for the northern location. These values equate to diapause beginning for some species in early August and ending by early November for essentially all summer-active insect species.…”

Evolutionary trade-offs in dormancy phenology

“…In these species and in addition to energetic benefits, dormancy occurs in a large number of situations that reduce competition and predation (Danks 1992, Satterthwaite 2010, Blath and Tóbiás 2020. The evolution of dormancy is explained as based, for example, on "evolutionarily stable strategies" (Hairston Jr andMunns Jr 1984, Kortessis andChesson 2019 ), "life history theory" (Ji 2011 , Watts andTenhumberg 2021 ), or as a "bet hedging strategy" (Hopper 1999 , Joschinski andBonte 2021 ).…”

Evolutionary trade-offs in dormancy phenology

“…In these species and in addition to energetic benefits, dormancy occurs in a large number of situations that reduce competition and predation (Danks 1992, Satterthwaite 2010, Blath and Tóbiás 2020). The evolution of dormancy is explained as based, for example, on “evolutionarily stable strategies” (Hairston Jr and Munns Jr 1984, Kortessis and Chesson 2019), “life history theory” (Ji 2011, Watts and Tenhumberg 2021), or as a “bet hedging strategy” (Hopper 1999, Joschinski and Bonte 2021).…”