Abstract
In seasonal environments, sinks that are more persistent than sources may serve as temporal stepping stones for specialists. However, this possibility has to our knowledge, not been demonstrated to date, as such environments are thought to select for generalists, and the role of sinks, both in the field and in the laboratory, is difficult to document. Here, we used laboratory experiments to show that herbivorous arthropods associated with seasonally absent main (source) habitats can endure on a suboptimal (sink) host for several generations, albeit with a negative growth rate. Additionally, they dispersed towards this host less often than towards the main host and accepted it less often than the main host. Finally, repeated experimental evolution attempts revealed no adaptation to the suboptimal host. Nevertheless, field observations showed that arthropods are found in suboptimal habitats when the main habitat is unavailable. Together, these results show that evolutionary rescue in the suboptimal habitat is not possible. Instead, the sink habitat functions as a temporal stepping stone, allowing for the persistence of a specialist when the source habitat is gone.
Highlights
Most organisms face temporal and spatial environmental variability
We used laboratory experiments to show that herbivorous arthropods associated with seasonally absent main habitats can endure on a suboptimal host for several generations, albeit with a negative growth rate
If evolutionary rescue occurs in sinks in temporally variable environments, theory predicts the evolution of generalists, which perform reasonably well, across a wide range of habitats [20,21,22,23]
Summary
Most organisms face temporal and spatial environmental variability. In extreme cases, environmental variation may lead to certain habitats becoming temporally entirely unavailable, for instance, owing to strong seasonality, pulsed resources or human activity [1,2,3,4]. If evolutionary rescue occurs in sinks in temporally variable environments, theory predicts the evolution of generalists, which perform reasonably well (i.e. have a positive growth rate in the long run), across a wide range of habitats [20,21,22,23] This prediction has been confirmed in some empirical studies To determine whether wheat and brome were source and sink environments, respectively, we assessed the WCM population growth rate on these plants. To test whether the population growth rates differed between wheat and smooth brome and changed across generations, a GLM was used with a Gaussian error structure, with the target host plant (wheat versus brome), generation number and their interaction as predictors. To test whether both dispersal and acceptance rates differed between wheat and brome, two separate GLMs were built In both models, a factor coding host species As the data were collected over several years (2007–2014), a year identifier was included as a random factor, which was assumed to be an independent and identically distributed random intercept representing between-year variability in the WCM infestation
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