Modeling the evolution of insect phenology: Can insect populations adapt to climate change?
by
Brian Yurk
Department of Mathematics and Statistics, Utah State University, Logan, Utah
Coauthors: James Powell (Department of Mathematics and Statistics, Utah State University)

Warming temperatures are likely to disrupt insect phenology (the timing of developmental events) to such an extent that some species will face local extinction while others will erupt in new habitats. It is unknown whether phenology can evolve rapidly enough to moderate these effects. Since phenology is a critical determinant of fitness in insect populations, there are strong selective pressures on maintaining appropriate phenology. For example, it is important that development is timed to avoid the coincidence of sensitive life stages with extreme weather. An individual's fitness may also be highly dependent on synchrony between its phenology and the phenology of its biotic resources, as in the case of plant-pollinator interactions. At low population densities, developmental synchrony within a population can also be an important determinant of fitness; the probability of finding mates increases when a large portion of the population reaches reproductive age within a short time period. Synchronized emergence within a population of herbivorous insects may also be necessary to overwhelm resource defenses, as is the case of mountain pine beetles attacking pine trees.

Temperature plays a major role in determining the phenology of insects, since the time it takes for an insect to develop through a life stage is highly dependent on the temperature that it experiences. Previous phenology models have described this plastic response of development time to temperature without considering genetic evolution of the response. Without evolution, these models predict that insect populations may lose developmental synchrony or synchrony with biotic resources. We will present a modeling approach that extends previous phenology models to allow for evolution of the dependence of development time on temperature. Our model results show that evolution may allow populations to adapt to warming temperatures and changing resource phenology, but there are limits to this adaptation. We will also discuss the existence of steady distributions of the evolution model, in which the temporal structure of the mean phenotype and phenotypic variance are invariant under the evolution map with periodic temperatures. Both long term and short term dynamics are controlled by the presence of phenotypes that allow for individuals and their offspring to be oviposited at the same time of year in consecutive years.

PDF

Date received: May 10, 2008