American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Evolution of reproduction periods in seasonal environments”

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Zepeng Sun, Kalle Parvinen, Mikko Heino, Johan A. J. Metz, André M. de Roos, and Ulf Dieckmann (June 2020)

The authors studied how individuals time their reproduction in response to environmental changes

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In significantly seasonal environments, individuals will attempt to store energy reserves for reproduction at a later time; otherwise, they will just reproduce when they can

Climate change is expected to drive shifts in phenology, or the timing of life history events. Of all the seasonal events affected by climate change, the timing of reproduction (or breeding) is thought to be the most important. When it comes to the negative impacts of climate change on the reproduction of species, a so-called "match-mismatch hypothesis" arises in our mind, stating that the changes in climate can result in a mismatch between the offspring's food requirements and the actual food availabilities and in turn reduce the recruitment success. Although lots of efforts have been made on this topic, it is still not well-known how populations adjust their reproduction schedules in order to cope with changing seasonal patterns in their environment.

In this study, Sun and his colleagues developed a theoretical model and investigated how the patterns in seasonal environments alter the evolution of the reproduction periods of populations. Besides the starting time, the model also allows the duration of the reproduction period to evolve independently. The authors present not only qualitative but also quantitative effects of the environmental patterns on evolution by reporting a rich array of evolutionary outcomes. Overall, the strength in seasonality of the environment determines whether energy reserves by adults is advantageous: in significantly seasonal environments, individuals will attempt to store energy reserves for reproduction at a later time; otherwise, they will just reproduce when they can. Surprisingly, in the former case, adults may start reproduction even while their offspring are still experiencing starvation. Furthermore, the competition ability on resource consumption between adults and juveniles also affects the outcomes: the more superior adults are on resource consumption, the more energy reserves (by adults) are favorable, and thus seasonality in reproduction becomes more significant.


Abstract

Many species are subject to seasonal cycles in resource availability, affecting the timing of their reproduction. Using a stage-structured consumer-resource model in which juvenile development and maturation are resource-dependent, we study how a species’ reproductive schedule evolves dependent on the seasonality of its resource. We find three qualitatively different reproduction modes. First, continuous income breeding (with adults reproducing throughout the year) evolves in absence of significant seasonality. Second, seasonal income breeding (with adults reproducing unless they are starving) evolves when resource availability is sufficiently seasonal and juveniles are more efficient resource foragers. Third, seasonal capital breeding (with adults reproducing partly through the use of energy reserves) evolves when resource availability is sufficiently seasonal and adults are more efficient resource foragers. Such capital breeders start reproduction already while their offspring are still experiencing starvation. Changes in seasonality lead to continuous transitions between continuous and seasonal income breeding, but the change between income and capital breeding involves a hysteresis pattern, such that a population’s evolutionarily stable reproduction pattern depends on its initial one. Taken together, our findings show how adaptation to seasonal environments can result in a rich array of outcomes, exhibiting seasonal or continuous reproduction, with or without energy reserves.