Presentation Information
[C09-02]Adaptive dynamics of emergence pattern in insects with dimorphic males
*Hidaka Kubo1, Yuuya Tachiki2, Ryo Yamaguchi1 (1. Hokkaido Univ. (Japan), 2. Tokyo Metropolitan Univ. (Japan))
Keywords:
Adaptive dynamics,Evolutionary branching,Male dimorphism,Protandry,Insect
Protandry, the emergence of males before females, is widespread in many insects, including butterflies. This phenomenon is interpreted as a strategy by which males maximize their reproductive success in species where females mate only once. This explanation has been supported by both mathematical models and empirical studies.
However, some emergence patterns remained unexplained by these theories. In the butterfly Fabriciana nerippe and the Dawson's burrowing bee Amegilla dawsoni, some males emerge earlier than females, while others emerge synchronously with females. In addition, males that emerge later tend to be larger in body size than those that emerge earlier. The reasons for the evolution of such body-size-related emergence pattern dimorphisms are still unclear.
In this study, we developed a mathematical model to reveal the conditions under which such emergence pattern dimorphism can evolve. We define male fitness as the expected number of matings opportunities. We assumed that there exists a trade-off between early emergence and competitiveness. We derived the evolutionarily stable timing of male emergence within the framework of adaptive dynamics.
As results, in the absence of a trade-off between emergence time and competitiveness, protandry evolved but the dimorphism in emergence patterns did not evolve. On the other hand, when a trade-off was present and the variance in male emergence timing was smaller than that in females, evolutionary branching occurred, leading to the evolution of dimorphism in emergence patterns. In this scenario, a subset of males emerged earlier than females, while the other emerged synchronously with them.
These findings suggest that similar dimorphisms in emergence patterns may occur in species that increase body size through extra molting as well as in species where the female emergence period is extended due to the phenology of host plants.
However, some emergence patterns remained unexplained by these theories. In the butterfly Fabriciana nerippe and the Dawson's burrowing bee Amegilla dawsoni, some males emerge earlier than females, while others emerge synchronously with females. In addition, males that emerge later tend to be larger in body size than those that emerge earlier. The reasons for the evolution of such body-size-related emergence pattern dimorphisms are still unclear.
In this study, we developed a mathematical model to reveal the conditions under which such emergence pattern dimorphism can evolve. We define male fitness as the expected number of matings opportunities. We assumed that there exists a trade-off between early emergence and competitiveness. We derived the evolutionarily stable timing of male emergence within the framework of adaptive dynamics.
As results, in the absence of a trade-off between emergence time and competitiveness, protandry evolved but the dimorphism in emergence patterns did not evolve. On the other hand, when a trade-off was present and the variance in male emergence timing was smaller than that in females, evolutionary branching occurred, leading to the evolution of dimorphism in emergence patterns. In this scenario, a subset of males emerged earlier than females, while the other emerged synchronously with them.
These findings suggest that similar dimorphisms in emergence patterns may occur in species that increase body size through extra molting as well as in species where the female emergence period is extended due to the phenology of host plants.