Evol Ecol Res 18: 621-636 (2017)     Full PDF if your library subscribes.

Evolution of the density response of juvenile hormone concentration in the determination of wing type

Takahiro Kamioka and Yoh Iwasa

Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan

Correspondence: T. Kamioka, Department of Biology, Faculty of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. email: t.kamioka.530@gmail.com

ABSTRACT

Question: What is the evolutionarily stable density-dependent juvenile hormone concentration that determines wing type in wing-polymorphic insects?

Key assumptions: An asexual species with larval and adult stages living in many patches. Larval growth rate depends on within-patch resources that are depleted by feeding larvae. Dispersal-type adults migrate out of the natal patch just before the reproductive stage, whereas reproductive-type adults do not disperse but are more fertile than dispersal types. The proportions of the two wing types are determined by juvenile hormone concentration, which follows a normal distribution with the mean decreasing linearly with density (larval biomass per unit resource). The carrying capacity of resources fluctuates between high and low values.

Method: We studied the evolution of three quantities controlling juvenile hormone concentration: (1) baseline value of the mean, γ₀; (2) density dependence of the mean, γ₁; and (3) variance, σ².

Results: If γ₀ and γ₁ evolved with σ² fixed, juvenile hormone production was high at low density and decreased with increasing density. If σ² evolved with γ₀ and γ₁ fixed, the variance evolved to be smaller for larger environmental fluctuations. If all three quantities (γ₀, γ₁, and σ²) evolved simultaneously, the variance attained a minimum value when environmental fluctuation was large. In all three cases, evolution increased the proportion of dispersal-type individuals, which increased with density in an accelerating manner.

Keywords: density response of mean juvenile hormone concentration, environmental fluctuation, juvenile hormone, resource dynamics, wing polymorphism, variance of juvenile hormone concentration.

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