Wed, Aug 17, 2022: 1:30 PM-1:45 PM
518B
Background/Question/MethodsDark pigmentation resulting from cooler rearing temperature is a type of developmental plasticity that is ubiquitous in insects. Yet, the costs associated with these responses have only been explored for a handful of species despite the broad implications of color variation for evolutionary responses to climate change. We explored two competing hypotheses relating to color plasticity of insects. First, if melanin is costly to synthesize and requires allocation of resources, increased melanisation should be negatively associated with performance traits or other aspects of fitness. Second, given the positive association between melanisation and traits such as immunity and desiccation resistance, we expect a positive coadaptation between melanisation and performance. We assessed whether temperature-induced melanisation of the globally invasive beetle Harmonia axyridis f. succinea (Pallas) was related to resting metabolic rate and flight performance parameters, such as mean and maximum flight speed and distance traveled, while accounting for rearing temperature regime and family affiliation.
Results/ConclusionsThe percentage melanisation and number of black spots of cold-reared beetles explained little variation in resting metabolic rate at most temperatures tested (15, 20, 25, 30 and 35 °C). For beetles reared at the warm regime, darker beetles tended to have lower resting metabolic rate, but the strength of this relationship varied depending on the temperature tested, body mass and sex investigated. For flight performance after the cold rearing regime, larger and lighter-colored beetles traveled further than small ones but this relationship was not found for darker (melanic) beetles. In addition, in warm-reared beetles, darker individuals had lower mean flight speeds. These results suggest performance costs associated with developmentally-induced melanisation but also reveal complex interactions with sex and body size. Our study also revealed substantial variation in the extent of melanisation within rearing regimes. This variation was particularly acute for females reared in the warm treatment compared to equally treated males and to cold-reared individuals. Consequently, we propose new hypotheses underlying differential selection for diverse color phenotypes between sexes in the wild.
Results/ConclusionsThe percentage melanisation and number of black spots of cold-reared beetles explained little variation in resting metabolic rate at most temperatures tested (15, 20, 25, 30 and 35 °C). For beetles reared at the warm regime, darker beetles tended to have lower resting metabolic rate, but the strength of this relationship varied depending on the temperature tested, body mass and sex investigated. For flight performance after the cold rearing regime, larger and lighter-colored beetles traveled further than small ones but this relationship was not found for darker (melanic) beetles. In addition, in warm-reared beetles, darker individuals had lower mean flight speeds. These results suggest performance costs associated with developmentally-induced melanisation but also reveal complex interactions with sex and body size. Our study also revealed substantial variation in the extent of melanisation within rearing regimes. This variation was particularly acute for females reared in the warm treatment compared to equally treated males and to cold-reared individuals. Consequently, we propose new hypotheses underlying differential selection for diverse color phenotypes between sexes in the wild.