Abstract
Food limitation is expected to reduce an individual’s body condition (body mass scaled to body size) and cause a trade-off between growth and other fitness-related traits, such as immunity. We tested the condition-dependence of growth and disease resistance in male and female Gryllus texensis field crickets by manipulating diet quality via nutrient content for their entire life and then subjecting individuals to a host resistance test using the live bacterium Serratia marcescens. As predicted, crickets on a high-quality diet eclosed more quickly, and at a larger body size and mass. Crickets on a high-quality diet were not in better condition at the time of eclosion, but they were in better condition 7–11 days after eclosion, with females also being in better condition than males. Despite being in better condition, however, females provided with a high-quality diet had significantly poorer disease resistance than females on a low-quality diet and in poor condition. Similarly, males on low- and high-quality diets did not differ in their disease resistance, despite differing in their body condition. A sex difference in disease resistance under diet-restriction suggests that females might allocate resources toward immunity during development if they expect harsh environmental conditions as an adult or it might suggest that females allocate resources toward other life history activities (i.e. reproduction) when food availability increases. We do not know what immune effectors were altered under diet-restriction to increase disease resistance, but our findings suggest that increased immune function might provide an explanation for the sexually-dimorphic increase in longevity generally observed in diet-restricted animals.
Highlights
The resource pool from which individuals allocate to competing fitness-related life history traits is known as condition [1]
MANOVA revealed a significant effect of diet treatment, but not sex, on the four life history traits measured for mature crickets (Figure 2)
Neither diet nor sex significantly affected body condition at eclosion, females were in significantly better condition at the time of the host resistance test (7–11 days post-eclosion) compared to males, (ANCOVA controlling for post-eclosion age, sex: F1,169 = 10.41, p = 0.002) and individuals fed a high-quality diet were in significantly better condition at the time of their host resistance test
Summary
The resource pool from which individuals allocate to competing fitness-related life history traits is known as condition [1]. That adult life history decisions are contingent upon the resources accumulated during the juvenile life stage means that the environment experienced during early growth and development can have permanent effects on the adult phenotype and its subsequent performance [3,4,5]. For example in stressful environments, such as when food quality or quantity is limited, insects tend to mature at a smaller body size, at an older age, and in poorer condition because rates of growth and development are diminished [9,10] This might prove costly to fitness if smaller adults in poorer condition suffer from decreased reproductive success and increased mortality [9,10,11]
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