Does it pay to delay? Flesh flies show adaptive plasticity in reproductive timing

Abstract

Life-history plasticity is widespread among organisms. However, an important question is whether this plasticity is adaptive, enhancing the organism’s fitness. Most models for plasticity in life-history timing predict that once they have reached the minimal nutritional threshold animals under poor conditions will accelerate timing to development or reproduction. Adaptive delays in reproductive timing are not common, especially in short-lived species. Examples of adaptive reproductive delays exist in mammalian populations experiencing strong interspecific (e.g. predation) and intraspecific (e.g. infanticide) competition. But are there other environmental factors that may trigger an adaptive delay in reproductive timing? We show that the short-lived flesh fly Sarcophaga crassipalpis will delay reproductive timing under nutrient poor conditions, even though it has already met the minimal nutritional threshold for reproduction. We test if this delay strategy is consistent with an adaptive response allowing the scavenger time to locate more resources by providing additional protein pulses (early, mid and late) throughout the reproductive delay period. Flies receiving additional protein produced more eggs and larger eggs, demonstrating a benefit of the delay. In addition, by tracking the allocation of carbon from the pulses using stable isotopes, we show that flies receiving earlier pulses incorporated more carbon into eggs and somatic tissue than those provided a later pulse. These results indicate that the reproductive delay in S. crassipalpis is consistent with adaptive post-threshold plasticity, a nutritionally-linked reproductive strategy that has not been previously reported in an invertebrate species.

The timing of resource availability does not affect reproductive allotment or the rate of oocyte development in the flesh fly, Sarcophaga crassipalpis

“…Flies that received additional resources during the reproductive delay provisioned oocytes faster and had more eggs, results consistent with an adaptive delay to find more resources (Wessels et al, 2011). However, the experimental design in Wessels et al (2011) did not test the alternative hypothesis that the reproductive delay might also be produced by a physiological constraint, for example if the flies take longer to reproduce because they require time to reallocate resources from other somatic pools towards reproduction. In this study, flies that were nutritionally stressed (up to 12 days post-eclosion without protein) did not reallocate somatic capital reserves to reproduction.…”

“…Wessels et al (2011) evaluated if this reproductive delay in poorly fed females might be adaptive in the context of the scavenging lifestyle of flesh flies, to provide more time to find additional protein sources. Flies that received additional resources during the reproductive delay provisioned oocytes faster and had more eggs, results consistent with an adaptive delay to find more resources (Wessels et al, 2011). However, the experimental design in Wessels et al (2011) did not test the alternative hypothesis that the reproductive delay might also be produced by a physiological constraint, for example if the flies take longer to reproduce because they require time to reallocate resources from other somatic pools towards reproduction.…”

“…However, the experimental design in Wessels et al (2011) did not test the alternative hypothesis that the reproductive delay might also be produced by a physiological constraint, for example if the flies take longer to reproduce because they require time to reallocate resources from other somatic pools towards reproduction. Therefore, the delay in egg development previously reported in this species is likely not the result of a physiological constraint that delays oogenesis while resources are reallocated from alternative stores (Hahn et al, 2008;Wessels et al, 2011). Therefore, the delay in egg development previously reported in this species is likely not the result of a physiological constraint that delays oogenesis while resources are reallocated from alternative stores (Hahn et al, 2008;Wessels et al, 2011).…”

Environmental interactions during host race formation: host fruit environment moderates a seasonal shift in phenology in host races of Rhagoletis pomonella

“…Although there is no direct evidence that lipid storage per se affects diapause status, many animals make life-history decisions based on internal condition (e.g. Wilbur & Collins 1973;Wessels et al 2011). Lipid stores constitute a large portion of energy reserves in R. pomonella (all treatment combinations in all experiments averaged above 30% lipid), and energy reserves that are continuously depleted during diapause are critical for survival overwinter and successful adult eclosion (Hahn & Denlinger 2007).…”

Age at mating and male quality influence female patterns of reproductive investment and survival

“…Yet, females—even in short‐lived species—vary in their timing of reproduction. While environmental circumstances, such as poor nutritional conditions, may arise in which it is advantageous for females to postpone reproduction (Bertness, ; Moehrlin & Juliano, ; Wessels, Kristal, Netter, Hatle, & Hahn, ), other factors, such as the availability of preferred or high‐quality mates, may also play a role in a female's decision to postpone mating. Given the trade‐off between reproduction and longevity, it is unclear whether postponing reproduction in hopes of locating a better mate is an advantageous strategy since the fitness benefits from mating with a high‐quality male may or may not outweigh the fitness costs associated with initiating offspring production later in life.…”