Life‐history plasticity after attaining a dietary threshold for reproduction is associated with protein storage in flesh flies

Abstract

Summary 1.Body condition affects the timing and magnitude of life-history transitions. Therefore, identifying proximate mechanisms involved in assessing condition is critical to understanding how these mechanisms affect the expression of life-history plasticity. Nutrient storage is an important body condition parameter, likely playing roles in both attaining minimum body-condition thresholds for life-history transitions and expression of life-history traits. 2. We manipulated protein availability for females of the flesh fly Sarcophaga crassipalpis to determine whether reproductive timing and output would remain plastic or become fixed. Liver was provided for 0, 2, 4 or 6 days of adult pre-reproductive development. Importantly, liver was removed after the feeding threshold had been attained and females had committed to producing a clutch. 3. We also identified the major storage proteins and monitored their abundances, because protein stores may serve as an index of body condition and therefore may play an important role in life-history transitions and plasticity. 4. Flesh flies showed clear post-threshold plasticity in reproductive timing. Females fed protein for 2 days took c. 30% longer to provision their clutch than those fed for 4 or 6 days. Observations of oogenesis showed the 2-day group expressed a different developmental program including slower egg provisioning. 5. Protein availability also affected reproductive output. Females fed protein for 2 days produced c. 20% fewer eggs than females fed 4 or 6 days. Six-day treated females provisioned larger eggs than 4-day treated females, followed by 2-day treated females with the smallest eggs. 6. Two storage proteins were identified, LSP-1 and LSP-2. LSP-2 accumulation differed across feeding treatments. The 2-and 4-day treatment groups accumulated LSP-2 stores but depleted them during provisioning of the first clutch, whereas the 6-day group accumulated the greatest quantity of LSP-2 and had substantial LSP-2 stores remaining at the end of the clutch. This pattern of accumulation and depletion suggests that LSP-2 could play roles in both provisioning the current clutch and future clutches, making it a good candidate molecule for affecting reproductive timing and allotment. LSP-1 was not associated with post-threshold plasticity; it was carried over from larval feeding into adulthood and depleted uniformly across all feeding groups.

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

“…Sarcophaga crassipalpis (flesh flies) used in this study were obtained from a laboratory colony maintained at the University of Florida according to procedures outlined in Hahn et al (2008a) and Denlinger (1972). Newly-eclosed flies were hand sorted by sex into twelve screened cages (30 × 30 × 30 cm); each cage contained 150 females and 150 males.…”

“…Females were thawed on ice and dissected in ultrapure water, the ovaries and any eggs in the uterus were removed. Oogenic development was characterized by dissecting the ovaries and observing the oocytes; the developing oocytes were staged using an eight point scale ranging from previtellogenic follicules (1) to mature chorionated eggs (8) as described in Hahn et al (2008a). Fully-mature eggs were removed from the uterus and counted as a measure of fecundity.…”

“…While canalization may be common, it is not necessarily the rule. Hahn et al (2008a) reported post-threshold plasticity in reproductive timing in the flesh fly, Sarcophaga crassipalpis Macquart. They found that adult female flesh flies that were switched to a protein-restricted diet after reaching their nutritional threshold for reproduction took longer to reproduce and had lower reproductive allotment (smaller and fewer eggs) than those fed a high protein diet (Hahn et al 2008a).…”

“…Hahn et al (2008a) reported post-threshold plasticity in reproductive timing in the flesh fly, Sarcophaga crassipalpis Macquart. They found that adult female flesh flies that were switched to a protein-restricted diet after reaching their nutritional threshold for reproduction took longer to reproduce and had lower reproductive allotment (smaller and fewer eggs) than those fed a high protein diet (Hahn et al 2008a). This plasticity differs from the Wilbur & Collins (1973) model in that resource poor individuals delay reproduction despite having already reached their minimum threshold, compared to resource poor anurans that undergo metamorphosis rapidly.…”

“…In addition, flesh flies undergo energetically-demanding synchronous oocyte development and provision large clutches of eggs at a time, but they are short lived as adults, suggesting that early reproduction is important. Considering the spatially and temporally patchy nature of their food sources (carrion and nectar), Hahn et al (2008a) proposed that the delay in flesh fly reproduction might be adaptive if it allows flies more time to acquire additional resources to maximize the quality of the first clutch.…”