Towards a synthesis of frameworks in nutritional ecology: interacting effects of protein, carbohydrate and phosphorus on field cricket fitness

Abstract

Phosphorus has been identified as an important determinant of nutritionrelated biological variation. The macronutrients protein (P) and carbohydrates (C), both alone and interactively, are known to affect animal performance. No study, however, has investigated the importance of phosphorus relative to dietary protein or carbohydrates, or the interactive effects of phosphorus with these macronutrients, on fitness-related traits in animals. We used a nutritional geometry framework to address this question in adult field crickets (Gryllus veletis). Our results showed that lifespan, weight gain, acoustic mate signalling and egg production were maximized on diets with different P : C ratios, that phosphorus did not positively affect any of these fitness traits, and that males and females had different optimal macronutrient intake ratios for reproductive performance. When given a choice, crickets selected diets that maximized both lifespan and reproductive performance by preferentially eating diets with low P : C ratios, and females selected diets with a higher P : C ratio than males. Conversely, phosphorus intake was not regulated. Overall, our findings highlight the importance of disentangling the influences of different nutrients, and of quantifying both their individual and interactive effects, on animal fitness traits, so as to gain a more integrative understanding of their nutritional ecology.

Dietary phosphate affects food selection, post-ingestive P fate, and performance of a polyphagous herbivore

“…However, diets with a P content of 0.1% and below or 1% and above could support maximal growth during 3 day time periods when animals had been fed on the optimal (0.5%) diets for most of their lives, suggesting insects have a considerable capacity to buffer effects of non-optimal P consumption. Long-term consumption of diets with a P content of 1.00% or higher suppressed growth, consistent with the 'intake target' behavior of S. americana and with observations of reduced performance of various aquatic consumers (Boersma and Elser, 2006) and some insect species when provided with diets well above the mean P levels for terrestrial leaves (Harrison et al, 2014;Loaiza et al, 2008;Smith, 1960). Together, these results demonstrate that ecologically relevant variation in plant P content affects the behavior and performance of this grasshopper.…”

“…However, the development rate of the grasshopper Melanoplus bivittatus was unaffected by dietary %P of artificial diets, except for negative effects at the highest levels (Loaiza et al, 2008). Smith (1960) found similar results for M. bivittatus using fertilized wheat, as did Harrison et al (2014), who found no effects of dietary P intake on most fitness parameters of crickets (Gryllus veletis) except for some negative effects of high dietary P on male chirping rate. Finally, fertilization of plots with phosphate increased survival, body size and development rate of one planthopper species but not another (Huberty and Denno, 2006).…”

“…However, we also did not find an effect of %P diet treatment on growth rate over this short duration, suggesting that grasshoppers have compensatory mechanisms beyond increasing total food consumption to cope with intermittent P shortage. Similarly, adult field crickets, G. veletis, did not preferentially consume high P foods when given pairings ranging from 0.20% to 1.1%P of dry diet (Harrison et al, 2014). These crickets were fed a P-rich diet as juveniles (1.1%P) and so may have fulfilled their P requirements before reaching adulthood.…”

“…In addition, we conducted a test to investigate the presence of a P intake target (sensu Simpson and Raubenheimer, 1993). Harrison et al (2014) recently reported that adult G. veletis crickets do not have a P target; however, their minimal dietary P was 0.20% (% of dry diet), with an estimated N:P ratio of 40 (atomic), which may not have captured a broad enough range of dietary P. Previously, grasshoppers (and many other animals) have been shown to exhibit intake targets for protein:carbohydrate ratios and NaCl levels (Simpson and Raubenheimer, 2012). In such tests, animals are provided with pairs of diets with high or low levels of the nutrients of interest.…”

Effects of macronutrient intake on the lifespan and fecundity of the marula fruit fly, Ceratitis cosyra (Tephritidae): Extreme lifespan in a host specialist

“…Thus, C. cosyra females opted for a protein and carbohydrate intake promoting strong egg production per day, rather than across their entire lives. The effects of protein and carbohydrate intake on lifespan in our study species were similar to those observed in other studies applying the GF to Tephritidae (Fanson & Taylor, 2012; Fanson et al., 2009), Diptera (Jensen et al., 2015; Lee et al., 2008), and other herbivorous insect orders (Harrison, Raubenheimer, Simpson, Godin, & Bertram, 2014; Maklakov et al., 2008). As in these other studies, we found that lifespan was optimized when flies consumed high quantities of a carbohydrate‐biased diet.…”