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1. Intralocus sexual conflict over optimal nutrient intake and the evolution of sex differences in life span and reproduction

   https://doi.org/10.1111/1365-2435.13995  

   Hawkes, Michael ; Lane, Sarah M. ; Rapkin, James ; Jensen, Kim ; House, Clarissa M. ; Sakaluk, Scott K. ; Hunt, John ( January 2022 , Functional Ecology)

   Despite widespread variation in life span across species, three clear patterns exist: sex differences in life span are ubiquitous, life span is commonly traded against reproduction, and nutrition has a major influence on these traits and how they trade‐off. One process that potentially unites these patterns is intralocus sexual conflict over the optimal intake of nutrients for life span and reproduction. If nutrient intake has sex‐specific effects on life span and reproduction but nutrient choice is genetically linked across the sexes, intralocus sexual conflict will occur and may prevent one or both sexes from feeding to their nutritional optima.

   Here we determine the potential for this process to operate in the decorated cricketGryllodes sigillatus. Using the Geometric Framework for Nutrition, we restrict male and female crickets to diets varying in the ratio of protein to carbohydrates and total nutrient content to quantify the effects on life span and daily reproductive effort in the sexes. We then use inbred lines to estimate the quantitative genetic basis of nutrient choice in males and females. We combine the nutrient effects and genetic estimates to predict the magnitude of evolutionary constraint for these traits in each sex. Finally, we present male and female crickets with a much broader range of diet pairs to determine how the sexes actively regulate their intake of nutrients.

   We show that protein and carbohydrate intake have contrasting effects on life span and reproduction in the sexes and that there are strong positive intersexual genetic correlations for the intake of these nutrients under dietary choice. This is predicted to accelerate the evolutionary response of nutrient intake in males but constrain it in females, suggesting they are losing the conflict. Supporting this view, males and females regulate nutrient intake to a common nutrient ratio that was not perfectly optimal for life span or reproduction in either sex, especially in females.

   Our findings show that intralocus sexual conflict over the optimal intake of nutrients is likely to be an important process generating sex differences in life span and reproduction and may help explain why females age faster and live shorter than males inG. sigillatus.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Sex-specific plasticity and the nutritional geometry of insulin-signaling gene expression in Drosophila melanogaster

   https://doi.org/10.1186/s13227-021-00175-0  

   McDonald, Jeanne M. C. ; Nabili, Pegah ; Thorsen, Lily ; Jeon, Sohee ; Shingleton, Alexander W. ( May 2021 , EvoDevo)

   Sexual-size dimorphism (SSD) is replete among animals, but while the selective pressures that drive the evolution of SSD have been well studied, the developmental mechanisms upon which these pressures act are poorly understood. Ours and others’ research has shown that SSD inD. melanogasterreflects elevated levels of nutritional plasticity in females versus males, such that SSD increases with dietary intake and body size, a phenomenon called sex-specific plasticity (SSP). Additional data indicate that while body size in both sexes responds to variation in protein level, only female body size is sensitive to variation in carbohydrate level. Here, we explore whether these difference in sensitivity at the morphological level are reflected by differences in how the insulin/IGF-signaling (IIS) and TOR-signaling pathways respond to changes in carbohydrates and proteins in females versus males, using a nutritional geometry approach.

   The IIS-regulated transcripts of4E-BPandInRmost strongly correlated with body size in females and males, respectively, but neither responded to carbohydrate level and so could not explain the sex-specific response to body size to dietary carbohydrate. Transcripts regulated by TOR-signaling did, however, respond to dietary carbohydrate in a sex-specific manner. In females, expression ofdILP5positively correlated with body size, while expression ofdILP2,3and8,was elevated on diets with a low concentration of both carbohydrate and protein. In contrast, we detected lower levels of dILP2 and 5 protein in the brains of females fed on low concentration diets. We could not detect any effect of diet ondILPexpression in males.

   Although females and males show sex-specific transcriptional responses to changes in protein and carbohydrate, the patterns of expression do not support a simple model of the regulation of body-size SSP by either insulin- or TOR-signaling. The data also indicate a complex relationship between carbohydrate and protein level,dILPexpression and dILP peptide levels in the brain. In general, diet quality and sex both affect the transcriptional response to changes in diet quantity, and so should be considered in future studies that explore the effect of nutrition on body size.

    

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3. Macronutrient intake and simulated infection threat independently affect life history traits of male decorated crickets

   https://doi.org/10.1002/ece3.6813  

   Duffield, Kristin_R ; Hampton, Kylie_J ; Houslay, Thomas_M ; Rapkin, James ; Hunt, John ; Sadd, Ben_M ; Sakaluk, Scott_K ( September 2020 , Ecology and Evolution)

   Nutritional geometry has advanced our understanding of how macronutrients (e.g., proteins and carbohydrates) influence the expression of life history traits and their corresponding trade‐offs. For example, recent work has revealed that reproduction and immune function in male decorated crickets are optimized at very different protein:carbohydrate (P:C) dietary ratios. However, it is unclear how an individual's macronutrient intake interacts with its perceived infection status to determine investment in reproduction or other key life history traits. Here, we employed a fully factorial design in which calling effort and immune function were quantified for male crickets fed either diets previously demonstrated to maximize calling effort (P:C = 1:8) or immune function (P:C = 5:1), and then administered a treatment from a spectrum of increasing infection cue intensity using heat‐killed bacteria. Both diet and a simulated infection threat independently influenced the survival, immunity, and reproductive effort of males. If they called, males increased calling effort at the low infection cue dose, consistent with the terminal investment hypothesis, but interpretation of responses at the higher threat levels was hampered by the differential mortality of males across infection cue and diet treatments. A high protein, low carbohydrate diet severely reduced the health, survival, and overall fitness of male crickets. There was, however, no evidence of an interaction between diet and infection cue dose on calling effort, suggesting that the threshold for terminal investment was not contingent on diet as investigated here.

    

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4. Glucose tolerance of iguanas is affected by high-sugar diets in the lab and supplemental feeding by ecotourists in the wild

   https://doi.org/10.1242/jeb.243932  

   French, Susannah S. ; Hudson, Spencer B. ; Webb, Alison C. ; Knapp, Charles R. ; Virgin, Emily E. ; Smith, Geoffrey D. ; Lewis, Erin L. ; Iverson, John B. ; DeNardo, Dale F. ( April 2022 , Journal of Experimental Biology)

   ABSTRACT There is great interspecific variation in the nutritional composition of natural diets, and the varied nutritional content is physiologically tolerated because of evolutionarily based balances between diet composition and processing ability. However, as a result of landscape change and human exposure, unnatural diets are becoming widespread among wildlife without the necessary time for evolutionary matching between the diet and its processing. We tested how a controlled, unnatural high glucose diet affects glucose tolerance using captive green iguanas, and we performed similar glucose tolerance tests on wild Northern Bahamian rock iguanas that are either frequently fed grapes by tourists or experience no such supplementation. We evaluated both short and longer-term blood glucose responses and corticosterone (CORT) concentrations as changes have been associated with altered diets. Experimental glucose supplementation in the laboratory and tourist feeding in the wild both significantly affected glucose metabolism. When iguanas received a glucose-rich diet, we found greater acute increases in blood glucose following a glucose challenge. Relative to unfed iguanas, tourist-fed iguanas had significantly lower baseline CORT, higher baseline blood glucose, and slower returns to baseline glucose levels following a glucose challenge. Therefore, unnatural consumption of high amounts of glucose alters glucose metabolism in laboratory iguanas with short-term glucose treatment and free-living iguanas exposed to long-term feeding by tourists. Based on these results and the increasing prevalence of anthropogenically altered wildlife diets, the consequences of dietary changes on glucose metabolism should be further investigated across species, as such changes in glucose metabolism have health consequences in humans (e.g. diabetes). 

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5. Variable digestibility of captive northern greater galagos ( Otolemur garnettii ) fed experimental “frugivorous” and “invertebrate” diets

   https://doi.org/10.1002/zoo.21773  

   Loudon, James E. ; Smith, B. Katherine ; Bianchi, Sydnie ; Howells, Michaela E. ; Krowka, Mead A. ; Gomez, Andres M. ; Davison, Samuel ; Paine, Oliver C. C. ; Sponheimer, Matt ( May 2023 , Zoo Biology)

   Few studies have addressed the nutritional ecology of galagos. Observations of galagos in the wild reveal that they rely on fruits and invertebrates to varying degrees depending on their availability. We conducted a 6‐week comparative dietary analysis of a colony of captive‐housed northern greater galagos (Otolemur garnettii), which included five females and six males with known life histories. We compared two experimental diets. The first was fruit dominated and the second was invertebrate dominated. For each diet, we examined dietary intake and apparent dry matter digestibility over the course of 6 weeks. We found significant differences between the apparent digestibility of the diets, with the “invertebrate” diet being more digestible than the “frugivorous” diet. The lower apparent digestibility of the “frugivorous” diet was driven by the higher fiber contents of the fruits provided to the colony. However, variation in apparent digestibility of both diets was found among individual galagos. The experimental design used in this study may provide useful dietary data for the management of captive colonies of galagos and other strepsirrhine primates. This study may also be helpful for understanding the nutritional challenges faced by free‐ranging galagos through time and across geographic space.

    

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