Micronutrient consumption by female Argiope bruennichi affects offspring survival

Multi-elemental consumer-driven nutrient cycling when predators feed on different prey

Predators play a fundamental role in cycling nutrients through ecosystems, by altering the amount and compositions of waste products and uneaten prey parts available to decomposers. Different prey can vary in their elemental content and the deposition of elements in predator waste can vary depending on which elements are preferentially retained versus eliminated as waste products. We tested how feeding on different prey (caterpillars, cockroaches, crickets, and flies) affected the concentrations of 23 elements in excreta deposited by wolf spider across 2 seasons (spring versus fall). Spider excreta had lower concentrations of carbon and higher concentrations of many other elements (Al, B, Ba, K, Li, P, S, Si, and Sr) compared to prey remains and whole prey carcasses. In addition, elemental concentrations in unconsumed whole prey carcasses and prey remains varied between prey species, while spider excreta had the lowest variation among prey species. Finally, the concentrations of elements deposited differed between seasons, with wolf spiders excreting greater concentrations of Fe, Mg, Mn, Mo, S, and V in the fall. However, in the spring, spiders excreted higher concentrations of Al, B, Ba, Ca, Cd, Cu, K, P, Na, Si, Sr, and Zn. These results highlight that prey identity and environmental variation can determine the role that predators play in regulating the cycling of many elements. A better understanding of these convoluted nutritional interactions is critical to disentangle specific consumer-driven effects on ecosystem function.

Variation among arthropod taxa in the amino acid content of exoskeleton and digestible tissue

Arthropod consumption provides amino acids to invertebrates and vertebrates alike, but not all amino acids in arthropods may be digestible as some are bound in the exoskeleton. Consumers may not be able to digest exoskeleton in significant amounts or avoid it entirely (e.g., extraoral digestion). Hence, measures that do not separate digestible amino acids from those in exoskeleton may not accurately represent the amino acids available to consumers. Additionally, arthropods are taxonomically diverse, and it remains unclear if taxonomic differences also reflect differences in amino acid availability. Thus, we tested: (1) if there were consistent differences in the content and balance of amino acids between the digestible tissue and exoskeleton of arthropods and (2) if arthropod Orders differ in amino acid content and balance. We measured the amino acid content (mg/100 mg dry mass) and balance (mg/100 mg protein) of whole bodies and exoskeleton of a variety of arthropods using acid hydrolysis. Overall, there was higher amino acid content in digestible tissue. There were also significant differences in the amino acid balance of proteins in digestible tissue and exoskeleton. Amino acid content and balance also varied among Orders; digestible tissues of Hemiptera contained more of some essential amino acids than other Orders. These results demonstrate that arthropod taxa vary in amino acid content, which could have implications for prey choice by insectivores. In addition, exoskeleton and digestible tissue content differ in arthropods, which means that whole body amino acid content of an arthropod is not necessarily a predictor of amino acid intake of a predator that feeds on that arthropod.

The effects of prey lipid on female mating and reproduction of a wolf spider

As predators, the macronutrients spiders extract from their prey play important roles in their mating and reproduction. Previous studies of macronutrients on spider mating and reproduction focus on protein, the potential impact of prey lipid content on spider mating and reproduction remains largely unexplored. Here, we tested the influence of prey varying in lipid content on female mating, sexual cannibalism, reproduction, and offspring fitness in the wolf spider Pardosa pseudoannulata. We acquired 2 groups of fruit fly Drosophila melanogaster that differed significantly in lipid but not protein content by supplementing cultural media with a high or low dose of sucrose on which the fruit flies were reared (HL: high lipid and LL: low lipid). Subadult (i.e., 1 molt before adult) female spiders that fed HL flies matured with significantly higher lipid content than those fed LL flies. We found that the mated females fed with HL flies significantly shortened pre-oviposition time and resulted in a significantly higher fecundity. However, there was no significant difference in female spiders varying in lipid content on other behaviors and traits, including the latency to courtship, courtship duration, mating, copulation duration, sexual cannibalism, offspring body size, and survival. Hence, our results suggest that the lipid content of prey may be a limiting factor for female reproduction, but not for other behavioral traits in the wolf spiders P. pseudoannulata.

The sublethal effects of neonicotinoids on spiders are independent of their nutritional status

Spiders were recently shown to be adversely affected by field-realistic concentrations of a broad scale of neonicotinoid insecticides. Among the reported effects of neonicotinoids on invertebrates were declines in lipid biosynthesis and upregulation of β-oxidation, while vertebrate models suggest increased adipogenesis following treatment with neonicotinoids. Therefore, we hypothesized that there exists synergy between the effects of diet and concurrent exposure to field-realistic concentrations of neonicotinoid insecticides. To address this hypothesis, we fed first instars of the large wolf spider Hogna antelucana with two types of diets and exposed them to field-realistic concentrations of three formulations of neonicotinoids (thiamethoxam, thiacloprid and acetamiprid). We then measured the growth of the tested spiders; the lipid and protein content of their bodies; and their behavior, including ballooning, rappelling, and locomotor parameters. The two tested diets consisted of casein-treated and sucrose-treated Drosophila melanogaster. The dietary treatments affected the lipid and protein content of the spiders, their body weight and carapace length but did not affect any of the measured behavioral parameters. Surprisingly, we did not find any effects of acute exposure to neonicotinoid insecticides on the lipid or protein reserves of spiders. Exposure to neonicotinoids altered the behavior of the spiders as reported previously in other spider species; however, these effects were not affected by dietary treatments. Overall, the dietary treatments did not have any major synergy with acute exposure to field-realistic concentrations of neonicotinoid insecticides.

High-lipid prey reduce juvenile survivorship and delay egg laying in a small linyphiid spider Hylyphantes graminicola

Prey proteins and lipids greatly impact predator life-history traits. However, life-history plasticity offers predators the opportunity to tune the life-history traits in response to the limited macronutrients to allocate among traits. A fast-growing predator species with a strict maturation time may be more likely to consume nutritionally imbalanced prey. Here, we tested this hypothesis by examining the effect of the protein-to-lipid ratio in prey on a small sheet web-building spider, Hylyphantes graminicola, with a short life span, using adult Drosophila melanogaster as the prey. By manipulating the macronutrient content of the prey to generate three prey types with different protein-to-lipid ratios (i.e. high, intermediate and low), we demonstrated that the majority of the spiders that consumed only these flies could reach full maturity. However, juvenile spiders that consumed high-lipid (low protein-to-lipid ratio) flies had a higher rate of mortality than those consuming medium-protein and high-protein flies. The prey protein-to-lipid ratio had no significant effects on the developmental duration and size at maturity. Although the prey protein-to-lipid ratio had no significant influence on mating behaviour and female fecundity, females reared on high-lipid flies exhibited a significant delay in oviposition compared with those reared on high-protein flies. We conclude that high-lipid prey has negative effects on the survival and reproductive function of H. graminicola Our study thus provides clear evidence that low plasticity with fast development to a certain size means a high nutritional requirement for protein at a cost of lower survival and prolonged time to egg laying when prey have low protein-to-lipid content in H. graminicola.

Influence of maternal diet on offspring survivorship, growth, and reproduction in a sheetweb spider

Prey vary dramatically in quality, and maternal diet is generally assumed to substantially influence offspring survivorship, growth, and reproduction in spiders. Numerous studies that have tested this hypothesis have focused exclusively on parental generation or have considered relatively few fitness components of juvenile offspring. However, maternal diet may have a substantial effect on fitness performance beyond juvenile offspring. Here, we investigated the influence of one-time maternal feeding on multiple offspring fitness components, including the survival rate and growth of juvenile offspring as well as the mating and reproductive success of adult offspring in Hylyphantes graminicola, a sheetweb spider with an extremely short lifespan (∼1 month). We fed field-collected adult female spiders two different diets only once immediately before oviposition: midges (Tendipes sp.) only (MO) or flies (Drosophila melanogaster) only (FO). Juvenile offspring of MO females had significantly higher survival rate, faster growth, and larger male size at maturity than FO offspring. Although maternal diet did not significantly influence mating behavior or fecundity of female offspring overall, those of MO females laid eggs earlier and their eggs also hatched earlier and had a higher hatching rate than those of FO females. Intriguingly, one-time maternal feeding was sufficient to have such an influence on offspring fitness even beyond juvenile offspring in Hgraminicola This one-time maternal effect may be widespread in other spiders and other invertebrates with a short lifespan.This article has an associated First Person interview with the first author of the paper.

Does sexual cannibalism secure genetic benefits of polyandry in a size-dimorphic spider?

Abstract

Females mate multiply despite numerous costs. It is well established that polyandry can result in sexual conflict, favoring male adaptations that prevent sperm competition often to the disadvantage of the female. Such adaptations are extreme in spiders with one-shot genitalia of which parts break off and act as mating plugs, rendering them dysfunctional. In the spider Argiope bruennichi, mating plugs effectively prevent further males from inseminating and males that inseminate and plug both genital openings of a female secure exclusive paternity. However, females frequently prevent monopolization by attacking and cannibalizing males during their first copulation, leaving their second spermatheca free for another male. Here, we test whether the high frequency of sexual cannibalism evolved as a female adaptation to resist monopolization and secure indirect benefits of polyandry. To standardize conditions, we double-mated females either with the same or two different males and prevented male consumption. Using a split-brood design, we raised offspring to maturity under poor and rich food conditions and measured their survival, duration of juvenile phase, and adult body mass. Under low food, daughters of polyandrous mothers matured later but slightly heavier than daughters of monandrous females. Since the adaptive value of this combination is unclear, these findings lend no conclusive support to our hypothesis. We discuss the stereotypic nature of the female attack in the context of antagonistic co-evolution considering previous studies that found modest direct benefits of cannibalism as well as a potential for non-additive benefits.

Significance statement

Sexual conflict is extreme in spiders where sexual cannibalism impairs male mating rates. Males of the spider Argiope bruennichi possess one-shot genitalia which they break off to plug female genital openings. They gain exclusive paternity with a female if two copulations are achieved and both genital openings plugged. Females, however, stereotypically attack every male at the onset of copulation, limiting most males to single copulation but retaining the option to secure potential benefits of polyandry. Previous studies revealed weak direct and non-additive indirect benefits of multiple mating. In this study, we tested for the presence of additive genetic benefits but again found only inconclusive evidence for adaptive differences in offspring quality between monandrous and polyandrous females. All results combined, we here speculate that the stereotypic female attack might be a ghost of a past antagonistic co-evolution.