Cooperative foraging during larval stage affects fitness in Drosophila

Influence of egg density on larval development and adult body size of cat fleas (Ctenocephalides felis)

Fleas (Siphonaptera) are holometabolous insects with larval and adult stages that exhibit vastly different ecologies from each other. Adult fleas are parasitic and feed exclusively on the blood of a vertebrate host, whereas flea larvae do not live on hosts and consume dried faecal blood from adult fleas. Because flea larvae rely on adult flea faeces for food, excrement and eggs must fall in the same location; thus, larval density is likely high in these restricted habitats. However, the influence of larval density on the subsequent adult stage has not been examined. In the present study, we utilized egg density to investigate density-dependent effects on larval development and adult body size in the cat flea (Ctenocephalides felis Bouché) (Siphonaptera: Pulicidae). Specifically, eggs were collected to create three different larval densities (n = 50, 100 and 150 per 56.7 cm2), and hatched larvae from all groups were fed an excess amount of adult faecal pellets. Larval development was measured by recording the proportion of eggs that developed to the pupal stage and the proportion of eggs that reached adulthood (eclosion). The body size of eclosed adults was quantified for both sexes using head length and length of the total body. We found that the number of eggs had no effect on the proportion of larvae that pupated or the proportion of larvae that eclosed; however, higher egg densities resulted in larger body sizes for both sexes. Overall, these data yield significant insight into how the ecology of larval fleas impacts the biology of the resultant adults.

The cluster digging behavior of larvae confers trophic benefits to fitness in insects

Collective behaviors efficiently impart benefits to a diversity of species ranging from bacteria to humans. Fly larvae tend to cluster and form coordinated digging groups under crowded conditions, yet understanding the rules governing this behavior is in its infancy. We primarily took advantage of the Drosophila model to investigate cooperative foraging behavior. Here, we report that Drosophila-related species and the black soldier fly have evolved a conserved strategy of cluster digging in food foraging. Subsequently, we investigated relative factors, including larval stage, population density, and food stiffness and quality, that affect the cluster digging behavior. Remarkably, oxygen supply through the posterior breathing spiracles is necessary for the organization of digging clusters. More importantly, we theoretically devise a mathematical model to accurately calculate how the cluster digging behavior expands food resources by diving depth, cross-section area, and food volume. We found that cluster digging behavior approximately increases 2.2 fold depth, 1.7-fold cross-section area, and 1.9 fold volume than control groups, respectively. Amplification of food sources significantly facilitates survival, larval development, and reproductive success of Drosophila challenged with competition for limited food resources, thereby conferring trophic benefits to fitness in insects. Overall, our findings highlight that the cluster digging behavior is a pivotal behavior for their adaptation to food scarcity, advancing a better understanding of how this cooperative behavior confers fitness benefits in the animal kingdom.

Population parameters of Drosophila larval cooperative foraging

Cooperative foraging behavior can be advantageous when there is a common exploitable resource. By cooperating, members of the group can take advantage of the potential of increased efficiency of working together as well as equitable distribution of the product. An experimental signature of cooperative foraging is an Allee effect where at a certain number of individuals, there is a peak of fitness. What happens when there are intruders especially ones that do not contribute to any work required for foraging? Drosophila larvae secrete digestive enzymes and exodigest food. Under crowded conditions in liquid food these larvae form synchronized feeding clusters which provides a fitness benefit. A key for this synchronized feeding behavior is the visually guided alignment between adjacent larvae in a feeding cluster. Larvae who do not align their movements are excluded from the groups and subsequently lose the benefit. This may be a way of editing the group to include only known members. To test the model, the fitness benefit from cooperative behavior was further investigated to establish an Allee effect for a number of strains including those who cannot exodigest or cluster. In a standard lab vial, about 40 larvae is the optimal number for fitness. Combinations of these larvae were also examined. The expectation was that larvae who do not contribute to exodigestion are obligate cheaters and would be expelled. Indeed, obligate cheaters gain greatly from the hosts but paradoxically, so do the hosts. Clusters that include cheaters are more stable. Therefore, clustering and the benefits from it are dependent on more than just the contribution to exodigestion. This experimental system should provide a rich future model to understand the metrics of cooperative behavior.

Aggregation in an heterospecific population of blowfly larvae: social behaviour is impacted by species-specific thermal requirements and settlement order

Larvae of several blowfly species grow on carcasses and actively aggregate together. They face harsh developmental conditions resulting in a strong pressure to reduce development time: this is achieved either through thermoregulation or aggregation. We investigate how these two developmental strategies are modulated within heterospecific groups. In a first experiment, larvae of two species with different thermal requirements were deposited simultaneously on a thermal gradient. This resulted in the formation of two monospecific groups, each located at the species-specific thermal preferendum. However, when Calliphora vomitoria (Linnaeus) larvae were placed first, the later arriving Lucilia sericata (Meigen) larvae attracted the whole group to its own thermal preferendum. In the reverse experiment, half of the replicates resulted in single dense heterospecific groups observed at temperatures ranging from C. vomitoria to L. sericata preferendum. The other half of the replicates resulted in loose groups spread out on the thermal gradient. These results highlight the emergence of collective decisions ranging from thermal optimization to heterospecific aggregation at suboptimal temperatures. They demonstrate that species settlement order strongly affects self-organization processes and mixed-species group formation. We conclude that thermal optimization and heterospecific niche construction are two developmental strategies of carrion fly larvae. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Nanoparticle-Shielded dsRNA Delivery for Enhancing RNAi Efficiency in Cotton Spotted Bollworm Earias vittella (Lepidoptera: Nolidae)

The spotted bollworm Earias vittella (Lepidoptera: Nolidae) is a polyphagous pest with enormous economic significance, primarily affecting cotton and okra. However, the lack of gene sequence information on this pest has a significant constraint on molecular investigations and the formulation of superior pest management strategies. An RNA-seq-based transcriptome study was conducted to alleviate such limitations, and de novo assembly was performed to obtain transcript sequences of this pest. Reference gene identification across E. vittella developmental stages and RNAi treatments were conducted using its sequence information, which resulted in identifying transcription elongation factor (TEF), V-type proton ATPase (V-ATPase), and Glyceraldehyde -3-phosphate dehydrogenase (GAPDH) as the most suitable reference genes for normalization in RT-qPCR-based gene expression studies. The present study also identified important developmental, RNAi pathway, and RNAi target genes and performed life-stage developmental expression analysis using RT-qPCR to select the optimal targets for RNAi. We found that naked dsRNA degradation in the E. vittella hemolymph is the primary reason for poor RNAi. A total of six genes including Juvenile hormone methyl transferase (JHAMT), Chitin synthase (CHS), Aminopeptidase (AMN), Cadherin (CAD), Alpha-amylase (AMY), and V-type proton ATPase (V-ATPase) were selected and knocked down significantly with three different nanoparticles encapsulated dsRNA conjugates, i.e., Chitosan-dsRNA, carbon quantum dots-dsRNA (CQD-dsRNA), and Lipofectamine-dsRNA conjugate. These results demonstrate that feeding nanoparticle-shielded dsRNA silences target genes and suggests that nanoparticle-based RNAi can efficiently manage this pest.

It's all about seeing and hearing: the Editors' and Readers' Choice Awards 2022

This year marks the inauguration of the annual Editors' Choice Award and the Readers' Choice Award, each presented for outstanding original papers and review articles published in the Journal of Comparative Physiology A. The winners of the 2022 Editors' Choice Award were determined by vote of the Editorial Board for the most highly recommended papers published in Volume 207 in 2021. They are 'Visual discrimination and resolution in freshwater stingrays (Potamotrygon motoro)' by Daniel et al. (J Comp Physiol A 207, 43-58, 2021) in the Original Paper category; and 'Neurophysiology goes wild: from exploring sensory coding in sound proof rooms to natural environments' by Römer (J Comp Physiol A 207, 303-319, 2021) in the Review Article category. The 2022 Readers' Choice Award was based on access number of articles published in Volume 206 in 2020, to ensure at least 12-month online presence. It is given to Nicholas et al. for their original paper titled 'Visual motion sensitivity in descending neurons in the hoverfly' (J Comp Physiol A 206, 149-163, 2020); and to Schnaitmann et al. for their review article entitled 'Color vision in insects: insights from Drosophila' (J Comp Physiol A 206, 183-198, 2020).

How Social Experience and Environment Impacts Behavioural Plasticity in Drosophila

An organism's behaviour is influenced by its social environment. Experiences such as social isolation or crowding may have profound short or long-term effects on an individual's behaviour. The composition of the social environment also depends on the genetics and previous experiences of the individuals present, leading to additional potential outcomes from each social interaction. In this article, we review selected literature related to the social environment of the model organism Drosophila melanogaster, and how Drosophila respond to variation in their social experiences throughout their lifetimes. We focus on the effects of social environment on behavioural phenotypes such as courtship, aggression, and group dynamics, as well as other phenotypes such as development and physiology. The consequences of phenotypic plasticity due to social environment are discussed with respect to the ecology and evolution of Drosophila. We also relate these studies to laboratory research practices involving Drosophila and other animals.

Birth temperature followed by a visual critical period determines cooperative group membership

Cooperative behavior often arises when a common exploitable resource is generated. Cooperation can provide equitable distribution and protection from raiding of a common resource such as processed food. Under crowded conditions in liquid food, Drosophila larvae adopt synchronized feeding behavior which provides a fitness benefit. A key for this synchronized feeding behavior is the visually guided alignment of a 1-2 s locomotion stride between adjacent larvae in a feeding cluster. The locomotion stride is thought to be set by embryonic incubation temperature. This raises a question as to whether sib larvae will only cluster efficiently if they hatch at the same temperature. To test this, larvae were first collected and incubated in outdoor conditions. Morning hatched lower temperature larvae move slower than their afternoon higher temperature sibs. Both temperature types synchronize but tend to exclude the other type of larvae from their clusters. In addition, fitness, as measured by adult wing size, is highest when larvae cluster with their own temperature type. Thus, the temperature at which an egg is laid sets a type of behavioral stamp or password which locks in membership for later cooperative feeding.

Parasites differentially impact crayfish personality in different contexts

The expression of an individual animal’s behaviour can be placed along many different personality spectra. Parasite load can alter animal behaviour and, thus, fitness. The personality traits of rusty crayfish, Faxonius rusticus, were analysed in three different behavioural contexts: foraging, exploration, and threatened. Each crayfish was tested in each context 3 times, giving a total of 9 assays per crayfish. After assays were completed, crayfish were dissected, and the hepatopancreas of each crayfish was photo analysed to determine the parasite load of the trematode, Microphallus spp. A composite personality score for each assay and parasite load was loaded into a PCA. The PCA model showed that as parasite load increased, crayfish became bolder in threatening contexts and less exploratory in novel environments, whether or not a food stimulus was present. Thus, parasite load alters the placement of crayfish on different personality spectra, but this change is context specific.

Critical periods shaping the social brain: A perspective from Drosophila

Many sensory processing regions of the central brain undergo critical periods of experience-dependent plasticity. During this time ethologically relevant information shapes circuit structure and function. The mechanisms that control critical period timing and duration are poorly understood, and this is of special importance for those later periods of development, which often give rise to complex cognitive functions such as social behavior. Here, we review recent findings in Drosophila, an organism that has some unique experimental advantages, and introduce novel views for manipulating plasticity in the post-embryonic brain. Critical periods in larval and young adult flies resemble classic vertebrate models with distinct onset and termination, display clear connections with complex behaviors, and provide opportunities to control the time course of plasticity. These findings may extend our knowledge about mechanisms underlying extension and reopening of critical periods, a concept that has great relevance to many human neurodevelopmental disorders.