Amanda Bretman

University of Leeds · School of Biology

It is increasingly clear that social environments have profound impacts on the life histories of ‘non-social’ animals. However, it is not yet well known how species with varying degrees of sociality respond to different social contexts and whether such effects are sex-specific. To survey the extent to which social environments specifically affect l...

In ovipositing animals, egg placement decisions can be key determinants of offspring survival. One oviposition strategy reported across taxa is egg clustering, whereby a female lays multiple eggs next to one another or next to the eggs of other females. The fitness benefits of egg clustering, especially in mixed maternity clusters, are unknown. In...

The ability to respond plastically to environmental cues is a key determinant of fitness. In changing environments, females plastically adjust the number and placement of eggs they lay, allowing them to optimise the level of resources available for offspring by minimising over-exploitation whilst also accruing potential cooperative benefits such as...

The social environment has myriad effects on individuals, altering reproduction, immune function, cognition, and aging. Phenotypic plasticity enables animals to respond to heterogeneous environments such as the social environment but requires that they assess those environments accurately. It has been suggested that combinations of sensory cues all...

Critical Thermal Limits (CTLs) gauge the physiological impact of temperature on survival or critical biological function, aiding predictions of species range shifts and climatic resilience. Two recent Drosophila species studies, using similar approaches to determine temperatures that induce sterility (Thermal Fertility Limits; TFLs), reveal that TF...

Plasticity in developmental processes gives rise to remarkable environmentally induced phenotypes. Some of the most striking and well-studied examples of developmental plasticity are seen in insects. For example, beetle horn size responds to nutritional state, butterfly eyespots are enlarged in response to temperature and humidity, and environmenta...

Background Animals can exhibit remarkable reproductive plasticity in response to their social surroundings, with profound fitness consequences. The presence of same-sex conspecifics can signal current or future expected competition for resources or mates. Plastic responses to elevated sexual competition caused by exposure to same-sex individuals ha...

Held out wings (HOW) is an RNA-binding protein essential for spermatogenesis in Drosophila melanogaster. HOW is a signal transduction and activation of RNA (STAR) protein, regulating post-transcriptional gene expression. The characteristics of RNA-binding by the conserved short cytoplasmic isoform, HOW(S), are unknown. In vivo RIP-seq identified 12...

Individuals can respond plastically to variation in their social environment. However, each sex may respond to different cues and contrasting aspects of competition. Theory suggests that the plastic phenotype expressed by one sex can influence evolutionary dynamics in the other, and that plasticity simultaneously expressed by both sexes can exert s...

Recently, it has been demonstrated that heat-induced male sterility is likely to shape population persistence as climate change progresses. However, an under-explored possibility is that females may be able to successfully store and preserve sperm at temperatures that sterilise males, which could ameliorate the impact of male infertility on populat...

BACKGROUND The discovery of coding variants in genes that confer risk of intellectual disability (ID) is an important step towards understanding the pathophysiology of this common developmental disability. METHODS Homozygosity mapping, whole-exome sequencing and co-segregation analyses were employed to identify gene variants responsible for syndro...

The impact of rising global temperatures on survival and reproduction is putting many species at risk of extinction. In particular, it has recently been shown that ther-mal effects on reproduction, especially limits to male fertility, can underpin species distributions in insects. However, the physiological factors influencing fertility at high tem...

Background Solitary bees, such as the red mason bee ( Osmia bicornis ), provide important ecosystem services including pollination. In the face of global declines of pollinator abundance, such haplodiploid Hymenopterans have a compounded extinction risk due to the potential for limited genetic diversity. In order to assess the genetic diversity of...

Recently, it has been demonstrated that heat-induced male sterility is likely to shape population persistence as climate change progresses. However, an under-explored possibility is that females may be able to successfully store and preserve sperm at temperatures that sterilise males, which could ameliorate the impact of male infertility on populat...

The impact of rising global temperatures on survival and reproduction is putting many species at risk of extinction. In particular, it has recently been shown that thermal effects on reproduction, especially limits to male fertility, can underpin species distributions in insects. However, the physiological factors influencing fertility at high temp...

Social environments influence multiple traits of individuals including immunity, stress and ageing, often in sex-specific ways. The composition of the microbiome (the assemblage of symbiotic microorganisms within a host) is determined by environmental factors and the host's immune, endocrine and neural systems. The social environment could alter ho...

Early-life environmental conditions can provide a source of individual variation in life-history strategies and senescence patterns. Conditions experienced in early life can be quantified by measuring telomere length, which can act as a biomarker of survival probability in some species. Here, we investigate whether seasonal changes, weather conditi...

Attempts to link physiological thermal tolerance to global species distributions have relied on lethal temperature limits, yet many organisms lose fertility at sublethal temperatures. Here we show that, across 43 Drosophila species, global distributions better match male-sterilizing temperatures than lethal temperatures. This suggests that species...

Animals can exhibit remarkable reproductive plasticity in response to their social surroundings, with profound fitness consequences. The study of such plasticity in females, particularly in same-sex interactions, has been severely neglected. Here we measured the impact of variation in the pre-mating social environment on reproductive success in fem...

Understanding individual variation in fitness‐related traits requires separating the environmental and genetic determinants. Telomeres are protective caps at the ends of chromosomes that are thought to be a biomarker of senescence as their length predicts mortality risk and reflect the physiological consequences of environmental conditions. The rel...

Organisms alter their phenotype in response to variation in their environment by expressing phenotypic plasticity. Both sexes exhibit such plasticity in response to contrasting environmental and social cues, and this can reflect the influence of sexual conflict. However, theory predicts that plasticity expressed by both sexes may either maximise th...

Early-life environmental conditions can provide a source of individual variation in life-history strategies and senescence patterns. Conditions experienced in early life can be quantified by measuring telomere length, which can act as a biomarker of survival probability. Here, we investigate whether seasonal changes, weather conditions, and group s...

Plants were traditionally seen as rather passive actors in their environment, interacting with each other only in so far as they competed for the same resources. In the last 30 years, this view has been spectacularly overturned, with a wealth of evidence showing that plants actively detect and respond to their neighbours. Moreover, there is evidenc...

Social interactions are thought to be a critical driver in the evolution of cognitive ability. Cooperative interactions, such as pair bonding, rather than competitive interactions have been largely implicated in the evolution of increased cognition. This is despite competition traditionally being a very strong driver of trait evolution. Males of ma...

Male reproductive phenotypes can evolve in response to the social and sexual environment. The expression of many such phenotypes may also be plastic within an individual's lifetime. For example, male Drosophila melanogaster show significantly extended mating duration following a period of exposure to conspecific male rivals. The costs and benefits...

Phenotypic plasticity can allow animals to adapt their behavior, such as their mating effort, to their social and sexual environment. However, this relies on the individual receiving accurate and reliable cues of the environmental conditions. This can be achieved via the receipt of multimodal cues, which may provide redundancy and robustness. Male...

Climate change is well understood to be a major threat to biodiversity, but sublethal impacts of high temperatures, such as reduced fertility, have been poorly studied. We examined a panel of 43 Drosophila species, finding that 19 experience significant fertility loss at temperatures up to 4.3oC cooler than their lethal temperature limits. We found...

Understanding individual variation in fitness-related traits requires separating the environmental and genetic determinants. Telomeres are protective caps at the ends of chromosomes that are thought to be a biomarker of senescence as their length predicts mortality risk and reflect the physiological consequences of environmental conditions. The rel...

Social environments influence multiple traits of individuals including immunity, stress and ageing, often in sex-specific ways. The composition of the microbiome (the assemblage of symbiotic microorganisms within a host) is determined by environmental factors and the host’s immune, endocrine and neural systems. The social environment could alter ho...

Individual variation in survival probability due to differential responses to early‐life environmental conditions is important in the evolution of life‐histories and senescence. A biomarker allowing quantification of such individual variation, and which links early‐life environmental conditions with survival by providing a measure of conditions exp...

Sperm competition favors large, costly ejaculates, and theory predicts the evolution of allocation strategies that enable males to plastically tailor ejaculate expenditure to sperm competition threat. While greater sperm transfer in response to a perceived increase in the risk of sperm competition is well-supported, we have a poor understanding of...

Social environments have been shown to have multiple effects on individual immune responses. For example, increased social contact might signal greater infection risk and prompt a prophylactic upregulation of immunity. This differential investment of resources may in part explain why social environments affect ageing and lifespan. Our previous work...

In Walsh et al. we call for research into the thermal fertility limits (TFLs) of species to better predict the impact of climate change, especially the increased frequency of heatwaves, on biodiversity. In a response to this, Graziella Iossa outlined the need to consider the sex specificity of TFLs within this framework. Broadly, we agree with this...

Increased exposure to males can affect females negatively, reducing female life span and fitness. These costs could derive from increased mating rate and also harassment by males. Additionally, early investment in reproduction can increase the onset or rate of senescence in reproductive traits. Hence, there is a tight link between reproduction and...

Rising global temperatures are threatening biodiversity. Studies on the impact of temperature on natural populations usually use lethal or viability thresholds, termed the ‘critical thermal limit’ (CTL). However, this overlooks important sublethal impacts of temperature that could affect species’ persistence. Here we discuss a critical but overlook...

Researchers of Drosophila have investigated a broad range of behaviours from aggression to alcohol preference, territoriality. and foraging. This chapter focuses on a small subset of this huge body of work and primarily discusses genetic and environmental influences on Drosophila sexual behaviours, with more focus on social environmental effects an...

The social environment provides males with information about the likelihood of reproductive competition. However, social context can be highly variable, and males must track their environment in order to alter reproductive investment appropriately. In addition to using information gained as adults to adjust reproductive strategies, males can use cu...

Telomeres, protective caps at the end of chromosomes, maintain genomic stability and function as a biomarker of senescence in many vertebrate species. Telomere length at different ages has been related to (subsequent) lifespan, but to date only one laboratory-based study has shown a direct link between early-life telomere length and lifespan. Wheth...

Phenotypic plasticity can be a key determinant of fitness. The degree to which the expression of plasticity is adaptive relies upon the accuracy with which information about the state of the environment is integrated. This step might be particularly beneficial when environments, e.g. the social and sexual context, change rapidly. Fluctuating tempor...

Males of many species use social cues to predict sperm competition (SC) and tailor their reproductive strategies, such as ejaculate or behavioural investment, accordingly. While these plastic strategies are widespread, the underlying mechanisms remain largely unknown. Plastic behaviour requires individuals to learn and memorize cues associated with...

Complex sets of cues can be important in recognising and responding to conspecific mating competitors and avoiding potentially costly heterospecific competitive interactions. Within Drosophila. melanogaster, males can detect sensory inputs from conspecifics to assess the level of competition. They respond to rivals by significantly extending mating...

RNA sequencing (RNA-seq) is widely used for RNA quantification in the environmental, biological and medical sciences. It enables the description of genome-wide patterns of expression and the identification of regulatory interactions and networks. The aim of RNA-seq data analyses is to achieve rigorous quantification of genes/transcripts to allow a...

Overview of the D. melanogaster samples used for the comparative analysis of different approaches for the identification of differentially expressed genes. From the study described in Mohorianu et al. 2017, RNA 23:1048–1059 [39], we selected four samples (each with 3 biological replicates, 1–3) comprising of 2 head-thorax (H) samples and 2 abdomen...

Subsampling normalization–pseudocode. A description with details for (1) Incremental subsampling and bootstrapping check for consistency of a sample, and (2) Subsampling to a fixed total. (PDF)

Two step (hierarchical) differential expression (HDE)—Pseudocode. A description with technical details for the two step (hierarchical) DE, including the identification of levels in the hierarchy. (PDF)

Example of intersection analysis for the 02-A, 02+A, 02-H and 02+H samples in the D. melanogaster dataset. Replicate 1 samples 02-A, 02+A, 02-H and 02+H (sample codes: 02h of exposure, ± rivals, HT or A tissue) were used to illustrate the proportion of reads mapping simultaneously to pairwise groups of CDSs, exons, 5’ and 3’ UTRs, introns and inter...

Distribution of point-to-point Pearson correlation coefficient (PCC) (y-axis) between gene expression profiles against gene expression levels (x-axis, log2 scale) for pairwise comparisons for the D. melanogaster data for the 3 replicates of the 02-H sample as an example (2h, HT body part, no rivals). Panel A shows replicate 1 vs 2, B replicate 1 vs...

Analysis of the effect of the subsampling normalization on technical (laboratory-laboratory) variation in mRNA-seq for human mRNA-seq data (Pickrell et al. 2010, Nature, 464:768–772). In the upper plots we show the coefficient of variation (CV), y-axis vs the average abundance, x-axis, obtained after the subsampling normalization (without replaceme...

Jaccard similarity indices computed on the top 1000 most abundant genes in each sample (out of a total of 15 513 genes expressed in at least one sample). Shown is a 12 by 12 matrix of all the original samples compared with each other. Samples are labelled by time point (2h), by ± rivals treatment, by body part (A or HT) and then by replicate number...

Example of incremental check for consistency done using subsampling without replacement for sample 02-H2 in the D. melanogaster dataset. For sample 02-H2 (sample code: 02h, no exposure to rivals, HT body part, replicate 2) we present the incremental subsampling, without replacement, from 99% to 40% of the data. To judge whether a sample is consiste...

Results from (A) DEseq2 and (B) edgeR analyses of the Drosophila melanogaster qRT-PCR 'validated' gene set from Mohorianu et al. 2017 (RNA 23:1048–1059). For the validations we used 3 reference genes and validated 15 A genes and 6 HT genes based on the DE selection using subsampling normalization and hierarchical DE. We investigated whether these g...

Analysis framework for the D. melanogaster mRNA-seq data. Required inputs (sequencing data in FASTQ format, the corresponding reference genome and transcriptome in FASTA/GFF) and the six main steps of the analysis are shown in a workflow diagram, following Conesa et al. 2016 (Genome Biology, 17:13). The steps, for which additional details are inclu...

Correlation analyses (Pearson (PCC), Spearman (SCC) and Kendall correlation coefficients (KCC)) between the gene expression levels for the D. melanogaster data for (A) all samples, (B) HT samples, (C) A samples. A1, B1, C1 show the PCC; A2, B2, C2 show the SCC; A3, B3 and C3 show the KCC. Each panel shows the distributions of correlation coefficien...

Identification of the hierarchy levels for the hierarchical differential expression (HDE) analysis based on the distribution of DE for the different classes of samples, i.e. replicates, body parts and ± rivals treatments (for the D. melanogaster data). Frequency density plots were used to show the distribution of DE between samples (offset fold cha...

Replicate-to-replicate MA plot on the 02-A samples for checking the efficiency of the A RPM, B quantile, C DESeq2 and D edgeR normalization methods. (Sample code: 02h, no rivals, A body part). On the x-axis we represent the average abundance between replicates (log2 scale), on the y-axis the FC (log2 scale). Although the quantile and the DESeq2 pro...

Distribution of abundances for the D. melanogaster data (for the ± rivals treatment DE) for the full set of genes identified as DE exclusively by each method. EdgeR only genes shown in S7A Fig, DEseq2 only in S7B Fig and subsampling normalization (without replacement) only in S7C Fig Genes are denoted by their FBgn identifiers. For each gene identi...

Point-to-point Pearson correlation coefficient (PCC) between the raw and subsampled data for the 02+H3 sample of the D. melanogaster data (sample code: 02h, + rivals. HT body part replicate 3). To indicate the consistency during the subsampling, without replacement, the plots show the point-to-point PCC between the original and incrementally subsam...

Comparison of the coefficients of variation across abundance (D. melanogaster data). On the x-axis is the abundance in log2 scale, on the y-axis the coefficient of variation (CV)—the ratio between the standard deviation and the mean. For clarity, the distributions are represented as standard boxplots. The upper panels (A,B,C,D) show the CV for the...

Social environments can have a major impact on ageing profiles in many animals. However, such patterns in variation in ageing and their underlying mechanisms are not well understood, particularly because both social contact and isolation can be stressful. Here, we use Drosophila melanogaster fruitflies to examine sex-specific effects of social cont...

Socio-sexual environments have profound effects on fitness. Local sex ratios can alter the threat of sexual competition, to which males respond via plasticity in reproductive behaviours and ejaculate composition. In Drosophila melanogaster, males detect the presence of conspecific mating rivals prior to mating using multiple, redundant sensory cues...

Phenotypic plasticity can increase fitness in rapidly changeable environments, but may be limited if the underlying mechanisms cause a lag between environmental change and individual response or if the information individuals receive is unreliable. Hence to understand the evolution of plasticity we need to assess whether individuals respond to fine...

Phenotypic plasticity will be favored whenever there are significant fitness benefits of responding to environmental variation. The extent and nature of the plasticity that evolves depends on the rate of environmental fluctuations and the capacity to track and respond to that variability. Reproductive environments represent one arena in which chang...

The extent of female multiple mating (polyandry) can strongly impact on the intensity of sexual selection, sexual conflict, and the evolution of cooperation and sociality. More subtly, polyandry may protect populations against intragenomic conflicts that result from the invasion of deleterious selfish genetic elements (SGEs). SGEs commonly impair s...

Phenotypic plasticity is a key mechanism by which animals can cope with rapidly changeable environments, but the evolutionary lability of such plasticity remains unclear. The socio-sexual environment can fluctuate very rapidly, affecting both the frequency of mating opportunities and the level of competition males may face. Males of many species sh...

Theory predicts that males should evolve mechanisms to assess competition and allocate resources accordingly. This requires phenotypic plasticity, to accurately match responses to the environment. Plastic responses in males to sexual competition are diverse and widespread. However, our ability to understand and predict how they evolve is limited be...

Males of many species assess the likely level of sperm competition and respond adaptively, for example by increasing the level of courtship they deliver, by transferring more sperm or seminal fluids or by extending matings. In mechanistic terms, it may be easier for males to adjust the level of their investment to the likely level of sperm competit...

Mechanisms that prevent different species from interbreeding are fundamental to the maintenance of biodiversity. Barriers to interspecific matings, such as failure to recognize a potential mate, are often relatively easy to identify. Those occurring after mating, such as differences in the how successful sperm are in competition for fertilisations,...

Plasticity in behaviour is of fundamental significance when environments are variable. Such plasticity is particularly important in the context of rapid changes in the socio-sexual environment. Males can exhibit adaptive plastic responses to variation in the overall level of reproductive competition. However, the extent of behavioural flexibility w...

Males frequently remain in close proximity to their mate immediately postcopulation. This behavior has generally been interpreted as a guarding tactic designed to reduce the likelihood that a rival male can rapidly displace the ejaculate of the guarding male [1, 2]. Such attempts by males to control their mates represent a potential source of confl...

Behavioural plasticity allows animals to attune their behaviour to rapid environmental changes. Here we focus on plasticity in male mating behaviour in response to socio-sexual conditions. We discuss existing theory, generate predictions to facilitate exploration of the benefits of plastic behaviour, and identify parameters with the highest leverag...

The ecological and evolutionary importance of fine-scale genetic structure within populations is increasingly appreciated. However, available data are largely restricted to wild vertebrates and eusocial insects. In addition, there is the expectation that most insects tend to have such large- and high-density populations and are so mobile that they...

In Drosophila melanogaster, the DDT resistance allele (DDT-R) is beneficial in the presence of DDT. Interestingly, DDT-R also elevates female fitness in the absence of DDT and existed in populations before DDT use. However, DDT-R did not spread regardless of DDT-independent selective advantages in females. We ask whether sexual antagonism could exp...

Many behavioural traits are considered to be condition-dependent, reflecting the differential allocation of resources to fitness-related traits and maintenance, although the physiological underpinnings of condition dependence are not well understood. In the present study, the hypothesis that condition dependence in male Gryllus bimaculatus De Geer...