Search

Cytosine methylation and its machinery influence the gene expression of many eukaryotes; however, insects are an exception to this general tenet despite many lineages retaining methyltransferases and methylated genomes. Here, we tested thea priorihypothesis that perturbed genetic pathways will be associated with meiosis using transcriptomics because previous our work usingOncopeltus fasciatusshows that gametogenesis is interrupted at meiosis following knockdown ofDNA methyltransferase 1(Dnmt1). Testes, which are almost exclusively contain gametes at varying stages of development, were sampled at 7-days and 14-days following knockdown ofDmnt1using RNAi. Using microscopy, we found actively dividing spermatocysts were reduced at both sampling points. However, we found limited support of perturbation for our predicted cell cycle and meiotic pathways and only at 14-days. We found that Gene Ontology terms had no preferential enrichment for meiosis-associated genes. Following oura prioritests, we used the full dataset to uncover further candidate pathways influenced byDnmt1knockdown. Very few genes were differentially expressed at 7-days, but nearly half were at 14-days. We did not find strong candidate pathways for howDnmt1knockdown was achieving its effect through Gene Ontology term overrepresentation analysis. Given the evidence from microscopy, we proposeDnmt1knockdown results in condensed nuclei after mitosis-meiosis transition and then cellular arrest. This explanation posits that differential gene expression is a product of comparing healthy to arrested cells and is not a targeted response.

When the likelihood of reproducing successfully is low, any prior investment in developing oocytes may be wasted. One means of recouping this investment is oosorption – where ova are absorbed and resources salvaged so they can be re-allocated to other traits. Food-limited female speckled cockroaches (Nauphoeta cinerea) appear to use this strategy. However, it is unclear if total food intake or the availability of specific nutrients induces this process. Here, we used the geometric framework of nutrition to determine how protein, carbohydrate and energy intake affect levels of ovarian apoptosis and necrosis (controlled versus uncontrolled cell death) in the terminal oocytes of female N. cinerea. We then compare the effects of nutrient intake on apoptosis (a key step towards oosorption) and offspring production to better understand the relationship between diet, apoptosis and female fitness. We found that even when food was abundant, females experienced high levels of apoptosis if their diet lacked carbohydrate. Necrosis was reduced when energy intake was high, but largely irrespective of nutrient ratio. Offspring production peaked on a low protein, high carbohydrate nutrient ratio (1P:7.96C), similar to that which minimized apoptosis (1P:7.34C) but not in the region of nutrient space that minimized necrosis. Thus, females consuming an ideal nutrient blend for reproduction can invest heavily in their current brood without needing to salvage nutrients from developing ova. However, offspring production was more dependent on carbohydrate consumption than apoptosis was, suggesting that the importance of carbohydrate in reproduction goes beyond regulating oosorption. This reliance on carbohydrate for female reproduction may reflect the unusual reproductive and nutritional physiology of speckled cockroaches; attributes that make this species an exciting model for understanding how diet regulates reproduction. When the likelihood of reproducing successfully is low, any prior investment in developing oocytes may be wasted. One means of recouping this investment is oosorption – where ova are absorbed and resources salvaged so they can be re-allocated to other traits. Food-limited female speckled cockroaches (Nauphoeta cinerea) appear to use this strategy. However, it is unclear if total food intake or the availability of specific nutrients induces this process. Here, we used the geometric framework of nutrition to determine how protein, carbohydrate and energy intake affect levels of ovarian apoptosis and necrosis (controlled versus uncontrolled cell death) in the terminal oocytes of female N. cinerea. We then compare the effects of nutrient intake on apoptosis (a key step towards oosorption) and offspring production to better understand the relationship between diet, apoptosis and female fitness. We found that even when food was abundant, females experienced high levels of apoptosis if their diet lacked carbohydrate. Necrosis was reduced when energy intake was high, but largely irrespective of nutrient ratio. Offspring production peaked on a low protein, high carbohydrate nutrient ratio (1 P:7.96 C), similar to that which minimized apoptosis (1 P:7.34 C) but not in the region of nutrient space that minimized necrosis. Thus, females consuming an ideal nutrient blend for reproduction can invest heavily in their current brood without needing to salvage nutrients from developing ova. However, offspring production was more dependent on carbohydrate consumption than apoptosis was, suggesting that the importance of carbohydrate in reproduction goes beyond regulating oosorption. This reliance on carbohydrate for female reproduction may reflect the unusual reproductive and nutritional physiology of speckled cockroaches; attributes that make this species an exciting model for understanding how diet regulates reproduction.

Nutrition is a dynamic environmental factor and compensatory growth may help animals handle seasonal fluctuations in their diets. Yet, how the dynamic changes in nutrition affect female reproduction is understudied. We took advantage of a specialist insect herbivore, Narnia femorata Stål (Hemiptera: Coreidae), that feeds and reproduces on cactus across three seasons. We first examined how cactus quality can affect female reproductive success. Then, we investigated the extent to which reproductive success can be improved by a switch in diet quality at adulthood. We placed N. femorata juveniles onto prickly pear cactus pads with early-season (low-quality) or late-season (high-quality) fruit and tracked survivorship and development time. A subset of the females raised on low-quality diets were provided with an improved adult diet to simulate a seasonal change in diet. Adult female survival and egg production were tracked over time. All fitness-related traits were lower for females fed low-quality diets compared with females fed high-quality diets. However, when females had access to an improved adult diet, egg production was partially rescued. These findings show that a seasonal improvement in diet can enhance reproduction, but juvenile nutrition still has lasting effects that females cannot overcome.

Neoliberal ideologies, marketization and performative regimes associated with recent reforms in universities have exerted considerable pressure on academic working conditions and subjects in recent years. While analysing these pressures is important, it is also productive to consider the ways in which academics engage in moments of resistance by mobilising resources beyond those of critique. This paper therefore focuses on joy and positive affect in the everyday moments of academic life. It utilises the feminist methodology of collective biography to explore ways of making the restricted spaces of our working day more expansive and finding within them unexpected openings for joy. Our analysis of the stories included in this paper traces the mercurial and ambiguous affective atmospheres of academic work. We suggest that joy is founded upon connections with others, that it arises in different academic spaces and that it can lead to revised knowing of ourselves. We argue that the glimpses of joy evident in this paper provoke affective attunement within the everyday, sensitizing us to other fragments of joy and providing strategies to strengthen that resistance.

Given the importance of DNA methylation in protection of the genome against transposable elements and transcriptional regulation in other taxonomic groups, the diversity in both levels and patterns of DNA methylation in the insects raises questions about its function and evolution. We show that the maintenance DNA methyltransferase, DNMT1, affects meiosis and is essential to fertility in milkweed bugs, Oncopeltus fasciatus, while DNA methylation is not required in somatic cells. Our results support the hypothesis that Dnmt1 is required for the transition of germ cells to gametes in O. fasciatus and that this function is conserved in male and female gametogenesis. They further suggest that DNMT1 has a function independent of DNA methylation in germ cells. Our results raise the question of how a gene so critical in fitness across multiple insect species can have diverged widely across the insect tree of life.

Males have the ability to compete for fertilizations through both pre-copulatory and post-copulatory intrasexual competition. Pre-copulatory competition has selected for large weapons and other adaptations to maximize access to females and mating opportunities while post-copulatory competition has resulted in ejaculate adaptations to maximize fertilization success. Negative associations between these strategies support the hypothesis that there is a trade-off between success at pre- and post-copulatory mating success. Recently, this trade-off has been demonstrated with experimental manipulation. Male leaf-footed cactus bugs, Narnia femorata, that lose a weapon by autotomy during development invest instead in large testes. While evolutionary outcomes of the trade-offs between pre- and post-copulatory strategies have been identified, less work has been done to identify proximate mechanisms by which the trade-off might occur, perhaps because the systems in which the trade-offs have been investigated are not ones that have the molecular tools required for exploring mechanism. Here we applied knowledge from a related model species for which we have developmental knowledge and molecular tools, the milkweed bug Oncopeltus fasciatus, to investigate the proximate mechanism by which autotomized N. femorata males developed larger testes. Autotomized males had evidence of a higher rate of transit amplification divisions in the spermatogonia, which would result in greater sperm numbers. Identification of mechanisms underlying a trade-off can help our understanding of the direction and constraints on evolutionary trajectories and thus the evolutionary potential under multiple forms of selection.

Males have the ability to compete for fertilizations through both precopulatory and postcopulatory intrasexual competition. Precopulatory competition has selected for large weapons and other adaptations to maximize access to females and mating opportunities, while postcopulatory competition has resulted in ejaculate adaptations to maximize fertilization success. Negative associations between these strategies support the hypothesis that there is a trade‐off between success at pre‐ and postcopulatory mating success. Recently, this trade‐off has been demonstrated with experimental manipulation. Males of the leaf‐footed cactus bug Narnia femorata use hind limbs as the primary weapon in male–male competition. However, males can drop a hind limb to avoid entrapment. When this autotomy occurs during development, they invest instead in large testes. While evolutionary outcomes of the trade‐offs between pre‐ and postcopulatory strategies have been identified, less work has been done to identify proximate mechanisms by which the trade‐off might occur, perhaps because the systems in which the trade‐offs have been investigated are not ones that have the molecular tools required for exploring mechanism. Here, we applied knowledge from a related model species for which we have developmental knowledge and molecular tools, the milkweed bug Oncopeltus fasciatus, to investigate the proximate mechanism by which autotomized N. femorata males developed larger testes. Autotomized males had evidence of a higher rate of transit amplification divisions in the spermatogonia, which would result more spermatocytes and thus in greater sperm numbers. Identification of mechanisms underlying a trade‐off can help our understanding of the direction and constraints on evolutionary trajectories and thus the evolutionary potential under multiple forms of selection., Male leaf‐footed cactus bugs that lose the ability to fully invest in weapons required for success in precopulatory contests invest instead in testis size that allows them to compete for postcopulatory fertilization success. In this study, we shed light on the mechanism by which this trade‐off occurs; males that lost their weapon during a key developmental stage have sperm progenitor cells that divided more rapidly than control males. Understanding proximate mechanisms can help us understand potential directions and constraints on the evolution of this trade‐off under different forms of selection.

The whitefly Bemisia tabaci is a globally important pest that is difficult to control through insecticides, transgenic crops, and natural enemies. Post-transcriptional gene silencing through RNA interference (RNAi) has shown potential as a pest management strategy against B. tabaci. While genomic data and other resources are available to create highly effective customizable pest management strategies with RNAi, current applications do not capitalize on species-specific biology. This lack of specificity has the potential to have substantial ecological impacts. Here, we discuss both short- and long-term considerations for sustainable RNAi pest management strategies for B. tabaci, focusing on the need for species specificity incorporating both life history and population genetic considerations. We provide a conceptual framework for selecting sublethal target genes based on their involvement in physiological pathways, which has the greatest potential to ameliorate unintended negative consequences. We suggest that these considerations allow an integrated pest management approach, with fewer negative ecological impacts and reduced likelihood of the evolution of resistant populations.

Given the importance of DNA methylation in protection of the genome against transposable elements and transcriptional regulation in other taxonomic groups, the diversity in both levels and patterns of DNA methylation in the insects raises questions about its function and evolution. We show that the maintenance DNA methyltransferase, DNMT1, affects meiosis and is essential to fertility in milkweed bugs, Oncopeltus fasciatus, while DNA methylation is not required in somatic cells. Our results support the hypothesis that Dnmt1 is required for the transition of germ cells to gametes in O. fasciatus and that this function is conserved in male and female gametogenesis. They further suggest that DNMT1 has a function independent of DNA methylation in germ cells. Our results raise thequestion as to how a gene that is so critical to fitness across multiple insect species is able to diverge widely across the insect tree of life.

Background In species with parental care, there is striking variation in offspring dependence at birth, ranging from feeding independence to complete dependency on parents for nutrition. Frequently, highly dependent offspring further evolve reductions or alterations of morphological traits that would otherwise promote self‐sufficiency. Here, we examine evidence for morphological evolution associated with dependence in burying beetles (Nicrophorus spp.), in which dependence upon parents appears to have several independent origins. In many species, precocial first instar larvae can survive without parenting, but several altricial species die at this stage on their own. We focused specifically on the mandibles, which are expected to be related to feeding ability and therefore independence from parents. Results We find no evidence that the size of the mandible is related to dependence on parents. However, we do find a developmental and phylogenetic correlation between independence and the presence of serrations on the inner edge of the mandible. Mandibles of independent species bear serrations at hatching, whereas dependent species hatch with smooth mandibles, only developing serrations in the second instar when these larvae gain the ability to survive on their own. Phylogenetic evidence suggests that serrations coincide with independence repeatedly. We note a single exception to this trend, a beetle with a serrated mandible that cannot survive without parents. However, this exception occurs in a species that has recently evolved the loss of independence. Conclusions We argue that the absence of mandible serrations occurs due to alternative selection pressures incurred in larvae dependent upon parents to survive. We suggest that this may have led to a variable function for mandibles, perhaps related to increased competitive ability among siblings or increased efficiency in receiving nutrition from parents. Furthermore, we propose that the phylogenetic pattern we see is consistent with the long‐held evolutionary hypothesis that evolutionary change in behavior and physiology precede morphological change.

Oncopeltus fasciatus males fed the ancestral diet of milkweed seeds prioritize reproduction over lifespan as evidenced by higher rates of fertility and shorter lifespans than males from the same population fed the adapted diet of sunflower seeds. We examined the proximate mechanisms by which milkweed-fed males maintained late-life fertility. We tested the hypothesis that older milkweed-fed males maintained fertility by producing more, higher quality sperm. Our results, that older males have more sperm, but their sperm do not have higher viability, are in general agreement with other recent studies on how nutrition affects male fertility in insects. We further examined the mechanisms by which sperm are produced by examining the progression of spermatogonial cells through the cell cycle during the transit amplification divisions. We demonstrated that diet affects the likelihood of a spermatocyst being in the S-phase or M-phase of the cell cycle. Given work in model systems, these results have implications for subtle effects on sperm quality either through replication stress or epigenetic markers. Thus, viability may not be the best marker for sperm quality and more work is called for on the mechanisms by which the germline and the production of sperm mediate the cost of reproduction.

Universities are dominated by marketisation, individualisation and competition, forces inimical to individual flourishing and collaborative endeavours. This article presents four stories from a collective biography workshop in which a group of women academics explored everyday moments in their university lives. The stories are grim tales of damage, silencing, frustration and cynicism, whose affects continue to reverberate. The article makes two contributions to higher education research. One, its focus on mundane moments offers insights into embodied dynamics of gender, power and affect within the neoliberal university. Two, it demonstrates how collective biography as a feminist methodology can mobilise increased awareness of shared experiences and, thereby, enable participants to work together to recognise and contest the affective grimness of their workplaces.

DNA methylation is an important chromatin modification that can stably alter gene expression in cells and maintain genome integrity in plants and vertebrates. The function of DNA methylation outside of these well-studied systems, however, is unclear. Insects, in particular, represent an understudied group. Variation in the level of DNA methylation and gains and losses in the maintenance methyltransferase, DNMT1, across the insect tree of life suggests that there is much we don’t understand about DMNT1 function and evolution. One constant across the studies examining patterns ofDnmt1expression in insects is that expression is consistently high in reproductive tissues compared to somatic tissue. The explanation for this has been that DNMT1 is required in tissues that have high levels of cell division. Our previous study found that downregulation ofDnmt1expression in the milkweed bugOncopeltus fasciatusresults in the expected reduction of DNA methylation, no global changes in gene expression reflecting changes in DNA methylation, and the loss of the ability to produce viable oocytes. Here, we show that females treated with ds-Dnmt1RNA during larval development have a more extreme phenotype; they lack oocytes entirely but develop a normal somatic ovary. Our results indicate a specific role for DNMT1 in the formation of gametes and are consistent with data from other systems, includingTribolium castaneum, a species does not have DNA methylation. We propose that DNMT1 has multiple functional roles in addition to methylating DNA, which explains its complex patterns of evolution, and suggests that previous inferences of causation from associations are premature.

Drosophila suzukii is a globally invasive fruit pest that costs millions in yield losses and increased pest management costs. Management practices for D. suzukii currently rely heavily on calendar-based applications of broad-spectrum insecticides, but decision-based applications are theoretically possible with refined population modeling and monitoring. Temperature conditions are strongly deterministic of insect growth rates, fecundity, fertility, and resulting population densities. Therefore, information about the effects of temperature can be incorporated into population modeling to accurately predict D. suzukii population densities in the field which is crucial to maximize pesticide application efficiency and improve sustainability. Here, we investigated the effects of chronic heat stress during all of juvenile development on egg-to-adult viability and fertility. We also investigated egg-to-adult viability under heat stress after heat shock of the maternal parent. We found that heat stress during development results in lower egg-to-adult viability, and reduced lifespan and fertility for surviving adults. However, heat-shock treatment of females prior to egg laying increased the egg-to-adult viability of their eggs under heat stress. Female flies that developed at 30 °C had smaller ovaries than the untreated group and male flies had less sperm in their testes, and no sperm in their seminal vesicles. We conclude that heat stress during development is likely to have negative effect on D. suzukii population dynamics in the field. However, the intensity of such negative impact will depend on the phenotypic state of their maternal parents.

The function of cytosine (DNA) methylation in insects remains unknown. Here we provide evidence for the functional role of the maintenance DNA methyltransferase 1 (Dnmt1) in an insect using experimental manipulation. Through RNA interference (RNAi) we successfully post-transcriptionally knocked downDnmt1in ovarian tissue of the hemipteranOncopeltus fasciatus(the large milkweed bug). Individuals depleted forDnmt1, and subsequently DNA methylation, failed to reproduce. Eggs were inviable and declined in number, and nuclei structure of follicular epithelium was aberrant. Depletion of DNA methylation did not result in changes in gene or transposable element expression revealing an important function of DNA methylation seemingly not contingent on gene expression. Our work provides direct experimental evidence for a functional role ofDnmt1and DNA methylation independent of gene expression in insects.

Strength of weak ties theory (SoWT) explains the social influences of weak ties as they facilitate access across social networks. An underlying assumption is that SoWT involves face-to-face interaction. Today, social media allow tie formation without necessarily being linked to time or place. We assert that building networks through online, text-based communication adds layers of complexity that are not fully part of the classic SoWT theory and application. We suggest discourse analysis constructs to extend SoWT to relationships formed and maintained with social media. We formulate propositions to extend SoWT to understand the consequences and opportunities afforded by online-only connections.

The variation in degree of offspring dependence in parents where parental care has evolved is striking, from feeding independence at birth to complete dependence on parents for all nutritional resources. This presents an evolutionary puzzle. Why lose the ability to feed as a contingency when parents may die or abandon broods? Comparisons of altricial and precocial vertebrates suggest that there may be life-history and developmental costs to early independence1-3. The generality of this beyond vertebrates is unclear, but we can extend the comparison as invertebrate species also vary in the level of independence in early life-history stages. For example, larvae of several burying beetle species (Nicrophorus), a genus in which parents regurgitate pre-digested food to begging larvae, have lost the ability to self-feed thus creating complete parental dependency for first instars4. Here, we ask whether variation in dependency amongst burying beetles is related to heterochrony in development of a more complex morphological structures. We show that the rate of development and allometry of mandibles of precocial larvae that can self-feed from birth are the same as those in altricial larvae that cannot survive without parenting. Instead, self-feeding is associated with shape variation in mandibles. In altricial species first instar larvae have smooth mandibles, whereas in precocial species mandibles are serrated. Later instars, which can self-feed in all species, have serrated mandibles. Serrations on teeth generally function to “grip and rip”5, whereas smooth blades function more to puncture6, and broods of altricial but not precocialNicrophoruslarvae show evidence for siblicide. We therefore suggest that altricial first-instar mandibles function more as weapons than feeding tools when released from self-feeding. This study presents a novel coevolution between developmental timing and parenting potentially mediated by sibling competition.

Most larval drosophilids eat the microorganisms that develop in rotting fruit, a relatively protein-rich resource. By contrast, the spotted-wing Drosophila suzukii Matsumara (Diptera: Drosophilidae) uniquely develops in ripening fruit, a protein-poor, carbohydrate-rich resource. This shift in larval nutritional niche has led to D. suzukii being a significant agricultural pest in the U.S.A. and Europe. Although occupying a new niche may benefit a species by reducing competition, adaptation in host use may generate trade-offs affecting fitness. To test the hypothesis that fitness trade-offs will change with adaptation to novel larval diets, D. suzukii larval development on either a diet of a fresh, ripe blueberry (a natural host) or standard artificial Drosophila media (protein-rich) is compared and the effect of diet on development time from egg to adult, adult body size and male wing spot area, and female fecundity is assessed. Larval development time differs, with larvae on the blueberry emerging as adults earlier than those on the artificial medium, although other fitness measures do not vary between the two diets. In addition, the faster development time on a blueberry does not trade off with body size as expected, although early fecundity is delayed in females that develop on blueberries. Thus, adaptation to a novel larval diet environment does not come at a cost to the ability to develop in protein-rich resources.

The environmental influences of mothers on offspring traits, or maternal effects, often arise from dietary differences experienced by mothers. However, few studies have explored if and how maternal effects facilitate adaptation to new host plants. To address this, we compared the maternal and direct effects arising from dietary differences in two populations of the large milkweed bug, Oncopeltus fasciatus that live on and feed on the seeds from different hosts. We compared a laboratory population, which has been reared for over 400 generations on sunflower seeds and is now adapted to use these as a host, to the wild population, which is adapted to the ancestral diet of toxic milkweed seeds. We first tested for changes in maternal effects, and then examined offspring performance and survivorship. We found evidence for evolution of the maternal effect facilitating the use of a novel host. However, the strongest effects were population differences and direct dietary effects for all traits. Offspring performance was more strongly influenced by diet than maternal effects. Survivorship depended on population and offspring diet, and their interaction, but was unaffected by maternal diet or other interactions. In the artificially evolved population, diet breadth was increased rather than evolving specialization. Our results suggest changes in maternal effects are likely to be weak compared to direct effects of host plants and other adaptations in adaptation to a novel host. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 202–211.

Migration evolves as a response to seasonally unfavourable environments but plasticity in reproductive physiology is another avenue by which insects can respond to resource-poor conditions. We investigated the relationship between individual variation in migratory propensity and the level of response to poor conditions modulated by the female reproductive physiology. We tested the hypothesis that, compared to migrants, residential behaviour is associated with a higher degree of phenotypic plasticity in oosorption, an adaptive physiological mechanism that allows females to recoup resources from undeveloped oocytes. Reallocation from reproduction to survival would allow females to skip migration and to cope with unfavourable environments. If this plasticity is evolved, we further predicted it would vary between as well as within populations. We examined variation associated with migratory behaviour in females from four populations of the milkweed bug, Oncopeltus fasciatus, using a behavioural assay to categorize females as either migrant or resident and observing the differences in oosorption between these groups. As expected, food availability, source population and wing length influenced the propensity for migratory flight, and food availability influenced levels of oosorption. We also found support for our key prediction that resident females are characterized by higher levels of ovarian oosorption than migrant females. Our study provides support for a physiological difference between migrant and resident females and suggests the presence of both physiological and behavioural tactics that interact with the potential for migration to provide adaptation to seasonally challenging environments.

A tenet of life history evolution is that allocation of limited resources results in trade-offs, such as that between reproduction and lifespan. Reproduction and lifespan are also influenced proximately by differences in the availability of specific nutrients. What is unknown is how the evolution of the ability to use a nutritionally novel diet is reflected in this fundamental trade-off. Does the evolution of the ability to use a nutritionally novel food maintain the trade-off in reproduction and longevity, or do the proximate effects of nutrition alter the adapted trade-off? We tested this by measuring trade-offs in male milkweed bugs, Oncopeltus fasciatus, fed either an adapted diet of sunflower or the ancestral diet of milkweed. Sunflower-fed males lived longer but invested less in reproduction, both in mating and fertility. Milkweed-fed males invested in both mating and fertility at the expense of survival. The evolution of an expanded diet was not constrained by the existing trade-off, but instead was accompanied by a different trade-off between reproduction and longevity. We suggest that this occurs because diets differ in promoting germ line development or longevity.

Plasticity in reproductive physiology is one avenue by which environmental signals, such as poor quality food, can be coordinated with adaptive responses. Insects have the ability to resorb oocytes that are not oviposited. Oosorption is proposed to be an adaptive mechanism to optimize fitness in hostile environments, recouping resources that might otherwise be lost, and reinvesting them into future reproductive potential. We tested the hypothesis that oosorption is an evolved mechanism by which females can reallocate resources from current reproductive effort to survival and future reproduction, when conditions for reproduction are poor, by examining the reproductive physiology and life-history outcome under poor quality food in populations of the milkweed bug (Oncopeltus fasciatus) that have adapted to live on sunflower seed. Females fed a diet of pumpkin seeds, known to be a poor host food, had higher levels of ovarian apoptosis (oosorption), lower reproductive output, but no reduction in life span under poor nutrition, as predicted under the oosorption hypothesis. However, the schedule of reproduction was surprising given the “wait to reproduce” assumption of oosorption as early fecundity was unaffected.

We expect organisms to have evolved mechanisms to gather and use the information available within their environments, to steer resource investment decisions toward the traits that will give the greatest fitness returns. Pheromones are social signals, a common purpose of which is to act as indicators of mate presence. Consequently, pheromones have the potential to act as signals to increase or maintain reproductive investment over that of competing life-history traits. In the cockroach, Nauphoeta cinerea (Oliver), females pay costs of maintaining investment in reproduction when there are no males, and males produce pheromones that are known to effect female reproductive outcomes. Whether the pheromones have an influence on resource physiology is unknown. We subjected newly eclosed females to either a synthetic blend of male pheromones or control. We dissected females at 7, 12, 17 or 22 days. We measured apoptosis levels and size of all oocytes within the vitellerium, and measured dry fat body mass. Synthetic male pheromone blend did not have an effect on any measure of female reproductive or somaticresourcephysiology.Althoughnegativeresultsarealwaysproblematic,thesuccess of the synthetic pheromone method in the past suggests that females may be insensitive to male pheromones in the pre-oviposition period, and may rely on mating stimulus rather than pheromone as the cue for oocyte maintenance and growth. Previous studies reporting effects of male pheromones on female reproduction suggest that the period of pheromone sensitivity may be between mating and birth.

Starvation and enforced virginity induce apoptosis (programmed cell death) in the oocytes of female cockroaches of Nauphoeta cinerea, yet the life-history outcome differs among fed and starved virgins. Consistent with the hypothesis that oocytes are absorbed to reallocate resources, apoptosis is followed by an increase in future reproduction and longevity in starved virgins. However, apoptosis induction by enforced virginity in fed females results in reduced fecundity and longevity. It is predicted that this life-history outcome occurs because oocyte apoptosis under these conditions is not part of an adaptive reproductive strategy but simply is the result of cellular ageing and clearance to maintain reproductive synchrony. In the present study, reproductive and somatic allocation are examined over time to test whether resources are recouped by the fat body, reinvested in reproduction or lost altogether when apoptosis is associated with enforced virginity. To assay reproductive investment, the number of ovarioles is counted, apoptosis levels are analysed and the size of all oocytes within the vitellaerium is measured. To assay somatic investment, dry fat body mass is measured. In conjunction with apoptosis, the number of ovarioles declines, whereas the size of surviving oocytes increases. By contrast to the cellular ageing hypothesis, apoptosis associated with enforced virginity appears to be adaptive if resources from sacrificed oocytes are recycled into the survivors to maintain the quality of ageing oocytes. This reinvestment in current reproduction may trade-off with future reproductive capacity.

We have yet to understand fully how conditions during different periods of development interact to influence life-history structure. Can the negative effects of poor juvenile nutrition be overcome by a good adult diet, or are life-history strategies set by early experience? Here, we tested the influence and interaction of different nutritional quality during juvenile and sexual development on female resource allocation physiology, life history and courtship behaviour in the cockroach, Nauphoeta cinerea . Nymphs were raised on either a good-quality or poor-quality diet. After adult eclosion, females were either switched to the opposite diet or remained on their original diet. We assessed mating behaviour and lifetime reproductive success for half of the females from each treatment. We evaluated reproductive investment, somatic investment and resource reallocation from reproduction to the soma via oocyte apoptosis in the remaining females. We found that poor juvenile conditions resulted in a fat phenotype with slow juvenile growth and short reproductive lifespan that could not be retrieved with a change in diet. Good juvenile conditions resulted in the converse, but again fixed, phenotype in adulthood. Thus, juvenile nutrition sets adult patterns of resource allocation.

Fertility loss in otherwise healthy individuals can be an evolutionary conundrum. Most studies on the evolution of post-reproductive lifespan focus on the fitness effects of survival past the age of last reproduction. A complementary approach, which has been largely neglected, is to develop an understanding of the nature of variation in the mechanism underlying loss of fertility, ovarian apoptosis. Variation in the genetics underlying the regulation of ovarian apoptosis could hold the key to understanding the evolution of midlife fertility loss. We estimated quantitative genetic variation in the regulation of ovarian apoptosis in females of the cockroach Nauphoeta cinerea, an insect with reproductive cycles. We have earlier shown that delaying reproduction incites loss of fertility. Here, we forced females to delay reproduction under conditions of excess or limited food and examined apoptosis under both conditions. We found substantial additive genetic variation in levels of apoptosis when females experienced a limited period of starvation during sexual maturation but not when females had unlimited access to food. Hence, selection could act on the regulation of ovarian apoptosis to change the rate of fertility loss with age at least under some environmental circumstances. Our results suggest that an understanding of how loss of fertility evolves requires an understanding of the interaction between genes involved in the regulation of apoptosis and environmental factors such as diet.

There is increasing recognition that male-male competition can take many forms, but as yet the form is not predictable a priori. Many recent studies have focused attention on how males in disadvantaged mating roles compensate through sperm competition. However, mating systems in which subordinate males are reproductively suppressed, particularly through the stress of social interactions, may limit the ability of males to respond by increasing investment in sperm quality. We examined the interaction between social status and ejaculate tactics in Nauphoeta cinerea, a cockroach that has a mating system with well-characterized dominance hierarchies. Both social experience with other males and social status influenced aspects of ejaculates. The stress of social interactions reduced the size of the ejaculate and number of sperm inseminated. In ejaculates formed prior to social experience, however, males that go on to become dominant inseminated more sperm than males that go on to become subordinate, suggesting innate differences among males. Our results show that though selection for increased success in sperm competition for subordinate males in a hierarchy can occur, both the traits and the way in which the balance between pre- and post-copulatory strategies is negotiated will depend on specific details of the mating system. These details will include how the physiological effects of social interactions may limit selection through male-male competition.

The extent to which females differ in their mating preferences has important consequences for the evolution of male sexual traits; yet, the way in which female mating preferences vary remains largely unexplored in most animal taxa. Even less is known about the implications of this variation to female fitness. Here, we examine the degree of between-female agreement in the mating preferences of the cockroach, Nauphoeta cinerea, and relate this variation to differences in female reproduction. Using a repeated-measures design, we mated a series of males sequentially to 5 different females. We found that females were largely in agreement in their mating preferences with a significant, albeit low (0.094 6 0.061), repeatability of male attractiveness as assessed by different females. This is surprising given that females experienced a consistent reduction in offspring production when mating to more experienced males and suggests that females have a limited ability to detect male mating history. This cost may, in part, be offset by a longer gestation time when mating with more experienced males, which is known to extend female longevity in this species. There appears to be good reason for females to agree in their mate choice in this species. Across males, we found a significant negative correlation between male attractiveness and gestation time, suggesting that females actively discriminate against males that accelerate gestation. We discuss the implications of our findings to the operation of sexual selection in N. cinerea. Key words: agreement, cockroach, female reproduction, male attractiveness, male mating history, mate choice, Nauphoeta cinerea. [Behav Ecol]

In a wide variety of species, a female's age of first reproduction influences offspring size and survival, suggesting that there exists an optimal timing of reproduction. Mothers in many species also influence offspring size and survival after birth through variation in parental care. We experimentally separated these effects in the burying beetle Nicrophorus vespilloides to test for coadaptation between prenatal and postnatal maternal effects associated with age at first reproduction. Females that reproduced early produced offspring with lower birth weight. The amount of parental care depended on the age of first reproduction of the caretaker, as did the extent of offspring begging. As predicted for a coadaptation of maternal effects, prenatal and postnatal effects were opposite for different-aged mothers, and larval weight gain and survival was greatest when the age of the caretaker and birth mother matched. Thus, prenatal effects intrinsically associated with age of first reproduction can be ameliorated by innate plasticity in postnatal care. A coadaptation of prenatal and postnatal maternal effects may evolve to allow variable timing of the first reproductive attempt. Such a coadaptation might be particularly valuable when females are constrained from reproducing at an optimal age, as, for example, in species that breed on scarce and unpredictable resources.

Understanding the processes underlying the origin of new species is a fundamental problem in evolutionary research. Whilst it has long been recognised that closely related taxa often differ markedly in reproductive characteristics, only relatively recently has sexual selection been evoked as a key promoter of speciation through its ability to generate reproductive isolation (RI). Sexual selection potentially can influence the probability that individuals from the same or different populations will reproduce successfully since it shapes precisely those traits involved in mating and reproduction. If reproductive characters diverge along different trajectories, then sexual selection can impact on the evolution of reproductive barriers operating both before and after mating. In this perspective, we consider some new advances in our understanding of the coevolution of male and female sexual signals and receptors and suggest how these developments may provide heretofore neglected insights into the mechanisms by which isolating barriers may emerge. Specifically, we explore how selfish genetic elements (SGEs) can mediate pre- and post-copulatory mate choice, thereby influencing gene flow and ultimately population divergence; we examine evidence from studies of intracellular sperm–egg interactions and propose that intracellular gametic incompatibilities may arise after sperm entry into the egg, and thus contribute to RI; we review findings from genomic studies demonstrating rapid, adaptive evolution of reproductive genes in both sexes and discuss whether such changes are causal in determining RI or simply associated with it; and finally, we consider genetic, developmental and functional mechanisms that might constrain reproductive trait diversification, thereby limiting the scope for reproductive barriers to arise via sexual selection. We hope to stimulate work that will further the understanding of the role sexual selection plays in generating RI and ultimately speciation.

Summary 1 Interspecific diversity in the morphology of animal sperm suggests adaptive evolutionary changes in size and structure. Little attention has been directed at patterns of intraspecific phenotypic variation in sperm morphology, although such variation is a prerequisite for the extreme diversity seen among male gametes. Despite well-developed sperm competition theory providing a basis for exploring how variation in sperm morphology may affect male fitness, the patterns of variation in sperm morphology remain unclear for most species. 2 We report systematic size variation in sperm length among different males and between successive ejaculates within the same male in the cockroach Nauphoeta cinerea. Both flagellum length and mid-piece length decreased between the first and second ejaculate. However, within the same ejaculate the sperm head (acrosome and nucleus), midpiece (centriole adjunct region) and tail length exhibited less variation than that present between males for both first and second ejaculates. 3 Our findings, combined with previous studies, suggest a focus on episodes of selection and lifetime selection on ejaculates may be instructive in understanding the selective forces influencing sperm evolution in a predictive framework.

In many species, females abandon mate choice to ensure that eggs are fertilized before they are lost. But why do females not just maintain oocytes longer if there is a benefit to mate choice? We conducted a quantitative genetic study in the cockroach Nauphoeta cinerea to test whether genetic constraints prevent the evolution of oocyte maintenance or selection against oocyte loss is weak when females mate late relative to sexual maturity. We found standing genetic variation within the population and no evidence for genetic constraints. Levels of genetic variation are of the magnitude found for life-history traits in general, suggesting that this trait has been exposed to selection. We unexpectedly found two categories of females: those that delay reproduction and those that reproduce at a normal time when mating late, which could indicate alternative strategies. However, frequency-dependent selection does not maintain this variation as females that delay always reproduce less well. Given these findings, we suggest that there may be advantages to egg degradation. The evolution of maintenance of fertilizable oocytes over time would then be constrained by the need to maintain the mechanism by which females control the distribution of resources between current and future reproductive events.

Flight in insects can be long-range migratory flights, intermediate-range dispersal flights, or short-range host-seeking flights. Previous studies have shown that flight mills are valuable tools for the experimental study of insect flight behavior, allowing researchers to examine how factors such as age, host plants, or population source can influence an insects' propensity to disperse. Flight mills allow researchers to measure components of flight such as speed and distance flown. Lack of detailed information about how to build such a device can make their construction appear to be prohibitively complex. We present a simple and relatively inexpensive flight mill for the study of tethered flight in insects. Experimental insects can be tethered with non-toxic adhesives and revolve around an axis by means of a very low friction magnetic bearing. The mill is designed for the study of flight in controlled conditions as it can be used inside an incubator or environmental chamber. The strongest points are the very simple electronic circuitry, the design that allows sixteen insects to fly simultaneously allowing the collection and analysis of a large number of samples in a short time and the potential to use the device in a very limited workspace. This design is extremely flexible, and we have adjusted the mill to accommodate different species of insects of various sizes.

Different aspects of male quality as a mate can vary independently. When this is the case, females may need to use multiple cues to accurately assess overall mate quality. We examined the pattern of mating preference in the cockroach Nauphoeta cinerea. Sexual conflict occurs in this species because male manipulation of female mating receptivity can result in reduced female fitness. We predicted that since females cannot remate within a single reproductive bout because of male manipulation, females should assess male mating history to avoid mating with males with low fertility caused by sperm exhaustion. In a mate-preference experiment, we found that females discriminated against males who had mated multiple times. Females also discriminated against males who had consorted with several females but had been prevented from mating with those females. Thus, females appeared to be able to detect cues on males that were derived from previous mates and to use this information to avoid mating with sperm-exhausted males. We suggest that females may commonly use multiple cues to assess different aspects of mate quality, especially when male quality changes over time. This is an under-studied phenomenon that could help explain individual variation in female mating preferences.

Selective pressure arising from sperm competition has been predicted to influence evolutionary and behavioural adjustment of ejaculate investment, but also may influence developmental adjustment of ejaculate investment. Immature males able to target resources strategically based on the competitive environment they will experience when they become sexually mature should be at a selective advantage. In our study we investigated how the presence of potential competitors or mates affects ejaculate and testes investment during development in the cockroach Nauphoeta cinerea, a species where males control female remating via their ejaculate size (large spermatophores prevent females from remating and therefore function to avoid sperm competition for males) and females store sperm. Our aim was to determine whether the social environment influences developmental adjustment of ejaculate investment and the relative importance of ejaculate components with different functions; avoidance of or engagement in sperm competition. We conclude that the social environment can influence developmental and behavioural flexibility in specific ejaculate components that may function to avoid or engage in sperm competition.

An evolutionary conflict often exists between the sexes in regard to female mating patterns. Females can benefit from polyandry, whereas males mating with polyandrous females lose reproductive opportunities because of sperm competition. Where this conflict occurs, the evolution of mechanisms whereby males can control female remating, often at a fitness cost to the female, are expected to evolve. The fitness cost to the female will be increased in systems where a few high status males monopolise mating opportunities and thus have limited sperm supplies. Here we show that in the cockroach Nauphoeta cinerea, a species where males enforce female monogamy in the first reproductive cycle, males that have become sperm depleted continue to be able to manipulate female remating behaviour. Although the manipulation severely decreases fecundity in females mated to sperm-depleted males, males benefit, increasing their relative fitness by preventing other males from reproducing. Our results suggest that there is selection on maintaining the mechanism of manipulation rather than maintaining sperm numbers. Taken with previous research on sexual conflict in N. cinerea, this study suggests that the causes and consequences of sexual conflict are complex and can change across the life history of an individual.