Competition For Mates Research Articles

Male diet affects female fitness and sperm competition in human- and bat-associated lineages of the common bedbug, Cimex lectularius

Sperm performance can vary in ecologically divergent populations, but it is often not clear whether the environment per se or genomic differences arising from divergent selection cause the difference. One powerful and easily manipulated environmental effect is diet. Populations of bedbugs (Cimex lectularius) naturally feed either on bat or human blood. These are diverging genetically into a bat-associated and a human-associated lineage. To measure how male diet affects sperm performance, we kept males of two HL and BL populations each on either their own or the foreign diet. Then we investigated male reproductive success in a single mating and sperm competition context. We found that male diet affected female fecundity and changed the outcome of sperm competition, at least in the human lineage. However, this influence of diet on sperm performance was moulded by an interaction. Bat blood generally had a beneficial effect on sperm competitiveness and seemed to be a better food source in both lineages. Few studies have examined the effects of male diet on sperm performance generally, and sperm competition specifically. Our results reinforce the importance to consider the environment in which sperm are produced. In the absence of gene flow, such differences may increase reproductive isolation. In the presence of gene flow, however, the generally better sperm performance after consuming bat blood suggests that the diet is likely to homogenise rather than isolate populations.

Body size is associated with yearling breeding and extra-pair mating in the Island Scrub-Jay

Abstract Large body size is an important determinant of individual fitness in many animal species, especially in island systems where habitat saturation may result in strong intraspecific competition for mates and breeding territories. Here we show that large body size is associated with benefits to yearling breeding and extra-pair mating in the Island Scrub-Jay (Aphelocoma insularis), endemic to Santa Cruz Island, California. This species is ~20% larger than its mainland congener, consistent with the island syndrome, indicating that body size may be a trait under selection. From 2009 to 2013, we quantified the reproductive success of a marked population of Island Scrub-Jays, tracked which yearlings acquired a breeding territory and bred, and measured the occurrence of extra-pair paternity. Two potential contributors to fitness were positively related to body size. Larger yearling males were more likely to breed, possibly due to greater behavioral dominance during aggressive encounters. Larger males were also less likely to lose paternity to extra-pair males and, anecdotally, extra-pair males were larger than the social male cuckolded. This study provides evidence that larger males may have a fitness advantage over smaller males by breeding earlier and avoiding paternity loss, but estimates of lifetime reproductive success are ultimately needed for Island Scrub-Jays and other long-lived species.

Is Play Sexually Dimorphic in the Polygamous Squirrel Monkey?

Play behavior is widespread in juvenile mammals and may be a mechanism for practicing skills needed in adulthood. In mammals characterized by strong adult male competition over females, juvenile males perform more social play than do females, and such play may assist in later mating competition. This study examined whether social play behavior is sexually dimorphic in a polygamous neotropical primate, the squirrel monkey (Saimiri collinsi), through a six-week field study of two groups of wild monkeys in Eastern Amazonia, Brazil. We hypothesized that males would conduct more rough-and-tumble play than females and that any sex-based play differences would be more evident in older juveniles. We video recorded juvenile play bouts and scored: age category (younger or older juvenile) and sex of players (male or female); and rough-and-tumble play behaviors (i.e., bite, grab, and wrestle). Juvenile males initiated more play bouts than did females. Most players were older juvenile males, while older juvenile females were the least represented. Older juvenile play bouts occurred mostly among males, while younger juvenile bouts consisted of a more even sex distribution. While younger juveniles did not significantly affect the number of rough-and-tumble behaviors in bouts, the number of behaviors was significantly affected by the sex of older individuals. These results indicate that social play is sexually dimorphic in juvenile S. collinsi; specifically, males play more than females and sex differences are more pronounced in older cohorts. KEYWORDS: Squirrel Monkeys; Mating System; Sexual Dimorphism; Juvenile Period; Development; Play Behavior; Social Behavior; Ethology

Differential allocation in a gift-giving spider: males adjust their reproductive investment in response to female condition

BackgroundWhen males are selective, they can either reject low-quality females or adjust their reproductive investment in response to traits that indicate female quality (e.g., body size or condition). According to the differential allocation hypothesis, males increase their reproductive investment when paired with high-quality females (positive differential allocation) or increase their reproductive investment when paired with low-quality females (negative differential allocation). This hypothesis has been proposed for monogamous species with biparental care, and most empirical studies focus on birds. Here we used the polygamous spider Paratrechalea ornata, in which males offer prey wrapped in silk as nuptial gifts, to test whether males adjust their reproductive investment in gift size, pre-copulatory and copulatory courtship, and sperm transfer in response to female body condition.ResultsMales exposed to females in good body condition added more flies to the gift, stimulated these females longer with abdominal touches during pre-copulatory courtship, and had longer pedipalp insertions than males exposed to females in poor body condition. Female condition affected neither silk investment in nuptial gift wrapping nor the quantity of sperm transferred by males. Finally, females in good body condition oviposited faster after copulation and laid more eggs than females in poor body condition.ConclusionsWe provide experimental evidence that males of a gift-giving spider exhibit positive differential allocation in three key aspects of their reproductive investment: the size of the nutritious gift, duration of pre-copulatory courtship, and duration of pedipalp insertions, which is regarded as a form of copulatory courtship in spiders. This positive differential allocation is likely associated with the benefits of copulating with females in good body condition. These females are more fecund and oviposit faster after copulation than females in poor body condition, which under natural field conditions probably reduces the risk of multiple matings and thus the level of sperm competition faced by the males. As a final remark, our findings indicate that the hypothesis of differential allocation also applies to species with a scramble competition mating system, in which males heavily invest in nuptial gift construction, but not in parental care.

Males of a Neotropical spider adjust prey‐gift construction but not mate search in response to sperm competition

AbstractIn scramble competition mating systems, males do not guard females and females usually mate polyandrously, leading to high levels of sperm competition. Mathematical models predict that males facing sperm competition can either decrease or increase their reproductive effort. To test how male reproductive responses vary according to sperm competition risk, we ran two experiments using the polyandrous gift‐giving spiderParatrechalea ornata. First, we tested whether males prefer substrates containing silk of unmated females than substrates containing silk of once‐mated females, competitor males or without silk. Males spent more time on substrates containing silk of females but showed no preference for unmated females, which indicates that males may optimize mate search by prioritizing substrates containing cues of potential mating partners. The lack of preference for unmated females suggests that males cannot detect female mating status from silk or that the costs of searching preferentially for unmated females are high in the field. Second, we tested whether males adjust prey‐gift construction when facing sperm competition risk. Experimental groups (substrate containing silk of an unmated female and silk of another malevs. substrate containing only silk of an unmated female) did not differ in the frequency of gift construction, latency to gift construction and number of flies added to the gift. However, males facing sperm competition risk constructed gifts with less silk, suggesting the occurrence of a less evident form of male mate choice based on differential allocation of resources to prey‐gift. Additionally, given the trade‐off between investing in prey‐gifts quantity or quality, a lower silk investment should enable males to increase the number of gifts constructed and the number of courted females. Taken together, our results indicate that males detect female and male pheromones on substrate and adjust the construction of prey‐gifts in response to apparent sperm competition risk.

Morphology of the male reproductive tract and spermatozoa of Lasioderma serricorne (Coleoptera: Ptinidae)

Xylophagous beetles (Ptinidae) are pests fed on dried and manufactured products from plants or animals. The tobacco weevil, Lasioderma serricorne (Fabricius) (Coleoptera: Ptinidae: Xyletininae) is cosmopolitan, polyphagous and damages stored products, including flour, tobacco and spices. This study describes the morphology of the male reproductive tract and spermatozoa of L. serricorne. The male reproductive tract has a pair of testes with two follicles each, a pair of vasa deferentia and seminal vesicles, five pairs of accessory glands and a single ejaculatory duct opening in the aedeagus. The testis follicles are filled with cysts containing 28 germ cells each. The spermatozoa are spiral and long (1378.6 ± 13.4 μm total length, including 9.2 ± 0.06 μm nucleus) and a tiny acrosome is present. The axoneme microtubular pattern is 9 + 9 + 2, with two symmetrical mitochondrial derivatives and two accessory bodies. The morphologies of the male reproductive tract and spermatozoa of L. serricorne indicate possible adaptations to increase the reproductive success of this beetle, such as mating competition and high population density. This is the first preliminary description of spermatozoa in Xyletininae beetles, which will allow future comparisons with other Coleoptera.

Evolution of large males is associated with female-skewed adult sex ratios in amniotes.

Body size often differs between the sexes (leading to sexual size dimorphism, SSD), as a consequence of differential responses by males and females to selection pressures. Adult sex ratio (ASR, the proportion of males in the adult population) should influence SSD because ASR relates to both the number of competitors and available mates, which shape the intensity of mating competition and thereby promotes SSD evolution. However, whether ASR correlates with SSD variation among species has not been yet tested across a broad range of taxa. Using phylogenetic comparative analyses of 462 amniotes (i.e., reptiles, birds, and mammals), we fill this knowledge gap by showing that male bias in SSD increases with increasingly female-skewed ASRs in both mammals and birds. This relationship is not explained by the higher mortality of the larger sex because SSD is not associated with sex differences in either juvenile or adult mortality. Phylogenetic path analysis indicates that higher mortality in one sex leads to skewed ASR, which in turn may generate selection for SSD biased toward the rare sex. Taken together, our findings provide evidence that skewed ASRs in amniote populations can result in the rarer sex evolving large size to capitalize on enhanced mating opportunities.

Mark-release-recapture of male Aedes aegypti (Diptera: Culicidae): Use of rhodamine B to estimate movement, mating and population parameters in preparation for an incompatible male program.

Rapid advances in biological and digital support systems are revolutionizing the population control of invasive disease vectors such as Aedes aegypti. Methods such as the sterile and incompatible insect techniques (SIT/IIT) rely on modified males to seek out and successfully mate with females, and in doing so outcompete the wild male population for mates. Currently, these interventions most frequently infer mating success through area-wide population surveillance and estimates of mating competitiveness are rare. Furthermore, little is known about male Ae. aegypti behaviour and biology in field settings. In preparation for a large, community scale IIT program, we undertook a series of mark- release-recapture experiments using rhodamine B to mark male Ae. aegypti sperm and measure mating interactions with females. We also developed a Spatial and Temporally Evolving Isotropic Kernel (STEIK) framework to assist researchers to estimate the movement of individuals through space and time. Results showed that ~40% of wild females captured daily were unmated, suggesting interventions will need to release males multiple times per week to be effective at suppressing Ae. aegypti populations. Males moved rapidly through the landscape, particularly when released during the night. Although males moved further than what is typically observed in females of the species, survival was considerably lower. These unique insights improve our understanding of mating interactions in wild Ae. aegypti populations and lay the foundation for robust suppression strategies in the future.

Bonobos and chimpanzees preferentially attend to familiar members of the dominant sex

Social animals must carefully track consequential events and opportunities for social learning. However, the competing demands of the social world produce trade-offs in social attention, defined as directed visual attention towards conspecifics. A key question is how socioecology shapes these biases in social attention over evolution and development. Chimpanzees, Pan troglodytes , and bonobos, Pan paniscus , provide ideal models for addressing this question because they have large communities with fission–fusion grouping, divergent sex-based dominance hierarchies and occasional intergroup encounters. Using noninvasive eye-tracking measures, we recorded captive apes’ attention to side-by-side images of familiar and unfamiliar conspecifics of the same sex. We tested four competing hypotheses about the influence of taxonomically widespread socioecological pressures on social attention, including intergroup conflict, dominance, dispersal and mating competition. Both species preferentially attended to familiar over unfamiliar conspecifics when viewing the sex that typically occupies the highest ranks in the group: females for bonobos, and males for chimpanzees. However, they did not demonstrate attentional biases between familiar and unfamiliar members of the subordinate sex. Findings were consistent across species despite differences in which sex tends to be more dominant. These results suggest that sex-based dominance patterns guide social attention across Pan . Our findings reveal how socioecological pressures shape social attention in apes and likely contribute to the evolution of social cognition across primates. • Bonobos and chimpanzees discriminate faces of familiar and unfamiliar conspecifics. • Great apes devote greater social attention to familiar members of the dominant sex. • Species differences in male vs female dominance shape patterns of social attention. • Both selective pressures and socialization likely drive patterns of social attention.

Sex-specific differences in somatic investment and strategies of physical activity among Portuguese schoolchildren.

Physical activity (PA) is required for healthy growth, development, and maturation and plays an important role in the prevention of overweight and obesity in childhood and adolescence. Sex-differences in PA levels are well documented, with boys spending more time in PA, especially in moderate-to-vigorous activities. Following the Life History Theory, our aim is to study if PA affects the fat tissues increases during childhood and juvenile phases in both sexes. Time spent in sedentary, light, and moderate-to-vigorous PA levels were measured in a sample of 415 Portuguese children and juveniles (207 females/208 males; aged 6-11 years), using an accelerometer for 7 days. Skinfolds related with body fat were objectively collected and socioeconomic status factors were reported using a parental questionnaire. The outcomes show that girls' and boys' fat variables increased during the end of the childhood and the juvenile phase. However, these variables were differently affected by PA. Girls increased fat variables with the sedentary activity while boys decreased fat variables with moderate-to-vigorous PA. Alike, active boys but not girls reduced the fat increase tendency with age. Although both sexes displayed a general fat increment with age, moderate-to-vigorous PA dampens the increase only in boys. In fact, active girls increased body fat in the same manner as non-active girls. From an evolutionary perspective, it could explain sex-specific somatic strategies related to future reproduction or, with future mating and intrasexual competition.

The dark-ventral-patch of male red deer, a sexual signal that conveys the degree of involvement in rutting behavior

BackgroundIn polygynous mammals, signalling may play a decisive role in mating behavior, mediating the intensity of male fights and female mate choice. During the rutting season, male red deer may show a visible dark patch in their ventral fur. Recently, this patch has been suggested to act as a flexible sexual signal, due to its relationships with other variables such as age, body size, antler development, volatile compounds, or the competitive environment. The analysis of fur pigmentation at the ventral patch suggests that this might also visually indicate the male intrinsic predisposition to take part in mating competition.ResultsTo assess the possible role of this trait as a communicative signal related to mate competition, we used red deer behavioral observations during the rut in Doñana National Park (Spain) to examine the link between the degree of expression of the dark ventral patch and the rutting activity (assessed from both intra-and-inter-sexual behaviors). Consistent with our predictions, we found in a field study that males with large dark patches showed a higher frequency of rutting behaviors (mainly roaring and flehmen), more interactions with females, and attained larger harem sizes.ConclusionsThe dark ventral patch was a better predictor of male behavior than antler tines or territory holding, thus standing as a short-term indicator of male willingness to invest in mating competition.

Advancing the Psychometric Study of Human Life History Indicators : K Does Not Measure Life History Speed, but Theory and Evidence Suggest It Deserves Further Attention.

In this article we attend to recent critiques of psychometric applications of life history (LH) theory to variance among humans and develop theory to advance the study of latent LH constructs. We then reanalyze data (n = 4,244) previously examined by Richardson et al. (Evolutionary Psychology, 15(1), 2017, https://doi.org/10.1177/1474704916666840 to determine whether (a) previously reported evidence of multidimensionality is robust to the modeling approach employed and (b) the structure of LH indicators is invariant by sex. Findings provide further evidence that a single LH dimension is implausible and that researchers should cease interpreting K-factor scores as empirical proxies for LH speed. In contrast to the original study, we detected a small inverse correlation between mating competition and Super-K that is consistent with a trade-off. Tests of measurement invariance across the sexes revealed evidence of metric invariance (i.e., equivalence of factor loadings), consistent with the theory that K is a proximate cause of its indicators; however, evidence of partial scalar invariance suggests use of scores likely introduces bias when the sexes are compared. We discuss limitations and identify approaches that researchers may use to further evaluate the validity of the K-factor and other applications of LH to human variation.

Brachytrupes megacephalus Lefèbvre, 1827 (Orthoptera, Gryllidae) in the Maltese Islands: notes on biogeography, behaviour, and habitat of populations in the central Mediterranean area and the Maghreb.

Brachytrupes megacephalus (Lefebvre, 1827) is of significant biogeographic importance. It occurs in Sicily and on some of the circum-Sicilian and Pelagian islands, as well as in the Maltese Islands, Sardinia and the Maghreb (notably but not exclusively, in Algeria and Tunisia, where it maintains populations in both coastal and desert regions). Within European territory, it occurs solely in Italy and Malta, where it is protected under the EU Habitats Directive and the Bern Convention. In northern Africa, the species is regarded as a polyphagous pest, particularly in Saharan locations. The present work is based on field observations, mostly from the Maltese Islands, that span more than three decades; it provides insights on spatial distribution, population trends and behaviour. In examining the relationship between the species' frequency during its mating season and weather conditions, results suggest a weak yet statistically significant correlation between mating strategies and ambient meteorological conditions. Moreover, patch occupancy in spring and autumn varied considerably within a specified area of study, primarily due to competitive mating strategies employed in spring, with an occupancy ratio of approximately 1:6. To-date, the species is known from 13 locations, one in Gozo and 12 in Malta, of which some constitute the Ahrax promontory metapopulation. Connectivity between the Ahrax subpopulation cluster is discussed in the light of habitat and topographical characteristics. Contrasting findings on variances in behaviour between Maltese populations and other populations in Sicily and the Maghreb are discussed. Discernible behavioural disparities include the length of excavated tunnels during spring and summer/autumn seasons in the different geographical locations, attraction to artificial sources of light, and the degree of damage to crops across geographic regions.

No risk to scrambling? Mating tactic does not affect the frequency of leg autotomy in a New Zealand harvestman

Intense sexual selection on males may drive the evolution of exaggerated weaponry, typically used in contests for females or reproductive sites. In some species, males have discontinuous variation in weapon morphology that is accompanied by alternative reproductive tactics (ARTs). Major males with enlarged weapons usually exhibit a mating tactic based on female or resource defence, which makes them relatively sedentary. Minor males with reduced or absent weapons may exhibit a scramble competition mating tactic, which involves increased movement in search of females. Thus, the main costs paid by majors involve the expression/maintenance of exaggerated structures and potential injuries during contests. In turn, the main costs paid by minors are likely related to increased exposure to predation during mate search, yet this cost has rarely been considered for minors. Harvestmen are an arachnid group with diverse male weaponry, including many cases of male polymorphism associated with ARTs. Species of the suborder Eupnoi use leg autotomy as a common antipredator defence. Here we investigated whether leg autotomy (a proxy for predation risk) is more frequent in minors of the weapon polymorphic harvestman Forsteropsalis pureora , which has three male morphs with drastically different cheliceral size and morphology. Leg autotomy was very common, with 54% of wild-caught individuals missing at least one leg (mostly leg II), but we found no evidence for differential predation risk between male morphs during adulthood. In a predator simulation experiment, we found no difference in the likelihood or latency to autotomize a leg between male morphs or leg types (legs I, II, III or IV). However, males already missing legs were more reluctant to autotomize an additional leg. Our results suggest that while leg autotomy is a common antipredator strategy, with no difference between male tactics, costs are compounded as additional legs are autotomized and males may strategically decide not to autotomize in future predator encounters. • New Zealand harvestmen autotomize (lose) legs to escape predators. • This defence strategy is common in wild populations. • Sensory legs are lost more often than locomotory legs. • Harvestmen that have lost legs in the past take longer to drop an additional leg. • Male reproductive strategy does not affect autotomy risk.

Sterile Insect Technique: Successful Suppression of an Aedes aegypti Field Population in Cuba.

Simple SummaryThe sterile insect technique (SIT) is a species-specific and environment-friendly method of insect control that relies on the release of large numbers of sterile insects. Mating released sterile males with wild females leads to a decrease in the reproductive potential and to the local suppression of the target population. There is increased interest in applying this approach to manage disease-transmitting mosquito populations. The main focus of this pilot trial was to assess the efficacy of the SIT for the suppression of Aedes aegypti populations. Two areas in Havana city, Cuba, were selected as control and release trial sites. The presence, density and fertility of the target wild population were monitored through a network of ovitraps. Approximately 1,270,000 irradiated Ae. aegypti males were released in the 50 ha target area over a period of 20 weeks. The released mosquitoes showed excellent mating competitiveness and induced high levels of sterility in the wild Ae. aegypti population. The target natural population was suppressed as reflected in the ovitrap index and in the mean number of eggs/trap values which dropped to zero by the last 3 weeks of the trial. We conclude that the released sterile male Ae. aegypti competed successfully and induced significant sterility in the local target Ae. aegypti population, resulting in suppression of the vector.Dengue virus infections are a serious public health problem worldwide. Aedes aegypti is the primary vector of dengue in Cuba. As there is no vaccine or specific treatment, the control efforts are directed to the reduction of mosquito populations. The indiscriminate use of insecticides can lead to adverse effects on ecosystems, including human health. The sterile insect technique is a species-specific and environment-friendly method of insect population control based on the release of large numbers of sterile insects, ideally males only. The success of this technique for the sustainable management of agricultural pests has encouraged its evaluation for the population suppression of mosquito vector species. Here, we describe an open field trial to evaluate the effect of the release of irradiated male Ae. aegypti on a wild population. The pilot trial was carried out in a suburb of Havana and compared the mosquito population density before and after the intervention, in both untreated control and release areas. The wild population was monitored by an ovitrap network, recording frequency and density of eggs as well as their hatch rate. A significant amount of sterility was induced in the field population of the release area, as compared with the untreated control area. The ovitrap index and the mean number of eggs/trap declined dramatically after 12 and 5 weeks of releases, respectively. For the last 3 weeks, no eggs were collected in the treatment area, clearly indicating a significant suppression of the wild target population. We conclude that the sterile males released competed successfully and induced enough sterility to suppress the local Ae. aegypti population.

Nesting strategy shapes territorial aggression but not testosterone: A comparative approach in female and male birds

Our understanding of the proximate and ultimate mechanisms shaping competitive reproductive phenotypes primarily stems from research on male-male competition for mates, even though competition is widespread in both sexes. We evaluate the hypothesis that the restricted nature of a resource required for reproduction, i.e. nest site, is a key variable driving territorial competition and testosterone secretion in female and male birds. Obligate secondary cavity-nesting has evolved repeatedly across avian lineages, providing a useful comparative context to explore how competition over limited nest cavities shapes aggression and its underlying mechanisms across species. Although evidence from one or another cavity-nesting species suggests that territorial aggression is adaptive in both females and males, this has not yet been tested in a comparative framework. We predicted that cavity-nesting generates more robust territorial aggression, in comparison to close relatives with less restrictive nesting strategies. Our focal species were two obligate secondary cavity-nesting species and two related species with more flexible nesting strategies in the same avian family: tree swallow (Tachycineta bicolor) vs. barn swallow (Hirundo rustica); Eastern bluebird (Sialia sialis) vs. American robin (Turdus migratorius). We assayed conspecific aggression using simulated territorial intrusion and found that cavity-nesting species displayed greater territorial aggression than their close relatives. This pattern held for both females and males. Because territorial aggression is often associated with elevated testosterone, we also hypothesized that cavity-nesting species would exhibit higher testosterone levels in circulation. However, cavity-nesting species did not have higher testosterone in circulation for either sex, despite some correlative evidence that testosterone is associated with higher rates of physical attack in female tree swallows. Our focus on a context that is relevant to both sexes – competition over essential breeding resources – provides a useful framework for co-consideration of proximate and ultimate drivers of reproductive competition in females and males.

The evolution of monogamy is associated with reversals from male to female bias in the survival cost of parasitism.

The extent to which parasites reduce host survival should depend upon how hosts balance trade-offs between reproduction and survival. For example, parasites are predicted to impose greater survival costs under polygynous or promiscuous mating systems in which competition for mates favours increased reproductive investment, particularly in males. We provide, to our knowledge, the first comparative test of the hypothesis that the mating system of the host is an important determinant of (i) the extent to which parasites reduce survival, and (ii) the extent to which males and females differ in the survival cost of parasitism. Using meta-analysis of 85 published estimates of the survival cost of parasitism from 72 studies of 64 species representing diverse animal lineages, we show that parasites impose a mean 3.5-fold increase in the odds of mortality on their hosts. Although this survival cost does not differ significantly across monogamous, polygynous and promiscuous mating systems, females incur a greater survival cost than males in monogamous species, whereas males incur a greater survival cost than females in polygynous and promiscuous species. Our results support the idea that mating systems shape the relative extent to which males and females invest in reproduction at the expense of defence against parasites.

Using the Fluorescent Dye, Rhodamine B, to Study Mating Competitiveness in Male Aedes aegypti Mosquitoes.

The success of sterile or incompatible insect technique-based population suppression programs depends on the ability of released males to compete for wild-type females and induce sterility in the target population. Hence, laboratory assessment of male mating competitiveness is essential for evaluating the release strain's fitness before field release. Conventionally, such an assay is performed by determining the proportion of viable eggs produced by the females after being simultaneously exposed to two sets of males (wild-type and release strains) for copulation. However, this process is time-consuming and laborious due to the need to first blood-feed the females for egg production and then hatch and enumerate the hatched eggs to determine egg viability. Moreover, this method cannot discern the degree of competitiveness between two sterile or Wolbachia-infected mosquito lines as wild-type female mosquitoes will only produce non-viable eggs upon mating with both. To circumvent these limitations, this paper describes a more direct method of measuring male mosquito mating competitiveness in laboratory settings using the fluorescent dye, rhodamine B (RhB), which can be used to mark males by feeding them in sucrose solution containing RhB. After the mating assay, the presence of fluorescing sperms in the spermathecae of a female can be used to determine her mating partner. This method is cost-effective, reduces the experimental time by 90% and allows comparison of mating fitness between two sterile or Wolbachia-infected lines.

Using the Fluorescent Dye, Rhodamine B, to Study Mating Competitiveness in Male <em>Aedes aegypti</em> Mosquitoes

The success of sterile or incompatible insect technique-based population suppression programs depends on the ability of released males to compete for wild-type females and induce sterility in the target population. Hence, laboratory assessment of male mating competitiveness is essential for evaluating the release strain’s fitness before field release. Conventionally, such an assay is performed by determining the proportion of viable eggs produced by the females after being simultaneously exposed to two sets of males (wild-type and release strains) for copulation. However, this process is time-consuming and laborious due to the need to first blood-feed the females for egg production and then hatch and enumerate the hatched eggs to determine egg viability. Moreover, this method cannot discern the degree of competitiveness between two sterile or Wolbachia-infected mosquito lines as wild-type female mosquitoes will only produce non-viable eggs upon mating with both. To circumvent these limitations, this paper describes a more direct method of measuring male mosquito mating competitiveness in laboratory settings using the fluorescent dye, rhodamine B (RhB), which can be used to mark males by feeding them in sucrose solution containing RhB. After the mating assay, the presence of fluorescing sperms in the spermathecae of a female can be used to determine her mating partner. This method is cost-effective, reduces the experimental time by 90% and allows comparison of mating fitness between two sterile or Wolbachia-infected lines.

The impact of sublethal permethrin exposure on susceptible and resistant genotypes of the urban disease vector Aedes aegypti.

BACKGROUNDIn urban environments, some of the most common control tools used against the mosquito disease vector Aedes aegypti are pyrethroid insecticides applied as aerosols, fogs or residual sprays. Their efficacy is compromised by patchy deployment, aging residues, and the evolution and invasion of pyrethroid‐resistant mosquitoes. A large proportion of mosquitoes in a given environment will therefore receive sublethal doses of insecticide. The potential impact of this sublethal exposure on the behaviour and biology of Ae. aegypti carrying commonly reported resistance alleles is poorly documented.RESULTSIn susceptible insects, sublethal exposure to permethrin resulted in reductions in egg viability (13.9%), blood avidity (16.7%) and male mating success (28.3%). It caused a 70% decrease in the lifespan of exposed susceptible females and a 66% decrease in the insecticide‐resistant females from the parental strain. Exposure to the same dose of insecticide in the presence of the isolated kdr genotype resulted in a smaller impact on female longevity (a 58% decrease) but a 26% increase in eggs per female and a 37% increase in male mating success. Sublethal permethrin exposure reduced host‐location success by 20–30% in all strains.CONCLUSIONThe detrimental effects of exposure on susceptible insects were expected, but resistant insects demonstrated a less predictable range of responses, including negative effects on longevity and host‐location but increases in fecundity and mating competitiveness. Overall, sublethal insecticide exposure is expected to increase the competitiveness of resistant phenotypes, acting as a selection pressure for the evolution of permethrin resistance. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.