Ejaculate economics: an experimental test in a moth

Plasticity in moth mating behavior and ejaculate proteomic diversity induced by male competition

In male competition, large and costly ejaculates are advantageous. Prior research on male accessory gland secretions in Plutella xylostella left open questions about how males modulate their mating behaviors and ejaculate composition allocation in response to varying levels of competition. The current study aimed to delve deeper into these unexplored facets. A totally of 928 ejaculate proteins were identified across males exposed to different competition conditions. Notably, males courting under non-, low-, and high-competition scenarios exhibited 867, 635, and 858 ejaculate proteins, respectively. Approximately 10% of these ejaculate proteins displayed variations that aligned with changes in competition intensity. Subsequent analyses focused on the proteins transferred to females, revealing that 44% of ejaculate proteins were transferred, with 37 proteins exhibiting differential expression. Functional analyses uncovered their crucial roles in sperm maturation, motility, and capacitation. Our findings reveal adaptive adjustments in ejaculate protein abundance and transmission in P. xylostella as a response to varying competition levels. Moreover, fluorescent sperm labeling indicated higher sperm transfer during low competition correlated with shorter sperm length. Furthermore, evidence suggests that males shorten their courtship duration and extend their mating duration when faced with competition. These results illustrate how competition drives ejaculate investment and behavioral plasticity, offering valuable insights for advancements in assisted reproductive technologies and pest management strategies.

Males conditionally inseminate at three female body locations according to female mating history and female maturity status in a squid

In some squids, such as those in the family Loliginidae, upon copulation, females receive and store male-delivered sperm capsules, spermatangia, at two different body locations: the buccal membrane and the distal end of the oviduct. This insemination site dimorphism is associated with alternative reproductive strategies. However, in Loliolus sumatrensis, a species of Loliginidae, the females possess three insemination sites: buccal membrane (BM), basal left IV arm (ARM) and lateral head behind the left eye (EYE), therefore we studied such the unusual phenomena. We developed microsatellite markers and genotyped the paternity of each spermatangium on three sites. We found multiple paternity at every single site and simultaneous usage of all three sites by a few males. The seasonal dynamics of a population in the Seto Inland Sea revealed a set priority for the initial use of insemination sites as BM, followed by ARM and then EYE, whereas the maximum number of stored spermatangia was greater in EYE > ARM > BM. Female maturity status was correlated with the usage pattern of insemination sites but not with the number of stored spermatangia at any insemination site. These results suggest that a male squid inseminates at different locations according to female mating history and female maturity status.

Male larval experience of cues from adult rivals alters lifetime sperm investment patterns in a sperm heteromorphic moth, Ephestia kuehniella

Male animals may adjust their resource allocations for reproduction and other fitness functions in response to cues from rivals. For instance, adult males increase their investment in sperm for a higher paternity share when they perceive sperm competition risk in their surroundings. In nature, both juveniles and adults may coexist spatially and temporally. Yet, it is not clear how juvenile males of different ages respond to cues from adult rivals and fine-tune their lifetime investment in sperm production and ejaculation in any insect. Here we used the Mediterranean flour moth, Ephestia kuehniella, which produces both fertile eupyrene and infertile apyrene sperm, to explore this question. We demonstrate that the late, but not early, instar larvae are sensitive to adult male cues. As a response, they produce more sperm before emergence and their resultant adults have shorter mating latency and ejaculate more sperm in the first few matings. When the juvenile stage produces more eupyrenes, the adult stops making these sperm, but regardless of the number of apyrenes produced during the juvenile stage, the adult continues to make them. These findings suggest that the number of spermatogonia for eupyrenes may be limited and that for apyrenes may be flexible. Our results show that the insect does not trade off survival, mating frequency, body size, or testis size for sperm production in response to adult males during the larval stage. Knowledge created in the present study offers insight into the stage-dependent sensitivity of juvenile males to cues from adult rivals and subsequent lifetime resource allocations.

Reproductive Behaviour of 150-Gy-Treated Female Lobesia botrana (Lepidoptera: Tortricidae)

Simple Summary

Environment-friendly and sustainable insect pest control approaches such as the sterile insect technique/inherited sterility (SIT/IS) have been proposed against the European grapevine moth Lobesia botrana. Reproductive behaviour, such as oviposition, mating ability, and multiple mating of 150 Gy-treated females, was studied. Moreover, the last-male sperm precedence (P2 value) and male’s flight response to treated females were also investigated. The present study aims to provide basic information which is essential to ensure successful implementation of SIT/IS as part of an integrated approach for the management of L. botrana.

Abstract

The sterile insect technique/inherited sterility (SIT/IS) has been suggested as an eco-friendly control tactic for area-wide integrated pest management approaches in order to control the European grapevine moth, Lobesia botrana. This study assessed the effects of an irradiation dose of 150 Gy administered to newly emerged female moths on their egg laying behaviour and mating ability at different ages at mating. Moreover, the effects of multiple mating on the mating ability of treated females, pattern of sperm precedence in twice-mated females and the flight response of treated and untreated males to treated and untreated calling females were also investigated. Females treated with 150 Gy initiated calling in a way similar to untreated females. When treated females were paired with untreated males, the mean number of eggs oviposited per female during 6 days was reduced (59.6 and 82.8 eggs/female, respectively), as was their mating ability and multiple mating compared with untreated females. The proportion of offspring fertilized by the second of the two males to mate with the female or last-male sperm precedence (P2 value) constituted 97% of the eggs, suggesting that the second male mate fathered the most offspring. The outcome of this work could be viewed as an integrated approach for improving effectiveness and enabling successful implementation of a SIT/IS program against L. botrana.

Pupal Cues Increase Sperm Production but Not Testis Size in an Insect

Theoretic and empirical studies show that social surroundings experienced by male insects during their larval or adult stage can influence their testicular investment in diverse ways. Although insect pupae do not feed and crawl, they can communicate using sex-specific and/or non-sex specific cues. Yet, it is unknown, in any insect, whether and how male pupae can fine-tune their resource allocation to sperm production and testis size in response to socio-sexual environments. We investigated this question using a moth, Ephestia kuehniella, which produces fertile eupyrene sperm and unfertile apyrene sperm. We held male pupae individually or in groups with different sex ratios, and dissected adults upon eclosion, measured their testis size, and counted both types of sperm. We demonstrated that after exposure to conspecific pupal cues regardless of sex, male pupae increased production of eupyrenes and apyrenes at the same rate but kept testis size unchanged. We suggest that testis size is fixed after pupation because most morphological traits are formed during the larval stage, allowing little room for pupae to adjust testis size. Like adults, male pupae with fully grown testes have sufficient resources to produce more sperm of both types according to the perceived increase in sperm competition risk.

Delayed Mating with Multiple Partners Decreases Indexes of Mating in Female and Male Spodoptera litura (Lepidoptera: Noctuidae)

Delayed mating is an effective strategy that can decrease the fecundity of a pest by reducing the time that females have to mate. This disruption does not completely inhibit mating and may lead to multiple matings. The effects of delayed mating with multiple partners on different indexes of mating in female and male Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) were determined in this study. The delay in mating significantly decreased the number of matings and the mating success of both sexes and the male contribution to reproduction. Compared with the effect on female fecundity, the delayed mating with multiple partners had a greater effect on the male mate contribution to fecundity. The longevity of females and males increased significantly with a 72 h delay in mating. Linear regression analysis showed negative relationships between delayed mating and fecundity and number of matings in both sexes. Thus, delayed mating with multiple partners can disrupt the mating and reproductive potential of S. litura.

Sperm allocation strategies in a sperm heteromorphic insect

Theories predict that in polyandrous species, the focal male should increase sperm allocation per mate in the presence of rivals to gain greater share of paternity, but in the presence of additional mates, he should reduce sperm allocation per mate to save sperm for insemination of more mates. However, empirical findings are often inconsistent and reasons behind are unclear. Furthermore, many studies use copulation duration as an estimate of the number of sperm transferred. Yet, empirical evidence for such assumption is largely lacking. Here, we used a sperm heteromorphic insect Ephestia kuehniella whose males produce two types of sperm, eupyrenes (fertile) and apyrenes (nonfertile), to test these postulations. We allowed focal males to detect chemical and acoustic but no tactile cues from rivals or additional mates both before and during mating and measured copulation duration and sperm allocation in successive copulations. We demonstrate that males transfer significantly more eupyrenes per mate in the presence of rivals and that the sperm allocation pattern persists in successive copulations under this condition. However, males do not adjust apyrene allocation in response to rivals probably because apyrenes play a relatively minor role in male reproductive success. Contrary to a previous study, focal males do not respond to additional mates most likely due to the lack of tactile cues in the present study. We reveal that sperm allocation is not a function of copulation duration in this insect for spermatophore formation and delivery occupy most of copulation duration and sperm transfer is complete near the end of copulation.

Mating-Induced Differential Expression in Genes Related to Reproduction and Immunity in Spodoptera litura (Lepidoptera: Noctuidae) Female Moths

Mating promotes reproductive activity, which may impact immune performance. Paradoxically, mating frequently challenges females' immunity (e.g., infections). Therefore, studies of postmating resource allocation between reproduction and survival are likely to shed new light on life-history trade-off and sexual selection. Here, we used RNAseq to test whether and how mating affected mRNA expression in genes related to reproduction and immunity in Spodoptera litura female moths. Results show a divergent change in the differentially expressed genes (DEGs) between reproduction and immunity: the immune response was largely downregulated shortly after mating (~6 h postmating), which has some recovery at 24 h postmating; reproductive response is trivial shortly after mating (~6 h postmating), but it largely upregulated at 24 h postmating (e.g., egg maturation related genes were highly upregulated). Considering the fact that most of the total DEGs downregulated from 0 to 6 h postmating (from 51/68 to 214/260) but most of the total DEGs upregulated at 24 h postmating (816/928), it is possible that trade-offs between reproduction and immunity occurred in mated females. For example, they may shut down immunity to favor sperm storage and save limited resources to support the increased energy required in reproduction (e.g., egg maturation and oviposition). Mating-induced infections should be trivial due to low polyandry in S. litura. A reduced immune defense may have no threat to S. litura survival but may benefit reproduction significantly. Furthermore, obvious expression changes were detected in genes related to hormone production, suggesting that endocrine changes could play important roles in postmating responses.

Current versus future reproductive investment adaptive responses in adult Anopheles coluzzii malaria mosquitoes: hydric-stressed males give it all

Background

Life history theory predicts that an individualʼs current reproductive investment should depend on its future reproductive value. A variety of intrinsic biotic and extrinsic factors influence reproductive value, including age, health status and current environmental conditions. Phenotypic plastic reproductive decisions are particularly crucial in species with limited mating and breeding opportunities. In the malaria mosquito Anopheles coluzzii, the combination of male-male competition and female monandry results in male reproductive success being dependent on limited mating opportunities and sperm reserves. Short life spans combined with 3–4 day gonotrophic cycles imply that females can produce only a limited number of egg-batches in their lifetime and rely on a single maleʼs insemination to do so. Here we experimentally tested the effect of hydric stress on male sperm transfer and female sperm maintenance in this important vector species.

Methods

Virgin males and females were stressed prior to mating to simulate environmental uncertainty, hence the prospect of a decreased lifespan. They were then paired overnight with non-stressed mates in standardized mating assays. Sperm transfer, uptake and maintenance were quantified using qPCR, and sperm activity determined via video recording.

Results

When exposed to hydric stress, males responded by increasing their current reproductive investment and transferred significantly larger amounts of sperm to females. There was no significant increase in the mean number of females inseminated overnight by stressed males. In contrast, females did not significantly change their sperm uptake following stress nor did they alter their sperm maintenance strategy after 7-day post-mating hydric stress as measured through sperm activity level and sperm cells quantification.

Conclusions

As predicted by life-history theory, pre-mating hydric stress was associated with an increase in male current reproductive effort in the form of increased sperm transfer. In contrast, pre and post-mating hydric stress had no impact on sperm uptake and maintenance by females, which is compatible with the prediction that females maximize their reproductive value by withstanding stress periods until a blood meal opportunity and maintain sperm quality towards future egg production.

Young male mating success is associated with sperm number but not with male sex pheromone titres

Background

Intraspecific communication is of crucial importance throughout the animal kingdom and may involve a combination of visual, gustatory, olfactory and acoustic cues. Variation in male sex pheromone amount and composition may convey important information to female conspecifics, for instance on species identity or age. However, whether increased male pheromone titres are associated with fitness benefits for the female, thus indicating a role as an honest signal, is under debate.

Results

Against this background, we tested in the butterfly Bicyclus anynana (1) whether young males being successful or unsuccessful in gaining a mating differed in sex pheromone titres and (2) for associations between male pheromone titres and spermatophore mass, eupyrene sperm number, and a variety of female and offspring life-history traits. Successful and unsuccessful males did not differ in pheromone titres, however eupyrene sperm number was much higher in successful males. Pheromone titres were not associated with any fitness-related female or offspring trait measured in our study, though correlation analyses yielded evidence for trade-offs among specific traits. Patterns did not differ among control and olfaction-blocked females.

Conclusion

Therefore, we suggest that in young B. anynana pheromone titres do not indicate male quality.

Flirtation reduces males' fecundity but not longevity

Theory predicts that due to limited resources males should strategically adjust their investment in reproduction and survival. Based on different conceptual framework, experimental designs, and study species, many studies support while others contradict this general prediction. Using a moth Ephestia kuehniella whose adults do not feed and thus have fixed resources for their lifetime fitness, we investigated whether males adjusted their investment in various life activities under dynamic socio-sexual environment. We allowed focal males to perceive rivals or additional females without physical contact. We show that males do not adjust the number of sperm they transfer to mates in a given copulation at different immediate or both immediate and mean sperm competition levels. Contradictory to general predictions, our results demonstrate that cues from additional females increase males' investment in courtship and reduce their lifetime number of copulations and sperm ejaculated, whereas cues from rivals have no effect on these parameters. Males have similar longevity in all treatments. We suggest that the sex pheromone produced by multiple females overstimulate males, increasing males' costly flirtations, and reducing their lifetime copulation frequency and fecundity. This finding offers a novel explanation for the success of mating disruption strategy using sex pheromones in pest management.