Ejaculate Production Research Articles

Effects of past mating behavior versus past ejaculation on male mate choice and male attractiveness.

Past reproductive effort allows males to assess their ability to acquire mates, but it also consumes resources that can reduce their future competitive ability. Few studies have examined how a male's reproductive history affects his subsequent mate choice, and, to date, no study has determined the relative contribution of past mating behavior and past ejaculate production because these two forms of investment are naturally highly correlated. Here, we disentangled the relative effects of past mating behavior and past ejaculate production in mosquitofish (Gambusia holbrooki) by experimentally preventing some males from ejaculating when trying to mate. We assessed the effect of mating behavior on mate choice by comparing males that had previously been with or without access to females and male rivals for 8 and 16 weeks and assessed the effect of ejaculation on mate choice by comparing males that either could or could not ejaculate when they had access to females for 16 weeks. Reproductive treatment did not affect male attractiveness, but it did affect male mate choice. Somewhat surprisingly, in five of the six treatment-by-age at testing combinations, males preferred a female in the vicinity of a male rival over a solitary female. This preference was marginally stronger for males that had previously engaged in mating behavior but were unaffected by past ejaculate production. We discuss the potential benefits to males of associating with another male when seeking mates. This is the first study to quantify the relative influence of pre- and post-copulatory reproductive investment on male mate choice.

Effect of age, mating history and temperature on male reproductive costs in the bean beetle Callosobruchus maculatus

Temperature and humidity determine seed viability, but their effect on seed pest reproduction, such as that of the bean beetle Callosobruchus maculatus, remains understudied. Adult male C. maculatus pass large ejaculates to mates while not feeding. Here, we studied ejaculate production and longevity in C. maculatus males at different temperatures and mating patterns. After development at 25, 27 and 29 °C, eclosing males were weighed and prevented from mating (m0) or allowed to mate once with virgin females three (m3) or five (m5) days after eclosion or to mate twice, three and five days after eclosion (m3+5). We weighed males before and after mating to estimate body mass loss due to ejaculate transfer and depletion of resources over time attributed to routine physiology/evaporation. Warmer conditions increased mortality and development rates and tended to decrease body mass. Males with a large body mass at eclosion survived longer than smaller males. The body mass of males was depleted at daily rates equal to 3–5% of body mass at eclosion. The rates of this loss increased in warmer conditions, suggesting that this process was the main determinant of the thermal pattern of mortality. During a single mating, males produced ejaculates that constituted 2–6% of their body mass at eclosion. Contrary to predictions, ejaculate production did not change with thermal conditions. Body mass losses through ejaculate transfer resulted in increased male mortality, and this effect was two times stronger than the effect of a comparable body mass loss through routine physiology/evaporation. Ejaculate mass decreased with age independent of mating history, suggesting that ejaculate production is restricted by routine physiology/evaporation losses. We conclude that the longevity of male C. maculatus is a function of body mass loss, but the two sources of body mass loss considered here, ejaculates and routine physiology, are not equally costly.

Ejaculate Allocation and Sperm Characteristics Differ among Alternative Male Types in a Species of Fish with Cooperation and Competition among Unrelated Males.

Sexual selection arising from sperm competition has driven the evolution of immense variation in ejaculate allocation and sperm characteristics not only among species, but also among males within a species. One question that has received little attention is how cooperation among males affects these patterns. Here we ask how male alternative reproductive types differ in testes size, ejaculate production, and sperm morphology in the ocellated wrasse, a marine fish in which unrelated males cooperate and compete during reproduction. Nesting males build nests, court females and provide care. Sneaker males only “sneak” spawn, while satellite males sneak, but also help by chasing away sneakers. We found that satellite males have larger absolute testes than either sneakers or nesting males, despite their cooperative role. Nesting males invested relatively less in testes than either sneakers or satellites. Though sneakers produced smaller ejaculates than either satellite or nesting males, we found no difference among male types in either sperm cell concentration or sperm number, implying sneakers may produce less seminal fluid. Sperm tail length did not differ significantly among male types, but sneaker sperm cells had significantly larger heads than either satellite or nesting male sperm, consistent with past research showing sneakers produce slower sperm. Our results highlight that social interactions among males can influence sperm and ejaculate production.

Food Limitation but Not Enhanced Rates of Ejaculate Production Imposes Reproductive and Survival Costs to Male Crickets.

Estimating costs of ejaculate production is challenging. Metabolic investment in ejaculates may come at the expense of other physiological functions and may negatively affect future reproduction and/or survival. These trade-offs are especially likely to occur under constrained resource pools (e.g., poor nutrition). Here, we investigated costs of ejaculate production via trade-offs in the field cricket Gryllus bimaculatus. We experimentally increased rates of ejaculate production, while keeping an unmanipulated group, in adult males kept at high and low feeding regimes and tested the effects of our treatments on (i) somatic maintenance (i.e., changes in male body mass), (ii) future reproduction (i.e., the likelihood of producing a spermatophore and the viability of its sperm), and (iii) lifetime survival and longevity. We predicted investment in ejaculates to impinge upon all measured responses, especially in low-fed individuals. Instead, we only found negative effects of food limitation, suggesting low or undetectable costs of spermatophore production. High mating rates may select for males to maximize their capacity of ejaculate production, making ejaculate traits less prone to trade-offs with other fitness-related life history traits. Nevertheless, males were impaired due to nutrient deficiency in producing viable ejaculates, suggesting condition-dependent costs for ejaculate production.

Strategic adjustment of ejaculate quality in response to variation of the socio-sexual environment

Strategic ejaculate adjustments occur when males modify their investment in sperm and nonsperm components of the ejaculate according to the context. This strategy is expected to evolve when ejaculate production is costly, the returns of the investment in the ejaculate depend on the environment and environmental conditions are variable. While adjustments of sperm numbers have been widely documented, only recently we have begun to investigate how males modify ejaculate quality, despite the recognized importance of this factor for sperm competition. Here I discuss and synthetize existing literature on strategic adjustments of ejaculate quality. I describe which ejaculate quality traits are most typically plastic and which environmental factors elicit such responses, focusing especially on the socio-sexual environment. I summarize information on the timeframe within which adjustments can occur and on the proximate mechanisms responsible for plasticity. I show that this phenomenon is widespread across taxa; it involves responses to several environmental factors and modifications of many ejaculate traits, with seminal fluid composition playing a central role, as a trait per se and as proximate mechanism for sperm performance adjustments. I point out the circumstances favoring the evolution of ejaculate quality plasticity, and evaluate the fitness consequences of these responses, highlighting the complexity of patterns of covariation with other traits. Finally, I consider implications for male and female behavior. I highlight two areas of research on ejaculate plasticity that may be particularly worth exploring further: 1) the proximate mechanisms responsible for plasticity; 2) the adaptive value of strategic ejaculate adjustments.

Patterns of Gonadic Development and Operational Sex Ratio Promote Promiscuity ofEuxesta bilimeki(Diptera:Ulidiidae)

AbstractPromiscuous mating systems are widely distributed among animals and can be promoted by operational sex ratios (number of receptive adults; OSR). In populations where OSR is not biased towards any sex, the possibility that males and females mate with several individuals increases. For both sexes to synchronize in time and space for reproduction, adults should possess or simultaneously acquire nutrients required to reach sexual maturity. Among synovigenic (without a full complement of eggs at eclosion) species, nutrient acquisition, protein in particular, may influence the OSR. In the Agave fly Euxesta bilimeki (Hendel) (Diptera: Ulidiidae), both sexes engage in multiple mating and females frequently expel all or part of the ejaculate. Here, we assessed the effect of protein intake on gonadic development, and estimated OSR from field-collected individuals. Body protein content was compared between wild and laboratory individuals with access to different diets, and mating frequency and individual mating rate were analyzed for cohorts at a 1:1 sex ratio. Both sexes required protein ingestion for gonadic development, but there were no differences in protein content between field-collected males and males fed protein and sugar in the laboratory, despite the fact that males assigned 9.3% of their corporal weight to testicles. Euxesta bilimeki is a promiscuous species where both males and females mate multiply with one or several individuals in short periods of time; thus, large testes size may be linked to the need of voluminous ejaculate production, and might be further exacerbated by female ejaculate expulsion.

Increased sperm production linked to competition in the maternal social environment.

Maternal or early life effects may prepare offspring for similar social conditions to those experienced by their mothers. For males, the ability to achieve mating and fertilization success is a key social challenge. Competitive conditions may therefore favour increased body size or ejaculate production in male offspring. We tested this experimentally by comparing reproductive traits of adult male bank voles (Myodes glareolus), whose mothers had experienced contrasting encounter regimes with female conspecifics while breeding. We found that daily sperm production rates and epididymis mass were significantly higher when dams had experienced more frequent encounters with female conspecifics. This response to maternal and early life experience was specific to sperm production and storage, with no evidence for effects on male body mass or the size of testes and accessory reproductive glands. Our findings reveal a potentially adaptive effect of maternal and early life experience on the development of sperm production, which is worthy of wider investigation.

Social status and ejaculate composition in the house mouse.

Sperm competition theory predicts that males should tailor ejaculates according to their social status. Here, we test this in a model vertebrate, the house mouse (Mus musculus domesticus), combining experimental data with a quantitative proteomics analysis of seminal fluid composition. Our analyses reveal that both sperm production and the composition of proteins found in seminal vesicle secretions differ according to social status. Dominant males invested more in ejaculate production overall. Their epididymides contained more sperm than those of subordinate or control males, despite similar testes size between the groups. Dominant males also had larger seminal vesicle glands than subordinate or control males, despite similar body size. However, the seminal vesicle secretions of subordinate males had a significantly higher protein concentration than those of dominant males. Moreover, detailed proteomic analysis revealed subtle but consistent differences in the composition of secreted seminal vesicle proteins according to social status, involving multiple proteins of potential functional significance in sperm competition. These findings have significant implications for understanding the dynamics and outcome of sperm competition, and highlight the importance of social status as a factor influencing both sperm and seminal fluid investment strategies.This article is part of the theme issue ‘Fifty years of sperm competition’.

Cost of mating in male Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae)

AbstractMating and reproduction not only provide benefits but can also incur substantial costs. An increasing number of recent studies have indicated that mate searching, mating, and ejaculate production requires large amount of energy which can result in high cost to males. Here, we examine the effect of number of matings of males and mating duration on mating and reproductive success in Menochilus sexmaculatus (Coleoptera: Coccinellidae) by subjecting them to 3 consecutive matings of 30, 60, 90 min, and complete mating (a) with no interval and (b) with interval of 24 hr between the matings. The results reveal a reduction in reproductive performance for both the setup and reduction is more when mating is consecutive without gap. This shows that between subsequent matings males require time to recuperate the sperm/ejaculate. As a male engages in a greater number of matings, the time it takes to begin mating when paired with a female increases and the overall duration of mating decreases. However, frequent mating attempts made by males result in reduction in their body weight. Thus, in this ladybird beetle mating and related physiological process consume lots of energy and the body weight of males tend to decrease which further modifies their reproductive performance. The study helps us to identify the cost of mating from male's perspective and indicates that males need to rejuvenate between the matings.

Trade-offs of strategic sperm adjustments and their consequences under phenotype–environment mismatches in guppies

In polyandrous species males invest significant resources in producing large and high-quality ejaculates. As ejaculates are costly, males are expected to modulate their investment in response to social cues associated with the expected level of sperm competition or mating opportunity, to anticipate future mating conditions. Another consequence of ejaculate costs is that the increase in ejaculate production may be traded against traits linked to mate acquisition. In such cases, the effect of this anticipatory plasticity in ejaculate investment on a male's reproductive success will depend on the balance between postcopulatory benefits and precopulatory costs in the sociosexual context subsequently encountered. Here, we used the guppy, Poecilia reticulata, a live-bearing fish characterized by intense sperm competition, to investigate how mismatches between anticipatory phenotypes and the social conditions subsequently experienced affect male reproductive success. Male guppies kept in visual contact with females, a social stimulus predicting high mating opportunities, increase their sperm production compared to female-deprived males which foresee fewer opportunities to mate, but simultaneously reduce their courtship rate. Using a paired experimental design, we manipulated the male's perceived mating opportunities by housing them in the presence (FP) or in the absence (FA) of females. We then measured male mating and insemination success under two conditions: (1) a female-biased sex ratio, matching expected FP cues; and (2) a male-biased sex ratio, matching expected FA cues. Under a female-biased sex ratio, mating and insemination success were not affected by previous exposure to females, although FP males experienced a lower risk of sperm depletion after several copulations. However, FP males showed a small, but significant, reduction in their mating success under a male-biased sex ratio, when directly competing with an FA male. Males showed significant repeatability in mating and insemination success within a sex ratio context, suggesting that the costs of mismatching anticipatory ejaculate responses are probably low in this species.

Seasonal effects on testes size and sustained semen quality in captive golden-headed lion tamarins, Leontopithecus chrysomelas

The golden-headed lion tamarin (Leontopithecus chrysomelas) is an endangered primate that, according to timing of births, there seems to have seasonal reproductive patterns in captive populations inhabiting the Southern Hemisphere. The extent to which male tamarins have circannual cyclic fluctuations in testicular functions, however, remains unknown. Changes in testis size and seminal variables, therefore, were evaluated during the rainy and dry seasons of the year in seven males. There was estimation of mating and birth seasons from the breeding colony using a 27 year database (229 birth records). Births were distributed throughout the year with peaks occurring in August-October and January-March (39.7 % and 30.5 % of all births, respectively). Semen collection using penile vibrostimulation was successfully induced in more than 96 % of the attempts regardless of the season (total of 75 ejaculates). Body mass did not vary significantly between seasons, but relative testes size was larger during the dry season. Values for none of the seminal variables (total sperm count, total and progressive motility, plasma membrane and acrosome integrity, and total sperm defects), however, were different during the rainy and dry seasons. These results indicate that testicular function in golden-headed lion tamarins may not be affected by daylength changes, and that seasonal patterns of female reproduction is perhaps more relevant for the reproductive timing of the species. Furthermore, the possibility of year-round production of ejaculates containing viable sperm broadens our perspective of preserving genetic diversity within the species because there is a greater opportunity for semen collection and freezing.

The sexual activity of the ram-sires, depending on their mode of use

Literary data are presented and their analysis is conducted regarding the mode of use of ram-sires and their effect on sexual activity and sperm productivity. The results of research of scientists with recommendations of optimal modes of use of fetuses for semen production and its cryopreservation in non-pairing and steaming periods are presented. According to the results of the analysis of many researchers, the activity of the sexual reflexes of the rams in the spring and summer decreases by 1.4 times compared to the winter. At the same time quantitative indicators of sperm productivity decrease. However, M.M. Aibazov (1987) experimentally confirmed that sheep-breeders of the Caucasian fine-breed and Australian merenos breed exhibit high sexual activity and produce sperm of satisfactory quality in all seasons. Similar results were obtained by British researchers in the study of sexual activity and sperm productivity of ram-sires of British breeds. A.A. Ivanov (1987) indicates the regime of use of ram sires, for five years with obtaining and subsequent freezing in the unpaired period 6 ejaculates (2 doublets 3 times) per week and in the breeding season 10 ejaculates (2 doublets 5 times) week. P.P. Kundyshev (2004) considers it possible and proposes to obtain from the breeding rams for cryopreservation and storage during the year, both unpaired and steaming periods, with daily ejaculate production. This mode, according to the author, provides a sufficiently high fertility sperm up to 50.3 percent. In the study of sexual activity and sperm productivity of ram-sires of different breeds, including the North Caucasian meat-wool, jalgin merino, Soviet merino, maniche merino, Russian meat merino, Edelbaev, polldore P.P. Mammoth and others. (2018) found that the most active were the rams of the Edinburgh breed, which took 22 seconds. ejaculate secretion, and the slowest texel breeders, which took 39 seconds to ejaculate. The rams of the other breeds listed above spent 25 to 34 seconds to ejaculate. In addition, rams of Texel breed produced the lowest activity sperm, and therefore only 19 sperm were frozen from one ejaculate, with an average of 20 to 26 sperm species tested.

Proteins, Transcripts, and Genetic Architecture of Seminal Fluid and Sperm in the Mosquito Aedes aegypti

The yellow fever mosquito, Aedes aegypti,, transmits several viruses causative of serious diseases, including dengue, Zika, and chikungunya. Some proposed efforts to control this vector involve manipulating reproduction to suppress wild populations or to replace them with disease-resistant mosquitoes. The design of such strategies requires an intimate knowledge of reproductive processes, yet our basic understanding of reproductive genetics in this vector remains largely incomplete. To accelerate future investigations, we have comprehensively catalogued sperm and seminal fluid proteins (SFPs) transferred to females in the ejaculate using tandem mass spectrometry. By excluding female-derived proteins using an isotopic labeling approach, we identified 870 sperm proteins and 280 SFPs. Functional composition analysis revealed parallels with known aspects of sperm biology and SFP function in other insects. To corroborate our proteome characterization, we also generated transcriptomes for testes and the male accessory glands-the primary contributors to Ae. aegypti, sperm and seminal fluid, respectively. Differential gene expression of accessory glands from virgin and mated males suggests that transcripts encoding proteins involved in protein translation are upregulated post-mating. Several SFP transcripts were also modulated after mating, but >90% remained unchanged. Finally, a significant enrichment of SFPs was observed on chromosome 1, which harbors the male sex determining locus in this species. Our study provides a comprehensive proteomic and transcriptomic characterization of ejaculate production and composition and thus provides a foundation for future investigations of Ae. aegypti, reproductive biology, from functional analysis of individual proteins to broader examination of reproductive processes.

From storage to delivery: sperm volume and number of spermatozoa inside storage organs and ejaculates in males ofTimogenes elegans(Scorpiones: Bothriuridae)

Sperm competition influences the evolution of many reproductive traits such as gonads, sperm or genitalia. Many sperm competition analyses concentrate in testes and ejaculates. Among arachnids, scorpions constitute an intriguing taxon for examining sperm production and usage. For example, in the family Bothriuridae the females of Timogenes elegans Mello-Leitão, 1931 accept more than one male per reproductive season and males produce spermatozoa continuously, storing them inside two elastic storage organs (i.e., two seminal vesicles plus two deferent ducts) before inseminating females, using a sclerotized spermatophore. In this study, we analyzed the sperm storage organs and the ejaculate volume transferred by T. elegans. We described the volume and number of spermatozoa at storage sites and in ejaculates, and investigated ejaculate volume and concentration in remating experiences. Storage organs varied in total size. Inside the spermatophore, the volume of the sperm drop represented 38% of the volume of both sperm storage sites. The remaining space around the sperm drop is filled with a gel-like substance. The ejaculate volume and spermatozoa number did not vary significantly between consecutive matings. Timogenes elegans stored abundant sperm inside the seminal vesicles. Available sperm was divided equally between both storage organs, and ejaculates were diluted in the spermatophore, presumably, with the gel stored in the trunk. There was no effect of body condition over any of the variables analyzed. Male sperm storage and ejaculate production are discussed considering the sperm depletion hypothesis and the sperm competition theory.

Epigenetic paternal effects as costly, condition-dependent traits.

It is now recognized that post-copulatory traits, such as sperm and ejaculate production can impose metabolic costs, and such traits are therefore expected to exhibit condition-dependent expression, whereby, low condition individuals experience a greater marginal cost of investment compared to high condition individuals. Ejaculates are especially costly in species where males invest in offspring quality through nutrient-rich spermatophores or other seminal nuptial gifts. However, recent evidence shows that, in species where males do not provision females or offspring, males can still influence offspring development through paternal effects mediated by epigenetic factors, such as non-coding RNAs, DNA methylation and chromatin structure. Because such epigenetic paternal effects do not involve the transfer of substantial quantities of resources, such as nutrients, the costs of conferring such effects have not been considered. Here we argue that if selection favours paternal investment in offspring quality through epigenetic factors, then the epigenetic machinery required to bring about such effects may also be expected to evolve strongly condition-dependent expression. We outline indirect evidence suggesting that epigenetic paternal effects could impose substantial metabolic costs, consider the conditions under which selection may act on such effects, and suggest ways to test for differential costs and condition-dependence of these effects. Incorporating epigenetic paternal effects into condition-dependent life history theory will further our understanding of the heritability of fitness and the evolution of paternal investment strategies.

Mating has No Effect on Male Longevity in the MothAmorbia cuneana(Tortricidae)

In some insects, males invest heavily in each mating thus reducing the typical sexual imbalance in potential reproductive rates which, in turn, influences the mode and intensity of sexual selection. In Lepidoptera, males invest in mate searching, courtship, ejaculate production and, in some species, in genital spines shed inside the female. Despite this substantial investment, evidence regarding its effect on male survival is contradictory. The effect of successful mating (i.e. copulations resulting in transfer of an ejaculate and deciduous genital spines) on male longevity was experimentally estimated in the moth Amorbia cuneana (Tortricidae), a pest of avocado. Our results do not support the prediction that mating costs result in a reduction in male longevity: virgin (n = 16) and mated (n = 26) males lived a similar number of days. It is hypothesized that reduced mating opportunities have selected for virgin males that are always ready to transfer large ejaculates and thus against the diversion of resources from reproductive tissues to somatic maintenance in unmated males.

Size-dependent ejaculation strategies and reproductive success in the yellow dung fly, Scathophaga stercoraria

Theory predicts that sperm competition will favour the production of larger ejaculates. However, because the benefits of greater reproductive investment are balanced by the costs of spermatogenesis, expenditure should depend on male physiology, mating rate and the relationship between additional investment and fertilization gains. In the yellow dung fly, Scathophaga stercoraria, males adopt size-dependent alternative mating tactics that are associated with discrete ecological resources (foraging and oviposition substrates), although males switch between these environments throughout their lives. By copulating on foraging substrate (fruit or flowers), males can bypass intense mate competition that occurs at oviposition sites (cow dung), but as a consequence, must occupy a disfavoured mating role (i.e. face a greater risk that their ejaculate will be displaced from storage prior to fertilization). Small males often mate on foraging substrate, whereas large males mate in this environment only during feeding bouts. Optimal ejaculate expenditure should therefore depend on male size and their current mating role. By measuring copula duration (i.e. ejaculate expenditure) of natural matings and assigning paternity to resulting offspring, we confirmed that copulations on dung sire approximately three times as many offspring as those on foraging substrate. Furthermore, large males reduced copula duration on fruit, as predicted, since this strategy enables greater investment into high-payoff matings on dung. Conversely, small males copulated for shorter durations on dung than on foraging substrate, perhaps to minimize the risk of being displaced from copula by a rival. These patterns of ejaculate expenditure translated into greater offspring production for large males on dung and for small males on fruit. We discuss the possible proximate factors driving these size- and context-dependent patterns of ejaculate allocation by yellow dung fly males. Together, our findings shed light on the allocation strategies and reproductive consequences of alternative mating tactics.

Evolution of male and female choice in polyandrous systems.

We study the evolution of male and female mating strategies and mate choice for female fecundity and male fertilization ability in a system where both sexes can mate with multiple partners, and where there is variation in individual quality (i.e. in the availability of resources individuals can allocate to matings, mate choice and production of gametes). We find that when the cost of mating differs between sexes, the sex with higher cost of mating is reluctant to accept matings and is often also choosy, while the other sex accepts all matings. With equal mating costs, the evolution of mating strategies depends on the strength of female sperm limitation, so that when sperm limitation is strong, males are often reluctant and choosy, whereas females tend to accept available matings. Male reluctance evolves because a male's benefit per mating diminishes rapidly as he mates too often, hence losing out in the process of sperm competition as he spends much of his resources on mating costs rather than ejaculate production. When sperm limitation is weaker, females become more reluctant and males are more eager to mate. The model thus suggests that reversed sex roles are plausible outcomes of polyandry and limited sperm production. Implications for empirical studies of mate choice are discussed.

Exposure time to rivals and sensory cues affect how quickly males respond to changes in sperm competition threat

Phenotypic plasticity can increase fitness in rapidly changeable environments, but may be limited if the underlying mechanisms cause a lag between environmental change and individual response or if the information individuals receive is unreliable. Hence to understand the evolution of plasticity we need to assess whether individuals respond to fine-scale variation in environmental cues. In this study we used a Drosophila melanogaster fruit fly model to investigate factors that determine how quickly males alter their behaviour in response to changes in sperm competition cues. Male D. melanogaster respond to exposure to rival males prior to mating by extending mating duration and increasing ejaculate investment. We have previously shown that to build-up the response, males need about 24 h exposure to a rival. We reasoned that this time lag was necessary to increase ejaculate production, but this physiological limitation should not apply when moving from high- to low-competition environments; hence we predicted that males should immediately decrease their investment when competition is removed. Here we tested this by measuring how long rival-exposed males maintained an extended mating duration after removal of the rival. We assessed how exposure time and sensory information affected the speed of change in behavioural state. Males maintained extended mating duration for hours after a rival was removed, but this was dependent on time of exposure to a rival. Furthermore, although sensory-impaired males were able to respond to rivals, the time required for the response to build and diminish depended on males possessing their full sensory repertoire. Our results suggest that males use exposure time and multiple sensory cues to assess whether the threat of sperm competition is transient (so unlikely to translate into realized competition) or sustained (requiring a response). Therefore, time lags between environmental changes and responses may buffer animals against making hasty decisions in fluctuating environments.

The effect of dietary restriction on reproduction: a meta-analytic perspective.

BackgroundDietary restriction (DR), a reduction in the amount of food or particular nutrients eaten, is the most consistent environmental manipulation to extend lifespan and protect against age related diseases. Current evolutionary theory explains this effect as a shift in the resolution of the trade-off between lifespan and reproduction. However, recent studies have questioned the role of reproduction in mediating the effect of DR on longevity and no study has quantitatively investigated the effect of DR on reproduction across species.ResultsHere we report a comprehensive comparative meta-analysis of the effect of DR on reproduction. In general, DR reduced reproduction across taxa, but several factors moderated this effect. The effect of DR on reproduction was greater in well-studied model species (yeast, nematode worms, fruit flies and rodents) than non-model species. This mirrors recent results for longevity and, for reproduction, seems to result from a faster rate of decline with decreasing resources in model species. Our results also suggested that not all reproductive traits are affected equally by DR. High and moderate cost reproductive traits suffered a significant reduction with DR, but low cost traits, such as ejaculate production, did not. Although the effect of DR on reproduction was stronger in females than males, this sex difference reduced to near zero when accounting for other co-factors such as the costliness of the reproductive trait. Thus, sex differences in the effect of DR on longevity may be due to a failure to expose males to as complete a range of the costs of reproduction as females.ConclusionsWe suggest that to better understand the generality of the effect of DR, future studies should attempt to address the cause of the apparent model species bias and ensure that individuals are exposed to as many of the costs of reproduction as possible. Furthermore, our meta-analytic approach reveals a general shortage of DR studies that record reproduction, particularly in males, as well as a lack of direct side-by-side comparisons of the effect of DR on males and females.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0768-z) contains supplementary material, which is available to authorized users.