Increases in egg production in multiply mated female bushcrickets Leptophyes punctatissima are not due to substances in the nuptial gift

Abstract. 1. A positive effect of the degree of polyandry on egg production is widespread in insects, particularly in species in which the male provides a nuptial gift.
2. This study aimed to determine whether or not this effect is due to females using nutrients from the nuptial gift (spermatophore and spermatophylax) to manufacture more eggs in the bushcricket Leptophyes punctatissima .
3. Females were permitted either a single or a double mating (with two different males) and, in both mating categories, were either prevented from consuming any part of the spermatophore or were permitted to consume the entire spermatophore.
4. Doubly mated females were found to lay over twice as many eggs over a 4-week period compared with singly mated females. This difference did not appear to be caused by the consumption of extra nuptial gift material: mating was found to have a significant positive effect on the number of eggs laid, while nuptial gift feeding had no effect.     

Variation in nuptial gift quality in bush crickets (Orthoptera: Tettigoniidae)

Males of many insect species provide the female, during courtshipand copulation, with a nuptial gift consisting of a prey itemor synthesized material (e.g., spermatophores). The studiesperformed so far have mainly focused on effects of nuptial giftsize on male and female reproductive success. However, the qualityof the nuptial gift can differ substantially between taxa andmay potentially have a large impact on male and female reproductiveperformance. In this study the effects of. variation in dieton nuptial gift quality is investigated in several bush cricketspecies with different diets. The effect of diet on nuptialgift quality (e.g., protein in the spermatophylax) and femalereproductive output and, in turn, die effect of variation inspermatophylax quality on female reproductive output are investigated.Female reproductive output and male spermatophore size weremainly found to be influenced by differences in diet betweenspecies. Spermatophylax quality (i.e., protein concentration)was also correlated with differences in diet. There was a largevariation in protein content of the spermatophylax widiin aswell as between species. Moreover, larger spermatophylaxes hada lower protein concentration, indicating a possible trade-offbetween spermatophylax size and quality. Consequendy, productionof larger spermatophylaxes, required for protection of the male'ssperm carrying ampulla during insemination, can lead to a reducedprotein concentration, because the total amount of protein maybe limited. This pattern is also consistent with die idea diatthe spermatophylax functions primarily to ensure sperm transfer.Finally, there was no correlation between the amount of proteinin the spermatophylax and female reproductive output eitheracross diets or within each diet category, further supportingthe finding that female reproductive output is mainly affectedby differences in diet.     

Monandry and polyandry as alternative lifestyles in a butterfly

Butterflies show considerable variability in female mating frequency, ranging from monandrous species to females mating several timesin their lifetime. Degree of polyandry also varies within species,with some females only mating once and others mating multiply.Previous studies have shown that one reason for female multiplemating is to obtain nutritious male donations that both increasethe longevity of females and result in higher lifetime fecundity.Despite the presence of male nutrient donations, some femalesof the green-veined white butterfly (Pieridae: Pieris napi)never mate more than once. In this study, we examined thisapparent paradox. We assessed to what degree polyandry is undergenetic control by a full-sib analysis, and we also estimatedthe broad sense heritability of female lifetime fecundity in singly mated females. Both polyandry and lifetime fecundityhave a genetic component. However, degree of polyandry appearsto be traded off against reduced longevity when denied theopportunity to mate more than once. It is possible that femaleP. napi display different reproductive strategies, with somefemales relying on male donations to realize their potentialfecundity and others relying on their own resources for egg production. In nature, polyandrous females may be preventedfrom mating multiply due to unfavorable weather. We discussthe possibility that the trade-off between degree of polyandryand life span when singly mated may affect the maintenanceof genetic variability in female mating frequency in this species.Possible reasons for these different reproductive strategiesare discussed.     

The conditional economics of sexual conflict

Sexual conflict is a fundamentally important aspect of male–female interactions. In this opinion piece, we emphasize two approaches that warrant significantly greater attention. First, we review the importance of understanding the ‘economics’ (costs and benefits) of sexual interactions and note surprisingly large, unrecognized gaps in our knowledge. Second, we highlight the novel obstacles and opportunities afforded by the dependence of sexually antagonistic (SA) selection on both the local environment and condition of the interacting individuals. We conclude that more research in these two areas is essential to fully understand the evolution of SA interactions and will provide significant new insights into the extent to which coevolution of the sexes is shaped by conflict. We argue that these approaches, although not new to the field, are undervalued and under-represented.     

Mating rate and fitness in female bean weevils

Females of most animal taxa mate with several males during theirlifespan. Yet our understanding of the ultimate causes of polyandryis incomplete. For example, it is not clear if and in what sensefemale mating rates are optimal. Most female insects are thoughtto maximize their fitness by mating at an intermediate rate,but it has been suggested that two alternative fitness peaksmay be observed if multiple costs and benefits interact in determiningthe relationship between mating rate and fitness. We studiedthe relationship between female fitness and mating rate in thebean weevil, Callosobruchus maculatus (Coleoptera: Bruchidae),a species in which several distinct direct effects of matingto females have been reported. Our results show that femalefitness, measured as lifetime offspring production, is lowestat an intermediate mating rate. We suggest that this patternis the result of multiple direct benefits to mating (e.g., spermreplenishment and hydration/nutrition effects) in combinationwith significant direct costs to mating (e.g., injury from malegenitalia). Females mating at low rates may efficiently minimizethe costs of mating, whereas females mating at high rates insteadmay maximize the benefits of mating. If common, the existenceof bimodal relationships between female mating rate and fitnessmay help explain the large intra- and interspecific variationin the degree of polyandry often seen in insects.     

Female preference for large males in the bushcricketRequena sp. 5 (Orthoptera: Tettigoniidae)

Receptive females of the bushcricketRequena sp. 5 (Orthoptera: Tettigoniidae) are attracted to male calls. In this experiment we investigate whether females discriminate between males on the basis of their calls. When virgin females were presented with two males of different size, they preferred the larger male. Larger males produce calls with a lower carrier frequency compared to smaller males, suggesting that females may use male carrier frequency as a predictor of male size. Furthermore, larger males produce heavier spermatophores. This suggests that females may prefer to mate with larger males to receive large nuptial gifts.     

Female remating in butterflies: interaction between female genotype and nonfertile sperm

Female mating rate is fundamental to evolutionary biology as it determines the pattern of sexual selection and sexual conflict. Despite its importance, the genetic basis for female remating rate is largely unknown and has only been demonstrated in one species. In paternally investing species there is often a conflict between the sexes over female mating rate, as females remate to obtain male nutrient donations and males try to prevent female remating to ensure high fertilization success. Butterflies produce two types of sperm: fertilizing, eupyrene sperm, and large numbers of nonfertile, apyrene sperm. The function of apyrene sperm in the polyandrous, paternally investing green‐veined white butterfly, Pieris napi, is to fill the female’s sperm storage organ thereby reducing her receptivity. However, there is large variation in number of apyrene sperm stored. Here, I examine the genetic basis to this variation, and if variation in number of apyrene sperm stored is related to females’ remating rate. The number of apyrene sperm stored at the time of remating has a genetic component and is correlated with female remating tendency, whereas no such relationship is found for fertilizing sperm. The duration of the nonreceptivity period in P. napi also has a genetic component and is inversely related to the degree of polyandry. Sexual conflict over female remating rate appears to be present in this species, with males using their apyrene sperm to exploit a female system designed to monitor sperm in storage. Ejaculates with a high proportion of nonfertile sperm may have evolved to induce females to store more of these sperm, thereby reducing remating. As a counter‐adaptation, females have evolved a better detection system to regain control over their remating rate. Sexually antagonistic co‐evolution of apyrene sperm number and female sperm storage may be responsible for ejaculates with predominantly nonfertile sperm in this butterfly.     

Sex Differences in “Time Out” from Reproductive Activity and Sexual Selection in Male Bushcrickets (Orthoptera: Zaprochilinae: <Emphasis Type="Italic">Kawanaphila mirla</Emphasis>)

Animals of many species prefer some partners over others. Discriminating among potential mates causes strong sexual selection that shapes characters and behaviors. In bushcrickets the sexes shows different latencies to remate due to differences in investment in production of the nuptial gift by males and the induced refractory period in females. We conducted experiments with the Australian bushcricket Kawanaphila mirla to test the variation in male mating success by female choice. Male remating intervals under unlimited access to food and mates were around two days, whereas most females did not remate within 12 days. Males had therefore a much shorter “time-out” from mating than females. The adult sex ratio from field samples was near to 1:1. Consequently, the OSR was male-biased with more males than females ready to mate. This male-biased OSR led to mating competition in males and choosiness in females. In a field enclosure with unlimited supply of receptive females the number of matings varied widely between males, with twenty percent of males neglected by the females. The number of matings within this enclosure was neither related to male size nor to song characters, recorded previously in the lab. However, the number of matings by individual males was positively correlated to the size of their spermatophore producing accessory gland. Females appear to prefer males with a large nutritive donation, thereby receiving a direct fitness benefit.     

Allocation of maternal- and ejaculate-derived proteins to reproduction in female crickets, Teleogryllus oceanicus

Female fitness has traditionally been thought to be maximized with one or a few matings. More recent research suggests that polyandry, mating with two or more males, can generate an increase in the viability of offspring females produce. However, the mechanism(s) underlying enhanced offspring viability remain largely unknown. The Australian field cricket Teleogryllus oceanicus has proved a useful model for examining the evolutionary significance of polyandry. Embryo viability appears to be associated with a male's investment in accessory gland tissue, implicating a role for seminal fluid. Here, I used amino acids labelled with different radio isotopes to identify proteins manufactured by males and females before they engaged in reproduction. Males incorporated 95% of the radiolabel into the testes, accessory glands and the ejaculate that was transferred to the female at mating. Male ejaculate compounds were incorporated predominantly into the female's somatic tissue. Relatively more female compounds were incorporated into the ovaries and into laid eggs than ejaculate compounds, and relatively fewer female compounds were sequestered in the somatic tissue than ejaculate compounds. The patterns observed suggest that while ejaculate compounds may be incorporated directly into eggs, they are likely to have a larger effect on maternal allocation to offspring.     

Ejaculate size, second male size, and moderate polyandry increase female fecundity in a seed beetle

Several hypotheses have been proposed to explain the evolutionof polyandry in species that provide nuptial gifts. When nuptialgifts are in the form of nutritional elements in the ejaculateand ejaculate size is correlated with male body size, femalescan accrue both direct (nutritional) and indirect (genetic)benefits from multiple mating. We examined remating decisionsin females of the seed beetle Stator limbatus and, using pathanalysis, examined the effects of male body size on the sizeof his ejaculate, the amount of ejaculate that was successfullytransferred to females, and the overall effect of these variableson female fecundity. Larger males produced larger ejaculatesand consequently transferred a larger ejaculate to females,but the effects on female fecundity differed between the females'first and second mates. Both larger first and second males wereable to transfer more of their ejaculate to females than weresmaller males. Both the total amount of ejaculate transferredby these males and polyandry (number of matings) were positivelycorrelated to female fecundity independently of each other.However, larger second males were more successful at stimulatingfemale fecundity independently of how much ejaculate they transferred.We also provide evidence that females are choosy during theirsecond mating opportunity. Both female choosiness and higherfemale investment after mating with larger second males suggestthat females may benefit from both direct and indirect effectsfrom multiple mating. We also conclude that male body size isunder both directional fecundity selection and directional sexualselection.     

Decoupling of reproductive rates and parental expenditure in a polyandrous butterfly

Current theory postulates that the operational sex ratio (OSR)determines the relative degree of mating competition in thetwo sexes and is in turn influenced by a sexual difference inthe potential reproductive rate (PRR) denned as 1/time out,where time out is the time an individual must spend recoveringfrom a bout of mating activity and/or caring for offspring.In bushcricket mating systems where males provide females witha nuptial gift, relative energy expenditure in offspring influencesthe PRR of males and females and underlies a diet-mediated shiftin the OSR. Here we investigated if there is a similar positiverelationship between relative parental nutrient expenditurein offspring and PRR in the polyandrous butterfly Pieris napi,where female fecundity is strongly dependent on male nuptialgifts at mating. By varying the amount of nutrients femalesreceive at mating and relating this to number of offspring produced,we show that male P. napi have, on average, a nutrient expenditurein offspring equaling that of females. In spite of this, themale reproductive rate is 8–13 times higher than thatof females. Hence the relative degree of parental expenditurein offspring is largely decoupled from the degree of matingcompetition in P. napi. Two alternative explanations are advancedto account for the difference between the butterfly and thebushcricket mating systems.