Strategic sperm allocation in the Small White butterfly Pieris rapae (Lepidoptera: Pieridae)

1. In species where females mate multiply, it is important for males to recuperate quickly in order to maximize their fertilization success. Butterflies produce a spermatophore at mating containing accessory secretions and sperm of two types: a large number of non-fertile 'apyrene' sperm and fewer fertile 'eupyrene' sperm. Many butterfly species eclose with most nutrients for reproduction already present. Males must therefore decide how to allocate resources to the various spermatophore components at any given mating.
2. Recovery rates of apyrene and eupyrene sperm number and spermatophore size was studied in the polyandrous Small White butterfly Pieris rapae . The mass of the first spermatophore increases with time since eclosion, as does the number of both types of sperm. Similarly, on a male's second mating, both the mass of the spermatophore and the number of sperm increases with time since the first mating.
3. However, the rate of increase in eupyrene sperm numbers is higher after the first mating. The difference in rate of increase may be the result of different probabilities of virgin and non-virgin males obtaining future matings.
4. Males have a sperm storage organ, the duplex, in which they retain sperm after their first mating. This ensures that high sperm numbers are available for their second mating, even when remating only 1 h later. Thus, males do not ejaculate all available sperm on any given mating, and seem to have different strategies on their first and second matings.
5. It can be argued that Small White butterfly males allocate sperm strategically according to the probability of obtaining subsequent matings, and the level of sperm competition.     

Seasonal Variation in Mate Choice of Photinus ignitus Fireflies

Mate choice by either sex may vary with changes in the associated costs and benefits, determined by factors such as the availability of potential mates and variation in mate quality. We examined seasonal variation in operational sex ratio, courtship behavior, spermatophore mass, egg count, and the relationship between morphological traits and mating success in Photinus ignitus fireflies to determine if mate choice in either sex varied with the availability and relative reproductive investment of fertilizable females and sexually active males. Successfully mating males had larger lanterns than unsuccessful males when the operational sex ratio was male‐biased. In addition, female responsiveness to male signals increased as the number of courting males decreased, and male spermatophore mass decreased with body size across the mating season. Successfully mating females had larger body mass than unsuccessful females. Female body mass predicted egg count and female rejection by males increased as the season progressed and female size decreased. These results suggest that both male and female P. ignitus exhibit mate choice, and that such choice is influenced by seasonal variation in the abundance and quality of potential mates.     

Gamete production and sexual size dimorphism in an insect (Orchesella cincta) with indeterminate growth

Abstract 1. The relationship of growth and body size with reproductive effort in animal species has been studied much less for males than for females. This imbalance applies to Orchesella cincta (L.) (Collembola), an insect with indeterminate growth, in which egg production is related positively to body size and negatively to growth.
2. To allow a comparison of the reproductive effort of male and female O. cincta , development and growth in immature stages of both sexes, and growth and spermatophore production for adult males were studied.
3. Embryonic development time and hatchling size did not differ between prospective males and females, but from hatching on the trajectories diverged, with males growing more slowly and maturing earlier and at a much smaller body size than females.
4. Neither the number of spermatophores deposited in the first adult instar (= inter-moult period) nor the total number of spermatophores deposited during seven instars was related to body size or growth.
5. Differences in growth rate between instars with and without spermatophore deposition indicated that the physiology of spermatophore production inhibits growth, which, however, was compensated for during the next instar.
6. The difference in the relationship of gamete production with body size and growth between males and females explains the divergence of their size at maturity.     

Sperm Numbers and Female Fertility in the Moth Plodia interpunctella (Hübner) (Lepidoptera; Pyralidae)

I investigated two possible reasons for remating in female Plodia interpunctella: i) females remate to obtain sufficient sperm to maintain fertility; and ii) male investment in non-sperm components increases female fecundity and longevity. The number of sperm and the mass of the spermatophore transferred by males decreases on successive matings. Sperm numbers and potential male investment were varied by allowing females to mate either once or twice with males either on their first or second mating. Females receiving a single small spermatophore containing few sperm (from a male on his second mating) had sufficient sperm to fertilize all their eggs. Females did not show increased fecundity or longevity as a result of obtaining more spermatophore material. I discuss why females remate when they already have sufficient sperm to fertilize all their eggs.     

Increased fecundity, as a function of multiple mating, in an arctiid moth, Utetheisa ornatrix

1. Female Utetheisa ornatrix mate multiply and may receive up to thirteen spermatophores. Spermatophores provide the female not only with sperm but also with a nuptial gift of pyrrolizidine alkaloid that she transmits to the eggs, protecting them against predation. Thus, through multiple mating the female accrues nuptial gifts that add to the defence of her offspring.
2. Multiple mating in female U. ornatrix brings about increases in fecundity, but not in longevity or egg mass. These increases occur through the third mating; the fourth and fifth matings, however, have no additional effect on fecundity.
3. These results, taken with the fact that spermatophores are sizeable and are digested within the female, suggest that they bear nutritive gifts that the female uses in egg construction. Multiple mating thus allows females to accrue the resources to build additional eggs.
4. These results are discussed in relation to the potential benefits accruing to donating such gifts and to male and female mating strategies.     

Polyandrous females provide sons with more competitive sperm: Support for the sexy‐sperm hypothesis in the rattlebox moth (Utetheisa ornatrix)

Given the costs of multiple mating, why has female polyandry evolved? Utetheisa ornatrix moths are well suited for studying multiple mating in females because females are highly polyandrous over their life span, with each male mate transferring a substantial spermatophore with both genetic and nongenetic material. The accumulation of resources might explain the prevalence of polyandry in this species, but another, not mutually exclusive, possibility is that females mate multiply to increase the probability that their sons will inherit more‐competitive sperm. This latter “sexy‐sperm” hypothesis posits that female multiple mating and male sperm competitiveness coevolve via a Fisherian runaway process. We tested the sexy‐sperm hypothesis by using competitive double matings to compare the sperm competition success of sons of polyandrous versus monandrous females. In accordance with sexy‐sperm theory, we found that in 511 offspring across 17 families, the male whose polyandrous mother mated once with each of three different males sired significantly more of all total offspring (81%) than did the male whose monandrous mother was mated thrice to a single male. Interestingly, sons of polyandrous mothers had a significantly biased sex ratio of their brood toward sons, also in support of the hypothesis.     

Male field crickets that provide reproductive benefits to females incur higher costs

Abstract.  1. Females often select mates based on signals correlated with the quality of the direct benefits that males will provide to them. A male's quality as a mate and the structure of his mating signals may covary because both traits are energetically expensive for males to produce and because both traits are affected by short-term changes in nutritional condition.
2. In the variable field cricket, Gryllus lineaticeps , previous work has shown that females receive reproductive benefits from males that produce higher chirp rates and lifespan benefits from males that produce longer chirp durations, even when they only receive the sperm and seminal fluid contained in male spermatophores. Higher chirp rates are energetically expensive for males to produce, and chirp rate is strongly affected by diet quality, whereas longer chirp durations do not appear to be expensive for males to produce, and chirp duration does not appear to be affected by male diet quality. In this study two hypotheses were tested about the energetic costs of spermatophore production: (1) that spermatophores are expensive for males to produce and (2) that males providing greater direct benefits to females incur higher costs of spermatophore production.
3. Males that were provided with a lower quality diet took longer to produce a new spermatophore. This result suggests that spermatophores are costly for males to produce.
4. Males that produced higher chirp rates took longer to produce a new spermatophore. This result suggests that male chirp rate and female reproductive benefits may covary because both traits are energetically expensive for males to produce and thus are affected by male nutritional condition. There was no association, however, between male chirp duration and spermatophore production time.     

Spermatophore and Sperm Allocation in Males of the Monandrous Butterfly Pararge aegeria: the Female’s Perspective

In insects, spermatophore production represents a non‐trivial cost to a male. Non‐virgin males have been shown to produce small spermatophores at subsequent matings. Particularly in monandrous species, it may be an issue to receive a sufficiently large spermatophore at the first and typically only mating. Females of the monandrous Speckled wood butterfly Pararge aegeria (L.) produce fewer offspring after mating with a non‐virgin male. After mating, females spend all their active time selecting oviposition sites and typically ignore other males. Here, we show that females did not discriminate between a virgin male and a recently mated male in our laboratory experiments. We demonstrate that the number of eupyrene sperm bundles relative to spermatophore mass differed with subsequent male matings. Males transferred a significantly smaller spermatophore after the first copulation, but the spermatophore mass did not decrease further with subsequent matings. However, the number of eupyrene sperm bundles decreased linearly. Therefore, there was proportionally more eupyrene sperm in the male’s second spermatophore compared with the first and the later spermatophores. Such a pattern has been shown in polyandrous species. Hence, it suggests that differences in sperm allocation strategy between polyandrous and monandrous butterflies may be quantitative rather than qualitative. There was also a tendency for females that had mated with a recently mated male to have higher propensity to remate than did females that had mated with a virgin male. We discuss the results relative to the mating system in P. aegeria, including female remating opportunities in the field and male mate‐locating behaviour.     

Mate Guarding in the Cricket Gryllodes sigillatus: Influence of Multiple Potential Partners

There are several hypotheses as to the function of postcopulatory mate guarding. Control over the mate-guarding period by either sex could potentially influence relative reproductive success. Mate-guarding behaviour in Gryllodes sigillatus was studied under several conditions: 1. undisturbed pairs; 2. pairs with a single male intruder; 3. pairs exposed acoustically, visually and olfactorily to several other males; 4. pairs exposed freely to several other males; and 5. pairs exposed freely to several other females. The results provide support for the spermatophore retention and rival defence hypotheses. The efficacy of mate guarding was not compromised by the pair being in acoustic, visual and olfactory contact with several other males. Once pairs were exposed to free contact with several other males, the spermatophore retention time by the female declined significantly, indicating that the mate guarder's efficiency declines under competition from several rivals. In pairs exposed to contact with several females after mating, the mate-guarding period and spermatophore retention time declined as the mate guarder abandoned the mated female and pursued the other females. Termination of the effective mate-guarding period by either sex seems to be influenced by the number of other potential partners present.     

Male monarch butterfly spermatophore mass and mating strategies

Male monarch butterflies, Danaus plexippus, produce a spermatophore which can represent approximately 10% of their body mass. Spermatophore mass increased with age in virgin males, and with the time since last mating in non-virgin males. Male monarchs did not delay re-mating until they were able to produce a large spermatophore. Recently mated males were as likely as virgins to copulate with both virgin and non-virgin females. Monarchs provide an example of Bateman's principle, mating whenever possible, despite the non-trivial cost involved.     

Limits to Nuptial Gift Production by Male Fireflies, Photinus ignitus

Males of diverse insect species provide females with nuptial gifts, and limits on males' ability to produce these gifts may influence courtship behavior and mating systems. In the firefly Photinus ignitus, males transfer a complex spermatophore to females during mating. We provided firefly males unlimited access to responsive females to examine whether spermatophore production limits male mating success. Male spermatophore mass decreased significantly across sequential matings, and the percentage of successful matings declined during the second half of each male's life span. Male body mass explained a significant proportion of variation in size of the first spermatophore produced by P. ignitus males, but this relationship disappeared with second spermatophores. This study indicates that males' ability to produce spermatophores declines over their lifetime and that limits on nuptial giftproduction can constrain male mating success in Photinus fireflies.     

Mating strategies based on foraging ability: an experiment with grasshoppers

Female mate choice and the benefits of this behavior are criticalaspects of Darwinian sexual selection, but they are seldom documentedbecause it is difficult to identify the male trait(s) that femalesmay be seeking. We conducted experiments with grasshoppers (Melanoplussangutnipes: Orthoptera, Acrididae) to examine this behavior.Males that feed more intensively and select a diet mix thatpermits greater food intake (food intake per body mass per time)in laboratory trials were preferentially selected by females.These better foraging males on average provide greater paternalinvestment (greater spermatophore mass) to the female, whichincreases her reproductive rate (eggs produced per body massper time). However, paternal investment may not entirely explainfemale choice of better foraging males, because these maleswere still selected even if they had their food intake restrictedor had been allowed to recently mate, which reduces spermatophoreproduction. Furthermore, males change their mating strategyin response to female choice and the foraging abilities of surroundingmales. Poorer foraging males attempt forcible copulation ratherthan displaying and allowing female choice. A male will facultativelyswitch between these strategies depending on the foraging abilitiesof the surrounding males. While females attempt to reject forciblecopulation, forcible copulation reduces the frequency with whichfemales successfully copulate with better foraging males. Therefore,males that are less "attractive" to females adopt alternativemating strategies to counter female choice which would excludethem from mating.[Behav Ecol 7: 438–444 (1996)]     

Correlated responses to selection on female egg size in male reproductive traits in a butterfly

Genetic correlations between male and female traits can act as evolutionary constraints and, if involving reproductive traits, potentially influence sexual selection. Artificial selection on egg size in the tropical butterfly Bicyclus anynana has yielded highly divergent lines. Here we report evidence for correlated evolution in male traits. Males from the large-egg selected lines produced significantly heavier spermatophores independent of body size and tended to have more fertile sperm stored in their reproductive tracts than those from the small-egg selected lines. This may be due to an underlying genetic correlation in reproductive effort between the sexes. However, non-fertile sperm number and testis size remained unaffected by selection on egg size. Phenotypic correlations within an unselected population revealed that spermatophore mass and fertile sperm number, but not testis size and non-fertile sperm number, were positively related to male body size, and that larger spermatophores contained more fertile, but not non-fertile sperm. In addition, males provided larger females with bigger spermatophores and more fertile sperm, indicating males may be exercising mate choice during copulation.     

Parental Body Mass as a Determinant of Egg Size and Egg Output in an Arctiid Moth (Utetheisa ornatrix)

Females of the moth Utetheisa ornatrix (family Arctiidae) mate preferentially with larger males. As a consequence, females have larger sons and daughters, which have been shown to be more acceptable in courtship and more fecund, respectively. We demonstrate that mating with larger males results in accelerated oviposition by the female on the day after mating and that females are intrinsically prone to lay larger eggs in the first days after mating. Both these additional size-dependent effects have potential adaptive consequences.     

Heritable variation in the timing of spermatophore removal, a mechanism of post-copulatory female choice in crickets

Female crickets can exert post-copulatory mating preferences by prematurely removing a male's spermatophore after copulation, which terminates sperm transfer. Although most models of sexual selection assume that female mating preferences are heritable, there has been little work addressing genetic variation underlying post-copulatory mate choice. We used a paternal half-sib design, in which different males were randomly assigned as mates to several females to create half-sib families, to determine the heritability of spermatophore retention time in female house crickets, Acheta domesticus. There was significant additive genetic variance in the timing of spermatophore removal by females [h(2) = 0.50 +/- 0.19 (+/- SE)], suggesting that the timing of spermatophore removal is determined, in part, by the female's own genotype independent of the quality of her mate. The relatively high heritability of spermatophore retention time may be reflective of the absence of strong selection on this trait, consistent with previous work showing no difference in the fitness of females permitted to freely remove the spermatophore of their mates and those forced to accept complete ejaculates.     

Is Bigger Better? Size and Pheromone Production in the Mountain Pine Beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)

Reproductive success in the mountain pine beetle, Dendroctonus ponderosae Hopkins, is determined by the production of aggregation and antiaggregation pheromones, as well as body size. In a laboratory experiment with beetles that emerged from naturally attacked hosts, there was no relationship between body size and the production of aggregation pheromones in either sex. In contrast, there were significant relationships between body size and the production of antiaggregation pheromones in males that were paired with females. Pheromone amounts decreased in paired females and antiaggregation pheromones correspondingly increased in paired males, suggesting that after pairing, males take over the role of pheromone production. Although males could potentially select large females by evaluating gallery size, and females could select large males on the basis of their strength in stridulation or physical courtship, we propose that mate choice occurs primarily by olfaction. Small individuals that produce large amounts of pheromone during initial attack could sabotage mate choice based on size-related criteria. This hypothesis is consistent with a lack of evidence for size assortative mating in 92 pairs of beetles. The production of antiaggregants by large male D. ponderosae after pairing with females appears to be an important factor in intraspecific resource partitioning, population regulation, and reproductive success.     

On the role of sexual selection in ecological divergence: a test of body‐size assortative mating in the eastern newt Notophthalmus viridescens

Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body‐size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two eastern newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life‐cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body‐size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body‐size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life‐cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 884–897.     

Female pheromonal chorusing in an arctiid moth, Utetheisa ornatrix

We report an unusual case of communal sexual display in thearctiid moth Utetheisa ornatrix that we designate "female pheromonalchorusing." As in most moths, female U. ornatrix release a long-distancesexual advertisement pheromone during a nightly activity period.We arranged U. ornatrix females in 2 types of signaling conditions:grouped and solitary. When the females were grouped with neighboringsignaling females (grouped), they initiated pheromone releasesooner, continued release with less interruption and over alonger total period, and performed the release with faster abdominalpumping than observed in isolated females (solitary). This differsfrom the usual form of sexual communication in moths: female(chemical) signalers, male receivers, and a general lack ofinteraction among females. At mating, male U. ornatrix transfera large spermatophore that may enhance female reproductive successand which represents either mating effort or paternal investment.This action results in an extended postmating male refractoryperiod leading to a female-biased operational sex ratio. Weargue that this biased sex ratio generates intrasexual competitionamong females, to which they respond by elevating signalingeffort such that the likelihood of at least matching their neighbors'signals is increased. In the field, U. ornatrix are clusteredaround patches of host plants, and we also explore the possibilitythat pheromonal chorusing is driven by cooperation among groupsof related—or nonrelated—females.     

Male Aggression,Female Mimicry and Female Choice in the Rove Beetle,Aleochara curtula (Coleoptera,Staphylinidae)

Causes, consequences and pheromonal regulation of male contest and female choice in the staphylinid beetle, Aleochara curtula (Goeze), have been investigated in the field and in the laboratory. At the feeding and mating site (carcass) the sex ratio is male biased. Polyandry is affected by prolonged copulations, spermatophore plugs and anti-aphrodisiac pheromones transferred from the male, and by female repulse behaviour as well. Aggression of competing males leads to expulsion of inferior males from the carcass. Young, starved and multiply mated males, which need access to the food resource, produce the female sex pheromone. They release homosexual responses, but also avoid intrasexual aggression. On the other hand, females behave aggressively towards individuals bearing the female sex pheromone or repulse their copulatory attempts. Those males of insufficient physiological condition produce a lighter spermatophore and fertilize less eggs. The adaptive significance of female mimicry, male mating tactics, and female choice is discussed.     

Male-male pheromone signalling in a lekking Drosophila

Interest in sex pheromones has mainly been focused on mate finding, while relatively little attention has been given to the role of sex pheromones in mate choice and almost none to competition over mates. Here, we study male response to male pheromones in the lekking Drosophila grimshawi, where males deposit long-lasting pheromone streaks that attract males and females to the leks and influence mate assessment. We used two stocks of flies and both stocks adjusted their pheromone depositing behaviour in response to experimental manipulation, strongly indicating male ability to distinguish between competitors from qualitative differences in pheromone streaks alone. This is the first example of an insect distinguishing between individual odour signatures. Pheromone signalling influenced competition over mates, as males adjusted their investment in pheromone deposition in response to foreign pheromone streaks. Both sexes adapt their behaviour according to information from olfactory cues in D. grimshawi, but the relative benefits from male-female, as compared to male-male signalling, remain unknown. It seems likely that the pheromone signalling system originally evolved for attracting females to leks. The transition to a signalling system for conveying information about individuals may well, however, at least in part have been driven by benefits from male-male signalling.