Determinants of reproductive success across sequential episodes of sexual selection in a firefly

Because females often mate with multiple males, it is critical to expand our view of sexual selection to encompass pre-, peri- and post-copulatory episodes to understand how selection drives trait evolution. In Photinus fireflies, females preferentially respond to males based on their bioluminescent courtship signals, but previous work has shown that male paternity success is negatively correlated with flash attractiveness. Here, we experimentally manipulated both the attractiveness of the courtship signal visible to female Photinus greeni fireflies before mating and male nuptial gift size to determine how these traits might each influence mate acceptance and paternity share. We also measured pericopulatory behaviours to examine their influence on male reproductive success. Firefly males with larger spermatophores experienced dual benefits in terms of both higher mate acceptance and increased paternity share. We found no effect of courtship signal attractiveness or pericopulatory behaviour on male reproductive success. Taken together with previous results, this suggests a possible trade-off for males between producing an attractive courtship signal and investing in nuptial gifts. By integrating multiple episodes of sexual selection, this study extends our understanding of sexual selection in Photinus fireflies and provides insight into the evolution of male traits in other polyandrous species.     

Function of the Hemolymph Nuptial Gift in the Ground Cricket,Allonemobius socius

Nuptial feeding, although common in the insect world, varies greatly in its form and function. Here, we test the function of the hemolymph nuptial gift in the southern ground cricket, Allonemobius socius, and attempt to determine if it functions as parental investment or mating effort. We manipulated the number of gifts a female received during courtship (one vs. none). We also recorded other aspect of courtship, such as feeding duration and spermatophore attachment duration. Female fecundity was measured for 7 d post‐mating. Our results indicate that female egg laying is significantly higher when a gift is provided, but the increase in egg laying is not related to gift size. In addition, the lack of a gift does not affect the male's ability to transfer a spermatophore. Together, these data suggest that the nuptial gift acts as parental investment and not as mating effort.     

Sexual selection in the gift-giving dance fly, Rhamphomyia sulcata, favors small males carrying small gifts

In some species of insects males transfer a gift to females during courtship or copulation. In the dance flies these nuptial gifts vary from nutritious prey items to inedible tokens such as a leaf, stone, or silk balloon. Nuptial gifts in dance flies are presumed to increase male mating success. We examined the strength and form of sexual selection on male Rhamphomyia sulcata, an empidid in which males provide females with a nutritious prey item as a nuptial gift. We found that whereas large males carried large gifts, neither large males nor gifts were targets of sexual selection. Indeed, correlational selection analysis and nonparametric examination of the fitness surfaces revealed that small males carrying small gifts were the most successful. Males may be more maneuverable or flight efficient with small gifts, or small males with large gifts may be unable to carry both a large gift and a female in the paired descent flight. These results suggest carrying constraints may be an important factor in determining selection on nuptial gift size. The largest target of sexual selection was old males. Old males were also paired with the largest and most fecund females, highlighting the role mate quality can further contribute to selection on males. Correlational selection analysis also revealed selection for an increase in covariance between male wing length and body size, and for an increase in slope between these traits. Males who deviate away from the optimal phenotypic relationship for two tightly related morphological traits, such as tibia and wing length, may have overall reduced performance. These findings highlight the role correlational sexual selection can play in optimizing nonsexual male morphology and scaling relationships. This study questions the role of the nuptial gift in dance flies as a resource for females.     

Nuptial food gifts influence female egg production in the scorpionfly Panorpa cognata

Abstract.  1. Before copulation, male Panorpa cognata scorpionflies offer females a salivary secretion, which is consumed by the female during copulation. It has previously been demonstrated that this nuptial food gift functions as mating effort by increasing male attractiveness and by increasing ejaculate transfer during copulation.
2. In this study, the effect of saliva consumption on female reproductive output was investigated, and thus the possibility that nuptial food gifts also serve as paternal investment. The experimental design enabled the effect of nuptial gift consumption to be disentangled from other possible effects of multiple mating or increased copula duration.
3. The results showed that saliva consumption increases female egg production by on average 8% (4.5 eggs) per consumed salivary mass, whereas mean egg weight was not influenced.4. These results have important implications for the evolution and maintenance of both male nuptial gifts and female polyandry in this and other species.     

Is diversification in male reproductive traits driven by evolutionary trade-offs between weapons and nuptial gifts?

Many male animals have evolved exaggerated traits that they use in combat with rival males to gain access to females and secure their reproductive success. But some male animals invest in nuptial gifts that gains them access to females. Both these reproductive strategies are costly in that resources are needed to produce the weapon or nuptial gift. In closely related species where both weapons and nuptial gifts are present, little is known about the potential evolutionary trade-off faced by males that have these traits. In this study, we use dobsonflies (order Megaloptera, family Corydalidae, subfamily Corydalinae) to examine the presence and absence of enlarged male weapons versus nuptial gifts within and among species. Many dobsonfly species are sexually dimorphic, and males possess extremely enlarged mandibles that they use in battles, whereas in other species, males produce large nuptial gifts that increase female fecundity. In our study, we show that male accessory gland size strongly correlates with nuptial gift size and that when male weapons are large, nuptial gifts are small and vice versa. We mapped weapons and nuptial gifts onto a phylogeny we constructed of 57 species of dobsonflies. Our among-species comparison shows that large nuptial gift production evolved in many species of dobsonfly but is absent from those with exaggerated weapons. This pattern supports the potential explanation that the trade-off in resource allocation between weapons and nuptial gifts is important in driving the diversity of male mating strategies seen in the dobsonflies, whereas reduced male–male competition in the species producing large spermatophores could be an alternative explanation on their loss of male weapons. Our results shed new light on the evolutionary interplay of multiple sexually selected traits in animals.     

The influence of nuptial feeding and sperm transfer on the immunological cost of reproduction in the ground cricket Allonemobius socius

Mating is often accompanied by decreased female immune function across numerous animals systems, suggesting that immune suppression is a widespread reproductive cost. However, the trade‐off between immunity and reproduction can be minimized when females have access to abundant nutrient resources. This observation suggests that the nuptial gifts provided by males in many insect systems may help to offset the common immunological cost to reproduction. In the present study, this hypothesis is tested in the ground cricket Allonemobius socius (Scudder), whose females receive a sizeable haemolymph‐based gift. Accordingly, male gift donation is controlled by covering the tibial spur (the source of the gift) of randomly chosen males with clear nail polish. The influence of sperm transfer on female immunity is disentangled from that of the nuptial gift by also examining females who fail to receive sperm during mating (spermatophore transfer has a 40% failure rate in virgin males). It is predicted that females who receive a nuptial gift will exhibit superior immune function compared with those who receive no gift. The results show that sperm transfer reduces female immune function, which is an expected immunological cost of reproduction. By contrast to the prediction, nuptial gifts do not minimize the immunological cost of reproduction in this system. Unexpectedly, the receipt of a gift appears to decrease female immune function independent of sperm transfer. The findings suggest that the nuptial gift, similar to sperm, signals the female to begin her reproductive investment, causing limited resources to be reallocated from immune function.     

SPERMATOPHORE SIZE IN BUSHCRICKETS: COMPARATIVE EVIDENCE FOR NUPTIAL GIFTS AS A SPERM PROTECTION DEVICE

During courtship and copulation, males of many insect species provide the female with a nuptial gift of a prey item or synthesized material. These gifts may be explained as a form of paternal investment by increasing female reproductive output, or in terms of mating effort by increasing male fertilization success. These explanations, while not mutually exclusive, are controversial. While experimental studies examine the maintenance of nuptial gifts in single species, comparative studies are required to indicate more general evolutionary trends. Male bushcrickets provide females with a nuptial gift, a spermatophylax, which is transferred to females at mating along with the sperm-containing ampulla. Analysis of comparative data of 28 species of bushcrickets (Orthoptera: Tettigoniidae), reveals that male spermatophore size (spermatophylax and ampulla weight) is positively correlated with female refractory period, which, in turn, correlates with male fertilization success. Moreover, gift size (the spermatophylax) covaries with ejaculate size (the ampulla), which is consistent with the hypothesis that it serves as a sperm protection device. In contrast, there is no significant correlation between any measure of female fecundity and male spermatophylax size. This indicates that the variation in spermatophore size among bushcrickets is better explained by a mating-effort function than a paternal investment function.     

All that Glisters is not Gold: Sensory Bias, Sexual Conflict and Nuptial Feeding in Insects and Spiders

It is becoming increasingly clear that the evolutionary interests of the sexes are often in conflict when it comes to mating. Sexual encounters involving nuptial gifts, however, have often been viewed as prime examples of sexual co‐operation, rather than conflict. In this review, I explore the proposition that nuptial gifts act as sensory traps: by exploiting the female's gustatory responses, the male may be able to entice females to accept superfluous matings and/or transfer greater volumes of ejaculate than are in the female's reproductive interests. Evidence suggests that the females’ sensory biases may have played an important role in shaping gift characteristics in at least four different systems, although relatively few forms of nuptial feeding have so far been examined from this perspective. I argue that gift composition is more likely to be tailored to increasing the attractiveness of the gift to the female and/or maximizing gift handling time than to suit the female's nutritional needs and that the fecundity‐enhancing benefits of nuptial gifts are often questionable and have been over‐stated in the literature. Fertilization biases associated with the female's attraction to the nuptial gift, however, could lead to in‐direct benefits for the female. On the other hand, nuptial feeding may also lead to significant costs to the female. Evidence suggests that some types of gift entice the female to mate, but it is not clear whether the resultant degree of polyandry is higher than optimal for the female. In other cases, evidence suggests that the gift enables the male to overcome the resistance of the female to accepting an extra large ejaculate and that large ejaculates are associated with longer post‐mating sexual refractory periods in the female. This could represent a cost to the female by delaying or preventing her from receiving the genetic benefits of polyandry. At present, it is not clear, however, whether such costs outweigh the potential benefits of nuptial feeding for the female.     

Mating tactic dependent sperm transfer rates in Panorpa similis (Mecoptera; Panorpidae): a case of female control?

Abstract 1. Male Panorpa scorpionflies offer salivary masses as nuptial gifts during copulation. Previous studies have shown that there is usually a strong correlation between the number or size of salivary masses provided and copulation duration. As a result of constant sperm transfer rates, copulation duration is the most important determinant of male fitness in these species. 2. Differences in copulation durations for gift‐giving and non‐gift‐giving males of the Caucasian scorpionfly Panorpa similis have been shown to be much smaller on average than those observed in other Panorpa species. In this study, we therefore focus on the number of sperm transferred in copulations of P. similis both with and without salivary masses. 3. We find that although the average copulation duration in the presence of nuptial gifts is only twice as long as the average copulation duration without nuptial gifts, gift‐giving males transfer almost 11 times more sperm during copulations than non‐gift‐giving males. This is as a result of substantially higher sperm transfer rates (sperm/minute) in copulations in which nuptial gifts are present. 4. Implications of this finding for the interpretation of the mating system of P. similis and the question of which sex controls sperm transfer rates are discussed.     

Biomechanical Diversity of Mating Structures among Harvestmen Species Is Consistent with a Spectrum of Precopulatory Strategies

Diversity in reproductive structures is frequently explained by selection acting at individual to generational timescales, but interspecific differences predicted by such models (e.g., female choice or sexual conflict) are often untestable in a phylogenetic framework. An alternative approach focuses on clade- or function-specific hypotheses that predict evolutionary patterns in terms neutral to specific modes of sexual selection. Here we test a hypothesis that diversity of reproductive structures in leiobunine harvestmen (daddy longlegs) of eastern North America reflects two sexually coevolved but non-overlapping precopulatory strategies, a primitive solicitous strategy (females enticed by penis-associated nuptial gifts), and a multiply derived antagonistic strategy (penis exerts mechanical force against armature of the female pregenital opening). Predictions of sexual coevolution and fidelity to precopulatory categories were tested using 10 continuously varying functional traits from 28 species. Multivariate analyses corroborated sexual coevolution but failed to partition species by precopulatory strategy, with multiple methods placing species along a spectrum of mechanical antagonistic potential. These findings suggest that precopulatory features within species reflect different co-occurring levels of solicitation and antagonism, and that gradualistic evolutionary pathways exist between extreme strategies. The ability to quantify antagonistic potential of precopulatory structures invites comparison with ecological variables that may promote evolutionary shifts in precopulatory strategies.     

Emerging issues in the evolution of animal nuptial gifts

Uniquely positioned at the intersection of sexual selection, nutritional ecology and life-history theory, nuptial gifts are widespread and diverse. Despite extensive empirical study, we still have only a rudimentary understanding of gift evolution because we lack a unified conceptual framework for considering these traits. In this opinion piece, we tackle several issues that we believe have substantively hindered progress in this area. Here, we: (i) present a comprehensive definition and classification scheme for nuptial gifts (including those transferred by simultaneous hermaphrodites), (ii) outline evolutionary predictions for different gift types, and (iii) highlight some research directions to help facilitate progress in this field.     

Why Do Males of the Spider Pisaura mirabilis Wrap Their Nuptial Gifts in Silk: Female Preference or Male Control?

Males of the spider Pisaura mirabilis present a nuptial prey gift to the female during courtship as a mating effort. The gift is usually round and wrapped in white silk. It was suggested that the wrapped gift functions as a sensory trap by mimicking the female's eggsac implying that males exploit the female maternal care instinct and not her foraging motivation in a sexual context. The shape of the gift (round) and appearance (white) should then increase female acceptance of males. We tested these predictions experimentally and found that neither gift shape (round or oblong) nor silk wrapping (wrapped or unwrapped) facilitated female acceptance, in contrast unwrapped gifts were accepted faster than wrapped ones. Instead, we found that silk wrapping benefited the males because it significantly decreased the risk of females stealing the gift without copulation and consequently directly increased male mating success. Large oblong gifts were difficult for males to handle during copulation, resulting in shorter copulations for oblong vs. round gifts. Thus, round gifts were not preferred by the females but were beneficial to the males. Our results indicate two adaptive benefits to males of wrapping the nuptial gift: to reduce the risk of losing the gift to females without copulation, and make it possible to reshape an oblong prey into a round gift that facilitates the male's access to the female's genitalia. Our results suggest that the male gift wrapping trait may be selected though sexual conflict over remating rate.     

Biting off more than you can chew: sexual selection on the free amino acid composition of the spermatophylax in decorated crickets

Nuptial food gifts function to enhance male fertilization success, but their consumption is not always beneficial to females. In decorated crickets, the spermatophore transferred at mating includes a gelatinous mass, the spermatophylax, which is consumed by females after mating. However, females often discard spermatophylaxes shortly after mating, whereupon they terminate sperm transfer. We hypothesized that females discard gifts based on their assessment of the gift itself, and specifically the composition of free amino acids. We tested this hypothesis by comparing spermatophylaxes discarded by females after mating with those that were destined to be fully consumed, and employed multivariate selection analysis to quantify the strength and form of multivariate sexual selection operating on the free amino acid composition of gifts. The analysis yielded a saddle-shaped fitness surface with two local peaks. Different amino acid profiles appear to elicit continued feeding on the spermatophylax either because they offer the same level of gustatory appeal, or because they differentially affect both the gustatory appeal and texture of the spermatophylax. We conclude that the gustatory response of females to males' nuptial food gifts represents an important avenue of post-copulatory mate choice, imposing significant sexual selection on the free amino acid composition of the spermatophylax.     

Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection

The nuptial prey gift in the spider Pisaura mirabilis has been suggested to function as a male protection against sexual cannibalismduring courtship and mating. This hypothesis together withtwo alternatives—male mating effort and paternal investment hypotheses—were tested in a laboratory experiment withsexually inexperienced males and females. One group of malesoffered no gift to the female while three groups of males offeredsmall, medium, or large sized gifts, respectively. No malewas cannibalized among 82 trials. Aggression was observed onlyin encounters where a gift was presented. Males without a gift courted females, and 40% of these males managed to copulate,compared to 90% of males offering a gift. The copulation durationwas positively correlated with gift size. In general, the femaleterminated the copulation and ran away with the gift. The proportionof eggs fertilized increased with copulation time. Presenceor size of the nuptial gift did not affect female fecundityor spiderling size significantly. The results refute the hypothesesof sexual cannibalism and paternal investment. The nuptialgift represents a male mating effort; it entices the femaleto copulate, facilitates coupling during copulation, and byprolonging copulation it may increase the amount of sperm transferred.I conclude that the nuptial prey gift in Pisaura mirabilisis maintained by sexual selection.     

The function of nuptial feeding in insects: a review of empirical studies

Nuptial feeding encompasses any form of nutrient transfer from the male to the female during or directly after courtship and/or copulation. In insects, nuptial gifts may take the form of food captured or collected by the male, parts, or even the whole of the male's body, or glandular products of the male such as salivary secretions, external glandular secretions, the spermatophore and substances in the ejaculate. Over the past decade, there has been considerable debate over the current function of nuptial feeding in insects. This debate has centred on the issue of whether nuptial gifts function as paternal investment (i.e. function to increase the fitness and/or number of the gift-giving male's own offspring) or as mating effort (i.e. function to attract females, facilitate coupling, and/or to maximize ejaculate transfer), although the two hypotheses are not mutually exclusive. In the present article, evidence for the potential of nuptial gifts to function as either paternal investment, mating effort, or both is reviewed for each form of nuptial feeding in each insect taxon for which sufficient data are available. Empirical evidence suggests that many diverse forms of nuptial feeding in different insect taxa function, at least in part, as mating effort. For example, nuptial prey and salivary masses in the Mecoptera, regurgitated food in Drosophila (Diptera), hind-wing feeding in Cyphoderris (Orthoptera) and the secretion of the male's cephalic gland in Neopyrochroa (Coleoptera) and Zorotypus (Zoraptera) appear to function to entice females to copulate and/or to facilitate coupling. Nuptial prey and salivary masses in the Mecoptera also appear to function to maximize ejaculate transfer (which is also a form of mating effort), as do nuptial prey in Empis (Diptera), external glandular secretions in Oecanthus and Allonemobius (Orthoptera) and the spermatophylax in gryllids and tettigoniids (Orthoptera). Large spermatophores in, for example, the Lepidoptera and Coleoptera, also appear to be maintained by selection on the male to maximize ejaculate transfer and thereby counter the effects of sperm competition. In contrast to the large amount of evidence in support of the mating effort hypothesis, there is a relative lack of good evidence to support the paternal investment hypothesis. Certain studies have demonstrated an increase in the weight and/or number of eggs laid as a result of the receipt of larger gifts, or a greater number of gifts, in tettigoniids, gryllids, acridids, mantids, bruchid beetles, drosophilids and lepidopterans. However, virtually all of these studies (with the possible exception of studies of the spermatophylax in tettigoniids) have failed to control adequately for hormonal substances in the ejaculate that are known to affect female reproductive output. Furthermore, in at least four tettigoniids (but not in the case of two species), three lepidopterans, a drosophilid and probably also bruchid beetles and bittacids, evidence suggests that the male has a low probability of fertilising the eggs that stand to benefit from his nuptial gift nutrients. Therefore, the hypothesis that paternal investment might account for the function of nuptial gifts in general is not supported.     

Terminal investment in the gustatory appeal of nuptial food gifts in crickets

Investment in current versus future reproduction represents a prominent trade‐off in life‐history theory and is likely dependent on an individual's life expectancy. The terminal investment hypothesis posits that a reduction in residual reproductive value (i.e. potential for future offspring) will result in increased investment in current reproduction. We tested the hypothesis that male decorated crickets (Gryllodes sigillatus), when cued to their impending mortality, should increase their reproductive effort by altering the composition of their nuptial food gifts (i.e. spermatophylaxes) to increase their gustatory appeal to females. Using a repeated‐measures design, we analysed the amino acid composition of spermatophylaxes derived from males both before and after injection of either a saline control or a solution of heat‐killed bacteria. The latter, although nonpathogenic, represents an immune challenge that may signal an impending survival threat. One principal component explaining amino acid variation in spermatophylaxes, characterized by a high loading to histidine, was significantly lower in immune‐challenged versus control males. The relevance of this difference for the gustatory appeal of gifts to females was assessed by mapping spermatophylax composition onto a fitness surface derived in an earlier study identifying the amino acid composition of spermatophylaxes preferred by females. We found that immune‐challenged males maintained the level of attractiveness of their gifts post‐treatment, whereas control males produced significantly less attractive gifts post‐injection. These results are consistent with the hypothesis that cues of a survival‐threatening infection stimulate terminal investment in male decorated crickets with respect to the gustatory appeal of their nuptial food gifts.     

FUNCTIONAL EQUIVALENCE OF GRASPING CERCI AND NUPTIAL FOOD GIFTS IN PROMOTING EJACULATE TRANSFER IN KATYDIDS

The function of nuptial gifts has generated longstanding debate. Nuptial gifts consumed during ejaculate transfer may allow males to transfer more ejaculate than is optimal for females. However, gifts may simultaneously represent male investment in offspring. Evolutionary loss of nuptial gifts can help elucidate pressures driving their evolution. In most katydids (Orthoptera: Tettigoniidae), males transfer a spermatophore comprising two parts: the ejaculate‐containing ampulla and the spermatophylax—a gelatinous gift that females eat during ejaculate transfer. Many species, however, have reduced or no spermatophylaces and many have prolonged copulation. Across 44 katydid species, we tested whether spermatophylaces and prolonged copulation following spermatophore transfer are alternative adaptations to protect the ejaculate. We also tested whether prolonged copulation was associated with (i) male cercal adaptations, helping prevent female disengagement, and (ii) female resistance behavior. As predicted, prolonged copulation following (but not before) spermatophore transfer was associated with reduced nuptial gifts, differences in the functional morphology of male cerci, and behavioral resistance by females during copulation. Furthermore, longer copulation following spermatophore transfer was associated with larger ejaculates, across species with reduced nuptial gifts. Our results demonstrate that nuptial gifts and the use of grasping cerci to prolong ejaculate transfer are functionally equivalent.     

Macronutrient intake regulates sexual conflict in decorated crickets

Sexual conflict results in a diversity of sex‐specific adaptations, including chemical additions to ejaculates. Male decorated crickets (Gryllodes sigillatus) produce a gelatinous nuptial gift (the spermatophylax) that varies in size and free amino acid composition, which influences a female's willingness to fully consume this gift. Complete consumption of this gift maximizes sperm transfer through increased retention of the sperm‐containing ampulla, but hinders post‐copulatory mate choice. Here, we examine the effects of protein (P) and carbohydrate (C) intake on the weight and amino acid composition of the spermatophylax that describes its gustatory appeal to the female, as well as the ability of this gift to regulate sexual conflict via ampulla attachment time. Nutrient intake had similar effects on the expression of these traits with each maximized at a high intake of nutrients with a P : C ratio of 1 : 1.3. Under dietary choice, males actively regulated their nutrient intake but this regulation did not coincide with the peak of the nutritional landscape for any trait. Our results therefore demonstrate that a balanced intake of nutrients is central to regulating sexual conflict in G. sigillatus, but males are constrained from reaching the optima needed to bias the outcome of this conflict in their favour.     

Nuptial gifts of male spiders function as sensory traps

While nuptial food gifts come in various forms in arthropods, their evolutionary origins are unclear. A previous study on insects has shown that such gifts may arise as a sensory trap that exploits a female's underlying motivation to feed. Here I present independent evidence of a sensory trap in spiders. In certain visually oriented spiders, I suggest that males initially exploit the maternal care instinct by producing a nuptial gift that closely resembles the female egg sac. Males of the spider Pisaura mirabilis cover their prey gift with a silk layer, transforming it into a white round object. In a laboratory experiment I tested whether the colour of the gift affected the rate that females accepted males displaying their gifts. I found that the brighter and the more alike the nuptial gift to a female's egg sac, the faster the female responded by grabbing the gift. My results support the hypothesis that the nuptial gift in P. mirabilis works as a sensory trap.     

Nuptial gifts and the evolution of male body size

In many insect systems, males donate nuptial gifts to insure an effective copulation or as a form of paternal investment. However, if gift magnitude is both body size-limited and positively related to fitness, then the opportunity exists for the gift to promote the evolution of large male size. In the striped ground cricket, Allonemobius socius, males transfer a body size-limited, somatic nuptial gift that is comprised primarily of hemolymph. To address the implications of this gift on male size evolution, we quantified the intensity and direction of natural (fecundity) and sexual (mating success) selection over multiple generations. We found that male size was under strong positive sexual selection throughout the breeding season. This pattern of selection was similar in successive generations spanning multiple years. Male size was also under strong natural selection, with the largest males siring the most offspring. However, multivariate selection gradients indicated that gift size, and not male size, was the best predictor of female fecundity. In other words, direct fecundity selection for larger gifts placed indirect positive selection on male body size, supporting the hypothesis that nuptial gifts can influence the evolution of male body size in this system. Although female size was also under strong selection due to a size related fecundity advantage, it did not exceed selection on male size. The implications of these results with regard to the maintenance of the female-biased size dimorphic system are discussed.