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

      Vahed, Karim; University of Derby (Wiley, 2007-02)
      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.
    • Coercive copulation in the alpine bushcricket anonconotus alpinus yersin (Tettigoniidae: Tettigoniinae: Platycleidini)

      Vahed, Karim; University of Derby (Wiley Blackwell, 2002-12)
      Sexual coercion in the form of forced copulation is widespread in the animal kingdom and has been documented in several insect taxa. In crickets and bushcrickets (sub-order Ensifera), however, mating typically involves luring acts as opposed to forcing acts. The mating behaviour of the tettigoniid Anonconotus alpinus Yersin, which is described in this paper, appears to be unique amongst the Tettigoniidae (and possibly amongst the Ensifera) in that it is coercive, involving forced matings. Males did not stridulate immediately prior to mating but instead leapt on passing females, using their anal cerci as pincers to maintain a hold on the female's abdomen (which was sometimes damaged in the process). Males appeared to lack a sexual refractory period and attempted to copulate again as little as 18 s following the previous mating.
    • Comparative evidence for a cost to males of manipulating females in bushcrickets

      Vahed, Karim; University of Derby (Oxford University Press, 2007-03-30)
      Recent theoretical and empirical research on sexual conflict has tended to focus on the costs to females of being manipulated by males. The costs to males associated with the production of manipulative traits have received relatively little attention. In numerous insects, including bushcrickets (Orthoptera: Tettigoniidae), males are known to transfer substances in the ejaculate that inhibit the receptivity of females to further matings in a dose-dependent manner. The aim of this study was to test the prediction that, across bushcricket taxa, larger ejaculates and nuptial gifts will be associated with, on the one hand, longer sexual refractory periods in females and, on the other hand, longer sexual refractory periods in males. Data on the duration of the sexual refractory period in both males and females, together with ejaculate mass, spermatophylax mass, and male body mass, were obtained for 23 species of bushcricket. Both comparative analysis by independent contrasts and species regression revealed a positive relationship, across taxa, between the duration of the female's sexual refractory period and both relative ejaculate mass and relative nuptial gift mass. Positive relationships were also found between the duration of the male's sexual refractory period and both relative ejaculate mass and relative nuptial gift mass, indicating that there is a trade-off between resources spent on spermatophore size and the male's potential mating rate. This appears to be the first comparative evidence that there is a cost to males associated with manipulating the re-mating behavior of their mates.
    • Comparison of forced mating behaviour in four taxa of Anonconotus, the Alpine bushcricket

      Vahed, Karim; Carron, G.; University of Derby (Wiley, 2008-08-27)
      Forced or coercive copulation is known to occur in a variety of insect taxa but until recently, this behaviour had not been recorded in crickets and bushcrickets (Orthoptera: Ensifera). The aim of the present study was to investigate forced mating behaviour in four taxa of Anonconotus Camerano 1878 (Orthoptera: Tettigoniidae), comparing the recently documented forced mating behaviour in the Alpine bushcricket Anonconotus alpinus ghilianii with those of Anonconotus alpinus alpinus, Anonconotus pusillus and Anonconotus baracunensis occidentalis under both laboratory and semi-natural field conditions. In all four taxa, males did not sing to attract females, but instead initiated copulation by stalking the female before leaping onto her and using the sharply pointed cercal spurs to maintain a hold on the female's abdomen. In A. a. ghilianii and A. a. alpinus, the positioning of the male's hind legs appeared to impede the movement of the female's hind legs during copulation. In Anonconotus baracunensis, the duration of copulation was considerably longer than in the other species, lasting a mean of 153 min in the laboratory and 40 min in field enclosures (compared with a mean of 7-9 min in the other taxa). This longer duration of copulation, which occurred following spermatophore attachment, is interpreted as functioning to prolong ejaculate transfer by preventing the female from eating the external portions of the spermatophore. In support of this, male A. baracunensis were found to produce a significantly greater ejaculate mass compared with the other Anonconotus taxa. We propose that members of the genus Anonconotus would make an excellent novel model system for the study of forced copulation from a sexual conflict perspective.
    • Cryptic female choice in crickets and relatives (Orthoptera: Ensifera)

      Vahed, Karim; University of Derby (Springer, 2015-05-26)
      In his pioneering work on cryptic female choice , Eberhard identified a wide range of mechanisms that potentially allow multiply-mated females to bias paternity in favour of certain types of male following the start of copulation. The aim of this chapter is to review critically the empirical evidence for a range of these mechanisms of cryptic female choice in crickets and relatives (Orthoptera : Ensifera ), while taking into account coevolutionary interactions between the sexes. There is compelling evidence that female crickets control the duration of spermatophore attachment and/or the uptake of sperm to the sperm storage organ to bias paternity in favour of males expressing a variety of favourable traits, or in favour of non-kin males. There is also some evidence that females can bias paternity to favour males with certain traits by choosing to remain with them for repeated mating. For other potential mechanisms of cryptic female choice, such as differential allocation of resources to the production of eggs, there is currently insufficient evidence to distinguish male-induced effects from cryptic female choice (if, indeed, such a distinction can be made). The evidence that mechanisms of cryptic female choice have resulted in coevolutionary adaptations in males is strong: males have evolved a wide range of behaviours to facilitate ejaculate transfer by deterring the female from removing the ampulla of the spermatophore prematurely, for example. How such adaptations affect the form and intensity of cryptic female choice and whether or not they result in ongoing sexually antagonistic coevolution deserve further investigation.
    • Emerging issues in the evolution of animal nuptial gifts

      Lewis, Sara M.; Vahed, Karim; Koene, Joris M.; Bussiere, Luc F.; Gwynne, Darryl; Engqvist, Leif; Perry, Jennifer; Lehmann, Gerlind; Tufts University, Medford MA USA; University of Derby (The Royal Society, 2014-07-16)
      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.
    • The evolution of large testes: Sperm competition or male mating rate?

      Vahed, Karim; Parker, Darren James; University of Derby (Wiley Blackwell, 2011-12)
      A positive relationship across species between the extent to which females mate with more than one male and relative testes mass has been demonstrated in a wide range of vertebrate taxa and certain insects. At least two hypotheses, which are not necessarily mutually exclusive, could account for this pattern: (1) the numerical sperm competition hypothesis, which assumes that larger testes enable the male to transfer more sperm to each female, giving the male an advantage in sperm competition and (2) the male mating rate hypothesis, which proposes that larger testes allow the male to produce a greater number of (potentially smaller) ejaculates to engage in frequent copulations with different females. Of these hypotheses, the former has won broad acceptance, while the latter has tended to be dismissed. Here, we argue that the lines of evidence commonly used to support the numerical sperm competition hypothesis in favour of the male mating rate hypothesis are not as clear cut or generally applicable as they are purported to be and that, consequently, the male mating rate hypothesis cannot be excluded with confidence on the basis of the current evidence. Furthermore, some evidence, such as the finding that ejaculate mass and/or sperm number is negatively correlated with testes mass across species in some insects, and that larger testes in Drosophila can evolve in response to an increase in the number of females available for mating in the laboratory, provides support for the male mating rate hypothesis. Further work is needed to disentangle the relative effects of these selective pressures on the evolution of testes size.
    • Free amino acids as phagostimulants in cricket nuptial gifts: support for the 'Candymaker' hypothesis

      Warwick, Stuart; Vahed, Karim; Raubenheimer, David; Simpson, Stephen, J.; University of Oxford; University of Derby (The Royal Society, 2009-01-20)
      Nuptial gifts that are manufactured by the male are found in numerous insect species and some spiders, but there have been very few studies of the composition of such gifts. If, as has been proposed recently, nuptial gifts represent sensory traps, males will be selected to produce gifts that are attractive to females but such gifts will not necessarily provide the female with nutritional benefits (the 'Candymaker' hypothesis). We examined the free amino acid content of the spermatophylax of the cricket Gryllodes sigillatus (Orthoptera: Gryllidae) using high performance liquid chromatography (HPLC). The spermatophylax (dry weight) consisted of approximately 7 per cent free amino acids. The free amino acid composition was highly imbalanced, with a low proportion of essential amino acids (18.7%) and a high proportion of proline and glycine. The main free amino acids found in the spermatophylax appeared to act as phagostimulants: the duration of feeding on artificial gels by females was positively related to the free amino acid content of the gels. The results therefore suggest that males use free amino acids to 'sweeten' a relatively low-value food item. A possible function of glycine in inhibiting female movement is also proposed.
    • The function of nuptial feeding in insects: a review of empirical studies

      Vahed, Karim; University of Derby (Wiley, 1998)
      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.
    • Functional equivalence of grasping cerci and nuptial food gifts in promoting ejaculate transfer in katydids.

      Vahed, Karim; Gilbert, James D. J.; Barrientos-Lozano, Ludivina; Weissman, David; University of Derby; Department of Biological and Forensic Sciences; College of Life and Natural Sciences; University of Derby; Kedleston Rd Derby DE22 1GB United Kingdom; University of Sussex; John Maynard Smith Building; Falmer Brighton BN1 9QG United Kingdom; Department of Entomology; California Academy of Sciences; San Francisco California 94118; Instituto Tecnológico de Cd. Victoria; Boulevard Emilio Portes Gil No. 1301, Cd. Victoria; Tamaulipas 87010 México (Wiley, 2014-05-21)
      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.
    • Increased copulation duration before ejaculate transfer is associated with larger spermatophores, and male genital titillators, across bushcricket taxa

      Vahed, Karim; Lehmann, Gerlind; Gilbert, James D. J.; Lehmann, A. W.; University of Derby (Wiley Blackwell, 2011-09)
      Copulation duration varies considerably across species, but few comparative studies have examined factors that might underlie such variation. We examined the relationship between copulation duration (prior to spermatophore transfer), the complexity of titillators (sclerotized male genital contact structures), spermatophore mass and male body mass across 54 species of bushcricket. Using phylogenetic comparative analyses, we found that copulation duration was much longer in species with titillators than those without, but it was not longer in species with complex compared with simple titillators. A positive relationship was found between spermatophore size and copulation duration prior to ejaculate transfer, which supports the hypothesis that this represents a period of mate assessment. The slope of this relationship was steeper in species with simple rather than complex titillators. Although the data suggest that the presence of titillators is necessary to maintain long copulation prior to ejaculate transfer, mechanisms underlying this association remain unclear.
    • Increases in egg production in multiply mated female bushcrickets Leptophyes punctatissima are not due to substances in the nuptial gift

      Vahed, Karim; University of Derby (Wiley, 2003-02)
      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.
    • The intensity of pre- and post-copulatory mate guarding in relation to spermatophore transfer in the cricket Gryllus bimaculatus

      Parker, Darren James; Vahed, Karim; University of Derby (Springer, 2009-07-22)
      While post-copulatory mate guarding has been well documented in field crickets (Orthoptera: Gryllidae), the occurrence of pre-copulatory mate guarding in this family has been largely overlooked. We examined the relationship between the intensity of two components of mate guarding (body judders and antennal whips) and the time before and after copulation. We found that when male Gryllus bimaculatus encounter a female but do not have a spermatophore ready to transfer, they engage in pre-copulatory mate guarding that is very similar to post-copulatory mate guarding. The intensity of pre-copulatory mate guarding increased up to the point at which the male was ready to transfer his spermatophore. Following copulation, the intensity of mate guarding initially remained high before declining, after which it began to increase again just before the male resumed courtship stridulation. We interpret this pattern of post-copulatory mate guarding as being consistent with both the ejaculate-protection and spermatophore-renewal hypotheses for the function of mate guarding. We found no significant relationship between mate guarding intensity and male body mass.
    • Larger ejaculate volumes are associated with a lower degree of polyandry across bushcricket taxa

      Vahed, Karim; University of Derby (The Royal Society, 2006-09-22)
      In numerous insects, including bushcrickets (Tettigoniidae), males are known to transfer substances in the ejaculate that inhibit the receptivity of females to further matings, but it has not yet been established whether these substances reduce the lifetime degree of polyandry of the female. The aim of this study was to test the hypothesis that larger ejaculate volumes should be associated with a lower degree of polyandry across tettigoniid taxa, controlling for male body mass and phylogeny. Data on ejaculate mass, sperm number, nuptial gift mass and male mass were taken primarily from the literature. The degree of polyandry for 14 species of European bushcrickets was estimated by counting the number of spermatodoses within the spermathecae of field-caught females towards the end of their adult lifespans. Data for four further species were obtained from the literature. Data were analysed by using both species regression and independent contrasts to control for phylogeny. Multiple regression analysis revealed that, as predicted, there was a significant negative association between the degree of polyandry and ejaculate mass, relative to male body mass, across bushcricket taxa. Nuptial gift size and sperm number, however, did not contribute further to interspecific variation in the degree of polyandry. A positive relationship was found, across bushcricket taxa, between relative nuptial gift size and relative ejaculate mass, indicating that larger nuptial gifts allow the male to overcome female resistance to accepting large ejaculates. This appears to be the first comparative evidence that males can manipulate the lifetime degree of polyandry of their mates through the transfer of large ejaculates.
    • Larger testes are associated with a higher level of polyandry, but a smaller ejaculate volume, across bushcricket species (Tettigoniidae)

      Vahed, Karim; Parker, Darren James; Gilbert, James D. J.; University of Derby (The Royal Society, 2010-11-10)
      While early models of ejaculate allocation predicted that both relative testes and ejaculate size should increase with sperm competition intensity across species, recent models predict that ejaculate size may actually decrease as testes size and sperm competition intensity increase, owing to the confounding effect of potential male mating rate. A recent study demonstrated that ejaculate volume decreased in relation to increased polyandry across bushcricket species, but testes mass was not measured. Here, we recorded testis mass for 21 bushcricket species, while ejaculate ( ampulla) mass, nuptial gift mass, sperm number and polyandry data were largely obtained from the literature. Using phylogenetic-comparative analyses, we found that testis mass increased with the degree of polyandry, but decreased with increasing ejaculate mass. We found no significant relationship between testis mass and either sperm number or nuptial gift mass. While these results are consistent with recent models of ejaculate allocation, they could alternatively be driven by substances in the ejaculate that affect the degree of polyandry and/or by a trade-off between resources spent on testes mass versus non-sperm components of the ejaculate.
    • Male genital titillators and the intensity of post-copulatory sexual selection across bushcrickets

      Lehmann, Gerlind; Gilbert, James D. J.; Vahed, Karim; Lehmann, Arne W.; University of Derby; University of Hull; Humbolt University Berlin (Oxford University Press, 2017-07-10)
      Animal genitalia are diverse and a growing body of evidence suggests that they evolve rapidly under post-copulatory sexual selection. This process is predicted to be more intense in polyandrous species, although there have been very few comparative studies of the relationship between the complexity of genital structures in males and measures of the degree of polyandry. In some bushcricket families, males possess sclerotised copulatory structures known as titillators, which are inserted into the female’s genital chamber and moved rhythmically. Like other genital structures, bushcricket titillators are widely used as important taxonomic characters and show considerable variation across species in structure, shape and the extent to which they are spined. Here, we examine relationships between the presence/absence of titillators, titillator complexity and both mating frequency and the degree of polyandry in bushcrickets, using phylogenetic comparative analyses. Using published sources combined with original observations, data were obtained for the mean level of polyandry, the duration of the male and female sexual refractory periods and the level of complexity of titillators. To analyse data, we fitted phylogenetic generalised least squares models. No significant relationships were found between titillator presence or complexity and either the level of polyandry, duration of the male’s sexual refractory period or the ratio of the female and male sexual refractory periods. The duration of the female’s refractory period, however, was positively associated with titillator presence and negatively associated with titillator complexity. The data therefore partially support the hypothesis that post-copulatory sexual selection drives genital evolution in this taxon.
    • Male gryllus bimaculatus guard females to delay them from mating with rival males and to obtain repeated copulations

      Wynn, Helen; Vahed, Karim; University of Derby (Springer, 2004-01)
      Three hypotheses for the function of postcopulatory mate guarding were tested in the field cricket Gryllus bimaculatus De Geer. The duration of spermatophore attachment was greater in the absence than in the presence of a guarding male. The ejaculate protection hypothesis was, therefore, rejected. The duration of mate guarding was found to be equal to the interval between copulations, supporting the spermatophore renewal hypothesis. In support of the rival exclusion hypothesis, the presence of a guarding male did increase the duration of spermatophore attachment when a rival male was also present. The presence of a guarding male also delayed the female from mating with the rival male. Female mating status had a significant effect on the duration of spermatophore attachment. Females mating for the first time retained the spermatophore for a significantly longer period of time than females that had mated previously.
    • Paternity analysis of wild-caught females shows that sperm package size and placement influence fertilization success in the bushcricket Pholidoptera griseoaptera

      Parker, Darren James; Zaborowska, Julia; Ritchie, Michael Gordon; Vahed, Karim; University of Lausanne; University of St Andrews; University of Derby; Centre for Biological Diversity; University of St Andrews; St Andrews KY16 9TH UK; Centre for Biological Diversity; University of St Andrews; St Andrews KY16 9TH UK; Centre for Biological Diversity; University of St Andrews; St Andrews KY16 9TH UK; et al. (Wiley, 2017-04-07)
      In species where females store sperm, males may try to influence paternity by the strategic placement of sperm within the female’s sperm storage organ. Sperm may be mixed or layered in storage organs and this can influence sperm use beyond a ‘fair raffle’. In some insects, sperm from different matings is packaged into discrete packets (spermatodoses) which retain their integrity in the female’s sperm storage organ (spermatheca), but little is known about how these may influence patterns of sperm use under natural mating conditions in wild populations. We examined the effect of the size and position of spermatodoses within the spermatheca and number of competing ejaculates on sperm use in female Dark bushcrickets (Pholidoptera griseoaptera) that had mated under unmanipulated field conditions. Females were collected near the end of the mating season and seven hypervariable microsatellite loci were used to assign paternity of eggs laid in the laboratory. Females contained a median of 3 spermatodoses (range 1-6) and only 6 of the 36 females contained more than one spermatodose of the same genotype. Both the size and relative placement of the spermatodoses within the spermatheca had a significant effect on paternity, with a bias against smaller spermatodoses and those further from the single entrance/exit of the spermatheca. A higher number of competing males reduced the chances of siring offspring for each male. Hence both spermatodose size and relative placement in the spermatheca influence paternity.
    • Structure of spermatodoses in shield-back bushcrickets (Tettigoniidae, Tettigoniinae)

      Vahed, Karim; University of Derby (Wiley, 2003-07)
      Many aspects of the reproductive anatomy and physiology of tettigoniids have been studied extensively. These include the large, externally visible spermatophores and the bundles of sperm, known as spermatodesms. However, spermatodoses, spermatophore-like structures found within the spermatheca, seem to have been almost completely overlooked: their structure has not been described since 1913 and they have subsequently received only passing mention in the literature. Each time the female mates, a separate spermatodose is formed. Here I use photographs, from light-microscopy, of whole and sectioned spermatodoses to describe the external and internal structure of spermatodoses of nine different genera within the subfamily Tettigoniinae. The structure of the spermatodoses is very similar for the different genera. Each spermatodose is pear- or onion-shaped and consists of a thin outer layer, enclosing a thick, gelatinous inner layer. A large sperm mass occupies the bulbous end of the spermatodose, while a thin sperm-tube leads from the sperm mass, along the center of the elongated neck of the spermatodose, and appears to exit at the pointed-tip of the spermatodose. Feather-like bundles of sperm (spermatodesms) were clearly visible within the sperm mass and also appeared to be present within the sperm-tube. The wall of the sperm tube appeared to be composed of material similar to that of the outer layer of the spermatodose. Within the spermatheca, spermatodoses appeared to be stratified in that only one of them ever occupied the position nearest to the spermathecal duct. The possible function of spermatodoses is discussed: it is proposed that they have evolved as a result of sexual conflict and function to protect the sperm from being destroyed by the female while they are in storage.