Sexual Selection: Do Flies Lie with Asymmetric Legs?

SummaryA newly described species of empidid or ‘dance fly’ shows a bizarre polymorphism in their forelegs, which presumably serve as a mating lure. This trait may have evolved by frequency-dependent deceptive male signalling

The evolution and function of the spermatophylax in bushcrickets (Orthoptera: Tettigoniidae)

In certain species of cricket and bushcricket (Orthoptera; Ensifera), the male transfers an elaborate spermatophore to the female at mating. This consists of a sperm-containing ampulla and an often substantial, sperm-free, gelatinous mass known as the spermatophylax. After mating, the female eats the spermatophylax before consuming the ampulla. The spermatophylax is particularly well developed in the bushcrickets (Tettigoniidae) and can contribute to a loss of as much as 40% of male body weigh at mating in some species. Recently, there has been considerable debate over the selective pressures responsible for the evolution and maintenance of the spermatophylax and other forms of nuptial feeding in insects. Two different, though not mutually exclusive, functions have been suggested for the spermatophylax: 1) nutrients from the spermatophylax may function to increase the weight and\or number of eggs laid by the female, i.e. may function as paternal investment; 2) the spermatophylax may function to prevent the female from eating the ampulla before complete ejaculate transfer, i.e. may be regarded as a form of mating effort. In this study, a comparative approach combined with laboratory manipulations were used in an attempt to elucidate the selective pressures responsible for the origin, evolutionary enlargement and maintenance (= function) of the spermatophylax in bushcrickets. The results suggest that the spermatophylax originated as an adaptation to maximise ejaculate transfer by countering the tendency of females to eat the ampulla prematurely. The spermatophylax appears to be analogous to a range of adaptations found in males of the sub-order Ensifera, which may be interpreted as functioning to maximise ejaculate transfer. These adaptations include prolonged copulation following spermatophore transfer, feeding the female with glandular secretions following spermatophore transfer, post-copulatory mate guarding and multiple copulations with the same female. The occurrence of prolonged copulation following spermatophore transfer appears to be associated with the total loss of the spermatophylax in the meconematine bushcricket Meconema and with the considerable reduction in spermatophylax size in the ephippigerine bushcricket Uromenus rugiscollis. This supports the hypothesis that prolonged copulation and the spermatophylax are analogous in function. The subsequent evolutionary enlargement of the spermatophylax appears to have accompanied the evolutionary enlargement of ejaculate volume and sperm number, i.e. appears to have proceeded to facilitate the transfer of larger ejaculates. A comparative study of 43 species of bushcricket revealed a positive relationship, across taxa, between evolutionary changes in spermatophylax size and changes in ampulla size (i.e. ejaculate volume) and sperm number, with male body weight controlled for. The current function of the large spermatophylax appears to be the same as that of the small spermatophylax, i.e. to ensure complete sperm \ ejaculate transfer. No significant difference in the shape of the sperm transfer curve relative to the mean duration of spermatophylax consumption was found between Leptophyes punctatissima (small spermatophylax) and L.laticauda (large spermatophylax). Furthermore, in L.laticauda, males appear to adjust the size of the spermatophylax in relation to the amount of sperm or volume of ejaculate they are able to produce: a positive relationship was found between spermatophylax mass and sperm number and between spermatophylax mass and ampulla mass (i.e. ejaculate volume). The possibility that the spermatophylax additionally functions as paternal investment cannot, however, be ruled out on this basis. In order for male-donated nutrients to function as paternal investment they must 1) have a positive effect on offspring fitness and\or number and 2) the nutrient donating male must stand to fertilise most or all of the offspring which benefit from his nutrients. A positive effect of spermatophylax consumption on egg weight and\or number has previously been documented in some species of bushcricket, though has not been found in others. In this study, no effect of spermatophylax consumption on female reproductive output was found in L.punctatissima, L.laticauda, or Steropleurus, even when, in the latter two cases, females were maintained on a restricted diet. Furthermore, in L.punctatissima and Steropleurus stali (though not in L.laticauda) it appears that the spermatophylax-donating male is unlikely to fertilise eggs in which his nutrients might be incorporated, in light of the short female re-mating interval, the pattern of last-male sperm precedence and the pattern of oviposition. The enormous spermatophylax of S.stali is unlikely, therefore, to function as paternal investment. Recent studies suggest that in a number of other bushcricket species, including some with very large spermatophylaxes, the spermatophylax is also unlikely to function as paternal investment for the above reasons. In conclusion, while the paternal investment hypothesis lacks generality, the ejaculate-protection hypothesis seems to be more widely applicable and appears to successfully account for the origin, evolutionary enlargement and current function of the spermatophylax in bushcrickets

Larger testes are associated with a higher level of polyandry, but a smaller ejaculate volume, across bushcricket species (Tettigoniidae)

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

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

Paternity analysis of wild-caught females shows the sperm package size and placement influence fertilization success in the bushcricket Pholidoptera griseoaptera

This work was funded by the University of Derby (KV), NERC (DJP), and Erasmus and Erasmus Plus (JZ).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 three spermatodoses (range 1–6), and only six 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 success.PostprintPeer reviewe

The Olive Ridley Project (ORP): a successful example of how to engage researchers, conservation practitioners and civil society

The Olive Ridley Project (ORP) was set up to protect sea turtles and their habitats. The project was formed in 2013, and it became a registered charity in the UK in 2016. From its inception, ORP took a multidisciplinary approach to achieve its goals. Part of its objectives, and the reason why the charity came to fruition, are related to the issue of olive ridley sea turtle (Lepidochelys olivacea) entanglement in abandoned, lost or discarded fishing gear (also known as ‘ghost gear’ or ‘ghost nets’), and the search for ghost gear and turtle entanglement ‘hot spots’ throughout the Indian Ocean. The initial ORP research questions were soon challenged by societal interests to develop inclusive educational programmes in local communities and tourist resorts that could raise awareness about the need for conservation of all sea turtle species. In February 2017, ORP opened the first veterinarian-run, fully equipped Marine Turtle Rescue Centre in the Maldives, bringing together the work of researchers, citizen scientists, volunteers, environmentalists, marine biologists and veterinarians. The present work of ORP sits on a strong and scientifically robust collaborative plan. Current ORP research projects range from sea turtle population analyses, spatial ecology, rehabilitation of injured and sick individuals, epibiont parasite analyses, precise turtle identification through photo-ID research, linking ghost gear to responsible fisheries, and analyses of ghost gear drift patterns. The programme enhances community education and outreach by engaging schoolchildren, organizing workshops, promoting sustainable use of ghost gear waste, and training citizen scientists and local fishing communities. The ORP programme encompasses many principles of research engagement, effectively combining scientific knowledge, education and action. This article explores all stages of the process (from research planning and design, to knowledge exchange and inter- and trans-disciplinary impact assessments), describing the active engagement originated by the ORP initiative. A reflective insight into the learning, enrichment and challenges of engaging researchers and community actors is also included, considering the current social and scientific framework

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

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

Coercive copulation in the alpine bushcricket anonconotus alpinus yersin (Tettigoniidae: Tettigoniinae: Platycleidini)

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