Spermatophore allocation strategy over successive matings in the bushcricketIsophya sikorai(Orthoptera Phaneropterinae)

Potential strategic allocation of nuptial gift proteins of the neotropical katydid Conocephalus ictus (Orthoptera Tettigoniidae)

In many katydids, the male feeds his mate with a large gelatinous spermatophore. While providing large spermatophores can increase female fecundity and lifespan, it may also decrease their sexual receptivity, benefiting male fitness. Allocating resources to these edible gifts may entail a lower apportionment of them to other functions, generating a trade-off between somatic and reproductive functions. Despite their effect on male and female fitness, little is known of the compounds associated with katydid spermatophores. Our study found 177 different putative proteins in the spermatophore of Conocephalus ictus, with no correlation between male body size with spermatophore mass, number, concentration and mass of proteins. However, we did observe a negative relationship between male forewing length and protein concentration, and a negative relationship between the mass of the spermatophore transferred to the females and their body size, suggesting a resource allocation trade-off in males, but also strategic transference of resources based on female quality.

Correlated sexual selection on male genitalia, copulatory performance and nuptial gifts in a bushcricket (Orthoptera: Tettigoniidae) indicated by allometric scaling

We adopt an allometric framework of scaling relationships for comparison between mating-related traits in the middle European bushcricket Roeseliana roeselii (Hagenbach, 1822). Eight characters, covering ontogenetic fitness (size traits; fixed at final moult), male condition (mass traits) and mating motivation (reproductive behaviours), were analysed in unrestricted matings and in matings involving genital manipulation. Shortening the male titillators had no effect on mating-related traits in males. However, titillators, known to be under sexual selection, scale hyperallometrically, with larger males possessing proportionally longer titillators, performing more titillator movements and exhibiting a reduced duration of copulation. Scaling was also hyperallometric for spermatophore mass, with larger males being heavier and transferring heavier nuptial gifts. Both titillator length and spermatophore mass might be condition-dependent indicators, because their variances were nearly twice as large those of body size or body mass. Mass traits were also dynamic, increasing by 11% for male body mass and 17% for spermatophore mass between the first and second matings. Sexual selection by female choice seems to favour larger trait size in the bushcricket R. roeselii, acting in concert on titillator length, intensity of titillator movements and spermatophore mass.

Differential allocation in a gift-giving spider: males adjust their reproductive investment in response to female condition

Background

When males are selective, they can either reject low-quality females or adjust their reproductive investment in response to traits that indicate female quality (e.g., body size or condition). According to the differential allocation hypothesis, males increase their reproductive investment when paired with high-quality females (positive differential allocation) or increase their reproductive investment when paired with low-quality females (negative differential allocation). This hypothesis has been proposed for monogamous species with biparental care, and most empirical studies focus on birds. Here we used the polygamous spider Paratrechalea ornata, in which males offer prey wrapped in silk as nuptial gifts, to test whether males adjust their reproductive investment in gift size, pre-copulatory and copulatory courtship, and sperm transfer in response to female body condition.

Results

Males exposed to females in good body condition added more flies to the gift, stimulated these females longer with abdominal touches during pre-copulatory courtship, and had longer pedipalp insertions than males exposed to females in poor body condition. Female condition affected neither silk investment in nuptial gift wrapping nor the quantity of sperm transferred by males. Finally, females in good body condition oviposited faster after copulation and laid more eggs than females in poor body condition.

Conclusions

We provide experimental evidence that males of a gift-giving spider exhibit positive differential allocation in three key aspects of their reproductive investment: the size of the nutritious gift, duration of pre-copulatory courtship, and duration of pedipalp insertions, which is regarded as a form of copulatory courtship in spiders. This positive differential allocation is likely associated with the benefits of copulating with females in good body condition. These females are more fecund and oviposit faster after copulation than females in poor body condition, which under natural field conditions probably reduces the risk of multiple matings and thus the level of sperm competition faced by the males. As a final remark, our findings indicate that the hypothesis of differential allocation also applies to species with a scramble competition mating system, in which males heavily invest in nuptial gift construction, but not in parental care.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01870-1.

Effects of body size divergence on male mating tactics in the ground beetle Carabus japonicus

Animal body size is involved in reproduction in various ways. Carabus japonicus exhibits considerable variation in adult body size across geographical locations depending on the larval environment. To investigate the effects of body size divergence on male mating traits, spermatophore deposition and weight, copulation duration, and post-copulatory mounting were observed using male-female pairs from C. japonicus populations with different body sizes. Then, variables with high predictive power on the mating traits were identified from individual characteristics. When the male was slightly smaller than his mate, spermatophore deposition likely succeeded, suggesting that mechanical size-assortative insemination determined male body size. Although male reproductive organ size was positively correlated with male body size, spermatophore weight was not significantly affected by male body size, whereas copulation duration decreased with increasing male body size. Enlarged males, with a high capacity for spermatophore production, could increase paternity by decreasing copulation duration and increasing mating frequency. Such shifts in mating tactics would alter selection pressures of intra- and intersexual interactions (e.g., sperm competition and sexual conflict). Genital dimensions also affected mating traits other than copulatory duration. Thus, ecological heterogeneity has the potential to lead to divergences in sexual traits, such as genital morphology, through body size divergence.

Successive matings produce opposite patterns on ejaculate volume and spermatozoa number in an ancient arthropod model with indirect sperm transfer

The production of spermatophore and ejaculate is energetically expensive for males. High mating rates may accelerate sperm depletion and progressively decrease the size of the ejaculates. Sperm competition can shape spermatozoon numbers according to different signals and cues such as number of potential rivals or female mating status. Factors influencing patterns of sperm allocation have been neglected in terrestrial arthropods that transfer sperm indirectly using a complex sclerotized spermatophore deposited on the soil. We used the Neotropical scorpion Bothriurus bonariensis (C.L. Koch, 1842) to examine ejaculate volume, spermatozoon number, and spermatophore’s trunk length along three successive matings and their relationship with body size of males. Males mated and deposited a pre-insemination spermatophore every 10 days. Ejaculate volume and trunk length decreased, whereas spermatozoon number increased over matings. Male body size positively influenced ejaculate volume and trunk length interacted with mating event. High mating rates may decrease ejaculate volume. Sperm competition may produce increased spermatozoon number. Ejaculates are more energetically expensive than spermatozoa and larger males may better face the energetic requirements. Larger spermatophore trunks contain bigger ejaculate volume in the first two mating events, but this relationship disappears at the third mating event. Our discussion focuses on the factors responsible for the observed patterns.