Polyandry in the mind bugLygocoris pabulinus(L.)—effects on sexual communication and fecundity

Mating plugs in polyandrous giants: which sex produces them, when, how and why?

Background

Males usually produce mating plugs to reduce sperm competition. However, females can conceivably also produce mating plugs in order to prevent unwanted, superfluous and energetically costly matings. In spiders–appropriate models for testing plugging biology hypotheses–mating plugs may consist of male genital parts and/or of amorphous covers consisting of glandular or sperm secretions. In the giant wood spider Nephila pilipes, a highly sexually dimorphic and polygamous species, males are known to produce ineffective embolic plugs through genital damage, but nothing is known about the origin and function of additional conspicuous amorphous plugs (AP) covering female genitals.

Methodology

We tested alternative hypotheses of the nature and function of AP in N. pilipes by staging mating trials with varying degrees of polyandry. No APs were ever formed during mating trials, which rules out the possibility of male AP formation. Instead, those females that oviposited produced the AP from a liquid secreted during egg sac formation. Polyandrous females were more likely to lay eggs and to produce the AP, as were those that mated longer and with more total insertions. Our further tests revealed that, in spite of being a side product of egg sac production, AP, when hardened, prevented any subsequent copulation.

Conclusions

We conclude that in the giant wood spider (Nephila pilipes), the amorphous mating plugs are not produced by the males, that repeated copulations (most likely polyandrous) are necessary for egg fertilization and AP formation, and that the AP represents a female adaptation to sexual conflict through prevention of unwanted, excessive copulations. Considering the largely unknown origin of amorphous plugs in spiders, we predict that a similar pattern might be detected in other clades, which would help elucidate the evolutionary interplay of various selection pressures responsible for the origin and maintenance of mating plugs.

Sperm storage by spermatodoses in the spermatheca of Trioza alacris (Flor, 1861) hemiptera, psylloidea, triozidae: a structural and ultrastructural study

Female insects generally store sperm received during mating in specific organs of their reproductive tract, i.e., the spermathecae, which keep the sperm alive for a long time until fertilization occurs. We investigated spermatheca morphology and ultrastructure in the psylloidean insect Trioza alacris (Flor,1861) in which spheroidal sperm packets that we refer to as 'spermatodoses' are found after mating. The ectoderm-derived epithelium of the sac-shaped spermatheca that has a proximal neck, consists of large secretory and flat cuticle-forming cells. Secretory cells are characterized by a wide extracellular cavity, bordered by microvilli, in which electron-dense secretion accumulates before discharge into the spermathecal lumen. The cuticle-forming cells produce the cuticular intima of the organ and a peculiar specialized apical structure, through which secretion flows into the lumen. At mating, the male transfers bundles of sperm cells embedded in seminal fluid into the spermathecal neck. Sperm cells proceed towards the spermathecal sac lumen, where they are progressively compacted and surrounded with an envelope that also encloses secretions of both male and female origin. We describe the formation of these sperm containing structures and document the contribution of the female secretion to spermatodose or female-determined spermatophore construction. We also discuss the choice of the term 'spermatodose' for T. alacris and suggest it be used to refer to sperm masses constructed in the female reproductive organs, at least when they involve the contribution of female secretion.

Monogamy and polygamy in two species of mirid bugs: a functional-based approach

Multiple mating in females is widespread among insects in spite of the risk of predation, disease acquisition and/or physical injury that may occur. One common consequence of female polyandry is competition among sperm from two or more males within the female to fertilize the ova. This competition is an evolutionary driving force that determines a series of adaptations in both males and females. In this work, we examine some behavioral, morphological and physiological characteristics of males and females of two Heteropteran species that are related to their monoandrous/polyandrous mating behavior. Females of Macrolophus pygmaeus (Het. Miridae), the monoandrous species, were coy about accepting a male partner, spent a short time in copula, and received only a small volume of ejaculate. Even so, with only one mating event, they received enough sperm to fertilize most of their ova (21 days after mating all females were still fertile). In contrast, females of Nesidiocoris tenuis (Het. Miridae), the polyandrous species, readily accepted any mating partner, spent a long time in copula and received a large volume of ejaculate. However, these latter females soon ran out of sperm and needed to mate periodically in order to maintain a sufficient sperm supply to fertilize their eggs. As predicted, based on current theory (Simmons, 2001b), an increased investment in spermatogenesis was detected in N. tenuis with relation to M. pygmaeus. The males of the polyandrous species had larger accessory reproductive glands, seminal vesicles, testes and sperm cells than those of the monoandrous species.

Structure of spermatodoses in shield-back bushcrickets (Tettigoniidae, Tettigoniinae)

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.