Female control of sperm ejection and retention in the cornsilk fly Euxesta eluta (Diptera: Ulidiidae).

Promiscuous mating systems provide the opportunity for females to bias fertilization toward particular males. However, distinguishing between male sperm competition and active female sperm choice is difficult for species with internal fertilization. Nevertheless, species that store and use sperm of different males in different storing structures and species where females are able to expel all or part of the ejaculates after copulation may be able to bias fertilization. We report a series of experiments aimed at providing evidence of female sperm choice in Euxesta eluta (Hendel), a species of ulidiid fly that expels and consumes ejaculates after copulation. We found no evidence of greater reproductive success for females mated singly, multiply with the same male, or mated multiply with different males. Female E. eluta possesses two spherical spermathecae and a bursa copulatrix for sperm storage, with a ventral receptacle. There was no significant difference in storing more sperm in spermathecae 24 h after copulation than immediately after copulation. Females mated with protein-fed males had greater reproductive success than similar females mated to protein-deprived males. Protein-fed females prevented to consume the ejaculate, retained more sperm when mated to protein-fed males than when mated to protein-deprived males. Our results suggest that female E. eluta can exert control of sperm retention of higher quality males through ejaculate ejection.

Functional morphology of the sperm-containing chambers of the sea slug Okenia polycerelloides in the context of sexual selection.

Sea slugs are interesting models to study post-copulatory sexual selection in simultaneous hermaphrodites due to the enormous variation of their reproductive systems. However, the knowledge of the functional morphology of their reproductive system is limited to few species, and it is rarely discussed in the context of sexual selection theory. In this study, we investigated the functional morphology of the sperm-containing chambers (i.e., ampulla, seminal receptacle, and bursa copulatrix) of the reproductive system of Okenia polycerelloides (Ortea & Bouchet, 1983), based on light, confocal, and electron microscopy. Although the morphology of the ampulla is similar to other species, indicating that it is a site for autosperm storage, we found some sperm facing the ampullar epithelium, a feature commonly regarded as characteristic of the seminal receptacle of sea slugs. The seminal receptacle of O. polycerelloides showed secretory activity and contained sperm with distribution and orientation suggestive of stratification of allosperm from distinct mating events, a feature that would affect sperm competition. The bursa copulatrix had epithelial cells with secretory and absorptive characteristics, and contained degraded sperm and yolk granules within its lumen. Comparative analyses of the contents of each organ demonstrated that sperm digestion occurs in the bursa copulatrix and affects sperm heads first, changing their morphology from slender and curved to shorter and ellipsoid before complete lysis. Although digestion and absorption of surplus sperm are currently the main hypothesized functions for the bursa copulatrix, its role in cryptic female choice should not be ruled out. The close structural connection between the seminal receptacle and bursa copulatrix, as well as their muscular walls, would enable control over the fate of the sperm received in each mating event, that is, storage or digestion.

Female sperm storage mediates post-copulatory costs and benefits of ejaculate anticipatory plasticity in the guppy.

Males of many species evolved the capability of adjusting their ejaculate phenotype in response to social cues to match the expected mating conditions. When females store sperm for a prolonged time, the expected fitness return of plastic adjustments of ejaculate phenotype may depend on the interval between mating and fertilization. Although prolonged female sperm storage (FSS) increases the opportunity for sperm competition, as a consequence of the longer temporal overlap of ejaculates from several males, it may also create variable selective forces on ejaculate phenotype, for example by exposing trade-offs between sperm velocity and sperm survival. We evaluated the relationship between the plasticity of ejaculate quality and FSS in the guppy, Poecilia reticulata, a polyandrous live-bearing fish in which females store sperm for several months and where stored sperm contribute significantly to a male's lifelong reproductive success. In this species, males respond to the perception of future mating opportunities by increasing the quantity (number) and quality (swimming velocity) of ready-to-use sperm (an anticipatory response called 'sperm priming'). Here we investigated (a) the effect of sperm priming on in vitro sperm viability at stripping and its temporal decline (as an estimate of sperm survival), and (b) the in vivo competitive fertilization success in relation to female sperm storage using artificial insemination. As expected, sperm-primed males produced more numerous and faster sperm, but with a reduced in vitro sperm viability at stripping and after 4 hr, compared with their counterparts. Artificial insemination revealed that the small (nonsignificant) advantage of primed sperm when fertilization immediately follows insemination is reversed when eggs are fertilized by female-stored sperm, weeks after insemination. By suggesting a plastic trade-off between sperm velocity and viability, these results demonstrate that prolonged female sperm storage generates divergent selection pressures on ejaculate phenotype.

Possible glimpses into early speciation: the effect of ovarian fluid on sperm velocity accords with post-copulatory isolation between two guppy populations.

Identifying mechanisms of reproductive isolation is key to understanding speciation. Among the putative mechanisms underlying reproductive isolation, sperm-female interactions (post-mating-prezygotic barriers) are arguably the hardest to identify, not least because these are likely to operate at the cellular or molecular level. Yet sperm-female interactions offer great potential to prevent the transfer of genetic information between different populations at the initial stages of speciation. Here, we provide a preliminary test for the presence of a putative post-mating-prezygotic barrier operating between three populations of Trinidadian guppies (Poecilia reticulata), an internally fertilizing fish that inhabits streams with different levels of connectivity across Trinidad. We experimentally evaluate the effect of female ovarian fluid on sperm velocity (a predictor of competitive fertilization success) according to whether males and females were from the same (native) or different (foreign) populations. Our results reveal the potential for ovarian fluid to act as a post-mating-prezygotic barrier between two populations from different drainages, but also that the strength of this barrier is different among populations. This result may explain the previous finding that, in some populations, sperm from native males have precedence over foreign sperm, which could eventually lead to reproductive isolation between these populations.

Behavioral Analysis and Ethogram of Mating in the Wasp Sphex latreillei (Lepeletier) (Hymenoptera: Crabronidae).

The present study reevaluates mating in Sphex latreillei (Lepeletier) based on the analysis of 69 filmed reproductive interactions from a population in central Chile. Behaviors recorded before, during, and after copulation were analyzed through Markov chains, identifying statistically significant behavioral transitions that are summarized in a mating ethogram. The results suggest that females exercise choice either during copulation by the means of an internal courtship, or via a post-copulation selection. Both types of inter-sexual selection proposed would explain, in both female and male, the dynamics of a sexual behavior crucial for a reproductive success.

Origins of female genital diversity: Predation risk and lock-and-key explain rapid divergence during an adaptive radiation.

The study of male genital diversity has long overshadowed evolutionary inquiry of female genitalia, despite its nontrivial diversity. Here, we identify four nonmutually exclusive mechanisms that could lead to genital divergence in females, and potentially generate patterns of correlated male-female genital evolution: (1) ecological variation alters the context of sexual selection ("ecology hypothesis"), (2) sexually antagonistic selection ("sexual-conflict hypothesis"), (3) female preferences for male genitalia mediated by female genital traits ("female-choice hypothesis"), and (4) selection against inter-population mating ("lock-and-key hypothesis"). We performed an empirical investigation of all four hypotheses using the model system of Bahamas mosquitofish inhabiting blue holes that vary in predation risk. We found unequivocal support for the ecology hypothesis, with females exhibiting a smaller genital opening in blue holes containing piscivorous fish. This is consistent with stronger postmating female choice/conflict when predators are present, but greater premating female choice in their absence. Our results additionally supported the lock-and-key hypothesis, uncovering a pattern of reproductive character displacement for genital shape. We found no support for the sexual conflict or female choice hypotheses. Our results demonstrate a strong role for ecology in generating female genital diversity, and suggest that lock-and-key may provide a viable cause of female genital diversification.

Genitalic stridulation during copulation in a species of crane fly, Tipula (Bellardina) sp. (Diptera: Tipulidae) / Estridulación genital durante la cópula en una especie de mosca grulla, Tipula (Bellardina) sp. (Dípteros: Tipulidae)

The male genitalia of many animal groups have elaborate and species-specific forms. One hypothesis  to explain why this is so is that male genitalia function as stimulatory devices that are under sexual selection by cryptic female choice. This report is based on a videotaped observation of a single male of an unidentified species of Tipula (Bellarina) from San José Province, Costa Rica. A male crane fly stridulated (produced vibrations) during copulation using sustained and stereotyped movements of file and scraper structures on his genitalia. Males of related species have similar file and scraper structures on their genitalia, suggesting that they probably also stridulate during copulation. Rev. Biol. Trop. 57 (Suppl. 1): 251-256. Epub 2009 November 30.

Un macho de Tipula (Bellardina) sp. estriduló (produjo vibraciones) por medio de movimientos estereotipados de estructuras de sus órganos genitales durante varios minutos de la cópula. Los machos de algunas especies relacionadas poseen estructuras similares, lo cual sugiere que también estridulan durante la cópula.

EVIDENCE FOR WIDESPREAD COURTSHIP DURING COPULATION IN 131 SPECIES OF INSECTS AND SPIDERS, AND IMPLICATIONS FOR CRYPTIC FEMALE CHOICE.

Male courtship behavior is generally thought to function prior to copulation, as an inducement to the female to allow the male to copulate with her; this study indicates however, that male courtship during and following copulation ("copulatory courtship") is common in insects and spiders (81% of 131 species in 102 genera and 49 families, mostly Coleoptera, Hemiptera, Diptera, and Araneioidea). Copulatory courtship is apparently evolutionarily labile, as expected if it is under sexual selection; intrageneric variation occurred in all 17 genera in which more than one species was observed. In 81% of 94 species with copulatory courtship, the male abandoned the female soon after copulation ended; thus, copulatory courtship appears not to function generally to induce acceptance of further copulatory attempts. The most likely explanation for copulatory courtship is that it represents attempts by males to influence cryptic female choice. This suggests that an aspect of sexual selection by female choice not considered by Darwin may be more important than previously appreciated and that the common practice in evolutionary studies of measuring male reproductive success by counting numbers of copulations may sometimes be misleading because of cryptic female choice during and after copulation.

SPECIES ISOLATION, GENITAL MECHANICS, AND THE EVOLUTION OF SPECIES-SPECIFIC GENITALIA IN THREE SPECIES OF MACRODACTYLUS BEETLES (COLEOPTERA, SCARABEIDAE, MELOLONTHINAE).

The question asked was why male genitalic structures have diverged in three syntopic species of Macrodactylus beetles. Four hypotheses were evaluated: 1. The ways in which male genitalia mesh with internal female structures indicate that selection for species isolation via mechanical exclusion ("lock and key") is unlikely to explain the genitalic differences. 2. The specific mate recognition hypothesis also clearly fails to explain genitalic differences due to the implausibility of postulated environmental effects on genitalia, and lack of postulated coevolution of male and female morphologies. 3. Selection for species isolation via differences in genitalic stimulation (sensory lock and key) is unlikely due to relatively infrequent cross-specific pair formation and intromission in the field, and "excessive" numbers of species-specific genitalic structures and male courtship behavior patterns which nevertheless occasionally fail. It also fails to explain the frequent failure of intraspecific copulations to result in sperm transfer. This hypothesis cannot, however, be rejected as confidently as the previous hypotheses. 4. Conditions under which sexual selection by cryptic female choice could take place are common. Females frequently exercise their ability to prevent sperm transfer by conspecific males even after intromission has occurred, and females generally mate repeatedly, probably with different males. Males behave as if cryptic female choice is occurring, courting assiduously while their genitalia are within the female. Sexual selection by female choice could thus contribute to the divergence in genitalic structures.