Simultaneous Hermaphrodites Research Articles

Kin selection in interactions between gametes: Gamete competition, gamete limitation, and sex allocation

Kin selection on one hand, and gamete interactions in post-ejaculatory sexual selection on the other are two major research themes that have risen to prominence over the past half century and have simultaneously developed into central fields of research in evolutionary biology. There is a natural connection between the two: when gametes interact with each other, very commonly many of them originate from the same parent and are thus siblings. For example, sperm competition will almost always involve competition between sibling gametes even if the interacting parents are not related to each other. If parents are related to each other, the relatedness between gametes increases further. Here we discuss the relation between kin selection on one hand, and gamete competition, gamete limitation, local gamete competition, and the evolution of sex allocation on the other. To illustrate these topics, we present a novel model on sex allocation in simultaneous hermaphrodites under sperm limitation and limited, costly dispersal. We find that sperm limitation can significantly increase allocation into male function, but limited dispersal (and thus increased relatedness) does not alter sex allocation regardless of the presence of sperm limitation.

Gametic cycle and gonadal maturity of Bulimulus bonariensis (Rafinesque, 1833) (Gastropoda: Bulimulidae), in a rural area of Buenos Aires, Argentina.

Bulimulus bonariensis, a snail distributed over a large part of Argentina, has generated negative effects on the agribusiness. We accordingly conducted a seasonal sampling during 2018-2019 in order to characterize the gametic cycle and establish the size of this gastropod at gonadal maturity. Three reproductive stages were identified: the mature in autumn; the spawn, which begins in winter but occurs mainly in the spring, followed by the post-spawn in summer, where an absence of gonadal rest was evidenced. In the fall, in maturity resorption was observed in addition to abundant primary spermatocytes, secondary spermatocytes, and growing vitellogenic oocytes. At the same time, could correlate the degree of spermioviduct development with the stage of gonadal development. Moreover, we used a logistic regression to calculate the size at gonadal maturity, which was established at the total shell length of 12 mm. In addition, we found that at the beginning of reproductive development those gastropods are protogynous hermaphrodites, but after reaching gonadal maturity became simultaneous hermaphrodites. Finally, B. bonariensis also proved to be an iteroparous species. The information provided here will be essential for delineating and establishing population control strategies.

Crustacean female sex hormone: More than a female phenotypes-related hormone in a protandric simultaneous hermaphroditism shrimp

Crustacean female sex hormone (CFSH) is believed to regulate the development of female-related phenotypes in crustaceans. However, its role in gonadal development has been understudied. This study identified a CFSH gene, Lvit-CFSH1b, in the peppermint shrimp Lysmata vittata, a protandric simultaneous hermaphroditism (PSH) species. Lvit-CFSH1b is only expressed in the eyestalk ganglion. qRT-PCR showed that the expression level of Lvit-CFSH1b significantly increased with the gonad development from stage I to III (male phase) and decreased at stage IV (euhermaphrodite phase). Gene knockdown of Lvit-CFSH1b resulted in retardation of female phenotypes and stimulated the development of male phenotypes. At the same time, ovarian development was inhibited, and spermatogenesis was promoted. In addition, injection of rCFSH1b increased ovarian expression of vitellogenin (Lvit-Vg) and hepatopancreas expression of vitellogenin receptor (Lvit-VgR), while suppressing the expressions of insulin-like androgenic gland hormones (Lvit-IAG1 and Lvit-IAG2) in androgenic glands. The addition of rCFSH1b induced the in vitro expression of Lvit-Vg in ovarian and Lvit-VgR in hepatopancreas explants. In conclusion, this study provides convincing evidence that CFSH expedites the feminization process and impedes masculinization by inhibiting IAG in hermaphroditic crustaceans.

Bidirectional sex change and plasticity of gonadal phases in the goby Lubricogobius exiguus.

Of the ca. 500 known hermaphroditic fish species, bidirectional sex change and simultaneous hermaphroditism are currently known in 69 and 57 species, respectively. Both bidirectional sex change and simultaneous hermaphroditism are predicted to evolve when mating opportunities are limited, such as in cases of low-density distribution and low mobility of individuals. However, the plasticity of sex is adaptive in obtaining mating opportunities, especially when there is mate loss. Pair-rearing experiments and histological observations of gonads of the goby Lubricogobius exiguus, which has low-density distributions and low mobility, showed bidirectional sex change. The male-role individuals in pairs had gonads in which only the testis was functional (male-phase), whereas the female-role individuals had two types of gonads: only the ovary was functional (female-phase) or both testis and ovary were functional (simultaneously hermaphroditic phase, SH-phase). In addition, single-rearing experiments showed SH-phase gonads in all individuals, and some cyclic spawning but no self-fertilization occurred. These results revealed that L. exiguus has an unusual sexual pattern among hermaphroditic fishes because they undergo bidirectional sex change and some maintain SH-phase gonads. These findings indicate that the low-density distribution and low mobility of L. exiguus in their natural habitat may have influenced the evolution of this unique sexual pattern.

Induced spawning with gamete release from body ruptures during reproduction of Xenoturbella bocki

Xenoturbella is a marine invertebrate with a simple body plan, with recent phylogenomic studies suggesting that it forms the phylum Xenacoelomorpha together with the acoelomorphs. The phylogenetic position of the phylum is still under debate, whether it is an early branching bilaterian or a sister group to the Ambulacraria. Phylogenetic traits often appear during development, and larva resembling the cnidarian planula has been reported for Xenoturbella. However, subsequent developmental studies on Xenoturbella have been scarce. This is mainly due to the difficulties in collecting and keeping adult animals, resulting in the lack of data on the reproduction of the animal, such as the breeding season and the spawning pattern. Here we report on the reproduction of X. bocki and confirm that its breeding season is winter. Spawning induction resulted in gametes being released from body ruptures and not the mouth. No evidence supported the animal as a simultaneous hermaphrodite.

Aquatic Hermaphrodite Snails Exposed to Polychlorinated Biphenyls (PCBs) Experience Increased Mortality, Reduced Reproduction, and Endocrine Disruption

Populations of freshwater gastropods are decreasing globally. To investigate one aspect of decline, we exposed the benthic dwelling hermaphroditic snail Planorbella (= Helisoma) trivolvis (Say) (Marsh Rams-horn) to polychlorinated biphenyls (PCBs). Marsh Rams-horn is a simultaneous hermaphrodite, suggesting that disruption of reproductive success is independent of snail interaction and more dependent on internal controls. We examined the impact of exposure to PCBs on mortality, reproductive success, and tissue hormone concentrations. Exposure to Aroclor®1254 in concentrations found in natural habitats caused higher mortality and reduced reproductive success. Additionally, tissue estrogens were significantly elevated while testosterone remined unchanged in PCB-exposed snails. Given the importance of hermaphroditic freshwater gastropods in ecosystems, worldwide population decline, and ubiquity of PCBs, identifying the impact of exposure informs our ability to combat population loss.

Multiple Doris "kerguelenensis" (Nudibranchia) species span the Antarctic Polar Front.

Despite strong historical biogeographical links between benthic faunal assemblages of the Magellan region of South America and the Antarctic Peninsula, very few studies have documented contemporary movement and gene flow in or out of the Southern Ocean, especially across the Antarctic Polar Front (APF). In fact, oceanographic barriers such as the APF and Antarctica's long geologic isolation have substantially separated the continents and facilitated the evolution of endemic marine taxa found within the Antarctic region. The Southern Ocean benthic sea slug complex, Doris “kerguelenensis,” are a group of direct‐developing, simultaneous hermaphrodites that lack a dispersive larval stage. To date, there are 59 highly divergent species known within this complex. Here, we provide evidence to show intraspecific genetic connectivity occurs across the APF for multiple species within the D. “kerguelenensis” nudibranch species complex. We addressed questions of genetic connectivity by examining the phylogeographic structure of the three best‐sampled D. “kerguelenensis” species and another three trans‐APF species using the protein coding mtDNA gene, cytochrome oxidase I. We also highlight alternative refugia uses among species with the same life history traits (i.e., benthic and direct developers) and for some species, extremely large distributions are established (e.g., circumpolarity). By improving our sampling of these nudibranchs, we gain better insight into the population structure and connectivity of the Antarctic region. This work also demonstrates how difficult it is to make generalizations across Antarctic marine species, even among ecologically‐similar, closely related species.

Histological characterization of sexual reproduction in the coral Pocillopora damicornis (Coelenterata: Scleractinia) from the Red Sea

The scleractinian coral is common along the Red Sea coast, and its reproductive mode and period of reproduction were assessed using histological preparations. the sexuality, and reproductive mod timing of reproductive of pocillopora damicornis from adjacent to the fringing reefs of the Ubhur Creek in the Red Sea, were assessed using a serial histological section. Sexual reproduction in pocillopora damicornis a shallow water hermatypic coral was studied from December 2011 to November 2012. pocillopora damicornis is a simultaneous hermaphrodite with ovary and testis in the project into the body cavity on the same mesentery. Sperm and eggs were usually released simultaneously from the same polyp. The onset of the reproductive period of pocillopora damicornis was found to be limited (April to May). In the number of eggs and testes observed in this period, the gonads were found in the polyps. The pocillopora damicornis egg size ranged from 49.80 µm (in March) to 125.0 µm (in May). Four stages were chosen, to reflect very immature ovaries, the early stages of oocyte development, ova near maturity, and mature ova, and also four distinct stages of sperm development were identified. The state of gonads development (eg. testis and eggs) was measured by a calibrated eyepiece micrometer of a compound light microscope. Zooxanthellae were presented in the mature oocytes in pocillopora damicornis. This study aimed to examine the reproduction mode and timing of pocillopora damicornis.

Precocious Sperm Exchange in the Simultaneously Hermaphroditic Nudibranch, Berghia stephanieae.

SynopsisSexual systems vary greatly across molluscs. This diversity includes simultaneous hermaphroditism, with both sexes functional at the same time. Most nudibranch molluscs are thought to be simultaneous hermaphrodites, but detailed studies of reproductive development and timing remain rare as most species cannot be cultured in the lab. The aeolid nudibranch, Berghia stephanieae, is one such species that can be cultured through multiple generations on the benchtop. We studied B. stephanieae reproductive timing to establish when animals first exchange sperm and how long sperm can be stored. We isolated age- and size-matched individuals at sequential timepoints to learn how early individuals can exchange sperm. Individuals isolated at 10 weeks post initial feeding (wpf; ∼13 weeks postlaying [wpl]) can produce fertilized eggs. This is 6 weeks before animals first lay egg masses, indicating that sperm exchange occurs well before individuals are capable of laying eggs. Our results indicate that male gonads become functional for animals between 6 mm (∼6 wpf, ∼9 wpl) and 9 mm (∼12 wpf, ∼15 wpl) in length. That is much smaller (and sooner) than the size (and age) of individuals at first laying (12–19 mm; ∼16 wpf, ∼19 wpl), indicating that male and female functions do not develop simultaneously. We also tracked the number of fertilized eggs in each egg mass, which remained steady for the first 10–15 egg masses, followed by a decline to near-to-no fertilization. This dataset provides insights into the precise timing of the onset of functionality of the male and female reproductive systems in B. stephanieae. These data contribute to a broader understanding of reproductive development and the potential for understanding the evolution of diverse sexual systems in molluscs.

Switches, stability and reversals in the evolutionary history of sexual systems in fish

Sexual systems are highly diverse and have profound consequences for population dynamics and resilience. Yet, little is known about how they evolved. Using phylogenetic Bayesian modelling and a sample of 4614 species, we show that gonochorism is the likely ancestral condition in teleost fish. While all hermaphroditic forms revert quickly to gonochorism, protogyny and simultaneous hermaphroditism are evolutionarily more stable than protandry. In line with theoretical expectations, simultaneous hermaphroditism does not evolve directly from gonochorism but can evolve slowly from sequential hermaphroditism, particularly protandry. We find support for the predictions from life history theory that protogynous, but not protandrous, species live longer than gonochoristic species and invest the least in male gonad mass. The distribution of teleosts’ sexual systems on the tree of life does not seem to reflect just adaptive predictions, suggesting that adaptations alone may not fully explain why some sexual forms evolve in some taxa but not others (Williams’ paradox). We propose that future studies should incorporate mating systems, spawning behaviours, and the diversity of sex determining mechanisms. Some of the latter might constrain the evolution of hermaphroditism, while the non-duality of the embryological origin of teleost gonads might explain why protogyny predominates over protandry in teleosts.

Consequences of artificial light at night on behavior, reproduction, and development of Lymnaea stagnalis

Light is an important zeitgeber that regulates many behavioral and physiological processes in animals. These processes may become disturbed due to the changes in natural patterns of light and dark via the introduction of artificial light at night (ALAN). The present study was designed to determine the effect of possible consequences of ALAN on reproduction, hatching success, developmental success, growth rate, feeding rate, mortality rate, and locomotor activity of the simultaneous hermaphrodite pond snail Lymnaea stagnalis. Snails were exposed to different light intensities at night that simulate actual ALAN measurements from the snail's night environment. The data revealed that exposure to ALAN at a low level significantly affected the cumulative number of laid eggs. At the same time, snails exposed to ALAN laid smaller eggs than those laid under normal light-dark cycles. Additionally, high light-intensity of ALAN delayed development and hatching of eggs of L. stagnalis while it showed no effect on hatching percentage. Furthermore, ALAN increased both the feeding and growth rates but did not lead to mortality. The results also show that snails exposed to dark conditions at night travel longer distances and do so faster than those exposed to ALAN. In light of these findings, it is clear that ALAN may have an influence on snails and their abundance in an environment, possibly disturbing ecological stability.

Evolution of sex allocation plasticity in a hermaphroditic flatworm genus.

Sex allocation theory in simultaneous hermaphrodites predicts that optimal sex allocation is influenced by local sperm competition, which occurs when related sperm compete to fertilize a given set of eggs. Different factors, including the mating strategy and the ability to self‐fertilize, are predicted to affect local sperm competition and hence the optimal SA. Moreover, since the local sperm competition experienced by an individual can vary temporally and spatially, this can favour the evolution of sex allocation plasticity. Here, using seven species of the free‐living flatworm genus Macrostomum, we document interspecific variation in sex allocation, but neither their mating strategy nor their ability to self‐fertilize significantly predicted sex allocation among these species. Since we also found interspecific variation in sex allocation plasticity, we further estimated standardized effect sizes for plasticity in response to (i) the presence of mating partners (i.e. in isolation vs. with partners) and (ii) the strength of local sperm competition (i.e. in small vs. large groups). We found that self‐fertilization predicted sex allocation plasticity with respect to the presence of mating partners, with plasticity being lower for self‐fertilizing species. Finally, we showed that interspecific variation in sex allocation is higher than intraspecific variation due to sex allocation plasticity. Our study suggests that both sex allocation and sex allocation plasticity are evolutionarily labile, with self‐fertilization predicting the latter in Macrostomum.

Rhynchospioaciliata sp. nov., a new spionid species (Annelida, Spionidae) from the Korea Strait.

A new spionid polychaete, Rhynchospioaciliata sp. nov., was discovered in the fine sandy sediments of an intertidal habitat from Korean waters. The new species is considered a simultaneous hermaphrodite, but no brooding embryos were found in any of the specimens collected in this study. This species is unique in the absence of ciliation in the anteriormost chaetigers. Rhynchospioaciliata sp. nov. is morphologically most similar to Rhynchospiofoliosa Imajima, 1991 from Japan in having an elevation on the prostomium, conspicuously large and foliaceous branchiae, and intersegmental lateral pouches. However, the new species differs from the latter by the following characteristics: (1) large and lanceolate notopodial postchaetal lamellae of chaetiger 1, (2) transverse ciliated bands and ciliation on the inner branchiae absent in anteriormost chaetigers, and (3) pygidium with one pair of ventral cirri and numerous elongated dorsolateral cirri. Detailed description and illustrations of the new species are provided with molecular information on mitochondrial cytochrome c oxidase subunit I (COI), 16S ribosomal DNA (rDNA), nuclear 18S rDNA, and 28S rDNA.

Protogynous hermaphroditism in Crustacea: a new example from Tanaidacea

Hermaphroditism has been widely reported in the Crustacea, but protogyny, in which females change to males, is apparently rare and restricted to the peracarid orders Isopoda and Tanaidacea. In the latter, protogyny has been demonstrated in only seven species representing six genera by rearing experiments and indicated for several other genera and species through morphology. Here, we show through rearing experiment and histological observations, protogynous hermaphroditism in the tanaidacean species Nesotanais sp. aff. ryukyuensis Kakui, Kajihara and Mawatari, 2010. Our rearing experiment and size distribution data for wild individuals showed that females can change sex at various sizes (= ages). We found one individual identified externally as a female containing both ovaries and testes, indicating that overt female individuals undergo a short transitional phase as simultaneous hermaphrodites before the sex-change molt. We discuss the relationship among the wide size distribution of sex-changing females, the short life span of males, and the tube-dwelling mode of life.

Life history and reproductive traits of the East Atlantic deep-sea quill worm Hyalinoecia robusta Southward, 1977 (Annelida: Onuphidae)

Polychaetes or bristle worms (Annelida) are one of the best represented invertebrate groups in marine environments worldwide. Although the reproductive biology and life histories of polychaetes from many marine and estuarine habitats are well documented, our knowledge of the reproduction and life cycles of deep-sea polychaetes is still far from comprehensive. Hyalinoeciinae, a subfamily of Onuphidae, one of the most dominant and successful tubicolous deep-sea polychaete families, are characterised by their peculiar lifestyle as free-living epibenthic species, as they protrude from their tubes in a caterpillar-like fashion known as epibenthic crawling. The reproductive biology, sexual strategies and developmental modes of Hyalinoecia spp. are largely unknown. We have studied quarterly samples of the East Atlantic deep-sea quill worm Hyalinoecia robusta Southward, 1977, collected during 2012–2013, from the adjacent slope of the Avilés submarine Canyons System (Bay of Biscay) at 1500 m depth. Here we report on the annual cycle, revealing that H. robusta is iteroparous, reproducing annually during a breeding season from early spring to summer. The performed histological study revealed that the species is a simultaneous hermaphrodite with a previous adolescent male phase. This is the first evidence of the occurrence of hermaphroditism in the subfamily Hyalinoeciinae. Mature sperm was of the ent-aquasperm type and was stored in modified nephridial chambers that develop into external papillae that may detach from the worm and act as spermatophores at the time of reproduction. In H. robusta, the egg fertilisation seems to occur within intersegmental dorsal openings of the worm body wall or inside the worm tube. This hypothesis is consistent with the finding of fertilised eggs and developing embryos attached to the body wall and/or inside the worm tube in some specimens. The herein reported H. robusta reproductive traits do not support their conspecificity with populations from outside North Atlantic Ocean. Thus, the name H. robusta may be hiding other deep-water Hyalinoecia species.

On the role of eviction in group living sex changers

In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group (harem). In a few species, the subordinates are simultaneous hermaphrodites that may act as sneakers. In this paper, we ask whether the subordinates in most sex changers choose to be female or whether they are forced to give up their male function to avoid eviction by the harem holder. We consider a game model in which (1) the dominant male evicts some hermaphroditic subordinates if the risk of sperm competition in regard to fertilizing eggs is high, and (2) each subordinate individual chooses its own sex allocation considering the risk of being evicted. In the evolutionarily stable state, the dominant male evicts subordinates only when the subordinates vary greatly in their reproductive resources. All the subordinate individuals are female if the summed male function of the subordinates is smaller than that of the dominant male. Otherwise, all the subordinates are hermaphrodites, and the large individuals have the same male investment but a greatly different female investment, while small individuals have a reduced male investment to avoid eviction risk. We conclude that situations in which the sex allocation of subordinates is affected by the possibility of eviction by the harem holder are rather limitedSignificance statementWe studied the role of eviction in social evolution. In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group. In a few species, subordinates are simultaneous hermaphrodites. We asked whether the subordinates are forced to give up their male function to avoid eviction by the harem holder. We examined a game model in which the dominant male evicts hermaphroditic subordinates with a high risk of sperm competition, and each subordinate chooses its own sex allocation considering the eviction risk. We derived mathematical conditions for when subordinates are females or hermaphrodites in the ESS. The model demonstrated that the control by the dominant over subordinate reproductive decisions is rather limited.

Factors Shaping Gender Role in the Freshwater Hermaphrodite Snail Physella acuta

Reproductive investment theory assumes that females invest more in mate choice than males do because eggs are more energetically costly to produce than sperm. However, recent studies indicate that the relationship between initial investment and patterns of sexual selection is more nuanced. Simultaneous hermaphrodite mating systems offer unique opportunities to explore reproductive investment theory, as individuals exhibit fluid preferences for donating or receiving sperm and eggs. Shifts in gender role can depend on environmental or physiological conditions such as size. However, environment factors (e.g. temperature) that affect mating role preference or behavior (e.g. latency to copulate, reciprocity) have not been explored, despite evidence that the physiological consequences of elevated temperature interfere with reproductive success. By constraining the amount of energy available during copulation, elevated temperature may directly impact individual investment, reflected in changes in gender role. We observed courtship and gender roles in Physella acuta (Draparnaud 1805) at standard (19-20°C) and elevated (28-29°C) temperature. Elevated temperature reduced duration and frequency of copulation but had no effect on latency to copulate or reciprocity. Contrary to previous studies, gender role was not found to be size-dependent in either temperature treatment. Lack of size dependence across temperature treatments could be due to low population density or climate in situ. Combined results indicate that although elevated temperature clearly has negative physiological consequences, its impact is not reflected in changes to gender role patterns. This relationship is more complicated than previously expected and requires further study.

A review of 263 years of taxonomic research on Hypoplectrus (Perciformes: Serranidae), with a redescription of Hypoplectrus affinis (Poey, 1861).

The hamlets (Hypoplectrus spp., Perciformes: Serranidae) constitute a distinctive model system for the study of a variety of ecological and evolutionary processes including the evolution and maintenance of simultaneous hermaphroditism and egg trading, sex allocation, sexual selection, social-trap, mimicry, dispersal, speciation, and adaptive radiation. Addressing such fundamental and complex processes requires a good knowledge of the taxonomy and natural history of the hamlets. Here, we review the taxonomy of the hamlets, from early ichthyological studies to the most recent species description in 2018. We report a total of 72 different binomial names for Hypoplectrus, synonymized or invalidated down to 17 unambiguously recognized species today. In addition, we redescribe Hypoplectrus affinis (Poey, 1861) as a valid species. In Bocas del Toro (Panama), this hamlet is distinct from eight sympatric congeners in terms of colour pattern, body size and behaviour. Whole-genome analysis and spawning observations indicate that it is genetically distinct from sympatric congeners and reproductively isolated through assortative pairing. Based on the colour pattern we detail in its redescription, live-fish photographs, videos, and earlier reports, H. affinis occurs in Panama, Nicaragua, Mexico, the Florida Keys, Cuba, Grand Cayman, Jamaica, the Dominican Republic, Los Roques (Venezuela), Bonaire, and Tobago. We conclude with a discussion of pending taxonomic issues in this group and the species status of the hamlets in general.

Roles of Crustacean Female Sex Hormone 1a in a Protandric Simultaneous Hermaphrodite Shrimp

Crustacean female sex hormone (CFSH) plays a pivotal role in the development of secondary sex characteristics in dioecious crustaceans. However, until now the knowledge concerning its functions in hermaphroditic species is scanty. Herein, we explored the function of CFSH (Lvit-CFSH1a) in the peppermint shrimp Lysmata vittata, a species characterized by a rare reproductive system of protandric simultaneous hermaphroditism (PSH). Lvit-CFSH1a cDNA was 1,220-bp in length with a 720-bp ORF encoded a polypeptide of 239-aa. RT-PCR showed that Lvit-CFSH1a was exclusively expressed in the eyestalk ganglion. For female physiology, it was found that Lvit-CFSH1a was indispensable for the development of female gonopores, but it might not involve vitellogenesis of the species. For male physiology, Lvit-CFSH1a suppressed Lvit-IAG2 expression in short-term silencing experiment and recombinant protein injection experiment, but did not affect male sexual differentiation in long-term silencing experiment. In addition, silencing the Lvit-CFSH1a gene impeded individual growth in L. vittata.

Environmental effects on the genetic architecture of fitness components in a simultaneous hermaphrodite.

Understanding how environmental change affects genetic variances and covariances of reproductive traits is key to formulate firm predictions on evolutionary responses. This is particularly true for sex-specific variance in reproductive success, which has been argued to affect how populations can adapt to environmental change. Our current knowledge on the impact of environmental stress on sex-specific genetic architecture of fitness components is still limited and restricted to separate-sexed organisms. However, hermaphroditism is widespread across animals and may entail interesting peculiarities with respect to genetic constraints imposed on the evolution of male and female reproduction. We explored how food restriction affects the genetic variance-covariance (G) matrix of body size and reproductive success of the simultaneously hermaphroditic freshwater snail Physa acuta. Our results provide strong evidence that the imposed environmental stress elevated the opportunity for selection in both sex functions. However, the G-matrix remained largely stable across the tested food treatments. Importantly, our results provide no support for cross-sex genetic correlations suggesting no strong evolutionary coupling of male and female reproductive traits. We discuss potential implications for the adaptation to changing environments and highlight the need for more quantitative genetic studies on male and female fitness components in simultaneous hermaphrodites.