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171 results for “hermaphroditism”
Data from: The evolution of egg trading in simultaneous hermaphrodites
Egg trading, whereby simultaneous hermaphrodites exchange each other's eggs for fertilization, constitutes one of the few rigorously documented and most widely cited examples of direct reciprocity among unrelated individuals. Yet how egg trading may initially invade a population of non-trading simultaneous hermaphrodites is still unresolved. Here, we address this question with an analytical model that considers mate encounter rates and costs of egg production in a population that may include traders (who provide eggs for fertilization only if their partners also have eggs to reciprocate), providers (who provide eggs regardless of whether their partners have eggs to reciprocate), and withholders ("cheaters" who only mate in the male role and just use their eggs to elicit egg release from traders). Our results indicate that a combination of intermediate mate encounter rates, sufficiently high costs of egg production, and a sufficiently high probability that traders detect withholders (in which case eggs are not provided) is conducive to the evolution of egg trading. Under these conditions traders can invade—and resist invasion from—providers and withholders alike. The prediction that egg trading evolves only under these specific conditions is consistent with the rare occurrence of this mating system among simultaneous hermaphrodites.
Data from: Experimental tests of sex allocation theory with two species of simultaneously hermaphroditic acorn barnacles
Sex allocation theory for simultaneous hermaphrodites predicts increases in relative allocation to male-specific function as competition for fertilizations increases. Theoretical models developed specifically for competing acorn barnacles predict that the proportional allocation to male function increases towards an asymptote of 50% as the number of competitors for fertilizations increases. Experimental manipulations were used to investigate how mate competition affected both relative and absolute allocation to the sex functions for two species of acorn barnacle: Semibalanus balanoides and Balanus glandula. The ratio of male to female allocation did not increase with the number of competitors for either species. However, both species showed increased allocation to male function (estimated as total mass of sex-specific tissues) with increased crowding. Allocation to female function seemed to be limited by other factors and did not vary with mating group size as predicted. Allocation to male and female function were both positively related to body size, but a trade-off between male and female function, a key assumption of prior models, was not observed.
Data from: Plastic expression of seminal fluid protein genes in a simultaneously hermaphroditic snail
Seminal fluid proteins (SFPs) are components of the ejaculate that often induce drastic changes in female physiology, such as reducing remating rate or shortening longevity. There is compelling evidence that these functions make SFPs a determinant of male reproductive success, and some evidence that males can strategically invest in their differential production. However, SFP-mediated effects have received relatively little attention in simultaneous hermaphrodites, i.e. organisms that are male and female at the same time. Since this reproductive mode is widespread in animals and their SFPs have unique functions compared to separate-sexed species, examining SFPs of hermaphrodites would help generalize our understanding of the impact of SFPs. We therefore examined if individuals strategically alter seminal fluid production in response to mate availability and sperm competition in the freshwater snail Lymnaea stagnalis. We exposed snails to different social group sizes, and measured the expression of six SFP genes. We found that the snails plastically elevated SFP expression in the presence of at least one mating partner. Specifically, paired snails showed higher SFP expression than isolated snails, while SFP expression of snails exposed to sperm competition, i.e. in a larger group size, was equivalent to that of paired snails. Furthermore, five out of six SFP genes we examined responded to mate availability in a very similar way, implying that overall seminal fluid production increases when the snails have mating opportunities. The plastic expression of seminal fluid depending on mate availability supports that SFPs play important roles in post-copulatory processes in this hermaphroditic species.
Data from: Hidden female physiological resistance to male accessory gland substances in a simultaneous hermaphrodite
To increase fertilization chances compared to rivals, males are favoured to transfer accessory gland proteins to females during mating. These substances, by influencing female physiology, cause alteration of her sperm usage and remating rate. Simultaneously hermaphroditic land snails with love-darts are a case in point. During courtship, a love-dart is pierced through the partner's body wall, thereby introducing accessory mucous gland products. This mucus physiologically increases paternity by inhibiting the digestion of donated sperm. The sperm, which are packaged in a spermatophore, are exchanged and received in an organ called the diverticulum. Because of its length, this organ was previously proposed to be a female anatomical adaptation that may limit the dart interference with the recipient's sperm usage. For reproductive success of the donor, an anatomically long spermatophore, relative to the partner's diverticulum, is beneficial since sperm can avoid digestion by exiting through the spermatophore's tail safely. However, the snail Eobania vermiculata possesses a diverticulum that is three times longer than the spermatophore it receives. Here we report that the love-dart mucus of this species contains a contraction-inducing substance that shortens the diverticulum, an effect that is only properly revealed when the mucus is applied to another helicid species, Cornu aspersum. This latter finding suggests that E. vermiculata may have evolved a physiological resistance to the manipulative substance received via the love-dart by becoming insensitive to it. This provides useful insight into evolution of female resistance to male manipulations, indicating that it can remain hidden if tested on a single-species.
Data from: Hermaphrodite life history and the maintenance of partial selfing in experimental populations of Caenorhabditis elegans
Background: Classic population genetics theory predicts that mixed reproductive systems, where self reproduction (selfing) and outcrossing co-exist, should not be as common as they are in nature. One means of reconciling theory with observations is to recognize that sexual conflict between males and hermaphrodites and/or constraints in the allocation of resources towards sex functions in hermaphrodites can balance the fitness components of selfing and outcrossing. Results: Using experimental evolution in Caenorhabditis elegans, we test whether the adaptive maintenance of partial selfing is due to sexual conflict and/or to the evolution of sex allocation towards male function in hermaphrodites. For this, we characterized the reproductive schedule and longevity patterns in hermaphrodites under selfing and under outcrossing with naïve males that did not have the opportunity to evolve with them. A shift in reproductive schedule towards earlier reproduction would be indicative of adaptation in our imposed life-cycle, while longevity is expected to evolve as a response to the harm that males impinge on hermaphrodites upon mating. To determine adaptation in the absence of constraints in sex allocation, we also characterized the life history of females that reproduced during experimental evolution through obligate mating with males. As expected with adaptation, we find that after 100 generations of experimental evolution, selfing hermaphrodites and females showed improved reproduction at earlier ages. We did not observe similar reproductive shifts in outcrossed hermaphrodites. We further find increased longevity in outcrossed females after evolution but not in outcrossed hermaphrodites, a result that indicates that sexual conflicts were likely more prevalent under male-female evolution than under male-hermaphrodite evolution. Conclusions: Taken together, our findings suggest that the adaptive maintenance of partial selfing during C. elegans experimental evolution resulted from the evolution of sex allocation towards male function in hermaphrodites.
Data from: Reduced mate availability leads to evolution of self-fertilization and purging of inbreeding depression in a hermaphrodite
Basic models of mating-system evolution predict that hermaphroditic organisms should mostly either cross-fertilize, or self-fertilize, due to self-reinforcing coevolution of inbreeding depression and outcrossing rates. However transitions between mating systems occur. A plausible scenario for such transitions assumes that a decrease in pollinator or mate availability temporarily constrains outcrossing populations to self-fertilize as a reproductive assurance strategy. This should trigger a purge of inbreeding depression which in turn encourages individuals to self-fertilize more often and finally to reduce male allocation. We tested the predictions of this scenario using the freshwater snail Physa acuta, a self-compatible hermaphrodite that preferentially outcrosses and exhibits high inbreeding depression in natural populations. From an outbred population, we built two types of experimental evolution lines, controls (outcrossing every generation) and constrained lines (in which mates were often unavailable, forcing individuals to self-fertilize). After ca. twenty generations, individuals from constrained lines initiated self-fertilization earlier in life and had purged most of their inbreeding depression compared to controls. However, their male allocation remained unchanged. Our study suggests that the mating system can rapidly evolve as a response to reduced mating opportunities, supporting the reproductive assurance scenario of transitions from outcrossing to selfing.
Data from: Experimentally evolved and phenotypically plastic responses to enforced monogamy in a hermaphroditic flatworm
Sexual selection is considered a potent evolutionary force in all sexually reproducing organisms, but direct tests in terms of experimental evolution of sexual traits are still lacking for simultaneously hermaphroditic animals. Here, we tested how evolution under enforced monogamy affected a suite of reproductive traits (including testis area, sex allocation, genital morphology, sperm morphology and mating behaviour) in the outcrossing hermaphroditic flatworm Macrostomum lignano, using an assay that also allowed the assessment of phenotypically plastic responses to group size. The experiment comprised 32 independent selection lines that evolved under either monogamy or polygamy for 20 generations. While we did not observe an evolutionary shift in sex allocation, we detected effects of the selection regime for two male morphological traits. Specifically, worms evolving under enforced monogamy had a distinct shape of the male copulatory organ and produced sperm with shorter appendages. Many traits that did not evolve under enforced monogamy showed phenotypic plasticity in response to group size. Notably, individuals that grew up in larger groups had a more male-biased sex allocation and produced slightly longer sperm than individuals raised in pairs. We conclude that, in this flatworm, enforced monogamy induced moderate evolutionary but substantial phenotypically plastic responses.
Data from: Evolutionary consequence of a change in life cycle complexity: a link between precocious development and evolution towards female-biased sex allocation in a hermaphroditic parasite
The evolutionary consequences of changes in the complex life cycles of parasites are not limited to the traits that directly affect transmission. For instance, mating systems that are altered due to precocious sexual maturation in what is typically regarded as an intermediate host may impact opportunities for outcrossing. In turn, reproductive traits may evolve to optimize sex allocation. Here we test the hypothesis that sex allocation evolved towards a more female-biased function in populations of the hermaphroditic digenean trematode Alloglossidium progeneticum that can precociously reproduce in their second hosts. In these precocious populations, parasites are forced to self-fertilize as they remain encysted in their second hosts. In contrast, parasites in obligate 3-host populations have more opportunities to outcross in their third host. We found strong support that in populations with precocious development, allocation to male resources was greatly reduced. We also identified a potential phenotypically plastic response in a body size-sex allocation relationship that may be driven by the competition for mates. These results emphasize how changes in life cycle patterns that alter mating systems can impact the evolution of reproductive traits in parasites.
Fig. 8 in Sexual development and reproductive pattern of the Mutton hamlet, Alphestes afer (Teleostei: Epinephelidae): a dyandric, hermaphroditic reef fish
Fig. 8. Monthly distribution percentages of gonadal stages per females (n = 183), immature bisexual female (Fbi) (n = 1), transitionals (Tr) (n = 16) and males (n = 57) from Pernambuco coast.
Fig. 6 in Sexual development and reproductive pattern of the Mutton hamlet, Alphestes afer (Teleostei: Epinephelidae): a dyandric, hermaphroditic reef fish
Fig. 6. Size-frequency distribution of females and males of A. afer during the reproductive period of 2008 and 2009. (Males, n=33; Females, n=31).
Figure 2 in Confirmation of functional hermaphroditism in six grouper species (Epinephelidae: Epinephelinae) from the Gulf of Mexico
Figure 2. - Histological sections of gonads from five groupers from Campeche Bank (Gabe and Martoja's one-step trichrome stain). A: Mycteroperca venenosa, female in regressing reproductive phase (71.5 cm FL), collected April 2009 at Bajos del Norte, showing atretic follicles in intermediate and advanced atretic stages. B: Mycteroperca microlepis, female in regenerating reproductive phase (97.0 cm FL), collected July 1998 in offshore waters, showing muscle bundles. C: Epinephelus guttatus, transitional individual (50.0 cm FL), collected February 2009 at Bajos del Norte, showing atretic follicles in advanced atretic stage and crypts of spermatocytes and spermatozoa. D: Epinephelus morio, transitional individual (40.5 cm FL), collected February 2003 in offshore waters, showing remnant of the former ovarian lumen, atretic follicles in advanced atretic stage, muscle bundles and crypts of spermatocytes. E: Mycteroperca tigris, transitional individual (48.2 cm FL), collected June 2008 at Bajos del Norte, showing remnant of the former ovarian lumen, atretic follicles in advanced atretic stage, muscle bundles and crypts of spermatocytes. F: Mycteroperca bonaci, transitional individual (121.5 cm FL), collected December 1997 in offshore waters, showing remnant of the former ovarian lumen, muscle bundle and crypts of spermatogonia and spermatocytes. G-H: Mycteroperca venenosa, transitional individual (55.0 cm FL), collected January 2009 at Bajos del Norte, showing muscle bundle and crypts of spermatogonia, spermatocytes and spermatozoa (G); and sperm sinus within gonad capsule (H). AF: atretic follicle; AAS: advanced atretic stage; IAS: intermediate atretic stage; GC: gonadal capsule; L: lumen; MB: muscle bundle; PG: primary growth oocyte; Sc: spermatocyte; Sg: spermatogonia; SS: sperm sinus; Sz: spermatozoa. Scale bars = 50 µm.
Figure 1 in Confirmation of functional hermaphroditism in six grouper species (Epinephelidae: Epinephelinae) from the Gulf of Mexico
Figure 1. - Sample collection areas for Epinephelus morio, Mycteroperca bonaci and Mycteroperca microlepis in inshore (●) and offshore (●) waters, and for Epinephelus guttatus, Mycteroperca tigris and Mycteroperca venenosa at (C) Arrecife Alacranes (22o21'44''N to 22o35'12''N; 89o36'30''W to 89o48'00''W) and (C) Bajos del Norte (23o20'N; 88o45'W), on Campeche Bank, southern Gulf of Mexico. Inshore water sites were: 1: Celestún; 2: Sisal; 3: Progreso; 4: Telchac Puerto; 5: Dzilam de Bravo; 6: San Felipe; 7: Río Lagartos; 8: El Cuyo; 9: Punta Caracol.
Data from: Bateman gradients in hermaphrodites: an extended approach to quantify sexual selection
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Data from: Sex allocation adjustment to mating group size in a simultaneous hermaphrodite
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Data from: Asymmetric evolutionary responses to sex-specific selection in a hermaphrodite
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Data from: The mutational decay of male-male and hermaphrodite-hermaphrodite competitive fitness in the androdioecious nematode C. elegans
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Data from: A targeted in situ hybridization screen identifies putative seminal fluid proteins in a simultaneously hermaphroditic flatworm
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Data from: Lifetime inbreeding depression, purging, and mating system evolution in a simultaneous hermaphrodite tapeworm
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Data from: Experimental tests of sex allocation theory with two species of simultaneously hermaphroditic acorn barnacles
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Data from: Experimentally evolved and phenotypically plastic responses to enforced monogamy in a hermaphroditic flatworm
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