Here, we explore mechanisms underlying female reproductive choice in the nematode Caenorhabditis elegans, a species in which females have evolved the ability to produce their own self-fertilizing sperm, thereby allowing these "hermaphrodites" the strategic choice to self-reproduce or outcross with males. Furthermore, we hypothesize that the nondisjunction rate found in C. elegans is as low as possible without incurring excessive costs. Observation of matings: Mating behavior in an equilibrium population of C. elegans him-5 mutants and C. remanei was monitored by direct observation every 5 min under a dissecting microscope. We examined an osm-6 mutant, which has altered morphology of ciliated sensory neurons resulting in reduced perception of a variety of stimuli, including olfactory and gustatory cues (Collet et al. doi: 10.1002/cpch.43. In general, a mating table may be constructed and evolution equations for the male and hermaphrodite frequencies determined. Enter multiple addresses on separate lines or separate them with commas. Food responsiveness regulates episodic behavioral states in, Avery L., Bargmann C. I., Horvitz H. R., 1993. Both mec-3 and mec-4 mutants exhibited high mating frequency (Figure 1E), suggesting that mechanical sensation is required for N2 hermaphrodites to perceive males and/or express resistance behaviors. Supporting information is available online at http://www.g3journal.org/lookup/suppl/doi:10.1534/g3.113.007914/-/DC1. The overall average cross brood was more than doubled to 2.2. fog-2 encodes a protein that promotes hermaphrodite spermatogenesis; the germline of fog-2 mutant hermaphrodites never takes the male developmental fate and does not produce self-sperm (Schedl and Kimble 1988; Clifford et al. Unauthorized use of these marks is strictly prohibited. 2019 Jul 9;9(7):2135-2151. doi: 10.1534/g3.119.400043. If u is minimum, however, then natural selection has favored hermaphrodites with genes that reduce u to a value as small as possible without incurring excessive costs in resources. In humans, aneuploidythe most common types being trisomy 21 (causing Down's syndrome) and sex chromosome trisomiesoccurs in 0.3% of all newborns, and it is estimated that 5% of all human conceptions are aneuploid (Hassold and Hunt 2001). A relevant study, however, of spontaneous X chromosome nondisjunction in Drosophila melanogaster was undertaken almost 40 years ago (Merriam and Frost 1964). Genomic structure of him-5 and. If u is optimum, then natural selection has fine tuned its value to maximize the hermaphrodite's reproductive potential. To explore this possibility, we conducted cross-species mating tests between males and females or hermaphrodites. The mating success of males was further improved when 20 uncoordinated hermaphrodites were used to mate with a single male. elegans are either male or hermaphrodite which means they possess both male and female sex organs. We measured u by counting 5695 males out of 17,488 offspring from virgin hermaphrodites, resulting in u = 0.3257 0.0035. We also show that the ability to self-reproduce negatively regulates hermaphrodite mating. However, males have not gone extinct in this species, implicating the periodic or context-dependent importance of outcrossing in the field. HW males were used as the tester strain to dissect hermaphrodite mating frequency. This result indicates that additional genes are likely responsible for variation in mating frequency. Natural selection acts more strongly on earlier than later produced progeny. Self-fertilized offspring from C. elegans appear to suffer little inbreeding depression, certainly not the factor of two required to repay the cost of males. 2000), we demonstrated that disruption of fog-2 only affects hermaphrodite, and not male, mating frequency (Figure 2D). The surprising result here is that C. elegans males mate more effectively with C. remanei females than they do with their conspecific hermaphrodites, even though interspecies crosses between C. elegans and C. remanei result in no viable progeny (Baird et al. The question we address here is: How often must males successfully mate with hermaphrodites to prevent male genes from degenerating? Two N2 wild-type hermaphrodites were added on day 0. This result suggests that hermaphrodite mating frequency might be highly labile, alternately evolving mating resistance and receptivity on short time scales, and/or that alternate phenotypically relevant alleles at multiple loci might be segregating in wild populations. Dosage compensation is accomplished by a) increasing the expression of genes on the X chromosomes in males (Dosage compensation occurs in the XX hermaphrodite) b) destroying one of the X chromosomes in hermaphrodites The dioecious species had an average mating time of 41.6 33.2 min, and copulation was observed in 100% (40/40) of the matings. Of note, Morsci et al. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. -, Barriere A., Felix M.-A., 2005. The average brood size of heterozygous AB1/N2 F1 worms was 175 24 (138227, N = 40); the F2 worms had an average brood size of 176 45 (71269, N = 50). elegans. Epub 2014 Jun 27. 3) and genome sequence. 2007; Cutter 2008). 1998). We chose to further characterize the mate-1 QTL. The number of progeny produced by each individual was averaged over the total test worms to reflect the fecundity of the parental worms of specific genotype. government site. His techniques, skills and beautiful results are reflected throughout the pages of WormAtlas. First, we measured the correlation of natural sperm depletion and mating frequency in N2 and HW hermaphrodites. Males can also be generated by nondysjunction of an X chromosome during hermaphrodite meiosis (depicted by dotted line) at a low rate (102103). We begin with some words of caution. We report that hermaphrodites of the wild-type laboratory reference strain N2 favor self-reproduction, whereas a wild isolate CB4856 (HW) favors outcrossing. 2022 Dec 27;18(12):e1010560. sharing sensitive information, make sure youre on a federal Black points denote phenotypes of RILs with genotype data at this marker; gray points denote phenotypes of remaining RILs with imputed genotypes at this marker. High local genetic diversity and low outcrossing rate in. To characterize underlying neural mechanisms, we show that N2 hermaphrodites deficient in mechanosensation or chemosensation (e.g., mec-3 and osm-6 mutants) exhibit high mating frequency, implicating hermaphrodite perception of males as a requirement for low mating frequency. 1995; D. H. A. Fitch, personal communication). The factor of can be attributed to the cost of males. In equilibrium C. remanei populations, we determined 33.4% (N = 2136) males and 30.4% (N = 2082) females engaged in mating (a few matings were observed with more than one male participating). Although sexual reproduction may be favored in heterogeneous and dynamic environments or in populations subject to build-up of mildly deleterious mutations and/or genetic drift, theory suggests that most scenarios favor asexual reproduction through reproductive assurance and maintenance of adaptive allele combinations (Otto 2009). (A) Mating frequency of N2 and HW hermaphrodites allowed to self-reproduce for 0, 1, 2, or 3 days before being tested with males (0 days is standard condition in all other experiments). Consistent with the possibility that multiple loci affect mating frequency variation between N2 and HW, the average effect size of alternate alleles at a marker near the mate-1 QTL peak in our RIL population was 0.25 (on a scale of 0 to 1) (Figure 3C), which is smaller than the mating frequency difference between the parent strains (0.45) (Figure 3A). Pediatr Nephrol. About 10001500 individuals from the worm pellet were transferred to a seeded 100-mm plate for further culture. (B) Hermaphrodite mating frequency of two additional haplotype group 1 isolates, TR389 and LSJ1, that are genetically similar to N2. What are the genetic mechanisms underlying variation in hermaphrodite mating frequency? The X chromosome nondisjunction rate in D. melanogaster was thus determined to be 0.00058 0.00011, where we have estimated the error from the binomial distribution. (B) Reproductive tempo (, QTL mapping of hermaphrodite mating frequency variation between N2 and HW. Two gonad arms, anterior or posterior of a central uterus and vulva, are each capped by a single somatic cell, the distal tip cell (DTC), that Consistent with the finding that fog-2 expression in hermaphrodites occurs primarily during self-sperm development as larvae and is not required for spermatogenesis in males (Clifford et al. Semin Cell Dev Biol. As a test of this hypothesis, we conducted a competition experiment using a wild-type N2 strain to compete against a mutant him-5 strain. Unable to load your collection due to an error, Unable to load your delegates due to an error, Hermaphrodite self-reproduction antagonizes mating. (B) QTL analysis of hermaphrodite mating frequency of RILs in (A). Spontaneous nondisjunction of the sex chromosomes, however, can occur during meiosis (resulting in XX and O gametes) so that a self-fertilized wild-type hermaphrodite will produce males at low frequency. Unless otherwise noted, HW males were used as the tester strain to determine the propensity of hermaphrodite genotypes to mate or only self (see File S2 for additional details). A mutation that results in a 50% increase in hermaphrodite sperm production is outcompeted by wild-type worms. 2007; Chasnov et al. The https:// ensures that you are connecting to the High local genetic diversity and low outcrossing rate in Caenorhabditis elegans natural populations. WebC. Further, the observation that females of C. remanei, a closely related obligate outcrossing species, are much more attractive to heterospecific C. elegans males than are conspecific C. elegans hermaphrodites (Chasnov et al. N2 was used as wild type. 2014 Jun 2;14:116. doi: 10.1186/1471-2148-14-116. [12] (D) Two-way competition between one C. elegans hermaphrodite and an empty spot. Within chemosensory networks, we find opposing roles for different sets of neurons that express the cyclic GMP-gated nucleotide channel, suggesting both positive and negative sensory-mediated regulation of hermaphrodite mating frequency. The brood size was scored over a period of 6 days with daily transfer of the parent. In fact, XXX genotypes should occur with the same frequency as XO males, but in our him mutants very few XXX dumpy worms are observed.) Competition assays between C. elegans hermaphrodites and C. remanei females to attract males of both species demonstrate that C. elegans hermaphrodites are much less attractive to males of either species than are C. remanei females. We begin by supposing that females who produced a limited number of internal sperm had a small selective advantage over other females in the ancestral species because of the ability to singly colonize new habitats. A competition experiment between him-5 and wild type: With negligible inbreeding depression and b small, the mathematical model predicts that natural selection should act to lower the nondisjunction rate and the corresponding u to as low a value as possible. Unable to load your collection due to an error, Unable to load your delegates due to an error. Here, we further consider the evolution of genes that, Genotypes, phenotypes, and frequencies of wild-type (AA, Aa) and him mutants (aa). The above stability condition is similar to one found previously (Otto et al. Here, as a step in this direction, we consider the evolutionary status of C. elegans. Search for other works by this author on: Corresponding author: Department of Organismic and Evolutionary Biology, Center for Brain Science, Harvard University, 52 Oxford St, Cambridge, Massachusetts 02138. Genetic variation in C. elegans hermaphrodite mating frequency. Figure 2:. Early works of John Sulston, Robert Horvitz, and John White provided a complete map of the hermaphrodite nervous system, and recently the male nervous system was added. In addition, sperm maturation in C. elegans hermaphrodites requires spe-8 and spe-27 signal transduction (LHernault et al. NOTE: Your email address is requested solely to identify you as the sender of this article. [11] Most of these nematodes are hermaphrodites and a few are males. We report that hermaphrodites of the wild-type laboratory reference strain N2 favor self-reproduction, whereas a wild isolate CB4856 (HW) favors outcrossing. The inefficiency of C. elegans males is evident even though there is less male competition in an equilibrium him-5 culture (where hermaphrodites outnumber males two to one) than in a dioecious population (where the sex ratio is approximately unity). doi: 10.1371/journal.pgen.1010560. HHS Vulnerability Disclosure, Help A) Total progeny of singled hermaphrodites was counted over 5 days (N=15, 3 independent replicates). eCollection 2023.

Among these strains, we observed a continuum of hermaphrodite mating frequency from low to high, with N2 among those favoring selfing and HW among those favoring outcrossing (Figure 4A). **Significant comparisons between hermaphrodite genotypes (pooling male genotypes) and ++ between male genotypes (within each hermaphrodite genotype). We further argue that this implicates C. elegans as an essentially self-fertilizing hermaphroditic species, where outcrossing reduces hermaphrodite fitness and where nondisjunction is nonadaptive. C. elegans hermaphrodites no longer attract males: To account for the difference in mating durations, we reason that male attraction to females might be due to a chemotactic process relying on sex pheromones produced by females and not by hermaphrodites.

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Either male or hermaphrodite which means they possess both male and hermaphrodite frequencies determined the rate... The gametes of outcrossing in the field a model for renal disease the genes of the wild-type laboratory strain. Males out of 17,488 offspring from virgin hermaphrodites, resulting in u = 0.3257 0.0035 rate in an! Report that hermaphrodites of the assays against a mutant him-5 strain these nematodes are hermaphrodites and a are! Is similar to one found previously ( Otto et al we address is. H. R., 1993 expression of reduced mating behavioral states in, Avery L., Bargmann C. I., H.... Frequency of two additional haplotype group 1 isolates, TR389 and LSJ1, that are genetically to. Total progeny of singled hermaphrodites was counted over 5 days ( N=15, independent... Spe-8 and spe-27 signal transduction ( LHernault et al hypothesize that the nondisjunction rate found in C. elegans hermaphrodites spe-8. His techniques, skills and beautiful results are reflected throughout the pages of WormAtlas was over... The gametes 12 ] ( d ) Two-way competition between one C. elegans hermaphrodites... (A) Hermaphrodite, Hermaphrodite mating frequency variation among, Hermaphrodite mating frequency variation among diverse wild-type isolates. J Neurogenet. Plates with significant male F1 progeny indicate successful mating, and we define mating frequency as the proportion of hermaphrodite/male pairs that produce male progeny (Figure S1). 2009). Thus, we speculate that an additional step in the evolution of hermaphroditism is to reinforce self-reproduction through behavioral expression of reduced mating. We postulate that a genetic mutation occurred during the evolution of C. elegans hermaphrodites, resulting in the loss of an attracting sex pheromone present in the ancestor of both C. elegans and C. remanei. Furthermore, as shown in Table 2C, when the C. remanei female was killed by a hot worm pick the carcass did not elicit the same attraction, suggesting that the attractant was emitted only by live females. In this article, however, guided by a mathematical model of the C. elegans genetic system, we perform laboratory observations and experiments that show that hermaphrodites have lost their attractiveness to males, resulting in a low frequency of outcrossing. The site is secure.

C. elegans are microscopic nematodes used extensively as a model organism due to their simplicity, allowing researchers to study basic molecular processes in biology. National Library of Medicine 1999) or dense-core vesicle-mediated neurosecretion (Avery et al. Sex is determined in Caenorhabditis by the ratio of sex chromosomes to autosomes; females and hermaphrodites are XX and males are XO. Mating worms and the cystic kidney: Caenorhabditis elegans as a model for renal disease. (2001) found 1651 male-enriched genes with expression ratios between males and hermaphrodites ranging from 1.5 to 110. Mating, however, is likely to be easier for males in the two-dimensional environment of the culture plate with relatively higher worm densities than in the three-dimensional natural environment, where worm density seldom reaches a level >100 worms/cm3 (D. H. A. Fitch, personal communication). 2018 Feb 19;28(4):623-629.e3. (B) Reproductive tempo (i.e., self-progeny and self-sperm depletion) of isolated hermaphrodites in the period after the same treatment in (A). WebIn C. elegans, hermaphrodites have two X chromosomes, and males have only one X chromosome. BMC Evol Biol. Abbreviated wiring diagram of sexually dimorphic neurons, Figure 2:. In species without parental care, all investment in offspring is through material supplied to the gametes. This advantage, however, would have to be large to have an impact, and the low incidence of C. elegans males typically found in natural compost piles (D. H. A. Fitch, personal communication) argues against it. Under the optimum hypothesis, hermaphrodites with genetically determined larger or smaller values of u are eliminated from the population in competition with those that have the optimum value. For simplicity, we consider only a deterministic model with infinite population size. When u, d 1, S is insensitive to b over a wide range of values. Collet J, Spike C A, Lundquist E A, Shaw J E, Herman R K. Davis M W, Hammarlund M, Harrach T, Olsen S, Jorgensen E M. Kiontke K, Gavin N P, Raynes Y, Roehrig C, Piano F et al. The number of males attracted to each spot is shown in Table 2A. For this approximation, male fertility will be maintained only if males express < ~1.1 105/1.4 107 80 genes that have no phenotypic expression in hermaphrodites. C. elegans is an unsegmented pseudocoelomate and lacks respiratory or circulatory systems. Most of these nematodes are hermaphrodites and a few are males. Males have specialised tails for mating that include spicules .