Caste development and sex ratio of the Ryukyu drywood termite Neotermes sugioi and its potential mechanisms

AbstractSex allocation is one of the most studied traits in evolutionary biology because its theoretical predictions match the empirical data. Here, using the Ryukyu dry-wood termite Neotermes sugioi, we investigated several factors that could bias the sex allocation in three populations (Okinawa, Ishigaki/Iriomote, and Yonaguni). Our survey showed that there were more queen-only colonies than king-only colonies in these populations, suggesting a longer lifespan of the queens than that of the kings. In this condition, sex-asymmetric reproductive value (SRV) theory predicts female bias, because even after the short-lived kings die, the long-lived queens can continue reproduction with their sons. However, sex allocation in this species seemed to be biased toward males. Furthermore, we examined the possibility of intrasexual competition among siblings (ICS). If ICS is the cause of the bias, the allocation is expected to change depending on the total investment in sexual offspring. However, the biomass of both male and female alates increased linearly with the increase in the total biomass of the alates in these populations. Thus, neither the SRV nor the ICS theory could explain the male-biased sex ratio of N. sugioi. On the basis of these results, we discuss the remaining possibilities in this species.

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Female-biased sex ratio of immature loggerhead sea turtles inhabiting the Atlantic coastal waters of Florida

Canadian Journal of Zoology ◽

10.1139/z91-419 ◽

1991 ◽

Vol 69 (12) ◽

pp. 2973-2977 ◽

Cited By ~ 28

Author(s):

Thane Wibbels ◽

R. Erik Martin ◽

David W. Owens ◽

Max S. Amoss Jr.

Keyword(s):

Sex Ratio ◽

Coastal Waters ◽

Sex Allocation ◽

Sea Turtles ◽

The United States ◽

Loggerhead Sea Turtles ◽

Blood Samples ◽

Sex Allocation Theory ◽

Biased Sex Ratio ◽

Atlantic Coastal

The sex ratio of immature loggerhead sea turtles, Caretta caretta, inhabiting the Atlantic coastal waters of Florida was investigated. Blood samples were obtained from 223 turtles that were captured in the intake channel of a power plant on Hutchinson Island. A serum androgen sexing technique was utilized to sex individual turtles. The sex ratio of the turtles (2.1 female: 1.0 male) differed significantly from 1:1 and thus appears to differ from predictions of sex allocation theory. These observations are consistent with those of a previous study, and collectively the results suggest that the sex ratio of immature C. caretta inhabiting the Atlantic coastal waters of the United States is significantly female biased: approximately two females per male.

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Linked supergenes underlie split sex ratio and social organization in an ant

10.1101/2021.01.22.427864 ◽

2021 ◽

Author(s):

German Lagunas-Robles ◽

Jessica Purcell ◽

Alan Brelsford

Keyword(s):

Sex Ratio ◽

Sex Allocation ◽

Empirical Studies ◽

Population Level ◽

Theoretical Work ◽

Female Offspring ◽

Genomic Region ◽

Genomic Conflict ◽

Theoretical Predictions ◽

Formica Podzolica

AbstractSexually reproducing organisms usually invest equally in male and female offspring. Deviations from this pattern have led researchers to new discoveries in the study of parent-offspring conflict, genomic conflict, and cooperation. Some social insect species exhibit the unusual population-level pattern of split sex ratio, wherein some colonies specialize in the production of future queens and others specialize in the production of males. Theoretical work focused on the relatedness asymmetries emerging from haplodiploid inheritance, whereby queens are equally related to daughters and sons, but their daughter workers are more closely related to sisters than to brothers, led to a series of testable predictions and spawned many empirical studies of this phenomenon. However, not all empirical systems follow predicted patterns, so questions remain about how split sex ratio emerges. Here, we sequence the genomes of 138 Formica glacialis workers from 34 male-producing and 34 gyne-producing colonies to determine whether split sex ratio is under genetic control. We identify a supergene spanning 5.5 Mbp that is closely associated with sex allocation in this system. Strikingly, this supergene is adjacent to another supergene spanning 5 Mbp that is associated with variation in colony queen number. We identify a similar pattern in a second related species, Formica podzolica. The discovery that split sex ratio is determined, at least in part, by a supergene in two species opens a new line of research on the evolutionary drivers of split sex ratio.Significance StatementSome social insects exhibit split sex ratio, wherein some colonies produce future queens and others produce males. This phenomenon spawned many influential theoretical studies and empirical tests, both of which have advanced our understanding of parent-offspring conflicts and cooperation. However, some empirical systems did not follow theoretical predictions, indicating that researchers lack a comprehensive understanding of the drivers of split sex ratio. Here, we show that split sex ratio is associated with a large genomic region in two ant species. The discovery of a genetic basis for sex allocation in ants provides a novel explanation for this phenomenon, particularly in systems where empirical observations deviate from theoretical predictions.

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Female-biased sex ratio in adults of the turtle Emys orbicularis at the northern limit of its distribution in France: a probable consequence of interaction of temperature with genotypic sex determination

Canadian Journal of Zoology ◽

10.1139/z89-182 ◽

1989 ◽

Vol 67 (5) ◽

pp. 1279-1284 ◽

Cited By ~ 17

Author(s):

J. Servan ◽

P. Zaborski ◽

M. Dorizzi ◽

C. Pieau

Keyword(s):

Sex Ratio ◽

Sex Determination ◽

Emys Orbicularis ◽

Gonad Differentiation ◽

Adult Sex Ratio ◽

Probable Consequence ◽

Genotypic Sex Determination ◽

Female Genotype ◽

Biased Sex Ratio ◽

Female Bias

Adult sex ratio in the turtle Emys orbicularis was determined in populations from seven ponds in Brenne (Indre, France). In all populations, the sex ratio was biased toward females. Among 290 captured animals, the male:female ratio was close to 0.5. Among different demographic factors that could affect the adult sex ratio, the most influential was probably the sex ratio of hatchlings. In Emys orbicularis, a ZZ male/ZW female system of genotypic sex determination has been postulated. Moreover, gonad differentiation is dependent on temperature and sex-reversed individuals can occur. To evaluate the importance of sex reversal among adult females, the blood of 78 animals was typed for the serologically detectable H-Y antigen, used as a tool to identify sexual genotype. In 73 of them, the H-Y phenotype was positive, conforming with female genotype, but in the other 5 females, it was negative (as in genotypic males), revealing that the sexual phenotype of these animals had been inverted. As the percentage of these sex-reversed genotypic males is low, the influence of temperature would appear not to be the sole cause of the observed unbalanced sex ratio. The female bias can be partly explained by the interaction of temperature with the ZZ/ZW system of genotypic sex determination. Indeed, in this system, sexual inversion under the influence of an epigenetic factor increases the ratio of genotypic females (ZW and WW) in the progeny.

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Maternal effects obscure condition-dependent sex allocation in changing environments

Royal Society Open Science ◽

10.1098/rsos.181885 ◽

2019 ◽

Vol 6 (4) ◽

pp. 181885 ◽

Cited By ~ 1

Author(s):

A. M. Edwards ◽

E. Z. Cameron ◽

E. Wapstra ◽

J. McEvoy

Keyword(s):

Climate Change ◽

Sex Ratio ◽

Environmental Change ◽

Maternal Effects ◽

Sex Allocation ◽

Good Condition ◽

Physiological Changes ◽

Temperature Dependent ◽

Changing Environments ◽

Theoretical Predictions

Climate change increases environmental fluctuations which thereby impact population demography. Species with temperature-dependent sex determination may experience more extreme sex ratio skews, but this has not been considered in species with chromosomally determined sex. However, anticipatory maternal effects cause lifelong physiological changes impacting sex ratios. Here we show, in mice, that more sons were born to mothers in good condition when their breeding environment matched their gestational environment, consistent with theoretical predictions, but mothers in mismatched environments have no condition–sex ratio relationship. Thus, the predicted effect of condition on sex ratio was obscured by maternal effects when the environment changed. This may explain extreme sex ratio skews in reintroduced or translocated populations, and sex ratio skews may become more common and less predictable with accelerating environmental change.

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The genetic basis of sex ratio in Silene alba (= S. latifolia).

Genetics ◽

10.1093/genetics/136.2.641 ◽

1994 ◽

Vol 136 (2) ◽

pp. 641-651

Author(s):

D R Taylor

Keyword(s):

Sex Ratio ◽

Sex Ratios ◽

Natural Populations ◽

Sex Ratio Bias ◽

Deleterious Alleles ◽

Silene Alba ◽

Biased Sex Ratio ◽

Paternal Parent ◽

Reciprocal Crossing ◽

Female Bias

Abstract A survey of maternal families collected from natural populations showed that the sex ratio in Silene alba was slightly female biased. Sex ratio varied among populations and among families within a female biased population. Crosses among plants from the most female biased population and the most male biased population showed that the sex ratio polymorphism was inherited through or expressed in the male parent. Males from one family in particular exhibited a severe female bias, characterized by less than 20% male progeny. The inheritance of sex ratio was investigated using a reciprocal crossing design. Sex ratios from reciprocal crosses were significantly different, indicating either sex-linkage or cytoplasmic inheritance of sex ratio. The sex ratios produced by males generally resembled the sex ratios produced by their male parents, indicating that the sex ratio modifier was Y linked. The maternal parent also significantly influenced sex ratio through an interaction with the genotype of the paternal parent. Sex ratio, therefore, is apparently controlled by several loci. Although sex ratio bias in this species may be due to deleterious alleles on the Y chromosome, it is more likely to involve an interaction between loci that cause the female bias and a Y-linked locus that enhances the proportion of males in the progeny.

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Sex ratio response of the two-spotted spider mite (Tetranychus urticae Koch) to changes in density under local mate competition

Canadian Journal of Zoology ◽

10.1139/z92-266 ◽

1992 ◽

Vol 70 (10) ◽

pp. 1965-1967 ◽

Cited By ~ 18

Author(s):

C. M. Roeder

Keyword(s):

Sex Ratio ◽

Tetranychus Urticae ◽

Local Mate Competition ◽

Mate Competition ◽

Local Mate ◽

Theoretical Predictions ◽

Female Bias ◽

Two Spotted Spider Mite ◽

Tetranychus Urticae Koch ◽

Ratio Response

The progeny sex ratios produced by mothers in populations that are subject to local mate competition are often a function of the number of females ovipositing in a patch. When the number of colonizing females changes during oviposition, by immigration, emigration, or death, the predicted sex ratio should also change. This was tested by quantifying the sex ratio response of Tetranychus urticae females to changes in the number of ovipositing females in their patch. When a solitary female is accompanied by other ovipositing females after she has oviposited for a period of time, she decreases the female bias of her progeny after the other females arrive. A female ovipositing with patch mates that are removed after a period of time, increases her progeny female bias after the patch mates are removed. Both of these progeny sex ratio patterns are consistent with theoretical predictions, and constitute a response by mothers to mitigate competition for mates among her sons. Females ovipositing alone throughout their ovipositional period produce more males during the first half of their ovipositional period than during the latter period of oviposition. This pattern of male production is not evident when a female is ovipositing with four other females. Solitary mothers may produce more males early during oviposition in anticipation of other females arriving on their patch and ovipositing, a form of bet hedging. If no other females arrive, mothers compensate for their overproduction of males and invest more in females later during oviposition.

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Sex allocation and field population sex ratio of Apanteles taragamae Viereck (Hymenoptera: Braconidae), a larval parasitoid of the cucumber moth Diaphania indica Saunders (Lepidoptera: Crambidae)

Open Agriculture ◽

10.1515/opag-2021-0045 ◽

2021 ◽

Vol 6 (1) ◽

pp. 673-681

Author(s):

Ihsan Nurkomar ◽

Azru Azhar ◽

Damayanti Buchori

Keyword(s):

Sex Ratio ◽

Brood Size ◽

Sex Allocation ◽

Natural Habitat ◽

Adult Emergence ◽

Female Offspring ◽

Individual Level ◽

Apanteles Taragamae ◽

Larval Parasitoid ◽

Biased Sex Ratio

Abstract Sex ratio is one of the most important biological characteristics of arthropods. In a parasitoid population, sex ratio can influence the suppression of host populations or the stability of host–parasitoid interactions in the field. In this study, a survey was carried out to determine the sex allocation through the sequence of male/female adult emergence and calculate the sex ratio of selected populations of Apanteles taragamae in their natural habitat. Assessment of sex ratio at the population and individual level (brood size per female) was examined. We found no difference in the likelihood that either sex would emerge before the other. Observations of sex ratio at the population and individual level reveal a females biased sex ratio. Analysis of the relationship between brood size and sex ratio of A. taragamae shows that brood size may influence the proportion of male to female offspring yielded. A male-biased sex ratio tends to be found in smaller brood size. However, sex ratio is shifted to female biased in larger brood size.

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The Trivers–Willard hypothesis: sex ratio or investment?

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.0126 ◽

2016 ◽

Vol 283 (1830) ◽

pp. 20160126 ◽

Cited By ~ 21

Author(s):

Carl Veller ◽

David Haig ◽

Martin A. Nowak

Keyword(s):

Simple Model ◽

Sex Ratio ◽

Sex Allocation ◽

Good Condition ◽

The Other ◽

Reproductive Value ◽

Small Subset ◽

Female Fitness ◽

Male And Female ◽

Fitness Functions

The Trivers–Willard hypothesis has commonly been considered to predict two things. First, that a mother in good condition should bias the sex ratio of her offspring towards males (if males exhibit greater variation in reproductive value). Second, that a mother in good condition should invest more per son than per daughter. These two predictions differ empirically, mechanistically and, as we demonstrate here, theoretically too. We construct a simple model of sex allocation that allows simultaneous analysis of both versions of the Trivers–Willard hypothesis. We show that the sex ratio version holds under very general conditions, being valid for a large class of male and female fitness functions. The investment version, on the other hand, is shown to hold only for a small subset of male and female fitness functions. Our results help to make sense of the observation that the sex ratio version is empirically more successful than the investment version.

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