Sex determination in the androdioecious plant Datisca glomerata and its dioecious sister species D. cannabina.

Datisca glomerata is an androdioecious plant species containing male and hermaphroditic individuals. Molecular markers and crossing data suggest that, in both D. glomerata and its dioecious sister species D. cannabina, sex is determined by a single nuclear locus, at which maleness is dominant. Supporting this conclusion, an amplified fragment length polymorphism (AFLP) is heterozygous in males and homozygous recessive in hermaphrodites in three populations of the androdioecious species. Additionally, hermaphrodite x male crosses produced 1:1 sex ratios, while hermaphrodite x hermaphrodite crosses produced almost entirely hermaphroditic offspring. No perfectly sex-linked marker was found in the dioecious species, but all markers associated with sex mapped to a single linkage group and were heterozygous in the male parent. There was no sex-ratio heterogeneity among crosses within D. cannabina collections, but males from one collection produced highly biased sex ratios (94% females), suggesting that there may be sex-linked meiotic drive or a cytoplasmic sex-ratio factor. Interspecific crosses produced only male and female offspring, but no hermaphrodites, suggesting that hermaphroditism is recessive to femaleness. This comparative approach suggests that the hermaphrodite form arose in a dioecious population from a recessive mutation that allowed females to produce pollen.     

Sex Differences in Polymorphism and Expression of AAT-1 in the Hiroshima Population of Buergeria buergeri (Anura, Rhacophoridae)

Buergeria buergeri is female heterozygous in sex determination; chromosome pair No. 7 in this species is a pair of sex chromosomes of the ZZ/ZW type. Genetic analysis of AAT-1 variants was carried out to elucidate the mode of inheritance of this locus by starch-gel electrophoresis using field-caught females and males and their offspring produced by artificial crossings. The results showed that the AAT-1 locus is sex-linked and that alleles are expressed on the Z chromosome, but not the W chromosome. It is evident that the AAT-1 gene of female offspring is hemizygous and that the allele present is on the Z chromosome, which is derived from the male parent.     

Male-Biased Sex Ratios in Offspring of Attractive Males in the Guppy

The attractiveness hypothesis predicts that females produce offspring with male-biased sex ratios when they mate with attractive males because their male offspring will inherit the paternal sexual attractiveness and may have high reproductive success. In this study, we examined the effect of the attractiveness of the male guppy Poecilia reticulata in terms of the conspicuousness of its orange spot patterns, important criteria affecting female choice in this species, on the offspring sex ratios. We found that food-manipulation treatment altered the conspicuousness of the orange spot patterns in a full-sibling male pair. When females were presented to these males, they showed a greater mate preference for males having brighter orange spots than for those having duller orange spots. Subsequently, half of the females were mated with the preferred males and the remaining females were mated with the less preferred males. When the females exhibited a greater preference for their mates, their offspring sex ratios were more male biased. These results appear to be consistent with the prediction of the attractiveness hypothesis. In the guppy, as male sexual attractiveness is heritable, the male-biased sex ratios of the broods of attractive males may be adaptive.     

Heritable determinants of left-right bias in the rat

The offspring of matings of rats having opposite or same-sided turning biases were tested for turning biases as adults and the degree of similarity to the parents' biases assessed. There were significant and equivalent tendencies for the male offspring to have the same bias as the male parent and the opposite bias as the female parent. Although, overall, female offspring were distributed randomly with respect to the parents' biases, a significant tendency for female offspring to have biases opposite those of the female parent was apparent in litters having more males than females. Based on reports indicating a relationship between the sex ratio of a litter and levels of testosterone in female fetuses, it was suggested that $\text{in utero}$ exposure to testosterone reverses the coding of a heritable female influence and induces a tendency for the offspring to have biases opposite those of the female parent. The origins of sidedness in the rat appear to involve a complex interaction between heredity and hormones.     

SEX-RATIO SELECTION IN A BIVOLTINE THRIPS. I. CONDITIONAL SEX-RATIO MANIPULATION AND FITNESS VARIATION

Females of the bivoltine thrips Elaphrothrips tuberculatus (Hood) (Insecta: Thysanoptera) produce broods of either all males (by viviparity) or all females (by oviparity). Measurements of the sex-allocation ratio, ecological and physiological conditions affecting male and female offspring body size, and correlates of the relative fitnesses of adult males and females in relation to size indicate that female parents tend to be viviparous (produce males) if their offspring will become relatively large adults, and that males gain more in fitness from large size than do females. However, the conditions that link sex allocation with offspring fitness differ between the spring and summer generations. In spring, when breeding is synchronous, 1) oviparous and viviparous females do not differ in body size, 2) females tend to be viviparous where the fungus upon which they feed is relatively dense and where their offspring will become relatively large adults, and 3) fungus density is highly correlated with male and female offspring size. In summer, when breeding is relatively asynchronous, 1) viviparous females are much larger than oviparous females early (but not late) in the season, 2) large viviparous females begin breeding earlier than smaller ones, 3) offspring developing earlier in the season become larger adults, and 4) a higher proportion of females are viviparous earlier than later. Field experiments and field collections show that the covariation among sex allocation, conditions, and fitness is not caused by differential mortality by size or sex. Differences between the spring and summer generations in the cues used by females to adjust offspring sex ratio may be caused by seasonal variation in the factors that affect offspring size. However, in both generations, females tend to produce sons only when their offspring will become relatively large adults, whereas daughters are produced regardless of offspring size. These data suggest that females of E. tuberculatus avoid production of males (the sex with higher variance in expected fitness) when the size of their offspring is relatively uncertain.     

No evidence for adjustment of sex allocation in relation to paternal ornamentation and paternity in barn swallows

Sex allocation theory predicts that parents should adjust investment in sons and daughters according to relative fitness of differently sexed offspring. In species with female preference for highly ornamented males, one advantage potentially accruing to parents from investing more in sons of the most ornamented males is that male offspring will inherit characters ensuring sexual attractiveness or high-quality genes, if ornaments honestly reveal male genetic quality. Furthermore, in species where extra-pair fertilizations occur, offspring sired by an extra-pair male are expected to more frequently be male than those of the legitimate male if the latter is of lower quality than the extra-pair male. We investigated adjustment of sex ratio of offspring in relation to ornamentation of the extra-pair and the social mate of females by direct manipulation of tails of male barn swallows Hirundo rustica . Molecular sexing of the offspring was performed using the W chromosome-linked avian chromo-helicase-DNA-binding protein (CHD) gene while paternity assessment was conducted by typing of hypervariable microsatellite loci. Extra-pair offspring sex ratio was not affected by ornamentation of their biological fathers relative to the experimental ornamentation of the parental male. Experimental ornamentation of the parental males did not affect the sex ratio of nestlings in their broods. Female barn swallows might be unable to bias offspring sex ratio at hatching according to the quality of the biological father. Alternatively, fitness benefits in terms of sexual attractiveness of sons might be balanced by the cost of compensating for little parental care provided by highly ornamented parental males, if sons are more costly to rear than daughters, or the advantage of producing more daughters, if males with large ornaments contribute differentially more to the viability of daughters than sons.     

Effect of the hereditary characteristics of male blue foxes Alopex lagopus L. on the sex ratio of their offspring

Family analysis of a commercial population of the blue fox (the Pushkinskoe Breeding Fur Farm, Moscow oblast) with respect to secondary sex ratio has been performed. The offspring of each individual male or female involved in crossing between 1984 and 1988 was analyzed. The study of all families formed by every male and every female has made it possible to determine a group of "outstanding" fathers (23 out of 287 males), whose offspring was predominantly male (62.1% of the offspring were males, versus 53.9% in the total population). The results of subsequent detailed study on the pedigrees of male blue foxes in whose offspring the sex ratio significantly deviates from 1:1 indicate that this character is transmitted from fathers to sons without the deterioration of other commercially valuable characters. It is presumed that the significant deviation of sex ratio from 1:1 in the offspring of some male blue foxes is determined by genetic factors.     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

Offspring sex ratio in the sequentially polygamous Penduline Tit Remiz pendulinus

Despite the growing literature on facultative sex-ratio adjustment in chromosomal sex-determining vertebrate taxa (birds, mammals), the consistency of results is often low between studies and species. Here, we investigate the primary and secondary offspring sex ratio of a small passerine bird, the Eurasian Penduline Tit (Remiz pendulinus) in three consecutive years. This species has a uniquely diverse breeding system, in which the male (and/or the female) abandons the nest during egg-laying, and starts a new breeding attempt. This allowed us to test (1) whether patterns of parental care, i.e., male-only care, female-only care or biparental desertion, influence offspring sex ratio, and (2) whether the offspring sex ratio is repeatable between successive clutches of males and females. Using molecular markers to sex 497 offspring in 176 broods, we show that (1) offspring sex ratio does not depend on which parent provides care, and (2) the offspring sex ratio is not repeatable between clutches of a given individual. The overall primary and secondary offspring sex ratio at a population level is not different from parity (54 ± 6% males, and 50 ± 3% (mean ± SE), respectively). We suggest that ecological and phenotypic factors, rather than individual traits of parents, may influence offspring’s sex, and conclude that there is currently no evidence for a facultative adjustment of offspring sex ratio in the Penduline Tit.     

Males paving the road to polyandry? Parental compensation in a monogamous nesting cuckoo and a classical polyandrous relative

Comparative studies have established the necessity for biparental care as an important factor for monogamy in freshwater fish and birds. However, whether two parents are really needed for offspring care remains an open question in many cases. I experimentally studied female and male contributions to offspring care in the white-browed coucal (Centropus superciliosus), a monogamous and biparental cuckoo with a balanced adult sex ratio, and contrasted it with the sympatric black coucal (C. grillii), a classically polyandrous species with a male-biased adult sex ratio and male-only care. To study the necessity for biparental care, I temporarily removed one partner for 2 days to see whether the remaining parent compensated for the absence of its partner. Both female and male white-browed coucals approximately doubled their feeding rates when their partner was absent, thus fully compensating the number of feeding visits to the nest. However, nestlings maintained their growth only, when males were present and females were removed. When males were removed and only females were present, nestling growth declined. Hence, only male white-browed coucals fully compensated for the temporary loss of the partner, suggesting that females could benefit most from nesting with additional males—if these should become available. Removing female black coucals had no consequence for nestling feeding rates of male black coucals. But male black coucals had to be returned to their territories within a few hours to avoid harming the brood because female black coucals typically would not commence feeding their offspring. In conclusion, the breeding system of white-browed coucals seems quite flexible and the relatively balanced adult sex ratio may stabilize monogamy in this species. Should ecological factors ever favour a stronger bias in the adult sex ratio towards males, female white-browed coucals may easily become polyandrous and relinquish parental care entirely to males.     

The Genetic Basis of Sex Ratio in Silene Alba (= S. Latifolia)

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.     

Genomic imprinting: male mice with uniparentally derived sex chromosomes

Although it has been known that there is an X-chromosome imprinting effect during early embryogenesis in female mammals, it remains unknown if parental origin of the X chromosome has an effect in males. Furthermore, it has not been possible to produce animals with normal sex chromosomes of uniparental origin to further evaluate such imprinting effects. We have devised a breeding scheme to produce male mice, designated XPYP males, in which both the X and Y chromosomes are paternally inherited. To our knowledge, these are the first mammals produced that have a normal sex chromosome constitution but with both sex chromosomes derived from one parent. Development and reproduction in these XPYP males and the sex ratio and chromosome constitution of their offspring appeared normal; thus there is no apparent effect in males of having both sex chromosomes derive from one parent or of having the X chromosome derived from an inappropriate parent. Although we have detected no X-chromosome imprinting effect in these males, evidence from other sources suggest that the X chromosome is parentally imprinted. Thus detection and definition of an imprint can depend on the assay used.     

Offspring sex ratio under inbreeding and outbreeding in a gynodioecious plant

Silene vulgaris is a gynodioecious plant native to Eurasia and now found throughout much of North America. Using hermaphrodite plants from three geographic regions (Stamford, NY; Broadway,VA; and Giles Co., VA) and four local populations within each region, we employed a hierarchical crossing design to explore the geographic structure of sex determining genes. Sex determination in this species is cytonuclear involving multiple cytoplasmic male sterility and nuclear restorer loci. Due to dominance effects within nuclear restorer loci, self-fertilization of hermaphrodites heterozygous at restorer loci should produce some homozygous recessive female offspring. Female offspring may also result from outcrossing among related individuals. At greater geographic and genetic distances, mismatches between cytoplasmic and nuclear sex determining genes should also produce high frequencies of female offspring if coevolution between cytoplasmic and nuclear sex determining alleles occurs independently among widely separated populations. We found evidence of dominance effects among nuclear restorer loci but no evidence of nuclear-cytoplasmic mismatches at the regional level. Of 63 maternal lines, 55 produced at least one female offspring when self-fertilized. Outcrossing within populations produced significantly fewer female offspring than self-fertilization. Outcrossing among regions produced the lowest proportion of female offspring, significantly fewer than outcrossing among populations within regions. Regions responded differently to among-region outcrossing with pollen donors from the two Virginia regions producing far fewer female offspring with New York dams than crosses among New York populations. These results indicate that nuclear restoration is complex, involving multiple loci with epistatic interactions and that most hermaphrodites in nature are heterozygous at one or more restorer locus. Further, regional differences in restorer frequencies indicate significant genetic structure for sex determining genes at large geographic scales, perhaps reflecting invasion history.     

Adaptive Offspring Sex Ratio Depends on Male Tail Length in the Guppy

A biased sex ratio in a brood is considered to be an adaptive strategy under certain circumstances. For example, if the expected reproductive success of one sex is greater than that of the other, parents should produce more offspring of the former sex than the latter. A previous study has documented that in the guppy, Poecilia reticulata, the female offspring of males possessing proportionally longer tails exhibit smaller body sizes and show decreased reproductive outputs than those of males having shorter tails. On the other hand, the total lengths of the male offspring of the long‐tailed males are larger because of their longer tails; consequently, they exhibit greater sexual attractiveness to females. Therefore, it has been hypothesized that this asymmetry in the expected reproductive success between the male and female offspring of long‐tailed males may result in a biased sex ratio that is dependent on the tail lengths of their fathers. This hypothesis was tested in the present study. The results showed that the females that mated with long‐tailed males produced more male offspring than those that mated with short‐tailed males. Logistic regression analysis showed that the ratio of tail length to the standard length of the fathers is a determinant factor of the sex of their offspring. These results suggest that the manipulation of the offspring sex ratios by parents enhances the overall fitness of the offspring.     

Mutation in a sex-determining gene in rainbow trout: detection and genetic analysis

In rainbow trout (Oncorhynchus mykiss), the acknowledged sex-determining system is genetic sex determination (GSD) with female homogamety (female symbolXX-male symbolXY). Subsequently, mitotic gynogens are all expected to be females. Unexpected maleness was fortuitously observed in a mitotic gynogenetic family of rainbow trout (13 males out of 27). An equal ratio of males and females suggested the possible segregation of some Mendelian sex-influencing factor. In order to perform a comprehensive analysis of the inheritance and expression of the factor involved, the transmission of maleness was studied across the next three generations, using both conventional and/or meiotic and mitotic gynogenetic offspring. On the whole, males as well as intersexes were observed in crosses between two expected carrier parents, and in gynogenetic offspring of expected carrier females, but not in crosses between one expected carrier parent and one normal XX control. Sex ratios in the different crosses often fitted Mendelian proportions, but not always. Both excess and lack of maleness were observed. The simplest hypothesis consistent with most results is a one-locus model, assuming the existence of a mutation (termed mal) of a sex-determining gene, which is able to override the primary XX mechanism of sex determination and to induce the development of testicular tissue in the gonads of expected XX individuals. The one-locus model requires that the mal mutation usually, but not systematically, behave as a recessive mutation and have a limited penetrance, that is, heterozygous (mal/+) may be sex reversed, homozygous (mal/mal) may remain female, and carrier individuals may undergo partial masculinization alone (many intersexes were recorded). Inconsistency in sex ratios among offspring of parents expected to respond the same way was recorded, indicating that other modifier loci may also be involved. Finally, the occurrence of both males and females in clonal progenies showed that epigenetic factors also likely influence the expression of maleness. The effects of the mal mutation are compared to similar mutations recently described in other fish species. The nature and location of the mal gene (carried by heterochromosomes or an autosomal pair) is briefly discussed in view of the knowledge recently acquired on the subject.     

Female choice for good genes and sex-biased broods in guppies

In a population of guppies Poecilia reticulata females were found to prefer large males and the offspring of these males had a higher survival rate than those sired by smaller males, suggesting that females were selecting their mates on the basis of their good genes. The possibility that females differentially invested in male or female offspring depending on the size or attractiveness of their mate was also investigated, but no relationship was found between a male's attractiveness or body size and the sex ratio of the offspring he sired. However, a strong female-biased sex ratio was detected in the broods and the proportion of males produced decreased with the amount of time that a female was confined with a male. The possible reasons for this are discussed.     

Don'T throw bateman out with the bathwater!

Bateman identified two aspects of sexual selection. The first,called Bateman's principle, is that sexual selection favorsincreased promiscuity of males but not of females as a resultof differences in parental investment in gametes. The secondis that the variance in mate number of males is the fundamentalcause of a sex difference in fitness variance. We argue thatBateman's insight about the source of sexual selection is morefundamental than his speculation about patterns of parentalinvestment. We show that, when the sex ratio is 1:1, the averagefemale must be as promiscuous as the average male, because eachcopulation involves one male and one female. Because mean maleand female promiscuity are tied together in the same manneras mean male and female fitness, a sex difference in matingpropensity must be the result of either (1) a sex differencein the covariance between matings and number offspring, or (2)Fisherian run-away sexual selection, wherein female reluctanceto mate is a weak form of female choice. We show how femalepromiscuity can limit the evolution of male promiscuity, turningthe central argument of parental investment theory on its head.     

The loss of Y-sperm in “sex ratio” (SR) males of Drosophila subobseura is compensated

In Drosophila subobscura sex ratio (SR) males, a mechanism compensating for the loss of Y-sperm is present since these males produced a higher number of female offspring than did males of three control strains. Moreover, the number of female offspring from SR-males was even higher (average 1719) than the number of female and male offspring together (average 1460) from T2, one of the control strains. The fertile life span of SR-males was found to lie between those of the control strains. The rate of insemination was the same for SR- and control males.     

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European Shags Phalacrocorax aristotelis , the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.     

A pronounced sex difference when two linked loci of the Japanese brown frogRana japonica are recombined

To investigate the sex differences of crossing-over inRana japonica, the recombination frequencies between two linked loci,LDH-B andMPI, were examined in offspring obtained from 29 matings involving either females or males heterozygous at both loci. No recombinants were found among 303 offspring bred from 6 heterozygous males, whereas 160 were parental and 138 were recombinants among 298 offspring bred from 9 heterozygous females. The recombination frequency was 46.3%. These results show that the sex difference when two loci were recombined was marked and significant inRana japonica.