Mechanism of Male Choice: Sex Ratios

2021 ◽  
pp. 109-118
Author(s):  
Ingo Schlupp
Keyword(s):  
Sex Ratio ◽  
Population Biology ◽  
Sex Ratios ◽  
Binary Choice ◽  
Mate Quality ◽  
Male And Female ◽  
Female Quality ◽  
Choice Tests

In this short chapter I want to discuss the role of sex ratios in choosiness. So far, we have mostly reviewed intrinsic reasons for male choosiness to be expressed such as male investment and female quality; however, sex ratios may also be important drivers of choosiness. Sex ratios are important in population biology and influence the evolution and structure of mating systems. Most important for the purpose of this book is that they can change quickly in time and space. Male and female choice are sensitive to such changes and can lead to situations where females are choosy when they are rare in a population but change to courtship and competition when males are rare. There are not many examples of this process, but there are likely some that have been overlooked. Interestingly, the majority of data on preferences are collected using binary choice tests, which almost always represent a 2:1 sex ratio. Furthermore, sex ratios do not take into account differences in mate quality, as all adult individuals are classified as either male or female without making any further distinction.

scholarly journals Sperm sex ratio adjustment in a mammal: perceived male competition leads to elevated proportions of female-producing sperm

2020 ◽  
Vol 16 (6) ◽  
pp. 20190929
Author(s):  
Renée C. Firman ◽  
Jamie N. Tedeschi ◽  
Francisco Garcia-Gonzalez
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Female Offspring ◽  
Male Competition ◽  
Offspring Sex ◽  
Sex Ratio Adjustment ◽  
Adaptive Adjustment ◽  
Male House

Mammal sex allocation research has focused almost exclusively on maternal traits, but it is now apparent that fathers can also influence offspring sex ratios. Parents that produce female offspring under conditions of intense male–male competition can benefit with greater assurance of maximized grand-parentage. Adaptive adjustment in the sperm sex ratio, for example with an increase in the production of X-chromosome bearing sperm (CBS), is one potential paternal mechanism for achieving female-biased sex ratios. Here, we tested this mechanistic hypothesis by varying the risk of male–male competition that male house mice perceived during development, and quantifying sperm sex ratios at sexual maturity. Our analyses revealed that males exposed to a competitive ‘risk’ produced lower proportions of Y-CBS compared to males that matured under ‘no risk’ of competition. We also explored whether testosterone production was linked to sperm sex ratio variation, but found no evidence to support this. We discuss our findings in relation to the adaptive value of sperm sex ratio adjustments and the role of steroid hormones in socially induced sex allocation.

Experimental observations on the sex ratio of adult Schistosoma mansoni, with comments on the natural male bias

Parasitology ◽  
2000 ◽  
Vol 121 (4) ◽  
pp. 379-383 ◽  
Author(s):  
J. BOISSIER ◽  
H. MONÉ
Keyword(s):  
Sex Ratio ◽  
Schistosoma Mansoni ◽  
Sex Ratios ◽  
Vertebrate Host ◽  
Natural Conditions ◽  
Male And Female ◽  
Male Bias ◽  
Biased Sex Ratio ◽  
And Bisexual

The sex ratio of adult worms has been observed biased towards males in Schistosoma mansoni under natural conditions. The origin of this bias is unknown. This paper determines whether males are more infective than females under controlled experimental bisexual conditions, and hence if the sex ratio is male-biased as a consequence of this. The male and female cercarial infectivities in uni- and bisexual vertebrate host infections using a range of controlled cercarial sex ratios were studied. The results showed that, in experimental unisexual infections, male cercariae were more infective than females, and that in experimental bisexual infections, male cercarial infectivity was similar to that of female, irrespective of cercarial sex ratio. Furthermore, cumulative male and female cercarial infectivity was maximal when sex ratio was equilibrated. The unbiased sex ratios obtained in our experimental bisexual infections are discussed in terms of behavioural and/or biochemical male–female interaction. Alternative explanations of the natural biased sex ratio are proposed.

scholarly journals Sex-Biased Mortality and Sex Reversal Shape Wild Frog Sex Ratios

2021 ◽  
Vol 9 ◽  
Author(s):  
Max R. Lambert ◽  
Tariq Ezaz ◽  
David K. Skelly
Keyword(s):  
Sex Ratio ◽  
Population Biology ◽  
Developmental Stages ◽  
Sex Ratios ◽  
Sex Reversal ◽  
Egg Mass ◽  
Molecular Sexing ◽  
Wild Populations ◽  
Ratio Variation ◽  
Animal Populations

Population sex ratio is a key demographic factor that influences population dynamics and persistence. Sex ratios can vary across ontogeny from embryogenesis to death and yet the conditions that shape changes in sex ratio across ontogeny are poorly understood. Here, we address this issue in amphibians, a clade for which sex ratios are generally understudied in wild populations. Ontogenetic sex ratio variation in amphibians is additionally complicated by the ability of individual tadpoles to develop a phenotypic (gonadal) sex opposite their genotypic sex. Because of sex reversal, the genotypic and phenotypic sex ratios of entire cohorts and populations may also contrast. Understanding proximate mechanisms underlying phenotypic sex ratio variation in amphibians is important given the role they play in population biology research and as model species in eco-toxicological research addressing toxicant impacts on sex ratios. While researchers have presumed that departures from a 50:50 sex ratio are due to sex reversal, sex-biased mortality is an alternative explanation that deserves consideration. Here, we use a molecular sexing approach to track genotypic sex ratio changes from egg mass to metamorphosis in two independent green frog (Rana clamitans) populations by assessing the genotypic sex ratios of multiple developmental stages at each breeding pond. Our findings imply that genotypic sex-biased mortality during tadpole development affects phenotypic sex ratio variation at metamorphosis. We also identified sex reversal in metamorphosing cohorts. However, sex reversal plays a relatively minor and inconsistent role in shaping phenotypic sex ratios across the populations we studied. Although we found that sex-biased mortality influences sex ratios within a population, our study cannot say at this time whether sex-biased mortality is responsible for sex ratio variation across populations. Our results illustrate how multiple processes shape sex ratio variation in wild populations and the value of testing assumptions underlying how we understand sex in wild animal populations.

Sexual imprinting on a novel blue ornament in zebra finches

Behaviour ◽  
2006 ◽  
Vol 143 (8) ◽  
pp. 969-991 ◽  
Author(s):  
Barbara Caspers ◽  
Klaudia Witte
Keyword(s):  
Cultural Evolution ◽  
Mate Preferences ◽  
Binary Choice ◽  
Zebra Finches ◽  
Sexual Imprinting ◽  
Choice Tests ◽  
Opposite Sex ◽  
Males And Females ◽  
Learned Preference

AbstractSexual imprinting plays an important role for the development of mate preferences in birds. We tested whether male and female zebra finches Taeniopygia guttata sexually imprinted on an evolutionary novel trait, a blue feather on the forehead in parents. Additionally, we tested whether males and females would transfer a learned preference for the blue feather to a preference for blue leg bands, and whether a potential mate with two novel blue traits can amplify its attractiveness. Offspring were raised by parents in four different imprinting groups: (1) both parents unadorned; (2) the mother adorned only; (3) the father adorned only; (4) both parents adorned with the blue feather. After young reached maturity, we tested their mate preference for adorned and unadorned conspecifics of the opposite sex in binary choice tests. Females of the father adorned imprinting group sexually imprinted on the blue feather, and females reared by adorned parents showed a tendency to prefer adorned males. None of the males sexually imprinted on the blue feather. Our study replicates the results of a previous study on sexual imprinting on a red feather in zebra finches. We, therefore, propose a sex difference in the learning process of sexual imprinting. Females sexually imprinted on the blue feather did not transfer the learned preference to males with blue leg bands, and two novel blue traits could not amplify the attractiveness in males and females for the opposite sex. Our study emphasizes the role of sexual imprinting for the cultural evolution in mate preferences in zebra finches.

scholarly journals In-Culture Selection and the Potential Effects of Changing Sex Ratios on the Reproductive Success of Multiannual Delayed Gametophytes of Saccharina latissima and Alaria esculenta

2021 ◽  
Vol 9 (11) ◽  
pp. 1250
Author(s):  
Alexander P. J. Ebbing ◽  
Gregory S. Fivash ◽  
Nuria B. Martin ◽  
Ronald Pierik ◽  
Tjeerd J. Bouma ◽  
...  
Keyword(s):  
Life Cycle ◽  
Reproductive Success ◽  
Sex Ratio ◽  
Female Gametophyte ◽  
Sex Ratios ◽  
Saccharina Latissima ◽  
Male And Female ◽  
Alaria Esculenta

Multiannual delayed gametophyte cultures can stay vegetative for years, while also having the ability to grow. This study aims to investigate whether male and female multiannual delayed gametophyte strains of the species Saccharina latissima and Alaria esculenta grow at different rates in culture. We furthermore assessed how changing sex ratios can affect the reproductive yields of these cultures. The results indicate that the reproductive yield of cultures declines with decreasing male:female ratios, a correlation that becomes especially apparent at higher culture densities for both species. Female gametophyte densities in particular affected the observed reproductive yield of the cultures, with S. latissima cultures showing a clear reproductive optimum (sporophytes·mL−1) at 0.013 mg·mL−1 DW female gametophyte biomass, while the reproductive success of A. esculenta peaked at a density of 0.025 mg·mL−1 DW of female gametophyte biomass, after which the reproductive yield started to decline in both species. The results show that the sex ratio of a gametophyte culture is an important biotic life cycle control, with higher amounts of female gametophyte biomass halting gametophyte reproduction. Understanding how these changing sex ratios in gametophyte cultures affect reproduction is especially important in the aquaculture of kelp, where reliable preforming cultures are key to long-term success.

scholarly journals Role of Sex Ratio and Density on Fertilization Success of Intensively Cultured Endangered Woundfin

2017 ◽  
Vol 8 (1) ◽  
pp. 249-254 ◽  
Author(s):  
Paige A.C. Maskill ◽  
Isaac R. Miller ◽  
Leif J. Halvorson ◽  
Hilary B. Treanor ◽  
Cal W. Fraser ◽  
...  
Keyword(s):  
Resource Management ◽  
Sex Ratio ◽  
Sex Ratios ◽  
Fertilization Success ◽  
Culture Conditions ◽  
Laboratory Setting ◽  
Intensive Culture ◽  
Virgin River ◽  
Recovery Program

Abstract Woundfin Plagopterus argentissimus are a small, endangered cyprinid found solely in the Virgin River across Utah, Arizona, and Nevada. As of now, only three facilities culture Woundfin for conservation propagation purposes, but there is growing concern that current extensive culture protocols are not meeting the conservation recovery goals outlined in the Virgin River Resource Management and Recovery Program. The development of alternative rearing methodology, like effective intensive culture conditions, could help increase production to more effectively meet the conservation propagation needs for this species. Our goal was to assess the effect of different sex ratios and fish densities on reproductive success at indoor facilities. We measured fertilization success at three different sex ratios (1:1, 1:3, 1:5; female:male) and three different fish densities (0.05, 0.21, and 0.47 fish/L) in a laboratory setting. Sex ratio did not significantly affect fertilization success (P = 0.73). Fertilization was completely inhibited at a density of 0.05 fish/L, but there was no difference in fertilization success between the two other density treatments (P = 0.92). Our findings suggest that a density greater than 0.05 fish/L and a sex ratio of 1:1, 1:3, or 1:5 will likely enhance fertilization success. The results and conclusions of this paper provide valuable rearing information for the Virgin River Resource Management and Recovery Program and hatchery managers attempting to increase production of Woundfin in an intensive culture setting.

Effects of sex ratio on different biological parameters of Engytatus varians (Distant) (Hemiptera: Miridae) adults and their offspring: prey preference for Bactericera cockerelli (Sulcer) (Hemiptera: Triozidae)

2021 ◽  
pp. 1-8
Author(s):  
Laura Verónica Mena-Mociño ◽  
Samuel Pineda ◽  
Ana Mabel Martínez ◽  
Luis Jesús Palma-Castillo ◽  
Benjamín Gómez-Ramos ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Developmental Stages ◽  
Sex Ratios ◽  
Prey Preference ◽  
Biological Parameters ◽  
Bactericera Cockerelli ◽  
Filial Generation ◽  
Choice Tests ◽  
Engytatus Varians ◽  
Early Instar

Abstract In the present study, the influence of three sex ratios (1:1, 1:2, and 1:3; female:male) of the mirid Engytatus varians (Distant) (Hemiptera) on different biological parameters and on its offspring was evaluated. The prey preference of different developmental stages of this predator for different nymphal instars (N) of Bactericera cockerelli (Sulcer) (Hemiptera: Triozidae) was also evaluated. The fertility was significantly higher (24 nymphs/female) in the 1:3 sex ratio than in the 1:1 and 1:2 sex ratios (14 and 16 nymphs/female, respectively). The females in the 1:1 and 1:2 sex ratios lived 1.14 and 1.43 days more (27 and 28 days, respectively) than those in the 1:3 sex ratio (26 days). The nymphs derived from the females of the three sex ratios (first filial generation, F1) had five instars and a duration of 17 or 18 days. The ratio of the F1 generation females was not affected by the sex ratio of their parents. In choice tests, independent of whether the preys were placed on a single or multiple tomato (Solanum lycopersicum L.) leaflets, the consumption of females and males and N3, N4, and N5 nymphs of E. varians on B. cockerelli, generally showed the order of N2>N3>N4>N5. In conclusion, the findings revealed in this study can help to improve the rearing methodology for increasing populations of E. varians. In addition, they can serve as a guideline for releasing this predator in times when there is an abundance of early instar nymphs of B. cockerelli.

Sexual differences in development and behaviour of larval Ischnura verticalis (Odonata: Coenagrionidae)

1992 ◽  
Vol 70 (6) ◽  
pp. 1161-1165 ◽  
Author(s):  
Robert L. Baker ◽  
Mark R. L. Forbes ◽  
Heather C. Proctor
Keyword(s):  
Life Cycle ◽  
Sex Ratio ◽  
Larval Development ◽  
Sex Ratios ◽  
Sexual Differences ◽  
Emergence Period ◽  
Southern Ontario ◽  
Male And Female ◽  
Ischnura Verticalis

The emergence period of Ischnura verticalis from a pond in southern Ontario lasted at least 97 days; the sex ratio of emerging larvae was not significantly different from 1:1. A 17-month study on larvae from the same pond indicated that the life cycle was univoltine and that male larvae tended to develop faster than female larvae. Analysis of instar distributions of larval I. verticalis collected from a series of ponds also indicated that males were in more advanced instars than females. In the laboratory, male I. verticalis larvae in the final instar developed faster than female larvae in the final instar but male and female larvae in the penultimate instar developed at approximately the same rate. Male larvae in the antepenultimate instar consistently spent more time moving and crawled farther than female larvae in the antepenultimate instar. Sexual differences in larval development and behaviour could help explain sexual differences in instar distributions and altered sex ratios at emergence.

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