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.

scholarly journals Sex Ratios in a Warming World: Thermal Effects on Sex-Biased Survival, Sex Determination, and Sex Reversal

2021 ◽  
Vol 112 (2) ◽  
pp. 155-164
Author(s):  
Suzanne Edmands
Keyword(s):  
High Temperature ◽  
Sex Ratio ◽  
Sex Determination ◽  
Heat Tolerance ◽  
Sex Ratios ◽  
Sex Reversal ◽  
Survival Sex ◽  
Ratio Distortion ◽  
Warming World ◽  
Sex Ratio Distortion

Abstract Rising global temperatures threaten to disrupt population sex ratios, which can in turn cause mate shortages, reduce population growth and adaptive potential, and increase extinction risk, particularly when ratios are male biased. Sex ratio distortion can then have cascading effects across other species and even ecosystems. Our understanding of the problem is limited by how often studies measure temperature effects in both sexes. To address this, the current review surveyed 194 published studies of heat tolerance, finding that the majority did not even mention the sex of the individuals used, with <10% reporting results for males and females separately. Although the data are incomplete, this review assessed phylogenetic patterns of thermally induced sex ratio bias for 3 different mechanisms: sex-biased heat tolerance, temperature-dependent sex determination (TSD), and temperature-induced sex reversal. For sex-biased heat tolerance, documented examples span a large taxonomic range including arthropods, chordates, protists, and plants. Here, superior heat tolerance is more common in females than males, but the direction of tolerance appears to be phylogenetically fluid, perhaps due to the large number of contributing factors. For TSD, well-documented examples are limited to reptiles, where high temperature usually favors females, and fishes, where high temperature consistently favors males. For temperature-induced sex reversal, unambiguous cases are again limited to vertebrates, and high temperature usually favors males in fishes and amphibians, with mixed effects in reptiles. There is urgent need for further work on the full taxonomic extent of temperature-induced sex ratio distortion, including joint effects of the multiple contributing mechanisms.

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.

Sex ratio variation in the yuma bat (Myotis yumanensis)

1993 ◽  
Vol 71 (5) ◽  
pp. 937-940 ◽  
Author(s):  
Barry N. Milligan ◽  
R. Mark Brigham
Keyword(s):  
British Columbia ◽  
Sex Ratio ◽  
Maternal Age ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Ratio Variation ◽  
Sex Allocation Theory

Sex allocation theory predicts that monomorphic species should produce natal sex ratios near unity. We measured natal sex ratios in a maternity colony of approximately 1600 yuma bats (Myotis yumanensis) near Squilax, British Columbia, during June and July 1991. Overall, the natal sex ratio did not differ from unity but the sex ratio did vary significantly throughout the summer. Variation appears to be related to an interaction between maternal age and date of birth. This evidence suggests that facultative manipulation of the sex of the offspring by individual females may occur within the population.

scholarly journals Nestling Sex Ratios in the Yellow-Naped Amazon: No Evidence for Adaptive Modification

The Condor ◽  
2002 ◽  
Vol 104 (2) ◽  
pp. 437-440 ◽  
Author(s):  
Jason M. South ◽  
Timothy F. Wright
Keyword(s):  
Sex Ratio ◽  
Clutch Size ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Relative Fitness ◽  
Molecular Sexing ◽  
Hatch Date ◽  
Adaptive Modification ◽  
Regional Dialects ◽  
Fitness Benefits

AbstractMany birds, including some parrots, may adjust the sex ratio of their offspring in relation to the relative fitness benefits of sons and daughters. We investigated nestling sex ratios in Yellow-naped Amazons (Amazona auropalliata) using a molecular sexing technique that amplifies intronic regions of the CHD-W and CHD-Z genes in birds. We examined all nestlings in 37 complete clutches comprising 77 chicks. The overall nestling sex ratio did not differ from unity. Sex allocation was not associated with hatch date, sequence of hatching, or clutch size. We also found no difference in sex ratio between two regional dialects. Female Yellow-naped Amazons may be unable to control their hatchling sex ratio. Alternatively, there may be no fitness benefits to females producing more of one sex in relation to the factors we measured here.No Existe Evidencia que Indique Modificaciones Adaptativas de la Proporción de Sexos en la Progenie de Amazona auropalliataResumen. En muchas aves, incluyendo los loros, la proporción de sexos en la progenie puede ajustarse en relación a los beneficios relativos de adecuación biológica de hembras y machos. Dichas tasas fueron investigadas en Amazona auropalliata por medio de una técnica molecular de determinación sexual por la cual se amplifican regiones intrónicas de los genes CHD-W y CHD-Z de aves. Se examinaron todos los pichones de 37 nidadas completas, constituidas por 77 pichones. La proporción de sexos total no resultó diferente a uno. La asignación sexual no estuvo correlacionada con la fecha de eclosión, la secuencia de eclosión, ni el tamaño de la nidada. Tampoco se encontraron diferencias en las proporciones de sexos entre dos dialectos vocales regionales. Las hembras de A. auropalliata podrían no tener la habilidad de controlar la proporción de sexos de su progenie. Alternativamente, es posible que en términos de adecuación biológica, no haya diferencia en el beneficio de producir una progenie enriquecida en un sexo determinado con respecto a los factores medidos en este estudio.

Sex ratio variation in gastrointestinal nematodes of Svalbard reindeer; density dependence and implications for estimates of species composition

Parasitology ◽  
2004 ◽  
Vol 130 (1) ◽  
pp. 99-107 ◽  
Author(s):  
A. STIEN ◽  
M. DALLIMER ◽  
R. J. IRVINE ◽  
O. HALVORSEN ◽  
R. LANGVATN ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Species Composition ◽  
Density Dependence ◽  
Sex Ratios ◽  
Gastrointestinal Nematodes ◽  
Late Winter ◽  
Adult Males ◽  
Svalbard Reindeer ◽  
Ratio Variation ◽  
Adult Sex Ratio

Estimates of the intensity and abundance of species provide essential data for ecological, evolutionary and epidemiological studies of gastrointestinal nematode communities. These estimates are typically derived from the species composition of adult males when only males have readily scorable species-specific morphological traits. Such estimation assumes that all species in the community have the same adult sex ratio. We evaluated this assumption for the trichostrongyle nematodes Ostertagia gruehneri and Marshallagia marshalli in infracommunities in Svalbard reindeer by identifying to species adult females using a polymerase chain reaction assay. The proportion of males was found to be slightly higher in O. gruehneri than in M. marshalli. Evidence for seasonal variation and density dependence in the adult sex ratio was only found for O. gruehneri. Possible demographic mechanisms for such sex ratio variation are discussed, and stochastic models that generate density-dependent sex ratios proposed. Sex ratio variation caused substantial bias in some male-based estimates of intensity of infection, while substantial and consistent bias in estimates of abundances was only evident in late winter samples. Our results suggest that estimating sex ratios can be particularly important in individual host level studies of nematode species of low abundance.

scholarly journals Estimating adult sex ratios in nature

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160313 ◽  
Author(s):  
Sergio Ancona ◽  
Francisco V. Dénes ◽  
Oliver Krüger ◽  
Tamás Székely ◽  
Steven R. Beissinger
Keyword(s):  
Sex Differences ◽  
Sex Ratio ◽  
Evolutionary Biology ◽  
Adult Population ◽  
Sex Ratios ◽  
Estimation Methods ◽  
Spatial And Temporal Variation ◽  
Animal Populations ◽  
Adult Sex Ratio ◽  
Males And Females

Adult sex ratio (ASR, the proportion of males in the adult population) is a central concept in population and evolutionary biology, and is also emerging as a major factor influencing mate choice, pair bonding and parental cooperation in both human and non-human societies. However, estimating ASR is fraught with difficulties stemming from the effects of spatial and temporal variation in the numbers of males and females, and detection/capture probabilities that differ between the sexes. Here, we critically evaluate methods for estimating ASR in wild animal populations, reviewing how recent statistical advances can be applied to handle some of these challenges. We review methods that directly account for detection differences between the sexes using counts of unmarked individuals (observed, trapped or killed) and counts of marked individuals using mark–recapture models. We review a third class of methods that do not directly sample the number of males and females, but instead estimate the sex ratio indirectly using relationships that emerge from demographic measures, such as survival, age structure, reproduction and assumed dynamics. We recommend that detection-based methods be used for estimating ASR in most situations, and point out that studies are needed that compare different ASR estimation methods and control for sex differences in dispersal. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

Changing Sex Ratios: The History of Havasupai Fertility and Its Implications for Human Sex Ratio Variation [and Comments and Reply]

1994 ◽  
Vol 35 (3) ◽  
pp. 255-280 ◽  
Author(s):  
John F. Martin ◽  
E. A. Hammel ◽  
Marvin Harris ◽  
William H. James ◽  
John H. Moore ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Ratio Variation ◽  
History Of

scholarly journals Sex-biased survival predicts adult sex ratio variation in wild birds

2014 ◽  
Vol 281 (1788) ◽  
pp. 20140342 ◽  
Author(s):  
Tamás Székely ◽  
András Liker ◽  
Robert P. Freckleton ◽  
Claudia Fichtel ◽  
Peter M. Kappeler
Keyword(s):  
Sex Ratio ◽  
Phylogenetic Analyses ◽  
Sex Ratios ◽  
Interspecific Variation ◽  
Adult Mortality ◽  
Breeding Systems ◽  
Adult Males ◽  
Wild Populations ◽  
Adult Sex Ratio ◽  
Phylogenetic Hypotheses

Adult sex ratio (ASR) is a central concept in population demography and breeding system evolution, and has implications for population viability and biodiversity conservation. ASR exhibits immense interspecific variation in wild populations, although the causes of this variation have remained elusive. Using phylogenetic analyses of 187 avian species from 59 families, we show that neither hatching sex ratios nor fledging sex ratios correlate with ASR. However, sex-biased adult mortality is a significant predictor of ASR, and this relationship is robust to 100 alternative phylogenetic hypotheses, and potential ecological and life-history confounds. A significant component of adult mortality bias is sexual selection acting on males, whereas increased reproductive output predicts higher mortality in females. These results provide the most comprehensive insights into ASR variation to date, and suggest that ASR is an outcome of selective processes operating differentially on adult males and females. Therefore, revealing the causes of ASR variation in wild populations is essential for understanding breeding systems and population dynamics.

Predicted female bias in sex ratios of hatchling loggerhead sea turtles from a Florida nesting beach

1998 ◽  
Vol 76 (10) ◽  
pp. 1850-1861 ◽  
Author(s):  
JoAnne Hanson ◽  
Thane Wibbels ◽  
R Erik Martin
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Atlantic Coast ◽  
Sea Turtle ◽  
Egg Mass ◽  
Loggerhead Sea Turtles ◽  
Data Loggers ◽  
Egg Chamber ◽  
Incubation Temperatures ◽  
Thermosensitive Period

Incubation temperatures in loggerhead sea turtle (Caretta caretta) nests were examined as a method for predicting hatchling sex ratios. Incubation temperatures were recorded in 40 nests that were laid on Hutchinson Island, Florida. Small temperature data loggers were placed directly in nests (in the center of the egg mass) and were programmed to record temperature every 1.2 h for the entire incubation period. Nests laid during the early, middle, and late portions of the peak nesting period (June and July) were examined. The nests were equally distributed on an untreated beach and a beach that had been artificially supplemented with sand to compensate for erosion. Three nests received multiple data loggers to assess temperature variation within the nest. The average daily temperatures within these nests varied from a maximum of 2.1°C at the top of the egg chamber to a minimum of 0.4°C at the bottom. During the thermosensitive period, temperatures in the center of the egg mass were significantly higher than those at the top and bottom of the egg chamber (average difference was 0.4 and 0.9°C, respectively). Incubation temperatures within all 40 nests were relatively high, suggesting an overall sex ratio that is highly female biased. Using nest temperature during the thermosensitive period as a predictor, the hatchlings from 37 of the 40 nests were predicted to be 100% female (i.e., 92.5% of the nests). The other three nests had been laid adjacent to or in contact with the vegetation bordering the beach and were shaded by the vegetation during the afternoon. Two of these nests were predicted to produce female-biased sex ratios and one was predicted to produce a sex ratio of nearly 1:1. For beaches examined, the sex ratios were highly female-biased; however, nest temperatures on the beach supplemented with sand were significantly higher than those on the untreated beach. The highly biased sex ratio predicted for Hutchinson Island is similar to that estimated for another C. caretta nesting beach located at Cape Canaveral, Florida. These data collectively suggest that C. caretta nesting along the Atlantic coast of Florida consistently produce hatchlings whose sex ratios are distinctly female-biased.

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.

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