Discord between field and laboratory sex ratios of the water mite Neumania papillator Marshall (Acari: Unionicolidae)

1992 ◽  
Vol 70 (12) ◽  
pp. 2483-2486 ◽  
Author(s):  
Heather C. Proctor
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Sex Ratios ◽  
Differential Susceptibility ◽  
Environmental Sex Determination ◽  
Water Mite ◽  
Southern Ontario ◽  
Field Samples ◽  
Biased Distribution

I regularly sampled a pond in southern Ontario throughout the ice-free season in 1990 to determine adult phenology of the water mite Neumania papillator. Adult mites were present from 23 April to 9 November. Sex ratios in field samples were strongly male biased from 25 June to 2 November; however, mites raised from deutonymphs (juveniles) in the laboratory showed strongly female-biased sex ratios. Experiments indicated that differences in field and laboratory sex ratios could not be explained by differential susceptibility of the sexes to predation or starvation. Sex-biased distribution or trappability, or environmental sex determination may explain sex-ratio differences.

scholarly journals Do Covariances Between Maternal Behavior and Embryonic Physiology Drive Sex-Ratio Evolution Under Environmental Sex Determination?

2019 ◽  
Vol 110 (4) ◽  
pp. 411-421 ◽  
Author(s):  
Fredric J Janzen ◽  
David M Delaney ◽  
Timothy S Mitchell ◽  
Daniel A Warner
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Environmental Conditions ◽  
Oviposition Behavior ◽  
Thermal Sensitivity ◽  
Sex Ratios ◽  
Theoretical Work ◽  
Environmental Sex Determination ◽  
Turtle Species ◽  
Primary Sex Ratio

Abstract Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to 2 traits predicted to be responsive to sex-ratio selection: 1) maternal oviposition behavior and 2) sensitivity of embryonic sex determination to environmental conditions, and much research has since focused on how these traits influence offspring sex ratios. However, relatively few studies have provided estimates of univariate quantitative genetic parameters for these 2 traits, and the existence of phenotypic or genetic covariances among these traits has not been assessed. Here, we leverage studies on 3 species of reptiles (2 turtle species and a lizard) with temperature-dependent sex determination (TSD) to assess phenotypic covariances between measures of maternal oviposition behavior and thermal sensitivity of the sex-determining pathway. These studies quantified maternal behaviors that relate to nest temperature and sex ratio of offspring incubated under controlled conditions. A positive covariance between these traits would enhance the efficiency of sex-ratio selection when primary sex ratio is unbalanced. However, we detected no such covariance between measures of these categories of traits in the 3 study species. These results suggest that maternal oviposition behavior and thermal sensitivity of sex determination in embryos might evolve independently. Such information is critical to understand how animals with TSD will respond to rapidly changing environments that induce sex-ratio selection.

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.

scholarly journals Fisher vs. The Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms That Produce Them

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1793
Author(s):  
Justin Van Goor ◽  
Diane C. Shakes ◽  
Eric S. Haag
Keyword(s):  
Sex Ratio ◽  
Sperm Competition ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Environmental Sex Determination ◽  
Fitness Advantage ◽  
Selection For ◽  
Facultative Parthenogenesis ◽  
Multicellular Organisms ◽  
Inbred Populations

Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two “seminal” contributions of G. A. Parker. 

scholarly journals Analysis of the sex ratio in Bradysia matogrossensis (Diptera, Sciaridae)

2000 ◽  
Vol 23 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Lincoln S. Rocha ◽  
André Luiz P. Perondini
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
X Chromosome ◽  
Control Mechanism ◽  
Sex Ratios ◽  
Laboratory Strain ◽  
Chromosome Elimination ◽  
Common Control ◽  
Males And Females ◽  
Successive Generations

In sciarid flies, the control of sex determination and of the progeny sex ratio is exercised by the parental females, and is based on differential X-chromosome elimination in the initial stages of embryogenesis. In some species, the females produce unisexual progenies (monogenic females) while in others, the progenies consist of males and females (digenic females). The sex ratio of bisexual progenies is variable, and departs considerably from 1:1. Bradysia matogrossensis shows both monogenic and digenic reproduction. In a recently established laboratory strain of this species, 15% of the females were digenic, 10% produced only females, 13% produced only males, and 62% produced progenies with one predominant sex (33% predominantly of female and 29% predominantly male progenies). These progeny sex ratios were maintained in successive generations. Females from female-skewed progenies yielded female- and male-producing daughters in a 1:1 ratio. In contrast, daughters of females from male-skewed progenies produce bisexual or male-skewed progenies. The X-chromosome of B. matogrossensis shows no inversion or other gross aberration. These results suggest that the control of the progeny sex ratio (or differential X-chromosome elimination) involves more than one locus or, at least, more than one pair of alleles. The data also suggest that, in sciarid flies, monogeny and digeny may share a common control mechanism.

scholarly journals Does sex-ratio selection influence nest-site choice in a reptile with temperature-dependent sex determination?

2013 ◽  
Vol 280 (1772) ◽  
pp. 20132460 ◽  
Author(s):  
Timothy S. Mitchell ◽  
Jessica A. Maciel ◽  
Fredric J. Janzen
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Nest Site ◽  
Sex Ratios ◽  
Temperature Dependent ◽  
Dioecious Species ◽  
Offspring Sex Ratio ◽  
Nest Sites ◽  
Offspring Sex ◽  
Nest Site Choice

Evolutionary theory predicts that dioecious species should produce a balanced primary sex ratio maintained by frequency-dependent selection. Organisms with environmental sex determination, however, are vulnerable to maladaptive sex ratios, because environmental conditions vary spatio-temporally. For reptiles with temperature-dependent sex determination, nest-site choice is a behavioural maternal effect that could respond to sex-ratio selection, as mothers could adjust offspring sex ratios by choosing nest sites that will have particular thermal properties. This theoretical prediction has generated decades of empirical research, yet convincing evidence that sex-ratio selection is influencing nesting behaviours remains absent. Here, we provide the first experimental evidence from nature that sex-ratio selection, rather than only viability selection, is probably an important component of nest-site choice in a reptile with temperature-dependent sex determination. We compare painted turtle ( Chrysemys picta ) neonates from maternally selected nest sites with those from randomly selected nest sites, observing no substantive difference in hatching success or survival, but finding a profound difference in offspring sex ratio in the direction expected based on historical records. Additionally, we leverage long-term data to reconstruct our sex ratio results had the experiment been repeated in multiple years. As predicted by theory, our results suggest that sex-ratio selection has shaped nesting behaviour in ways likely to enhance maternal fitness.

scholarly journals Extraordinarily precise nematode sex ratios: Adaptive responses to vanishingly rare mating options

2021 ◽  
Author(s):  
Justin Van Goor ◽  
Edward Allen Herre ◽  
Adalberto Gomez ◽  
John D Nason
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Nematode Species ◽  
Environmental Sex Determination ◽  
Adaptive Responses ◽  
Wasp Species ◽  
Population Structures ◽  
Subdivided Populations ◽  
Sex Ratio Theory ◽  
Evolutionary Persistence

Sex ratio theory predicts both mean sex ratio and variance under a range of population structures. Here, we compare two genera of phoretic nematodes (Parasitodiplogaster and Ficophagus spp.) associated with twelve fig-pollinating wasp species in Panama. The host wasps exhibit classic Local Mate Competition: only inseminated females disperse from natal figs, and their offspring form mating pools that consist of scores of the adult offspring contributed by one or a few foundress mothers. In contrast, in both nematode genera, only sexually undifferentiated juveniles disperse, and their mating pools routinely consist of eight or fewer adults. Across all mating pool sizes, the sex ratios observed in both nematode genera are consistently female-biased (~0.34 males), which is markedly less female-biased than is often observed in the host wasps (~0.10 males). In further contrast with their hosts, variances in nematode sex ratios are also consistently precise (significantly less than binomial). The constraints associated with predictably small mating pools within highly subdivided populations appear to select for precise sex ratios that contribute both to the reproductive success of individual nematodes, and to the evolutionary persistence of nematode species. We suggest that some form of environmental sex determination underlies these precise sex ratios.

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