Effects of hatchery shading and nest depth on the development and quality of Chelonia mydas hatchlings: implications for hatchery management in Peninsular, Malaysia

2005 ◽  
Vol 53 (3) ◽  
pp. 205 ◽  
Author(s):  
Jason van de Merwe ◽  
Kamarruddin Ibrahim ◽  
Joan Whittier
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Natural Populations ◽  
Chelonia Mydas ◽  
Condition Index ◽  
Peninsular Malaysia ◽  
Sex Characteristics ◽  
Poor Correlation ◽  
Emergence Success ◽  
Nest Depth

One of the decisions made by hatchery managers around the world is what degree of shading and nest depth are required to maximise the production of high-quality hatchlings at optimal sex ratios. The primary objectives of this study were to determine the effects of (1) hatchery shading and nest depth on nest temperatures and emergence lag, and (2) nest temperatures and nest depth on hatchling sex ratio and quality. In 2001, 26 Chelonia mydas clutches from Ma’Daerah beach, Terengganu, Malaysia, were relocated alternatively at depths of 50 cm and 75 cm into a 70%-shaded and a 100%-shaded hatchery. Data loggers were placed into the centre of each relocated clutch to record the temperature every hour over the course of incubation. When the hatchlings emerged, a sample of the clutch was run, measured and weighed and a separate sample was examined histologically for sex characteristics. Nest temperatures ranged between 28°C and 30°C and generally showed increases over the second half of incubation due to metabolic heating of the clutch. There was no significant correlation found between nest temperature and any of the hatchling parameters measured. Hatchlings from 75-cm-deep nests had a longer emergence lag (46.4 (±10.2) h) than hatchlings from 50-cm-deep nests. Hatch and emergence success were similar to those of natural populations and hatchling sex ratios were male dominant, with an average of 72% males. There was a poor correlation between mean middle-third incubation temperatures and sex ratio. Hatchlings from 75-cm-deep nests had similar running speeds but lower condition index than their conspecifics from 50-cm-deep nests.

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

scholarly journals Climate change and green sea turtle sex ratio – Preventing possible extinction

2020 ◽  
Author(s):  
Jana Blechschmidt ◽  
Meike J. Wittmann ◽  
Chantal Blüml
Keyword(s):  
Climate Change ◽  
Sex Ratio ◽  
Nest Site ◽  
Sea Turtles ◽  
Chelonia Mydas ◽  
Sea Turtle ◽  
Change Scenario ◽  
Green Sea Turtles ◽  
The Face ◽  
Nest Depth

AbstractClimate change poses a threat to species with temperature-dependent sex determination. A recent study on green sea turtles (Chelonia mydas) at the northern Great Barrier Reef (GBR) showed a highly female-skewed sex ratio with almost all juvenile turtles being female. This shortage of males might eventually cause population extinction, unless rapid evolutionary rescue, migration or conservation efforts ensure a sufficient number of males. We built a stochastic individual-based model inspired by C. mydas, but potentially transferrable to other species with TSD. Nest depth, level of shade, and pivotal temperature were evolvable traits. Additionally, we considered the effect of crossbreeding between the northern and southern GBR, nest-site philopatry, and conservation efforts. Among the evolvable traits, nest depth was the most likely to rescue the population in the face of climate change, but even here the more extreme climate-change scenario led to extinction. Surprisingly, nest-site philopatry elevated extinction rates. Conservation efforts to artificially increase nest depth promoted population survival and did not preclude trait evolution. Although extra information is needed to make reliable predictions for the fate of green sea turtles, our results illustrate how evolution can shape the fate of long lived, vulnerable species in the face of climate change.Graphical Abstract

Sex ratios and survival in fluctuating populations of the deer mouse, Peromyscus mamculatus borealis

1970 ◽  
Vol 48 (4) ◽  
pp. 809-811 ◽  
Author(s):  
Raymond P. Canham
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Deer Mouse ◽  
Sex Ratios ◽  
Natural Populations ◽  
In Captivity ◽  
Males And Females ◽  
Young Of The Year ◽  
Fluctuating Populations ◽  
Number Of Males

In litters of the deer mouse, Peromyscus mamculatus borealis, born in captivity there was a significantly greater number of males than females. In natural populations of the same subspecies, an excess of males caused the sex ratio in captured young of the year to differ significantly from 1:1 only in those summers in which population density increased considerably. The sex ratio did not change appreciably during a winter in which density remained stable, but in winters of low survival the proportion of males declined. A difference between males and females in the amplitude of the fluctuations in postnatal survival thus appeared responsible for variations in the sex ratio.

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

Genetics ◽  
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.

Gametocyte sex ratios as indirect measures of outcrossing rates in malaria

Parasitology ◽  
1992 ◽  
Vol 104 (3) ◽  
pp. 387-395 ◽  
Author(s):  
A. F. Read ◽  
A. Narara ◽  
S. Nee ◽  
A. E. Keymer ◽  
K. P. Day
Keyword(s):  
Sex Ratio ◽  
Evolutionary Biology ◽  
Geometric Mean ◽  
Sex Ratios ◽  
Simple Game ◽  
Natural Populations ◽  
Theory Model ◽  
Indirect Measures ◽  
Epidemiological Surveys ◽  
Outcrossing Rates

The frequency of recombination between unlike genotypes is central to understanding the generation of genetic diversity in natural populations of malaria. Here we suggest a way of investigating the problem which could complement conventional biochemical approaches to the population genetics of malaria. Sex allocation theory is one of the most successful areas of evolutionary biology. A well-supported prediction is that progressively less female-biased sex ratios are favoured with more outcrossing; equal numbers of males and females being evolutionarily stable in randomly mating outbred populations. We present a simple game theory model to support the idea that outcrossing rates in malaria will be correlated with the sex ratio of gametocytes in the peripheral blood of vertebrate hosts. Blood films from epidemiological surveys and culture-adapted isolates from Madang Province, Papua New Guinea, were used to estimate average gametocyte sex ratio of Plasmodium falciparum in the area. The geometric mean proportion of males in the population was 0.18 (95% confidence limits: 0.15–0.22). From our model, we estimate that, on average, 36% of zygotes are the result of outcrossing. This estimate assumes that most microgametes released following exflagellation are capable of fertilization. If, on average, fewer than about 70% of microgametes are capable of fertilization (as is the case in at least one other species of Plasmodium), the observed sex ratio would be consistent with between zero and 36% of zygotes being the result of outcrossing. These estimates suggest that there is usually a numerically dominant genotype in the gametocyte population in a blood meal, and that a considerable amount of selfing is occurring in P. falciparum populations in the Madang region, even though it is an area of intense year-round transmission.

scholarly journals Effect of manipulated sex ratio on insemination of the red mason bee Osmia bicornis L. under net cage conditions

2013 ◽  
Vol 57 (2) ◽  
pp. 73-79 ◽  
Author(s):  
Monika Fliszkiewicz ◽  
Aleksandra Langowska ◽  
Piotr Tryjanowski
Keyword(s):  
Sex Ratio ◽  
Plant Breeding ◽  
Sperm Count ◽  
Sex Ratios ◽  
Natural Populations ◽  
Osmia Bicornis ◽  
Strong Interest ◽  
Female Survival ◽  
Net Cage ◽  
Fruit Plants

Abstract The red mason bee Osmia bicornis L. (Hymenoptera: Megachilidae) is a solitary gregarious species that is known to be a good pollinator of pear, apple, and several other Rosaceae fruit plants. Mainly females are active in plant pollination, and therefore they are of strong interest to farmers. As natural populations are usually male biased, here we studied the possibility of rearing a female-biased population of Osmia bicornis by examining the effects of sex ratio changes on female survival, insemination rate, and sperm count in the spermatheca. Using bees that had completed their winter diapause and were maintained in flying cages, we created three groups with different male:female sex ratios: 1:1, 1:2, and 1:3. The 1:3 sex-ratio group exhibited the best survival of females, but the lowest spermathecae sperm count. The insemination rate did not differ between groups. Our results indicate that-at least among bees housed in isolator cages for plant breeding- skewing the sex ratio towards more females does not affect bee survival, and efficient insemination can be expected with twice as many females as males.

scholarly journals Effects of Selection on the Evolution of the Sex Ratio

1982 ◽  
Vol 35 (1) ◽  
pp. 95 ◽  
Author(s):  
DJ Colgan
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Parental Investment ◽  
Sex Ratios ◽  
Natural Populations ◽  
Viability Selection

Hypotheses as to the biological bases of observed sex ratios must explain the departures found in natural populations from the ratio which might be expected from the mechanism of sex determination in the species. Models based on the concept of parental investment (Fisher 1930) have been used to explain such departures but do not predict equilibrium sex ratios when viability selection discriminates between the sexes in the period between the end of parental investment and the maturity of the offspring.

scholarly journals Sex expression and genotypic sex ratio vary with region and environment in the wetland moss Drepanocladus lycopodioides

2019 ◽  
Vol 192 (2) ◽  
pp. 421-434
Author(s):  
Irene Bisang ◽  
Johan Ehrlén ◽  
Lars Hedenäs
Keyword(s):  
Sex Ratio ◽  
Life Histories ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Environmental Parameters ◽  
Sex Expression ◽  
Ratio Variation ◽  
Female Flowering ◽  
Female Bias

Abstract Sex ratio variation is common among organisms with separate sexes. In bryophytes, sex chromosome segregation at meiosis suggests a balanced progeny sex ratio. However, most bryophyte populations exhibit female-biased phenotypic sex ratios based on the presence of reproductive structures on gametophytes. Many bryophyte populations do not form sexual organs, and genotypic sex ratio variation in such populations is mostly unknown. We tested sex expression, and phenotypic and genotypic sex ratios against environmental parameters in natural populations of the unisexual wetland moss Drepanocladus lycopodiodes at 11 sites in each of three regions in southern Sweden. We identified sex in 660 individual ramets, based on sexual structures, when present, or with a specifically designed molecular marker, when absent. All regions exhibited a female bias in phenotypic and genotypic sex ratios. Sex ratio biases and sex expression differed between regions. Sex ratios were less female-biased in larger patches. Wetter patches exhibited a stronger female bias in genotypic sex ratio and lower sex expression. This is the first evidence of environmental effects on genotypic sex ratio in mosses. A higher frequency of females in wet patches could be due to higher female resource demands for sporophyte production or higher male sensitivity to wetness. A higher incidence of females than males in moister sites aligns with female flowering plants, but differs from reproductive bryophytes in drier environments. Taken together with previous results, our data indicate that sex ratio variation and its drivers differ among species, their life histories and environments.

scholarly journals Turtle mating patterns buffer against disruptive effects of climate change

2012 ◽  
Vol 279 (1736) ◽  
pp. 2122-2127 ◽  
Author(s):  
Lucy I. Wright ◽  
Kimberley L. Stokes ◽  
Wayne J. Fuller ◽  
Brendan J. Godley ◽  
Andrew McGowan ◽  
...  
Keyword(s):  
Climate Change ◽  
Sex Ratio ◽  
Sex Ratios ◽  
Chelonia Mydas ◽  
Marine Turtle ◽  
Male Mating ◽  
Offspring Sex Ratio ◽  
Mating Patterns ◽  
Offspring Sex ◽  
The Impact

For organisms with temperature-dependent sex determination (TSD), skewed offspring sex ratios are common. However, climate warming poses the unique threat of producing extreme sex ratio biases that could ultimately lead to population extinctions. In marine turtles, highly female-skewed hatchling sex ratios already occur and predicted increases in global temperatures are expected to exacerbate this trend, unless species can adapt. However, it is not known whether offspring sex ratios persist into adulthood, or whether variation in male mating success intensifies the impact of a shortage of males on effective population size. Here, we use parentage analysis to show that in a rookery of the endangered green turtle ( Chelonia mydas ), despite an offspring sex ratio of 95 per cent females, there were at least 1.4 reproductive males to every breeding female. Our results suggest that male reproductive intervals may be shorter than the 2–4 years typical for females, and/or that males move between aggregations of receptive females, an inference supported by our satellite tracking, which shows that male turtles may visit multiple rookeries. We suggest that male mating patterns have the potential to buffer the disruptive effects of climate change on marine turtle populations, many of which are already seriously threatened.

scholarly journals Climate Change and Green Sea Turtle Sex Ratio—Preventing Possible Extinction

Genes ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 588 ◽  
Author(s):  
Jana Blechschmidt ◽  
Meike J. Wittmann ◽  
Chantal Blüml
Keyword(s):  
Climate Change ◽  
Sex Ratio ◽  
Nest Site ◽  
Sea Turtles ◽  
Chelonia Mydas ◽  
Sea Turtle ◽  
Climate Change Scenarios ◽  
Population Extinction ◽  
Green Sea Turtles ◽  
Nest Depth

Climate change poses a threat to species with temperature-dependent sex determination (TSD). A recent study on green sea turtles (Chelonia mydas) at the northern Great Barrier Reef (GBR) showed a highly female-skewed sex ratio with almost all juvenile turtles being female. This shortage of males might eventually cause population extinction, unless rapid evolutionary rescue, migration, range shifts, or conservation efforts ensure a sufficient number of males. We built a stochastic individual-based model inspired by C. mydas but potentially transferrable to other species with TSD. Pivotal temperature, nest depth, and shading were evolvable traits. Additionally, we considered the effect of crossbreeding between northern and southern GBR, nest site philopatry, and conservation efforts. Among the evolvable traits, nest depth was the most likely to rescue the population, but even here the warmer climate change scenarios led to extinction. We expected turtles to choose colder beaches under rising temperatures, but surprisingly, nest site philopatry did not improve persistence. Conservation efforts promoted population survival and did not preclude trait evolution. Although extra information is needed to make reliable predictions for the fate of green sea turtles, our results illustrate how evolution can shape the fate of long lived, vulnerable species in the face of climate change.

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