Sex Ratio and Differential Mortality between the Sexes

1970 ◽  
Vol 104 (936) ◽  
pp. 205-210 ◽  
Author(s):  
Egbert G. Leigh,
Keyword(s):  
Sex Ratio ◽  
Differential Mortality

Sex ratios of Sitodiplosis mosellana (Diptera: Cecidomyiidae): implications for pest management in wheat (Poaceae)

2004 ◽  
Vol 94 (6) ◽  
pp. 569-575 ◽  
Author(s):  
M.A.H. Smith ◽  
I.L. Wise ◽  
R.J. Lamb
Keyword(s):  
Life Cycle ◽  
Sex Ratio ◽  
Sex Ratios ◽  
Adult Emergence ◽  
Differential Mortality ◽  
Sitodiplosis Mosellana ◽  
Single Sex ◽  
Crop Resistance ◽  
Wheat Midge ◽  
Population Average

AbstractSex ratios of populations of the wheat midge Sitodiplosis mosellana Géhin, developing on wheat Triticum aestivum L., were determined at reproduction, adult emergence, and dispersal. The patterns of sex ratio through the life cycle of S. mosellana result from: (i) a genetic mechanism that causes all or nearly all of the progeny of individual females to be a single sex, with an overall sex ratio that is slightly biased at 54–57% females; (ii) a differential mortality during diapause that increases the sex ratio to 60–65% females; (iii) mating which occurs near the emergence site followed by female dispersal which causes the post-dispersal sex ratio to rise to nearly 100% females; and (iv) oviposition which spreads eggs among different plants and assures that the next generation has a local sex ratio close to the population average. These changes in sex ratio through the life cycle have implications for using crop resistance or pheromones to manage S. mosellana, because mating takes place quickly near emergence sites, and because mated females but not males disperse from emergence sites to oviposition sites. Crop refuges used to protect resistance genes against the evolution of virulence by S. mosellana must be interspersed to prevent assortative mating that would occur in separate blocks of resistant and susceptible plants. Monitoring or mating disruption using a pheromone would be ineffective when wheat is grown in rotation with a non-host crop.

scholarly journals Population traits of the burrowing toad Rhinella fernandezae (Gallardo, 1957) (Anura, Bufonidae)

2008 ◽  
Vol 68 (1) ◽  
pp. 137-140 ◽  
Author(s):  
LC. Sanchez ◽  
M. Busch
Keyword(s):  
Sex Ratio ◽  
Size Distribution ◽  
Total Population ◽  
Buenos Aires ◽  
The Other ◽  
Differential Mortality ◽  
Buenos Aires Province ◽  
Country House

Size distribution, sex ratio and use of burrows of the burrowing toad Rhinella fernandezae were studied in Buenos Aires province, Argentina. Two sites separated by approximately 300 m were studied: one was a road next to a swamp, and the other a garden of a country house located further from the swamp. We identified toad burrows, and individuals were sexed, measured and given an individual mark. Burrows were examined in subsequent months after the first sampling to assess the presence of toads. We found significant differences in the size distribution between areas, being the proportion of juveniles greater at the site next to the swamp where the reproduction of the species was observed. This result may suggest that the site located near to the swamp functions as a source habitat of individuals that migrate to the other site, where recruitment would be very scarce. Sex proportion of adults did not differ from 1:1 in neither the total population nor in each site, suggesting that there was not differential mortality by sex. Some toads changed burrows throughout the study period, but there were not differences in the frequency of change between adults and juveniles.

EARLY DIFFERENTIAL MORTALITY IN NEODIPRION SERTIFER (HYMENOPTERA: DIPRIONIDAE)

1974 ◽  
Vol 106 (1) ◽  
pp. 1-10 ◽  
Author(s):  
L. A. Lyons ◽  
C. R. Sullivan
Keyword(s):  
Sex Ratio ◽  
Larval Period ◽  
Differential Mortality ◽  
Neodiprion Sertifer ◽  
Primary Sex Ratio ◽  
Secondary Sex Ratio ◽  
The Difference ◽  
Relationship Of ◽  
The Relationship ◽  
Early Larvae

AbstractIn Neodiprion sertifer (Geoff.), mortality is greater in males than in females in the egg stage and probably also among early larvae, but in the late larval period females are more susceptible. The evidence consists of the difference in mortality between all-male and mixed (male + female) colonies, as well as the relationship of secondary sex ratio to preceding mortality and the number of survivors per colony. The effect of differential mortality on estimation of the primary sex ratio is discussed.

scholarly journals Sex Ratio of Small Hive Beetles: The Role of Pupation and Adult Longevity

Insects ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 133 ◽  
Author(s):  
Anna Papach ◽  
Jérémy Gonthier ◽  
Geoffrey R. Williams ◽  
Peter Neumann
Keyword(s):  
Sex Ratio ◽  
Field Studies ◽  
Differential Mortality ◽  
Adult Longevity ◽  
Published Data ◽  
Larval Feeding ◽  
Intraspecific Interactions ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Small Hive Beetles

The sex ratio of sexually reproducing animal species tends to be 1:1, which is known as Fisher’s principle. However, differential mortality and intraspecific competition during pupation can result in a biased adult sex ratio in insects. The female-biased sex ratio of small hive beetles (SHBs) is known from both laboratory and field studies, but the underlying reasons are not well understood. Here, we used laboratory mass and individual pupation to test if differential mortality between sexes and/or intraspecific interactions can explain this sex ratio. The data show a significant female-biased adult sex ratio in both mass and individual rearing, even when assuming that all dead individuals were males. Our results therefore suggest that neither differential mortality during pupation nor intraspecific interactions are likely to explain the female-biased sex ratio of freshly emerged adult SHBs. We regard it as more likely that either competition during the larval feeding stage or genetic mechanisms are involved. In addition, we compared our data with previously published data on the sex ratio of both freshly emerged and field-collected SHBs to investigate possible gender differences in adult longevity. The data show a significantly greater female bias in the sex ratio upon emergence, compared to field-collected SHBs, suggesting that adult females have a shorter longevity.

Unexpected offspring sex ratios in response to habitat quality in a size-dimorphic bark beetle

1999 ◽  
Vol 77 (4) ◽  
pp. 524-529 ◽  
Author(s):  
Risa D Sargent ◽  
Mary L Reid
Keyword(s):  
Body Size ◽  
Reproductive Success ◽  
Sex Ratio ◽  
Habitat Quality ◽  
Bark Beetle ◽  
Sex Ratios ◽  
Diploid Species ◽  
Differential Mortality ◽  
Male Reproductive Success ◽  
Offspring Sex

Facultative sex ratio manipulation has been examined in a limited number of diploid species, mainly vertebrates. We tested the prediction that mothers would preferentially place males in conditions conducive to large size in the diploid pine engraver bark beetle, Ips pini. In this species, males are the larger sex and therefore male reproductive success was expected to be more dependent on body size than female reproductive success. Because body size is largely environmentally determined in bark beetles, mothers were expected to alter sex ratios in response to habitat quality. Contrary to predictions, offspring sex ratios tended to be more female biased in situations conducive to large offspring size than in situations producing offspring of small size. We were able to rule out nonadaptive explanations such as differential mortality or development times of males and females, suggesting that the observed pattern is adaptive. This study provides a rare example of sex ratio manipulation in diploid insects. However, the unexpected direction of sex ratio biases suggests that daughters gain a yet unknown benefit from being reared in high-quality conditions that surpasses the fitness that would be gained from producing relatively larger sons.

Some Factors that Distort the Sex Ratio of the Gypsy Moth Porthetria dispar (L.) (Lepidoptera: Lymantriidae)

1963 ◽  
Vol 95 (5) ◽  
pp. 465-474 ◽  
Author(s):  
Robert W. Campbell
Keyword(s):  
New York ◽  
Sex Ratio ◽  
Gypsy Moth ◽  
Larval Density ◽  
Mortality Factor ◽  
Differential Mortality ◽  
Porthetria Dispar ◽  
Population Consequences ◽  
Adult Sex Ratio ◽  
The Town

AbstractDuring a study on the population dynamics of the gypsy moth, Porthetria dispar (L.), conducted in the Town of Glenville, New York, some factors were found to affect the sexes differentially. The importance of this differential mortality is indicated by the fact that 78 per cent of the variation in the logarithm of an index of population trend (the ratio of population density from year to year) was associated with the logarithm of adult sex ratio.Disease and desiccation during instars IV-VI and among pre-pupae were strongly selective against the female insects. This differential mortality caused a change in the pupal sex ratio from about 70 per cent females where no disease occurred to less than 25 per cent female pupae following an epizoötic. Ichneumonids, on the other hand, usually killed more male pupae than females, except when host size was reduced by excessive larval density and competition. The net result from this series of factors that distort the sex ratio has been to produce adult sex ratios varying from more than 80 per cent female moths to only 2 per cent females.In this host species, as in most other animals, it seems that the population consequences of a mortality factor that kills the host sexes in different proportions should be evaluated in terms of the more critical (female) sex destroyed.

Male-biased adult sex ratios in a red squirrel population

1987 ◽  
Vol 65 (5) ◽  
pp. 1284-1286 ◽  
Author(s):  
T. Andrew Hurly
Keyword(s):  
Sex Ratio ◽  
Habitat Use ◽  
Sex Ratios ◽  
Sexual Differences ◽  
Differential Mortality ◽  
Red Squirrel ◽  
Red Squirrels ◽  
Male Mortality ◽  
Adult Sex Ratio ◽  
Sampling Biases

A 3-year study of a red squirrel population revealed that the adult sex ratio was biased towards males. There is no evidence that the skewed sex ratio was prejudiced by sampling biases due to sexual differences in mobility, observability, trappability, or habitat use. The tertiary juvenile sex ratio was even and therefore not the cause of the biased adult sex ratio. The data suggest that the skewed sex ratio may be the result of differential mortality. This is consistent with other reports of higher female than male mortality in red squirrels.

scholarly journals Reproduction, infant survival and productivity of a colony of common marmosets (Callithrix jacchus jacchus)

1982 ◽  
Vol 16 (1) ◽  
pp. 88-97 ◽  
Author(s):  
Trevor B. Poole ◽  
Rosemary G. Evans
Keyword(s):  
Linear Regression ◽  
Sex Ratio ◽  
Relative Efficiency ◽  
Differential Mortality ◽  
Interbirth Interval ◽  
Breeding Methods ◽  
Infant Survival ◽  
Common Marmosets ◽  
Annual Increase ◽  
The Mean

Starting with 4 pairs of marmosets, 204 young were successfully reared during 6 years. They were kept in family groups of 2-10. Litter size varied from 1-4; singletons (2%), twins (35%), triplets (55%), and quadruplets (8%). The mean annual increase of weaned young was 3·24 per pair. The median interbirth interval was 154 days. Of 46 pairs of marmosets, 8 failed to produce young. Approximately 11% of young born were stillborn and a further 32% of all young born died within 3 weeks; perinatal mortality is largely a result of the failure of parents to rear more than 2 young. In only 2 of 68 triplet births did the parents rear the young unaided. 53% of young born were males but differential mortality reduced the final sex ratio for live young to 50·5% males. Females did not accept and rear the young after caesarian sections. The linear regression of the growth curve from 5-17 months (where y = weight in grams and x = months) could be expressed as y = 16·6 x + 163·6. The data from 4 marmoset colonies are compared and the relative efficiency of breeding methods discussed.

Demography, sex ratio, and sexual size dimorphism in a northern population of common musk turtles (Sternotherus odoratus)

1996 ◽  
Vol 74 (5) ◽  
pp. 918-925 ◽  
Author(s):  
Jonathan H. Edmonds ◽  
Ronald J. Brooks
Keyword(s):  
Sex Ratio ◽  
Sexual Size Dimorphism ◽  
Differential Mortality ◽  
Adult Males ◽  
Differential Growth ◽  
Size Dimorphism ◽  
Georgian Bay ◽  
Differential Movement ◽  
Sternotherus Odoratus ◽  
Biased Sex Ratio

A population of common musk turtles (Sternotherus odoratus) was studied in Georgian Bay, Ontario, near the northern limit of the species' range, during the summers of 1991–1994. A total of 314 (229 adult males, 68 adult females, and 17 juveniles) turtles were captured, marked, measured, and released. Over the geographic range of S. odoratus there was a positive relationship between body size and latitude, the musk turtles of the Georgian Bay population being significantly larger than those in any of the more southerly populations. The sex ratio was significantly male-biased, and the study population was unique in having sexual size dimorphism, with significantly larger males. We have hypothesized that this dimorphism has arisen through sexual selection that is being driven by the male-biased sex ratio. Male–male competition for mates is intensified and thereby selects for larger males. Proximately, biased sex ratios and sexual size dimorphism in turtles have been attributed to differential ages and sizes at sexual maturity. However, we found no support for this hypothesis in our population. We have attributed sexual size dimorphism to either differential growth rates after maturity or differential mortality of adults. The male-biased sex ratio may be due to differential movement patterns, differential mortality of the sexes, or the effects of ambient temperature on sex determination.

Sex ratio and mortality in a laboratory colony of the common marmoset (Callithrix jacchus)

1992 ◽  
Vol 26 (2) ◽  
pp. 88-99 ◽  
Author(s):  
Hartmut Rothe ◽  
Kurt Darms ◽  
Andreas Koenig
Keyword(s):  
Sex Ratio ◽  
Common Marmoset ◽  
Callithrix Jacchus ◽  
High Ratio ◽  
Differential Mortality ◽  
Common Marmosets ◽  
Laboratory Colony ◽  
Filial Generation ◽  
The Common ◽  
Males And Females

In a retrospective study sex ratio and mortality were analysed in a captive colony of common marmosets ( Callithrix jacchus). Seven hundred and thirty-five infants in 294 litters (20 singletons, 119 twins, 140 triplets, 14 quadruplets) out of 57 breeding females were evaluated. The sex ratio at birth was 0·95 males: 1·0 females. The frequency of males and females, as well as the sex composition of twins and triplets confirm the assumption of dizygotic twinning in the common marmoset. According to age at death, 9 categories were differentiated, with perinatal mortality being the highest. Once early infancy had passed the probability of a common marmoset infant of our colony reaching childhood is nearly 95%. Sixty per cent of all live-born infants survived beyond 18 months. Morta1ity of infants at birth from primiparous mothers did not differ from that of pluriparous females, nor did the survival rate of infants with the filial generation the respective female had reached (F1 to F6). Females with a high ratio of triplets and quadruplets had a lower reproductive success than females with a majority of singleton or twin deliveries. Differential mortality between males and females was not observed. The frequency of stillbirths was not strongly related to parity, but was to litter-size. Most stillborn babies were seen in sets of quadruplets, most abortions in singletons. A normal socialization in a stable social environment, as well as not pairing the animals before they are fully adult, are considered important factors in good breeding success and infant survival.

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