Effects of phytoseiid predators on the sex ratio of the spider mite Panonychus ulmi

1991 ◽  
Vol 69 (1) ◽  
pp. 208-212 ◽  
Author(s):  
Dan L. Johnson ◽  
Heather C. Proctor
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Spider Mite ◽  
Total Population ◽  
Panonychus Ulmi ◽  
Encounter Rate ◽  
Male Mortality ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Male Activity

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

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.

Female-biased sex ratio in adults of the turtle Emys orbicularis at the northern limit of its distribution in France: a probable consequence of interaction of temperature with genotypic sex determination

1989 ◽  
Vol 67 (5) ◽  
pp. 1279-1284 ◽  
Author(s):  
J. Servan ◽  
P. Zaborski ◽  
M. Dorizzi ◽  
C. Pieau
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Emys Orbicularis ◽  
Gonad Differentiation ◽  
Adult Sex Ratio ◽  
Probable Consequence ◽  
Genotypic Sex Determination ◽  
Female Genotype ◽  
Biased Sex Ratio ◽  
Female Bias

Adult sex ratio in the turtle Emys orbicularis was determined in populations from seven ponds in Brenne (Indre, France). In all populations, the sex ratio was biased toward females. Among 290 captured animals, the male:female ratio was close to 0.5. Among different demographic factors that could affect the adult sex ratio, the most influential was probably the sex ratio of hatchlings. In Emys orbicularis, a ZZ male/ZW female system of genotypic sex determination has been postulated. Moreover, gonad differentiation is dependent on temperature and sex-reversed individuals can occur. To evaluate the importance of sex reversal among adult females, the blood of 78 animals was typed for the serologically detectable H-Y antigen, used as a tool to identify sexual genotype. In 73 of them, the H-Y phenotype was positive, conforming with female genotype, but in the other 5 females, it was negative (as in genotypic males), revealing that the sexual phenotype of these animals had been inverted. As the percentage of these sex-reversed genotypic males is low, the influence of temperature would appear not to be the sole cause of the observed unbalanced sex ratio. The female bias can be partly explained by the interaction of temperature with the ZZ/ZW system of genotypic sex determination. Indeed, in this system, sexual inversion under the influence of an epigenetic factor increases the ratio of genotypic females (ZW and WW) in the progeny.

Adult survival and recruitment and the explanation of an uneven sex ratio in a tortoise population

1990 ◽  
Vol 68 (3) ◽  
pp. 547-555 ◽  
Author(s):  
Adrian Hailey
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Adult Survival ◽  
Adult Longevity ◽  
Adult Males ◽  
Northern Greece ◽  
Female Population ◽  
Lower Survival Rate ◽  
Adult Sex Ratio ◽  
Testudo Hermanni

Survival, recruitment, and dynamics of adult Testudo hermanni at Alyki (northern Greece) were studied from 1980 to 1988. Recruitment of adult males was greater than that of females owing to their shorter time to maturity (9 vs. 11 years); recruitment of subadults (6 years old) was equal in males and females. Mean annual survival was slightly greater in males (0.914) than females (0.877), equivalent to mean adult longevity values of 11.6 and 8.1 years, respectively. Excluding tortoises that die before maturity, male and female T. hermanni are mature for about 56 and 42% of their life, respectively. Generation time was roughly twice the age at maturity, and three times the age at which secondary sexual characters develop, a pattern which may apply to other tortoises. The combination of adult survival and recruitment should lead to a stable sex ratio (males/females) of 2.1. The adult sex ratio was higher than this, but decreasing, from4.1 in 1982to3.0 in 1986, with an increase in the female population; the number of males was stable. The observed sex ratio showed a similar decline and a further fall to 2.4 in 1988. The cause of the lower survival rate of females compared with males is proposed to be damage during courtship attempts. The courtship behaviour and related anatomy of T. hermanni are compared with those of T. graeca, a species with even population sex ratios. The level of male-induced female mortality would depend on population density; the increasing number of females during the study follows the approximate halving of population density in 1980.

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.

A natural population of the butterfly Eurema hecabe with Wolbachia-induced female-biased sex ratio not by feminization

Genome ◽  
2007 ◽  
Vol 50 (4) ◽  
pp. 365-372 ◽  
Author(s):  
Satoko Narita ◽  
Masashi Nomura ◽  
Daisuke Kageyama
Keyword(s):  
Sex Ratio ◽  
Underlying Mechanism ◽  
Single Nucleotide ◽  
Egg Hatch ◽  
Single Strain ◽  
Eurema Hecabe ◽  
Adult Sex Ratio ◽  
Ratio Distortion ◽  
Biased Sex Ratio ◽  
Sex Ratio Distortion

In butterflies, the adult sex ratio observed in the field is usually male-biased, although the sex ratio of their progeny is 1:1. This is due to the higher motility and larger behavioral range of males than females. As expected, the sex ratio of Eurema hecabe butterflies collected at 6 localities throughout Japan was male-biased. However, in Tsukuba, located in the central part of Japan, the sex ratio was found to be biased toward females. Their progeny reared in the laboratory also exhibited a female-biased sex ratio. A single strain of Wolbachia is considered to be the cause of the sex-ratio distortion, because antibiotic treatment reversed the sex ratio to 1:1, and only a single nucleotide sequence of wsp, a highly variable Wolbachia gene, was detected by molecular analysis. Cytogenetic analysis excluded the possibility of feminization as the underlying mechanism. In addition, when the wild-caught females that had already mated in nature were treated with antibiotics before oviposition, egg-hatch rates were extremely low, suggesting that the same Wolbachia strain also caused cytoplasmic incompatibility. Our findings suggest the possibility that a single strain of Wolbachia induces 2 distinct reproductive manipulations in the same host.

Biased sex ratio and low population density increase male mating success in the bug Nysius huttoni (Heteroptera: Lygaeidae)

2008 ◽  
Vol 96 (1) ◽  
pp. 87-91 ◽  
Author(s):  
Qiao Wang ◽  
Xiong Zhao He ◽  
Linghuan Yang ◽  
Duncan Hedderley ◽  
Lorraine K. Davis
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Mating Success ◽  
Density Increase ◽  
Male Mating ◽  
Male Mating Success ◽  
Biased Sex Ratio

SEX RATIO OF THE EUROPEAN RED MITE, PANONYCHUS ULMI (ACARINA: TETRANYCHIDAE), IN APPLE ORCHARDS IN NOVA SCOTIA

1975 ◽  
Vol 107 (8) ◽  
pp. 825-828 ◽  
Author(s):  
H. J. Herbert ◽  
K. P. Butler
Keyword(s):  
Nova Scotia ◽  
Population Density ◽  
Sex Ratio ◽  
First Generation ◽  
Panonychus Ulmi ◽  
Apple Orchards ◽  
Male And Female ◽  
Average Percentage ◽  
European Red Mite ◽  
Different Levels

AbstractThe number of male and female first generation Panonychus ulmi (Koch) were recorded from 13 apple orchards representing widely different levels of mite infestation on four different varieties. The average percentage of males was 27.5. Statistically significant differences were found among orchards, varieties, observers, and their interactions. No relationship between sex ratio and population density was evident.

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