Changes in sex ratio over time in the endangered iguana Cyclura cychlura inornata

2006 ◽  
Vol 84 (10) ◽  
pp. 1522-1527 ◽  
Author(s):  
Geoffrey R. Smith ◽  
John B. Iverson
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Population Estimates ◽  
The Bahamas ◽  
Males And Females ◽  
Two Populations ◽  
Over Time

Changes in sex ratio of a population over time can indicate possible conservation concerns. Using population estimates for males and females, we examined changes in the sex ratio of two populations of the endangered Allen’s Cay Rock Iguana ( Cyclura cychlura inornata Barbour and Noble, 1916) in the Bahamas over nearly 25 years. The sex ratios of both populations changed from strongly male-biased early in the study to nearly 1:1 in recent years. We hypothesize that this shift has occurred because of the recovery of these populations from intense harvesting (particularly of females) over the previous 100 years and, more recently, because of the removal of large males from the islands either by poachers or by tourists.

A new male-killing parasitism:Spiroplasmabacteria infect the ladybird beetleAnisosticta novemdecimpunctata(Coleoptera: Coccinellidae)

Parasitology ◽  
2006 ◽  
Vol 132 (6) ◽  
pp. 757-765 ◽  
Author(s):  
M. C. TINSLEY ◽  
M. E. N. MAJERUS
Keyword(s):  
Phylogenetic Analysis ◽  
Sex Ratio ◽  
High Efficiency ◽  
Sex Ratios ◽  
Egg Hatch ◽  
Hatch Rate ◽  
Male Killing ◽  
Offspring Sex ◽  
Novel Host ◽  
Males And Females

Whilst most animals invest equally in males and females when they reproduce, a variety of vertically transmitted parasites has evolved the ability to distort the offspring sex ratios of their hosts. One such group of parasites are male-killing bacteria. Here we report the discovery of females of the ladybirdAnisosticta novemdecimpunctatathat produced highly female-biased offspring sex ratios associated with a 50% reduction in egg hatch rate. This trait was maternally transmitted with high efficiency, was antibiotic sensitive and was infectious following experimental haemolymph injection. We identified the cause as a male-killingSpiroplasmabacterium and phylogenetic analysis of rDNA revealed that it belongs to theSpiroplasma ixodetisclade in which other sex ratio distorters lie. We tested the potential for interspecific horizontal transfer by injection from an infectedA. novemdecimpunctataline into uninfected individuals of the two-spot ladybirdAdalia bipunctata. In this novel host, the bacterium was able to establish infection, transmit vertically and kill male embryos.

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.

Sex-Ratios and Related Characteristics in Spinifex sericeus (Poaceae)

1990 ◽  
Vol 38 (2) ◽  
pp. 153 ◽  
Author(s):  
KM Maze ◽  
RDB Whalley
Keyword(s):  
Sex Ratio ◽  
New Caledonia ◽  
New South ◽  
Sand Dunes ◽  
Sex Ratios ◽  
Experimental Period ◽  
North Coast ◽  
Male Bias ◽  
South Wales ◽  
Males And Females

Spinifex sericeus R.Br. is a dioecious, stoloniferous grass which occurs on sand dunes around much of the south-eastern coastline of Australia, New Zealand and New Caledonia. Sex ratios of ramets of S. sericeus and some associated characteristics were studied on the mid-north coast of New South Wales. Generally there was a male bias in the observed ramet sex ratio, although the extent of this bias varied with the beach investigated, the position in the dunes and the time of sampling. Male inflorescences matured and died more rapidly than females, and hence the observed male bias was greatest at the beginning of the flowering period. Male ramets were found to have more sexual tillers per clump than female ramets. The genet sex ratio was estimated from plants grown from seed and separated from each other throughout the experimental period. Males and females were found to be equal in number, although this equality may not be a true reflection of the genet sex ratio in the field.

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.

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’.

scholarly journals Best in the company of nearby males: female success in the threatened cycad,Zamia portoricensis

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5252 ◽  
Author(s):  
Julio C. Lazcano-Lara ◽  
James D. Ackerman
Keyword(s):  
Spatial Distribution ◽  
Reproductive Success ◽  
Sex Ratios ◽  
Mate Finding ◽  
Plant Reproductive Success ◽  
Successful Recruitment ◽  
Males And Females ◽  
Plant Pollinator ◽  
Two Populations ◽  
Operational Sex Ratios

Variation in plant reproductive success is affected by ecological conditions including the proximity of potential mates. We address the hypothesis that spatial distribution of sexes affects female reproductive success (RS) in the dioecious cycad,Zamia portoricensis.Are the frequencies of males, operational sex ratios, and distances to the nearest mate associated with RS in females? We studied the spatial distribution of sexes in two populations in Puerto Rico and compared RS of target females with the number of males and operational sex ratios. Population structure suggests regular successful recruitment. Adults, males, and females were randomly distributed with respect to one another. Reproductive success of females was highly variable, but was higher in neighborhoods with more males than females and generally decreased with increasing distance to the nearest male, becoming statistically significant beyond 190 cm. This possible mate-finding Allee effect indicates that pollinator movement among plants may be limited for this mutually dependent plant-pollinator interaction. Yet being close to male plants is a matter of chance, perhaps a factor generating the high intra-population genetic diversity inZ. portoricensis.

scholarly journals Are hermaphrodites better adapted to the colonization process in trioecious populations of Salix myrsinifolia?

2015 ◽  
Vol 84 (2) ◽  
pp. 167-175 ◽  
Author(s):  
Paweł Mirski ◽  
Emilia Brzosko
Keyword(s):  
Sex Ratio ◽  
Reproductive Number ◽  
Vegetative Traits ◽  
Average Share ◽  
Northeastern Poland ◽  
Colonization Process ◽  
Males And Females ◽  
Salix Myrsinifolia ◽  
Two Populations

In trioecious plant populations, the role of hermaphroditism is often uncertain. We investigated the advantages of hermaphroditism in the dioecious shrub <em>Salix myrsinifolia</em>. The sex ratio of 30 <em>S. myrsinifolia</em> populations in northeastern Poland (secondary range) and Lithuania (primary range) was investigated in 2010–2011. Measures of reproductive (number of catkins, number of flowers in catkins) and vegetative traits (height, diameter, number of shoots, vitality) were taken and compared among sexual morphs. In two populations, measurements collected 14 years prior on marked individuals were used to determine the rate of changes in height, crown diameter and survivorship rates. We found trioecy mostly in the secondary part of the range with an average share of hermaphrodites reaching 21% in the trioecious populations. The sex ratio varied between populations, but tended mostly towards female domination. Several traits differed significantly among sexes. The characteristics of hermaphrodites were often intermediate between males and females and provided no evidence for the higher competitive abilities of hermaphrodites. We concluded that the possible gain of hermaphroditism in the colonization process is restricted to reproduction. We consider hermaphroditism in <em>S. myrsinifolia</em> as an equilibrium between the allocation of resources for growth and reproduction in unstable conditions on the margins of the range.

scholarly journals Adolescent school injuries and classroom sex compositions in German secondary schools

2021 ◽  
Author(s):  
Andreas Filser ◽  
Sven Stadtmüller ◽  
Robert Lipp ◽  
Richard Preetz
Keyword(s):  
Sex Ratio ◽  
Secondary Schools ◽  
Risk Taking ◽  
Regression Models ◽  
Sex Ratios ◽  
Peer Groups ◽  
Positive Association ◽  
Logistic Regression Models ◽  
Adolescent Students ◽  
Males And Females

School injuries are an important adolescent health problem. Previous research suggests that relevant risk behaviors for school injuries, risk-taking and aggression, are highly susceptible to peer effects. Specifically, evidence suggests that the ratio of males and females in peer groups (sex ratio) affects individuals’ propensity for aggression and risk-taking. However, research so far has ignored potential associations of classroom sex ratios with adolescent school injury risks. In this paper, we investigate the association of classroom sex compositions with adolescent school injuries in a longitudinal survey dataset containing 13,131 observations from 9,204 adolescent students (ages 13-16) from secondary schools in Germany. The data also allow us to identify injuries that were due to aggressive behavior and analyze these injuries in detail. Results from multilevel logistic regression models reveal that adolescent students’ risk for school injuries is significantly and positively associated with male-skewed classroom sex ratios. Moreover, we find an even stronger positive association between male-dominated classrooms and aggression-injury risks. Finally, we find that both boys’ and girls’ injury risks equally increase with a higher proportion of males in their classroom. We discuss the implications of our findings with regard to the sex ratio literature and potential interventions.

Biology of The Southern Brown Bandicoot (Isoodon Obesulus) In South-Eastern Tasmania. II. Demography.

1998 ◽  
Vol 20 (3) ◽  
pp. 339
Author(s):  
S.A. Mallick ◽  
M.M. Driessen ◽  
G.J. Hocking
Keyword(s):  
Sex Ratio ◽  
Significant Decline ◽  
Home Ranges ◽  
Sexually Dimorphic ◽  
South Eastern ◽  
Live Trapping ◽  
Dry Conditions ◽  
Males And Females ◽  
The Mean ◽  
Two Populations

We used live-trapping to study the demography of two populations of the southern brown bandicoot, Isoodon obesulus, in south-eastern Tasmania from March 1992 to March 1995. The bulk of I. obesulus captures were in woodland/forest or within 3 m of its verge, with &lt;10% of captures in &apos;open&apos; pasture. Densities ranged from 0-0.35 animals/hectare. Both populations underwent a significant decline over the study period. This decline is thought to be the result of the exceptionally dry conditions over the three years of the study. Adult sex ratios (male/female) ranged from 0.6- 1.17. The sex ratio of pouch young was female-biased on both grids (range of 0.53-0.73). Isoodon obesulus were sexually dimorphic, with males being both heavier and larger than females. Only two juveniles were recruited to the populations over the entire three years of the study. Breeding among female I. obesulus was greatest in the December, low in the March, moderate in the September, and absent in the June trapping sessions. Mean litter size was 3.05 ± 0.26, with a range of 1-5 pouch young. For males and females, mean longevity for resident animals was 10.0 ± 3.7 and 13.5 ± 3.3 months, respectively. The mean home range area for the two resident males and the five resident females with ≥8 captures was 6.95 ± 1.95 and 3.28 ± 1.02 hectares, respectively. There was minimal overlap between the home ranges of individual I. obesulus.

Sex ratio, flowering and fruit set in dioecious Rubus chamaemorus (Rosaceae) in Labrador

Botany ◽  
2008 ◽  
Vol 86 (2) ◽  
pp. 204-212 ◽  
Author(s):  
Amanda L. Karst ◽  
Joseph A. Antos ◽  
Geraldine A. Allen
Keyword(s):  
Sex Ratio ◽  
Fruit Set ◽  
Seed Set ◽  
Sex Ratios ◽  
Fruit Production ◽  
Habitat Characteristics ◽  
Rubus Chamaemorus ◽  
Males And Females ◽  
Unpredictable Environment ◽  
Female Flowers

Rubus chamaemorus L. is a dioecious clonal herb with highly variable fruit production. Our overall objective was to determine how fruit production (and the reproductive stages leading to fruit) for R. chamaemorus varied with habitat and population (especially sex ratio) characteristics at scales from 1 m2 quadrats to whole populations in southeastern Labrador, Canada. During the climatically favourable year studied, reproductive variables were only weakly correlated with habitat characteristics. Strongly biased sex ratios were found at scales of 1–10 m. Male-dominated quadrats exhibited a significantly higher proportion of flowering ramets than did female-dominated quadrats. Female-biased sex ratios of flowering ramets and large distances between male and female flowers were correlated with decreased seed set. We found no differences in microhabitats of males and females. Although the biased local sex ratios could limit sexual reproduction, the high fruit set we measured clearly indicates that populations are able to produce abundant fruit during favourable years in this unpredictable environment.

Sign in / Sign up

Export Citation Format

Share Document