Estimated Sex Ratio Research Articles

Sustainable monitoring of roe deer in public hunting areas in the Spanish Pyrenees

Aim of study: Monitoring trends in animal populations is essential for the development of appropriate wildlife management strategies.Area of study: The area is situated in the southern Pyrenees (Aragon), Spain.Material and methods: To measure the abundance, population trends, sex ratio, and mortality of roe deer populations, we analyzed data from i) driven hunts for wild boar (hunting seasons 1995/96 – 2009/10, n = 1,417, ii) itineraries, which were used to calculate the KAI and density using DS (2003 – 2010, n = 310 itineraries), iii) roe deer carcass recoveries (2006 – 2010, n = 100), and iv) data from the deer hunting quota fulfillment (2006 – 2010, n = 325 hunted animals.Main results: Based on DS, in 2010, the average density of roe deer populations was 2.3 km-2 (CV 17%). Based on the KAI and the battues, the estimated average annual rate of increase was 5.8% and 4.3%, respectively. Based on the KAI and the carcass recoveries, the estimates of the population sex ratio were 0.75 (n = 641) and 0.9 (n = 100) males per female, respectively. Carcass recoveries indicated that mortality was highest in late winter and early spring. The average body masses and sizes of males and females were within the ranges reported for other Iberian and European populations.Research highlights: Monitoring should be continued in the Aragon population of roe deer, although larger sample sizes are required to increase the accuracy of estimates and assessments of the impact of management actions.Key words: Capreolus capreolus; hunting bag; distance sampling; KAI; Spain; rangers; long-term monitoring.

Reproduction of tank goby(Glossogobius giuris) in Ujung Pangkah Waters, East Java

<p>Tank goby (<em>Glossogobius giuris</em>) is a commonly fish found in coastal area. This study was aimed to investigate reproduction of the fish. Samples were collected from July to December 2005 from fish caught by fishermen using gill net and trap net in Ujung Pangkah Waters. Analysis was done to estimate sex ratio, gonad maturity, gonado somatic index, fecundity, and oocyte diameter. During the observation, the tank goby fish was 198 individual consisted of 112 male and 86 female fish varied 63‒230 mm in total body length. Sex ratio was around 1:1.1. First maturity gonad of male was 111‒134mm and female was 87‒110 mm total body length, respectively. According to gonad maturity stage and gonado somatic index, the fish was estimated to spawn from July to December. During July and August, the gonad maturity stage and gonado somatic index were higher indicating a lot of spawning fish during those months. Fecundity was 10,640‒150,639eggs and oocyte diameter was 49‒372 µm. Based on the oocyte distribution, the fish was estimated apartial spawner<em>.</em></p> <p>Keywords: Ujung Pangkah Waters, reproduction,tank goby,<em>Glossogobius giuris</em></p>

Sex ratios in naturally incubating Macrochelys temminckii nests, a species with type II temperature-dependent sex determination

The alligator snapping turtle, Macrochelys temminckii, exhibits type II temperature-dependent sex determination (TSD), wherein females are produced at high and low incubation temperatures. This TSD pattern is well studied at constant temperatures, but little work has focused on sex ratios in natural nests that experience daily and seasonal temperature fluctuations. We monitored nesting activity of reintroduced Macrochelys temminckii at Tishomingo National Wildlife Refuge in 2010–2011. Nests located prior to predation were excavated to determine clutch size and the eggs were reburied with a temperature data logger to collect nest temperatures. Overall, 24% of nests were protected with wire mesh prior to predation, and the average clutch size in intact nests was 22.4 eggs. Nest predation rates in the study population will likely approach 100% if nest protection efforts do not continue. Temperature profiles were used to compare estimated sex ratios using two methods—mean nest temperature during middle third of incubation and the degree-day model—to actual sex ratios in naturally incubated Macrochelys temminckii nests. The sex ratio in all 2010 recruits was female-biased (91.8% female); 2011 nests did not produce any hatchlings, likely the result of severe drought. The predicted sex ratios based on mean nest temperature and the degree-day model matched actual sex ratios in the warmer nests (0% male), but the degree-day model estimate proved more accurate in the cooler nest. A strongly skewed population sex ratio could become a threat to this reintroduced population if the strongly female-biased sex ratio in 2010 reflects a long-term trend.

Estimating the sex ratio of green sea turtles (Chelonia mydas) in Taiwan by the nest temperature and histological methods

Sex ratio is an important population characteristic. It is especially important for endangered species with temperature-dependent sex determination, such as sea turtles. As turtle sex ratio at hatching is primarily influenced by the environmental temperature, the ability to estimate sex ratio is crucial to the success of conservation measures. Green turtles (Chelonia mydas) are the only sea turtles that nest in Taiwan. Despite much regional research on the ecology of this species, the sex ratio has not yet been determined in Taiwan. We combined measures of nest temperature during the thermally sensitive period with a histological method to estimate the hatchling sex ratio from three nesting islands in Taiwan from 2010 to 2011. We determined that the sex ratios for green turtle populations in Taiwan were female biased during the study period. In line with that overall trend, Wan-an Island with drier and hotter weather during the nesting season, produced more female hatchlings than the other main nesting island—Lanyu Island. Results of this study stress that differences in sex ratio are important to consider when developing conservation strategies, even among closely located sites such as Wan-an and Lanyu Islands. This is the first study of the hatchling sex ratio of green sea turtles in the East Asian region.

Toward a non-invasive inuit polar bear survey: Genetic data from polar bear hair snags

We explore the feasibility of collecting microsatellite genotypes of non-invasively collected hair from free-ranging polar bears (Ursus maritimus) in M'Clintock Channel, Nunavut, Canada. We estimate the minimum number of individuals in a region of the M'Clintock Channel population and evaluate potential sampling biases associated with corral sampling stations. We optimized 6 variable microsatellite loci for genotyping hair-snag DNA with low genotyping error (mean allelic dropout and false allele error rates <5%). In May of 4 sequential years (2006–2009), we collected 595 hair-snag samples from 145 baited corral sampling stations, from which 319 hair snags were used to detect 59–82 individuals using 4–6 microsatellite loci; we also genetically sexed these individuals. Although genetic sex estimates of matching genotypes are generally in agreement, the estimated sex ratio differs from that previously reported from aerial mark–recapture, which suggests a potential male bias in our sampling stations. These noninvasive methods of identifying individual and sex of bears hold promise for frequent and inexpensive estimates of polar bear population activity informed by Inuit hunters. © 2013 The Wildlife Society.

A highly informative microsatellite panel for individual identification and sex determination of jungle cats (Felis chaus)

The jungle cat (Felis chaus), a small-sized felid, is distributed across Southeast and South Asia to Egypt in Africa. In India, it is one of the most common small cat species but no reliable methods are available to monitor its population status. We describe a non-invasive genetic monitoring technique using fecal samples for individual identification and sex determination of jungle cats. We evaluated 21 feline microsatellites and optimized a panel of 11 highly polymorphic microsatellite loci that yield a cumulative Probability of Identity between siblings value of 5.51910 -6 . We used this panel to identify 110 individuals from 118 jungle cat scats collected from tiger reserves in Central India. We identified 22 males and 35 females by amplifying a fragment of the Amelogenin protein gene. This panel will be helpful to study genetic structure, gene flow, relatedness, sex ratio, and population estimation in jungle cats.

A method for estimating population sex ratio for sage‐grouse using noninvasive genetic samples

Population sex ratio is an important metric for wildlife management and conservation, but estimates can be difficult to obtain, particularly for sexually monomorphic species or for species that differ in detection probability between the sexes. Noninvasive genetic sampling (NGS) using polymerase chain reaction (PCR) has become a common method for identifying sex from sources such as hair, feathers or faeces, and is a potential source for estimating sex ratio. If, however, PCR success is sex-biased, naively using NGS could lead to a biased sex ratio estimator. We measured PCR success rates and error rates for amplifying the W and Z chromosomes from greater sage-grouse (Centrocercus urophasianus) faecal samples, examined how success and error rates for sex identification changed in response to faecal sample exposure time, and used simulation models to evaluate precision and bias of three sex assignment criteria for estimating population sex ratio with variable sample sizes and levels of PCR replication. We found PCR success rates were higher for females than males and that choice of sex assignment criteria influenced the bias and precision of corresponding sex ratio estimates. Our simulations demonstrate the importance of considering the interplay between the sex bias of PCR success, number of genotyping replicates, sample size, true population sex ratio and accuracy of assignment rules for designing future studies. Our results suggest that using faecal DNA for estimating the sex ratio of sage-grouse populations has great potential and, with minor adaptations and similar marker evaluations, should be applicable to numerous species.

High jaguar densities and large population sizes in the core habitat of the southwestern Amazon

Over 80% of the currently occupied range of the jaguar (Panthera onca) lies in the Amazon. However, few density estimates exist for this habitat. Between 2005 and 2010 we carried out six camera trap surveys at three different sites in the department of Madre de Dios in the Peruvian Amazon. We analyzed our data using a Bayesian spatially explicit capture recapture model (SECR) with sex covariates to account for differences in home range size and detection probabilities of male and female jaguars. As several of our camera grids where too small for reliable density estimates, we used estimates for the σ parameter from the largest camera grid to correct for the bias. Density estimates for our surveys were similar with an average density of 4.4±0.7 jaguar 100km−2. Both home range size and encounter rates varied significantly between sexes with males having a larger home range and higher encounter rate than females. Our estimated sex ratio was 1:1.5 compared to an observed ratio of 1.9:1. Not accounting for sex would have resulted in an underestimation of the true density. The densities found in this study are among the highest documented and show that the Amazon is indeed a core habitat for the jaguar. We estimate that three jaguar conservation units in our study region (areas defined by experts as having a high conservation priority) could harbor as many as 6000 jaguars (CI: 4278–8142).

Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects

Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestra- diol-17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher con centrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, sug- gesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages.

Lessons from the use of non-invasive genetic sampling as a way to estimate Eurasian otter population size and sex ratio

Given the difficulties in establishing population parameters of elusive animals in the wild by traditional methods, such as trapping, much attention has been given in recent years to non-invasive genetic sampling. Our work compared estimates of population size and sex ratio derived from genetic sampling with the known number and sex of animals released during an otter reintroduction and reports on the pitfalls and opportunities that may be encountered in studies of this kind. This study makes use of 121 samples of otter spraints (faeces) collected over 7 months during a reintroduction in the Upper Thames (UK) where a total of 17 otters was released in two consecutive phases. Spraints were processed with a multiple tubes approach and seven microsatellites were used. Of all collected samples, 19 % were complete for at least five loci, the minimum required for discrimination between individuals. Six out of nine of the otters that were released in the first phase were detected, four males and two females, while none of the otters released in the second phase was detected probably due to a combination of sampling pitfalls and otter behaviour. In particular, the specific sex (mostly females) and dominance composition (lower) of the individuals in the second release group may explain our failure to detect individuals in this group. Taken together, our results add further evidence that genetic sampling approaches represent a potentially accurate and non-invasive route to census populations of otters but that the sampling design should take into account factors like the sex ratio and dominance composition of the population in order to maximise detection and minimise error.

Population Abundance and Sex Ratio of the Viviparous Freshwater FishPoeciliopsis baenschi(Poeciliidae) Throughout its Range in Western Mexico

We estimated population abundance and sex ratio for a freshwater live-bearing fish species (Poeciliopsis baenschi) that inhabits fluvial systems in western Mexico. We conducted mark-recapture experiments in 6 distinct populations. We used both our catch data as well as estimates of capture probability to calculate the number of individuals per unit water volume for adult males, adult females, and juveniles. Overall, abundance varied among sites from 23.8 individuals · m-3 to 363.2 individuals · m-3. In most of our study sites, the estimated sex ratio was markedly biased toward females (up to 11 females per male). We discuss the potential causes and implications of the observed demographic features.

Sex expression and sex ratios in dwarf male-producing pleurocarpous mosses – have we missed something?

Background: We recently demonstrated that dwarf male plants are much more common among mosses than hitherto thought. Dwarf plants, producing functional male sexual organs occur in 10–20% of the moss species worldwide. Aims: We investigated how an inadvertent omission of dwarf males affects estimates of male sex expression rates and sex ratios. Methods: We recorded frequencies of specimens with female-expressing plants, male-expressing normal-sized and/or dwarf plants, and sporophytes in herbarium material of five model species from Macaronesia. We analysed how frequency estimates of male occurrence and sex ratios were affected by excluding dwarf males. Results: Occurrence of dwarf males was positively associated with sporophyte formation. When dwarf males were excluded, male mate availability was missed in 51–61% of specimens (in 74–76% of sporophyte-containing specimens). Specimen-level sex ratio was balanced in material with sporophytes in the three species exhibiting male dwarfism, but strongly female biased if dwarf males were omitted. Conclusions: We provide the first quantitative evidence that sex-expressing dwarf males are essential for sexual reproduction and sporophyte production in mosses that form such males. Considering its abundance, male dwarfism therefore deserves more attention among plant biologists. Innovative approaches are required to further study the minute male plants.

Child Mortality Estimation: Estimating Sex Differences in Childhood Mortality since the 1970s

Producing estimates of infant (under age 1 y), child (age 1-4 y), and under-five (under age 5 y) mortality rates disaggregated by sex is complicated by problems with data quality and availability. Interpretation of sex differences requires nuanced analysis: girls have a biological advantage against many causes of death that may be eroded if they are disadvantaged in access to resources. Earlier studies found that girls in some regions were not experiencing the survival advantage expected at given levels of mortality. In this paper I generate new estimates of sex differences for the 1970s to the 2000s. Simple fitting methods were applied to male-to-female ratios of infant and under-five mortality rates from vital registration, surveys, and censuses. The sex ratio estimates were used to disaggregate published series of both-sexes mortality rates that were based on a larger number of sources. In many developing countries, I found that sex ratios of mortality have changed in the same direction as historically occurred in developed countries, but typically had a lower degree of female advantage for a given level of mortality. Regional average sex ratios weighted by numbers of births were found to be highly influenced by China and India, the only countries where both infant mortality and overall under-five mortality were estimated to be higher for girls than for boys in the 2000s. For the less developed regions (comprising Africa, Asia excluding Japan, Latin America/Caribbean, and Oceania excluding Australia and New Zealand), on average, boys' under-five mortality in the 2000s was about 2% higher than girls'. A number of countries were found to still experience higher mortality for girls than boys in the 1-4-y age group, with concentrations in southern Asia, northern Africa/western Asia, and western Africa. In the more developed regions (comprising Europe, northern America, Japan, Australia, and New Zealand), I found that the sex ratio of infant mortality peaked in the 1970s or 1980s and declined thereafter. The methods developed here pinpoint regions and countries where sex differences in mortality merit closer examination to ensure that both sexes are sharing equally in access to health resources. Further study of the distribution of causes of death in different settings will aid the interpretation of differences in survival for boys and girls. Please see later in the article for the Editors' Summary.

When to estimate sex ratio in natural populations of insects? A study on sex ratio variations of gall midges within a generation

AbstractPrecise estimation of arthropods' sex ratio is an important issue in a wide range of ecological studies and biological control programs. Although, in many cases changes in arthropods' sex ratio may be under the control of parents or some symbiotic microorganisms, biased sex ratios in some other species are caused by some extrinsic factors, neglect of which may lead to under/overestimation of true sex ratio. In this paper, we pursued those factors that cause false estimation of sex ratio in insects' species. We studied the predatory gall midge, Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), an important biological control agent of aphids, that shows protandry (i.e. early male emergence), differential lifespan of sexes, and differential distribution of sexes across habitat. Ten populations of A. aphidimyza were released separately in transparent cages and their sex ratio variations were recorded every 12 hours. The primary sex ratio in this species seems to be slightly male‐biased (52.41% males), however early emergence of males biases the sex ratio up to 72% males in a few hours after emergence. Shortly after the emergence of females, the sex ratio reaches its primary situation, but as a result of male‐biased mortality after mating, the proportion of females increases gradually to 97% by the fourth and fifth days after emergence. These results explicitly suggest that direct estimation of sex ratio in natural populations may be affected by some secondary factors such as differential mortality of sexes, protandry, and differential distribution of males and females over time and/or across habitat.

Sex ratio of multiple sclerosis in the National Swedish MS Register (SMSreg)

Background: Sex ratio in multiple sclerosis has been reported from several geographical areas. The disease is more common in women. In Europe the female-to-male ratio varies from 1.1 to 3.4. A recent study from Canada has reported a significant increase, with time, in female-to-male ratio in multiple sclerosis over the last 100 years. Objective: The aim of this study was to analyse any change in sex ratio in multiple sclerosis in the Swedish population. Methods: Data from the Swedish MS Register and data from the Swedish National Statistics Office were used to estimate sex ratio by year of birth and year of onset. Results: In the analysis of sex ratio by year of birth there were 8834 patients (6271 women and 2563 men) born between 1931 and 1985. The mean women-to-men ratio was 2.62. No clear trend was noted for the women-to-men ratio by year of birth (Spearman’s rho = 0.345, p = 0.298, n = 11). The number of patients analysed by year of onset was 9098 during the time period 1946 until 2005. The mean women-to-men ratio was 2.57. No significant change in women-to-men ratio (Spearman’s rho = −0.007, p = 0.983, n = 12) with time was observed. Conclusion: There is no evidence for an increasing women-to-men ratio with time amongst Swedish multiple sclerosis patients.

An equal sex ratio followed by differential sex mortality causes overestimation of females in gall midges: no evidence for sex ratio regulation

Monogeny, the production of unisexual broods by individual females, has been recognized for nearly 80 years. The genetic nature of gall midges' sex determination predicts an equal numbers of male-producing and female-producing females in the populations such that the overall sex ratio is expected to be nearly 1:1. However, observations of some strictly monogenous populations with biased sex ratio, mainly toward females, have raised the question of whether gall midges are able to adjust their offspring sex ratio in response to changes in environmental conditions, and some authors have even considered sex ratio regulation as a strong force in the course of the evolution of monogeny. In this paper, first, by studying the sex ratio variations of the predatory gall midge, Aphidoletes aphidimyza within a generation, we showed that adult males emerge up to 1 day earlier and have shorter life span than females (less than 4 days and up to 6 days, respectively). Although, the sex ratio of A. aphidimyza at the time of emergence was nearly 1:1 (52.41% males), a simple population simulation indicated that the differential mortality of sexes can lead to a female-biased sex ratio estimation (57.88% females) under random sampling in the natural environments. Our results imply that the primary sex ratio of monogenous gall midges is nearly 1:1 and that the arrhenogenic/thelygenic gall midges are not able to alter the number of their male/female progenies in response to changes in environmental conditions.

Age, sex ratio, length-weight relationships and reproductive biology of Mediterranean swordfish, Xiphias gladius L., 1758, in the eastern Mediterranean

In this study, a total of 87 swordfish were collected from the Aegean Sea and northern Levantine Sea. The range of the lower jaw fork length was 99.0 to 161.0 cm (mean 15.45 cm) for males and 87.0 to 188.5 cm (mean 26.02 cm) for females. Females were slightly more numerous than males (39 males and 48 females). The estimated sex ratio was calculated as 1.23. The maximum value of gonadsomatic index (GSI) for the males (2.16) and females (10.09) were observed in June and May respectively. High GSI value which were observed in May (10.09) indicated that the female reproductive cycle started depends on the size of the individuals. In the present study, the length-weight relationship was calculated as W = 1x10 -6 L 3, 4627 , R 2 = (0.95). The coefficient “b” was close to positive allometric values (b = 3.46). Total of 48 anal spines (25 males and 23 females) were examined. The ages varied from 1 to 7 and the maximum age was determined as 7. Two-year-old fish were dominant (35.4%).

Estimates of sex ratio require the incorporation of unequal catchability between sexes

Context Estimates of the sex ratio of a population are a common summary statistic used for ecological studies and conservation planning. However, methods to determine the sex ratio often ignore capture probability, which can lead to a perceived bias in the sex ratio when the sexes are detected at different rates. Aims To illustrate the bias from conventional count-based analysis methods for determining sex ratio by comparison with analytical methods that include capture probability. Methods Closed-population mark–recapture analysis was used to determine the population size of each sex within a population of green and golden bell frogs (Litoria aurea). This was then compared with the traditional count-based methods of estimating sex ratio to determine the effect of incorporating capture probability on the sex ratio estimate. Key results More males than females were detected during surveys, producing a male-biased sex ratio when there was no incorporation of capture probability. Mark–recapture results indicated a similar population size between the two sexes, suggesting that the sex ratio is closer to even. Conclusions Methods to estimate sex ratio that incorporate capture probability can significantly reduce the bias obtained from count data. Implications We suggest that population studies must incorporate capture probability to determine the sex ratio of a population.

Sex Ratio Estimation of the Most Eastern Main Loggerhead Sea Turtle Nesting Site: Anamur Beach, Mersin, Turkey

The nesting activities of loggerhead turtles (Caretta caretta) at Anamur Beach, one of their main nesting grounds along the Mediterranean coast of Turkey, were investigated during the 2006 and 2007 nesting seasons. The mean sex ratios were estimated based on gonad histology of dead hatchlings and late stage embryos and were calculated as 72.1% and 79% as females for the years 2006 (n = 366) and 2007 (n = 271), respectively. The nest temperatures of two nests and sand temperatures at nest depths were also recorded by placing electronic temperature recorders into the nests. The recorded sand temperatures were lower when close to the sea and higher towards inland. The mean temperatures of two nests during the entire incubation period were 28.9 and 31.2 °C, with 8 days' difference in their incubation period. Based on mean temperature during the middle third of the incubation period, which ranged from 28.6 to 30.8 °C, the sex ratios were calculated as 49.3% and 79.9% females, respectively. These data are stati...

GETTING PAST NATURE AS A GUIDE TO THE HUMAN SEX RATIO

Sex selection of children by pre-conception and post-conception techniques remains morally controversial and even illegal in some jurisdictions. Among other things, some critics fear that sex selection will distort the sex ratio, making opposite-sex relationships more difficult to secure, while other critics worry that sex selection will tilt some nations toward military aggression. The human sex ratio varies depending on how one estimates it; there is certainly no one-to-one correspondence between males and females either at birth or across the human lifespan. Complications about who qualifies as 'male' and 'female' complicate judgments about the ratio even further. Even a judiciously estimated sex ratio does not have, however, the kind of normative status that requires society to refrain from antenatal sex selection. Some societies exhibit lopsided sex ratios as a consequence of social policies and practices, and pragmatic estimates of social needs are a better guide to what the sex ratio should be, as against looking to 'nature'. The natural sex ratio cannot be a sound moral basis for prohibiting parents from selecting the sex of their children, since it ultimately lacks any normative meaning for social choices.