Variation In Sex Ratio Research Articles

Geographic Variation in Sex Ratios of the US Immigrant Population: Identifying Sources of Difference

This paper describes geographic variation in the sex composition of the foreign-born population in the US since 1990, and uses Blinder-Oaxaca decomposition to identify key sources of variation in regional sex ratios. We use data from the 1990 and 2000 US Censuses, and from the 2007–2011 American Community Survey, to create estimates of the size and characteristics of foreign-born populations at the level of Consistent Public-Use Microdata Areas. We find substantial local- and region-level variation in population sex ratios, with the highest sex ratios in the South and Midwest. This variation is partly explained by differences in the age- and national origin-composition of immigrants, but the effects of immigration history, age, and national origin on sex ratio vary substantially by region. The West in particular stands out as having high levels of unexplained difference from other regions. Future research is necessary to understand these regional differences in gendered immigration patterns.

Demographic causes of adult sex ratio variation and their consequences for parental cooperation

The adult sex ratio (ASR) is a fundamental concept in population biology, sexual selection, and social evolution. However, it remains unclear which demographic processes generate ASR variation and how biases in ASR in turn affect social behaviour. Here, we evaluate the demographic mechanisms shaping ASR and their potential consequences for parental cooperation using detailed survival, fecundity, and behavioural data on 6119 individuals from six wild shorebird populations exhibiting flexible parental strategies. We show that these closely related populations express strikingly different ASRs, despite having similar ecologies and life histories, and that ASR variation is largely driven by sex differences in the apparent survival of juveniles. Furthermore, families in populations with biased ASRs were predominantly tended by a single parent, suggesting that parental cooperation breaks down with unbalanced sex ratios. Taken together, our results indicate that sex biases emerging during early life have profound consequences for social behaviour.

Social context alters host behavior and infection risk

Disease risk is influenced by hosts’ traits and their social environment. We tested how variation in host behavior and group sex ratio alter transmission of a fungal pathogen in Drosophila melanogaster. Hosts varied in behaviors that influence pathogen transmission, though factors of social context were the only predictors of infection risk: more infections were observed in female-biased groups. Social context may therefore be a more powerful predictor of disease risk compared to individual traits.

Revisiting the first report of temperature‐dependent sex determination in a vertebrate, the African redhead agama

AbstractVertebrates display a wide variety of sex‐determining mechanisms (SDMs). Identifying SDMs for different taxa is important for understanding the origins and phylogenetic history of sex‐determining mechanisms. Temperature‐dependent sex determination (TSD) is found in several vertebrate and invertebrate species, and has been studied most extensively in reptiles. The initial discovery of TSD was in a lizard, the African redhead agama (Agama agama), over 50 years ago. The original study of A. agama used only two incubation temperature treatments and had a small sample size, thus it could not fully characterize the pattern of TSD in this species. The goal of this study is to revisit this research to better characterize the pattern of TSD. We also assessed the effect of fluctuating incubation temperatures on offspring sex ratio to provide insight into how variation in offspring sex ratio is produced under natural conditions. After incubating eggs across six constant temperature treatments, we demonstrated that females are produced at relatively cool temperatures and males at warmer temperatures (30°C); fluctuating thermal regimes showed this same pattern. However, some females are again produced at even warmer temperatures, resulting in relatively balanced sex ratios toward the end of the sex‐determining reaction norm. Though the shape of the sex‐determining reaction norm shown here is unusual, it shows some similarities to that of other agamid lizards. Future studies that explore the diversity of TSD reaction norms and underlying physiological mechanisms will provide new insights into the evolution of TSD.

Annual variation in the offspring sex ratio of Saltmarsh Sparrows supports Fisher's hypothesis

ABSTRACT Evolutionary theory suggests that natural selection should favor the ability of animals to modify their offspring sex ratios when the fitness benefits of producing one sex over the other vary in relation to environmental conditions. The Saltmarsh Sparrow (Ammodramus caudacutus) is an extreme habitat specialist, with breeding behavior influenced by the tidal cycle. The challenges of nesting in the harsh environment of salt marshes and the unique promiscuous mating system of the Saltmarsh Sparrow provide a context for offspring sex ratio manipulation. We investigated adaptive sex ratio manipulation in this system across multiple sites and years using a mixed modeling approach. We collected data on nest initiation and nestling survival from 370 nests of 210 females during 2011–2015 in 4 marshes in the northeastern United States. Using molecular techniques, we determined the sex of 990 offspring and characterized variation in site- and population-level sex ratios. Using binomial linear mixed-effects ...

Does Adult Sex Ratio Predict Regional Variation in Facial Dominance Perceptions? Evidence From an Analysis of U.S. States.

When the adult sex ratio of the local population is biased toward women, men face greater costs due to increased direct intrasexual competition. In order to mitigate these costs, men may be more attuned to cues of other men's physical dominance under these conditions. Consequently, we investigated the relationships between the extent to which people ( N = 3,586) ascribed high dominance to masculinized versus feminized faces and variation in adult sex ratio across U.S. states. Linear mixed models showed that masculinized faces were perceived as more dominant than feminized faces, particularly for judgments of men's facial dominance. Dominance perceptions were weakly related to adult sex ratio, and this relationship was not moderated by face sex, participant sex, or their interaction. Thus, our results suggest that dominance perceptions are relatively unaffected by broad geographical differences in adult sex ratios.

Grazing pressure affects offspring sex ratio in a socially monogamous passerine on the Tibet Plateau

Livestock grazing can affect habitat structure and availability of arthropod prey for grassland birds, and ultimately determines habitat quality. The habitat quality may affect breeding strategies (e.g. sex ratio adjustment) in bird species, but studies investigating grazing intensity on offspring sex ratio are still rare. In this paper, we examined the effect of grazing intensity by livestock on the secondary sex ratio of an alpine‐steppe passerine, the isabelline wheatear Oenanthe isabellina, on the Tibet Plateau. Offspring sex ratio of isabelline wheatears significantly correlated with a quadratic term – (grazing intensity)2. The wheatears nesting in areas grazed at low intensity by mixed livestocks produced significantly more sons than those in ungrazed area (0.41 vs 0.58, Z = –2.836, p = 0.005), while brood sex ratios from other treatments (ungrazing vs intensive grazing and low‐intensity grazing vs intensive grazing) did not differ significantly. Variation in offspring sex ratio was not related to other factors such as maternal condition, paternal condition and other two‐way interactions. These results suggest that breeding birds of grasslands are sensitive to variation in habitat conditions, and provide additional evidence that grazing intensity affects avian reproduction in cryptic ways that are rarely studied. Our findings suggest that flexible management including timely rotational grazing is needed to optimize bird species reproduction and maintain ecosystem health.

Hydroxylysine deficiency, conspicuous skeletal lesions and a strange burial practice in a historical German island population

AbstractEighty‐two complete and partial human skeletons were excavated from a burial site on the island of Borkum in the North Sea. The site covers a period of 400 years from the middle of the 14th century AD until 1720 AD. The position of the skeletons in situ suggests rapid disposal of the bodies. About 75% of the skeletons were male and of a quite robust constitution, and about 60% of all individuals died rather young between 20 and 40 years of age. All male skeletons exhibited particular pathological alterations as a result of the typical daily activities of seafaring men, including severe degenerative joint disease and pronounced osteochondropathies. In juvenile skeletons, these pathologies were accompanied by inflammatory processes without exception. Palaeodietary reconstruction by stable isotope analysis resulted in a protein rich diet, confirming fishing as an important part of the subsistence economy. The juveniles derived substantially more protein from plant food than the adults. Bone collagen amino acid profiles were short of hydroxylysine, suggesting that the conspicuous pathological lesions could also have been caused by a systemic connective tissue disease. Possible etiology of the disease is discussed and related to both the uneven sex ratio of the inhumations and the burial context.

Camera‐trapping provides insights into adult sex ratio variability in felids

Abstract Adult sex ratio (ASR) plays a pivotal role in many ecological processes, such as population dynamics in time and space, extinction risk and reproductive success, but few patterns in the variability in ASR have been found across species. Due to the socio‐spatial structure and polygynous mating system found in felids, ASR is expected to be female‐biased in felids in a finite area; however, ASR is also commonly found to be either balanced or male‐biased in this taxonomic group. Therefore, investigating ecological correlates of the pattern of ASR variability in felids is of prime importance both for a better understanding of evolutionary ecology and for a more evidence‐based conservation of these threatened taxa. The aim of this review was to investigate whether the expected female‐biased ASR occurs in felids, and whether ASR is influenced by the size of the study area, the species’ body mass and the population density, taking into account the species‐specific home‐range requirements. We reviewed the camera‐trapping literature on felids to build a large global multi‐species data set on ASR variation. We used general linear mixed models to investigate ecological correlates of ASR. In small study areas, the ASR was balanced for all species, but in large areas the ASR was female‐biased for large and medium cats and male‐biased for small cats; sampling designs that are unsuitable for small cats (due to ‘gaps’ within the trapping grid) might explain this latter finding. Moreover, in large study areas, an increase in cat density was associated with more females, whereas in small areas the reverse was true. Our study provides a scientifically sound background for management and conservation actions of these flagship‐threatened taxa of carnivores, by indicating the importance of the study area on ASR in felids. Large areas can promote the recovery of large and medium cats, as more females can be hosted.

Evidence of oligogenic sex determination in the apple snail Pomacea canaliculata.

A small number of genes may interact to determine sex, but few such examples have been demonstrated in animals, especially through comprehensive mating experiments. The highly invasive apple snail Pomacea canaliculata is gonochoristic and shows a large variation in brood sex ratio, and the involvement of multiple genes has been suggested for this phenomenon. We conducted mating experiments to determine whether their sex determination involves a few or many genes (i.e., oligogenic or polygenic sex determination, respectively). Full-sib females or males that were born from the same parents were mated to an adult of the opposite sex, and the brood sex ratios of the parents and their offspring were investigated. Analysis of a total of 4288 offspring showed that the sex ratios of offspring from the full-sib females were variable but clustered into only a few values. Similar patterns were observed for the full-sib males, although the effect was less clear because fewer offspring were used (n = 747). Notably, the offspring sex ratios of all full-sib females in some families were nearly 0.5 (proportion of males) with little variation. These results indicate that the number of genotypes of the full-sibs, and hence genes involved in sex determination, is small in this snail. Such oligogenic systems may be a major sex-determining system among animals, especially those with variable sex ratios.

Multi-decadal variation in cohort specific sex ratios and otolith increment growth characteristics of juvenile blue grenadier (Macruronus novaezelandiae)

This study presents inter-annual variability of otolith growth from 1993 to 2011 and cohort specific sex ratios from 1976 to 2011 in blue grenadier Macruronus novaezelandiae on the west coast of Tasmania. Length-at-age data highlighted that M. novaezelandiae females grow larger than males with mean length-at-age statistically diverging by three years of age and remaining separated thereafter. Statistical differences in both cumulative, and age specific otolith increment widths-at-age between sexes were detected at earlier ages, but these effects were variable and not consistent with the sexual dimorphism observed for mean length at age. No differences between sexes were evident for the ages 8–14 or 7–11 for cumulative increment widths or age specific otolith increment widths-at-age respectively. Inter-annual variation in mean otolith increment widths for the first five increment zones (juvenile zones) showed a trend of declining increment widths from 2006 to 2010. Inter-annual cohort sex ratio variation across year-of-birth was also significant displaying a similar trend to the first-year otolith increment growth profiles. Regression analysis of birth year sex ratio with mean otolith increment widths indicated a significant negative relationship for first year growth with increasing numbers of male offspring. The inter-annual variation in cohort specific sex ratio suggests that environmental factors may be involved with sex determination. When coupled with climate change these influences could have long term consequences for the fitness of the stock and corresponding flow-on effects into the stock assessment process and future management of the stock.

Comparability in dietary elements, sex ratio and fecundity of portunidae crabs <i>Callinectes amnicola</i> (De Rocheburne) and <i>Portunus validus</i> (Herklots) off Lagos coast

Crabs of the Portunidae family are distinguished by their paddle-shaped fifth pair of legs adapted for swimming and are good source of protein for the coastal communities. A total of 1002 samples (472 specimens of Callinectes amnicola and 530 specimens of Portunus validus) were collected from trawl catches off Lagos Coast and studied for their dietary elements, sex ratio and fecundity. A comparative analysis was done on both Portunidae crabs during the period April to September 2016. From the specimens of C. amnicola examined for food and feeding habits, 110 (23.3%) had empty stomachs while 49 (9.2%) of the P. validus examined had empty stomachs. The diet of crabs studied constituted mainly fishes, crustaceans, molluscs, annelids, plants materials and unidentifiable matter. In both crabs, fishes constituted the dominant food source and these were present in 44.1% and 41.1% of the stomachs analysed for C. amnicola and P. validus respectively. A Chi square (χ2) test for the sex ratio of C. amnicola (1:0.98) was not significant at P<0.05, however, P. validus with sex ratio 1:1.45 showed significant difference. C. amnicola was observed to be a low fecund crab with fecundity estimates varying from 278,000 to 2,150,500 eggs for mature crabs measuring 8.0-14.9 cm carapace length and 58.0 – 125.0 g total body weight, while P. validus was highly fecund with fecundity estimates ranging from 606,400 to 5,300,520 eggs inmatured female crabs measuring 11.0 cm to 18.0 cm carapace length and 270.0 g to 616.0 g total body weight. Conclusively, this study revealed that C. amnicola and P. validus showed similarity in dietary items but variations in sex ratio and fecundity.Keywords: Fecundity, sex ratio, nutrients, Portunidae, Lagos Coast

Genome-wide association study uncovers a novel QTL allele of AtS40-3 that affects the sex ratio of cyst nematodes in Arabidopsis.

Plant-parasitic cyst nematodes are obligate sedentary parasites that infect the roots of a broad range of host plants. Cyst nematodes are sexually dimorphic, but differentiation into male or female is strongly influenced by interactions with the host environment. Female populations typically predominate under favorable conditions, whereas male populations predominate under adverse conditions. Here, we performed a genome-wide association study (GWAS) in an Arabidopsis diversity panel to identify host loci underlying variation in susceptibility to cyst nematode infection. Three different susceptibility parameters were examined, with the aim of providing insights into the infection process, the number of females and males present in the infected plant, and the female-to-male sex ratio. GWAS results suggested that variation in sex ratio is associated with a novel quantitative trait locus allele on chromosome 4. Subsequent candidate genes and functional analyses revealed that a senescence-associated transcription factor, AtS40-3, and PPR may act in combination to influence nematode sex ratio. A detailed molecular characterization revealed that variation in nematode sex ratio was due to the disturbed common promoter of AtS40-3 and PPR genes. Additionally, single nucleotide polymorphisms in the coding sequence of AtS40-3 might contribute to the natural variation in nematode sex ratio.

Measurement and modelling of primary sex ratios for species with temperature-dependent sex determination.

For many oviparous animals, incubation temperature influences sex through temperature-dependent sex determination (TSD). Although climate change may skew sex ratios in species with TSD, few available methods predict sex under natural conditions, fewer still are based on mechanistic hypotheses of development, and field tests of existing methods are rare. We propose a new approach that calculates the probability of masculinization (PM) in natural nests. This approach subsumes the mechanistic hypotheses describing the outcome of TSD, by integrating embryonic development with the temperature-dependent reaction norm for sex determination. Further, we modify a commonly used method of sex ratio estimation, the constant temperature equivalent (CTE), to provide quantitative estimates of sex ratios. We test our new approaches using snapping turtles (Chelydra serpentina). We experimentally manipulated nests in the field, and found that the PM method is better supported than the modified CTE, explaining 69% of the variation in sex ratios across 27 semi-natural nests. Next, we used the PM method to predict variation in sex ratios across 14 natural nests over 2years, explaining 67% of the variation. We suggest that the PM approach is effective and broadly applicable to species with TSD, particularly for forecasting how sex ratios may respond to climate change. Interestingly, we also found that the modified CTE explained up to 64% of variation in sex ratios in a Type II TSD species, suggesting that our modifications will be useful for future research. Finally, our data suggest that the Algonquin Park population of snapping turtles possesses resilience to biased sex ratios under climate change.

Can Economic Pressure Overcome Social Norms? The Case of Female Labor Force Participation

We investigate the potential channels that drive female labor force participation to rise in response to unbalanced sex ratios, in the presence of strong social norms against female employment. One such channel is women's desired labor supply, operating through the marriage market, and the other is employers' de­ mand for female labor. If faced with a reduction in male workforce, do employers turn to women to fill in the gap? Do women enter traditionally male occupations and industries, so that segregation decreases? Does the gender pay gap decline? We exploit exogenous variation in sex ratios across cohorts and regions, by using instruments based on casualties from the Portuguese Colonial War and massive emigration in the 1960s combined with its historical regional patterns. We find that as the sex ratio declined, female participation increased, women entered tra­ traditionally male-dominated occupations and industries, and the gender pay gap declined. These findings are consistent with a demand shock. Our estimated impact of sex ratios on marriage market points to a muted supply channel. We complement the quantitative analysis with an archival case. Our findings help to explain an apparent puzzle, a decades-long high female participation in Portugal, as opposed to the other Southern European countries.

Life history characteristics of the potentially invasive Ponto-Caspian goby Neogobius fluviatilis in natural lakes from its native range (Black Sea region of Turkey)

The aim of this study was to provide baseline data and fill an outstanding knowledge gap in our understanding of factors affecting the invasiveness of the Ponto-Caspian gobiid Neogobius fluviatilis. To this end, the life history traits (as somatic growth and reproduction) of N. fluviatilis were studied in three natural freshwater lakes in its native range. These populations were characterised by slow somatic growth rates, being the slowest reported across all the native and non-native ranges of N. fluviatilis. Ages were recorded to 7 years. Across the three lakes, there was considerable variability in sex ratios and reproductive traits (including length at maturity and fecundity at length and age), revealing considerable interpopulation variability. These data suggest that N. fluviatilis has considerable plasticity in the expression of its life history traits, with this plasticity argued as a key factor in facilitating the ability of N. fluviatilis to establish and invade new waters following introductions.

Evaluation of Effective Number of Breeders and Coancestry among Progeny Produced Using Common Hatchery Mating Strategies

AbstractHatcheries are used as a conservation strategy to supplement native fish populations. Mating strategies used by hatcheries can employ different numbers of males and females, varying sex ratios, and different strategies to mix gametes. Due to sex ratio skew and variation in reproductive success, the effective number of breeders (Nb) contributing gametes to subsequent generations is often significantly less than the total number spawned. Accordingly, mating strategies can affect levels of genetic diversity, coancestry, and, concomitantly, long‐term fitness of hatchery stocks or natural populations into which hatchery fish are placed. Using steelhead Oncorhynchus mykiss, we mimicked six commonly employed hatchery mating regimes. We genotyped both parents and offspring at microsatellite loci and used likelihood‐based estimators implemented in the program COLONY to determine parentage. We calculated the mean and variance in reproductive success for each sex in each mating regime. In addition, we calculated coancestry and the inbreeding effective number of breeding adults for each mating regime to provide guidelines more consistent with the conservation goal of maintaining genetic diversity. Finally, we used the Ryman and Laikre equation to evaluate how estimates of Nb for each mating regime can influence the total effective population size. For all treatments, when gametes from multiple females and/or males were pooled, we found that the mean number of offspring was less for males than females, and there was a significantly higher reproductive variance for males than for females. In addition, when male gametes were pooled, a comparatively lower Nb was estimated. Single‐pair mating regimes and those that limited repeated use of males were most efficient at reducing levels of coancestry and maintaining genetic diversity in a hatchery or other closed populations.

Impact of male alternative reproductive tactics on female costs of sexual conflict under variation in operational sex ratio and population density.

Sexual conflict over mating rate is both pervasive and evolutionarily costly. For females, the lifetime reproductive fitness costs that arise through interactions with potential mates will be influenced by the frequency of such interactions, and the fitness cost of each interaction. Both of these factors are likely to be influenced by variation in operational sex ratio (OSR) and population density. Variation in OSR‐ and density‐dependent male alternative reproductive tactics (ARTs) may be particularly important if the fitness costs that females experience vary with the reproductive tactics that males express. Using a simple model, we consider several examples of OSR‐ and/or density‐dependent variation in male ARTs and the frequency of male–female interactions, and find that variation in the expression of male ARTs has the potential to augment or diminish the costs of frequent male interactions for females. Accurately documenting variation in the expression of male ARTs and associated female fitness costs will benefit future work in this area.

Variations Saisonnières Des Paramètres De Reproduction Et Relation Taille-Poids De Auxis thazard (Lacepède, 1800) Capturé Dans Le Golfe De Guinée Par La Flottille Artisanale Ivoirienne

In this study, the seasonal variation in sex ratio, macroscopic stages of sexual maturity, gonado-somatic ratio, hepatostatic ratio, condition factor, and size-weight relationship in Auxis thazard from Gulf of Guinea were studied from January to December 2016. Sex ratio observed was in favor of males (1: 0,78; X² observed = 20,16 ˃ theoretical X² = 3,84 ; p ˂ 0,05). The variation of maturity stages associated with GSI, HSI, and K during different seasons of the year showed that this specie spawns throughout the year. Length-weight relationship was W = 0,0039 L 3, 4108 (R2 = 0,93 ; N = 291) for males, W = 0,0036 L 3, 4376 (R2 = 0,91 ; N = 227) for females, and W = 0,004 L 3, 4118 (R2 = 0,92 ; N = 519) for the combined sexes. The b value was significantly higher than the theoretical value of 3 for males (t-test, t = 233,218, p ˂ 0,05), for females (t-test, t = 227,776, p ˂ 0,05), and for all individuals (t-test, t = 315,821, p ˂ 0,05). This situation however indicates a faster increase of the fish in weight rather than in length.

Population dynamics of Melanorivulus rossoi, a restricted geographic distribution killifish species

Species of Melanorivulus present behaviour and physiological traits that allow them to live in marginal aquatic habitats. In particular, Melanorivulus rossoi is a small nonannual fish only known from its type locality in the Brazilian Cerrado. In this study, we aimed to characterize the distribution and temporal variation in body size, sex ratio, density, length-weight relationship (LWR) and condition factor (CF) of M. rossoi in its natural habitat. To accomplish this, fish samples were taken monthly for a year using sieve nets every 30 min. Body size of males and females increased throughout the year until early summer. LWR was significant, and general coefficient of determination (r2) was 92%. Juveniles showed negative allometric growth, but adults showed positive allometric growth. Both sexes presented the same tendency of temporal variation in CF, with lower values in October and January and peaks in September and February. Fire occurred in June, but no difference in population parameters was observed after this event. A decrease in the abundance of Melanorivulus was related with an increase in the abundance of Erythrinidae juveniles. This might be explained by an increased predation of this species over the M. rossoi individuals, when the population was reduced to about 30% of that in the previous months. We report four new locations where this species was recorded; thus, similar to most Rivulidae members, M. rossoi has a restricted distribution area and is threatened with extinction. Therefore, our results may be useful in developing management strategies aimed at conservation of this species and its habitat in Brazil.