Female-biased Sex Ratio Research Articles

Aggression in a western Amazonian colonial spider, Philoponella republicana (Araneae: Uloboridae)

Group-living spiders are rare, and can be divided into multiple subcategories based on their tolerance of group mates. While social spiders are cooperative, colonial spiders are often antagonistic towards conspecifics. We examined colony dynamics in a colonial species, Philoponella republicana (Simon, 1891), focusing on aggressive behaviors to further understand this understudied species. We studied whether web region, sex ratio, web size, or spider size affected aggression. We also tested whether colony members discriminate against conspecific intruders, since this behavior, known as group closure, is prevalent in many other group-living animals but had not yet been tested in colonial spiders. Colony mates were often aggressive due to competition for limited resources, such as mates and orb webs, yet several characteristics of this species may reduce these competitive forces. First, female-biased secondary sex ratios appear to reduce male-male and female-male competition. Moreover, although some individuals defended orb webs, other areas in the communal web were not defended. Philoponella republicana also did not exhibit group closure. Our results further confirm that aggression between males decreases in colonies with more female-biased secondary sex ratios, and larger individuals correlate with a higher frequency of aggressive interactions. Moreover, we raise new questions concerning the evolutionary pressures that shape coloniality in spiders.

A haplodiploid mite adjusts fecundity and sex ratio in response to density changes during the reproductive period.

Population density is one of the main socio-environmental factors that have critical impacts on reproduction of animals. Consequently, they need to adjust their reproductive strategies in response to changes of local population density. In this study we used a haplodiploid spider mite, Tetranychus ludeni Zacher (Acari: Tetranychidae), to test how population density dynamics during the reproductive period altered female reproductive performance. We demonstrate that females produced fewer eggs with a significantly higher female-biased sex ratio in dense populations. Reducing fecundity and increasing daughter production in a dense environment could be an advantageous strategy to minimise the intensity of local food competition. However, females also reduced their fecundity after arrival in a new site of larger area from a dense population, which may be associated with higher web production costs because females need to produce more webs to cover the larger area. There was no trade-off between egg number and size, and egg size had little impact on reproductive fitness. Therefore, T. ludeni females could adapt to the shift of population density during their reproductive period by manipulating the fecundity and offspring sex ratio but not the egg size.

Comparative biology of the grenadiers Macrourus caml and M. whitsoni in the Ross Sea region, Antarctica

The grenadiersMacrourus camlandM. whitsoniform a significant bycatch component of longline fisheries for Antarctic toothfish (Dissostichus mawsoni) in the Southern Ocean. A lack of species-level biological and catch data has to date hindered the development of quantitative assessments for these deepwater species. This paper examines species- and sex-specific life histories ofM.camlandM.whitsoniin the Ross Sea region, Antarctica, from samples collected from the commercial fishery and research collections.Macrourus camlwas found to live longer, grow slower, and attain a larger maximum length thanM.whitsoni, reaching at least 65 years of age and 97 cm total length (TL) vs. 43 years and 78 cm TL forM.whitsoni. In addition,M.camlattains a larger length for a given age and a greater weight for a given length. For each species, females of a given age were larger and reached a greater maximum age than males. Assuming that selectivity of the fishing gear is related to fish size, greater fishing pressure on females than males is likely, and was evidenced by female-biased sex ratios of both species. Estimates of natural and fishing mortality rates were low for both species. Despite having a shorter lifespan and attaining a smaller maximum length,M.whitsonimatured later in life and at larger lengths thanM.caml. Although sampling opportunities are constrained seasonally due to sea ice cover, gonad staging and interannual patterns in gonadosomatic indices suggest prolonged spawning for both species, with available data indicating peak spawning during austral summer. The differences in life history observed between these two closely related and morphologically similar species illustrates the importance of understanding species-specific life histories to infer responses to exploitation, provide key biological inputs to inform parameters for future risk assessments and ecosystem models as well as baseline information for comparative work over both time and space, contribute to greater clarity in managing fisheries that interact with these two species, and further our understanding of grenadier life history.

Effects of social and environmental contexts on multi-male mating and mixed paternity in socially monogamous female prairie voles.

With whom and how often to mate are fundamental questions that impact individual reproductive success and the mating system. Relatively few studies have investigated female mating tactics compared with males. Here, we asked how differential access to mates influences the occurrence of mixed paternity and overall reproductive success in socially monogamous female prairie voles (Microtus ochrogaster). We created male- and female-biased sex ratios of prairie voles living in semi-natural outdoor enclosures. We ran paternity analyses to determine the identity and number of mating partners females had and the number of offspring produced. We found that 57.1% of females had litters fathered by two or more males when males outnumbered females, and 87.5% of females had litters with more than one father when females outnumbered males. However, the percentage of mixed paternity and the total number of embryos were not statistically different between social contexts. We determined that female fecundity (i.e. number of embryos) correlated with the number of male fathers in each litter across social contexts. Although our study did not support the hypothesis that social context directly influences female mating decisions, it did suggest that female multi-male mating might lead to increased fertilization success under semi-natural conditions.

Ecology of Indian wolf Canis lupus pallipes in the Great Indian Bustard Sanctuary, Nannaj, Solapur, Maharashtra, India

The Indian wolf, Canis lupus pallipes is an endangered carnivore of India listed in Schedule-1 of the Indian Wildlife (Protection) Act, 1972. There is not much information available on the species and with this perspective, the present study was initiated in the Great Indian Bustard Sanctuary in Maharashtra. Direct and indirect evidences were used to assess its population status and distribution, habitat use, feeding ecology, denning behaviour and wolf-human conflict emanating due to livestock depredation. Intensive ecological and behavioural studies were conducted at Nannaj on one pack between 1991 and 1994. The wolf survives all over the Sanctuary, which is densely populated by humans as elsewhere in its distribution range in India where wolf-human conflicts are common arising either due to livestock depredation or child-lifting. Usually, large packs were present in Blackbuck Antilope cervicapra areas whereas smaller packs inhabited areas not supporting healthy populations of Blackbuck. In Blackbuck poor areas, the wolf survived mainly on livestock. The Sanctuary supports 40-58 wolves. The wolves had a seasonal pattern of habitat use related to movement of prey and livestock. Wolves selected those areas as rendezvous sites which had higher prey density, vegetation cover, minimum human disturbance and were located close to water source. On an average wolves consumed 3.68 (S.E.=0.17) kg/wolf/kill and kill periodicity was 3.65 days (S.E.=0.58). Wolves preyed largely on blackbuck during the non-breeding period and livestock during denning period. Predation was higher on male blackbuck than females despite female biased sex ratio. The average litter size of three packs was recorded to be 5 (range 4-6). The dominant male and female wolves guarded the dens more often than the helpers. They used multiple dens for raising pups that were excavated and/or renewed during denning period. Important conservation problems of wolf have also been discussed in the paper.

Ecology of Indian wolf Canis lupus pallipes in the Great Indian Bustard Sanctuary, Nannaj, Solapur, Maharashtra, India

The Indian wolf, Canis lupus pallipes is an endangered carnivore of India listed in Schedule-1 of the Indian Wildlife (Protection) Act, 1972. There is not much information available on the species and with this perspective, the present study was initiated in the Great Indian Bustard Sanctuary in Maharashtra. Direct and indirect evidences were used to assess its population status and distribution, habitat use, feeding ecology, denning behaviour and wolf-human conflict emanating due to livestock depredation. Intensive ecological and behavioural studies were conducted at Nannaj on one pack between 1991 and 1994. The wolf survives all over the Sanctuary, which is densely populated by humans as elsewhere in its distribution range in India where wolf-human conflicts are common arising either due to livestock depredation or child-lifting. Usually, large packs were present in Blackbuck Antilope cervicapra areas whereas smaller packs inhabited areas not supporting healthy populations of Blackbuck. In Blackbuck poor areas, the wolf survived mainly on livestock. The Sanctuary supports 40-58 wolves. The wolves had a seasonal pattern of habitat use related to movement of prey and livestock. Wolves selected those areas as rendezvous sites which had higher prey density, vegetation cover, minimum human disturbance and were located close to water source. On an average wolves consumed 3.68 (S.E.=0.17) kg/wolf/kill and kill periodicity was 3.65 days (S.E.=0.58). Wolves preyed largely on blackbuck during the non-breeding period and livestock during denning period. Predation was higher on male blackbuck than females despite female biased sex ratio. The average litter size of three packs was recorded to be 5 (range 4-6). The dominant male and female wolves guarded the dens more often than the helpers. They used multiple dens for raising pups that were excavated and/or renewed during denning period. Important conservation problems of wolf have also been discussed in the paper.

Responses of adult spotted lanternflies to artificial aggregations composed of all males or females.

Spotted lanternflies (SLF) Lycorma delicatula are economically important invasive planthoppers discovered in North America in 2014. SLF are gregarious, but how they locate each other, or who finds whom and when, is poorly understood. Here we describe adult SLF behavior and phenology on their preferred host, Ailanthus altissima, under field conditions, in the context of both aggregation and mate-location, since SLF demonstrated aggregation prior to mating. We documented aggregation behavior of adults and found we could manipulate free-living SLF populations in both number and sex ratio by the placement of confined populations of SLF males or females on trees. Trap capture of arriving SLF was significantly higher on trees with confined SLF aggregations than on control trees, and was corroborated with photographic data, demonstrating the manipulation of attraction and aggregation behavior. Sex ratios of trapped SLF arrivals were significantly more male-biased on trees with confined males and more female-biased on trees with confined females, evidence that the male- and female-biased sex ratios observed on trees naturally can be explained by sex-specific conspecific signals. SLF sex ratios shifted over time in the same pattern over two consecutive years. A mark-release-recapture study over time found that 1) SLF behavior is density dependent and strongly influenced by natural populations, 2) released females were captured significantly more on trees with caged females, particularly prior to mating, and 3) released males were captured significantly more on trees with caged females starting at mating time. Photographic data revealed that most clustering behavior (a measure of courtship) of free-living SLF began on trees with caged females during mating time, but not on trees with caged males or controls. We describe adult male and female SLF phenology whereby 1) aggregation behavior occurs, 2) males and females arrive at different times, 3) females began to aggregate several weeks prior to mating, 4) males subsequently joined aggregations at the time of mating, and 5) aggregation continued into oviposition. Population density and aggregation behavior were found to be key factors in their natural history which can be manipulated, providing a foothold for future research. Possible mechanisms for future exploration are discussed.

Room for Females Only? Exploring Strongly Female-Biased Sex Ratios in Ingolfiella (Crustacea: Peracarida: Ingolfiellida) in Relation to Ecological Condition

Abstract While in most species the adult sex ratio is around 1:1, it can be strongly skewed in some species; some of this can be explained by ecological conditions and limits to dispersal. We hypothesize that stronger isolation imposed by ecological conditions leads to more pronounced female-biased sex ratios in the groundwater peracarid genus Ingolfiella Hansen, 1903. About 75% of all adults are female, and female-biased sex ratios are present in 30/42 of species for which individuals have been sexed. Sex ratios were not correlated with sexual size dimorphism. The adult sex ratio varied little between species found in different habitats (caves, beach sand, and seabed) thus not supporting our hypothesis that ecological conditions shape adult sex ratios. It appears that sediment structure in most habitats restrict ingolfiellids in their movement. Limited dispersal abilities and small mating assemblages may favour strongly female-biased sex ratios.

Density-dependent dispersal promotes female-biased sex allocation in viscous populations

A surprising result emerging from the theory of sex allocation is that the optimal sex ratio is predicted to be completely independent of the rate of dispersal. This striking invariance result has stimulated a huge amount of theoretical and empirical attention in the social evolution literature. However, this sex-allocation invariant has been derived under the assumption that an individual's dispersal behaviour is not modulated by population density. Here, we investigate how density-dependent dispersal shapes patterns of sex allocation in a viscous-population setting. Specifically, we find that if individuals are able to adjust their dispersal behaviour according to local population density, then they are favoured to do so, and this drives the evolution of female-biased sex allocation. This result obtains because, whereas under density-independent dispersal, population viscosity is associated not only with higher relatedness—which promotes female bias—but also with higher kin competition—which inhibits female bias—under density-dependent dispersal, the kin-competition consequences of a female-biased sex ratio are entirely abolished. We derive analytical results for the full range of group sizes and costs of dispersal, under haploid, diploid and haplodiploid modes of inheritance. These results show that population viscosity promotes female-biased sex ratios in the context of density-dependent dispersal.

Demographic changes in an Atlantic Forest primate community following a yellow fever outbreak.

We investigated demographic changes in three primate species (Alouatta guariba, Sapajus nigritus, and Callithrix flaviceps) at the Reserva Particular do Patrimônio Natural-Feliciano Miguel Abdala,Caratinga, Minas Gerais, Brazil, following a yellow fever outbreak (YFO) by comparing their population sizes before (2015) and after the outbreak (2017-2018), and by monitoring the size, composition, and reproductive status of groups from 2017 to 2021. Comparisons of pre- and post-YFO census data indicate the A. guariba population declined by 86.6%, from an estimated minimum of 522 individuals to 70 individuals. However, by October 2021, the population had grown to at least 86 individuals, with an adult sex ratio (N = 53) that was female-biased (0.61). Eleven of the 13 groups being monitored systematically were reproductively active with high survivorship to 12 months of age. S. nigritus declined by 40%, from 377 to 226 individuals. The sex ratio of 33 adult S. nigritus is also female-biased (0.71), and at least 8 of 15 groups being monitored are reproductively active. C. flaviceps declined by 80%, from 85 individuals to the 15-17 individuals observed from 2017 to 2021. The female-biased adult sex ratio and presence of infants and juveniles in the A. guariba and S. nigritus groups are encouraging signs, but there is still great concern, especially for C. flaviceps. Continued monitoring of the demographics of these primates is needed as their persistence appears to still be at risk.

Provision of carbohydrate resources to support Apanteles polychrosidis, to increase parasitism of Caloptilia fraxinella in horticultural ash trees

The provision of nutritional resources for beneficial insects that support pest control, such as parasitoid wasps, is one tactic in conservation biological control. This tactic could be an important element for the development of a biological control program to help control the ash leaf-cone roller, Caloptilia fraxinella Ely (Lepidoptera: Gracillariidae), an introduced pest of horticultural ash trees (Fraxinus) in Canadian Prairie cities, including Edmonton, AB, Canada. In the current study, we test the efficacy of carbohydrate food provision to support parasitism of C. fraxinella by its primary parasitoid, Apanteles polychrosidis Viereck (Hymenoptera: Braconidae). Laboratory experiments compared the longevity, parasitism rate and offspring fitness of wasps fed sucrose solutions at one of two concentrations (10 and 25% v/v) or flowers of buckwheat, Fagopyrum esculentum (Polygonaceae). Fed wasps lived longer than wasps with access to water only. Mated, but not unmated, males and females lived longer when fed 25% than 10% sucrose. Female A. polychrosidis had similar longevity when fed 25% sucrose or buckwheat flowers. Egg load did not change with sucrose provision. Adult longevity of fed unmated female A. polychrosidis was negatively correlated with egg load. Female A. polychrosidis fed 25% sucrose produced offspring with a slightly female-biased sex ratio and higher fecundity than offspring from female A. polychrosidis fed the 10% sucrose solution.

Nonreproductive effects are more important than reproductive effects in a host feeding parasitoid

When female host feeding parasitoids encounter a potential host, they face a complicated trade-off between either laying an egg for investing in current reproduction or feeding on or killing the host for future reproduction. Few studies have measured these behavioral shift patterns in a given host-parasitoid association thus far. We systematically assessed the behavioral shifts and life history traits of a host feeding parasitoid, Necremnus tutae, on different instars of its host Tuta absoluta. N. tutae females, as idiobiont host feeding parasitoids, can act on the 1st–4th instar larvae of T. absoluta by either host feeding, parasitizing or host killing. Moreover, a significant behavioral shift was observed on different instar hosts. N. tutae preferred to feed on the young hosts (1st and 2nd instars), lay eggs on middle-aged hosts (3rd instars) and kill old hosts (4th instars) by ovipositor-mediated stinging. The offspring of N. tutae showed a significant female-biased sex ratio, with the number of instars of T. absoluta larvae that were parasitized increasing. Specifically, nonreproductive host mortality induced by host feeding and host killing accounted for high percentages of the total mortality (ranging from 70% on 3rd instar hosts to 88% on 1st instar and 4th instar hosts). We hypothesize that N. tutae could be not merely a parasitoid but also a predator. Our results shed light on the nonreproductive abilities of a host feeding parasitoid that should be given further attention, especially when evaluating the efficacy of parasitoids.

P-256 The influence of artificial intelligence embryo scoring on male-female sex ratio

Abstract Study question Are there correlations among male-female sex ratio, human blastocyst ploidy status and artificial intelligence (AI)-based morphokinetics embryo selection? Summary answer Embryo selection based on morphological evaluation by time-lapse system (TLS) with AI technology could lead to a female-biased sex ratio of resulting newborns. What is known already As of now, there have been only limited attempts to evaluate how AI-based TLS embryo selection for priority transfer could affect male-to-female sex ratio in human population, and the results of different publications were contradicting. However, the morphokinetic assessment was made without calculating the embryos KID Score (Embryos with Known Implantation Data), which significantly improves and make faster the decision-making process. Study design, size, duration This is a monocentric, retrospective study from October 2019 to December 2021 including 251 blastocysts with PGT-A results. Embryos were cultured in time-lapse incubator (EmbryoScope, Vitrolife) up to the time of trophectoderm biopsy. All embryos were evaluated based on the KIDscoreTM D5 algorithm (Vitrolife) under routine supervision by experienced embryologists. The PGT-A results were obtained by using next-generation sequencing (NGS) platform from Medical Genomics LLC laboratory (Illumina MiSeq, Illumina). Participants/materials, setting, methods Sample size was 251 embryos from 101 women (mean female age was 36.0 ± 5.6 years). All embryos were divided in four groups in accordance with their final KID score: <2.5 ( n = 7), 2.6-5.0 ( n = 33), 5.1-7.5 ( n = 123) and >7.5 ( n = 88). The embryos with sex chromosome abnormalities were also included in research to assess the frequency of occurrence in embryos with low and high KID score. Main results and the role of chance As expected, the percentage of aneuploid blastocysts, as well as the rate of sex chromosome abnormalities, decreased with increasing the embryo KID score. The highest male-female sex ratio among all embryos was observed for the group with KID score <2.5 (1.33), and gradually decreased to values of 0.92 and 0.74 in groups with KID score 5.1-7.5 and >7.5, respectively. At the same time, the highest male-female sex ratio among euploid blastocysts was maximal in the group with KID score 2.6-5.0. The obtained data contradict results of some other studies, which reported faster development of male embryos (which should mean their higher KID score). However, the KID score was not evaluated in them, and thus these results cannot be directly compared to ours. Limitations, reasons for caution Most patients in this study had complicated reproductive history, with repeated failures in IVF programs, often with a stop in embryo development. Also, the present investigation is retrospective. A following multicenter researches with larger sample size and cross-centered validation of embryologist-performed annotation is considered in our future approach. Wider implications of the findings Obtained data doesn’t allow to establish the female-gender prevalence among embryos. Nevertheless, further accumulation of knowledge about relation between KID Embryo Score and embryo gender can be used for presumptive sex determination in special cases with sex-linked diseases, where poor embryo morphology doesn’t allow to perform biopsy for genetic analysis. Trial registration number -

On the Spread of Microbes That Manipulate Reproduction in Marine Invertebrates.

AbstractBacterial symbionts are functionally integral to animal reproduction and development, some of which have evolved additional mechanisms to override these host programs. One habitat that is increasingly recognized to contain phylogenetically related lineages of reproductive manipulators is the ocean. The reproduction of marine invertebrates often occurs by free spawning instead of by the physical contact of copulation in terrestrial systems. We developed an integrated model to understand whether and when microbes that manipulate host reproduction by cytoplasmic incompatibility, feminization, and male killing spread within populations of free-spawning marine invertebrates. Our model supports three primary findings. First, sex ratio distortion leads to suboptimal fertilization and zygote production in planktotrophs (feeding larvae) but enhance these processes in lecithotrophs (nonfeeding larvae). Second, feminization and a combination of male killing plus enhanced growth are effective at spreading reproductive manipulators while also inducing a female-biased sex ratio. Third, the majority of free-spawning marine invertebrates could be infected across a range of life history combinations, with infections harming species with smaller eggs and longer pelagic durations while benefiting species with larger eggs and shorter pelagic durations. Together, this supports the general premise that microbes may manipulate the reproduction of free-spawning marine invertebrates (e.g., by inducing changes in developmental life history) and that these types of manipulations overlap considerably with terrestrial systems.

A gene deriving from the ancestral sex chromosomes was lost from the X and retained on the Y chromosome in eutherian mammals.

BackgroundThe mammalian X and Y chromosomes originated from a pair of ordinary autosomes. Over the past ~180 million years, the X and Y have become highly differentiated and now only recombine with each other within a short pseudoautosomal region. While the X chromosome broadly preserved its gene content, the Y chromosome lost ~92% of the genes it once shared with the X chromosome. PRSSLY is a Y-linked gene identified in only a few mammalian species that was thought to be acquired, not ancestral. However, PRSSLY’s presence in widely divergent species—bull and mouse—led us to further investigate its evolutionary history.ResultsWe discovered that PRSSLY is broadly conserved across eutherians and has ancient origins. PRSSLY homologs are found in syntenic regions on the X chromosome in marsupials and on autosomes in more distant animals, including lizards, indicating that PRSSLY was present on the ancestral autosomes but was lost from the X and retained on the Y in eutherian mammals. We found that across eutheria, PRSSLY’s expression is testis-specific, and, in mouse, it is most robustly expressed in post-meiotic germ cells. The closest paralog to PRSSLY is the autosomal gene PRSS55, which is expressed exclusively in testes, involved in sperm differentiation and migration, and essential for male fertility in mice. Outside of eutheria, in species where PRSSLY orthologs are not Y-linked, we find expression in a broader range of somatic tissues, suggesting that PRSSLY has adopted a germ-cell-specific function in eutherians. Finally, we generated Prssly mutant mice and found that they are fully fertile but produce offspring with a modest female-biased sex ratio compared to controls.Conclusions PRSSLY appears to be the first example of a gene that derives from the mammalian ancestral sex chromosomes that was lost from the X and retained on the Y. Although the function of PRSSLY remains to be determined, it may influence the sex ratio by promoting the survival or propagation of Y-bearing sperm.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12915-022-01338-8.

The reproductive biology of Mystus mysticetus Robert, 1992 in the Mekong Delta, Vietnam

This investigation aims to study the reproductive traits, including sex ratio, spawning season and pattern, batch fecundity (F), and length at first maturity (Lm), of the commercial catfish Mystus mysticetus living in the freshwater of the Mekong and Chao Phraya basins. A collection of 596 individuals was caught using trawl nets from Cai Rang, Can Tho (CT) and Long Phu, Soc Trang (ST) from October 2020 to September 2021. The results showed a female-biased sex ratio (0.64 males: 1.00 females) and a pattern of multi-spawner as ripe ovaries contained different developmental stages of oocytes. A combined analysis of gonadal occurrence frequency and gonadosomatic index showed that this fish spawned during the wet season with a peak in June-July at CT and September-October at ST. The F ranged from 4,470–22,457 eggs/female (CT) to 4,104–23,651 eggs/female (ST) and these values increased with fish size. The egg diameter ranged from 0.63 ± 0.06 to 0.64 ± 0.06 SD mm, and Lm was higher in males (11.6 at CT and 11.2 at ST) than in females (10.9 at CT and 10.4 at ST). To conclude, it is recommended that the fish should be caught at length > Lm and avoid fishing in the main spawning period in order to exploit this fish resource sustainably.

Sex reversal explains some, but not all, climate-mediated sex ratio variation within a viviparous reptile.

Evolutionary transitions in sex-determining systems have occurred frequently yet understanding how they occur remains a major challenge. In reptiles, transitions from genetic to temperature-dependent sex determination can occur if the gene products that determine sex evolve thermal sensitivity, resulting in sex-reversed individuals. However, evidence of sex reversal is limited to oviparous reptiles. Here we used thermal experiments to test whether sex reversal is responsible for differences in sex determination in a viviparous reptile, Carinascincus ocellatus, a species with XY sex chromosomes and population-specific sex ratio response to temperature. We show that sex reversal is occurring and that its frequency is related to temperature. Sex reversal was unidirectional (phenotypic males with XX genotype) and observed in both high- and low-elevation populations. We propose that XX-biased genotypic sex ratios could produce either male- or female-biased phenotypic sex ratios as observed in low-elevation C. ocellatus under variable rates of XX sex reversal. We discuss reasons why sex reversal may not influence sex ratios at high elevation. Our results suggest that the mechanism responsible for evolutionary transitions from genotypic to temperature-dependent sex determination is more complex than can be explained by a single process such as sex reversal.

Male mating success evolves in response to increased levels of male-male competition.

Male-biased operational sex ratios can increase male-male competition and can potentially select for both increased pre- and postcopulatory male success. In the present study, using populations of Drosophila melanogaster evolved under male-biased (M) or female-biased (F) sex ratios, we asked whether (a) male mating success can evolve, (b) males are better at mating females that they have coevolved with, (c) males mating success is affected by female mating status, and (d) male mating success is correlated with their courtship effort. We directly competed M and F males for mating with (a) virgin ancestral (common) females, (b) virgin females from the M and F populations, and (c) singly mated females from the M and F populations. We also assessed the courtship frequency of the males when paired with mated M or F females. Our results show that M males, evolving under an increased level of male-male competition, have higher mating success than F males irrespective of the female evolutionary history. However, the difference in mating success is more pronounced if the females had mated before. M males also have a higher courtship frequency than F males, but we did not find any correlation between mating success and courtship frequency.

Capture-Recapture Reveals Heterogeneity in Habitat-Specific Mongoose Densities and Spatiotemporal Variability in Trapping Success in St. Kitts, West Indies

The small Indian mongoose (Urva auropunctata) is a non-native invasive species across the Caribbean and a rabies reservoir on at least four islands in the region. Although previous studies reported mongoose density estimates in their non-native range, the variability in trapping designs, study seasonality, and analytical methods among studies precludes direct comparisons. This study is the first to report mongoose densities for the island of St. Kitts, West Indies. Our objective was to quantify mongoose densities across four habitats characteristic for the island. High capture and recapture rates in this study resulted in detailed estimates of spatial heterogeneity in mongoose densities, ranging from 0.53 (CI95: 0.46–0.61) mongooses/ha in suburban habitat to 5.85 (CI95: 4.42–7.76) mongooses/ha in nearby dry forest. Estimates were robust to the estimation method used (correlation among methods, r > 0.9). Female-biased sex ratios estimated from fall season versus mostly unbiased sex ratios estimated from summer season suggests seasonality in capture success resulting from differences in sex-specific activity patterns of mongooses. We found no effect of habitat characteristics, at the scale of trap placements, associated with mongoose capture success.

Sinhcaf-dependent histone deacetylation is essential for primordial germ cell specification.

Primordial germ cells (PGCs) are the progenitor cells that give rise to sperm and eggs. Sinhcaf is a recently identified subunit of the Sin3 histone deacetylase complex (SIN3A-HDAC). Here, we provide evidence that Sinhcaf-dependent histone deacetylation is essential for germ plasm aggregation and primordial germ cell specification. Specifically, maternal-zygotic sinhcaf zebrafish mutants exhibit germ plasm aggregation defects, decreased PGC abundance and male-biased sex ratio, which can be rescued by re-expressing sinhcaf. Overexpression of sinhcaf results in excess PGCs and a female-biased sex ratio. Sinhcaf binds to the promoter region of kif26ab. Loss of sinhcaf epigenetically switches off kif26ab expression by increasing histone 3 acetylation in the promoter region. Injection of kif26ab mRNA could partially rescue the germ plasm aggregation defects in sinhcaf mutant embryos. Taken together, we demonstrate a role of Sinhcaf in germ plasm aggregation and PGC specialization that is mediated by regulating the histone acetylation status of the kif26ab promoter to activate its transcription. Our findings provide novel insights into the function and regulatory mechanisms of Sinhcaf-mediated histone deacetylation in PGC specification.