Male-biased Sex Ratio Research Articles

Birth Spacing and Fertility in the Presence of Son Preference and Sex-Selective Abortions: India's Experience Over Four Decades.

Since the advent of prenatal sex-determination technologies in the mid-1980s, India has experienced an increasingly male-biased sex ratio at birth, presumably from sex-selective abortions. Abortions lengthen birth intervals, but we know little about how birth spacing has changed or the effects of these changes. I show that, although the overall length of birth intervals increased from 1970 to the mid-2010s, well-educated women with no sons had the most substantial lengthening, as well as the most male-biased sex ratios. Furthermore, most of these changes took place immediately after the introduction of prenatal sex-determination technologies. Consequently, some women without sons now have longer birth intervals than those with sons, reversing India's traditional spacing pattern. Women with low education continue short birth spacing when they have no sons, with only limited evidence of male-biased sex ratios. Because of the rapid lengthening of birth intervals, period fertility rates substantially overestimated how fast cohort fertility fell. Moreover, predicted cohort fertility is still 10%-20% above the period fertility rate. If the lengthening of birth intervals arises from repeated abortions, the associated short pregnancy spacing may counteract any positive effects of longer birth spacing. There is, however, no evidence of this effect on infant mortality. Judging from sex ratios, sex-selective abortion use is not declining.

Incel Activity on Social Media Linked to Local Mating Ecology

Young men with few prospects of attracting a mate have historically threatened the internal peace and stability of societies. In some contemporary societies, such involuntary celibate—or incel—men promote much online misogyny and perpetrate real-world violence. We tested the prediction that online incel activity arises via local real-world mating-market forces that affect relationship formation. From a database of 4 billion Twitter posts (2012–2018), we geolocated 321 million tweets to 582 commuting zones in the continental United States, of which 3,649 tweets used words peculiar to incels and 3,745 were about incels. We show that such tweets arise disproportionately within places where mating competition among men is likely to be high because of male-biased sex ratios, few single women, high income inequality, and small gender gaps in income. Our results suggest a role for social media in monitoring and mitigating factors that lead young men toward antisocial behavior in real-world societies.

Diptera (Dryomyzidae, Fanniidae, Muscidae, Piophilidae) Associated With Pig Carcasses in a Forest Habitat of Poland: Sex-Related Patterns of Visitation and Effectiveness of Sampling Methods.

Our knowledge on many necrophilous dipterans was limited for a long time mainly due to taxonomic issues. Therefore, findings on the sex-related associations with pig carcasses in Dryomyzidae, Fanniidae, Muscidae, and Piophilidae are presented. Moreover, the effectiveness of pitfall traps and sweep nets in fly sampling were compared, since the correct method of collecting insects is critical for the development and application of entomological tools for forensic purposes. The trapped numbers of all species differed significantly in respect to both sexes. The sex ratios were strongly female-biased in most species of Muscidae and in Fanniidae. More females were also collected in Piophilidae, but the proportion of males was higher when compared to muscids. Within Dryomyzidae, the sex ratio differed according to species. Only Dryomyza flaveola (Fabricius, 1794) (Diptera: Dryomyzidae) and Muscina pascuorum (Meigen, 1826) (Diptera: Muscidae) had male-biased sex ratios. Differences in residency patterns between sexes in Stearibia nigriceps (Meigen, 1826) (Diptera: Piophilidae), Liopiophila varipes (Meigen, 1830) (Diptera: Piophilidae), and D. flaveola were statistically insignificant. All studied species were recorded for each sampling method. The effect of the sampling method on the number of individuals was statistically significant for all dipterans but Piophilidae. Pitfall traps outcompeted the aerial sweep net in representing Dryomyzidae and Muscidae, whereas both methods were almost equally effective in the collection of Piophilidae. A varied effectiveness of sampling methods was observed in Fanniidae. The sampling method significantly affected the determination of the appearance time of flies on carcasses, but the effect of species and sampling method was insignificant. Implications for forensic entomology are discussed.

Autonomous recordings suggest contrasting patterns in Prairie Warbler (Setophaga discolor) vocal activity between coastal and inland locations in Ontario, Canada

To inform the design of targeted, species-specific surveys of Prairie Warbler (Setophaga discolor) in Ontario, Canada, we used autonomous recording units (ARUs) to document patterns in male vocal activity. We deployed recorders within the territories of breeding males at coastal sites near Georgian Bay, and at inland sites near Kaladar, in June 2015 and 2016, respectively. Although coastal and inland sites are <250 km apart, we observed distinct differences in the patterns and frequency of male singing. Overall, the mean number of songs per minute of males at inland sites near Kaladar was nearly triple that of coastal sites near Georgian Bay. Daily singing activity peaked shortly after sunrise and declined throughout the day at both sites. Daily singing activity was uniformly high across the entire morning period at coastal sites, whereas at inland sites the highest rates of singing were during the post-dawn morning period. Singing activity varied by chronological day at inland sites, with distinct peaks at the beginning and end of June. Singing at coastal sites did not vary by chronological day and was consistently low throughout June. Although our sample sizes are small, with minimal replication, we discuss our results in the context of reduced pairing success and male-biased sex ratios in small, isolated populations. In addition to documenting singing activity patterns to optimize future surveys for species of conservation concern, ARUs may also signal potential demographic differences important for population persistence that warrant further exploration.

Siricid Parasitoids (Hymenoptera: Ichneumonidae) From Eastern White Pine and Associated Pine Species in Southern Appalachia

Siricid Parasitoids (Hymenoptera: Ichneumonidae) From Eastern White Pine and Associated Pine Species in Southern Appalachia

Sex allocation and field population sex ratio of Apanteles taragamae Viereck (Hymenoptera: Braconidae), a larval parasitoid of the cucumber moth Diaphania indica Saunders (Lepidoptera: Crambidae)

Abstract Sex ratio is one of the most important biological characteristics of arthropods. In a parasitoid population, sex ratio can influence the suppression of host populations or the stability of host–parasitoid interactions in the field. In this study, a survey was carried out to determine the sex allocation through the sequence of male/female adult emergence and calculate the sex ratio of selected populations of Apanteles taragamae in their natural habitat. Assessment of sex ratio at the population and individual level (brood size per female) was examined. We found no difference in the likelihood that either sex would emerge before the other. Observations of sex ratio at the population and individual level reveal a females biased sex ratio. Analysis of the relationship between brood size and sex ratio of A. taragamae shows that brood size may influence the proportion of male to female offspring yielded. A male-biased sex ratio tends to be found in smaller brood size. However, sex ratio is shifted to female biased in larger brood size.

Oviposition of Culicoides insignis (Diptera: Ceratopogonidae) under laboratory conditions with notes on the developmental life history traits of its immature stages

BackgroundCulicoides insignis is a confirmed vector of bluetongue virus (BTV) throughout the American tropics and a possible vector of epizootic hemorrhagic disease virus (EHDV) in Florida. Despite its importance, fundamental information on the biology and ecology of this vector species is lacking. In this study, we examined the oviposition of C. insignis under laboratory conditions, monitored the development of immature stages and attempted colonization of this species.MethodsLive C. insignis females were collected from the field using CDC-UV-LED traps, allowed to blood-feed on live chicken and given various natural substrates for oviposition in two-choice assays. The eggs deposited were transferred to 0.3% agar slants, and the hatched larvae were provided a diet of Panagrellus redivivus Linnaeus nematodes and the development of all immature stages was monitored.ResultsCulicoides insignis females exhibited an overall oviposition preference for dishes containing mud from their larval habitat as gravid females deposited a significantly higher number of eggs on these dishes (35.3 eggs/female) than on controls (17.7 eggs/female). The ovipositing females also deposited a higher percentage of eggs on substrates with habitat mud and other organically enriched muds (≥ 75.2%) compared to controls (31.0%). The larvae developed successfully to adulthood on the nematode diet, exhibiting high overall larval survival rates (85.0%). Sex ratios of the F1 generation were male biased, approximately 3:1 (male:female). Captive mating could not be induced in the F1 adults.ConclusionsMud from the larval habitat and other organically enriched muds provide strong oviposition cues to C. insignis under laboratory conditions. Further studies will be needed to identify the key biotic/abiotic factors influencing midge oviposition in the field. The agar/nematode method is effective for the rearing of C. insignis larvae. However, further studies will be needed to address the issue of male-biased sex ratios in the progeny and to examine the mating habits/cues of C. insignis in nature, which may provide clues towards inducing captive mating in the F1 adults.Graphical abstract

Adults have more male-biased sex ratios than first-winter juveniles in wintering duck populations

BackgroundThe long-term monitoring of demographic changes in waterbird populations remains limited, but such information can be valuable for conservationists and waterbird managers. Biased sex ratios can indicate differences in survival rates between sexes. In particular, differences in the sex ratios of fledged juveniles and adults can provide insight into the development of male bias among populations.MethodsIn this study, we used data from individual birds captured over a 57-year period to assess the extent, and temporal variability in male bias in nine populations of ducks wintering in the United Kingdom: Gadwall (Mareca strepera), Northern Mallard (Anas platyrhynchos), Northern Pintail (Anas acuta), Common Pochard (Aythya ferina), Common Shelduck (Tadorna tadorna), Northern Shoveler (Spatula clypeata), Eurasian Teal (Anas crecca), Tufted Duck (Aythya fuligula), and Eurasian Wigeon (Mareca penelope).ResultsOverall, eight of these populations were significantly male-biased and adults were more male-biased than first-winter juveniles for all nine populations. The increased male bias among adults is consistent with the hypothesis that factors such as higher mortality of reproductive-age females during the breeding season is a major cause of male bias in duck populations. However, such predation cannot explain the male bias detected in first-winter juveniles in four of the populations. The temporal trends in male bias differed between adults and first-winter juveniles in Northern Mallard, Northern Pintail, Common Pochard, Common Shelduck, Eurasian Teal, Tufted Duck, and Eurasian Wigeon. Over the study period we found increased male bias among adult Northern Mallard, Northern Pintail, Common Pochard, Common Shelduck, and Tufted Duck as well as both adult and first-winter juvenile Northern Shoveler.ConclusionsWe provide evidence that among wintering duck populations, sex ratios are typically male-biased, with adults exhibiting stronger male-biased sex ratios than first-winter juveniles. Improved monitoring of sex ratios of wintering waterbirds would help to increase our understanding of changes in waterbird demography, population structure, and observed population trends; our study shows that birds caught during ringing projects can be a valuable source of such data.

Effect of the Social Environment on Spring Migration Timing of a Songbird

The influence of the social environment on the timing of the annual cycle is poorly understood. Seasonally migratory birds are under pressure to accurately time their spring migration, and throughout the annual cycle, they may experience variability of the local sex-ratio. A population-level male-biased sex ratio is predicted to advance spring migration timing in males and is attributed to the increased intra-specific competition for access to females and/or breeding territories. The present study had two goals. First, to develop a method that utilizes digitally coded radio-transmitters to quantify the activity of flocked individuals in captivity. Second, to use this method to test the hypothesis that the social environment influences the spring migration traits of male yellow-rumped warblers (Setophaga coronata coronata). To accomplish this, birds were captured in the fall in Long Point, Ontario, and transferred to the Advanced Facility for Avian Research, London, Ontario. In the winter, they were assigned to a slightly male- or female-biased treatment and housed in flocks in large free-flight rooms. Throughout the experimental period, we took body mass measurements and standardized photos to monitor body condition and molt progression. To measure locomotor activity, the birds were outfitted with digitally coded radio-transmitters in April and photo-triggered to enter a migratory phenotype. The tagged birds were released at their capture site in May and the Motus Wildlife Tracking System was used to determine stopover departure timing and migratory movements. Sex ratio did not influence body mass or molt progression. However, males from the male-biased treatment had significantly less locomotor movement than those from the female-biased treatment. Additionally, a lower proportion of males from the male-biased treatment initiated migratory restlessness, an indicator of the urge to migrate. Overall, these findings suggest that the social environment can influence behavior of songbirds, but do not support the hypothesis that a male-biased sex ratio accelerates migration.

Male-biased in-water population of loggerhead turtle (Caretta caretta) in Dalyan, Turkey as a possible important marine turtle area in the Mediterranean

In this study, we present the first in-water monitoring results of loggerhead turtles (Caretta caretta) in Köyceğiz-Dalyan specially protected area (SPA), Turkey. The capture-mark-recapture (CMR) study encompassed a total of 113 capture events of 88 individuals across two sampling years. The majority of the population was adults (88.6%) with a highly male-biased (70.5%) sex ratio. Our results indicate that some of the overwintering individuals also contribute to the nesting population in the region. Biometric characteristics of captured individuals were also presented. Additionally, we found the population to be under heavy anthropogenic threats with 54.5% of the captured individuals exhibiting results of previous anthropogenically caused injuries. Our results suggest that Köyceğiz-Dalyan SPA is an important overwintering and foraging area for loggerhead turtles, which is currently an indexed nesting site for loggerhead turtles in the Mediterranean. Given the possible feminization effects of climate change on future marine turtle populations, the male-biased population in the study area is of the greatest importance, and together with having an indexed nesting site, the area should therefore be regarded as an important marine turtle area.

Bat-ectoparasitic fly relationships in a seasonally dry tropical forest in Brazil.

Bat ectoparasitic flies are hematophagous insects highly specialized to parasitize only bats. Knowledge about how biotic and abiotic factors can influence ecological relationships between parasites and hosts is in general incipient. Large information gaps are even worst in biodiversity-rich, but poorly sampled areas like Brazil's Caatinga, the largest tropical dry forest in South America. We used bats and their highly specialized ectoparasitic flies as a study model to clarify some aspects of this host-parasite system in this semiarid environment. We conducted fieldwork at 55 sites in the Caatinga, between April 2017 and March 2020 and collected 1300 flies (19 species) on 333 bats (15 species). Bat ectoparasitic flies were highly host-specific, had an aggregated distribution, frequently formed infracommunities with only one species, and had a male-biased sex ratio. Except for the prevalence of the streblid fly Strebla guajiro on Carollia perspicillata, which was significantly higher in the rainy season, bat flies showed no preference - expressed by frequency and intensity of infestation - for host sex, and their interspecific relationships were not mediated by rainfall. Other variables that could potentially be interfering in this host-parasite relationship deserve further attention, especially in environments such as the Caatinga where there is great seasonal variation. Furthermore, the existence of species-specific responses must be taken into account.

Caste development and sex ratio of the Ryukyu drywood termite Neotermes sugioi and its potential mechanisms

Sex allocation is one of the most studied traits in evolutionary biology because its theoretical predictions match the empirical data. Here, using the Ryukyu dry-wood termite Neotermes sugioi, we investigated several factors that could bias the sex allocation in three populations (Okinawa, Ishigaki/Iriomote, and Yonaguni). Our survey showed that there were more queen-only colonies than king-only colonies in these populations, suggesting a longer lifespan of the queens than that of the kings. In this condition, sex-asymmetric reproductive value (SRV) theory predicts female bias, because even after the short-lived kings die, the long-lived queens can continue reproduction with their sons. However, sex allocation in this species seemed to be biased toward males. Furthermore, we examined the possibility of intrasexual competition among siblings (ICS). If ICS is the cause of the bias, the allocation is expected to change depending on the total investment in sexual offspring. However, the biomass of both male and female alates increased linearly with the increase in the total biomass of the alates in these populations. Thus, neither the SRV nor the ICS theory could explain the male-biased sex ratio of N. sugioi. On the basis of these results, we discuss the remaining possibilities in this species.

Reproductive success and progeny sex ratio of a laboratory colony of Anagyrus fusciventris (Hymenoptera: Encyrtidae)

ABSTRACT Anagyrus fusciventris (Girault) is a parasitoid of both Pseudococcus calceolariae (Maskell) and P. longispinus (Targioni Tozzetti), two economically important mealybug pests in New Zealand. A male-biased sex ratio was often observed in a laboratory colony of A. fusciventris. We investigated the effect of mating status on female A. fusciventris longevity, fecundity, progeny sex ratio and the rate of parasitism achieved under controlled laboratory conditions. In addition, the impact of host body size on progeny sex ratio was investigated. The progeny sex ratio of unmated (virgin) females (VF) and two types of mated females (24hM: opportunities for mating limited to 24 h or LtM – lifetime opportunities for mating) was tested under similar conditions. Results indicated that females can be reproductively active within 24 h. On average, 24hM females produced 23% female offspring while LtM females produced 45% females, suggesting that multiple mating is required for a balanced sex ratio. VF produced only male offspring through arrhenotokous parthenogenesis. When reared at 23°C and 16 h photoperiod, VF, 24hM and LtM females lived for 25, 44, 51 days, and parasitised 46, 67 and 87 mealybugs respectively. The average lifetime reproductive output (total number of offspring emerged) of VF, 24hM and LtM females was 41, 58 and 75 offspring, respectively. Female-biased progeny emerged from larger hosts while male-biased progeny often emerged from smaller hosts. Implications of these results are discussed in relation to opportunities to improve the quality of a laboratory colony with a balanced progeny sex ratio.

Blow flies, synanthropy and sex ratio: Are the deviations in the sex proportion linked to human transformation of landscapes?

In most species, several factors like time of emergence, age at maturation, reproductive life span, survival of males and females, mating behavior, differential resource use, and migration patterns may affect the adult sex ratio. Anthropogenic landscape transformation is known to change diversity, favoring colonization by exotic species but other populational parameters, such as the sex ratio, have not been assessed. The aim of the present study was to describe the sex-ratio patterns of adult necrophagous blow flies captured using carrion-baited traps along habitats representing different levels of human impact. We describe the sex bias for four species: the exotic Chrysomya albiceps, Chrysomya megacephala, Chrysomya putoria, and the native Cochliomyia macellaria. Three types of habitats were selected: highly anthropized (urbanized), moderately anthropized (rural), and native forest (natural) within a humid subtropical ecoregion in Northeastern Argentina. We found an overall trend to female bias among the four species when considering the total number of each sex. However, our study showed a changing sex-ratio pattern along the gradient of human influence. Our results indicate that a higher likelihood of trapping more males in unsuitable habitats seems to be widespread among blow flies. Urban exploiters, such as Ch. megacephala and Ch. putoria, locally shifted their trends, becoming male-biased in natural habitats. The opposite trend was detected in the urban avoider Co. macellaria (which shifted to male-biased in urban habitats). The exception was Ch. albiceps, whose sex proportion did not shift to a male-biased sex ratio. The results of this study highlight the changing sex-ratio patterns displayed by Calliphoridae in response to different conditions along a human-influence gradient. The biological traits and underlying mechanisms promoting the intraspecific changes of the sex ratio are discussed.

The endangered Brown Shrike subspecies Lanius cristatus superciliosus has a male-biased sex ratio and only early arriving males are paired

SummaryAlong with many long-distance migrant passerine species in the East Asian-Australasian Flyway, the migratory Brown Shrike Lanius cristatus superciliosus has been sharply declining throughout its breeding range. Its breeding range in Japan shrank by 90.9% between the 1910s and 2010s. In contrast, the closely related but resident Bull-headed Shrike L. bucephalus bucephalus has been gradually declining but is still a common resident in Japan. To better understand the drastic decline of Brown Shrike, we compared the pairing success during three consecutive breeding seasons of these two species. About 60–70% of Brown Shrike males were unpaired, which was much higher than the percentage of unpaired male Bull-headed Shrike (c.0–20%). Brown Shrike males arriving later did not pair because the population’s sex proportion is heavily biased toward males. One of the factors of male-biased population of Brown Shrike may be female-biased mortality in wintering sites, or on the migratory journey, and tracking studies will be required to test this.

A management plan for a declining population of the Souss valley tortoise in an arid steppe-land of west-central Morocco

The endangered Moorish tortoise Testudo graeca is the unique terrestrial chelonian species in Northwest Africa. In west-central Morocco, the endemic subspecies, the Souss valley tortoise T. g. soussensis, occupies semi-arid to arid low-quality habitats, and is subject to serious threats. A long-term mark-recapture programme from 2001 to 2012 allowed estimating population size and structure, sex ratio, and survivorship in one of the well-known populations in a degraded and overgrazed arid steppe-land of west-central Morocco. Spring population size considerably decreased to more than half in less than 10 years, with a mean density lower than 3 ind.ha-1 in 2012 compared to its last known density estimated in 2003. In spring 2012, the population structure exhibited an unbalanced male-biased sex ratio (61:39) and a scarcity of juveniles (&lt;5%). We identified five major conservation problems in the study area: (i) habitat destruction and overgrazing; (ii) over-collecting of tortoises for pet trade , iii) direct disturbance; iv) tortoise handling mostly for field research, and v) increased extinction risk due to the small population size. We carried out a population viability analysis using the VORTEX software based on published and obtained data on population and life history parameters. With no management action, the population will go extinct during the forthcoming 40 years after the last estimate. The most efficient management option for a long-term persistence of the population would be reducing the nest and neonate mortality by 90%. To attenuate the impact of the threatening factors, we developed a management plan that includes population reinforcement and habitat restoration options.

Can an introduced predator select for adaptive sex allocation?

Most species produce equal numbers of sons and daughters, and sex differences in survival after parental care do not usually affect this pattern. Temporary overproduction of the scarcer sex can be adaptive when generations overlap, the sexes differ in life-history expectations, and parents can anticipate future mating opportunities. However, an alternative strategy of maximizing the competitiveness of the more abundant sex in these circumstances remains unexplored. We develop theory showing how mothers can maximize reproductive value when future mate competition will be high by producing more sons in the advantageous early hatching positions within their broods. Our model for optimal birth order was supported by long-term data of offspring sex in a parrot facing catastrophic female mortality caused by introduced predators. Swift parrots (Lathamus discolor) suffer high female mortality due to introduced sugar gliders (Petaurus breviceps) creating fluctuating male-biased adult sex ratios. Offspring hatched early within broods fledged in better condition, and in support of our model were more likely to be male in years with higher adult female mortality. We found a highly significant rank-order correlation between observed and predicted birth sex ratios. Our study shows the potential for mothers to maximize reproductive value via strategic biases in offspring sex depending on the advantages conferred by birth order and the predictability of future mate competition. Our long-term data support the predictions and appear to suggest that sex allocation strategies may evolve surprisingly quickly when anthropogenic pressures on populations are severe.

Global expression response of genes in sex-undifferentiated Nile tilapia gonads after exposure to trace letrozole

The aromatase inhibitor letrozole can be found in rivers, effluents, and even drinking water. Studies have demonstrated that letrozole affects various metabolic pathways and may cause reproductive toxicity, especially in fish exposed during development. However, studies on the effect of a low concentration of letrozole at the whole-gonad transcriptomic level in the early stage of fish sexual development have not been investigated. The aim of our study was to explore the potential effects of a low concentration of letrozole on the gonad transcriptome of Nile tilapia at an early stage of sexual development. In this study, 9 dpf (days postfertilization) Nile tilapia were exposed to trace letrozole for 12 days. Letrozole exposure from 9 dpf to 21 dpf persistently altered phenotypic sex development and induced the male-biased sex ratio. The transcriptome results showed that 1173 differentially expressed genes (DEGs) were present in the female control vs 1.5 μg/L letrozole-treated female comparison group and that 1576 DEGs were present in the 1.5 μg/L letrozole-treated female vs male control comparison group. Differentially expressed gene enrichment analysis revealed several crucial pathways, including the drug metabolism-cytochrome P450 pathway, the ErbB-PI3K/Akt/mTOR pathway, and the calcium signalling pathway. Further analysis of these identified DEGs indicated that some key genes correlated with metabolism and epigenetic regulation were significantly affected by letrozole, such as UDP-glucuronosyltransferase (Ugt), glutathione S-transferase omega-1 (Gsto1), lysine-specific demethylase 6bb (Kdm6bb, original name is Kdm6a), jumonji and AT-rich interaction domain containing 2 (Jarid2b, original name is Jarid2), growth arrest and DNA damage inducible gamma (Gadd45g), and chromobox protein 7 (Cbx7). The qRT-PCR validation results for twelve DEGs showed that the Pearson’s correlation of the log10fold change values between the qPCR and RNA-Seq results was 0.90, indicating the accuracy and reliability of the RNA-Seq results. Our study is the first to report the effect of letrozole on the transcriptome of gonads from fish during early-stage sexual development. These findings will be useful for understanding the toxic effects and molecular mechanisms of letrozole exposure at the early stage of gonad development on the sexual development of aquatic organisms.

Multigenerational exposure to warming and fishing causes recruitment collapse, but size diversity and periodic cooling can aid recovery

Global warming and fisheries harvest are significantly impacting wild fish stocks, yet their interactive influence on population resilience to stress remains unclear. We explored these interactive effects on early-life development and survival by experimentally manipulating the thermal and harvest regimes in 18 zebrafish (Danio rerio) populations over six consecutive generations. Warming advanced development rates across generations, but after three generations, it caused a sudden and large (30-50%) decline in recruitment. This warming impact was most severe in populations where size-selective harvesting reduced the average size of spawners. We then explored whether our observed recruitment decline could be explained by changes in egg size, early egg and larval survival, population sex ratio, and developmental costs. We found that it was most likely driven by temperature-induced shifts in embryonic development rate and fishing-induced male-biased sex ratios. Importantly, once harvest and warming were relaxed, recruitment rates rapidly recovered. Our study suggests that the effects of warming and fishing could have strong impacts on wild stock recruitment, but this may take several generations to manifest. However, resilience of wild populations may be higher if fishing preserves sufficient body size diversity, and windows of suitable temperature periodically occur.

Contrasting patterns of natal dispersal of a south temperate House Wren population at local and regional scales

Dispersal constitutes one of the main processes that shape population genetic structure and dynamics. Combining a capture-mark-resighting methodology and molecular genetics analyses, we studied the natal dispersal behaviour of House Wrens (Troglodytes aedon bonariae) inhabiting a naturally fragmented habitat in south temperate Argentina. Based on data collected over 12 breeding seasons (2005–2016), we tested if males and females differ in natal dispersal behaviour at different spatial scales. At local scale (within study sites), both resighting of banded individuals and genetic analysis showed that females dispersed greater distances than males. At a broader spatial scale (between study sites) resighting of banded individuals could not verify that females were the dispersing sex since long-distance dispersal was rare. However, genetic analyses revealed paradoxical evidence: while the females of populations separated by more than 5 km showed slight but significant genotypic differences among them, males showed genetic differences at a greater distance (> 16 km). Given that genetic analyses can provide evidence of both historical and present-day dispersal the observed genetic differentiation does not necessarily imply that the sex dispersal pattern is reversed at a regional scale. We propose that females have a higher probability of acquiring a partner/territory at closer distances due existing male-biased population sex ratio caused but higher female mortality. Also, although males are less likely to disperse, when they do, they must travel greater distances to find a suitable territory or mate. Such movements would prevent the occurrence of genetic differences among male populations.