Increase In Sex Ratio Research Articles

Low and high temperatures decrease the mating success of an egg parasitoid and the proportion of females in the population

Temperature influences all aspects of insect physiology and behaviour, including reproduction. Adverse temperatures can decrease mating success and sperm transfer, leading to increased sex ratio (more males) in populations of haplodiploid organisms. We tested the effect of five temperatures on the reproduction of the egg parasitoid Anaphes listronoti. Temperatures above and below 24.5°C decreased mating success by 30%–80%. Mating failures can arise from lack of encounters between sexes, absence of courting by the male, or the female refusing to mate. Both courtship and copulation duration decreased with increasing temperature. For mated females, there was no effect of mating temperature on offspring number and sex ratio. However, the increased number of virgin females at adverse temperatures did modify the simulated population sex ratio of the next generation, which increased from 0.2 at 24.5°C to 0.4, 0.5, 0.4 and 0.8 at 15.7°C, 20°C and 30°C and 35°C, respectively. The effect of temperature on courtship and copulation success of A. listronoti could lead to a decrease of the number of females in the population.

Transcriptome sequencing of Coccinella septempunctata adults (Coleoptera: Coccinellidae) feeding on artificial diet and Aphis craccivora.

BackgroundThe insect predator Coccinella septempunctata can effectively control many types of pests, such as aphids, whiteflies, and small lepidopteran larvae. We previously found that C. septempunctata fed an artificial diet showed diminished biological properties(e.g. fecundity, egg hatching rate, survival rate, etc.) compared with those fed natural prey (Aphis craccivora), likely due to different nutritional characteristics of the diet. In this study, we used transcriptome sequencing analysis to identify nutrition- and metabolism-related genes of C. septempunctata that were differentially expressed depending on diet.Methodology/Principal findingsThe Illumina HiSeq2000 was used to sequence 691,942,058 total clean reads from artificial diet-fed and A. craccivora-fed C. septempunctata libraries, and the clean reads were assembled using Trinity de novo software (Tabel 2). Comparison of transcriptome sequences revealed that expression of 38,315 genes was affected by the artificial diet, and 1,182 of these genes showed a significant change in expression levels (FDR ≤ 0.05,|log2FC|≥1, “FC” stands for “fold change”). These differentially expressed genes (DEGs) were likely associated with the decreased egg laying capacity, hatching rate, longevity, and increased sex ratio (♀:♂) of adult C. septempunctata observed in the group fed the artificial diet. Furthermore, in the most DEGs metabolic pathways for C. septempunctata feeding on the artificial diet accumulated amino acid metabolic pathways, lipid metabolic pathways, and starch and glucose metabolism were down-regulated.Conclusions/SignificanceWe found some differentially expressed genes and metabolic pathways are related to nutrition, from which a more informative feedback for diet formulation was obtained and the artificial diet could be more efficiently optimized.

Ambient outdoor air pollutants and sex ratio of singletons born after in vitro fertilization: the effect of single blastocyst transfer

To evaluate the impact of air pollution on the sex ratio in singletons after IVF treatment and to evaluate the influence of the number of and the developmental stage of transferred embryos on the sex ratio. Retrospective cohort study. University-affiliated IVF unit. A total of 7,004 singletons born after fresh transfer or frozen-thawed embryo transfer (FET) between January 2013 and December2017. None. Male-to-female ratio in live-born singletons. The estimated medians (interquartile range) of particle matter (PM)10, PM2.5, CO, NO2, O3, and SO2 at the IVF site were 51.4 (39.5-64.6), 27.7 (20.7-37.4), 0.62 (0.5-0.72), 32.5 (25.4-40.1), 79.6 (63.3-96.6), and 11.9 (9.3-15.9) μg/m3, respectively. Multivariate analysis indicated that SO2 was the only pollutant clearly associated with sex ratio. In singletons from single blastocyst transfer (SBT), as indicated by the generalized additive model, the SO2 concentration and sex ratio showed an inverted-U-shape association. In singletons after non-SBT, a monotonic decreasing in the sex ratio was observed with increased SO2 concentration. Compared with the referent category (SO2 < 7.57 μg/m3), the sex ratio at the 5th decile of SO2 (10.81-11.94 μg/m3) was increased by 2.1-fold (95% confidence interval [CI], 1.3-3.14) after adjusting covariates. In singletons born from non-SBT, the sex ratio significantly decreased only in the 9th (odds ratio = 0.69; 95% CI, 0.53-0.90) and 10th (OR = 0.74, 95% CI, 0.56-0.98) deciles. Low concentrations of SO2 showed an association with increased sex ratio in singletons of SBT, while in singletons born from another ET system the sex ratios did not show an association at low concentrations of SO2.

Causes and consequences of spatial variation in sex ratios in a declining bird species.

Summary Male‐biased sex ratios occur in many bird species, particularly in those with small or declining populations, but the causes of these skews and their consequences for local population demography are rarely known. Within‐species variation in sex ratios can help to identify the demographic and behavioural processes associated with such biases.Small populations may be more likely to have skewed sex ratios if sex differences in survival, recruitment or dispersal vary with local abundance. Analyses of species with highly variable local abundances can help to identify these mechanisms and the implications for spatial variation in demography. Many migratory bird species are currently undergoing rapid and severe declines in abundance in parts of their breeding ranges and thus have sufficient spatial variation in abundance to explore the extent of sex ratio biases, their causes and implications.Using national‐scale bird ringing data for one such species (willow warbler, Phylloscopus trochilus), we show that sex ratios vary greatly across Britain and that male‐biased sites are more frequent in areas of low abundance, which are now widespread across much of south and east England. These sex ratio biases are sufficient to impact local productivity, as the relative number of juveniles caught at survey sites declines significantly with increasing sex ratio skew.Sex differences in survival could influence this sex ratio variation, but we find little evidence for sex differences in survival increasing with sex ratio skew. In addition, sex ratios have become male‐biased over the last two decades, but there are no such trends in adult survival rates for males or females. This suggests that lower female recruitment into low abundance sites is contributing to these skews.These findings suggest that male‐biased sex ratios in small and declining populations can arise through local‐scale sex differences in survival and dispersal, with females recruiting disproportionately into larger populations. Given the high level of spatial variation in population declines and abundance of many migratory bird species across Europe at present, male‐biased small populations may be increasingly common. As singing males are the primary records used in surveys of these species, and as unpaired males often sing throughout the breeding season, local sex ratio biases could also be masking the true extent of these population declines.

An elevated blood glucose level and increased incidence of gestational diabetes mellitus in pregnant women with latent toxoplasmosis.

About 30-50% of the world human population are infected with the protozoan parasite Toxoplasma gondii (Nicolle et Manceaux, 1908). Latent toxoplasmosis has many specific behavioural and physiological effects on the human body and influences the course of pregnancy, including secondary sex ratio of children of infected mothers. It was suggested that an increased concentration of glucose could be the proximate cause of increased sex ratio. There are some indirect indications of possible association between toxoplasmosis and certain forms of diabetes. Here we searched for a possible link between latent toxoplasmosis and the level of glucose in the blood. In a cross-sectional study, we found that pregnant women with latent toxoplasmosis had significantly higher blood glucose levels during the oral glucose tolerance test (n = 191, p = 0.010; the level of fasting plasma glucose: mean = 5.04 mmol/l vs mean = 4.88 mmol/l; blood glucose level at 1 hour mean = 7.73 mmol/l vs mean = 6.89 mmol/l and blood glucose level at two hours mean = 6.43 mmol/l vs mean = 5.74 mmol/l) and higher prevalence (19.5 %) of gestational diabetes mellitus (n = 532, p = 0.033, odds ratio = 1.78) in the 24-28th gestational weeks than T. gondii-free women (12.0 %). Increased level of glucose and increased incidence of gestational diabetes mellitus could have considerable clinical impact as contributors to the development of the metabolic syndrome and type 2 diabetes in T. gondii-infected women. Our results also brought the first empirical support for the hypothesis that the glucose concentration may play a role in T. gondii-associated offspring sex ratio shifts.

The patterns of patents in China

Innovations are a key driver of long-term economic growth. There has been an explosion of patent filings in China in the past three decades. But empirical studies on the pattern of innovations at the firm level are rather scant primarily due to lack of firm-specific patent data. We have made concerted efforts to match Chinese patent data with a large firm-level database. The matched dataset enables us to examine the patterns of patents at the firm level. Our analysis has revealed several interesting patterns: (1) domestic firms have become increasingly more innovative in terms of patent application; (2) private firms, rather than state-owned enterprises, have been the engine of innovation; (3) rising wages have propelled labor-intensive sectors to become more innovative; and (4) in response to increasing sex ratio imbalances, firms in female-intensive industries have exhibited more innovations than those in male-intensive industries.

New data identify an increasing sex ratio of multiple sclerosis in Sweden

Background: An increasing women-to-men ratio in later birth cohorts of patients with multiple sclerosis (MS) has been observed in several populations and has been hypothesised to be due to one or several environmental factors of importance for disease aetiology. However, in a study based on data from the Swedish MS registry (SMSreg) this ratio was recently reported to be rather stable during the 20th century. Objective: The purpose of this study was to reinvestigate the women-to-men ratio in Sweden based on data from all available data sources, including deceased patients. Method: We combined data from the SMSreg with data from national patient registers. Results: In total we obtained information on 19,510 MS patients born 1931–1985, 13,321 women and 6189 men. The women-to-men ratio increased from 1.70 for patients born in the 1930s to 2.67 for patients born in the 1980s. When comparing the coverage of SMSreg to the full data set, a significantly higher proportion of women born 1931–1935 compared to men born in the same period were found in SMSreg, resulting in a sampling bias hiding the increasing sex ratio in the full material. Conclusion: The women-to-men ratio in MS has increased in Sweden during the 20th century similarly to observations in other western countries.

Invagination intestinale aiguë du nourrisson et de l’enfant : peut-on encore parler de prédominance automno-hivernale ? Étude épidémiologique sur 10 ans

Intussusceptions in infants and children are a medical and surgical emergency. A seasonal pattern, with fall and winter predominance, is usually taught in medical schools, but in France the epidemiological characteristics of intussusceptions are not clearly described. We conducted a retrospective study concerning children with idiopathic ileocolic intussusceptions admitted and treated at our institution (Emergency Department and Pediatric Surgery Department, Toulouse University Hospital) between January 2002 and December 2011. The main purpose was to evaluate the seasonality of intussusceptions. We describe the sex ratio, age of occurrence, rate of recurrence, and rate of failed enema reduction. A total of 306 idiopathic ileocolic intussusceptions (280 patients) were included over a 10-year period with an average of 31 cases per year [21-42]. No seasonal pattern of intussusceptions or fall/winter predominance was shown (P=0.6) in the cumulative number of monthly cases: 24% of the intussusceptions occurred during fall, 21% during winter, 29% during spring, and 27% during summer. There were two peaks: April (35 cases over 10 years) and June (34 cases). The mean age was 18.7 months [2.3-159.4]: 19.5 months [3-159.4] in boys and 14.8 months [2.3-77.5] for girls (P=0.02). Two peaks were shown: one between six and nine months, the other one between 18 and 21 months. Male children had a higher incidence than female children: the sex ratio was 2:1, with 65.4% boys and 34.6% girls (P=0.0003), with an increasing sex ratio for older children. The recurrence rate was 8.2% among all (26 recurrences): 10.1% in boys and 4.9% in girls (P=0.08). The rate of surgery after failed enema reduction was 7.5% (21/280 children). There was no case of recurrence after operation. These results were consistent with previous reports. We did not show any seasonal pattern of idiopathic ileocolic intussusceptions in our patients. A new survey of childhood intussusceptions would be relevant to confirm these results and would make it possible to modify academic teachings about seasonality in intussusceptions.

‘Maternity migration’ and the increased sex ratio at birth in Hong Kong SAR

The sex ratio at birth (SRB) in Hong Kong SAR (Special Administrative Region) has recently increased dramatically. Using a data set (N = 850,331) of all recorded births in Hong Kong between 1995 and 2009, we calculated SRBs by parity and immigrant status. The findings indicate a strong son preference among Mainland Chinese who have travelled to Hong Kong to give birth, especially at parity two or above. Logistic regression models show that this tendency is significantly greater among more affluent couples and remains strong even among Mainland Chinese women resident in Hong Kong for any length of time. The SRB of Hong Kong-born couples, though elevated at higher parities, is less skewed. Hong Kong has been serving as an outlet for ‘elite’ Mainland couples to circumvent family planning restrictions. The analysis also suggests the advantages of a wider set of immigrant variables over a binary construct.

Increased sex ratio in Russia and Cuba after Chernobyl: a radiological hypothesis

BackgroundThe ratio of male to female offspring at birth may be a simple and non-invasive way to monitor the reproductive health of a population. Except in societies where selective abortion skews the sex ratio, approximately 105 boys are born for every 100 girls. Generally, the human sex ratio at birth is remarkably constant in large populations. After the Chernobyl nuclear power plant accident in April 1986, a long lasting significant elevation in the sex ratio has been found in Russia, i.e. more boys or fewer girls compared to expectation were born. Recently, also for Cuba an escalated sex ratio from 1987 onward has been documented and discussed in the scientific literature.Presentation of the hypothesisBy the end of the eighties of the last century in Cuba as much as about 60% of the food imports were provided by the former Soviet Union. Due to its difficult economic situation, Cuba had neither the necessary insight nor the political strength to circumvent the detrimental genetic effects of imported radioactively contaminated foodstuffs after Chernobyl. We propose that the long term stable sex ratio increase in Cuba is essentially due to ionizing radiation.Testing of the hypothesisA synoptic trend analysis of Russian and Cuban annual sex ratios discloses upward jumps in 1987. The estimated jump height from 1986 to 1987 in Russia measures 0.51% with a 95% confidence interval (0.28, 0.75), p value < 0.0001. In Cuba the estimated jump height measures 2.99% (2.39, 3.60), p value < 0.0001. The hypothesis may be tested by reconstruction of imports from the world markets to Cuba and by radiological analyses of remains in Cuba for Cs-137 and Sr-90.Implications of the hypothesisIf the evidence for the hypothesis is strengthened, there is potential to learn about genetic radiation risks and to prevent similar effects in present and future exposure situations.

China’s Missing Girls in the Three Decades from 1980 to 2010

The strictly implemented fertility policy that has been in force in China since 1980 has led to a continuously increasing sex ratio at birth and in turn to a large number of missing girls. Based on China’s four recent censuses, we find that the number of missing girls accounted for 2.93 percent of all girls expected to have been born during 1980 to 1989, 9.31 percent during 1990 to 1999, and 10.85 percent during 2000 to 2010. The 1980?2010 birth cohorts have 20 million missing girls, namely 7.34 percent. For cohorts born from 1980 to 2010, males outnumber females by 36 million at the census times, 20 million as a result of the phenomenon of missing girls, while the remaining 16 million is biologically determined, as there are about 5 percent more male births under normal sex ratio at birth. We discuss possible adjustment of the fertility policy in China and measures that might lead to a more normal sex ratio at birth.

Is there an expected relationship between parental expenditure and sex ratio of litters or broods?

Parents may be selected to adjust the sex ratio of their offspring when parental expenditure yields different fitness returns from sons and daughters. This prediction is clear when parents produce only one offspring per reproductive attempt, but more complicated when parental resources are shared by several offspring, and parents may potentially influence the resource allocation among offspring as well as their number and sex. Here we present an optimization model to make predictions on how total parental expenditure may relate to the number and sex of offspring at every rank position within the litter or brood as well as the sex ratio of the litter/brood for the case of a large population with stable Fisherian sex ratio. We show that selection for sex ratio adjustment should be stronger for offspring at higher-ranking positions, for which the amount of resources received can be more predictable. Also, the relationship between parental resources devoted to a litter/brood of a given size and the primary sex ratio (proportion of males) is not expected to be a monotonically increasing function but rather a J-shaped relationship, steeper for small litters/broods and more extreme sexual dimorphism. Parental expenditure relates to increased sex ratio only for small variations in parental expenditure and for a given brood/litter size. For variable litter/brood sizes, a general relationship between parental resources and litter/brood sex ratio is not expected, although in practice pooling litters or broods of different sizes may produce negative relationships between parental expenditure and sex ratio of the litter/brood.

Modulation of immunity in mice with latent toxoplasmosis—the experimental support for the immunosuppression hypothesis of Toxoplasma-induced changes in reproduction of mice and humans

The immunosuppression hypothesis suggests that the increased sex ratio in mice and women with latent toxoplasmosis, retarded embryonic growth in the early phases of pregnancy, prolonged pregnancy of Toxoplasma-infected women, and increased prevalence of toxoplasmosis in mothers of children with Down syndrome can be explained by the presumed immunosuppressive effects of latent toxoplasmosis. Here, we searched for indices of immunosuppression in mice experimentally infected with Toxoplasma gondii. Our results showed that mice in the early phase of latent infection exhibited temporarily increased production of interleukin (IL)-12 and decreased production of IL-10. In accordance with the immunosuppression hypothesis, the mice showed decreased production of IL-2 and nitric oxide and decreased proliferation reaction (synthesis of DNA) in the mixed lymphocyte culture in the early and also in the late phases of latent toxoplasmosis. Since about 30% of the world population are latently infected by T. gondii, the toxoplasmosis-associated immunosuppression might have serious public health consequences.

Sex ratio of multiple sclerosis and clinical phenotype

In a longitudinal population-based dataset of patients with multiple sclerosis (MS), we have previously observed a substantial increase in the female to male sex ratio in Canada over the last 50 years. Here, we aimed to determine whether this change in sex ratio is related to the clinical course of MS. We calculated sex ratios by birth year in 11 868 patients with relapsing-remitting (RR) MS and 2825 patients with primary progressive (PP) MS identified as part of the Canadian Collaborative Project on the Genetic Susceptibility to MS. Year of birth was a significant predictor for sex ratio in RR MS (P < 0.0001, chi(2) = 21.2; Spearman's rank correlation r = 0.67), but not for PP MS (P = 0.44, chi(2) = 0.6; Spearman's rank correlation r = 0.11). An increase in the number of female RR MS patients over time accounts for the increasing sex ratio of MS. This has implications for pathogenesis, for assessment of clinical trial results and for disease prevention. The factors underlying the selective increase in MS in females need to be uncovered.

Plasmodium falciparum gametocyte sex ratios in symptomatic children treated with antimalarial drugs

The sex ratios of Plasmodium falciparum gametocytes, defined as the proportion of gametocytes in peripheral blood that were male, were evaluated in 1609 children with acute, symptomatic, uncomplicated malaria, pre- and post-treatment with various antimalarial drugs, over an 8-year period (1999–2006) in an endemic area of southwest Nigeria. Gametocyte carriage on presentation was 10% (162 children). In 162 children in whom 5797 gametocytes were sexed on presentation, the weighted mean sex ratio was 0.18 (95% confidence interval 0.13–0.25). Following therapy, in 446 children in whom 38,519 gametocytes were sexed, the weighted mean sex ratio was 0.38 (95% CI 0.33–0.43) on day 3 and 0.70 (95% CI 0.63–0.75) ( P < 0.000001) by day 7 after therapy commenced. Non-artemisinin monotherapy significantly increased sex ratio producing a male-biased ratio, but artemisinin combination therapy significantly reduced the sex ratio producing a female biased ratio. Pre-treatment sex ratio correlated negatively with haematocrit ( r = −0.229, P = 0.003) or gametocytaemia ( r = −0.435, P < 0.0001) but not with other clinical or parasitological parameters. The ratio of the sex-specific half lives male:female, the ‘gametocyte maleness index’ (GMI), was >1 with non-artemisinin monotherapy but <1 with artesunate and artemisinin-based combinations. In a multiple regression model, anaemia, low gametocytaemia, and enrolment before 2004 were independent predictors of a male-biased sex ratio pre-treatment. A pre-treatment haematocrit <25%, enrolment before 2004 and treatment with non-artemisinin monotherapy were independent predictors of a male-biased sex ratio 7 days postinitiation of therapy. These findings may have implications for malaria management efforts in sub-Saharan Africa.

How can economic schemes curtail the increasing sex ratio at birth in China?

Fertility decline, driven by the one-child policy, and son preference have contributed to an alarming difference in the number of live male and female births in China. We present a quantitative model where people choose to sex-select because they perceive that married sons are more valuable than married daughters. Due to the predominant patrilocal kinship system in China, daughters-in-law provide valuable emotional and financial support, enhancing the perceived present value of married sons. We argue that inter-generational transfer data will help ascertain the extent to which economic schemes (such as pension plans for families with no sons) can curtail the increasing sex ratio at birth.

Plasmodium falciparum gametocyte sex ratios in children with acute, symptomatic, uncomplicated infections treated with amodiaquine

BackgroundAmodiaquine is frequently used as a partner drug in combination therapy or in some setting as monotherapy, but little is known about its effects on gametocyte production and sex ratio and its potential influence on transmission in Africa. The effects of amodiaquine on sexual stage parasites and gametocyte sex ratio, and the factors associated with a male-biased sex ratio were evaluated in 612 children with uncomplicated Plasmodium falciparum malaria who were treated with amodiaquine during the period 2000 – 2006 in an endemic area.MethodsClinical, parasitological and laboratory parameters were evaluated before treatment and during follow-up for 28–42 days, and according to standard methods. Gametocyte sex ratio was defined as the proportion of peripheral gametocytes that are male.ResultsClinical recovery from illness occurred in all children. Gametocytaemia was detected in 66 patients (11%) before treatment and in another 56 patients (9%) after treatment. Gametocyte densities were significantly higher by days 3–7 following treatment compared with pre-treatment (P < 0.0001). Overall, mean gametocyte sex ratio increased significantly during follow-up and over the study periods from 2000–2006 (P < 0.001 in both cases), but was female-biased at enrolment throughout the study periods. Absence of fever, a haematocrit < 25%, asexual parasitaemia > 20,000/μL, gametocytaemia < 18/μL, and enrolment in 2006 were associated with a male-biased sex ratio pre-treatment. Anaemia and high parasitaemia were independent predictors of gametocyte maleness 7 days post treatment.ConclusionAmodiaquine may significantly increase gametocyte carriage, density and sex ratio, and may potentially influence transmission. It is possible that anaemia could have contributed to the increased sex ratio. These findings may have implications for malaria control efforts in Africa.

Analysis of socio-political and health practices influencing sex ratio at birth in Viet Nam

Viet Nam has experienced rapid social change over the last decade, with a remarkable decline in fertility to just below replacement level. The combination of fertility decline, son preference, antenatal sex determination using ultrasound and sex selective abortion are key factors driving increased sex ratios at birth in favour of boys in some Asian countries. Whether or not this is taking place in Viet Nam as well is the subject of heightened debate. In this paper, we analyse the nature and determinants of sex ratio at birth in Viet Nam, including a small family size norm, recent reinforcement by the Government of the “one-to-two child” family policy, traditional son preference, easy access to antenatal ultrasound screening and legal abortion, and an increase in the proportion of one-child families. In order to prevent an increased sex ratio at birth in Viet Nam, we argue for the relaxation of the one-to-two child family policy and a return to the policy of “small family size” as determined by families, in tandem with a comprehensive approach to promoting the value of women and girls in society, countering traditional gender roles, and raising public awareness of the negative social consequences of a high sex ratio at birth.

Sex ratio and dynamic behavior in populations of the exotic blowfly Chrysomya albiceps (Diptera, Calliphoridae)

Sex ratio is an essential component of life history to be considered in population growth. Chrysomya albiceps is a blowfly species with a naturally biased sex ratio. In this study, we evaluated the impact of changes in sex ratio on the dynamic behavior of C. albiceps using a density-dependent mathematical model that incorporated demographic parameters such as survival and fecundity. These parameters were obtained by exponential regression, with survival and fecundity being estimated experimentally as a function of larval density. Bifurcation diagram of the results indicated the evolution of stable equilibrium points as a function of sex ratio. A continually increasing sex ratio yielded a hierarchy of bifurcating stable equilibrium points that evolved into a chaotic regime. The demographic parameters obtained by exponential regression were also changed to maximum and minimum values in order to analyze their influence on dynamic behavior with sex ratio being considered as an independent variable. Bifurcations with periodicity windows between chaos regimes were also found.

Biogeography and incipient speciation in Ophryotrocha labronica (Polychaeta, Dorvilleidae)

Crossing experiments were conducted between the Naples I (NI) strain of Ophryotrocha labronica labronica, three strains of O. l. pacifica from Japan (M3), Hawaii (WH) and Los Angeles (LA), two strains of O. labronica from Australia and one from an unknown origin, discovered in a Moscow aquarium, to determine the relationships between the European and Pacific subspecies, and the newly discovered strains. Previously published data combined with new results revealed several stages in the process of speciation within the sibling group. Interpopulation crosses yielded an increased sex ratio that appears to be positively related to genetic distance and to the sex ratio of the parent strains. Fecundity data demonstrated that the three northern Pacific strains are more closely related to each other than to any other strain, confirming that they are a valid subspecies, and indicate that they are the result of natural distribution. The strain of unknown origin as well as the Australian strains clearly belong to O. l. labronica. Its isolated presence in the South Pacific may be a remnant of an earlier wider distribution or an introduction of the Mediterranean population, as the life histories of Ophryotrocha species have made them prime candidates for anthropogenic dispersals.