Genetic relationships among five nemipterid fish species from the Indian coast using allozyme analysis

Based on Nei's genetic distance Nemipterus peronii and Nemipterus japonicus showed a greater affinity to Parascolopsis aspinosa than to the other Nemipterus species studied. Significant differences between the Indian west and east coast samples of N. japonicus were detected. Polymorphic (P<0.95) and diagnostic loci suitable for stock delineation and species identification were observed.     

Sex ratios

Sex ratio theory attempts to explain variation at all levels (species, population, individual, brood) in the proportion of offspring that are male (the sex ratio). In many cases this work has been extremely successful, providing qualitative and even quantitative explanations of sex ratio variation. However, this is not always the situation, and one of the greatest remaining problems is explaining broad taxonomic patterns. Specifically, why do different organisms show so much variation in the amount and precision with which they adjust their offspring sex ratios?     

Sex ratios and mental health: Evidence from China

While sex ratios (i.e., relative numbers of men and women) have been linked to various economic and social outcomes, how sex ratios affect mental health is underexplored. Using nationally representative data from the China Family Panel studies (CFPS) and Population Census, we evaluate the impact of sex ratios on mental health among Chinese men and explore potential mechanisms. Employing the instrumental variables (IV) approach where the One-Child Policy’s mandated fertility limits and implementation are used as exogenous variations in local sex ratios, we find that higher local sex ratios increase depressive symptoms and probability of depression among Chinese men. The impact is stronger for men with lower levels of education and living in rural areas. Analyses of potential mechanisms show that higher sex ratios increase the likelihood of marriage delay and unemployment for men, and prolong working hours for the employed men. The findings are of direct relevance to the health and population policy in China.     

Sexuality and hermaphroditism in fishes. I. Synchronous functional hermaphroditism in the serranid fish Serranus scriba L

Anatomical and histological examination of Serranus scriba L. showed the existence of primary females (67%), hermaphrodites (31%) and primary males (2%). Synchronous functional hermaphroditism is described on the basis of an anatomical and histological study of the gonads. Although they function simultaneously, the testicular and ovarian parts of hermaphrodite gonads have completely separate ducts. Females and hermaphrodites have the same annual reproduction cycle. In hermaphrodites, the testicular part matures one month sooner than the ovarian part. Cross fertilization between primary females and hermaphrodite individuals and between two different hermaphrodites probably occurs, while self-fertilization is less likely. The testicular tissues of primary males are of the acinar type and those of hermaphrodites are of the radial type. It is possible that primary males do not take part in reproduction. Serranus scriba in Egyptian Mediterranean waters is a longperiod spawner, which spawns from June to the end of October, i.e. it is a summer-autumn spawner.     

Sex ratios in bumble bees

The median proportion of investment in females among 11 populations of seven bumble bee (Bombus) species was 0.32 (range 0.07 to 0.64). By contrast, two species of workerless social parasites in the related genus Psithyrus had female-biased sex allocation, the reasons for which remain unclear. Male-biased sex allocation in Bombus contradicts the predictions of Trivers and Hare''s sex ratio model for the social Hymenoptera, which are that the population sex investment ratio should be 0.5 (1:1) under queen control and 0.75 (3:1 females:males) under worker control (assuming single, once-mated, outbred queens and non-reproductive workers). Male bias in Bombus does not appear to be either an artefact, or purely the result of symbiotic sex ratio distorters. According to modifications of the Trivers–Hare model, the level of worker male-production in Bombus is insufficient to account for observed levels of male bias. There is also no evidence that male bias arises from either local resource competition (related females compete for resources) or local mate enhancement (related males cooperate in securing mates). Bulmer presented models predicting sexual selection for protandry (males are produced before females) in annual social Hymenoptera and, as a consequence (given some parameter values), male-biased sex allocation. Bumble bees fit the assumptions of Bulmer''s models and are protandrous. These models therefore represent the best current explanation for the bees'' male-biased sex investment ratios. This conclusion suggests that the relative timing of the production of the sexes strongly influences sex allocation in the social Hymenoptera.     

Effects of frequent fires and grazing on stable nitrogen isotope ratios of vegetation in northern Australia

The ratios of stable nitrogen isotopes expressed as δ¹⁵N values can indicate the openness of nitrogen cycles in ecosystems. Southwards through the Northern Territory, values of foliar δ¹⁵N in savanna trees increase as mean annual rainfall decreases from approximately 1800 mm to approximately 750 mm, with foliar δ¹⁵N thereafter decreasing toward arid central Australia. Recent literature argues that this pattern is caused by higher grazing intensity in semi‐arid savannas, but counter views have attributed the pattern more directly to variations in aridity. In this paper, grazed and ungrazed sites in a semi‐arid savanna are compared, and it is shown that grazing has a relatively small effect on the positive foliar δ¹⁵N values of grasses, but no effect on δ¹⁵N values of trees. This gives little support to the argument that variations in grazing pressure at the scale of hundreds of kilometres could result in detectable differences in the foliar δ¹⁵N values of trees. I then compare the semi‐arid savannas with mesic savannas, where fires are frequent, and with mesic rainforests, which are rarely burnt. Greater foliar δ¹⁵N values in rainforest and fire‐excluded mesic savannas than in frequently burnt savannas suggests that fire regimes affect foliar δ¹⁵N. The previously observed pattern in δ¹⁵N values along the rainfall gradient in the Northern Territory is consistent with trends in fire frequency and possible direct effects of fire, but further work is required to determine the relative impacts of aridity and fire. Within a particular rainfall regime, foliar δ¹⁵N values may indicate historical fire frequencies.     

Sex roles and sex ratios in animals

In species with separate sexes, females and males often differ in their morphology, physiology and behaviour. Such sex-specific traits are functionally linked to variation in reproductive competition, mate choice and parental care, which have all been linked to sex roles. At the 150th anniversary of Darwin's theory on sexual selection, the question of why patterns of sex roles vary within and across species remains a key topic in behavioural and evolutionary ecology. New theoretical, experimental and comparative evidence suggests that variation in the adult sex ratio (ASR) is a key driver of variation in sex roles. Here, we first define and discuss the historical emergence of the sex role concept, including recent criticisms and rebuttals. Second, we review the various sex ratios with a focus on ASR, and explore its theoretical links to sex roles. Third, we explore the causes, and especially the consequences, of biased ASRs, focusing on the results of correlational and experimental studies of the effect of ASR variation on mate choice, sexual conflict, parental care and mating systems, social behaviour, hormone physiology and fitness. We present evidence that animals in diverse societies are sensitive to variation in local ASR, even on short timescales, and propose explanations for conflicting results. We conclude with an overview of open questions in this field integrating demography, life history and behaviour.     

Sex ratios in geographically structured populations

In his book on sexual selection (1), Darwin documented evidence that the primary sex ratio (the proportion of males at conception) is about 1/2 in a wide variety of species. Otherwise, he explained, a newly conceived member of the rare sex will, on average, have more offspring than one of the common sex, since each offspring has one mother and one father; thus there is frequency-dependent selection in favour of parents producing the rare sex. Darwin formulated this explanation in the first edition (1871) for monogamous species, but he failed to extend it to polygamous species, and in the second edition (1874) he retracted it completely. It was left to Fisher (2) to develop the theory in the more general form that there should be equal parental expenditure on the two sexes, allowing for the possibility that one sex may cost more to produce than the other. Despite the wide applicability of Fisher's principle, recent work on sex ratio evolution has focused on situations where it breaks down (3). Hamilton (4) first pointed out that Fisher's argument assumes population-wide competition for mates, whereas most natural populations have a geographical population structure in which limited dispersal imposes constraints on mating patterns. What are the consequences for the sex ratio?     

Sex change and sequential hermaphroditism in Tegillarca granosa (Bivalvia: Arcidae)

This study aimed to confirm sex change in Tegillarca granosa to determine whether this species is a sequential hermaphrodite. Samples of bivalves were divided into two groups, namely, a 1+ year class (14 months) and a 2+ year class (26 months), for analysis. At the beginning of the study, 44.3% of T. granosa were female, and after one year, this increased to 53.9% in the same population. The increase of females in the population was greater in the 1+ year class (12.3%), when compared with the 2+ year class (6.5%). Overall, a sex change ratio of 15.1% (n = 104/688) was recorded for T. granosa. The sex change ratio of the 1+ year class (17.8%) was higher than that of the 2+ year class (12.1%), and displayed the tendency of being higher in the males (21.2%), than the females (6.2%). The results of this study indicate that T. granosa is a sequential hermaphrodite.     

Borrowing contextual inflection: evidence from northern Australia

Gurindji Kriol is a north Australian mixed language which combines lexical and structural elements from Gurindji (Pama-Nyungan), and Kriol (English-lexifier). One of the more striking features of the grammar of Gurindji Kriol is the presence of the Gurindji case paradigm including ergative and dative case-markers within a Kriol verbal frame. Given the fragility of inflectional morphology in other language contact situations, particularly contextual inflections such as structural case markers, this situation bears closer scrunity. This paper argues that the presence of Gurindji case morphology is the result of pervasive code-switching practices which immediately preceded the genesis of the mixed language. As the code-switching stabilised into a mixed language, case-marking was integrated into predicate argument structure of Gurindji Kriol via nominal adjunct structures. Yet, these case markers were not absorbed unscathed. Although the Gurindji Kriol case paradigm bears a close resemblance to its Gurindji source in form, these case markers have not been perfectly replicated in function and distribution. Contact with Kriol functional equivalents such as prepositions and word order have altered the function and distribution of these case markers. The last part of this paper examines the shift that has occurred in Gurindji-derived case morphology in Gurindji Kriol.     

Analysis of stable isotope ratios to investigate stock structure of red emperor and Rankin cod in northern Western Australia

The ratios of stable isotopes ¹⁸O/¹⁶O and ¹³C/¹²C, in sagittal otolith carbonate from two tropical demersal teleosts, red emperor Lutjanus sebae and Rankin cod Epinephelis multinotatus , from several locations in northern Western Australia, differed between sites. On a broad scale, fish from the four locations, Shark Bay, Ningaloo, Pilbara, and Broome had stable isotope values that were sufficiently different to indicate separate stocks, and it is appropriate to manage these populations of the two species independently in these areas. On a smaller scale, there may be limited mixing of these species between the Pilbara trawl fishery and the trap and line fisheries operating out of Onslow and Broome. Values of stable oxygen isotopes were strongly related to sea surface temperature, although there were some sites in shallow water where low values of stable oxygen isotopes indicated that fish were living in warm water. The use of stable oxygen and carbon isotope values is a valuable, cost effective method of determining the degree of mixing of fish stocks.     

Sex ratios among Canadian liveborn infants of mothers from different countries

Background:

There has been much discussion about whether female feticide occurs in certain immigrant groups in Canada. We examined data on live births in Ontario and compared sex ratios in different groups according to the mother’s country or region of birth and parity.

Methods:

We completed a population-based study of 766 688 singleton live births between 2002 and 2007. We used birth records provided by Ontario Vital Statistics for live births in the province between 23 and 41 weeks’ gestation. We categorized each newborn according to the mother’s country or region of birth, namely Canada (n = 486 599), Europe (n = 58 505), South Korea (n = 3663), China (n = 23 818), Philippines (n = 15 367), rest of East Asia (n = 18 971), Pakistan (n = 18 018), India (n = 31 978), rest of South Asia (n = 20 695) and other countries (n = 89 074). We calculated male:female ratios and 95% confidence intervals (CIs) for all live births by these regions and stratified them by maternal parity at the time of delivery (0, 1, 2 or ≥ 3).

Results:

Among infants of nulliparous women, the male:female ratio was about 1.05 overall. As parity increased, the ratio remained unchanged among infants of Canadian-born women. In contrast, the male:female ratio was significantly higher among infants of primiparous women born in South Korea (1.20, 95% CI 1.09–1.34) and India (1.11, 95% CI 1.07–1.15) than among infants of Canadian-born primiparous women. Among multiparous women, those born in India were significantly more likely than Canadian-born women to have a male infant (parity 2, ratio 1.36, 95% CI 1.27–1.46; parity ≥ 3, ratio 1.25, 95% CI 1.09–1.43).

Interpretation:

Our study of male:female ratios in Ontario showed that multiparous women born in India were significantly more likely than multiparous women born in Canada to have a male infant.Although there are some myths about correctly guessing the sex of a fetus,¹ modern-day prenatal ultrasound enables the identification of whether a fetus is a boy or girl with 99% accuracy.² There has been much discussion about whether female fetuses are at higher risk of pregnancy termination than male fetuses in certain ethnic groups. In India, a study of data from the National Family Health Survey for 265 516 births showed a sharp increase in the male:female ratio among second-order births when the firstborn was a girl, and no significant increase when the firstborn was a boy.³ The authors attributed this trend to the practice of selective abortion of female fetuses. A recent editorial⁴ and news item⁵ in CMAJ suggested that female feticide may also be occurring in Canada.⁶ Rather than using live-birth statistics, the Canadian study cited in CMAJ used data from the 2001 and 2006 Canada Census long-form questionnaires, which were completed by 20% of the population and relied on self-reporting of additional information, including the number of family members in a given household.We used contemporary data on live births in Ontario, Canada’s most populous and ethnically diverse province, and compared sex ratios among infants of Canadian-born women with sex ratios in different immigrant groups. We focused on immigrant groups from countries purported to have the highest rates of preference for a son following the birth of one or more daughters.^3–6 We determined whether the male:female ratio increased with increasing parity in certain immigrant groups, as has been previously suggested.^3,6     

Pigment ratios and phytoplankton assessment in northern Wisconsin lakes

Nine lakes in northern Wisconsin were sampled from February through September 1996, and HPLC analysis of water column pigments was carried out on epilimnetic seston. Pigment distributions were evaluated throughout the water column during summer in Crystal Lake and Little Rock Lake. The purpose of our study was to investigate the use of phytopigments as markers of the main taxonomic groups of algae. As a first approach, multiple regression of marker pigments against chlorophyll a (chl a) was used to derive the best linear combination of the main xanthophylls (peridinin, fucoxanthin, alloxanthin, lutein, and zeaxanthin). A significant regression equation (r²= 0.98) was obtained for epilimnion data. The good fit indicates that the chl a:xanthophyll ratios were fairly constant in the epilimnion of the nine lakes over time. Chlorophyll a recalculated from the main xanthophylls in each sample showed good agreement with measured chl a in epilimnetic waters. A second approach used the CHEMTAX program to analyze the same data set. CHEMTAX provided estimates of chl a biomass for all algal classes and allowed distinction between diatoms and chrysophytes, and between chlorophytes and euglenophytes. These results showed a reasonably good agreement with biomass estimates from microscope counts, despite uncertainties associated with differences in sampling procedure. Changes of pigment ratios over time in the epilimnetic waters were also investigated, as well as differences between surface and deep samples of Little Rock Lake and Crystal Lake. We found evidence that changes in the ratio of photoprotective pigments to chl a occurred as a response to changes in light climate. Changes were also observed for certain light‐harvesting pigments. The comparison between multiple regression and CHEMTAX analyses for inferring chl a biomass from concentrations of marker pigments highlighted the need to take account of variations in pigment ratio, as well as the need to acquire additional data on the pigment composition of planktonic algae.     

Sex ratios in dairy cattle under various conditions

Current calving information was obtained on 35,102 single births in 2254 dairy herds. The overall proportion of males to females was 50.8%. The 5 dairy breeds did not differ. Only 6 of 111 sires studied produced calves with a sex ratio different from breed average at P≤0.5. This is the number expected by chance alone. A slight bias seems to occur when reporting the sires of the cows according to the sex of the cow's calf. The sex ratio deviated from expected in a small sample of repeat breeder cows, but when a new and larger sample of 2,084 such cows which calved was obtained, there was no change associated with service number. The time of insemination was recorded for 12,764 heifers and cows first seen in estrus in the morning and 4,799 animals first seen in estrus in the evening. There was no effect of time of insemination on sex ratio. Likewise there was no effect of age of cows or season of breeding on sex ratio at birth. Because the sex ratio for cows requiring one insemination per pregnancy was not different from repeat breeders it is suggested that the sex ratio at fertilization and birth may be similar.