Mixed-sex Population Research Articles

Sex expression, skewed sex ratios, and microhabitat distribution in the dioecious desert moss Syntrichia caninervis (Pottiaceae)

The moss Syntrichia caninervis is the dominant soil bryophyte in a blackbrush (Coleogyne ramosissima) community in the southern Nevada Mojave Desert, with a mean cover of 6.3%. A survey of the 10-ha study site revealed an expressed ramet sex ratio of 14♀ : 1♂ (N = 890), with 85% of ramets not expressing sex over their life span, and an expressed population sex ratio of 40♀ : 2♂ : 1♀♂ (female : male : mixed-sex, N = 89), with 52% of populations not expressing sex. A greater incidence of sex expression was associated with shaded microsites, higher soil moisture content, and taller ramets. Shaded microsites had higher surface soil moisture levels than exposed microsites. In the exposed microhabitat, surface soil moisture was positively correlated with ramet height but not with sex expression. Male ramets and populations were restricted to shaded microhabitats, whereas female ramets and populations were found in both shaded and exposed microhabitats, suggesting gender specialization. The rarity of mature sporophytes, found in 0% of the ramets sampled and in only 3% of the populations, is probably due to the rarity of mixed-sex populations. We hypothesize that mixed-sex populations are rare because of factors relating to male rarity and that the differential cost of sex expression reduces the clonal growth capacity of male individuals.

Physiological stress responses to confinement in diploid and triploid Atlantic salmon

Confinement of juvenile Atlantic salmon Salmo salar from four different populations (all–female diploids, all–female triploids, mixed sex diploids and mixed sex triploids) either before (FW parr) or after (SW smolts) transfer to sea elevated plasma cortisol and plasma lactate from control levels irrespective of ploidy status. Both before and after confinement, plasma cortisol levels in SW smolts (6–174 ng ml–1) were higher than those in FW parr (4–58 ng ml–1), which possibly reflected the physiological challenge of acclimation to SW. Mixed sex populations of SW smolts had higher cortisol levels than all–female populations. The duration of confinement (1, 3 or 6 h) affected the magnitude of the plasma cortisol and lactate responses in SW smolts. Plasma cortisol levels in diploid and triploid SW smolts subjected to 2 h of confinement decreased to pre–stress levels within 6 h post–confinement. Plasma lactate levels were not significantly different from pre–stress levels 48 h after confinement. As no difference exists in primary and secondary stress responses of Atlantic salmon of differing ploidy status, it is unlikely that differences in mortality rates between diploid and triploid populations under commercial conditions can be attributed to differences in their physiological responses to periods of stress lasting up to 6 h.

Physiological stress responses to confinement in diploid and triploid Atlantic salmon

Confinement of juvenile Atlantic salmon Salmo salar from four different populations (all–female diploids, all–female triploids, mixed sex diploids and mixed sex triploids) either before (FW parr) or after (SW smolts) transfer to sea elevated plasma cortisol and plasma lactate from control levels irrespective of ploidy status. Both before and after confinement, plasma cortisol levels in SW smolts (6–174 ng ml–1) were higher than those in FW parr (4–58 ng ml–1), which possibly reflected the physiological challenge of acclimation to SW. Mixed sex populations of SW smolts had higher cortisol levels than all–female populations. The duration of confinement (1, 3 or 6 h) affected the magnitude of the plasma cortisol and lactate responses in SW smolts. Plasma cortisol levels in diploid and triploid SW smolts subjected to 2 h of confinement decreased to pre–stress levels within 6 h post–confinement. Plasma lactate levels were not significantly different from pre–stress levels 48 h after confinement. As no difference exists in primary and secondary stress responses of Atlantic salmon of differing ploidy status, it is unlikely that differences in mortality rates between diploid and triploid populations under commercial conditions can be attributed to differences in their physiological responses to periods of stress lasting up to 6 h.

Sex-specific vitellogenin production in immature rainbow trout.

Vitellogenin (Vg) was measured in sexually immature rainbow trout (Oncorhynchus mykiss) exposed to 17β-estradiol (E2 ) in the diet. Mixed-sex populations of trout aged 3, 6, 12, or 18 months were maintained separately and fed E2 at 0.05 or 2.5 mg/kg for 7 d. Females fed E2 at 0.05 mg/kg consistently produced three- to fourfold greater amounts of Vg than similarly aged males. Age- and sex-matched fish fed E2 at 2.5 mg/kg produced equivalent amounts of Vg. Sex differences in Vg production were apparent only at a dose of E2 (0.05 mg/kg) that results in submaximal Vg induction. Our results document the importance of considering the sex of juvenile fish when using Vg production as a marker of xenoestrogen exposure.

ECOLOGICAL GENETICS OF GYNODIOECY IN SILENE VULGARIS: RELATIVE FITNESS OF FEMALES AND HERMAPHRODITES DURING THE COLONIZATION PROCESS.

Recent theoretical models have addressed the influence of metapopulation dynamics on the fitness of females and hermaphrodites in gynodioecious plants. In particular, selection is thought to favor hermaphrodites during population establishment because that sex should be less prone to pollen limitation, especially if self-fertilization is possible. However, inbreeding depression could limit this advantage. In this experimental study of Silene vulgaris, a weedy gynodioecious plant, the fitness of females and hermaphrodites was estimated from seed production in both mixed-sex populations and for individuals isolated from these populations by 20, 40, 80, or 160 m. In mixed populations females display statistically significant greater per capita seed production owing to higher capsule production and higher rates of seed germination. The fitness of both sexes declines with increasing isolation, but at different rates, such that in the 160-m treatment hermaphrodites are by far the more fit sex. Allozyme studies suggest that this differential decline is because the selfing rate in hermaphrodites increases as a function of isolation, at least partially compensating for a decline in the availability of outcross pollen. Overall, the negative effects of pollen limitation on females far outweighs the negative effects of inbreeding depression following selfing in hermaphrodites. Thus, extinction/recolonization dynamics would appear to favor hermaphrodites as long as seed dispersal events exceed some critical distance.

Steroid Levels and Steroid Metabolism in Relation to Early Gonadal Development in the TilapiaOreochromis niloticus(Teleostei: Cyprinoidei)

Sex steroid levels and steroid metabolism were investigated in relation to early gonadal development in a mixed sex population of the tilapiaOreochromis niloticus.Androstenedione (AD), testosterone (T), 11-ketotestosterone (KT), and estradiol (E2) were quantified by radioimmunoassay (RIA) of whole body extracts. Androstenedione metabolism was assessed by incubationsin vitrowith3H-AD and metabolites were identified by thin-layer chromatography coupled with radioisotope image analysis. Histology revealed the presence of gonadal structures at 15 days postfertilization (dpf) and ovaries at 36 dpf, with other individuals exhibiting undifferentiated gonads containing germinal cells, presumably eventual testes. Androgen levels were initially high in eggs then decreased severalfold prior to the emergence of gonads. A transient increase in the levels of T and KT occurred at 22 dpf. Levels of E2 were either low or undetectable except for a transient increase (43 dpf) after ovaries were present. Levels of T approached bimodality from 57 to 64 dpf. Steroid metabolism generally increased throughout development. Metabolites were generally similar, consisting of T predominantly as well as 5β-reduced androgen derivatives and 11-oyxgenated derivatives. Estriol was tentatively identified. Conjugated steroids were not formed. Two types of steroid metabolic profiles occurred at 50 dpf. These results demonstrate that changes in the steroidogenic profile occur during early transitions of gonadal development. Notably, (1) steroid biosynthetic capacity preceeds gonadal differentiation, (2) evidence for estrogens occurs after ovarian development has begun, and (3) bimodality of levels of T and differential steroid metabolism later in development may reflect the onset of sexual divergence.

Sex differentiation of channel catfish gonads: Normal development and effects of temperature

Channel catfish have an XX female-XY male sex determination system. Although genetic males of this species are readily feminized with exogenous steroid, the pattern of gonadal sex differentiation and the effect of temperature on genetic sex determination are unknown. To document the pattern of gonadal sex differentiation, catfish from a mixed-sex progeny (XX female-XY made cross), known XY males (XX female-YY male cross), and steroid sex-reversed (XY) females were reared at 28°C and collected for histological analysis from Day 7 to Day 90 postfertilization. No signs of gonadal sex differentiation were detected from Day 7 to Day 16. On Day 19, about half the fish from the mixed-sex population as well as the sex-reversed females had gonads with proximal and distal tissue outgrowths. These outgrowths eventually fused to form an ovarian cavity. Germ cell meiosis in these gonads was first detected on Day 22 and growing ovarian follicles were seen at later stages. Thus, ovarian differentiation began about Day 19. Although presumptive testes lose their sensitivity to feminizing steroids about Day 19, the gonads of known males and of putative males from the mixed-sex population showed no clear signs of sex differentiation up to Day 90. Thus, the prolonged temporal dissociation between testicular commitment and differentiation indicates that these two events may be mediated by separate stimuli. To determine the effects of temperature on sex determination, fish of a mixed-sex population were reared at 27°C until Day 10; at 20°, 27°, or 34°C from Day 10 to Day 24; and then at 27°C until Day 102 when sex ratios and gonadal histology were determined. The sex ratio was significantly skewed toward females in fish treated at 34°C (1 male:1.68 female; P < 0.01) but no effects were seen at 20° or 27°C. This observation suggests that genetic and temperature-dependent mechanisms of sex determination are both functional in channel catfish and that this phenomenon is more widespread in fishes than previously believed. The testes of the Day 102 males examined had developed positive histological signs of sex differentiation, suggesting that testicular formation in channel catfish normally starts between Day 90 and 102. © 1996 Wiley-Liss, Inc.

Brain–Pituitary–Gonadal Axis during Early Development and Sexual Differentiation in the Rainbow Trout,Oncorhynchus mykiss

Profiles of testosterone, 11-ketotestosterone, androstenedione, and estradiol were determined by RIA, and immunocytochemical techniques were employed to identify gonadotropin (GTH) I and II and gonadotropin releasing hormone (GnRH) in monosex and mixed sex populations of rainbow trout from 1 to 126 days postfertilization (dpf). Steroid levels were relatively high at 1 dpf and declined until 25 dpf. At 30 and 48 dpf (hatching) steroid levels increased slightly before they fell by 78 dpf and remained relatively constant thereafter. Trends toward differences in steroid content between males and females became evident around the time gonadal differentiation was histologically discernible (78 and 90 dpf). GTH I was present in the proximal pars distalis at all dates (48–126 dpf), whereas GTH II was not detectable. GnRH was found at all dates (48–126 dpf) and was distributed in several areas of the brain including the nucleus preopticus periventricularis, nucleus lateralis tuberis, and the pituitary in the region where GTH I was found. No differences were seen between males and females in the timing of appearance, localization, or intensity of staining of these peptide hormones. Given that the brain–pituitary–gonadal axis seems to be intact during the process of sexual differentiation and the fluctuations of steroid levels during this process, sex steroids may play the driving role for sexual differentiation of rainbow trout.

Observations on Monosex Culture of Redclaw Crayfish Cherax quadricarinatus von Martens (Decapoda: Parastacidae) in Earthen Ponds

AbstractManual sexing of redclaw crayfish Cherar quadricurinatus was undertaken to evaluate the feasibility of monosex culture and to establish growth and yield characteristics of single sex populations. Although the all‐male population exhibited greater mean weight after 10 mo of growout, all‐female and mixed sex populations achieved greater total yields due to significant juvenile recruitment. Commercial cultivation of all‐male populations would be advantageous as in‐pond reproduction is greatly abated, growth is superior and marketable yield is higher. Apparent sexual lability of juveniles combined with the laborious nature of manual sexing may render manual sexing unsuitable for commercial applications.

Growth and nutrient digestibility by male and female Penaeus monodon: evidence of sexual dimorphism

Quadruplicate groups of 10 Penaeus monodon were grown in tanks in monosex and mixed-sex populations from 8.6 to 17.0 g (mean wet weight) over a period of 69 days. Measurements of feed intake and the apparent digestibility of dietary protein and energy were made in the second and tenth weeks of the experiment. Monosex female prawns grew significantly faster than monosex males and male prawns from mixed-sex tanks. The weight increment per moult of monosex females was greater ( P<0.05) than that of monosex males, but no difference in intermoult period was seen between any of the groups. Feed intake of monosex females tended to be greater than that of monosex males but not significantly so. No significant difference between the sexes was detected for either apparent digestibilities of dietary protein and energy or feed conversion.

Paraoxonase distribution in caucasian males

Mean plasma paraoxonase activity was lower in a population of all males than in a mixed sex population with no evidence of the higher activity group. It is suggested that sex differences in plasma lipid may contribute to the observed differences, and that factors other than genetics may influence observed plasma paraoxonase levels.

Variation in the mode of reproduction among individuals of the ostracod Candonocypris novaezelandiae

This study describes the results of laboratory breeding experiments designed to determine the mode of reproduction of female Candonocypris novaezelandiae from populations with and without males. Two morphological forms of this species were studied: a large-green and small-brown morph. Large-green females from populations without large-green males invariably generated genotypically identical daughters by parthenogenesis, regardless of the presence or absence of males in the laboratory cultures. In contrast large-green females from a population that included large-green males, when they had the opportunity for fertilization, usually produced genotypically diverse offspring of both sexes. These females were probably sexually reproducing. Unmated females from the mixed-sex population did not reproduce. The small-brown morph was collected from a single water body in which it was represented by both sexes and co-occurred with large-green parthenogenetic females. Most of the small-brown females tested reproduced sexually in the presence of males or did not reproduce in the absence of males. One small-brown unmated female, however, reproduced by parthenogenesis. Available evidence indicates that the field population of the small-brown morph includes both sexual and parthenogenetic females and that the relative abundance of the parthenogenetic females is increasing with time. The sexual and asexual forms within and between morphs are probably independent.

Variation in human nasal height and breadth

It has been suggested that the long-standing association of variability in the human nasal index [100 x (nasal breadth)/(nasal height)] with climatic variation is spurious evidence for natural selection in humans (Hoyme, 1965; St. Hoyme and Işcan, 1989). The argument is based principally on the observation that nasal height is globally more variable than nasal breadth, with nasal breadth thus contributing little to variation in the index. This argument does not take into account the confounding effect of absolute size of these variables on their variances. In this study we compare the intrinsic variation in skeletal nasal height and breadth within and among 26 mixed-sex populations (N = 2,408) at globally diverse localities (Howells, 1989), using 2 x 2 variance-covariance matrices of the logarithmically transformed variates. Hypothesis tests for homogeneity of matrices and equal-variance/equal-covariance indicate that the intrinsic variation in nasal breadth is greater than that for nasal height within populations, and that nasal breadth and nasal height exhibit equivalent intrinsic variation among populations. The argument that nasal breadth contributes little to the world-wide variation in the human nasal index is rejected. Given our present understanding of nasal physiological morpho-function, these results support, but do not demonstrate, an adaptive role for human nasal index variation. Promising methods for elucidating natural selection on human nasal form are suggested.

Serum biochemical parameters are greatly correlated to haematologic findings and may serve as indicators of the proliferative activity in chronic myelomonocytic leukaemia (CMML) : F. López, G.F. Sanz, T. Vallespi, M. Torrabadella, M.C. del Cañizo, M. Guinot, D. Irriguible, A. Juliá, J.F. San Miguel, M.A. Sanz. Department of Haematology, Hospital La Fe, Valencia; Hospital Vall d'Hebron, Barcelona; and Hospital Clínico,

The purpose of this study was to test polyculture of Nile tilapia and the native Mayan cichlid, as an alternative production method of tilapia. The experiment had a 2 × 4 factorial design: the first factor was the population of tilapia (mixed-sex and 95% males) and the second factor was the proportion of Nile tilapia: Mayan cichlid (3:1, 5:1, 7:1 and 1:0). Proportion of 1:0 was tilapia monoculture. At stocking, tilapias were 11 weeks old and weighed 24.0 g and Mayan cichlids weighed 5.0 g. Recirculating water systems were used, with 24 fiberglass tanks 1 m3 with permanent water flow (7 L min− 1) and aeration. Each treatment had 3 replicates distributed randomly, and 24 fish were introduced in each tank (30 fish m− 3). The experiment lasted 21 weeks, until tilapia reached marketable size. Fish were fed with extruded formulated diets for tilapia (40% and 30% crude protein). Daily feeding rate was restricted to between 4% and 1.8% of the fish biomass. Temperature, DO and pH (28.0 ± 1.1 °C, 5.2 ± 1.2 mg L− 1 and 7.9 ± 0.2) were within the appropriate ranges for growth, and TAN, nitrites and total alkalinity (0.29 ± 0.22 mg L− 1, 0.04 ± 0.03 mg L− 1 and 238 ± 27 mg L− 1) were within safe ranges. Average survival was high (99%) and no differences were found between populations and among proportions. Nile tilapia Stirling strain showed early (45 g after 3 experimental weeks) sexual maturation and growth dimorphism. Significantly better total yield, FCR and final tilapia body weight were obtained in the 95% male population (9.26 kg m− 3, 1.39 and 383 g) than in the mixed-sex population (7.70 kg m− 3, 1.52 and 315 g). The presence of the Mayan cichlid did not affect tilapia performance. The final weight of Mayan cichlid was significantly higher in the mixed-sex tilapia population (45.9 g) than in the 95% male population (34.4 g). Mayan cichlid growth was inversely proportional to its density, with final weights of 45.5 g, 39.0 g and 34.3 g (7:1 > 5:1 > 3:1). The differences in Mayan cichlid growth are associated with intraspecific competition for available tilapia larvae. Mouth brooding tilapia females with eggs or larvae were observed in both tilapia populations and in all proportions. When fish were weighed some tilapia females released their larvae in the tanks, and both Mayan cichlid and tilapia males were observed preying on them.

GCMS-identified steroids and steroid glucuronides in ovarian growth-stimulating holding water from adult African catfish, Clarias gariepinus

1. 1. Pubertal vitellogenic and previtellogenic female Clarias gariepinus were exposed to holding water from a mixed-sex population of adult conspecifics. 2. 2. Exposure to holding water caused an accelerated ovarian growth in both cases. 3. 3. Analysis of holding water by gas chromatography and mass spectrometry (GCMS) yielded the presence of several steroids and steroid glucuronides known to be produced in adult, prespawning C. gariepinus. 4. 4. The possible role of these compounds in stimulating ovarian growth is discussed in relation to earlier findings on their pheromonal properties.

Pheromonal stimulation of ovarian recrudescence in hatchery-raised adult African catfish, Clarias gariepinus

Adult female African catfish, Clarias gariepinus, were manipulated to enter the phase of ovarian recrudescence by induced ovulation and stripping. These females were exposed to various conspecific stimuli for 33 days. At the end of the experimental period, gonadosomatic indexes (GSIs) were higher in females which had received holding water from a mixed-sex population than in comparable controls. The effect was abolished when recipient females had been rendered anosmic, indicating the presence of chemical substances perceptible through olfaction. Fecundity estimates and histological analysis suggest that the increase in GSI due to pheromonal stimulation is caused by both an increased recruitment of oocytes into the stage of exogenous vitellogenesis and by an enhanced deposition of yolk material in the oocytes. It is concluded that male C. gariepinus release pheromones with a stimulatory effect on vitellogenesis. Neither anosmia itself nor metabolites in holding water affected ovarian recrudescence or body weight increase. The biological significance of such pheromones is discussed in the context of observations on reproduction of C. gariepinus made in the natural environment.

The Performance of Male Broiler Genotypes Reared to Roaster Weight and Females Reared to Broiler Weight on a Low Protein Dietary Regimen

An experiment was conducted with 2400 birds (1200 of each sex) of four commercial broiler genotypes (300 males and 300 females) to study their performance reared to roaster weight on a low protein, three stage (16–20–16) feeding program. Birds were housed separately by sex and genotype, and each of 16 pens (25.64 m2) housed 150 birds. The assignment of genotype and sex to pens was completely randomized with a duplicate pen of each genotype and sex. The results indicate that this roaster program is not genotype specific and that males reached the marketable roaster weight by 70 days of age and yielded comparative monetary returns regardless of genotype used. The study also showed that the program supported good growth of females, which on average reached marketable broiler weight (1865 g) in 49 days. Thus, the results indicate that this feeding program could be used with a mixed sex population with the males marketed as roasters at 70 days and the females marketed earlier as broilers.

Dosage-Mortality Response of the Southern Corn Rootworm to Several Insecticides1

LD50 values expressed in µ g/insect for mixed-sex populations of Diabrotica undecimpunctata howardi Barber were: carbofuran 0.0783; parathion 0.1413; phorate 0.4807; diazinon 0.7431; Landrin® (3,4,5-trimethylphenyl methylcarbamate, 75% 2,3,5-trimethylphenyl methylcarbamate, 18%) 1.0305; fonophos 1.4886; and aldrin 6.8306. On a live tissue weight basis, females required 51.2% more phorate and 114.5% more diazinon for 50% mortality than did males.