Sex-related Variation Research Articles

Abstract P105: Women with Atrial Fibrillation have Increased Risk of Incident Stroke: Insights from a Propensity-Matched Study of the AFFIRM Trial

Background: Women with atrial fibrillation (AF) have been reported to have poor outcomes. It remains unclear if this association is intrinsic or mediated by the higher comorbidity burden of female AF patients. Therefore, we examined the association between sex and outcomes in a balanced cohort of propensity-matched AF patients who participated in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial. Methods: Of the 4060 AFFIRM patients, 1594 (39%) were women. Propensity scores for female sex were calculated for each of the 4060 patients, and were used to assemble a cohort of 1097 pairs of men and women who were balanced on 51 baseline characteristics, including major cardiovascular (CV) risk factors and medication use, including warfarin. Matched Cox regression models were used to estimate the association between female sex and outcomes during 6 years of follow-up. Results: Patients (n=4060) had a mean (±SD) age of 70 (±8) years and 13% were African American. All-cause mortality occurred in 19% and 15% of matched men and women, respectively (matched HR when women were compared to men, 0.88; 95% CI, 0.69-1.11; p=0.279). All-cause hospitalization occurred in 61% of both men and women (matched HR for women, 1.06; 95% CI, 0.93-1.21; p=0.372). Sex was not associated with CV hospitalization (matched HR for women, 1.13; 95% CI, 0.97-1.32; p=0.111). Ischemic stroke occurred in 3% and 5% of matched men and women, respectively (OR when women were compared to men, 2.02; 95% CI, 1.28-3.18; p=0.002). There was no sex-related difference in major bleeding (7% each). Conclusion: In a cohort of AF patient in which men and women were well-balanced on 51 baseline characteristics including warfarin use, women had increased risk of stroke, but there was no sex-related variation in all-cause mortality or CV hospitalization.

Age and sex variations of the index finger flexion and extension strength in adult Bengalee population

This investigation was aimed to assess age and sex related variation in the index finger flexion and extension strength and its association with some anthropometric characteristics. A total of 400 subjects (200 male and 200 female), 18-60 years were selected at random and divided into three age groups: 18-34, 35-50 and 51-60 years. Strength was measured using a dedicated device. Results revealed that finger flexion and extension strength was significantly greater ( p< 0.001) in men than in women. Irrespective of gender the right hand was significantly stronger ( p< 0.001) than that of left hand. A significant variation in finger extension strength with age was noted for both genders. Positive correlations between strength and some anthropometry were indicated only in case of male subjects.

Sex roles during conspecific territorial defence in the Zenaida dove, Zenaida aurita

Social monogamy in vertebrates often involves the joint defence of an all-purpose territory by pair members. Although both sexes presumably benefit from holding a territory, sex-related variation is often observed in territory defence at the interspecific level, particularly in birds. Most studies of territorial defence in monogamous birds, however, have been conducted on songbirds or on bird species living in temperate areas. In contrast, data on nonoscine tropical bird species remain scarce. We experimentally studied territorial defence in 20 pairs of Zenaida doves, a tropical and territorial monogamous bird species that maintains year-round pair bonds. Overall, males responded to intrusions more frequently than females. However, sex of the intruder had no effect on the reactivity of male or female residents. The use of aggressive behaviours of various intensities did not differ between males and females, irrespective of the sex of intruder. Although the percentage of male responses was correlated significantly and negatively with that of the females, the observed percentage of joint defence was significantly lower than would have been expected if pair members were reacting independently of each other. Finally, variation in reactivity of females to intruders was positively related to variation in intrusion pressure between trials, whereas no such trend was observed in males. We discuss our results in relation to the mating system of Zenaida doves and previous studies of territorial defence in birds.

Sex- and age-related morphofunctional differences in skulls ofTayassu pecariandPecari tajacu(Artiodactyla: Tayassuidae)

Tayassuids exhibit little sexual dimorphism. Sex-related craniomandibular variation was tested in 2 tayassuid species with regard to morphology and function. We analyzed skull features from 61 adult and 37 subadult white-lipped peccaries (Tayassu pecari) and 49 adult collared peccaries (Pecari tajacu) of both sexes. Seventeen skull measurements were used for the morphological characterization, and from these, indexes were obtained for the functional analysis of bite performance (temporal and masseter muscular systems) and head elevation (semispinalis capitis/complexus muscular system). Skull sexual dimorphism of the 2 species and 2 age groups were evaluated independently through discriminant function analysis (DFA), principal component analysis (PCA), and univariate methods. The DFA characterized a slight secondary sexual dimorphism in adult T. pecari and P. tajacu skulls and provided sex classification functions. However, no sexual variation was detected in skull function of adults in either species. Nevertheless, subadult males and females of T. pecari displayed marked morphological and functional skull variation. Subadult females displayed greater skull robustness, and their force indexes indicate an enhancement on bite strength and in head elevation. This could suggest ecomorphological dissimilarities between subadult male and female T. pecari. The sexual precocity of the females reported in the literature could be the main determinant of the marked morphofunctional variation among the T. pecari subadults. These sexual differences in skull morphology seem to become reduced as males mature.

Sex-related effects of an immune challenge on growth and begging behavior of barn swallow nestlings.

Parent-offspring conflicts lead the offspring to evolve reliable signals of individual quality, including parasite burden, which may allow parents to adaptively modulate investment in the progeny. Sex-related variation in offspring reproductive value, however, may entail differential investment in sons and daughters. Here, we experimentally manipulated offspring condition in the barn swallow (Hirundo rustica) by subjecting nestlings to an immune challenge (injection with bacterial lipopolysaccharide, LPS) that simulates a bacterial infection, and assessed the effects on growth, feather quality, expression of morphological (gape coloration) and behavioral (posture) begging displays involved in parent-offspring communication, as well as on food allocation by parents. Compared to sham-injected controls, LPS-treated chicks suffered a depression of body mass and a reduction of palate color saturation. In addition, LPS treatment resulted in lower feather quality, with an increase in the occurrence of fault bars on wing feathers. The color of beak flanges, feather growth and the intensity of postural begging were affected by LPS treatment only in females, suggesting that chicks of either sex are differently susceptible to the immune challenge. However, irrespective of the effects of LPS, parents equally allocated food among control and challenged offspring both under normal food provisioning and after a short period of food deprivation of the chicks. These results indicate that bacterial infection and the associated immune response entail different costs to offspring of either sex, but a decrease in nestling conditions does not affect parental care allocation, possibly because the barn swallow adopts a brood-survival strategy. Finally, we showed that physiological stress induced by pathogens impairs plumage quality, a previously neglected major negative impact of bacterial infection which could severely affect fitness, particularly among long-distance migratory birds.

Diversity, Seasonal Activity and Habitat Associations of Robber Flies (Diptera: Asilidae) in West-Central Illinois

Robber fly diversity, seasonal activity and habitat associations were studied in prairie and forest habitats in west-central Illinois from May to Oct. 2005. The greatest numbers of individuals and species were collected in recently burned prairie and forest habitats, although richness in the recently burned prairie was lower than expected based on rarefaction. Six of the eight most abundant species had primarily mid-season or earlier flight activity patterns; the other two species were mid- to late or late season fliers. There was significant variation in robber fly species composition among habitats. Forest habitats had greater within-habitat variation in species composition than did prairie habitats. Three indicator species (Cerotainia macrocera Say, Nerax aestuans (L.) and Promachus hinei Bromley) were found, all for prairie habitats. Two species (Ommatius ouachitensis Bullington & Lavigne and P. hinei) showed significant sex-related variation in habitat associations. These results show that significant variation in robber fly assemblages can occur over relatively small geographic areas and that fire may affect robber fly abundance and diversity.

Plumage Bacterial Assemblages in a Breeding Wild Passerine: Relationships with Ecological Factors and Body Condition

Microorganisms have been shown to play an important role in shaping the life histories of animals, and it has recently been suggested that feather-degrading bacteria influence the trade-off between parental effort and self-preening behavior in birds. We studied a wild breeding population of great tits (Parus major) to explore habitat-, seasonal-, and sex-related variation in feather-degrading and free-living bacteria inhabiting the birds' yellow ventral feathers and to investigate associations with body condition. The density and species richness of bacterial assemblages was studied using flow cytometry and ribosomal intergenic spacer analysis. The density of studied bacteria declined between the nest-building period and the first brood. The number of bacterial phylotypes per bird was higher in coniferous habitat, while bacterial densities were higher in deciduous habitat. Free-living bacterial density was positively correlated with female mass; conversely, there was a negative correlation between attached bacterial density and female mass during the period of peak reproductive effort. Bacterial species richness was sex dependent, with more diverse bacterial assemblages present on males than females. Thus, this study revealed that bacterial assemblages on the feathers of breeding birds are affected both by life history and ecological factors and are related to body condition.

Disappearance of gender‐related difference in the toxicity of benzotriazole ultraviolet absorber in juvenile rats

2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole (HDBB) is an ultraviolet absorber used in plastic resin products, such as building materials and automobile components. In oral repeated dose toxicity studies using 5- or 6-week-old rats, this chemical induced hepatic histopathological changes, such as hypertrophy accompanied with eosinophilic granular changes and focal necrosis of hepatocytes, and male rats showed nearly 25 times higher susceptibility to the toxic effects than females. Castration at approximately 4 weeks of age markedly reduced the sex-related variation in HDBB toxicity, but some difference, less than five times, remained between male and female castrated rats. Following oral HDBB administration to male and female juvenile rats from postnatal days 4-21, such gender-related difference in toxic susceptibility was not detected; therefore, it is speculated that the determinants of susceptibility to HDBB toxicity are differentiated between sexes after weaning. In young rats given HDBB, there was no gender-related difference in plasma HDBB concentration, and no metabolites were detected in the plasma of either sex. HDBB induced lauric acid 12-hydroxylase activity in the liver and this change was more pronounced in males than in females. These findings indicate that HDBB could show hepatic peroxisome proliferation activity, and the difference in the susceptibility of male and female rats to this effect might lead to marked gender-related differences in toxicity.

Avian hind‐limb digit length ratios measured from radiographs are sexually dimorphic

Sexual dimorphism in digit length ratios is well established in humans, and has been reported in other vertebrate species as well, including birds. The sign of sexual dimorphism in digit ratios may, however, vary both within and between vertebrate classes. It has been hypothesized that sex differences in digit ratios arise via differential prenatal exposure of the two sexes to steroids, which may affect the expression of the Hox genes controlling the osteometric development of digits and appendices. Among birds, the evidence for sex dimorphism in hind-limb digit ratios is conflicting, though all previous studies were based on measurements of undissected digits, implying that results could be confounded by sex-related variation in soft tissues. Here we report that digit ratios derived from radiographs of both feet of a large passerine bird, the hooded crow (Corvus corone), are sexually dimorphic, males showing larger 2D : 3D (effect size, r = 0.33) and 2D : 4D than females (effect size, r = 0.28). We also observed a good agreement (r = 0.45) between radiographic estimates of digit ratios and digit ratios calculated based on undissected digit measurements (thus including soft tissues). Importantly, we found that the patterns of sex and side differences were largely coherent between the two methods. Therefore, our findings show for the first time in avian species that sex differences in digit ratios have an osteometric basis, a fundamental prerequisite for a role of Hox genes in originating such dimorphism.

Seasonal and sex-related variation in song control nuclei in a species with near-monomorphic song, the northern cardinal

Studies concerning the song control system (SCS) in songbirds generally focus on males due to their prodigious song production. Both seasonal and age related differences have been found in the size of male SCS regions. Among those studies that have addressed females some level of sexual size dimorphism has been found, with females generally having smaller SCS area than males. Among those species where female song has been studied, typically females either sing much less than males, or they duet with their mates, but in general do not produce independent song. Here we present information on seasonal and sex differences in SCS in the northern cardinal (Cardinalis cardinalis) a species where both sexes sing, females sing independent of their mates, and song is produced by males over a prolonged period of time (7-8 months). We collected brains from free-living adult cardinals, both in the late non-breeding season and during the early breeding season, and measured three song control nuclei; HVC, Area X and RA. There were sex differences in all three areas assessed at the two time points considered. Additionally, there was a seasonal difference in both sexes for all areas assessed. In both time points male SCS nuclei were 1.5-2.0 times larger than female SCS nuclei. These data show that even in those species with independent female song there may still exist sex differences in the SCS nuclei. Similarity in song between the sexes could be related to differences in hormone receptors or hormone levels in the brain, while the small-observed changes in SCS area in males may allow for early breeding season song production and song production outside of the breeding season.

RESOURCE-MEDIATED CONDITION DEPENDENCE IN SEXUALLY DICHROMATIC BUTTERFLY WING COLORATION

Theory predicts that traits subject to strong sexual selection should evolve to be more exaggerated and developmentally integrated than nonsexual traits, thus leading to heightened condition dependence. Until recently, however, efforts to evaluate this prediction have suffered from either a purely correlational (nonmanipulative) approach, or from using manipulations of doubtful ecological relevance. Here I address these issues by integrating observation and manipulation to study condition- and sex-related color variation in a butterfly. The focal species, Eurema hecabe (Pieridae), possesses three sexually homologous and morphogenetically discrete dorsal wing color elements-coherently scattered ultraviolet (UV), pteridine yellow, and melaninic black. The UV is most strongly sexually selected, and is also the only color element with restricted distribution across female wings. Condition dependence and sexual dichromatism were pervasive, characterizing all color traits except the melanic black, and acting such that low condition males resembled high condition females. Although female coloration tended to exhibit greater phenotypic variation, size-scaled UV was more variable and condition dependent in males. Importantly, manipulation of larval resources was sufficient to closely reconstruct the extent and patterns of field-observed phenotypic variation in condition, and color trait expression, which implicates larval resource acquisition as a primary driver of condition dependence. These results support theories regarding phenotypic variation in sexually selected traits.

Sex-related variation in compact bone microstructure of the femoral diaphysis in juvenile rabbits

BackgroundWhile gross morphological changes in the skeleton between males and females are well know, differences between sexes in the histomorphology are less known. It is important to have knowledge on the bone structure of rabbits, as this is a widely used species in biomedical research. A study was performed to evaluate the association between sex and the compact bone morphology of the femoral diaphysis in juvenile rabbits.MethodsSeventeen clinically healthy 2–3 month-old rabbits (9 females, 8 males) were included in the study. The rabbits were euthanized and the right femur was sampled for analysis. 70–80 microns thick bone sections of the femoral diaphysis were prepared using standard histological equipment. The qualitative histological characteristics were determined according to internationally accepted classification systems while the quantitative parameters were assessed using the software Scion Image. Areas, perimeters, minimum and maximum diameters of primary osteons' vascular canals, Haversian canals and secondary osteons were measured. Additionally, blood plasma concentrations of progesterone, corticosterone, IGF-I, testosterone and estradiol were analyzed.ResultsQualitative histological characteristics were similar for both sexes. However, variations of certain quantitative histological characteristics were identified. Measured parameters of the primary osteons' vascular canals were higher in males than for females. On the other hand, females had significant higher values of secondary osteons parameters. Differences in Haversian canals parameters were only significant for minimum diameter.ConclusionThe study demonstrated that quantitative histological characteristics of compact bone tissue of the femoral diaphysis in juvenile rabbits were sex dependent. The variations may be associated with different growth and modeling of the femur through influence by sex-specific steroids, mechanical loads, genetic factors and a multitude of other sources. The results can be applied in experimental studies focusing on comparison of the skeletal biology of the sexes.

Sexual Variation in Fisheries Research and Management: When Does Sex Matter?

In fish, sex determination is a plastic process regulated by a relatively small number of genes that, in turn, leads to a cascade of organism level effects. In other animal taxa, intersexual variation is widespread and has implications in the realms of morphology, behavior, physiology, and bioenergetics. Although relatively well documented in the literature focusing on mammals, birds, and reptiles, the degree to which sex-specific variation is considered is unknown in fish and fisheries research. We examined the scientific literature to evaluate the important sex-related differences in fish and highlighted why some of these differences are of great biological consequence. Sex-specific differences in morphology included sexual size dimorphism, external traits such as coloration, and internal anatomy such as neuron structure. Behavioral differences between the sexes are often linked to reproduction, but there are some documented differences (i.e., variation in aggression and predator avoidance) that are independent of the reproductive period. The potential for sex-related physiological differences are relatively unexplored for fish, although there is strong evidence for disparity in hormone regulation, stress, and immune responses between the sexes. Sex-related variation is also poorly examined in the field of bioenergetics despite the fact that differences in energy requirements and expenditure should and do vary between the sexes. A quantitative literature review of several prominent fisheries journals revealed that sex is often overlooked in fish and fisheries research (between 15 and 44% of articles), which may impair the ability of researchers to detect biologically relevant differences, which in turn can greatly affect management decisions. Although there has been a growing recognition that intra-specific variation (at the population level) is important in fisheries management and research, there is also a need to consider that intersexual diversity exists and is important to understand, conserve, and manage fish and fisheries resources.

Epidemiological study of Bonamia sp. in the native flat oyster, Ostrea puelchana from San Matías Gulf (NW Patagonia, Argentina)

In 1996 a mass mortality was reported in Ostrea puelchana culture in San Antonio Bay (San Matías Gulf, North Patagonia, Argentina) and Bonamia sp. was identified as a possible aetiological agent. The presence of this pathogen was the first record for this genus in the SW Atlantic Ocean and is the only know OIE (Office International des Epizooties) Notifiable Disease of aquatic organisms known in Argentina. In this study we surveyed natural beds for five years, in order to describe the spread, as well as size and sex-related variation in the prevalence of the Bonamia sp. infection, into San Matías Gulf. The prevalence of infection by Bonamia sp. in 1996–2001 clearly defined the focus of infection from which the parasite spread. Infection radiated from this focus, in the culture area inside San Antonio Bay in 1996, through the oysters beds located at the SW and NE of the bay. Statistical analysis indicated that there were no differences between the mean height of the parasitized and non-parasitized oysters and infections with Bonamia sp. were observed in all sexual categories. Their prevalence varied between beds. Statistical analysis indicated that the probability of infection by Bonamia sp. was independent of the sex. We propose that Bonamia sp. is an enzootic parasite of San Matías Gulf, because of the demographic isolation of the native oyster populations, as San Matías Gulf is a relative close geographical area. Also, there is not existence of other banks with similar densities in the geographical distribution range of O. puelchana. Furthermore, the presence of natural dense beds close to the oyster culture, the existence of strong tide currents in the area, the hydrodynamic of the marine bottom and environmental modifications are all factors that may contribute to the spread of Bonamia sp. infection among SW and NE natural beds of O. puelchana in San Matías Gulf.

Sex- and age-related variation in neurosteroidogenic enzyme mRNA levels during quail embryonic development

Brain can synthesize steroids de novo from cholesterol and this biochemical feature is a conserved property of vertebrates. There is growing evidence indicating that neurosteroids might participate in sexual differentiation of the brain. Therefore, in this study we investigated the presence, the sex differences, and the development-dependent variation of mRNAs coding for key neurosteroidogenic enzymes, namely cytochrome P450 side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid-dehydrogenase/Δ5-Δ4-isomerase (3β-HSD), cytochrome P450 17α-hydroxylase/c17, 20-lyase (P450c17), and aromatase in embryonic prosencephali. Our results indicated that 3β-HSD mRNA levels were sexually dimorphic and developmental age-dependent. In particular, 3β-HSD mRNA levels were higher in females than in males at E7, whereas, this dimorphism was reversed at E9 and E15. In females, the relative levels of 3β-HSD mRNA were highest at E7, whereas, in males they were significantly higher at E9 and E15 than at E7 and at E11. This sexual dimorphism was a peculiar feature of the prosencephalon, it could not be observed before gonadal sexual differentiation and it was not paralleled by a dimorphism in the brain content of progesterone. The level of mRNA coding for P450scc and for P450c17 did not show obvious developmental- or sex-related variation. Aromatase mRNA varied as a function of the embryonic age but not of the sex. These results, taken together, are suggestive of a potential role of some neurosteroidogenic enzymes in the development of quail brain and suggest that sexual differences in the hormonal environment may occur during brain development.

Sex-related asymmetry in competitive ability of sexually monomorphic barn swallow nestlings

In diverse taxa, offspring solicit parental care using complex displays, which may evolve as reliable signals of condition or as mechanisms to manipulate parental investment. Differential sex allocation may therefore result from adaptive parental decisions or sex-related variation in competitive ability or because of sex-related asymmetries in kin selection. Under normal food provisioning, female barn swallow (Hirundo rustica) nestlings begged more loudly but did not receive more food than male nestlings. After food deprivation, begging call loudness of males but not females increased. Begging loudness positively predicted the number of feedings received by the nestlings, and males gained more mass than females after food deprivation. Male nestlings are more severely affected by chronic food reduction and may therefore accrue a larger benefit compared to females by increasing their food intake under short-term conditions of food scarcity. These results suggest that either females do not increase begging intensity to favour male broodmates which are more vulnerable to prolonged food stress, or that males prevail in scramble competition despite being similar in size to females.

A propensity-matched study of the effect of diabetes on the natural history of heart failure: variations by sex and age

Background:Poor prognosis in heart failure (HF) patients with diabetes is often attributed to increased co-morbidity and advanced disease. Further, this effect may be worse in women.Objective:To determine whether the effect...

Electrocardiographic reference ranges derived from 79,743 ambulatory subjects

Background Reference ranges for electrocardiogram (ECG) intervals, heart rate, and QRS axis in general use by medical personnel and ECG readers are unrepresentative of true age- and sex-related values in large populations and are not based on modern electrocardiographic and ECG reading technology. Methods and Results The results of ECG interpretation by cardiologists using digital technology for viewing and interpreting ECGs were compiled from single, baseline ECGs of 79,743 individuals included in pharmaceutical company–sponsored clinical trials. Women comprised 48% of the total population. Ages ranged from 3 months to 99 years, and the bulk of the population (56%) was aged 40 to 70 years. Striking differences in numerical ECG values based on age and sex were observed. A subgroup of 46,129 individuals with a very low probability of cardiovascular disease was identified. The following were the reference ranges for this subgroup, determined using the 2nd and 98th percentiles: heart rate, 48 to 98 beats/min; PR interval, 113 to 212 milliseconds; QRS interval, 69 to 109 milliseconds; frontal plane QRS axis, −40° to 91°; QT interval, 325 to 452 milliseconds; QTc-Bazett, 361 to 457 milliseconds; and QTc-Fridericia, 359 to 445 milliseconds. There were marked age- and sex-related variations in the reference ranges of this subgroup, and they differ substantially from previously reported norms. Small differences were observed in ECG values obtained using our digital methods as compared with readings done using paper tracings and values computed by 2 commercial computer algorithms. Conclusions We observed large differences in electrocardiographic heart rate, interval, and axis reference ranges in this study compared with those reported previously and with reference ranges in general use. We also observed a large influence of age and sex upon normal values. Very large cohorts are required to fully assess age- and sex-related variation of reference ranges. Electrocardiographic reference ranges should be modernized.

Fat Patterning of Santhal Children--a Tribal Population of West Bengal, India

A cross sectional study was undertaken to examine the body composition including fat patterning among 1012 Santal children, aged 5-12 years, in Puruliya district of West Bengal, India. The anthropometric variable measured included height, weight and skinfold thickness of triceps and subscapular. The body mass index (BMI) was also calculated. The measurements were used to estimate body fat percent (%BF) and fat-free mass (FFM) from skinfolds. Fat mass and FFM were each divided by height squared to produce the fat mass index (FMI) and fat-free mass index (FFMI). Maximum gaining of %BF and FFM was found at ages 11-12 years in both sexes. Difference of-FFM between 5 and 12 years of age was found to be highest in girls (18.7 kg) than in boys (14.92 kg). Body fat percentage of girls was significantly (p < 0.05) higher (except in 8 and 9 years old) than that of boys. FMI and FFMI of girls showed different pattern than that of boys. FFM and %BF showed significant (p < 0.01) relationship with all anthropometric variables. Results suggests a clear evidence of sexual dimorphism in fat patterning; girls showing a greater subcutaneous adiposity in comparison with boys. FMI and FFMI, both indices indicate an age-and sex-related variation among Santal children. The data of the present study could be serving as reference data in other studies of Santal children.

Karyology of the redfin minnows, genus Pseudobarbus Smith, 1841 (Teleostei: Cyprinidae): one of the evolutionarily tetraploid lineages of South African barbines

The karyotypes of six species of Pseudobarbus Smith, 1841, namely P. afer (Peters, 1864), P. asper (Boulenger, 1911), P. burchelli Smith, 1841, P. burgi (Boulenger, 1911), P. phlegethon (Barnard, 1938) and P. tenuis (Barnard, 1938), were examined by conventional Giemsa staining and described. All six karyotypes have 2n = 100 chromosomes, dominated by bi-armed chromosomes, as does the only other member of the genus, P. quathlambae (Barnard, 1938). Sex-related intraspecific karyotype variation was not found. The shared chromosome numbers and general similarity of the karyotypes (FN = 186–192) provide a new synapomorphy to support their monophyly, which is already indicated by anatomical and mtDNA markers. Karyotype evolution within the genus has been accompanied by chromosomal inversions and centromeric shifts. Comparison of the diploid number found in Pseudobarbus with other African barbine cyprinines, which have in the region of 2n = 50 and lower FNs, suggests a tetraploid evolutionary origin of the genus, possibly by allotetraploidy.