Fertile male tortoiseshell cats. Mosaicism due to gene instability?

Two fertile male tortoiseshell Burmese cats with atypical coat color distribution were found to have normal 38XY karyotypes. Synaptonemal complex analysis of one of these cats revealed normal meiotic pairing. Progeny data indicated that both cats were transmitting both alleles at the sex-linked orange locus, but with unequal frequencies. For one of these cats, analysis of pedigree and progeny data indicated that gene instability at the orange locus was the only possible explanation for its mosaicism. A third male tortoiseshell Burmese cat with typical tortoiseshell phenotype was found to be 39XXY and sterile.     

Skeletal muscle characteristics in sedentary black and Caucasian males

Twenty-three male Black African and 23 male Caucasian subjects, ascertained as sedentary, participated in this study designed to determine whether there were differences in skeletal muscle histochemical and biochemical characteristics between racial groups. Muscle fiber type proportions (I, IIa, and IIb), fiber areas and activities of several enzyme markers of different energy metabolic pathways were determined from a biopsy of the vastus lateralis. Results indicated that Caucasians had a higher percent type I (8%, P less than 0.01) and a lower percent type IIa (6.7%, P less than 0.05) fiber proportions than Africans. No significant differences were observed between the two racial groups in the type IIb fiber proportion or in the three fiber type areas. Enzymes catalyzing reactions in phosphagenic [creatine kinase (CK)] and glycolytic [hexokinase (HK), phosphofructokinase (PFK), and lactate dehydrogenase (LDH)] metabolic pathways had significantly higher activities (about 30-40%) in the Black African group than in the Caucasian group (P less than 0.01). No significant difference was noted in the activities of oxidative enzymes [malate dehydrogenase (MDH), oxoglutarate dehydrogenase (OGDH), and 3-hydroxyacyl-CoA dehydrogenase (HADH)]. Consequently, the PFK/OGDH ratio was significantly elevated in Africans (P less than 0.05). The racial differences observed between Africans and Caucasians in fiber type proportion and enzyme activities of the phosphagenic and glycolytic metabolic pathways may well result from inherited variation. These data suggest that sedentary male Black individuals are, in terms of skeletal muscle characteristics, well endowed for sport events of short duration.     

The sodium-22 influx in erythrocytes from black males and females

In order to establish a standard for sodium influx in erythrocytes for the black population, 22Na+ uptake was measured in 29 normotensive black volunteers. Nineteen males and 10 females during the follicular phase of the menstrual cycle were studied utilizing the procedure of Gambhir et al. (1). In the males, cell concentrations ranging from 0.64 to 2.0 X 10(9)/ml showed an influx of 0.42 to 1.34% of the total 22Na+ added, and in the females, using the same erythrocyte concentrations, the 22Na+ influx ranged from 0.37 to 1.1%; these differences were not significant. Intraassay variation of the 22Na+ data was 4.8%. Interassay variations have been explained elsewhere (1). These data provided a range of observed values for 22Na+ uptake in erythrocytes from a subpopulation of normotensive black males and females for comparison with hypertensive patients.     

Competing females and caring males. Sex steroids in African black coucals, Centropus grillii

The black coucal is the only known altricial bird species in which females mate with and lay eggs for more than one male and males are responsible for all parental care (classical polyandry). In this species, the left testis is atrophied and it has been speculated that this may result in a reduction of circulating androgens, providing a unique mechanism for reversals in sex roles. We therefore investigated whether there is a reversal in circulating androgens and oestrogens in black coucals. Despite the reversals in sex roles, males had significantly higher levels of plasma testosterone than females, in a pattern typical of that of monogamous male passerines. Testosterone levels of both sexes were higher during the mating than during the premating stage and were low in males during the nestling stage. The concentrations of androstenedione, dehydroepiandrosterone and oestradiol did not differ between the sexes and were generally low. A physiological challenge with gonadotropin-releasing hormone (GnRH) resulted in a significant increase in testosterone in males but not in females, suggesting either that females are not responsive to GnRH or that they express patterns of testosterone that are similar to those of males of species with a polygynous mating system without paternal care, in which testosterone is expressed at maximum levels throughout the breeding season. We conclude that the absence of one testis does not provide a mechanism for sex role reversal in black coucals. Either androgens are not involved in the regulation of male-like traits in females or females are sensitive to relatively low levels of these steroids.     

Female choice selects for lifetime lekking performance in black grouse males

''Good genes'' models assume that females can use a signal such as mating effort to assess a male''s lifetime fitness. Inferring long-term performance from short-term behavioural observations can be unreliable, and repeated sampling may be needed for more accurate assessment of males. Additionally, if sexual advertisement is viewed as a life-history trait subject to trade-offs, reliable comparison of mates should yield information on all life-history components rather than on one trait value in one season. We show that in the lekking black grouse (Tetrao tetrix), a male''s success is best explained by assuming that females are informed of the past history of males up to the beginning of the study (eight years). Much of this extremely lasting ''memory'' can be attributed to females observing long-term outcomes of male–male competition: current territory position is the only momentarily observable variable that has high power in predicting female choice, and it correlates to a male''s past lekking effort on a cumulative lifetime scale. We conclude that females can use territory position as a signal that conveys information of a male''s lifetime performance that combines lekking effort and longevity. Females may thus overcome the problem of male allocations varying in time, without the need to pay costs associated with repeated sampling.     

MMP13 promoter polymorphism is associated with atherosclerosis in the abdominal aorta of young black males.

Previous studies suggested that remodeling of connective tissue is important in progression of atherosclerosis. We investigated the importance of matrix metalloproteinase 13 (MMP13), in the pathogenesis of atherosclerosis using 995 samples from the Pathobiological Determinants of Atherosclerosis in Youth collection in an association study. We identified two new MMP13 promoter polymorphisms. The genotype for one of the MMP13 polymorphisms was associated with fibrous plaque (P=0.024) in black males. Immunohistochemistry using antibodies for MMP13 showed that MMP13 is expressed in all layers of the aorta. In-vitro transfection experiments with reporter gene constructs and electrophoretic mobility-shift assays showed that the MMP13 polymorphism was a functional variant. MMP13 is therefore, a genetic risk factor for extent of fibrous plaque in the abdominal aorta in young black males. Elucidation of the currently unknown mechanism of the MMP13 polymorphism's action may provide for pharmacological intervention to reduce the severity of atherosclerotic changes in susceptible individuals.     

Evolution of black grouse leks: female preferences benefit males in larger leks

Leks, communal display grounds in which males display and femalesonly attend to mate, represent one of the most remarkable outcomesof sexual selection. There have been no detailed studies thatcompare the behavior of males and females between leks of differentsizes to test if there is any benefit for male clumping andto test the many hypotheses suggested to explain lekking. Inthe black grouse, Tetrao tetrix, larger leks have many morefemale visits and copulations, leading to a higher average malemating success. Females visiting larger leks are also more likelyto mate, indicating that female preferences of males are importantfor the evolution of leks. Yearling males seldom copulate, buttheir presence on the lek increases the mating success of adultmales, suggesting that lek size per se and not only male qualityaffects female preferences for larger leks. The distributionof males over lek sizes agrees with a game theory model of idealfree distribution with unequal competitors, in which less competitivemales go to smaller leks.     

Predation, sensitivity, and sex: why female black rhinoceroses outlive males

Among sexually dimorphic, polygynous mammals, adult femalestend to outlive males and respond more strongly to predatorsthan males. We asked whether a monomorphic, polygynous speciesvirtually immune to predation due to large size (black rhinoceros,Diceros bicornis) conforms to this pattern. Data on 193 interactionswith lions (Panthera leo) and spotted hyenas (Crocuta crocuta)in two nonhabituated populations in Namibia studied from 1991to 1993 revealed that: (1) females were more vigilant or aggressivethan males to either of the potential predators; and (2) whethersolitary or with calves, females attacked more often than males.Although solitary females tended to be more aggressive to lionsthan to hyenas, neither females with calves or males seemedto discriminate between the two carnivores. We also simulatedthe behavior of human predators (poachers) during 69 encounterswith rhinoceroses. While both sexes abandoned local sites becauseof our presence, females ran farther than males, covering upto 40 km in a day. These findings implicate a behavioral mechanismto explain why secondary sex ratios favor females - males aremore prone to human predation, a prediction consistent withdata from 12 populations throughout Africa. Black rhinocerosesappear to be an unanticipated exception to the well-establishedpattern of male-biased mortality in polygynous mammals; in theabsence of intense human predation (a recent event), male mortalityfails to exceed that of females, suggesting that intrasexualcompetition in a polygynous mammal: may not be the primary causeof unbalanced secondary sex ratios. Our results on the causesof sex differences in mortality and in responsiveness to differentpredators reinforce the relevance of behavioral ecology to conservation;such information is necessary for planning how best to minimizenegative human influences on the few remaining wild Africanrhinos.