Following trails of partners in the monogamous lizard, Tiliqua rugosa

The sleepy lizard, Tiliqua rugosa, is an Australian scincid lizard that forms monogamous pairs for 6–8 weeks in the spring before mating occurs. Previous observations and experiments have shown that when partners are separated they can relocate each other, and one suggested mechanism has been trail following. In this article we report results from field-based Y-maze experiments to investigate trail following. In the first part of the spring season, female lizards were more likely to use the arm of the maze previously taken by their male partner than either a blank arm of the maze or the arm taken by an unfamiliar adult male. Females that were more frequently found with their male partner during the spring season were more likely to follow the path of their male partner than less strongly bonded females. In the second part of the spring, after mating had occurred in the natural population, females no longer showed a preference in the maze. Males showed no significant tendency to follow their female partner in any part of the season. The results suggest there is trail following, at least by females, and that females play an active role in maintaining the partnership. This refutes male-based explanations, like mate guarding, for monogamy. Electronic Publication     

CNTF genotype is associated with muscular strength and quality in humans across the adult age span.

The relationship between ciliary neurotrophic factor (CNTF) genotype and muscle strength was examined in 494 healthy men and women across the entire adult age span (20-90 yr). Concentric (Con) and eccentric (Ecc) peak torque were assessed using a Kin-Com isokinetic dynamometer for the knee extensors (KE) and knee flexors (KF) at slow (0.52 rad/s) and faster (3.14 rad/s) velocities. The results were covaried for age, gender, and body mass or fat-free mass (FFM). Individuals heterozygous for the CNTF null (A allele) mutation (G/A) exhibited significantly higher Con peak torque of the KE and KF at 3.14 rad/s than G/G homozygotes when age, gender, and body mass were covaried (P < 0.05). When the dominant leg FFM (estimated muscle mass) was used in place of body mass as a covariate, Con peak torque of the KE at 3.14 rad/s was also significantly greater in the G/A individuals (P < 0.05). In addition, muscle quality of the KE (peak torque at 3.14 rad x s(-1) x leg muscle mass(-1)) was significantly greater in the G/A heterozygotes (P < 0.05). Similar results were seen in a subanalysis of subjects 60 yr and older, as well as in Caucasian subjects. In contrast, A/A homozygotes demonstrated significantly lower Ecc peak torque at 0.52 rad/s for both KE and KF compared with G/G and G/A groups (P < 0.05). No significant relationships were observed at 0.52 rad/s between genotype and Con peak torque. These data indicate that individuals exhibiting the G/A genotype possess significantly greater muscular strength and muscle quality at relatively fast contraction speeds than do G/G individuals. Because of high positive correlations between fast-velocity peak torque and muscular power, these findings suggest that further investigations should address the relationship between CNTF genotype and muscular power.     

Insulin-like growth factor-2 genotype, fat-free mass, and muscle performance across the adult life span.

The influence of insulin-like growth factor-2 (IGF2) genotype on total body fat-free mass (FFM), muscle strength, and sustained power (SP) was evaluated repeatedly at approximately 2-yr intervals in two cohorts from the Baltimore Longitudinal Study of Aging. Cohort 1 was comprised of 94 men tested for isometric grip strength and SP. Cohort 2 was comprised of 246 men and 239 women tested for total body FFM and isokinetic peak torque. Subjects were retrospectively genotyped for the IGF2 gene's ApaI polymorphism. Differences between genotype groups for total FFM, strength, and SP at first visit, at peak age (35 yr), at age 65, and across the adult age span were analyzed using either two-sample t-tests or mixed-effects models, depending on the specific comparisons made. Isokinetic arm strength at the time of first visit was lower in A/A men than in G/G men (P < 0.05). Compared with G/G women, A/A women had lower total body FFM, lower isokinetic arm and leg strength at the time of first visit, and lower values at age 35 (all P < 0.05) for these muscle phenotypes. Furthermore, this difference between the genotype groups was maintained at age 65 and across the adult age span (P < 0.05). No genotype-associated differences in rates of loss of grip strength or SP were found in cohort 1. These results from cohort 2 support the hypothesis that variation within a gene known to influence developing muscle affects muscle mass and muscle function in later life.     

Muscle quality. I.Age-associated differences between arm and leg muscle groups

To determine the differences between armand leg muscle quality (MQ) across the adult life span in men andwomen, concentric (Con) and eccentric (Ecc) peak torque (PT) weremeasured in 703 subjects (364 men and 339 women, age range 19-93yr) and appendicular skeletal muscle mass (MM) was determined in thearm and leg in a subgroup of 502 of these subjects (224 men and 278 women). Regression analysis showed that MQ, defined as PT per unit ofMM, was significantly higher in the arm (~30%) than in the legacross age in both genders (P < 0.01). Arm and leg MQ declined at a similar rate with age in men,whereas leg MQ declined ~20% more than arm MQ with increasing age inwomen (P  0.01 andP < 0.05 for Con and Ecc PT,respectively). Moreover, the age-associated decrease in arm MQ wassteeper in men than in women whether Con or Ecc PT was used (bothP < 0.05). Arm MQ as determined byCon PT showed a linear age-related decline in men and women (28 and20%, respectively, P < 0.001),whereas arm MQ as determined by Ecc PT showed a linear age-relateddecline in men (25%, P < 0.001) butnot in women (not significant). In contrast, both genders exhibited anage-related quadratic decline in leg MQ as determined by Con PT(~40%) and Ecc PT (~25%; both P < 0.001), and the rate of decline was similar for men and women. ThusMQ is affected by age and gender, but the magnitude of this effectdepends on the muscle group studied and the type of muscle action (Convs. Ecc) used to assess strength.

     

Age and gender comparisons of muscle strength in 654women and men aged 20-93 yr

Lindle, R. S., E. J. Metter, N. A. Lynch, J. L. Fleg, J. L. Fozard, J. Tobin, T. A. Roy, and B. F. Hurley. Age and gendercomparisons of muscle strength in 654 women and men aged 20-93 yr.J. Appl. Physiol. 83(5): 1581-1587, 1997.To assess ageand gender differences in muscle strength, isometric, concentric (Con),and eccentric (Ecc) peak torque was measured in the knee extensors at aslow (0.52 rad/s) and fast (3.14 rad/s) velocity in 654 subjects (346 men and 308 women, aged 20-93 yr) from the Baltimore LongitudinalStudy of Aging. Regression analysis revealed significant(P < 0.001) age-related reductions in Con and Ecc peaktorque for men and women at both velocities, but no differences wereobserved between the gender groups or velocities. Age explained lossesin Con better than Ecc peak torque, accounting for 30% (Con) vs. 19%(Ecc) of the variance in men and 28% (Con) vs. 11% (Ecc) in women. Toassess age and gender differences in the ability to store and utilizeelastic energy, the stretch-shortening cycle was determined in a subsetof subjects (n = 47). The older women (mean age = 70 yr)showed a significantly greater enhancement in the stretch-shorteningcycle, compared with men of similar age (P < 0.01) andcompared with younger men and women (each P < 0.05). Bothmen and women showed significant declines in muscle quality for Conpeak torque (P < 0.01), but no gender differences were observed. Only the men showed a significant decline in muscle quality(P < 0.001) for Ecc peak torque. Thus both men and women experience age-related losses in isometric, Con, and Ecc knee extensorpeak torque; however, age accounted for less of the variance in Eccpeak torque in women, and women tend to better preserve muscle qualitywith age for Ecc peak torque. In addition, older women have an enhancedcapacity to store and utilize elastic energy compared with similarlyaged men as well as with younger women and men.

     

Multinomial Distribution and Ascertainment Models

In this paper general ascertainment models are studied relaxing the strong assumption of complete dominance. Probabilitis of ascertaiment for both the complete and incomplete models depending on family size and register size for two types of affected individuals are derived.     

Multinomial Distribution and Ascertainment by Sex

New ascertainment models taking into account partitioning by sex and without any constraint concerning dominance of alleles are proposed. These originate beginning from two major pathways. The first pathway assumes independence and that the family sizes for both males and females are known. The second pathway assumes dependence and that only the total family size is known. Ascertainment probabilities based on several different types of dependence are found. Results are obtained for incomplete multiple ascertainment.