Genetic parameters of serum cholesterol levels, activity and growth in mice

Effects of selection on food intake in the adult mouse

SUMMARY

Replicated lines of mice were selected High and Low for adjusted food intake and contemporaneous control lines were maintained. The selection criterion was food intake between 8 and 10 weeks, adjusted by phenotypic regression on mean body weight at 8 and 10 weeks of age to reduce correlated changes in body weight. Responses are given for the first 23 generations of selection, after which adjusted food intake had diverged by a factor of 1.7-1.95. A small correlated response in body weight occurred and mice from the High line were slightly heavier: at 10 weeks of age body weight had diverged by a factor of 1.09-1.11. The realized within-family heritability varied between the replicates from 0.16-0.27 from which a mean estimated mass selection heritability (h(2) = 0.35±0.05) was derived. Mice from the Low line were fatter, however not significantly, because of a High between replicate variance (p > 0.05). Differences in growth over the selection period may account for around 5% of the divergence and increased maintenance costs associated with the larger lean mass of the high lines may explain a further 5%. Mice from the High lines spilled significantly (p < 0.05) more food which accounted for 23% of the divergence in apparent food intake. The heat increment of feeding, brown adipose tissue activity and locomotor activity all appear to be unchanged. ZUSAMMENFASSUNG: Auswirkungen der Selektion auf Futteraufnahme in der adulten Maus In einem Experiment mit Wiederholungen wurden Mäuselinien auf hohe und niedrige korrigierte Futteraufnahme selektiert und korrespondierende Konttrollen gehalten. Das Selektionskriterium war die Futteraufnahme im Alter von 8 bis 10 Wochen, die mittels phänotypischer Regression korrigiert wurde, um die Körpermasse möglichst konstant zu halten. Der direkte Selektionserfolg über die ersten 23 Generationen ist beschrieben. Die Linien divergierten zu diesem Zeitpunkt bezüglich des Selektionsmerkmals um 70 bis 95%. In der Körpermasse trat ein geringfügiger korrelierter Selektionserfolg auf. Die Tiere der 'high'-Linie waren im Alter von 8 bis Wochen ca. um 6 bis 11% schwerer. Die realisierte Intra-Familien-Heritabilität variierte zwischen den Wiederholungen zwischen 0.16 und 0.27, woraus sich eine mittlerer Heritabilitätskoeffizient von h(2) = 0.35±0.05 für die Massenselektion ergab. Mäuse der 'low'-Linie hatten mit 10 Wochen 2.4% (P > 0.05) und mit 17 Wochen ca. 7% (P < 0.05%) mehr Fett. Mit Unterschieden im Wachstum lassen sich weniger als 5% der Linienunterschiede in der Futteraufnahme erklären. Der höhere Erhaltungsbedarf, der aus einer höheren fett-freien Körpermasse in der 'high'-Linie resultiert, könnte weitere 5% erklären. Tiere der 'high'-Linie verstreuten deutlich (P < 0.05) mehr Futter, worauf sich 23% der Divergenz in der scheinbaren Futteraufnahme zurückführen ließen. Die Aktivät des braunen Fettgewebes, die lokomotorische Aktivität und die fütterungsbedingte Wàrmeproduktion sind scheinbar unverändert.

Behaviour influences cholesterol plasma levels in a pig model

Little is known about the relationship between feed intake behaviour and cholesterol levels in humans. This can be attributed to the fact that feed intake behaviour in humans is difficult to assess. The relationships between feed intake, feed efficiency and feed intake behaviour, and cholesterol and triglyceride levels were investigated at an average age of 187 days, in a pig model consisting of 202 Duroc barrows. Feed intake and feed intake behaviour were recorded individually and daily by means of an electronic identification system. Animals with high levels of total cholesterol also had high levels of high-density lipoprotein (HDL), low-density lipoprotein (LDL) cholesterol and triglycerides. Animals with high levels of HDL also had high levels of LDL and triglycerides, and animals with high levels of LDL also had high levels of triglycerides. Animals with higher BW, higher backfat thickness, higher BW gain, higher gain of backfat deposition, higher feed intake, higher residual feed intake (RFI) and higher feed intake rate had higher levels of total, HDL and LDL plasma cholesterol. Results indicate that the relationship between feed intake and cholesterol levels is a long-term relationship, while the relationship between RFI and cholesterol levels is more of a short-term nature. The relationship between intake rate and cholesterol plasma levels disappeared after correction for the amount of feed consumed. Results indicate that feed intake independent of metabolic BW, growth and fatness, i.e. 'RFI', was positively correlated with cholesterol plasma levels. This suggests that eating food over and above the maintenance and growth requirements constitutes a health risk independent of the level of fatness.

How heritable is innate behaviour?

The relations between innateness and heritability of behaviour, environmental heterogeneity, genetic diversity of populations, and rates of evolution of behaviour are discussed on the basis of a simple quantitative model. An index I of innateness is proposed which can be related to the heritability index h2. I and h2 are positively related but the degree of correlation depends on the genetic variability of the population, the heterogeneity of the conditioning environment, and the level of spontaneous behavioural variability. The influence of innateness on rates of evolution is moderate. The frequency distributions of I and h2 are unimodal, there is no evidence for an innate-acquired dichotomy.

Individual differences in physical activity are closely associated with changes in body weight in adult female rhesus monkeys (Macaca mulatta)

The increased prevalence of overweight adults has serious health consequences. Epidemiological studies suggest an association between low activity and being overweight; however, few studies have objectively measured activity during a period of weight gain, so it is unknown whether low activity is a cause or consequence of being overweight. To determine whether individual differences in adult weight gain are linked to an individual's activity level, we measured activity, via accelerometry, over a prolonged period (9 mo) in 18 adult female rhesus monkeys. Weight, food intake, metabolic rate, and activity were first monitored over a 3-mo period. During this period, there was mild but significant weight gain (5.5 +/- 0.88%; t =-6.3, df = 17, P < 0.0001), whereas caloric intake and activity remained stable. Metabolic rate increased, as expected, with weight gain. Activity level correlated with weight gain (r = -0.52, P = 0.04), and the most active monkeys gained less weight than the least active monkeys (t = -2.74, df = 8, P = 0.03). Moreover, there was an eightfold difference in activity between the most and least active monkeys, and initial activity of each monkey was highly correlated with their activity after 9 mo (r = 0.85, P < 0.0001). In contrast, food intake did not correlate with weight gain, and there was no difference in weight gain between monkeys with the highest vs. lowest caloric intake, total metabolic rate, or basal metabolic rate. We conclude that physical activity is a particularly important factor contributing to weight change in adulthood and that there are large, but stable, differences in physical activity among individuals.

Phenotypic and genetic variability of estimated growth curve parameters in mice

Data from 1,919 outbred ICR mice were used to examine the potential usefulness of growth curve parameters as selection criteria for altering the relationship between body weight and age. A logistic growth function was used to model growth through 12 weeks of age. Estimates of asymptotic weight (A), maximum growth rate (r) and age at point of inflection (t(*)) were obtained by nonlinear least-squares. A log transformation was also used to stabilize residual variance. Phenotypic and genetic parameters were estimated for the estimated growth curve parameters and for body weights at 2, 3, 4.5, 6, 8 and 12 weeks of age. Heritabilities of estimated growth curve parameters (obtained with and without a log transformation, respectively) were: A (0.28±0.07, 0.28±0.07), r (0.35±0.07, 0.53±0.09) and t(*) (0.41±0.08, 0.44±0.08). Estimated genetic correlations suggest that t(*) may be useful in selecting for rapid early growth without increasing mature weight.

Selection for serum cholesterol, voluntary physical activity, 56-day body weight and feed intake in randombred mice. I. Direct responses

A five-generation selection experiment was conducted with randomly bred ICR mice. Lines were developed for high (CH) and low (CL) serum cholesterol (SC), voluntary physical activity (lines AH and AL), 56-day body weight (lines WH and WL), and feed intake (lines IH and IL). An unselected randomly bred control line was maintained with each pair of selection lines (CC, AC, WC and IC, respectively). Selection was based on individual performance in SC, activity and weight lines, and on within-sex, among full-sib family selection in intake lines. Genetic responses (selected line generation means deviated from control line generation means and regressed on generation number) were different from zero (P less than 0.05) in CH males and females, CL males, AH males and females, AL males, WH males and females, WL males and females, and IH females. Realized heritabilities which did not differ (P less than 0.05) between sexes were: 0.43 +/- 0.05 (line CH), 0.37 +/- 0.06 (line CL), 0.26 +/- 0.08 (line AH), 0.16 +/- 0.04 (line AL), 0.33 +/- 0.05 (line WH), 0.40 +/- 0.05 (line WL), 0.42 +/- 0.06 (line IH). In Line IL heritabilities of males and females differed (P less than 0.05) from each other (0.08 +/- 0.06 and 0.29 +/- 0.06, respectively).

Selection for serum cholesterol, voluntary physical activity, 56-day weight and feed intake in randombred mice. II. Correlated responses

Randomly bred ICR mice were selected for five generations for high and low serum cholesterol (SC), voluntary physical activity, 56-day body weight and feed intake. An unselected, randomly bred control line was maintained with each pair of selection lines. Significant increases in mature body weight occurred in males of high weight and high intake lines and in females of high SC, high weight and high intake lines. Significant decreases in mature body weights occurred in males of low weight line and in females of low SC and low weight lines. Both high and low selected SC lines had greater (P less than 0.05) activity scores and consumed more feed than the SC control. Mice selected for high activity consumed more (P less than 0.05) feed than mice selected for low activity. Mice selected for high 56-day body weight consumed more (P less than 0.05) feed and had higher SC than mice selected for low 56-day body weight. Mice selected for high feed intake were heavier (P less than 0.05) and more active (P less than 0.05) than low feed intake mice but had significantly lower SC levels.

Divergent selection in Japanese quail for the plasma cholesterol response to ACTH

Two lines of Japanese quail were divergently selected for high and low plasma cholesterol levels after three daily injections with 2 IU of adrenocorticotropen (ACTH)/100 g of body weight. Plasma cholesterols were obtained at 31 days of age, just before the first injection, and at 34 days of age, after the last injection. After eight generations of selection, the plasma cholesterol level after ACTH injections in the high line was 34% greater than the level in the control line, whereas the low line level was approximately 14% less than that in the control. Selection differentials were significantly greater in the high line than in the low line. The realized heritability for plasma cholesterol before ACTH treatment calculated by regression of progeny on mid-parent was .25 in the high line and .16 in the low line.