LIFE HISTORY VARIATION IN PRIMATES

Extensive variation in life-history patterns is documented across primate species. Variables included are gestation length, neonatal weight, litter size, age at weaning, age at sexual maturity, age at first breeding, longevity, and length of the estrous cycle. Species within genera and genera within subfamilies tend to be very similar on most measures, and about 85% of the variation remains when the subfamily is used as the level for statistical analysis. Variation in most life-history measures is highly correlated with variation in body size, and differences in body size are associated with differences in behavior and ecology. Allometric relationships between life-history variables and adult body weight are described; subfamily deviations from best-fit lines do not reveal strong correlations with behavior or ecology. However, for their body size, some subfamilies show consistently fast development across life-history stages while others are characteristically slow. One exception to the tendency for relative values to be positively correlated is brain growth: those primates with relatively large brains at birth have relatively less postnatal brain growth. Humans are a notable exception, with large brains at birth and high postnatal brain growth.     

Larger brains spur species diversification in birds

Evidence is accumulating that species traits can spur their evolutionary diversification by influencing niche shifts, range expansions, and extinction risk. Previous work has shown that larger brains (relative to body size) facilitate niche shifts and range expansions by enhancing behavioral plasticity but whether larger brains also promote evolutionary diversification is currently backed by insufficient evidence. We addressed this gap by combining a brain size dataset for >1900 avian species worldwide with estimates of diversification rates based on two conceptually different phylogenetic‐based approaches. We found consistent evidence that lineages with larger brains (relative to body size) have diversified faster than lineages with relatively smaller brains. The best supported trait‐dependent model suggests that brain size primarily affects diversification rates by increasing speciation rather than decreasing extinction rates. In addition, we found that the effect of relatively brain size on species‐level diversification rate is additive to the effect of other intrinsic and extrinsic factors. Altogether, our results highlight the importance of brain size as an important factor in evolution and reinforce the view that intrinsic features of species have the potential to influence the pace of evolution.     

Does the weight of the brain depend on the body height?]

Brains of 1664 subjects (895 males and 769 females) aged from 20 to 89 years have been studied. The whole material being investigated was divided, within sex groups, into body-height classes and age classes. The class interval within the age classes was 10 years, that in height classes 5 cm. Mean arithmetics, standard deviations, standard error as well as coefficients of variation and correlation for respective classes have been calculated. It has been ascertained that the brain weight depends on the body height. In tall subjects no brains of extremely low absolute weight are encountered and, adversely, high brain weight is seldom met in short individuals. The body height also exerts certain influence upon the relative weight of the brain. More favourable proportion between the brain weight and the body length has been revealed in short subjects. Tall individuals are characterized by a low relative weight of the brain. It should be supposed that the spinal cord weight is higher in the latter subjects. The differences between the mean absolute weight of women's brains and that in men of the same age class are conditioned by the difference in the body length. A constant magnitude of difference in the mean brain weight in subjects of the same body height claims 100 g. The paper provides 2 enclosed tables representing obtained results for arithmetic mean of the absolute brain weight both in the age classes and body height classes. The differences between the mean weights of brains in women as well as in men are not significant. The coefficient of correlation between the brain weight and the body height is for men r male1 = 0.2008 for women r female1 = 0.2630, wherease the coefficient of regression for the brain weight is r male2 = 3.67 and r female2 = 3.906 respectively.     

Results of the anthropologic studies of school children in Jena between 1880 and 1985

The present report is based on the results from anthropological examinations on schoolchildren, which have been carried out in Jena since 1880. The introduction to the paper gives a survey on the goals of these inquiries, followed by remarks on secular changes in selected measurements of the body (body height, body weight, chest circumference). Besides the extent of the changes in these features, the anticipation of the pubertal growth period and--by means of the relation of body height to chest circumference--a becoming slimmer of today's population of schoolchildren is documented. The comparison of the findings of 1975 and 1985 shows that, regarding the features mentioned, the acceleration in the Jena probands (although in part with reduced intensity) has lasted up to the present time.     

Body Weight and Relative Brain Size (Encephalization) in Eocene Archaeoceti (Cetacea)

Calibration of the Brownian diffusion model of Felsenstein indicates that phylogeny may have an influence on body length and other phenotypic measures in Cetacea for as many as 10,000 generations or about 180,000 years, which is negligible in the 35 million year history of extant Cetacea. Observations of phenotypic traits in cetacean species living today are independent of phylogeny and independent statistically. Four methods for estimating body weight in fossil cetaceans are compared: (1) median serial regression involving a set of multiple regressions of log body weight on log centrum length, width, and height for core vertebrae; (2) regression of log whole body weight on log body length for individuals; (3) regression of log whole body weight on log body length for species means; and (4) regression of log lean body weight on log body length for individuals. These yield body weight estimates for the Eocene archaeocete Dorudon atrox of 1126, 1118, 1132, and 847 kg, respectively, with consistency and applicability to partial skeletons favoring the first approach. The whole-body weight expected, P_e (in kg), for a given body length, L_i (in cm), is given by log₁₀ P_e?=?2.784 ? log₁₀ L_i???4.429. Negative allometry of body weight and body length (slope 2.784?<?3.000) means that small cetaceans are shorter and more maneuverable than expected for their weight, while large cetaceans are longer and more efficient energetically than expected for their weight. Encephalization is necessarily quantified relative to a reference sample, most mammals are terrestrial, and terrestrial mammals provide a logical baseline. The encephalization residual for living terrestrial mammals as a class (ER_TC), is the difference between observed log₂ brain weight (E_i in g) and expected log₂ brain weight (E_e in g), where the latter is estimated from body weight (P_i in g), as log₂ E_e?=?0.740 ? log₂ P_i???4.004. ER_TC is positive for brains that are larger than expected for a given body size, and negative for brains that are smaller than expected. Base-2 logarithms make the ER_TC scale intuitive, in uniform units of halving or doubling. Encephalization quotients (EQ) are unsuitable for comparison because they are proportions on a non-uniform scale. Middle Eocene archaeocetes have ER_TC values close to ?2 (two halvings compared to expectation), while late Eocene archaeocetes have ER_TC values close to ?1 (one halving compared to expectation). ER_TC is not known for fossil mysticetes, but living mysticetes have ER_TC values averaging about ?2. Oligocene-Recent odontocetes appear to have ER_TC values averaging about +1 (one doubling compared to expectation) through their temporal range. Definitive interpretation of the evolution of encephalization in Cetacea will require better documentation for Oligocene–Recent mysticetes and odontocetes.     

Gregariousness increases brain size in ungulates

The brain’s main function is to organise the physiological and behavioural responses to environmental and social challenges in order to keep the organism alive. Here, we studied the effects that gregariousness (as a measurement of sociality), dietary habits, gestation length and sex have on brain size of extant ungulates. The analysis controlled for the effects of phylogeny and for random variability implicit in the data set. We tested the following groups of hypotheses: (1) Social brain hypothesis—gregarious species are more likely to have larger brains than non-gregarious species because the former are subjected to demanding and complex social interactions; (2) Ecological hypothesis—dietary habits impose challenging cognitive tasks associated with finding and manipulating food (foraging strategy); (3) Developmental hypotheses (a) energy strategy: selection for larger brains operates, primarily, on maternal metabolic turnover (i.e. gestation length) in relation to food quality because the majority of the brain’s growth takes place in utero, and finally (b) sex hypothesis: females are expected to have larger brains than males, relative to body size, because of the differential growth rates of the soma and brain between the sexes. We found that, after adjusting for body mass, gregariousness and gestation length explained most of the variation in brain mass across the ungulate species studied. Larger species had larger brains; gregarious species and those with longer gestation lengths, relative to body mass, had larger brains than non-gregarious species and those with shorter gestation lengths. The effect of diet was negligible and subrogated by gestation length, and sex had no significant effect on brain size. The ultimate cause that could have triggered the co-evolution between gestation length and brain size remains unclear.     

Secular changes in height, body weight, body mass index and pubertal development in male children and adolescents in Krakow, Poland

This study examined the secular changes in height, body weight, body mass index and pubertal development in male children and adolescents in Krakow (Poland) over the past 80 years, with an emphasis on the last decade (2000-2010). The survey of the population of Krakow is a continuation of observations conducted in that area for many years. The analysis aims to determine whether in the last decade Krakow still witnessed the secular trend, and what form the trend took. The body height and weight, and body mass index (BMI), of 1862 boys aged 3.5-18.5 years were analysed, against the background of a survey series from the years 1938 (N = 1801), 1971 (N = 2045), 1983 (N = 3124) and 2000 (N = 2328). The mean body height, in almost all age categories, was greater than in the past; however the final height over the last decade remained the same. The mean values of body weight and BMI increased, especially in the last decade. Also, an acceleration of puberty in boys was observed. The last 10 years saw an over 3-month decrease in the age of initial appearance of pubic hair in boys. In conclusion, the last decade saw cessation of the growing taller trend: maximum body height stabilized at approximately 179 cm, but weight and BMI increased. Also, a distinct acceleration of puberty was noticed. Lack of height increase, at the same time as weight gain and puberty acceleration, indicate a progressing developmental disharmony.     

No gains for bigger brains: Functional and neuroanatomical consequences of relative brain size in a parasitic wasp

Heritable genetic variation in relative brain size can underlie the relationship between brain performance and the relative size of the brain. We used bidirectional artificial selection to study the consequences of genetic variation in relative brain size on brain morphology, cognition and longevity in Nasonia vitripennis parasitoid wasps. Our results show a robust change in relative brain size after 26 generations of selection and six generations of relaxation. Total average neuropil volume of the brain was 16% larger in wasps selected for relatively large brains than in wasps selected for relatively small brains, whereas the body length of the large‐brained wasps was smaller. Furthermore, the relative volume of the antennal lobes was larger in wasps with relatively large brains. Relative brain size did not influence olfactory memory retention, whereas wasps that were selected for larger relative brain size had a shorter longevity, which was even further reduced after a learning experience. These effects of genetic variation on neuropil composition and memory retention are different from previously described effects of phenotypic plasticity in absolute brain size. In conclusion, having relatively large brains may be costly for N. vitripennis, whereas no cognitive benefits were recorded.     

Evolutionary Divergence in Brain Size between Migratory and Resident Birds

Despite important recent progress in our understanding of brain evolution, controversy remains regarding the evolutionary forces that have driven its enormous diversification in size. Here, we report that in passerine birds, migratory species tend to have brains that are substantially smaller (relative to body size) than those of resident species, confirming and generalizing previous studies. Phylogenetic reconstructions based on Bayesian Markov chain methods suggest an evolutionary scenario in which some large brained tropical passerines that invaded more seasonal regions evolved migratory behavior and migration itself selected for smaller brain size. Selection for smaller brains in migratory birds may arise from the energetic and developmental costs associated with a highly mobile life cycle, a possibility that is supported by a path analysis. Nevertheless, an important fraction (over 68%) of the correlation between brain mass and migratory distance comes from a direct effect of migration on brain size, perhaps reflecting costs associated with cognitive functions that have become less necessary in migratory species. Overall, our results highlight the importance of retrospective analyses in identifying selective pressures that have shaped brain evolution, and indicate that when it comes to the brain, larger is not always better.     

Secular change in growth of native children and adolescents at high altitude I. Puno,Peru (3800 meters)

A cross sectional sample of 969 native males from Puno (Peru), altitude 3800 m, ranging in age from 7–20 years, and studied for body height, weight, sitting height, leg length, and chest circumference in 1980, were compared, from the point of view of secular trend, with another cross sectional sample of 992 native males from the same place, which were investigated in 1945. In addition, similar observations were carried out in 1980, in a group of 112 females. The data indicate that in Puno there has been no secular increment in the adult body size. However for all ages between 7 and 19 years, body weight and height were significantly greater in 1980 than in 1945. This may be due to earlier sexual maturation in the present generation.     

Differential reproductive success and body size in !Kung San people from northern Namibia

The associations patterns between reproductive success, measured by the total number of offspring, number of living offspring and number of dead offspring, and parental body size, estimated by stature, body weight and Body mass index, were tested in 65 female and 103 male members of a !Kung San population ageing between 25 and 40 years (x = 30.2 yr.) from northern Namibia. In both sexes a significant interaction between fertility patterns and body dimensions was found. Nevertheless, the association patterns differed markedly between the two sexes. While in males tallness and an improved weight status was associated significantly with a higher number of surviving offspring, smaller and lighter females had significantly more surviving children. In males a directional selection towards increased stature and better weight status is in accordance with the well known secular trend of acceleration. In females first of all the postpartum changes in body composition and body weight, resulting from exhausting infant feeding practices seem to support the maternal depletion hypothesis.     

Size and position of the human adhaesio interthalamica

In 50 human brains, we investigated the size of the adhaesio interthalamica, length of CA-CP line, position of the centre of adhaesio interthalamica, and the distance between the corpus callosum and adhaesio interthalamica. Interthalamic adhesion was absent in 11 brains (22%) and was duplicated in 1 brain. In all 50 brains, length of the intercommissural line (CA-CP) had a mean value of 2.56 cm, in brains with the interthalamic adhesion 2.48 cm, and 2.56 cm in brains without it. t-test for this difference showed no significant result for a probability of 0.05 (t = 1.95). Midsagittal section area of adhaesio interthalamica had a mean value of 13.1 mm2 (min = 1.5 mm2; max = 34 mm2). There is no correlation between the length of CA-CP line and the size of the midsagittal section area of adhaesio interthalamica (the correlation coefficient was 0.06). The centre of adhaesio interthalamica was most often situated above the CA-CP line and around the perpendicular line through its middle portion. The distance between the corpus callosum and interthalamic adhesion, measured in standardized system of CA-CP line, had a mean value 1.4 cm (min = 0.7 cm; max = 2.3 cm). Our results confirm the opinions that the presence of size of the interthalamic adhaesion depends not directly on the size of the corresponding brain (diencephalon).     

Light enough to travel or wise enough to stay? Brain size evolution and migratory behavior in birds

Brain size relative to body size is smaller in migratory than in nonmigratory birds. Two mutually nonexclusive hypotheses had been proposed to explain this association. On the one hand, the “energetic trade‐off hypothesis” claims that migratory species were selected to have smaller brains because of the interplay between neural tissue volume and migratory flight. On the other hand, the “behavioral flexibility hypothesis” argues that resident species are selected to have higher cognitive capacities, and therefore larger brains, to enable survival in harsh winters, or to deal with environmental seasonality. Here, I test the validity and setting of these two hypotheses using 1466 globally distributed bird species. First, I show that the negative association between migration distance and relative brain size is very robust across species and phylogeny. Second, I provide strong support for the energetic trade‐off hypothesis, by showing the validity of the trade‐off among long‐distance migratory species alone. Third, using resident and short‐distance migratory species, I demonstrate that environmental harshness is associated with enlarged relative brain size, therefore arguably better cognition. My study provides the strongest comparative support to date for both the energetic trade‐off and the behavioral flexibility hypotheses, and highlights that both mechanisms contribute to brain size evolution, but on different ends of the migratory spectrum.     

Sociality, ecology, and relative brain size in lemurs

The social brain hypothesis proposes that haplorhine primates have evolved relatively large brains for their body size primarily as an adaptation for living in complex social groups. Studies that support this hypothesis have shown a strong relationship between relative brain size and group size in these taxa. Recent reports suggest that this pattern is unique to haplorhine primates; many nonprimate taxa do not show a relationship between group size and relative brain size. Rather, pairbonded social monogamy appears to be a better predictor of a large relative brain size in many nonprimate taxa. It has been suggested that haplorhine primates may have expanded the pairbonded relationship beyond simple dyads towards the evolution of complex social groups. We examined the relationship between group size, pairbonding, and relative brain size in a sample of 19 lemurs; strepsirrhine primates that last share a common ancestor with monkeys and apes approximately 75 Ma. First, we evaluated the social brain hypothesis, which predicts that species with larger social groups will have relatively larger brains. Secondly, we tested the pairbonded hypothesis, which predicts that species with a pairbonded social organization will have relatively larger brains than non-pairbonded species. We found no relationship between group size or pairbonding and relative brain size in lemurs. We conducted two further analyses to test for possible relationships between two nonsocial variables, activity pattern and diet, and relative brain size. Both diet and activity pattern are significantly associated with relative brain size in our sample. Specifically, frugivorous species have relatively larger brains than folivorous species, and cathemeral species have relatively larger brains than diurnal, but not nocturnal species. These findings highlight meaningful differences between Malagasy strepsirrhines and haplorhines, and between Malagasy strepsirrhines and nonprimate taxa, regarding the social and ecological factors associated with increases in relative brain size. The results suggest that factors such as foraging complexity and flexibility of activity patterns may have driven selection for increases in brain size in lemurs.     

Primates, brains and ecology

The paper examines systematic relationships among primates between brain size (relative to body size) and differences in ecology and social system. Marked differences in relative brain size exist between families. These are correlated with inter-family differences in body size and home range size. Variation in comparative brain size within families is related to diet (folivores have comparatively smaller brains than frugivores), home range size and possibly also to breeding system. The adaptive significance of these relationships is discussed.     

Heritability estimates and adjustment factors for the effects of bull age and age of dam on yearling testicular size in breeds of bulls

Scrotal circumference, testicular length and body weight were measured in 3,090 yearling bulls of 12 breed groups finishing growth performance tests during a 5 yr period. Breeds were Limousin, Hereford, Charolais, Angus, Red Poll, Simmental, Pinzgauer, Brown Swiss, Gelbvieh and three crossbred breed groups. All bulls were born during a 60-d calving season starting in late March of each year and were subjected to similar management and environmental influences during the study. The bulls were the progeny of 307 sires averaging approximately 26 sires per breed group and 10 sons per sire. Breed group, sire within breed group, year and age-of-dam effects were important (P<0.01) for all testicular traits at both a constant age (354 d) and constant body weight (418 kg). Paternal half-sib estimates of heritability were 0.41 +/- 0.06 for ageconstant scrotal circumference, 0.34 +/- 0.06 for testicular length and 0.37 +/- 0.06 for calculated paired testicular volume, respectively. Age-constant genetic correlations between yearling body weight and testicular traits were small, indicating that testicular growth and body growth rates are largely independent, regardless of breed. Testicular size of bulls from 2-yr-old dams was smaller than that of bulls from older dams. Most of these age-of-dam effects on testicular size were removed when testicular size was adjusted for the effects of body weight, suggesting that age-of-dam effects on testicular size are primarily the result of age-of-dam effects on body weight. Age adjustment factors for yearling scrotal circumference did not differ (P>0.20) among breed groups and averaged 0.032 cm per day of age. Adjustment factors for age of dam were +1.3, +0.8, +0.4, and +0.0 cm for sons of 2-, 3-, 4- and 5-yr-old dams, respectively.     

Secular trend in body size among college athletes.

Height and weight were compared across five birth decades (1850-1899) among 1,121 Harvard athletes who were lettermen in various sports. There were considerable differences in the magnitude of the secular trend among the sport categories (crew, baseball, football, track, ice hockey, and two or more sports). Comparing the 1890-1899 and 1860-1869 birth-cohort samples, football lettermen were 2.6 inches (6.6 cm) taller (p less than 0.001) and 20 pounds (9.1 kg) heavier (p less than 0.001). Crew lettermen were 2.6 inches taller (p less than 0.001) and 8.5 pounds (3.9 kg) heavier (p less than 0.05). For lettermen in other sports, changes in mean height and weight were smaller in magnitude. Differential selection for body size may explain the differences in the magnitude of the secular trend when analyzed by specific sport.     

Grooming and resting of otters Lutra lutra in a marine habitat

The weight gain in lactating harbour seal pups and sex-specific growth curves are described. The relationship between body length, body weight and age were derived by regression analysis based on length and age data from 365 seals, and weight values from 136 seals. The asymptotic values of the curves describing body length were 148.0 cm and 147.2 cm in females and 153.9 cm and 155.5 cm in males using Gompertz and von Bertalanffy, respectively. The corresponding body weight values were 72.8 kg and 76.7 kg in females and 90.7 kg and 88.4 kg in males.     

The effect of temperature on maturation threshold body-length in Daphnia magna

Aquatic invertebrates are usually larger at maturity when water temperatures are lower. For the freshwater cladoceran Daphnia, it has been suggested that a threshold size must be attained to initiate maturation, which results two instars later in the deposition of eggs into the brood chamber. This threshold size is believed to temperature on maturation threshold body-length in Daphnia magna. Daphnids were raised from birth to maturity under three constant-temperature regimes (12°C, 16°C, 22°C), and two food-level conditions. Animals were measured daily, and a body-length based maturation threshold determined for each individual. We demonstrate that mean maturation threshold length is negatively correlated with ambient water temperature. Further, daphnids with a larger threshold length tended to be larger at maturity. A maturation threshold linked to body length suggests that reduced variation in size at maturity is adaptive, even at the cost of additional variation in instar number or age at maturity.     

Secular trend in body height and weight of Australian children and adolescents

Secular changes in growth and maturation have been well documented in various world populations, with secular increase especially noticeable in the developed countries. To assess the trend in both adult size and tempo of growth we compared the data on stature and body weight obtained in 1992-1993 from 1,804 Melbourne school students aged 5 to 17 with historical data collected from white Australians during the last 100 years. We illustrate the age-dependent trend in stature and body weight by means of regression surfaces. These were constructed by fitting local regression models to historical data and by simple plots showing the overall, and per decade, secular increase in both these measures at peripubertal and adult ages. Because of limited information on sample sizes and variability provided by the historical data, statistical comparisons have been performed only between the present 1992-1993 survey and two earlier independent surveys conducted in 1985 and 1970. The results have shown secular increase in adult stature over the last century, with the rate of increase varying between 0.4 and 2.1 cm/decade in males and 0.01 and 1.6 cm/decade in females. While secular increase in stature has significantly slowed down during the last two decades, the increase in body weight is still continuing at a high rate, and this increase is more pronounced in females. The period of strong secular increase, especially in the tempo of growth, coincided both with the shift toward earlier menarche and the improvement of socioeconomic conditions of the Australian population. The need for further studies to identify factors determining the continuing increase in body weight is emphasized, and caution in using the existing national growth standards for stature and weight is recommended.