Sexual Dimorphism In Body Mass Research Articles

Effects of temperature on metabolic rate during metamorphosis in the alfalfa leafcutting bee.

Spring conditions, especially in temperate regions, may fluctuate abruptly and drastically. Environmental variability can expose organisms to temperatures outside of their optimal thermal ranges. For ectotherms, sudden changes in temperature may cause short- and long-term physiological effects, including changes in respiration, morphology, and reproduction. Exposure to variable temperatures during active development, which is likely to occur for insects developing in spring, can cause detrimental effects. Using the alfalfa leafcutting bee, Megachile rotundata, we aimed to determine if oxygen consumption could be measured using a new system and to test the hypothesis that female and male M. rotundata have a thermal performance curve with a wide optimal range. Oxygen consumption of M. rotundata pupae was measured across a large range of temperatures (6-48°C) using an optical oxygen sensor in a closed respirometry system. Absolute and mass-specific metabolic rates were calculated and compared between bees that were extracted from their brood cells and those remaining in the brood cell to determine whether pupae could be accurately measured inside their brood cells. The metabolic response to temperature was non-linear, which is an assumption of a thermal performance curve; however, the predicted negative slope at higher temperatures was not observed. Despite sexual dimorphism in body mass, sex differences only occurred in mass-specific metabolic rates. Higher metabolic rates in males may be attributed to faster development times, which could explain why there were no differences in absolute metabolic rate measurements. Understanding the physiological and ecological effects of thermal environmental variability on M. rotundata will help to better predict their response to climate change.

Ontogenetic Development of Sexual Dimorphism in Body Mass of Wild Black-and-White Snub-Nosed Monkey (Rhinopithecus bieti).

Sexual dimorphism exists widely in animals, manifesting in different forms, such as body size, color, shape, unique characteristics, behavior, and sound. Of these, body mass dimorphism is the most obvious. Studies of evolutionary and ontogenetic development and adaptation mechanisms of animals' sexual dimorphism in body mass (SDBM), allow us to understand how environment, social group size, diet, and other external factors have driven the selection of sexual dimorphism. There are fewer reports of the ontogenetic development of sexual dimorphism in body mass in Rhinopithecus. This study explores the ontogenetic development pattern of SDBM in wild black-and-white snub-nosed monkeys (R. bieti), and the causes resulting in extreme sexual dimorphism compared to other colobines. A significant dimorphism with a ratio of 1.27 (p < 0.001) appears when females enter the reproductive period around six years old, reaching a peak (1.85, p < 0.001) when males become sexually mature. After the age of eight, the SDBM falls to 1.78, but is still significant (p < 0.001). The results also indicate that males had a longer body mass growth period than females (8 years vs. 5 years); females in larger breeding units had a significantly higher SDBM than those in smaller ones (2.12 vs. 1.93, p < 0.01). A comparative analysis with other colobines further clarifies that Rhinopithecus and Nasalis, which both have multilevel social organization, have the highest degree of SDBM among all colobines. The large SDBM in R. bieti can be explained through Bergman's and Rensch's rules. Overall, environmental adaptation, a distinctive alimentary system, and a complex social structure contribute to R. bieti having such a remarkable SDBM compared to other colobines. In addition, we found that females' choice for males may not be significantly related to the development of SDBM.

Sexual dimorphism in postcranial skeletal shape suggests male-biased specialization for physical competition in anthropoid primates.

Sexual dimorphism often arises as a response to selection on traits that improve a male's ability to physically compete for access to mates. In primates, sexual dimorphism in body mass and canine size is more common in species with intense male-male competition. However, in addition to these traits, other musculoskeletal adaptations may improve male fighting performance. Postcranial traits that increase strength, agility, and maneuverability may also be under selection. To test the hypothesis that males, as compared to females, are more specialized for physical competition in their postcranial anatomy, we compared sex-specific skeletal shape using a set of functional indices predicted to improve fighting performance. Across species, we found significant sexual dimorphism in a subset of these indices, indicating the presence of skeletal shape sexual dimorphism in our sample of anthropoid primates. Mean skeletal shape sexual dimorphism was positively correlated with sexual dimorphism in body size, an indicator of the intensity of male-male competition, even when controlling for both body mass and phylogenetic relatedness. These results suggest that selection on male fighting ability has played a role in the evolution of postcranial sexual dimorphism in primates.

Lower limb articular scaling and body mass estimation in Pliocene and Pleistocene hominins

Previous attempts to estimate body mass in pre-Holocene hominins have relied on prediction equations derived from relatively limited extant samples. Here we derive new equations to predict body mass from femoral head breadth and proximal tibial plateau breadth based on a large and diverse sample of modern humans (avoiding the problems associated with using diaphyseal dimensions and/or cadaveric reference samples). In addition, an adjustment for the relatively small femoral heads of non-Homo taxa is developed based on observed differences in hip to knee joint scaling. Body mass is then estimated for 214 terminal Miocene through Pleistocene hominin specimens. Mean body masses for non-Homo taxa range between 39 and 49 kg (39–45 kg if sex-specific means are averaged), with no consistent temporal trend (6–1.85 Ma). Mean body mass increases in early Homo (2.04–1.77 Ma) to 55–59 kg, and then again dramatically in Homo erectus and later archaic middle Pleistocene Homo, to about 70 kg. The same average body mass is maintained in late Pleistocene archaic Homo and early anatomically modern humans through the early/middle Upper Paleolithic (0.024 Ma), only declining in the late Upper Paleolithic, with regional variation. Sexual dimorphism in body mass is greatest in Australopithecus afarensis (log[male/female] = 1.54), declines in Australopithecus africanus and Paranthropus robustus (log ratio 1.36), and then again in early Homo and middle and late Pleistocene archaic Homo (log ratio 1.20–1.27), although it remains somewhat elevated above that of living and middle/late Pleistocene anatomically modern humans (log ratio about 1.15).

Body mass in wild bearded capuchins, (Sapajus libidinosus): Ontogeny and sexual dimorphism.

Body mass is fundamental for understanding growth, health, and aspects of life history but records of body mass are rarely available for wild primates. We documented the body mass of all individuals in a group of wild bearded capuchin monkeys (Sapajus libidinosus) at annual intervals for seven consecutive years. Sexual dimorphism in body mass was more pronounced than reported in the literature for adults in this genus: females in our sample were relatively light (average 2.1 kg), while males had average body mass (3.5 kg). Three other notable differences between males and females were evident. First, males grew more rapidly and for a longer period than females. We estimate that males attained full body mass at 9.8 years of age and females at 7.5 years. Second, males showed greater inter-individual variability than females in growth rates and adult mass. Third, males gained about 20% above their baseline body mass upon becoming alpha, and lost that amount when they lost that status, but body mass in females was unrelated to social status. We also report preliminary data on mass and age of natal males at dispersal and mass and age at first reproduction for one female. The pattern of sexual dimorphism in ontogeny and inter-individual variability in body mass in bearded capuchins suggests different competitive risks in the two sexes commensurate with a mating system characterized by female choice of mates in multi-male, multi-female groups. Am. J. Primatol. 78:473-484, 2016. © 2015 Wiley Periodicals, Inc.

Home range and activity patterns measured with GPS collars in spotted-tailed quolls

The spotted-tailed quoll (Dasyurus maculatus) is the largest marsupial carnivore on mainland Australia. It usually occurs at relatively low population densities and its cryptic nature makes it exceedingly difficult to observe in its natural habitat. On the mainland the species is also listed as nationally endangered and more information is needed to direct any meaningful conservation effort. In this study we aimed to elucidate quolls’ spatial requirements and activity patterns using GPS collars on 10 males and 4 females. Quolls were predominantly nocturnal but some individuals showed pronounced daytime activity. There was no apparent seasonal shift in the timing of activity. The movement of quolls appeared to be confined to home ranges that were relatively large for predators of their size. Furthermore, males used home ranges about three times as large as that of the smaller females. There appeared to be some spatial segregation between not only females, which have been considered territorial, but also males. Overall, it is likely that the larger areas used by males is partly caused by the sexual dimorphism in body mass that entails differences in prey requirements and spectrum, but probably is also a function of a promiscuous mating system. All of these could explain the observed more unidirectional movement and larger distances travelled per day by males.

Reproductive aspects of Dendropsophus sanborni (Anura, Hylidae) in northeastern Argentina

Reproductive aspects of Dendropsophus sanborni (Anura, Hylidae) in northeastern Argentina. The aim of this investigation was to characterize reproductive aspects of Dendropsophus sanborni (Schmidt, 1944) (Anura, Hylidae) in the northwest of Corrientes province, in northeastern Argentina. The reproductive cycles of males and females, the existence of sexual dimorphism and the male’s vocalization period were analyzed. Samplings were made from September 2011 to August 2012. Dendropsophus sanborni showed a prolonged reproductive pattern because reproductive activity was observed during most part of the year. Calling males were recorded all months except in July. The spermatogenic cycle can be characterized as potentially continuous. In males, snout-vent length was significantly correlated with mean testicular volume. The species showed sexual dimorphism in body mass, with females larger than males. Post-ovulatory females were found from March to June and most females had oocytes at different stages of maturity, with abundant post-vitellogenic oocytes from August to December.

Sexual Dimorphism and Facial Growth Beyond Dental Maturity in Great Apes and Gibbons

The great apes and gibbons are characterized by extensive variation in degree of body size and cranial dimorphism, but although some studies have investigated how sexual dimorphism in body mass is attained in these species, for the majority of taxa concerned, no corresponding work has explored the full extent of how sexual dimorphism is attained in the facial skeleton. In addition, most studies of sexual dimorphism combine dentally mature individuals into a single “adult” category, thereby assuming that no substantial changes in size or dimorphism take place after dental maturity. We investigated degree and pattern of male and female facial growth in Pan troglodytes troglodytes, Pan paniscus, Gorilla gorilla gorilla, Pongo pygmaeus, and Hylobates lar after dental maturity through cross-sectional analyses of linear measurements and geometric mean values of the facial skeleton and age-ranking of individuals based on molar occlusal wear. Results show that overall facial size continues to increase after dental maturity is reached in males and females of Gorilla gorilla gorilla and Pongo pygmaeus, as well as in the females of Hylobates lar. In male Pongo pygmaeus, adult growth patterns imply the presence of a secondary growth spurt in craniofacial dimensions. There is suggestive evidence of growth beyond dental maturity in the females of Pan troglodytes troglodytes and Pan paniscus, but not in the males of those species. The results show the presence of statistically significant facial size dimorphism in young adults of Pan paniscus and Hylobates lar, and of near statistical significance in Pan troglodytes troglodytes, but not in older adults of those species; adults of Gorilla gorilla gorilla and Pongo pygmaeus are sexually dimorphic at all ages after dental maturity. The presence of sex-specific growth patterns in these hominoid taxa indicates a complex relationship between socioecological selective pressures and growth of the facial skeleton.

The human operational sex ratio: Effects of marriage, concealed ovulation, and menopause on mate competition

Among mammals, male–male competition for sexual access to females frequently involves fighting. Larger body size gives males an advantage in fighting, which explains why males tend to be larger than females in many species, including anthropoid primates. Mitani et al. derived a formula to measure the operational sex ratio (OSR) to reflect the degree of male–male competition using the number of reproductively available males to females who are cycling and capable of conceiving. The OSR should predict the degree of sexual dimorphism in body mass—at least if male–male competition involves much fighting or threatening. Here, we use hunter-gatherer demographic data and the Mitani et al. formula to calculate the human OSR. We show that humans have a much lower degree of body mass sexual dimorphism than is predicted by our OSR. We suggest this is because human competition rarely involves fighting. In human hunter-gatherer societies, differences in the ages of marriage have an impact on competition in that the age of males at first marriage is younger when there is a lower percentage of married men with two or more wives, and older when there is a higher percentage of married men with two or more wives. We discuss the implications of this for females, along with the effects of two key life history traits that influence the OSR, concealed ovulation and menopause. While menopause decreases the number of reproductively available females to males and thus increases male–male competition, concealed ovulation decreases male–male competition. Finally, we discuss the importance of mostly monogamous mate bonds in human evolution.

Seasonal decline of offspring quality in the European starling Sturnus vulgaris: an immune challenge experiment

In seasonally fluctuating environments, timing of reproduction is a crucial determinant of fitness. Studies of birds show that late breeding attempts generally result in offspring of lower reproductive value, with lower recruitment and long-term survival prospects. Several proximate mechanisms, including a seasonal decline of immune system functioning, may lead to a seasonal decline of offspring fitness. We investigated seasonal variation in offspring quality by subjecting first- and second-brood chicks of a sexually size dimorphic species, the European starling Sturnus vulgaris, to an immune challenge with a bacterial endotoxin (LPS), and evaluated their growth and physiological response in terms of total plasma antioxidant capacity (TAC), concentration of reactive oxygen metabolites and hematocrit. LPS challenge did not affect chick growth or oxidative status. However, hematocrit of second-brood chicks was higher in LPS chicks compared to controls. Body mass halfway through the rearing period (days 8–9 post-hatching), TAC and hematocrit were lower among second- vs. first-brood chicks. Interestingly, sexual dimorphism in body mass at days 8–9 post-hatching markedly differed between broods, first-brood males being 4.7% and second-brood males 22.7% heavier than their sisters, respectively. Pre-fledging mortality occurred among second-brood chicks only and was strongly female-biased. Our findings suggest that starling chicks, even if in poor conditions, are little affected by a bacterial challenge, at least in the short-term. Moreover, our study indicates that sex differences in body size, possibly mediated by sex-specific maternal investment in egg size, may heavily impact on pre-fledging survival in a different way in the course of the breeding season, resulting in sex-specific seasonal decline of offspring fitness. Finally, we suggest that levels of circulating antioxidants should be regarded among the proximate causes of the association between timing of fledging and long-term survival in avian species.

Sexual dimorphism in photoperiodic plasticity of body mass in the green dock leaf beetle Gastrophysa viridula (Coleoptera, Chrysomelidae)

Sexual dimorphism in body mass was studied in prepupae, pupae and immature adults of the green dock leaf beetle Gastrophysa viridula under a constant temperature of 24°C and two photoperiods (12L:12D and 22L:2D). Females were significantly heavier compared to males at all the three developmental stages; just after emergence from pupae they weighed, on average, 11.4 mg, while males—10.3 mg. Sex differences in photoperiodic body mass plasticity were revealed: under short-day conditions pupal and adult mass in females was significantly higher compared to long day, but not in males. Such a response to short day (the factor inducing reproductive diapause in this species) is likely to promote accumulation of greater amount of nutrients by females which is necessary for earlier oviposition after overwintering.

Rensch's rule, Bergmann's effect and adult sexual dimorphism in wild monogamous owl monkeys (Aotus azarai) of Argentina

Some monogamous primates are characterized by biparental care, territoriality, and a reduced level of physical dimorphism. In others, the relationship between those behavioral patterns and dimorphism is less clear. I tested Bergmann's and Rensch's rules using Aotus spp. body mass data and I characterized the extent of sexual dimorphism in body mass, dental and physical measurements in a socially monogamous owl monkey population (n = 91 adults) from the Argentinean Gran Chaco. A. azarai azarai from the Argentinean Chaco is larger than the more tropical owl monkey species (r = 0.7, N = 6 species), but there is no apparent increase in sexual dimorphism with increased body mass. The body masses of adult male and female A. a. azarai were remarkably similar (Mean = 1.26 kg); there were no marked sex differences in most skeletal measurements, but males had higher and wider upper and lower canines than did females. Body mass and neck circumference were positively and strongly related (r = 0.533, n = 52), and the body mass of adults was not a reliable indicator of their age (r = 0.03, n = 10). The data illustrate the complexities inherent in examining and summarizing within population variation in skeletal and nonskeletal measurements and contribute to a better understanding of the relationships between monogamous behavioral patterns and sexual dimorphism.

Habitat use, population dynamics and species identification of mulgara, Dasycercus blythi and D. cristicauda, in a zone of sympatry in central Australia

Dasycercus cristicauda and Dasycercus blythi are significant mesopredators in arid Australia and both species are threatened nationally. We investigated size dimorphism, habitat use, and population dynamics of sympatric populations during a low rainfall period in central Australia and examined congruence between morphological and molecular methods of species identification. Our molecular analyses confirmed the presence of two Dasycercus species in sympatry and showed that the descriptions of Woolley (2005) allowed confident identification of the two species in the field. We captured 23 D. cristicauda and 55 D. blythi over 39 months on 20 monitoring plots and another 49 survey sites stratified across five habitat types within a 7000 km2 area. Both species showed sexual dimorphism in body mass with males being significantly heavier. The species typically occupied non-overlapping habitat; D. cristicauda was restricted to sandridges (n = 4 sites) with an understorey dominated by spinifex (Triodia), whereas D. blythi occupied sand plain and gibber plain, the latter being a new habitat for the species. Capture rate of D. cristicauda peaked in autumn-winter 2008 and winter 2009. D. blythi exhibited similar variability with peaks in winter 2009 and summer-autumn 2010. We consider that the relatively low abundance of each species during low rainfall periods makes them vulnerable to predation by feral house cats and European red foxes.

Body size and body shape in early hominins – implications of the Gona Pelvis

Discovery of the first complete Early Pleistocene hominin pelvis, Gona BSN49/P27, attributed to Homo erectus, raises a number of issues regarding early hominin body size and shape variation. Here, acetabular breadth, femoral head breadth, and body mass calculated from femoral head breadth are compared in 37 early hominin (6.0–0.26 Ma) specimens, including BSN49/P27. Acetabular and estimated femoral head sizes in the Gona specimen fall close to the means for non- Homo specimens ( Orrorin tugenesis, Australopithecus africanus, Paranthropus robustus), and well below the ranges of all previously described Early and Middle Pleistocene Homo specimens. The Gona specimen has an estimated body mass of 33.2 kg, close to the mean for the non- Homo sample (34.1 kg, range 24–51.5 kg, n = 19) and far outside the range for any previously known Homo specimen (mean = 70.5 kg; range 52–82 kg, n = 17). Inclusion of the Gona specimen within H. erectus increases inferred sexual dimorphism in body mass in this taxon to a level greater than that observed here for any other hominin taxon, and increases variation in body mass within H. erectus females to a level much greater than that observed for any living primate species. This raises questions regarding the taxonomic attribution of the Gona specimen. When considered within the context of overall variation in body breadth among early hominins, the mediolaterally very wide Gona pelvis fits within the distribution of other lower latitude Early and Middle Pleistocene specimens, and below that of higher latitude specimens. Thus, ecogeographic variation in body breadth was present among earlier hominins as it is in living humans. The increased M-L pelvic breadth in all earlier hominins relative to modern humans is related to an increase in ellipticity of the birth canal, possibly as a result of a non-rotational birth mechanism that was common to both australopithecines and archaic Homo.

The Round‐Eared Sengi and the Evolution of Social Monogamy: Factors that Constrain Males to Live with a Single Female

AbstractAnimal dispersion in space and time results from environmental pressures, and affects the outcome of a species’ social organization. When females are solitary, males may either roam or be pair‐living. We studied possible environmental influences affecting the social organization of the round‐eared sengi (Macroscelides proboscideus) in a semi‐desert in South Africa, using trapping and radio‐tracking across 2.5 yr. Adult sex ratios did not deviate from 1:1 and we found no indication of sexual dimorphism in body mass. Females maintained exclusive areas, which had little overlap (&lt;4%) with neighbouring females (NF), and males overlapped predominately only with the home range of single females. Generally, inter‐ and intra‐sexual overlap with neighbouring individuals was low (3–6%) for both sexes, indicating territoriality and pair‐living. Pairs were perennial and territories were maintained year‐round. However, males generally maintained much larger areas than females, which were sensitive to population density. Male space use appeared to be primarily limited by the presence of neighbouring males. Female home ranges were smaller‐sized despite changes in population density, possibly for energetic efficiency. Some paired males attempted to take over widowed females, but shifted back to their original home range following the intrusion of an un‐paired male. We conclude that social monogamy is the predominant social organization in round‐eared sengis in a semi‐desert that may have resulted from females living solitarily in small exclusive territories, balanced sex ratios, and from a low variation of body mass between males.

Sexual size dimorphism in Asian colobines revisited

Asian colobines exhibit a wide range of sexual dimorphism in body mass. Some species are monomorphic, whereas others are strongly dimorphic. Strong sexual dimorphism is generally viewed as the consequence of intense male contest competition over access to mates, but this idea appears not to explain variation in sexual dimorphism in Asian colobines. Our results show that modular colobines, i.e. species in which social units aggregate into higher-level bands or often associate, have significantly higher levels of sexual dimorphism in body mass than the nonmodular ones. This finding was corroborated by means of phylogenetically controlled methods and multiple regression analyses. The results suggest that living in a modular society intensifies the contest competition among males, which is further exacerbated by the continuous presence of all-male units.

Social Structure and Mating System of the Buffy Flower Bat,Erophylla sezekorni(Chiroptera, Phyllostomidae)

Polygyny and promiscuity are the 2 most common mammalian mating systems, whereas monogamy and lek mating are rare. Mammalian mating systems are thought to be influenced by the amount of paternal investment required, defensibility of females, and the stability and size of female groups. With some notable exceptions, male bats typically make no paternal investment and, because of high mobility and broad foraging areas of females, ranges of females often are not defensible. Thus, we would expect most bats to be polygynous or promiscuous; however, mating systems of only about 6% of bat species have been studied. Mating systems of leaf-nosed bats in the family Phyllostomidae have not been well studied, and no species in subfamilies Glossophaginae and Phyllonycterinae, a major radiation of nectar-feeding phyllostomids, have been studied. The buffy flower bat (Erophylla sezekorni) is a phyllonycterine bat endemic to islands of the Greater Antilles. We describe the social structure and mating system of E. sezekorni on Exuma, Bahamas, using capture data, roost observations, and paternity analysis. E. sezekorni roosts in multimale‐multifemale groups and female groups are large (50‐350 bats) and labile. Males of E. sezekorni aggregate at display areas where they exhibit wing displays and hold territories throughout the 2-month mating season. Mature males also produce garlic-scented supraorbital secretions and ultrasonic display calls. Paternity analysis revealed that females do not mate exclusively with displaying males and that there is limited polygyny and reproductive skew. We also found sexual dimorphism in body mass and condition, with males being both heavier and in better condition than females. Based on large female group size, female group lability, and existence of male mating territories, we hypothesize that E. sezekorni employs a form of promiscuous mating system. More data about female mating behavior are required to test this hypothesis.

Female dominance over males in primates: self-organisation and sexual dimorphism.

The processes that underlie the formation of the dominance hierarchy in a group are since long under debate. Models of self-organisation suggest that dominance hierarchies develop by the self-reinforcing effects of winning and losing fights (the so-called winner-loser effect), but according to ‘the prior attribute hypothesis’, dominance hierarchies develop from pre-existing individual differences, such as in body mass. In the present paper, we investigate the relevance of each of these two theories for the degree of female dominance over males. We investigate this in a correlative study in which we compare female dominance between groups of 22 species throughout the primate order. In our study female dominance may range from 0 (no female dominance) to 1 (complete female dominance). As regards ‘the prior attribute hypothesis’, we expected a negative correlation between female dominance over males and species-specific sexual dimorphism in body mass. However, to our surprise we found none (we use the method of independent contrasts). Instead, we confirm the self-organisation hypothesis: our model based on the winner-loser effect predicts that female dominance over males increases with the percentage of males in the group. We confirm this pattern at several levels in empirical data (among groups of a single species and between species of the same genus and of different ones). Since the winner-loser effect has been shown to work in many taxa including humans, these results may have broad implications.

Does the Jarman–Bell principle at intra-specific level explain sexual segregation in polygynous ungulates? Sex differences in forage digestibility in Soay sheep

The Jarman-Bell principle states that large-bodied mammalian herbivores can subsist on lower quality diets because of their lower metabolism requirement/gut capacity ratio. Two major hypotheses for sexual segregation (the behaviour in which animals of the same species aggregate by sex) base their foundations on extending this principle to the intraspecific level, despite the lack of experimental evidence to support this. The first proposes that the larger males can process fibre (low-quality diet) more efficiently than the smaller females, leading to sexual segregation by habitat partitioning due to selection of different food quality and/or quantity (sexual dimorphism-body size hypothesis). The second suggests that the longer time and extra rumination required to digest low-quality food will cause asynchrony of behaviour between males and females, which then leads to sexual segregation (activity budget hypothesis). To provide experimental evidence for the Jarman-Bell principle at the intraspecific level we carried out a set of digestibility trials in Soay sheep (Ovis aries) using grass hay as the diet to test whether sexual dimorphism in body mass can produce significant sexual differences in the efficiency of food digestion. Males were slightly more efficient in digesting forage than females that were at least 30% smaller than the males. Overall, there was a decrease in faecal output of 1 g/kg body mass in favour of males. These differences were not due to differences in food selection, passage rates or faecal particle size and it was not clear why males were more efficient in digesting forage. Although these results do not directly support arguments for either the sexual dimorphism-body size or activity budget hypotheses, they do indicate that the physiological argument upon which the Jarman-Bell principle is founded also operates at the intraspecific level and may be an important factor influencing sexual segregation.

Does body mass dimorphism increase male–female dietary niche separation? A comparative study of primates

Summary Body mass plays an important role in shaping an individual’s behavior, especially with respect to dietary behavior. Larger animals tend to consume higher quantities of low quality foods. In contrast, smaller individuals, with relatively higher metabolic rates require a high quality diet. Therefore, species that exhibit high amounts of sexual dimorphism in body mass should also display high levels of male–female dietary differentiation. This study investigated the relationship between body mass dimorphism and dietary sex differences for 38 primate species. We conducted multiple regressions using female body mass and body mass dimorphism as independent variables. We found that body mass dimorphism was significantly negatively correlated with male–female differences in fauna consumption using species values as well as phylogenetically independent contrasts. In addition, body mass dimorphism was positively related to male–female differences in percent time feeding using phylogenetically independent contrasts. Body mass dimorphism was not significantly related to male–female differences in the percent of fruit and leaves in the diet. The results suggest that, as body mass dimorphism increases, there is some degree of dietary niche separation between the sexes of primates. These results will be discussed in the context of existing studies of intersexual niche separation.