Article

Sexual selection is not the origin of long necks in giraffes

Journal of Zoology

April 2009
278(4):281 - 286

DOI:10.1111/j.1469-7998.2009.00573.x

Authors:

Sybrand van Sittert

University of Pretoria

The evolutionary origin of the long neck of giraffes is enigmatic. One theory (the ‘sexual selection’ theory) is that their shape evolved because males use their necks and heads to achieve sexual dominance. Support for this theory would be that males invest more in neck and head growth than do females. We have investigated this hypothesis in 17 male and 21 female giraffes with body masses ranging from juvenile to mature animals, by measuring head mass, neck mass, neck and leg length and the neck length to leg length ratio. We found no significant differences in any of these dimensions between males and females of the same mass, although mature males, whose body mass is significantly (50%) greater than that of mature females, do have significantly heavier (but not longer) necks and heavier heads than mature females. We conclude that morphological differences between males and females are minimal, that differences that do exist can be accounted for by the larger final mass of males and that sexual selection is not the origin of a long neck in giraffes.

Sexual dimorphisms in body proportions of Masai giraffes and the evolution of the giraffe’s neck

Article

Full-text available

Jun 2024

Giraffes exhibit a large sexual dimorphism in body size. Whether sexual dimorphisms also exist in body proportions of the axial and appendicular skeleton has been debated, particularly regarding the giraffe’s iconic long neck. We examined the anatomical proportions of the neck, forelegs, hindlegs, and body trunk of the Masai giraffe ( G. tippelskirchi ) in captive and wild populations. We found that female Masai giraffes have proportionally longer necks relative to their forelegs than males in contradiction to the original necks-for-sex hypothesis that proposed that the evolution of the giraffe’s long neck was driven by male-male competition. However, male neck width and apparent mass are proportionally larger than females’, supporting a modification of the necks-for-sex hypothesis. Moreover, male foreleg length is proportionally longer whereas female trunk length is proportionally longer. These sexual dimorphisms were found in both captive and wild Masai giraffes. We speculate that the initial evolution of the giraffe’s long neck and legs was driven by interspecific competition and the maternal nutritional demands of gestation and lactation through natural selection to gain a competitive advantage in browsing, and then later the neck mass was further increased as a consequence of male-male competition and sexual selection. Differences in the proportions of major body components define sex phenotypes, but several giraffes display opposite-sex phenotypes with a significantly higher level of discordancy seen in captive males. We speculate that body proportion sexual dimorphisms are maintained in the wild by natural and/or sexual selection, but in captivity selection is relaxed resulting in a higher occurrence of discordances in sexual phenotypes.

Sexual dimorphisms in body proportions of Masai giraffe

Preprint

Full-text available

May 2023

Giraffes exhibit a large sexual dimorphism in stature and body mass. Whether sexual dimorphisms also exist in relative body proportions of the axial and appendicular skeleton has been debated, particularly regarding the evolution of the giraffe’s iconic long neck. We measured and analyzed the relative anatomical proportions of the neck, legs, and body trunk of the Masai giraffe ( G.c. tippelskirchi ) in captive and wild populations. We found that female Masai giraffes have proportionally longer necks relative to their forelegs than males. Moreover, the female body trunk is proportionally longer whereas male foreleg length and neck width are proportionally greater. The sexual dimorphisms in body proportions were found in both captive and wild Masai giraffes suggesting that these differences are genetically determined. We speculate that the proportionally longer female neck is to compensate for females’ overall shorter stature to expand access to forage and their longer trunk is to accommodate fetal growth. Males’ longer forelegs, which contribute to the overall anterior body stature, likely provides some advantage in physical intrasexual competitions. Differences in the proportions of major body components define sex phenotypes, but several male and female giraffes display opposite-sex phenotypes with a significantly higher level of discordancy seen in captive males. We speculate that body proportion sexual dimorphisms are maintained in the wild by natural and/or sexual selection, but in captivity selection is relaxed because of human-altered mating and feeding behavior resulting in a higher proportion of sexual dimorphism discordances.

Necks for sex or food: Giraffes stand to gain

Preprint

Oct 2022

Evolution of the giraffe neck was originally proposed as an adaptation to foraging at the tops of acacia trees, but this theory has been overshadowed by the “necks for sex” hypothesis that proposed that long necks evolved via sexual selection associated with male neck fighting. The necks for sex hypothesis predicted that males would have longer necks than females and that their necks would continue to grow throughout their lives. Because adult giraffe males are much larger than adult females, male giraffe necks are indeed longer but this is also true for all the core anatomy. We measured and analyzed the relative anatomical proportions of the neck, legs, and body trunk of the Masai giraffe (G.c. tippelskirchi) in captivity in North America and from wild populations in Tanzania. In contradiction to the necks for sex hypothesis, female giraffe have proportionally longer necks compared to their forelegs than males. Moreover, the female body trunk is proportionally longer whereas male forelegs are proportionally longer. We speculate that the proportionally longer female neck is to compensate for female’s overall shorter stature in foraging and their longer trunk is to accommodate fetal growth. Male’s longer forelegs may be an adaptation for mounting females during mating. Mean differences in these major body components define sex phenotypes, but several male and female giraffe display opposite-sex phenotypes with a significantly higher level of discordancy is seen in captive males. We speculate that the sex-differential phenotype is maintained by mate choice selection in the wild, and this selection is relaxed in captivity where mates are arranged by humans.

An Exploratory Study into the Influence of Sex on Body Measurements, Carcass Weights and Meat Yields of Giraffe (Giraffa camelopardalis angolensis)

Article

Full-text available

Sep 2021

Various body measurements and commercial carcass yields of relatively young (2½–6 yrs old) giraffe (Giraffa camelopardalis angolensis) were investigated to quantify the effect of sex there upon. Eight male and eight female giraffe were culled by standard practice in Namibia, where body and horn measurements were taken, before the carcasses were dressed. There were no significant differences between the mean dead weights of the two sexes (bulls = 691.1 kg; cows = 636.5 kg; p = 0.096), the only body measurements found to differ significantly were those of the forelegs, with the shoulder to hoof (p = 0.046) and the knee to hoof (p = 0.025) both being significantly longer in the bulls. The horn measurements were all found to be significantly larger in the bulls than the cows even at this young age. The neck weight as a percentage of the carcass weight was found to be significantly heavier for the bulls compared to the cows, however, the back percentage values were significantly heavier in the cows than the bulls. There was a strong positive correlation between the body weight and most of the body lengths, as well as between most of the individual body measurements. The giraffe used had an average age of 3.7 years old, and had therefore not yet reached their growth plateau, which may be why sex had no influence on most of the body measurements recorded.

Giraffes and hominins: reductionist model predictions of compressive loads at the spine base for erect exponents of the animal kingdom

Article

Full-text available

Dec 2020
Biol Open

In humans, compressive stress on intervertebral discs is commonly deployed as a measurand for assessing the loads that act within the spine. Examining this physical quantity is crucially beneficial: the intradiscal pressure can be directly measured in vivo in humans, and is immediately related to compressive stress . Hence, measured intradiscal pressure data are utterly useful for validating such biomechanical animal models that have the spine incorporated, and can, thus, compute compressive stress values. Here, we utilise human intradiscal pressure data to verify the predictions of a reductionist spine model, which has in fact only one joint degree of freedom. We calculate the pulling force of one lumped anatomical structure that acts past this (intervertebral) joint at the base of the spine—lumbar in hominins, cervical in giraffes—to compensate the torque that is induced by the weight of all masses located cranially to the base. Given morphometric estimates of the human and australopith trunks, respectively, and the giraffe's neck, as well as the respective structures’ lever arms and disc areas, we predict, for all three species, the compressive stress on the intervertebral disc at the spine base, while systematically varying the angular orientation of the species’ spinal columns with respect to gravity. The comparison between these species demonstrates that hominin everyday compressive disc stresses are lower than such in big quadrupedal animals. Within each species, erecting the spine from being bent forward by, for example, thirty degrees to fully upright posture reduces the compressive disc stress roughly to a third. We conclude that erecting the spine immediately allows to carry extra loads of the order of body weight, and yet the compressive disc stress is lower than in a moderately forward-bent posture with none extra load.

Chapter 5: “Extraordinary claims, extraordinary proof.”

Preprint

Full-text available

Oct 2019

Tom Nolen

From: "Evolutionary Studies: Unfolding Darwin’s Roadmap across the Curriculum," edited by Glenn Geher, David Sloan Wilson, Hadassah Head, and Andrew Gallup. Oxford University Press. https://www.oxfordscholarship.com/view/10.1093/oso/9780190624965.001.0001/oso-9780190624965

Body surface area and thermoregulation in giraffes

Article

May 2017
J ARID ENVIRON

One of several hypotheses for the evolution of the shape of giraffes is that it evolved to maximize heat loss via a high surface area to mass ratio. We calculated the surface area (SA) of the head, neck, trunk and upper legs, and the lower legs in 60 giraffes of both sexes and a body mass range of 141–1358 kg. No sex differences were found for giraffes of equivalent body mass. Relative surface area (cm² kg⁻¹ body mass) declined from 145 in juvenile giraffes to 90 in adults. Average total body SA was 7.3 ± 2.5 m² (range 2.2–11.7), which is not significantly different to that of mammals of equivalent mass. The extra area of the neck and legs was offset by smaller trunk area. However, the narrow diameters of the neck and lower legs enhance the rate of convective and evaporative heat loss and reduce the incident solar radiant heat load when giraffe face the sun, a behaviour supplemented by seeking shade if it is available. We have concluded that giraffes do not have an unusually large SA for their mass, but their shape confers other thermoregulatory benefits that have advantages for survival in the arid habitat they prefer.

Ontogenetic allometry of the postcranial skeleton of the giraffe (Giraffa camelopardalis), with application to giraffe life history, evolution and palaeontology

Thesis

Full-text available

Jan 2016

Sybrand van Sittert

Giraffes (Giraffa camelopardalis) have evolved into a unique and extreme shape. The principle determinant of its shape is the skeleton and the overarching theme of the study was to describe how this shape is achieved throughout ontogeny. Accordingly, the study had three main objectives: 1) To describe the growth of the giraffe postcranial skeleton allometrically, 2) To interpret the allometric patterns described in an evolutionary and functional sense and 3) To reconstruct the size and shape of the extinct Giraffa sivalensis using, if feasible, allometric equations obtained in this study. Secondary objectives were to a) establish if sexual dimorphism was evident in G. camelopardalis and b) determine if growth patterns in the foetus differed from those in postnatal G. camelopardalis. Data were collected from giraffes culled as part of conservancy management in Zimbabwe. The sample included 59 animals from which vertebral dimensions were taken in 48 animals and long bone dimensions in 47 animals. Body masses ranged from 21 kg to 77 kg in foetuses and 147 kg to 1412 kg postnatally, representing 29 males and 30 females. In addition to body mass, external body dimensions were recorded from each animal. Each vertebra and unilateral long bone was dissected from the carcasses and cleaned, after which dimensions were measured with a vernier calliper, measuring board or measuring tape. Vertebral dimensions measured included body (centrum) length, height and width as well as vertebral spinous process length. Long bone dimensions included length, two midshaft diameters and circumference. Allometric equations (y=bxk) were constructed from the data, with special interest in the scaling exponent (k) to illustrate regions of positively allometric, isometric or negatively allometric growth. In the first series of analyses the growth patterns of the components of the postcranial axial skeleton were analysed. The adaptations in vertebral growth to create and maintain extraordinary shape were identified as disproportionate elongation of the cervical vertebrae after birth, increasing cross sectional diameters of the cervical vertebrae from cranial to caudal and positively allometric spinal process growth. The theory of sexual selection as a driver for neck elongation in giraffes was brought into question by showing that male and female vertebral elongation rates are similar relative to increases in body mass. The second series of analyses described the growth pattern of the long bones of the appendicular skeleton. The allometric exponents seemed unremarkable compared to the few species described previously, and it was shown that the giraffe appendicular skeleton does not elongate in the dramatic way the neck does. Limbs at birth, after lengthening with positive allometry in utero, are already elongated and slender in shape and a further increase in the gracility of the bones is either not possible or not desirable. This result implies that it is neck elongation rather than leg elongation that is the dominant factor in the evolution of the giraffe shape. Nevertheless, the front limb bones and especially the humerus may show responsiveness to increasing high loads and/ or bending moments, which may be caused by the neck mass which increases with positive allometry, or with behaviours such as splaying the forelegs during drinking. In the third component of the study ontogenetic allometric equations in extant giraffes were applied to the remains of an extinct giraffid, G. sivalensis. The procedure was unusual as it employed ontogenetic regressions instead of the more commonly used interspecific regressions. The appropriateness of each equation to estimate body mass was evaluated by calculating the prediction error incurred in both extant giraffes and okapis (Okapia johnstoni). It was concluded that, due to body shape, ontogenetic equations were adequate and perhaps preferable to interspecific equations to estimate proportions in Giraffa species. This analysis showed that G sivalensis was smaller than extant giraffes and weighed around 400 kg (range 228 kg 575 kg), with a neck length of about 147 cm and a height of 390 cm. There may be evidence of sexual dimorphism in this species, with males being about twice the body weight of females. However, if sexual dimorphism was not present and all the bones were correctly attributed to this species, then G. sivalensis had a slender neck with a relatively stocky body. In conclusion, this study established ontogenetic regression equations for the skeleton of an animal of which the body shape seems to be at the extreme limits of mammalian possibility. The value of the current study lies especially in its sample size and quality, which included an unprecedented number of giraffe body masses, vertebral and long bone dimensions. This dataset had applications in the giraffe s evolutionary biology, palaeontology and even ecology. Future studies still need to compare the findings from giraffe growth with similar data from other taxa, especially those with long legs and necks. Specifically, it would interesting to determine if positively allometric neck growth combined with isometric leg growth is found in other mammalian species. In addition, the strength of giraffe long bones and vertebrae needs to be investigated with more accuracy using parameters like second moment of area. Lastly, further palaeontological studies on other giraffid sizes are necessary to validate the current and future interpretations of fossil giraffid findings.

Scaling of the Appendicular Skeleton of the Giraffe (Giraffa camelopardalis)

Article

May 2015
J MORPHOL

Giraffes have remarkably long and slender limb bones, but it is unknown how they grow with regard to body mass, sex, and neck length. In this study, we measured the length, mediolateral (ML) diameter, craniocaudal (CC) diameter and circumference of the humerus, radius, metacarpus, femur, tibia, and metatarsus in 10 fetuses, 21 females, and 23 males of known body masses. Allometric exponents were determined and compared. We found the average bone length increased from 340 ± 50 mm at birth to 700 ± 120 mm at maturity, while average diameters increased from 30 ± 3 to 70 ± 11 mm. Fetal bones increased with positive allometry in length (relative to body mass) and in diameter (relative to body mass and length). In postnatal giraffes bone lengths and diameters increased iso- or negatively allometric relative to increases in body mass, except for the humerus CC diameter which increased with positive allometry. Humerus circumference also increased with positive allometry, that of the radius and tibia isometrically and the femur and metapodials with negative allometry. Relative to increases in bone length, both the humerus and femur widened with positive allometry. In the distal limb bones, ML diameters increased isometrically (radius, metacarpus) or positively allometric (tibia, metatarsus) while the corresponding CC widths increased with negative allometry and isometrically, respectively. Except for the humerus and femur, exponents were not significantly different between corresponding front and hind limb segments. We concluded that the patterns of bone growth in males and females are identical. In fetuses, the growth of the appendicular skeleton is faster than it is after birth which is a pattern opposite to that reported for the neck. Allometric exponents seemed unremarkable compared to the few species described previously, and pointed to the importance of neck elongation rather than leg elongation during evolution. Nevertheless, the front limb bones and especially the humerus may show adaptation to behaviors such as drinking posture.

Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe: Giraffid evolution revisited

Article

Full-text available

Sep 2010
J ZOOL

Recent years have witnessed a resurgence in tests of the evolution and origin of the great height and long neck of the giraffe Giraffa camelopardalis. The two main hypotheses are (1) long necks evolved through competition with other browsers allowing giraffe to feed above them ('competing browsers' hypothesis); or (2) the necks evolved for direct use in intra-sexual combat to gain access to oestrous females ('necks-for-sex' hypothesis). Here, we review recent developments and their relative contribution in explaining giraffe evolution. Trends from Zimbabwean giraffes show positive allometry for male necks and isometry for female necks relative to body mass, while comparative analyses of the cervical versus the total vertebral column of the giraffe, okapi and fossil giraffe suggest selection specifically on neck length rather than on overall height. Both support the necks-for-sex idea. Neither study, however, allows us to refute one of the two ideas. We suggest new approaches for quantifying the relative importance of the two hypotheses. A direct analysis of selection pressure on neck length via survival and reproduction should clarify the mechanism maintaining the trait, while we predict that short robust ossicones should have arisen concurrently with incipient neck elongation if sexual selection was the main selective driver. The main challenge for the competing browser hypothesis is to explain why giraffe have remained about 2 m taller than their tallest competitors for over 1 Myr, whereas the sexual selection hypothesis cannot provide an adaptive explanation for the long neck of female giraffe. We conclude that probably both mechanisms have contributed to the evolution and maintenance of the long neck, and their relative importance can be clarified further.

Growth patterns and masses of the heads and necks of male and female giraffe

Article

May 2013

We have analyzed the growth patterns of the head and neck of 65 male and 71 female giraffes from two different populations of giraffes, and also the dimensions of 19 different components of the head and neck in 8 female and 13 male giraffes, to establish if they showed sexual dimorphism and if sexual selection for a weapon was a possible origin of the long neck of giraffes. We found that in both genders, the rate of increase in head mass was hypoallometric with respect to body mass. The rate of increase in neck length was similar in both genders and faster than the rate of increase in body mass. Increases in neck mass tend to be isometric relative to increases in body mass in both genders before puberty (c. 650kg body mass in male and 700kg in female giraffes), but in giraffes of greater body mass increases in neck mass are iso- to hyperallometric in both genders, with final neck, body and head mass being greater in male giraffes. The only significant gender difference we found for the dimensions of the 19 different head and neck components was that ossicones and skulls were heavier in mature male than in mature female giraffes, but increases in skull mass did not alter the growth pattern of head mass significantly. These data suggest that the morphology and growth patterns of the heads and necks of male and female giraffes are similar, that sexual dimorphism of the head and neck is minimal and can be attributed to secretion of sex steroids. We have concluded that there is no evidence that sexual selection was a factor in the evolution of giraffe morphology and that the long neck of giraffes did not evolve as a weapon in males. The more likely selective advantage of a long neck was improvement of access to high-level browse. © 2013 The Zoological Society of London.

The Brain of the Giraffe (Giraffa Camelopardalis): Surface Configuration, Encephalization Quotient, and Analysis of the Existing Literature

Article

Mar 2017
ANAT REC

The anatomy of the giraffe (Giraffa camelopardalis Linnaeus, 1758) has been poorly studied, except for the circulatory system. In particular, only a handful of studies have concerned the brain of this species since the first description in 1839. Accordingly, only a very few articles discussing encephalization mentioned the giraffe or used it in their calculations. In this article, we performed a thorough examination of the literature including old and grey, regarding the central nervous system of the giraffe. Furthermore, we examined the brain of 3 giraffes, and calculated the encephalization quotient (EQ) of the species, based on our own data and the values found in the literature. We also revised the pre-existing literature and re-mapped the main sulci based on current comparative interpretation and anatomical nomenclature. Our results were compared to those of other selected significant mammals. The mean brain weight was of 719.9???12.5 g. Our data indicate that the EQ of the giraffe is 0.64 and matches that of the typical ungulate, despite having the largest brain among terrestrial Cetartiodactyla. This emphasizes that the giraffe is a highly specialized mammal, within the limitations of its clad. Anat Rec, 2017. ? 2017 Wiley Periodicals, Inc.

Dynamic Imbalance Analysis and Stability Control of Galloping Gait for a Passive Quadruped Robot

Article

Full-text available

Jun 2015

Some imbalance and balance postures of a passive quadruped robot with a simplified mathematical model are studied. Through analyzing the influence of the touchdown angle of the rear leg on the posture of the trunk during the flight phase, the stability criterion is concluded: the closer are the twomoments which are the zero time of the pitching angle and the peak time of the center of mass, the better is the stability of the trunk posture during the flight phase. Additionally, the validity of the stability criterion is verified for the cat, greyhound, lion, racehorse, basset hound, and giraffe. Furthermore, the stability criterion is also applicable when the center of the mass of body is shifted. Based on the stability criterion, the necessary and sufficient condition of the galloping stability for the quadruped robot is proposed to attain a controlled thrust. The control strategy is designed by an optimization dichotomy algorithm for seeking the zero point of the balance condition.Through the control results, it is demonstrated that the imbalance posture of the trunk could be stabilized by adjusting the stiffness of four legs.

The digestive morphophysiology of wild, free-living, giraffes

Article

Full-text available

May 2015

We have measured rumen-complex (rumen, reticulum, omasum, abomasum) and intestine (small and large combined) mass in 32 wild giraffes of both sexes with body masses ranging from 289 -1441kg, and parotid gland mass, tongue length and mass, masseter and mandible mass in 9 other giraffes ranging in body mass from 181 to 1396kg. We have estimated metabolic and energy production rates, feed intake and home range size. Interspecific analysis of mature ruminants show that components of the digestive system increase linearly (Mb(1)) or positively allometric (Mb(>1)) with body mass while variables associated with feed intake scale with metabolic rate (Mb(.75)). Conversely, in giraffes ontogenetic increases in rumen-complex mass were negatively allometric (Mb(<1)), and increases in intestine mass, parotid gland mass, masseter mass, and mandible mass were isometric (Mb(1)). The relative masseter muscle mass (0.14% of Mb) and the relative parotid mass (0.03% of Mb) are smaller than in other ruminants. Increases in tongue length scale with head length(0.72) and Mb(.32) and tongue mass with Mb(.69). Absolute mass of the gastrointestinal tract increased throughout growth but its relative mass declined from 20% to 15% of Mb. Rumen-complex fermentation provides ca43% of daily energy needs, large intestine fermentation 24% and 33% by digestion of soluble carbohydrates, proteins, and lipids. Dry matter intake (kg) was 2.4 % of body mass in juveniles and 1.6% in adults. Energy requirements increased from 35Mj/day to 190 Mj/day. Browse production rate sustains a core home range of 2.2- 11.8 km(2). Copyright © 2015. Published by Elsevier Inc.

Understanding selection for long necks in different taxa

Article

Dec 2011
BIOL REV

There has been recent discussion about the evolutionary pressures underlying the long necks of extant giraffes and extinct sauropod dinosaurs. Here we summarise these debates and place them in a wider taxonomic context. We consider the evolution of long necks across a wide range of (both living and extinct) taxa and ask whether there has been a common selective factor or whether each case has a separate explanation. We conclude that in most cases long necks can be explained in terms of foraging requirements, and that alternative explanations in terms of sexual selection, thermoregulation and predation pressure are not as well supported. Specifically, in giraffe, tortoises, and perhaps sauropods there is likely to have been selection for high browsing. It the last case there may also have been selection for reaching otherwise inaccessible aquatic plants or for increasing the energetic efficiency of low browsing. For camels, wading birds and ratites, original selection was likely for increased leg length, with correlated selection for a longer neck to allow feeding and drinking at or near substrate level. For fish-eating long-necked birds and plesiosaurs a small head at the end of a long neck allows fast acceleration of the mouth to allow capture of elusive prey. A swan's long neck allows access to benthic vegetation, for vultures the long neck allows reaching deep into a carcass. Geese may be an unusual case where anti-predator vigilance is important, but so may be energetically efficient low browsing. The one group for which we feel unable to draw firm conclusions are the pterosaurs, this is in keeping with the current uncertainty about the biology of this group. Despite foraging emerging as a dominant theme in selection for long necks, for almost every taxonomic group we have identified useful empirical work that would increase understanding of the selective costs and benefits of a long neck.

Predicting the buoyancy, equilibrium and potential swimming ability of giraffes by computational analysis

Article

Full-text available

Apr 2010
J THEOR BIOL

Giraffes (Giraffa camelopardalis) are often stated to be unable to swim, and while few observations supporting this have ever been offered, we sought to test the hypothesis that giraffes exhibited a body shape or density unsuited for locomotion in water. We assessed the floating capability of giraffes by simulating their buoyancy with a three-dimensional mathematical/computational model. A similar model of a horse (Equus caballus) was used as a control, and its floating behaviour replicates the observed orientations of immersed horses. The floating giraffe model has its neck sub-horizontal, and the animal would struggle to keep its head clear of the water surface. Using an isometrically scaled-down giraffe model with a total mass equal to that of the horse, the giraffe's proportionally larger limbs have much higher rotational inertias than do those of horses, and their wetted surface areas are 13.5% greater relative to that of the horse, thus making rapid swimming motions more strenuous. The mean density of the giraffe model (960 gm/l) is also higher than that of the horse (930 gm/l), and closer to that causing negative buoyancy (1000 gm/l). A swimming giraffe - forced into a posture where the neck is sub-horizontal and with a thorax that is pulled downwards by the large fore limbs - would not be able to move the neck and limbs synchronously as giraffes do when moving on land, possibly further hampering the animal's ability to move its limbs effectively underwater. We found that a full-sized, adult giraffe will become buoyant in water deeper than 2.8m. While it is not impossible for giraffes to swim, we speculate that they would perform poorly compared to other mammals and are hence likely to avoid swimming if possible.

The Inverse Krogh Principle: All Organisms Are Worthy of Study

Article

Full-text available

Jul 2022

Krogh’s principle states, “For such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied.” The downside of picking a question first and then finding an ideal organism on which to study it is that it will inevitably leave many organisms neglected. Here, we promote the inverse Krogh principle: all organisms are worthy of study. The inverse Krogh principle and the Krogh principle are not opposites. Rather, the inverse Krogh principle emphasizes a different starting point for research: start with a biological unit, such as an organism, clade, or specific organism trait, then seek or create tractable research questions. Even the hardest-to-study species have research questions that can be asked of them: Where does it fall within the tree of life? What resources does it need to survive and reproduce? How does it differ from close relatives? Does it have unique adaptations? The Krogh and inverse Krogh approaches are complementary, and many research programs naturally include both. Other considerations for picking a study species include extreme species, species informative for phylogenetic analyses, and the creation of models when a suitable species does not exist. The inverse Krogh principle also has pitfalls. A scientist that picks the organism first might choose a research question not really suited to the organism, and funding agencies rarely fund organism-centered grant proposals. The inverse Krogh principle does not call for all organisms to receive the same amount of research attention. As knowledge continues to accumulate, some organisms—models—will inevitably have more known about them than others. Rather, it urges a broader search across organismal diversity to find sources of inspiration for research questions and the motivation needed to pursue them.

evolution through communication 2021

Book

Full-text available

Jul 2021

Foreword to 2021 edition from Covid19 perspective: The present book has written in 2013, at the time when we could only speculate on the consequences of a mono-disciplinary/one-sided approach while facing a global ordeal. However, Covid-19 has confirmed what we said in 2013: the scarcity of a mono-disciplinary, gene/molecular approach and the negative consequences of underestimating social behaviour (communication) in the evolution of living organisms can lead to certain important negative outcomes. We wrote then that discussing the evolution of living organisms with only molecular and genetically random mutations is not only incorrect but also poses a threat that we will not be able to adequately predict the development of life forms. According to our theory, the axis of evolution of living organisms is communication (social behaviour) between them: from the individuals involved in communication will multiply those whose behaviour is successful and promising from the ‘point of view’ of this particular community. Adaptation to the physical environment is secondary in this case: a population with genetically enhanced traits searches for its own natural niche and usually finds it. In addition to explaining why organisms attain more complexity through their evolution (the simplest organism adapts best to the environment and its variation), such an approach allows us to see the evolution process holistically in kingdoms of microbes as well as those of plants and animals. The behaviour that results in the survival and safe reproduction of individuals and populations is reproduced and genetically proven in offspring. Obviously, genetic mutations occur at the molecular level, but these mutations are being ‘verified’ for safety and productivity of a particular population. However, what is the case with viruses that, according to even the boldest theories, do not have mechanisms for non-genetic change in behaviour? The fact is that the ‘task’ of the virus population is not to kill their host (including us). It would be impossible, because the virus can only live in another living organism. For this to be the case, we must assume that the living organism is directed towards the destruction of its own living environment and, consequently, of its own population. The population of viruses is selected to find a variant that spreads as fast as possible so that its population is neither harmed nor endangered. This, of course, does not happen consciously: simply, every mutation that is dangerous to human bodies dies with those particular human bodies, while the mutation that travels safely from organism to organism multiplies. Finally, the ‘ideal’ virus is a virus that is not detected by the body's antibodies and T-cells and continues to exist in living organisms not being detrimental to either its environment or itself. Today, the development of Covid-19 demonstrates this process: each subsequent mutation is less fatal but more prevalent. Such increased prevalence generates an illusion that each subsequent strain is more deadly than the previous one. However, it is not the case: As each subsequent strain of the virus affects more people, including those who protected themselves against the previous variant of the virus, it appears that the number of illnesses and deaths caused by the virus is increasing. However, the case-fatality ratio, the so-called fatality rate in fact decreases with each subsequent variant. In addition, each subsequent, faster spreading variant mostly kills those who were already unconditional candidates for death. The latter is an explanation for why mortality statistics does not change with a wider spread of the virus. Hence the benefits of vaccination: on the one hand, the vaccine ‘helps’ a person to cope with the virus, and on the other hand, ‘helps’ the virus, which is able to spread as an unnoticed mutation and survive. Vaccination is not a fight against a virus, but, by cooperating and communicating with it, aiding its evolution. However, the described view is not appreciated, and the epidemiological battle with Covid-19 was waged around the world based on a mono-disciplinary approach, feeding the beliefs that the virus is destroying humanity according to its biological calling and that each subsequent mutation was insidiously trying to kill more people than the previous one. This is exactly the danger we only assumed in 2013: Can a one-sided evolutionary theory be really harmful? Now the harm becomes clear and includes a near collapse of many businesses in the world economy. We hope that with this foreword, the 2013 text will be more intriguing and exciting for the readers.

Is there evidence for a trade-off between sperm competition traits and forelimb musculature in the western grey kangaroo?

Article

Full-text available

Feb 2018

Males may use tactics before, during and after mating to increase their reproductive success. With finite energy resources available, theory predicts that there should be a trade-off between investment in pre-copulatory traits (e.g. body size, armaments) and post-copulatory traits (e.g. testes size, spermatogenic efficiency). Western grey kangaroos (Macropus fuliginosus) are found in large, labile mixed-sex groups, in which the males show a dominance hierarchy. Males show indeterminate growth, and will reach up to six times the body mass of females. While the largest males use their size as a reproductive advantage, forelimb musculature further aids male-male contest, female attraction and/or female coercion. Under a trade-off scenario, we therefore predicted that larger, more muscular males would show less investment in sperm competitive traits. Consistent with this prediction, more muscular males showed decreased spermatozoa velocity. However, muscularity was also positively correlated with mass of two pairs of bulbourethral accessory glands, as well as mass of the penis and its muscles of erection. Seasonal changes in muscularity and accessory gland masses were also evident. Male kangaroos therefore invest in multiple reproductive traits on which selection can work.

Growth Pattern and Functional Morphology of the Cervical Vertebrae in the Gerenuk (Litocranius walleri): The Evolution of Neck Elongation in Antilopini (Bovidae, Artiodactyla)

Article

Full-text available

Jun 2019
J Mamm Evol

Long necks have evolved independently in several different taxa, but the processes underlying the evolution of this trait are not yet fully understood. In this study, we examined the skeletal mechanism underlying the neck elongation in the tribe Antilopini (Bovidae, Artiodactyla). We calculated the growth patterns of the cervical vertebrae in the gerenuk (Litocranius walleri), which possesses the longest neck in this tribe, and compared it with those in two related species. The growth rates of the vertebrae were not significantly different between species, suggesting that the long neck of the gerenuk has resulted from the elongation of the cervical vertebrae during the fetal or juvenile stage. The morphology of the cervical vertebrae of gerenuks differed from that of the closely related, relatively long-necked dama gazelle (Nanger dama), with protrusions occurring on the dorsal surface of the ventral arch of the atlas. This implies that gerenuks possess a well-developed transverse ligament of the atlas that functions to hold the dens of the axis against the atlas. We also found that the atlas lies in close proximity to the neural spine of the axis in the gerenuk, suggesting that hyperextension of the atlantoaxial joint is osteologically limited in this species. While foraging on high foliage, gerenuks flex and extend their necks freely in a bipedal posture without moving their entire body. These morphological characteristics peculiar to the gerenuk enhance the rigidity of the atlantoaxial joint and decrease the risk of subluxation of the joint during this unique foraging behavior.

Orbit orientation and eye morphometrics in giraffes (Giraffa camelopardalis)

Article

Oct 2013

Giraffe are thought to have excellent vision. We measured eye size, orbit orientation and retina surface area in 27 giraffes of both sexes ranging in age from neonates to mature adults (>10 yrs), to assess how it changes with growth, whether their eye anatomy correlates with their apparently excellent vision and lifestyle, and we have compared our findings with those for other large mammals to assess whether giraffe eye anatomy is unique. We found that giraffe eye volume increases from 33 cm³ at birth to approximately 65 cm³ in adults. The focal (axial) length increases from c. 40 to 48 mm in adults and retina surface area from c. 3000 mm² at birth to 4320 mm² in adults. The orbital axis angle at birth is c. 73° and the horizontal visual field mainly monocular and panoramic. With age the axis angle becomes more acute to c. 50° in adults and the visual field more binocular, changes that occur concurrently with increasing neck length. These results show that the giraffe eye and retinal surface area are larger than in all other ungulates, and their visual fields more binocular, attributes which are consistent with the idea that they have excellent vision.

Giraffe Stature and Neck Elongation: Vigilance as an Evolutionary Mechanism

Article

Full-text available

Sep 2016

Edgar Mark Williams

Giraffe (Giraffa camelopardalis), with their long neck and legs, are unique amongst mammals. How these features evolved is a matter of conjecture. The two leading ideas are the high browse and the sexual-selection hypotheses. While both explain many of the characteristics and the behaviour of giraffe, neither is fully supported by the available evidence. The extended viewing horizon afforded by increased height and a need to maintain horizon vigilance, as a mechanism favouring the evolution of increased height is reviewed. In giraffe, vigilance of predators whilst feeding and drinking are important survival factors, as is the ability to interact with immediate herd members, young and male suitors. The evidence regarding giraffe vigilance behaviour is sparse and suggests that over-vigilance has a negative cost, serving as a distraction to feeding. In woodland savannah, increased height allows giraffe to see further, allowing each giraffe to increase the distance between its neighbours while browsing. Increased height allows the giraffe to see the early approach of predators, as well as bull males. It is postulated that the wider panorama afforded by an increase in height and longer neck has improved survival via allowing giraffe to browse safely over wider areas, decreasing competition within groups and with other herbivores.

Lee et al. 2016 JoM Supporting Information

Data

Full-text available

May 2016

The First Description of Dominance Hierarchy in Captive Giraffe: Not Loose and Egalitarian, but Clear and Linear

Article

Full-text available

May 2015
PLOS ONE

Wild giraffes live in extensive groups in the fission fusion system, maintaining long social distances and loose social bonds. Within these groups, resources are widely distributed, agonistic encounters are scarce and the dominance hierarchy was reported in males only, while never deeply analysed. In captivity, the possibility to maintain inter-individual distances is limited and part of the resources is not evenly distributed. Consequently, we suggest that agonistic encounters should be more frequent, leading to the establishment of the dominance hierarchy. Based on the differences in resource-holding potential, we suggested that the rank of an individual would be affected by age and sex. Based on hypotheses of prior ownership, we tested whether rank was positively affected by the time spent in a herd and whether it was stable in adult females, which were present long-term in the same herd. We originally monitored four herds of Rothschild giraffes (Giraffa camelopardalis rothschildii) in Dvůr Králové zoo (n = 8), Liberec zoo (n = 6), and two herds in Prague zoo: Prague 1 (n = 8) and Prague 2 (n = 9). The Prague 1 and Prague 2 herds were then combined and the resulting fifth herd was observed over three consecutive years (2009, 2010, and 2011) (n = 14, 13, and 14, respectively). We revealed a significantly linear hierarchy in Dvůr Králové, Prague 2 and in the combined herd in Prague. Rank was significantly affected by age in all herds; older individuals dominated the younger ones. In females, rank was positively affected by the time spent in the herd and adult females in Prague maintained their rank during three consecutive years. This study represents the first analysis of the dominance hierarchy in the captive giraffe, and discusses the behavioural flexibility of the social structure in response to monopolisable resources in a captive environment.

Orbit Orientation and Eye Morphometrics in Giraffes (Giraffa camelopardalis)

Article

Full-text available

Oct 2013

Giraffe are thought to have excellent vision.We measured eye size, orbit orientation and retina surface area in 27 giraffes of both sexes ranging in age from neonates to mature adults (>10 yrs), to assess how it changes with growth, whether their eye anatomy correlates with their apparently excellent vision and lifestyle, and we have compared our findings with those for other large mammals to assess whether giraffe eye anatomy is unique.We found that giraffe eye volume increases from 33 cmat birth to approximately 65 cmin adults. The focal (axial) length increases from c. 40 to 48 mm in adults and retina surface area from c. 3000 mmat birth to 4320 mmin adults. The orbital axis angle at birth is c. 73&Deg; and the horizontal visual field mainly monocular and panoramic.With age the axis angle becomes more acute to c. 50&Deg; in adults and the visual field more binocular, changes that occur concurrently with increasing neck length. These results show that the giraffe eye and retinal surface area are larger than in all other ungulates, and their visual fields more binocular, attributes which are consistent with the idea that they have excellent vision.

Sexual selection on forelimb muscles of western grey kangaroos (Skippy was clearly a female)

Article

Aug 2013

Studies of sexual selection have tended to concentrate on obvious morphological dimorphisms such as crests, horns, antlers, and other physical displays or weapons; however, traits that show no obvious sexual dimorphism may nevertheless still be under sexual selection. Sexual selection theory generally predicts positive allometry for sexually selected traits. When fighting, male kangaroos use their forelimbs to clasp and hold their opponent and, standing on their tail, bring up their hind legs to kick their opponent. This action requires substantial strength and balance. We examined allometry of forelimb musculature in male and female western grey kangaroos (Macropus fuliginosus) to determine whether selection through male–male competition is associated with sex differences in muscle development. Forelimbs of males are more exaggerated than in females, with relatively greater muscle mass in males than the equivalent muscles in females. Furthermore, while muscles generally showed isometric growth in female forelimbs, every muscle demonstrated positive allometry in males. The significant positive allometry in male forelimb musculature, particularly those muscles most likely involved in male–male combat (a group of muscles involved in grasping: shoulder adduction, elbow flexion; and pulling: arm retraction, elbow flexion), clearly suggests that this musculature is subject to sexual selection. In addition to contributing to locomotion, the forelimbs of male kangaroos can also act as a signal, a weapon, and help in clasping,features that would contribute towards their importance as a sexually selected trait. Males would therefore benefit from well-developed musculature of the arms and upper body during competition for mates.

The long necks of sauropods did not evolve primarily through sexual selection

Article

Sep 2011
J ZOOL

It has recently been argued that the elongate necks of sauropod dinosaurs evolved primarily through selection for their use as sexual and dominance signals, and not as an adaptation for accessing a large ‘feeding envelope’ as traditionally thought. Here we explore this idea and show that all six arguments that have been advanced in support of the sexual selection hypothesis are flawed: there is no evidence for sexual dimorphism in the necks of sauropods; neither is there any evidence that they were used in dominance displays; long necks provided significant survival benefits in allowing high browsing and energetically efficient grazing; their fitness cost was likely less than has been assumed; their positive allometry through ontogeny is uninformative given that ontogenetic allometry is common in animals; apparent lack of correlation between neck and leg length across phylogeny is illusory due to over-representation of mamenchisaurids in a previously analysed dataset, and in any case is not informative as the unique morphology of sauropod necks suggests they, rather than legs, may have been cheaper to elongate when evolving increased vertical reach. In no speciose, morphologically varied, long-lived tetrapod clade has sexual selection consistently acted on a single part of the body, and it is unlikely that Sauropoda is the exception to this. In summary, there is no convincing evidence that sexual selection was the primary force driving the evolution of sauropod necks. While a subsidiary role for sexual selection cannot be discounted, the traditional hypothesis that sauropod necks evolved primarily due to the feeding benefits that they conferred is, by comparison, far better supported.

The demography of giraffe deaths in a drought

Article

Full-text available

Jan 2010

Darwin’s theory for the evolution of the long neck of giraffes is that height confers access to browse free of competition from smaller browsers. The theory predicts that survivors of a drought will be the tallest animals in a population. All studies so far have tested this hypothesis by analysis of feeding patterns and behaviour.We have studied it by analysing the demography of deaths in a drought. Using skeletal material from 26 giraffes that died as a result of a drought in southeastern Zimbabwe in 2008, we established the body mass, height, and age of the dead giraffes using allometric equations developed from culled animals. Typical giraffe populations consist of 55% adults (>6 years old), 15% young adults (3–6 years old), 15% juveniles (1–3 years old), and 15% neonates (<1 year old). Skeletons came from 54% adults, 14% young adults, and 32% juveniles. No neonatal skeletons were found. More juveniles died than expected because they have to compete with other browsers for nutrients. Most adult deaths occurred in the tallest and largest males because their daily requirements for browse are highest and could not be met by the amounts available at any level. Thus the survivors of this drought were young adults, a finding contrary to the predictions of Darwin’s feeding hypothesis.

Chez la girafe, tous les cous sont permis

Article

Jul 2022

Le Guyader pierre Herve

How the giraffe got its neck: ‘unicorn’ fossil could shed light on puzzle

Article

Jun 2022

Nicola Jones

A newly described species of ancient giraffoid had a thick helmet designed for fierce headbutting. A newly described species of ancient giraffoid had a thick helmet designed for fierce headbutting. Credit: Y. Wang and X. Guo Artists impression of two fighting male Discokeryx xiezhi giraffoids. Artists impression of two fighting male Discokeryx xiezhi giraffoids.

Giraffe Neck Robot: First Step Toward a Powerful and Flexible Robot Prototyping Based on Giraffe Anatomy

Article

Full-text available

Apr 2022

The neck of a giraffe has excellent characteristics that can serve as a good alternative for designing a large robotic mechanism. For example, the neck can rapidly move when performing necking, a motion where the giraffes strike each other’s necks. Furthermore, the neck of a giraffe helps prevent impacts and adapts to the shape and hardness of the opponent’s neck during necking. In contrast, a conventional robotic mechanism is limited in its capability to achieve such powerfulness and flexibility characteristics; that is, being powerful while having robustness against impacts and kinematic and dynamic adaptability to the opponent. This study focuses on applying those excellent characteristics of a giraffe neck to develop robotic mechanisms. Specifically, roboticists and animal anatomists have combined efforts to develop a powerful and flexible long musculoskeletal robot based on the anatomy of a giraffe neck. The musculoskeletal robot prototype is actuated using thin McKibben pneumatic artificial muscles that bend easily. The results confirm the coordination between the muscles and ligaments and the shape adaptability to an external force.

Prototyping of musculoskeletal robot based on anatomy of neck of giraffes and performance testキリンの首の解剖学知見に基づく筋骨格ロボットの試作と動作試験

Article

Full-text available

Nov 2020

The neck of Giraffe has excellent characteristics as a long robot mechanism. The neck of giraffe can move violently represented in necking, a motion striking necks each other. Further, in a necking motion, a neck of a giraffe wards off impacts and adapts to the shape of the opponent. On the other hand, conventional robot mechanisms have hardly achieved both powerfulness and kinematic and dynamic flexibility to the opponent. In order to apply these excellent characteristics of necks of a giraffe to robot mechanisms, we developed a half-size musculoskeletal robot prototype based on anatomical knowledge of the neck of giraffes and the skeletal shape of an actual giraffe. The musculoskeletal robot protype is actuated by thin McKibben pneumatic artificial muscles, which bent flexibly, and we confirmed adaptability to an external force.

Milestones in the Evolving Theory of Evolution

Book

Sep 2020

Restoring Maximum Vertical Browsing Reach in Sauropod Dinosaurs

Article

May 2017
ANAT REC

Gregory S Paul

The ongoing controversy centered on neck posture and function in sauropod dinosaurs is misplaced for a number of reasons. Because of an absence of pertinent data it is not possible to accurately restore the posture and range of motion in long necked fossil animals, only gross approximations are possible. The existence of a single "neutral posture" in animals with long, slender necks may not exist, and its relationship to feeding habits is weak. Restorations of neutral osteological neck posture based on seemingly detailed diagrams of cervical articulations are not reliable because the pictures are not sufficiently accurate due to a combination of illustration errors, and distortion of the fossil cervicals. This is all the more true because fossil cervical series lack the critical inter-centra cartilage. Maximum vertical reach is more readily restorable and biologically informative for long necked herbivores. Modest extension of 10 degree between each caudal cervical allowed high shouldered sauropods to raise the cranial portion of their necks to vertical postures that allowed them to reach floral resources far higher than seen in the tallest mammals. This hypothesis is supported by the dorsally extended articulation of the only known co-fused sauropod cervicals. Many sauropods appear to have been well adapted for rearing in order to boost vertical reach, some possessed retroverted pelves that may have allowed them to walk slowly while bipedal. A combination of improved high browsing abilities and sexual selection probably explains the unusually long necks of tall ungulates and super tall sauropods. This article is protected by copyright. All rights reserved.

References

Chapter

Aug 2016

Bryan Shorrocks

Evolutionary Approach of the Logistics Collaboration System

Article

Aug 2015

김세인

On reconstructing Giraffa sivalensis, an extinct giraffid from the Siwalik Hills, India

Article

Full-text available

Aug 2015

Giraffa sivalensis occurred during the Plio-Pleistocene period and probably represents the terminal species of the genus in Southern Asia. The holotype is an almost perfectly preserved cervical vertebra of disputed anatomical location. Although there is also uncertainty regarding this animal’s size, other specimens that have been assigned to this species include fragments of two humeri, a radius, metacarpi and teeth. Here we estimate neck length, leg length and body mass using interspecific and, unusually, ontogenetic allometry of extant giraffe skeletal parameters. The appropriateness of each equation to estimate body mass was evaluated by calculating the prediction error incurred in both extant giraffes (G. camelopardalis) and okapis (Okapia johnstoni). It followed that the equations with the lowest prediction error in both species were considered robust enough to use in G. sivalensis. The size of G. sivalensis, based on the holotype, is proposed as 400 kg (range 228 kg–575 kg), with a neck length of approximately 147 cm and a height of 390 cm. The molar lengths of tooth specimens considered agree with this size estimate. The humerus was the most appropriate long bone to establish body mass, which estimates a heavier animal of ca 790 kg. The discrepancy with the vertebral body weight estimate might indicate sexual dimorphism. Radial and metacarpal specimens estimate G. sivalensis to be as heavy as extant giraffes. This may indicate that the radius and metacarpus are unsuitable for body mass predictions in Giraffa spp. Alternatively, certain long bones may have belonged to another long legged giraffid that occurred during the same period and locality as G. sivalensis. We have concluded that if sexual dimorphism was present then males would have been about twice the size of females. If sexual dimorphism was not present and all bones were correctly attributed to this species, then G. sivalensis had a slender neck with a relatively stocky body.

Demography of Giraffe in the Fragmented Tarangire Ecosystem

Research

Full-text available

May 2015

Derek Edward Lee

PhD Dissertation Documenting whether variation in demographic parameters such as births, deaths, and movements exists, and how temporal and spatial environmental variability influences demography, is critical to understanding and affecting changes in animal populations. Natural populations often exhibit variation in demographic parameters, and while the examination of temporal variation has long been a central theme in population ecology, spatial variation among or within populations of the same species has received much less attention. Although the vast majority of the world’s ungulate species live in the tropics and sub-tropics, few studies have investigated the demography of large, tropical herbivores. Giraffe (Giraffa camelopardalis) are believed to be declining rapidly, as their habitat throughout Africa has been lost and fragmented, thus the fragmented Tarangire Ecosystem in Tanzania was representative of much of the remaining landscape for these iconic megaherbivores. The goal of this study was to fill this knowledge gap by examining whether spatial variation in demography of giraffe existed in a fragmented ecosystem, and how key demographic parameters of reproduction, adult and juvenile survival, and movements of a large tropical ungulate were affected by spatial variation in land use, poaching (illegal hunting), and predation. I also assessed the source-sink structure of the study area and examined the implications of sub-population demography and movements for metapopulation dynamics. Finally, I examined temporal seasonal variation in reproduction and calf survival, and whether observed patterns fit specific theories of synchronous and asynchronous reproduction. My research used data from 1,857 individually identified giraffe at 5 sites within the Tarangire Ecosystem to estimate site-specific population size, probabilities of reproduction, calf survival, adult survival, and movements among sites to understand a suspected declining overall population trend. My research was organized around three questions: 1) How does survival, reproduction, and population growth rate vary among sites? Does spatial variation in land management, giraffe density, lion density, or poaching affect adult survival, calf survival, and reproduction? Do patterns of spatial variation reflect the paradigm of ungulate population dynamics from studies of temporal variation?; 2) How does movement link the sub-populations in this fragmented landscape? Does land management, predation, or density explain movement rates? How do differences in demography and movement among sub-populations affect the metapopulation?; and 3) How do reproduction and juvenile survival vary by season? Do observed seasonal patterns in reproduction and survival relative to changes in vegetation quality and/or predation pressure fit specific theories of synchronous and asynchronous reproduction? I found significant spatial variation in adult female survival, reproduction, movements, and density existed. Only adult female survival was significantly correlated with a spatial covariate (positively correlated with anti-poaching efforts). A matrix population model using site-specific estimates of survival and reproduction showed adult female survival was the highest elasticity parameter, and thus had the greatest proportional effect on population growth rate (lambda). Population growth rate also varied significantly by site, and was best explained by the spatial covariate of distance to Mtowambu, the main bushmeat market town in the area. Population growth rate was ≥ 1.0 (indicating a growing sub-population) only in Tarangire National Park (TNP), but lambda at all other sites was less than 1.0 indicating decreasing sub-populations. A decreasing metapopulation 〖(λ〗^M ≈ 0.99) was estimated by two methods of computing the metapopulation growth rate. TNP was identified as the dominant engine of metapopulation growth, but movement of individuals out of TNP and into “attractive sink” sites, where more poaching of adults occurs, is the most likely explanation for the shrinking metapopulation. However, these movements are also responsible for preventing extirpation of giraffe sub-populations in the smaller sites. I also examined how temporal variation affected calving and calf survival. I found significant seasonal variation in proportion of births, with more births in the short rains and dry seasons relative to the long rains, and calf survival was affected by season of birth in accordance with both the “phenological match” theory of reproductive synchrony and the “temporal resource partitioning” theory of asynchrony. Calf survival also was positively correlated with the seasonal abundance of migratory herds of zebra and wildebeest, the local abundance of which apparently reduced predation pressure on young giraffe. Based on my results, for conservation of the species and the large-scale processes of giraffe interactions across the landscape, I recommend efforts to disrupt bushmeat markets and expand anti-poaching patrols such as those employed in the Tanzanian national parks, to bring down harvest rates of adult females to sustainable levels, while simultaneously maintaining or improving linkage habitat between all sites to facilitate natural movements. This should increase adult survival to the point where sink sub-populations are less of a drain on the metapopulation, and having multiple linked, healthy sub-populations reduces the risk of total extinction. Additionally, conservation of migratory herds by protecting their calving grounds and migration routes would maintain their indirect benefit to giraffe calf survival. Identifying source and sink habitats using the methods described herein is superior to monitoring via abundance or density estimates alone because when managers understand movements, population growth rates, and metapopulation dynamics, they can effectively prioritize actions to ensure the security of sources while addressing the causes of sinks.

Evolution and the Origin of Life

Article

Behavioural inventory of the giraffe (Giraffa camelopardalis)

Article

Full-text available

Nov 2012
BMC Res Notes

Background Numerous factors like continuous habitat reduction or fragmentation for free-ranging giraffes (Giraffa camelopardalis) as well as e.g. suboptimal housing conditions for animals in captivity might lead to behavioural alterations as part of the overall adaptation process to the changing living conditions. In order to facilitate current and future studies on giraffe behaviour, a comprehensive ethogram was compiled based on existing literature, as well as observations on giraffes in the wild (Hwange National Park, Zimbabwe; Entabeni Game Reserve, South Africa), and in captivity (National Zoological Gardens of South Africa, Pretoria). Findings The resulting ethogram lists 65 different behavioural patterns, which were described and grouped into seven categories: General activities, Abnormal repetitive behaviours, General interactions, Bull-Cow behaviour, Bull-Bull behaviour, Cow-Bull behaviour, Maternal behaviours, and Interactions by calves. The behaviours were further described regarding a presumed purpose, particularly with respect to social interactions and sexual behaviour. Contradictory descriptions from previous studies were considered and discussed in comparison with our own observations. Conclusions This ethogram provides a basis for current and future studies by suggesting a terminology which can be used for harmonizing behavioural observations, thus helping to facilitate comparability of future results. Subsequently, a better understanding of the behavioural ecology of giraffes in the wild as well as in captivity could aid future conservation efforts.

From Fetus to Adult-An Allometric Analysis of the Giraffe Vertebral Column

Article

Sep 2010
J EXP ZOOL PART B

As mammalian cervical vertebral count is almost always limited to seven, the vertebral column of the giraffe (Giraffa camelopardalis) provides an interesting study on scaling and adaptation to shape in light of these constraints. We have defined and described the growth rates of the lengths, widths, and heights of the vertebrae from fetal through neonatal life to maturity. We found that the disproportionate elongation of the cervical vertebrae is not a fetal process but occurs after birth, and that each cervical (C2-C7) vertebrae elongates at the same rate. C7 is able to specialize toward elongation as its function has been shifted to T1. We concluded that T1 is a transitional vertebra whose scaling exponent and length is between that of the cervical and thoracic series. Despite its transitional nature, T1 is still regarded as thoracic, as it possesses an articulating rib that attaches to the sternum. The other dimensions taken (width, height, and spinous process length) show that giraffe vertebral morphology exhibit adaptations to biomechanical strain, and we have underlined the importance of the thoracic spinous processes in supporting the head and neck.

Winning by a Neck: Sexual Selection in the Evolution of Giraffe

Article

Full-text available

Nov 1996

A classic example of extreme morphological adaptation to the environment is the neck of the giraffe (Giraffa camelopardalis), a trait that most biologists since Darwin have attributed to competition with other mammalian browsers. However, in searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffe generally feed from low shrubs, not tall trees; females spend over 50% of their time feeding with their necks horizontal; both sexes feed faster and most often with their necks bent; and other sympatric browsers show little foraging height partitioning. Each result suggests that long necks did not evolve specifically for feeding at higher levers. Isometric scaling of neck-to-leg ratios from the okapi Okapia johnstoni indicates that giraffe neck length has increased proportionately more than leg length-an unexpected and physiologically costly method of gaining height. We thus find little critical support for the Darwinian feeding competition idea. Ne suggest a novel alternative: increased neck length has a sexually selected origin. Males fight for dominance and access to females in a unique way: by clubbing opponents with well-armored heads on long necks. Injury and death during intrasexual combat is not uncommon, and larger-necked males are dominant and gain the greatest access to estrous females. Males' necks and skulls are not only larger and more armored than those of females' (which do not fight), but they also continue growing with age. Larger males also exhibit positive allometry, a prediction of sexually selected characters, investing relatively more in massive necks than smaller males. Despite being larger, males also incur higher predation costs than females. We conclude that sexual selection has been overlooked as a possible explanation for the giraffe's long neck, and on present evidence it provides abetter explanation than one of natural selection via feeding competition.

Predator-Prey Relationships among the Larger Mammals of the Kruger National Park

Article

Full-text available

May 1969
Koedoe

U. De V. Pienaar Ph.D

Predator-prey relationships amongst the larger mammals of the Kruger National Park

Necks for sex

Article

Jan 2006

P. Senter

Necking behaviour in the giraffe

Article

Jan 1967

M.J. Coe

Previous references to “necking” behaviour, and the main features of the study area are briefly outlined. “Necking” behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance. The significance of “necking” is discussed, and it is suggested that these ritualized actions form an important sexuo‐social bonding mechanism whereby a hierarchy is created amongst the males,and movement between strictly bachelor and mixed herds helps to maintain contact between the sexesin this polygamous mammal.

Seasonal utilization of leaves by giraffes Giraffa camelopardalis , and the relationship of the seasonal utilization to the chemical composition of the leaves

Article

Jan 1982

The crude protein of the leaves of Acacia spp. is generally higher than in those of other species and they are therefore a better food source. The leaves of preferred plants show the following seasonal trends: a decrease in moisture and protein content from January until August/September when they again increase; conversely, the two carbohydrate fractions, crude fibre and N-free extract, increase during the corresponding period until August/September, whereafter they decrease again. Leaf moisture content was always greater during the night than during the day. This may be important for supplementing water gain in times of drought.-from Authors

The relationships of the okapi

Article

Feb 1938

E.H. Colbert

The fossil Giraffidae of India

Article

Jan 1911

G.E. Pilgrim

Giraffe Weight Estimation Using Dissected Leg Weight and Body Measurements

Article

Oct 1977

A. J. Hall-Martin

Data from 44 adult giraffes (Giraffa camelopardalis) showed that leg weight as a percentage of body weight is sufficiently constant to provide regression equations useful for estimating body or carcass weight. Data from 53 giraffes of various ages show that reliable estimates of body weight can be made from linear body measurements, regardless of sex or age. The best for field use are linear regressions between body weight and chest girth; however, shoulder height is usually the only measurement obtained from predator kills and this can also be used. Measures of the volume of the animals such as length ×

\text{girth}^{2}

and log transformations give superior correlations.

The Giraffe. Its Biology, Behavior and Ecology

Article

Jul 1978

On the origin, evolution and phylogeny of giraffes Giraffa camelopardalis

Article

Jan 2003

The origin, phylogeny, and evolution of modem giraffes (Giraffa camelopardalis) is obscure. We review here the literature and conclude that the proximate ancestors of modern giraffes probably evolved in southern central Europe about 8 million years ago (Mya). These ancestors appear to have arisen from the gelocid ancestral assemblage of 20–25 Mya via the family Palaeomerycidae. From the palaeomerycids arose the Antilocaprinae (Pronghorns) via the subfamily Dromomerycinae, and two subfamilies of giraffids, the Climacoceratidae and Canthumerycidae. The terminal genus of the Climacoceratid line was the now extinct massive giraffid Sivatherium sp. The Canthumerycids gave rise to the okapi and giraffes via the intermediate forms of Giraffokeryx, Palaeotragus sp. (of which the okapi is the extant form), Samotherium sp. and Bohlinia sp. All of which are extinct. Stimulated by climate change, progeny of Bohlinia entered China and north India, evolved into typical Giraffa species and became extinct there about 4 Mya. Similarly, following their preferred habitat, African Giraffa entered Africa via Ethiopia about 7 Mya. Here, seemingly unaffected by the climate changes occurring to the east and causing extinction of its Asian counterparts, Giraffa radiated into several sequential and coeval species culminating with the evolution of G. camelopardalis in East Africa from where it dispersed to its modern range. Fossils of G. camelopardalis appear about 1 Mya in East Africa.The underlying stimulus for Giraffa evolution seems to have been the vegetation change that began about 8 Mya, from the prevalent forest (C3) biome to a savannah/woodland/shrub (C4) biome. Giraffa's success as a genus is attributed to its great height and unique coat markings. Its height is a consequence of elongation of all seven cervical vertebrae and of the lower more than the upper limb bones. Advantages conferred by its height include protection from predation, increased vigilance, and in males sexual dominance and access to nutrients. Its coat colourings are highly hereditable and provide protection from predation by camouflage, especially in the young. As giraffe are unable to sweat and pant, the patches may also act as thermal windows and may have an important thermoregulatory function.

Fossil Giraffes from the Miocene of Africa and a Revision of the Phylogeny of the Giraffoidea

Article

May 1978
PHILOS T R SOC B

W. R. Hamilton

Specimens of Climacoceras africanus are described from Maboko, Kenya. The new species Climacoceras gentryi is established on the basis of ossicones, mandibles, and upper and lower dentitions from Fort Ternan and Baringo, Kenya. By interpretation of its lower canines Climacoceras is identified as a giraffoid and is placed in the new family Climacoceridae. Canthumeryx sirtensis is identified from Muruarot and Rusinga, Kenya. A dentition and associated partial skeleton of this species are described. The teeth agree closely with specimens of the same species from Gebel Zelten, Libya. Zarafa zelteni from Gebel Zelten is synonymized with Canthumeryx sirtensis. Again on the basis of its lower canines Canthumeryx is identified as a giraffoid and is placed in the new family Canthumerycidae. Specimens of Palaeotragus primaevus are described from Baringo, Kenya. This material includes a cranium with the ossicones, skull roof, occipital and basicranial regions preserved. Palaeotragus primaevus specimens from Fort Ternan are used in this description and some of these are redescribed. The relations of the giraffoids are assessed by methods of phylogenetic systematics. Palaeomeryx, Prolibytherium and Propalaeoryx are excluded from the Giraffoidea as their lower canines are not known. The Palaeotraginae is shown to be an invalid polyphyletic grouping and the genus Palaeotragus is also shown to be polyphyletic. Palaeotragus microdon is probably synonymous with Palaeotragus rouenii and the three species Palaeotragus rouenii (P. microdon), Palaeotragus coelophrys and Palaeotragus quadricornis are retained in the genus Palaeotragus. It is suggested that 'Palaeotragus' expectans and 'Palaeotragus' decipiens are closely related to Samotherium. Palaeotragus primaevus is probably synonymous with Palaeotragus tungurensis and this species is closely related to the giraffines. With slight changes the subfamilies Sivatheriinae and Giraffinae are valid monophyletic groups. Hydaspitherium is synonymized with Bramatherium and the Sivatheriinae includes the genera Giraffokeryx, Birgerbohlinia, Bramatherium and Sivatherium while the Giraffinae includes the genera Honanotherium, Bohlinia and Giraffa and the species 'Palaeotragus' tungurensis (P. primaevus). Okapia is identified as the sister-group of the other giraffids. Triceromeryx is the sister-group of the Giraffidae. Canthumeryx is the sister-group of Triceromeryx plus the Giraffidae while Climacoceras is the sister-group of the other giraffoids.

The calcium and phosphorus content of giraffe ( Giraffa camelopardalis ) and buffalo ( Syncerus caffer ) skeletons

Article

Sep 2005

Osteophagia, variable serum calcium (Ca) and phosphorus (P) concentration, high serum alkaline phosphatase activity, a high growth rate, and a large skeletal mass, all suggest that Ca and P requirements and availability are finely balanced in giraffes. The mineral content of some marker bones in skeletons obtained from adult male giraffes (browsers) and adult male African buffaloes (grazers of similar body mass) were compared to assess the idea of critical Ca and P balance. Our results show that the P concentration of plasma varies more than Ca concentration, and that the Ca content of giraffe bones (0.196 +/- 0.01 g/g) and buffalo (0.202 +/- 0.006 g/g) varies more than P content (0.095 +/- 0.002 in both). The average Ca and P content of the bones analysed was similar in both species (Ca = similar to 20.0%, P = similar to 9.5%). Giraffe skeletons, however, contain three times more Ca and P than do buffalo skeletons. This translates into a 1.5-2.0 fold higher Ca requirement for giraffes, with which they seem to cope effectively by selection for Ca-rich, dicotyledonous, browse. Sources of P to meet requirements are not obvious and a seasonal deficiency of P is a more likely cause of observed osteophagia than Ca deficiency. Giraffe rib P density, the best measure of P balance, of 0.142 +/- 0.01 g/cm(3) is, however, above the deficiency threshold. Bone mineral content (Ca and P) correlates well with bone density and shows only slight differences between adult males of the two species.

Evolutionary Analysis

Book

Jan 2004
CRUSTACEANA

Population, distribution, and behaviour of giraffe in the Arusha National Park, Tanzania

Article

Jul 1982

In a year's study of the giraffe population of the Arusha National Park we identified 462 individuals. The cumulative first sightings of individuals were fitted to a logistic model that gave an estimated total population of 471. Immatures accounted for only 24% of the population. Twenty-two calves were born during the period of study.The giraffe of the Park are divided into ‘North’ (more precisely northeastern) and ‘South’ (southeastern) subpopulations, and although there is no barrier between them, only 3% of the population (all bulls) were ever seen in both the northern and southern parts of the Park. The northern region is further divided into four areas, each with its own assemblage of individuals, which were seldom seen elsewhere. Bulls and male juveniles were seen less often relative to their numbers than were cows and female juveniles. This indicates that they spend a greater proportion of the time in the forest than do the females.A partial list of plants eaten by giraffe in the Park is given. Acacias are an insignificant component of the diet.Calves were usually accompanied by their mothers; typically they did not lie out. Each calf was usually seen in the company of the same few individual peers. Calves spent a higher percentage of the time with calves than with their own mothers, they were closer to one another than to their mothers, and there was much physical contact between them.Bulls of each age class occurred less frequently with individuals of their own class and more frequently with bulls of other age calsses than would be expected. Young bulls were frequently seen in the company of other bulls, cows and immatures, and they often engaged in sparring. Older bulls were more solitary, tended to avoid other bulls in the presence of cows and immatures, and instead of sparring they tested and courted cows.The inadequate recruitment of this senescent population is attributed mainly to low birth rate and, in the South, high mortality in the first year. A decline in numbers is anticipated.

Necks for sex: Sexual selection as an explanation for sauropod dinosaur neck elongation

Article

Aug 2006
J ZOOL

Philip Senter

The immensely long neck of a sauropod is one of the most familiar and striking of anatomical specializations among dinosaurs. Here, I use recently collected neontological and paleontological information to test the predictions of two competing hypotheses proposed to explain the significance of the long neck. According to the traditional hypothesis, neck elongation in sauropods increased feeding height, thereby reducing competition with contemporaries for food. According to the other hypothesis, which is advanced for the first time here, neck elongation in sauropods was driven by sexual selection. Available data match the predictions of the sexual selection hypothesis and contradict the predictions of the feeding competition hypothesis. It is therefore more plausible that increases in sauropod neck lengths were driven by sexual selection than by competition for foliage.

A note on foetal growth and development of the giraffe Giraffa camelopardalis giraffa

Article

Aug 2009
J ZOOL

The growth of the foetus of the southern giraffe is discussed. Gestation period is calculated as 457 days being the mean of 48 observations of other workers. Birthmass is taken as 102 kg from measurements on wild giraffe. This is almost twice as great as some published figures for captive giraffe. However, subspecies also differ. Foetal growth followed a typical “J” shaped curve when plotted from the mass of 24 foetuses. The increase in vertebral column length followed a straight line. Crown/rump measurements could not always be accurately taken.

The giraffe of Nairobi National Park: Home range, sex ratios, the herd, and food

Article

Apr 2008
AFR J ECOL

J. B. Foster

The giraffe of Nairobi National Park, Kenya have been studied for one year. Each animal seen has been photographed from the left side and the pattern on the neck used to recognize each individual. While the pattern may become darker with age, it does not significantly change in detail even over many years. At present 65 adult male, 72 adult female and 30 immature giraffe can be recognized. Movements of individuals are described as well as associations with other individuals. The 3ex ratio of the giraffe is discussed in relation to that found in the plains ungulates. The population of giraffe in the Park is considered to be particularly high and the relation of giraffe to the vegetation is discussed briefly.

“Necking” behaviour in the giraffe

Article

Mar 1967
J ZOOL

Malcolm J. Coe

Previous references to “necking” behaviour, and the main features of the study area are briefly outlined. “Necking” behaviour in giraffe takes place only in all male herds. When the animals are in a head to head posture the intensity is either high or low, but when animals take up a head to tail posture the actions are always of high intensity and appear to have greater sexual significance. The significance of “necking” is discussed, and it is suggested that these ritualized actions form an important sexuo-social bonding mechanism whereby a hierarchy is created amongst the males,and movement between strictly bachelor and mixed herds helps to maintain contact between the sexesin this polygamous mammal.

Social influence on vigilance behaviour in giraffes, Giraffa Camelopardalis

Article

Jun 2005

Vigilance in ungulates is considered to have a predominantly antipredator function, with the frequency and duration of scans per individual decreasing with increasing group size. Social influences on vigilance scans have been overlooked in studies on ungulates, although studies in primates and birds show that conspecific scans are important determinants of vigilance behaviour. We investigated group size effects in giraffes and examined social influences on their scanning behaviour, as well as the influence of feeding posture. We found that group size has little effect on scanning behaviour in either bulls or cows, which may be attributable to our inability to measure a group as perceived by a giraffe. Time spent scanning by lone cows did not differ from that of cows in any other group type, but time spent scanning by bulls when alone was less than that in groups. The presence of calves in a group did not influence scanning behaviour. Predation risk does not appear to be a significant modifier of vigilance behaviour, although a constant level of antipredator vigilance is probably maintained. Social factors were a significant modifier of vigilance scanning. Bulls scanned the most when they were in groups with larger bulls, and least when they were with smaller bulls. A similar pattern was seen with nearest-neighbour identity, and the identity of individuals within 10 m of a focal animal. Cows were significantly more vigilant when an adult bull was close, or was the nearest neighbour. Finally, vigilance advantages have been postulated as a determinant of sexual segregation in giraffe foraging heights but we found that the posture associated with high foraging heights imposes a vigilance cost, not an advantage. We therefore conclude that differential vigilance requirements are not a determinant of feeding height segregation between giraffe bulls and cows.

Die Familie Giraffidae mit bes. Berücks. der fossilen Formen aus China /

Article

Birger. Bohlin

Zugl.: Upsala, Phil. Diss., 1926.

The origin of mean arterial and jugular venous blood pressures in giraffes

Article

Aug 2006

Using a mechanical model of the giraffe neck and head circulation consisting of a rigid, ascending, `carotid' limb, a `cranial' circulation that could be rigid or collapsible, and a descending, `jugular' limb that also could be rigid or collapsible, we have analyzed the origin of the high arterial and venous pressures in giraffe, and whether blood flow is assisted by a siphon. When the tubes were rigid and the `jugular' limb exit was lower than the `carotid' limb entrance a siphon operated, `carotid' hydrostatic pressures became more negative, and flow was 3.3 l min–1 but ceased when the `cranial' and `jugular' limbs were collapsible or when the`jugular' limb was opened to the atmosphere. Pumping water through the model produced positive pressures in the `carotid' limb similar to those found in giraffe. Applying an external `tissue' pressure to the `jugular' tube during pump flow produced the typical pressures found in the jugular vein in giraffe. Constriction of the lowest, `jugular cuff', portion of the `jugular' limb showed that the cuff may augment the orthostatic reflex during head raising. Except when all tubes were rigid, pressures were unaffected by a siphon. We conclude that mean arterial blood pressure in giraffes is a consequence of the hydrostatic pressure generated by the column of blood in the neck, that tissue pressure around the collapsible jugular vein produces the known jugular pressures, and that a siphon does not assist flow through the cranial circulation.

Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers

Article

Feb 2007
AM NAT

With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.

Tall tales or how the giraffe got its neck

R E Simmons

Simmons, R.E. (2008). Tall tales, or how the giraffe got its neck. Africa Geographic, March, 32-39.

Carcass composition of the giraffe, Giraffa camelopardalis giraffa

A J Hall-Martin
M Von La Chevallerie
J D Skinner

Hall-Martin, A.J., von la Chevallerie, M. & Skinner, J.D. (1977). Carcass composition of the giraffe, Giraffa camelopardalis giraffa. S. Afr. J. Anim. Sci. 7, 55-64.

The Zoological Society of London 286 Giraffe evolutionary morphology G

Jan 2009
281-286

Mitchell

Journal of Zoology 278 (2009) 281–286 c 2009 The Authors. Journal compilation c 2009 The Zoological Society of London 286 Giraffe evolutionary morphology G. Mitchell et al.

The giraffe of Nairobi national park

Jan 1966
139

Foster J.B.

Sexual selection is not the origin of long necks in giraffes

Abstract

No full-text available

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