Post by King Kodiak on Mar 20, 2021 12:25:32 GMT -5
Sagittal crest formation in great apes and gibbons
Abstract
The frequency of sagittal crest expression and patterns of sagittal crest growth and development have been documented in hominoids, including some extinct hominin taxa, and the more frequent expression of the sagittal crest in males has been traditionally linked with the need for larger-bodied individuals to have enough attachment area for the temporalis muscle. In the present study, we investigate sagittal cresting in a dentally mature sample of four hominoid taxa (Pan troglodytes schweinfurthii, Gorilla gorilla gorilla, Pongo pygmaeus pygmaeus and Hylobates lar). We investigate whether sagittal crest size increases with age beyond dental maturity in males and females of G. g. gorilla and Po. pyg. pygmaeus, and whether these taxa show sex differences in the timing of sagittal crest development. We evaluate the hypothesis that the larger sagittal crest of males may not be solely due to the requirement for a larger surface area than the un-crested cranial vault can provide for the attachment of the temporalis muscle, and present data on sex differences in temporalis muscle attachment area and sagittal crest size relative to cranial size. Gorilla g. gorilla and Po. pyg. pygmaeus males show significant relationships between tooth wear rank and sagittal crest size, and they show sagittal crest size differences between age groups that are not found in females. The sagittal crest emerges in early adulthood in the majority of G. g. gorilla males, whereas the percentage of G. g. gorilla females possessing a sagittal crest increases more gradually. Pongo pyg. pygmaeus males experience a three-fold increase in the number of specimens exhibiting a sagittal crest in mid-adulthood, consistent with a secondary growth spurt. Gorilla g. gorilla and Po. pyg. pygmaeus show significant sex differences in the size of the temporalis muscle attachment area, relative to cranial size, with males of both taxa showing positive allometry not shown in females. Gorilla g. gorilla males also show positive allometry for sagittal crest size relative to cranial size. Our results suggest that although patterns of sagittal crest expression have limited utility for taxonomy and phylogeny reconstruction, they could be useful for reconstructing aspects of social behaviour in some extinct hominin taxa. In particular, our results in G. g. gorilla and Po. pyg. pygmaeus, which suggest that the size of sagittal crests in males cannot be solely explained by the surface area required for attachment of the temporalis muscle, offer partial support for the hypothesis that large sagittal crests form in response to sexual selection and may play a role in social signalling.
.. Whilst sagittal crest height and length could not be analysed statistically, it was noted that three out of the four bachelor individuals did not have a sagittal crest present. Whilst the sagittal crest is thought to be an evolutionary mechanism to support strong jaw muscles, recent research has suggested it may have implications for sexual selection too (Balolia et al, 2017). Studies into Western lowland gorillas, Eastern chimpanzees (Pan troglodytes schweinfurthii), Northwest Bornean orangutans (Pongo pygmaeus pygmaeus) and lar gibbons (Hylobates lar) found that males with larger crests were more likely to gain female attention during breeding seasons (Balolia et al, 2017). ...
... Whilst the sagittal crest is thought to be an evolutionary mechanism to support strong jaw muscles, recent research has suggested it may have implications for sexual selection too (Balolia et al, 2017). Studies into Western lowland gorillas, Eastern chimpanzees (Pan troglodytes schweinfurthii), Northwest Bornean orangutans (Pongo pygmaeus pygmaeus) and lar gibbons (Hylobates lar) found that males with larger crests were more likely to gain female attention during breeding seasons (Balolia et al, 2017). It may be that male sea lions living amongst other males repress the growth of their crest due to the lack of female presence. ...
... The apparent self-domestication of bonobos (Hare et al., 2012), observable as behavioural sociability, low aggression, paedomorphism, and relatively lower sexual dimorphism, when compared to chimpanzees, appears to result from elevated female social status and a consequent capacity for female mate choice (Tokuyama & Furuichi, 2016;White, Waller, & Boose, 2013;Wrangham, 1986). A contrasting example of sexual selection in favour of masculine primate traits is provided by the gorilla, where an exaggerated sagittal crest has recently been shown to perform a role in sexual selection processes in this highly sexually dimorphic species (Balolia, Soligo, & Wood, 2017). The sagittal crest may be a particularly revealing indication of relative masculinity and high NCC presence and activity, since it consists of a late-maturing ridge of cranial bone located directly over the inter-parietal region, an area that, like the frontal and facial skeleton, is composed entirely from NNC's (Jiang, Iseki, Maxson, Sucov, & Morriss-Kay, 2002). ...
... Both crest height and back breadth are likely to reflect muscle mass, fat tissue and bone structure and therefore these traits may better indicate body condition and strength than body length, which is predominantly a function of bone length. Crest size has been suggested to reflect temporal muscle size and therefore bite force as well as energy reserves and overall health status (Balolia, Soligo, & Wood, 2017;Breuer et al., 2012;Caillaud et al., 2008). Crest height and back breadth also show larger between-male variation (Appendix Table A8) and higher sexual dimorphism than body length (Galbany et al., 2017), suggesting that crest height and back breadth are under stronger selection and play a more important role in maleemale competition. ...
... (B) Musculoskeletal traits that confer advantages in combat to adult male gorillas, such as support for neck, upper back, and biting muscles, and enlarged (with respect to females) and powerful arms. (C) The main weapons that gorillas use to inflict damage to each other during male-male fights are their canines and fists (reviews Caillaud et al., 2008;Balolia, Soligo & Wood, 2017). that help in assessment of the opponent's fighting ability, but they are not fighting tools per se...
www.researchgate.net/publication/316195180_Sagittal_crest_formation_in_great_apes_and_gibbons
Abstract
The frequency of sagittal crest expression and patterns of sagittal crest growth and development have been documented in hominoids, including some extinct hominin taxa, and the more frequent expression of the sagittal crest in males has been traditionally linked with the need for larger-bodied individuals to have enough attachment area for the temporalis muscle. In the present study, we investigate sagittal cresting in a dentally mature sample of four hominoid taxa (Pan troglodytes schweinfurthii, Gorilla gorilla gorilla, Pongo pygmaeus pygmaeus and Hylobates lar). We investigate whether sagittal crest size increases with age beyond dental maturity in males and females of G. g. gorilla and Po. pyg. pygmaeus, and whether these taxa show sex differences in the timing of sagittal crest development. We evaluate the hypothesis that the larger sagittal crest of males may not be solely due to the requirement for a larger surface area than the un-crested cranial vault can provide for the attachment of the temporalis muscle, and present data on sex differences in temporalis muscle attachment area and sagittal crest size relative to cranial size. Gorilla g. gorilla and Po. pyg. pygmaeus males show significant relationships between tooth wear rank and sagittal crest size, and they show sagittal crest size differences between age groups that are not found in females. The sagittal crest emerges in early adulthood in the majority of G. g. gorilla males, whereas the percentage of G. g. gorilla females possessing a sagittal crest increases more gradually. Pongo pyg. pygmaeus males experience a three-fold increase in the number of specimens exhibiting a sagittal crest in mid-adulthood, consistent with a secondary growth spurt. Gorilla g. gorilla and Po. pyg. pygmaeus show significant sex differences in the size of the temporalis muscle attachment area, relative to cranial size, with males of both taxa showing positive allometry not shown in females. Gorilla g. gorilla males also show positive allometry for sagittal crest size relative to cranial size. Our results suggest that although patterns of sagittal crest expression have limited utility for taxonomy and phylogeny reconstruction, they could be useful for reconstructing aspects of social behaviour in some extinct hominin taxa. In particular, our results in G. g. gorilla and Po. pyg. pygmaeus, which suggest that the size of sagittal crests in males cannot be solely explained by the surface area required for attachment of the temporalis muscle, offer partial support for the hypothesis that large sagittal crests form in response to sexual selection and may play a role in social signalling.
.. Whilst sagittal crest height and length could not be analysed statistically, it was noted that three out of the four bachelor individuals did not have a sagittal crest present. Whilst the sagittal crest is thought to be an evolutionary mechanism to support strong jaw muscles, recent research has suggested it may have implications for sexual selection too (Balolia et al, 2017). Studies into Western lowland gorillas, Eastern chimpanzees (Pan troglodytes schweinfurthii), Northwest Bornean orangutans (Pongo pygmaeus pygmaeus) and lar gibbons (Hylobates lar) found that males with larger crests were more likely to gain female attention during breeding seasons (Balolia et al, 2017). ...
... Whilst the sagittal crest is thought to be an evolutionary mechanism to support strong jaw muscles, recent research has suggested it may have implications for sexual selection too (Balolia et al, 2017). Studies into Western lowland gorillas, Eastern chimpanzees (Pan troglodytes schweinfurthii), Northwest Bornean orangutans (Pongo pygmaeus pygmaeus) and lar gibbons (Hylobates lar) found that males with larger crests were more likely to gain female attention during breeding seasons (Balolia et al, 2017). It may be that male sea lions living amongst other males repress the growth of their crest due to the lack of female presence. ...
... The apparent self-domestication of bonobos (Hare et al., 2012), observable as behavioural sociability, low aggression, paedomorphism, and relatively lower sexual dimorphism, when compared to chimpanzees, appears to result from elevated female social status and a consequent capacity for female mate choice (Tokuyama & Furuichi, 2016;White, Waller, & Boose, 2013;Wrangham, 1986). A contrasting example of sexual selection in favour of masculine primate traits is provided by the gorilla, where an exaggerated sagittal crest has recently been shown to perform a role in sexual selection processes in this highly sexually dimorphic species (Balolia, Soligo, & Wood, 2017). The sagittal crest may be a particularly revealing indication of relative masculinity and high NCC presence and activity, since it consists of a late-maturing ridge of cranial bone located directly over the inter-parietal region, an area that, like the frontal and facial skeleton, is composed entirely from NNC's (Jiang, Iseki, Maxson, Sucov, & Morriss-Kay, 2002). ...
... Both crest height and back breadth are likely to reflect muscle mass, fat tissue and bone structure and therefore these traits may better indicate body condition and strength than body length, which is predominantly a function of bone length. Crest size has been suggested to reflect temporal muscle size and therefore bite force as well as energy reserves and overall health status (Balolia, Soligo, & Wood, 2017;Breuer et al., 2012;Caillaud et al., 2008). Crest height and back breadth also show larger between-male variation (Appendix Table A8) and higher sexual dimorphism than body length (Galbany et al., 2017), suggesting that crest height and back breadth are under stronger selection and play a more important role in maleemale competition. ...
... (B) Musculoskeletal traits that confer advantages in combat to adult male gorillas, such as support for neck, upper back, and biting muscles, and enlarged (with respect to females) and powerful arms. (C) The main weapons that gorillas use to inflict damage to each other during male-male fights are their canines and fists (reviews Caillaud et al., 2008;Balolia, Soligo & Wood, 2017). that help in assessment of the opponent's fighting ability, but they are not fighting tools per se...
www.researchgate.net/publication/316195180_Sagittal_crest_formation_in_great_apes_and_gibbons