Supplementary material – Caro Sexual dichromatism in mammals

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Supplementary material – Caro
Sexual dichromatism in mammals

Some mammals show contrasting colouration patterns that are limited to one sex only but sexual dichromatism, in contrast to sexual dimorphism in body size and weaponry, is uncommon in mammals, particularly in comparison to birds (Darwin 1871; Andersson 1994). For convenience, we can divide dichromatism into three categories in mammals: differences in pelage hue, possession of coloured ornaments, and colourful genitalia. Spotted cuscuses, some large lemurs, sakis, gibbons, gorillas and several artiodactyl genera (Supplementary Table 1) exhibit pelage differences where, generally, older adult males are darker than adult females. Why are these particular species dichromatic? Dichromatism does not seem to be an alternative to nor an amplifier of sex differences in body size as female spotted cuscuses are larger than males; in lemurs, sakis and gibbons, sexes of similar size; whereas males are larger than females in howler monkeys, gorillas and ungulates. Nor are there obvious associations with mating system: cuscuses, sakis and gibbons (but see Barelli et al. 2008) are monogamous, lemurs show variable mating systems; whereas howlers, gorillas and dichromatic artiodactyls are polygynous. While female choice may be involved in some of these species (Small 1993), systematic study of dichromatism in mammals is long overdue.

In species such as the markhor Capra falconeri, males have ornaments of variable colour. In lions, manes range from tawny to black with darker manes signifying better nutrition (melanin also signals condition in some birds, Roulin & Altwegg 2007). Lionesses prefer, but other males are more reluctant to approach black-maned males. Despite higher reproductive success, dark manes are held in check because of high body temperatures (West & Packer 2002). Male mandrills Mandrillus sphinx have prominent bright blue ridges on either side of the nasal bones with purple grooves and a scarlet nose, alterations in which are associated with change in alpha status (Setchell & Dixson 2001; Setchell & Wickings 2003).

Aquamarine scrota are found in Erythrocebus patas, Miopithecus talapoin and mandrills too; male savannah guenons (Chlorocebus) have bright red penises and blue scrota, with darker blue signaling dominance (Gerald 2001; but see Berkovitch 1996). Females of certain species of Macaca, Cercocebus, Papio, Theropithecus, Allenopithecus, Procolobus and Pan show exaggerated bright pink or red sexual swellings around the vulva at time of ovulation. Several hypotheses have been proposed including signaling individual quality or ovulation (Nunn 1999; Domb & Pagel 2001). Across primates, both red pelage and red skin are more likely to evolve in species with capacity for trichromatic colour vision (Changizi et al. 2006) and that are gregarious suggesting that this colouration serves in sexual selection (Fernandez & Morris 2007).

Supplementary material – References
Andersson, M. 1994. Sexual selection. Princeton, NJ, Princeton University Press.
Barelli, C., Heistermann, M., Boesch, C. & Reichard, U.H. 2008 Mating patterns and sexual swellings in pair-living and multimale groups of wild white-handed gibbons, Hylobates lar. Anim Behav. 75, 991-1001.
Bercovitch, F.B. 1996 Testicular function and scrotal coloration in patas monkeys. J. Zool. Lond. 239, 93-100.
Changizi, M.A., Zhang, Q. & Shimojo, S. 2006 Bare skin, blood and the evolution of primate colour vision. Biol. Lett. 2, 217-221.
Darwin, C. 1871. The descent of man, and selection in relation to sex. London, Metheun & Co.
Domb, L.G. & Pagel, M. 2001 Sexual swellings advertise female quality in wild baboons. Nature 410, 204-206.
Fernandez, A.A. & M.R. Morris. 2007. Sexual selection and trichromatic color vision in primates: statistical support for the preexisting-bias hypothesis. Amer. Nat. 170, 10-20.
Gerald, M.S. 2001 Primate colour predicts social status and aggressive outcome. Anim. Behav. 61, 559-566.
Nunn, C.L. 1999. The evolution of exaggerated sexual swellings in primates and the graded-signal hypothesis. Anim. Behav. 58, 229-246.
Roulin, A. & Altwegg, R. 2007. Breeding rate is associated with pheomelanism in male and with eumelanism in female barn owls. Behav. Ecol. 18, 563-570.
Setchell, J.M. & Dixson, A.F. 2001. Changes in the secondary sexual adornments of male mandrills (Mandrillus sphinx) are associated with gain and loss of alpha status. Horm. Behav. 39, 177-184.
Setchell, J.M. & Wickings, E.J. 2003. Sexual swellings in mandrills (Mandrillus sphinx): a test of the reliable indicator hypothesis. Behav. Ecol. 15, 438-445.
Small, M. 1993 Female choices. Ithaca, NY, Cornell University Press.
West, P.M. & Packer, C. 2002. Sexual selection, temperature and the lion’s mane. Science 297, 1339-1343.

Supplementary material, Table 1. Sexual dichromatism in pelage of terrestrial mammals.

Species Males Females

Spotted cuscuses Spilocuscus
Short-tailed spotted cuscus S. maculatus White or gray spotted, with Uniformly grey and

white above and below. not spotted.

Black spotted cuscus S. rufoniger Mottling or spotted. Dark saddle on back.
Lemurs Eulemur
Crowned lemur E. coronatus Medium grey back, lighter Upperparts, head and

limbs and underparts, with cap lighter.

V-shaped orange marking

above forehead, crown of

head black.

Red-bellied lemur E. rubriventer Upperparts chestnut brown, Same but whitish

tail black, face dark, underparts.

reddish brown underparts.

Black lemur E. macaco Black. Light chestnut brown,

darker face, heavy

white ear tufts.

Mongoose lemur E. mongoz Grey with pale face, red Browner back, dark

cheeks and beard. face, white cheeks

and beard.

Howler monkeys Alouatta
Brown howler A. guariba Black to brown to dark red, Paler.

paler below.

Black howler A. caraya Black. Olive to buff.
Sakis Pithecia
White-faced saki P. pithecia Black, but forehead, face Brown to brownish

and throat white to reddish. grey above, paler

below, with white to

pale red-brown stripes

from eyes to corner of


Monk or red-bearded saki P. monachus Mat or buff-coloured hair Absent.

on forehead and crown.

Gibbons Hylobates
Crested gibbon H. concolor All black or with white Golden or grey

beard. brown.

White-browed gibbon H. hoolock Black with white eyebrows. Golden with darker

cheeks, has eyebrows.

Capped gibbon H. pileatus Black with white hands and Silver-grey or ash

feet, headring. blonde, black cap,

chest and cheeks.

Agile or dark-handed gibbon H. agilis Very dark brown to light White eyebrows

buff often with reddish only.

tinge, bright brows and


White-cheeked gibbon H. leucogenys Black with silvery hairs, More richly coloured

white patches on cheeks. no conical tuft on


Red-cheeked gibbon H. gabriellae Pinkish cheeks. Short crown patch.

Muller’s Bornean gibbon H. muelleri Mouse grey to brown, pale Cap and chest darker.

face ring often incomplete.
Gorilla Gorilla
Gorilla G. gorilla Mature have silvery back. Absent.
Lion Panthera
Lion P. leo Black mane in some Absent.


Artiodactlys Tragelaphus
Bushbuck T. scriptus Dark brown to black. Bright chestnut to

dark brown.

Bongo T. eurycerus Iron grey with white Lighter coloured.


Artiodactyls Taurotragus
Eland T. oryx Dark grey in mature males. Light tan.

Derby’s eland T. derbianus Dear grey in mature males. Light tan.

Artiodactyls Boselaphus
Nilgai B. tragocamelus Iron gray with white Lighter coloured.


Artiodactyls Tetracerus
Four-hourned antelope T. quadricornis Old males yellowish. Brownish bay.
Artiodactyls Bos
Banteng B. javanicus Dark chestnut or black. Reddish-brown.

Kouprey B. sauveli Old bulls black or very Grey.

dark brown.
Artiodactyls Hippotragus
Sable antelope H. niger Black with white Russet coat with

underparts. pale to black

Artiodactyls Antilope
Blackbuck A. cervicapra Upperparts and neck dark Lighter coloured.

brown to black, white chin,

eyes and underparts.
Goats Capra
Wild goat C. aegagrus Silver white winter coat; Yellowish-brown to

chest, throat and face sooty reddish-grey; dark

grey; belly, outside of lower brown dorsal

limbs, beard, lower face mid-line; dark brown

black to deep chestnut markings on face; no

brown; dark dorsal crest; beard.

black stripe from withers

to front of chest.

Ibex C. ibex Rich chocolate brown Reddish-tan to

summer coat, circular golden.

patches of yellow-white

hair on middle back and


Markhor C. falconeri Reddish-grey coat with Beard absent

black beard.

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