Frugivory, Flolivery, discuss pls?

Question 1

Human colour vision

Answer 1

Characterised by an enhanced ability to discriminate medium to long wavelength light (red/green)
This is due to three cone pigments: s/m/l = trichromatic vision
Trichromacy is found in some primates…
- Old world (C) monkeys have 3 types of cone pigments
- New world (P) monkeys have polymorphic colour vision: trichromatic and dichromatic females + dichromatic males
Performance of C and P monkeys have been investigated to identify selective pressures
Outline: frugivory, folivory, social, predator

Question 2

Sumner and Mollen

Answer 2

(2002)
Support Frugivory
- Ripeness of fruit inversely correlated with its chromaticity value in the R/G colour system

• 14x more effective to use R/G subsystem compared to luminance when detecting ripe fruits
• Although fruit can be detected using the B/Y channel, as seen in dichromats, due to the high noise:signal ratio, fruit is dwarfed by the foliage
• Therefore, R/G channel offers advantage
• Authors used this signal:noise ratio to calculate the optimum peak absorbance rates of cones to minimise noise of foliage
• Found that these values = 530 and 560
• These values match those seen in trichromatic primates

Question 3

Dominy and Lucas

Answer 3

(2001)
Support Folivory
Young leaves protein:toughness ratio correlated with its chromaticity value in the R/G colour system

R-G 7x better at detecting edible leaves than luminance

B-Y channel unable to discriminate between leaves and thus the R-G channel needed

THEREFORE
Primary spectroradiometric data provide evidence for both hypotheses

Question 4

Secondary evidence

Answer 4

C monkeys eat more leaves than P monkeys
Ancestral C monkeys eat more fruit
Both C and P monkeys can use other cues 
C and P monkeys eat similar fruit 
No report of P monkeys struggling to find leaves

Question 5

Socio-signal hypothesis

Answer 5

Changizi (2006)
Trichromacy developed so that social signals such as reddening of the skin on the face can be better detected so that inferences about fertility, mood and threat can be made about conspecifics

Evidence: Hiramatsu (2017)
Found that when human observers saw pairs of images of female macaque monkeys, they were better at selecting the proceptive face when viewed through a filter that emulated C monkey vision compared to P vision

Question 6

Pre-existing bias hypothesis

Answer 6

Fernandez and Morris (2007)
Colour vision developed before red patches of skin + social structures that allowed for social signalling
This supports pre-existing bias hypothesis
Trichromacy influenced the development of colour modulating skin patches (not the other way round)
Negates socio-signal hypothesis

Question 7

Predator detection hypothesis

Answer 7

Pessoa (2014)

Trichromatic observers were sig. faster at detecting predator against foliage than dichromats

Question 8

Conclusion

Answer 8

Data suggest that trichromacy offers an advantage in fruit finding.
However, it is unclear if this was the primary selective pressure.
Instead, a general advantage hypothesis is proposed Gegenfurtner (2003)