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Holding-on: co-evolution between infant carrying and grasping behaviour in strepsirrhines

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ABSTRACT

The origin and evolution of manual grasping remain poorly understood. The ability to cling requires important grasping abilities and is essential to survive in species where the young are carried in the fur. A previous study has suggested that this behaviour could be a pre-adaptation for the evolution of fine manipulative skills. In this study we tested the co-evolution between infant carrying in the fur and manual grasping abilities in the context of food manipulation. As strepsirrhines vary in the way infants are carried (mouth vs. fur), they are an excellent model to test this hypothesis. Data on food manipulation behaviour were collected for 21 species of strepsirrhines. Our results show that fur-carrying species exhibited significantly more frequent manual grasping of food items. This study clearly illustrates the potential novel insights that a behaviour (infant carrying) that has previously been largely ignored in the discussion of the evolution of primate manipulation can bring.

No MeSH data available.


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Schematic representation illustrating the three possible evolutionary scenariosas described in the discussion.Pictures of Coquerel’s sifaka (Propithecus coquereli); photo credit David Haring.
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f3: Schematic representation illustrating the three possible evolutionary scenariosas described in the discussion.Pictures of Coquerel’s sifaka (Propithecus coquereli); photo credit David Haring.

Mentions: Based on these results three evolutionary scenarios can be imagined (Fig. 3). The first scenario (Fig. 3 Scenario 1) fits to Bishop’s suggestion that fur-grasping was a potential precursor for enhanced manipulative skills in primates13. The grip used by young lemurs to hold on the mother is a grip type with each finger pressed toward the next and the fingertips pressed toward the palm13. Hence, for all species analysed, fur-gripping depends on the close contact between the distal phalanges of digits two to five and the second phalanx of the first digit, hence, engaging different contacts than those imposed by the gripping of branches involving the whole palm and all palmar parts of the fingers25 (Fig. 4). Bishop considered this particular fur grip as a “direct approximation of touch-pads” constituting therefore an interesting potential “forerunner of fine control of the hand”13. Hence, specific selective pressures (e.g. nest parasites and nest predator avoidance) could have led some species to continually cling to their mother’s fur, developing in this way the use of the hand for fine grasping (Fig. 3 Scenario 1A). These dexterous abilities could then have been more frequently expressed later on in other contexts such as foraging. This hypothesis is supported by the fact that once it has evolved, fur grasping was conserved in nearly all lineages, possibly because of behavioural and physiological co-adaptations16. Moreover, even if in most of the human societies infants do not grasp their mother but are rather held actively by her or a related person2627, touching the palm of a baby’s hand readily elicits a reflex called a “palmar grasp reflex” or “clinging reflex”. This reflex consist of the flexion of all the fingers around the elicitor’s finger followed by a clinging phase28. This reflex allows newborn primates to support their own weight for several minutes when holding onto a horizontal rod2930. This reflex is likely phylogenetically primitive, supporting even more strongly the fact that fur-grasping could be a potential precursor for enhanced manipulative skills in humans and primates in general. However, previous studies have shown that fur-carrying has likely evolved several times independently from a mouth carrying ancestor1618 (Fig. 5). This suggests that in these species the young were pre-adapted to cling. A more prehensile and sensitive hand may, indeed, constitute a prerequisite condition for the young to be able to cling to the fur of their mother (Fig. 3 Scenario 1a). Strepsirrhine species are all predominantly arboreal and, therefore, submitted to similar selective pressures, which are in all likelihood responsible for rendering the hand more sensitive and prehensile. Nevertheless, the gripping of branches is quite different than the gripping of fur and a more specific pre-adaptation could be needed.


Holding-on: co-evolution between infant carrying and grasping behaviour in strepsirrhines
Schematic representation illustrating the three possible evolutionary scenariosas described in the discussion.Pictures of Coquerel’s sifaka (Propithecus coquereli); photo credit David Haring.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121892&req=5

f3: Schematic representation illustrating the three possible evolutionary scenariosas described in the discussion.Pictures of Coquerel’s sifaka (Propithecus coquereli); photo credit David Haring.
Mentions: Based on these results three evolutionary scenarios can be imagined (Fig. 3). The first scenario (Fig. 3 Scenario 1) fits to Bishop’s suggestion that fur-grasping was a potential precursor for enhanced manipulative skills in primates13. The grip used by young lemurs to hold on the mother is a grip type with each finger pressed toward the next and the fingertips pressed toward the palm13. Hence, for all species analysed, fur-gripping depends on the close contact between the distal phalanges of digits two to five and the second phalanx of the first digit, hence, engaging different contacts than those imposed by the gripping of branches involving the whole palm and all palmar parts of the fingers25 (Fig. 4). Bishop considered this particular fur grip as a “direct approximation of touch-pads” constituting therefore an interesting potential “forerunner of fine control of the hand”13. Hence, specific selective pressures (e.g. nest parasites and nest predator avoidance) could have led some species to continually cling to their mother’s fur, developing in this way the use of the hand for fine grasping (Fig. 3 Scenario 1A). These dexterous abilities could then have been more frequently expressed later on in other contexts such as foraging. This hypothesis is supported by the fact that once it has evolved, fur grasping was conserved in nearly all lineages, possibly because of behavioural and physiological co-adaptations16. Moreover, even if in most of the human societies infants do not grasp their mother but are rather held actively by her or a related person2627, touching the palm of a baby’s hand readily elicits a reflex called a “palmar grasp reflex” or “clinging reflex”. This reflex consist of the flexion of all the fingers around the elicitor’s finger followed by a clinging phase28. This reflex allows newborn primates to support their own weight for several minutes when holding onto a horizontal rod2930. This reflex is likely phylogenetically primitive, supporting even more strongly the fact that fur-grasping could be a potential precursor for enhanced manipulative skills in humans and primates in general. However, previous studies have shown that fur-carrying has likely evolved several times independently from a mouth carrying ancestor1618 (Fig. 5). This suggests that in these species the young were pre-adapted to cling. A more prehensile and sensitive hand may, indeed, constitute a prerequisite condition for the young to be able to cling to the fur of their mother (Fig. 3 Scenario 1a). Strepsirrhine species are all predominantly arboreal and, therefore, submitted to similar selective pressures, which are in all likelihood responsible for rendering the hand more sensitive and prehensile. Nevertheless, the gripping of branches is quite different than the gripping of fur and a more specific pre-adaptation could be needed.

View Article: PubMed Central - PubMed

ABSTRACT

The origin and evolution of manual grasping remain poorly understood. The ability to cling requires important grasping abilities and is essential to survive in species where the young are carried in the fur. A previous study has suggested that this behaviour could be a pre-adaptation for the evolution of fine manipulative skills. In this study we tested the co-evolution between infant carrying in the fur and manual grasping abilities in the context of food manipulation. As strepsirrhines vary in the way infants are carried (mouth vs. fur), they are an excellent model to test this hypothesis. Data on food manipulation behaviour were collected for 21 species of strepsirrhines. Our results show that fur-carrying species exhibited significantly more frequent manual grasping of food items. This study clearly illustrates the potential novel insights that a behaviour (infant carrying) that has previously been largely ignored in the discussion of the evolution of primate manipulation can bring.

No MeSH data available.


Related in: MedlinePlus