A syndrome of mutualism reinforces the lifestyle of a sloth.
Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy. A three-toed sloth will, however, descend its tree weekly to defecate, which is risky, energetically costly and, until now, inexplicable. We hypothesized that this behaviour sustains an ecosystem in the fur of sloths, which confers cryptic nutritional benefits to sloths. We found that the more specialized three-toed sloths harboured more phoretic moths, greater concentrations of inorganic nitrogen and higher algal biomass than the generalist two-toed sloths. Moth density was positively related to inorganic nitrogen concentration and algal biomass in the fur. We discovered that sloths consumed algae from their fur, which was highly digestible and lipid-rich. By descending a tree to defecate, sloths transport moths to their oviposition sites in sloth dung, which facilitates moth colonization of sloth fur. Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth. Sloths consume these algae-gardens, presumably to augment their limited diet. These linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle.
Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, , Madison, WI 53706, USA, USDA-ARS, Department of Entomology, University of Wisconsin-Madison, , Madison, WI 53706, USA, Center for Limnology, University of Wisconsin-Madison, , Madison, WI 53706, USA, USDA-ARS, Department of Bacteriology, University of Wisconsin-Madison, , Madison, WI 53706, USA, Department of Biological Sciences, Virginia Tech, , Blacksburg, VA 24061, USA.
Jonathan N
JN
Pauli
Jorge E
JE
Mendoza
Shawn A
SA
Steffan
Cayelan C
CC
Carey
Paul J
PJ
Weimer
M Zachariah
MZ
Peery
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001522:Behavior, Animal; D018533:Biomass; D000460:Chlorophyta / Q000378:metabolism / Q000502:physiology; D003672:Defecation; D017753:Ecosystem; D005247:Feeding Behavior; D060434:Herbivory; D009036:Moths / Q000502:physiology*; D009584:Nitrogen / Q000032:analysis; D010058:Oviposition; D012896:Sloths / Q000502:physiology*; D013559:Symbiosis
D009584:Nitrogen
Costa Rica; Cryptoses; Trichophilus; commensalism