Exploring the Esoteric Lives of Two- and Three-Toed Sloths

Date of Award

2007

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Lowman, Margaret

Keywords

Ecology, Sloth, Radio-Tracking, DNA, Barro Colorado Island, Smithsonian, Rainforest, Tree-Climbing

Area of Concentration

Biology

Abstract

The life histories of Bradypus variegatus (three-toed sloth) and Choloepus hoffmanni (two-toed sloth) are perhaps some of the most intriguing and mysterious of all arboreal mammals in the NeoTropics. Although they range from humid tropical forest from Nicaragua to central Brazil, their extremely cryptic lifestyle has greatly inhibited scientific studies. These animals live astonishingly slow and cryptic lives, often masquerading as a coconut or insect nest. In this exploratory study, four biological questions were addressed in effort to shed light on the enigmatic lives of these shadowy mammals. General movement behavior, reasons for ground-based elimination behaviors, possible sloth and algal symbioses, and island speciation / biogeography were all independently investigated on sloth populations through the Smithsonian Tropical Institute in the Republic of Panama. Using radio collars and an Automated Radio Tracking System (ARTS) on Barro Colorado Island, seven individuals were tracked 24 hours a day over the course of 13 months, addressing hourly and daily activity patterns, seasonal activity patterns, differences in species activity, and home range. Over the course of the study, B. variegatus was found to be active about 20 % of a typical day. The animals were mainly diurnal, but were found to be slightly active throughout the night with some movement bouts. The average home range was 4.05 HA. C. hoffmanni was active approximately 22% of the time in a strongly nocturnal pattern. Their home range was somewhat larger averaging 6.73 HA. Both animals were found overall to be less active in the wet season and more active during the dry season. The relationship between sloths and potential symbiotic algae was investigated in detail. Through close-up hair examination and scanning electron microscope photography, we concluded that algae living inside the hairs of B. variegatus are likely to be responsible for decay in the hairs which creates their characteristic fissures. Thus, we feel that in three-toed species, the algae act in a parasitic manner. In C. hoffmanni, hairs are adapted for water drainage and are inhabited by similar algae and fungi, but in this case acting only as a commensal organism. The odd ground-based elimination behavior of sloths has puzzled scientists since the 19th century. Using radio frequencies, camera traps, and closeup video recordings, we overviewed and systematically invalidated the major hypotheses for the behavior. We conclude with the hypothesis that sloths take up nutrients and trace elements from soils when on the ground. These particles become lodged in their claws while defecating on the ground, and are inadvertently ingested while feeding. Lastly, phylogenetic analysis was done on the 16S mitochondrial DNA gene sequence for C. hoffmanni, B. variegatus, and B. pygmaeusi. Animals from mainland Panama, its surrounding Atlantic islands, and Brazil were compared. Although, pending further testing for conclusive determination, we feel at this moment there is little to no evidence supporting claims that the Pygmy three-toed sloth is a separate, independent species. We suggest it should be categorized as a sub-species or island variation of B. variegatus.

Rights

This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

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