First Advisor

Natalie Vasey

Term of Graduation

Winter 2024

Date of Publication

4-1-2024

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Anthropology

Department

Anthropology

Language

English

Subjects

Activity Pattern, Cathemerality, Chronobiology, Masking factor, Synchronizing agent, Varecia rubra

DOI

10.15760/etd.3733

Physical Description

1 online resource (xiii, 98 pages)

Abstract

With respect to the natural variation in abiotic and biotic conditions present between daytime and nighttime periods, many animal species show evolutionary adaptations specialized for diurnality, nocturnality, or crepuscularity. Biologists have traditionally viewed categorizations of this kind as fixed within taxonomic groups, emphasizing how intricately species’ survival is contingent on the ability to adapt to low light, high light, or twilight conditions. However, movement away from such distinct temporal niche categories began within chronobiological studies following the discovery of more flexible patterns of activity in numerous taxa during the late 1970s. This shift generated increased interest in elucidating the complex interactions between circadian rhythms, synchronizing agents, masking factors, and biotic factors in the shaping of animal activity patterns. Due to the notable diversity in activity patterns found within Malagasy lemurs, a monophyletic primate radiation, researchers have used this group as a model for examining the adaptive functions and conditions through which activity patterns evolved within the Mammalian Class. In an effort to further contribute to this body of research, we investigated the activity of Varecia rubra (Red Ruffed Lemur) over the 24-hour daily cycle (i.e., diel) at the Andranobe Forest field site in Masoala National Park, Madagascar. Traditionally classified as diurnal, the genus Varecia is the exception within the largely cathemeral Lemuridae family consisting of Varecia, Hapalemur, Prolemur, Lemur, and Eulemur. To address a notable absence in the systematic documentation of Varecia activity outside of a strictly diurnal context, we recorded traveling, feeding, resting, and vocalization data over the diel. Data collection shifts covered each portion of the diel in 4-hour increments (time blocks) at two observation posts weekly. Activity (feed and travel) and call data were independently analyzed to establish their distributions across hours, time blocks, and weeks from a ten-week sampling period during austral spring (hot-dry season of 2022).

In terms of overall activity pattern, results indicate that V. rubra rest, feed, travel, and call throughout the 24-hour daily cycle at Andranobe Forest. Feeding and traveling occur mostly during daytime, with a late night/early morning (2:00-6:00 hours) activity pulse measuring almost two-thirds of their late afternoon (14:00-18:00 hours) pulse, and nearly one-third of their daily activity peak, which occurs during morning (6:00-10:00 hours). V. rubra also have a late night/early morning pulse in vocal activity that is more than two times greater than during twilight/early night (18:00-22:00 hours), resembling more closely the higher call frequencies of morning, midday (10:00-14:00 hours), and late afternoon. The least feeding, traveling, and calling occurs during mid-night (22:00- 2:00 hours). Activity and calls at morning twilight (i.e., dawn) account for just over 10% of feeding and traveling events and for ~30% of call events during the late night/early morning time block, whereas 20% of feeding and traveling events and a considerable 60% of call events occur at evening twilight (i.e., dusk) within the twilight/early night time block. High amplitude calls (i.e., loud calls) most frequently emitted by V. rubra, including the "roar-shriek", "bark", "pulsed rah", and "roar". The "hum", a lower amplitude contact call given while traveling, is also emitted at a relatively high frequency (ranked fourth). V. rubra feed, travel, and call more frequently during higher ambient temperatures (i.e., during daytime) and with longer day length from the beginning to the end of the hot-dry season (austral spring). They also call more frequently during periods of greater lunar luminosity.

The findings of this study offer evidence for V. rubra activity outside of a strictly diurnal context. These data, along with possession of an array of retinal traits suited to either daytime or nighttime vision (or of intermediate value), and their status as the basal genus of a largely cathemeral family, Lemuridae, prompt reconsideration of their diurnal classification. We recommend qualifying this classification by recognizing that they are also facultatively cathemeral.

Rights

©2024 Hannah Elena Hilden-Reid

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/41699

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