Strontium isotopes track female dispersal in Taï chimpanzees

Area of Science:

• Primate Ecology
• Paleoecology
• Isotope Geochemistry

Background:

• Chimpanzees exhibit patrilocal social systems, with males staying in their natal groups and females dispersing.
• Understanding female dispersal origins is crucial for primate behavioral ecology but challenging to ascertain.
• Skeletal collections offer a historical window into chimpanzee populations, but individual origins are often unknown.

Purpose of the Study:

• To evaluate the efficacy of 87Sr/86Sr analysis in distinguishing between natal and immigrant female chimpanzees.
• To establish local strontium (Sr) baseline differences across chimpanzee territories in Taï National Park.
• To identify the origins of females with unknown provenance within neighboring chimpanzee communities.

Main Methods:

• Environmental and chimpanzee skeletal samples (n=69) were collected from Taï National Park.
• Strontium isotope ratios (87Sr/86Sr) were analyzed using mass spectrometry.
• Generalized linear mixed models (GLMMs) were employed to statistically assess differences in isotope ratios and identify dispersal patterns.

Main Results:

• A local strontium isoscape was developed for the study area, with a root-mean-square error of 0.0048.
• Significant differences in 87Sr/86Sr ratios were found between natal and unknown origin chimpanzee groups.
• Analysis suggested that seven females of unknown origin in the North community after 1980 were likely immigrants (p < 0.0001).

Conclusions:

• 87Sr/86Sr analysis is a viable method for identifying immigrant females in historical chimpanzee skeletal collections.
• This technique allows for the reconstruction of past female dispersal patterns.
• Limitations include the need for reliable mapping, expanded environmental sampling, larger sample sizes, and consideration of tooth formation processes.