Contextual complexity of chemical signals in callitrichids

Abstract

In nearly four decades our research and that of others on chemical signaling in callitrichid primates suggest a high degree of contextual complexity in both the use of signals and the response to these signals. We describe our research including observational field studies, behavioral bioassays ("playbacks"), functional imaging, and conditioning studies. Scent marking in both captivity and the wild is used for more than just territorial marking. Social contextual effects are seen in responses by subordinate females responding with ovulatory inhibition only to chemical signals from familiar dominant reproductive females. Males detect ovulation through changes in scent marks. Males responded behaviorally and hormonally to chemical signals of novel ovulating females as a function of their reproductive status (fathers, males paired with a female but not fathers, and single males). Multiple brain areas are activated in males by female chemical signals of ovulation including areas relating to memory, evaluation, and motivation. Furthermore, males can be conditioned to respond sexually to a nonsexual odor demonstrating that learning plays an important role in response to chemical signals. Male androgen and estrone levels changed significantly in response to infant chemical signals as a function of whether the males were fathers or not, whether the odors were from their own versus other infants, as well as the infant's stage of development. Chemical signals in callitrichids are providing a rich source of understanding the context and function of the chemical sensory system and its stimulation of neural, behavioral, and hormonal actions in the recipients.

Keywords: behavioral bioassays; chemical signals; cognition; conditioning; fMRI; hormonal; marmosets; neural; tamarins.

Figure 1.

Days to ovulation in previously subordinate female cotton-top tamarins and common marmosets after removal from their natal group and pairing with a mate as a function of transfer of odors from a familiar or unfamiliar reproductive female. Data from Savage et al. (1988), Barrett et al. (1990), Abbott et al. (1997).

Figure 2.

Changes in testosterone levels within 30 minutes of presentation of an odor from a novel, ovulating female as a function of male social status. There was no difference in levels for parental males, but significant increases in testosterone for paired and single males (P’s < 0.05) (adapted from Ziegler et al., 2005).

Figure 3.

Mean number of voxels activated in some brain areas involved in sensory integration, learning, memory, attention and movement in response to odors from ovulating and ovariectomized females. Within subject comparisons significant at p < 0.05. (Adapted from Ferris et al., 2004).