Socioecological and phylogenetic patterns in the chemical signals of strepsirrhine primates

Our understanding of chemical signals in mammals derives principally from studies in which researchers examine signal structure or function within a single species. Despite the unique information to be gained from applying comparable methods across multiple species, comparative studies of chemical signals are extremely limited. Here, we review the available literature on the evolution of chemosignals in male and female strepsirrhine primates (galagos, lorises and lemurs), all of which rely heavily on chemical communication. We draw from a few case studies, but focus our review on two comparative studies. In one, researchers examined the volatile chemical composition of urinary signals across 12 species representing most families within Strepsirrhini, including six 'urine-marking' species and six glandular or 'nonurine-marking' species. In the other, researchers examined the volatile chemical composition of glandular signals in eight Eulemur species differing in social or dominance structure. We highlight five findings. (1) Regardless of the scent source, chemical profiles differ substantially between species, providing reliable species 'scent signatures'. None the less, (2) urine markers express more compounds and have more distinguishable species scent signatures in their urine than do nonurine markers, suggesting specialization of function. Within Eulemur (3) chemical richness is greater in multimale-multifemale species than in pair-bonded species. Moreover, (4) whereas chemical richness of male signals is greater in sexually codominant species, chemical richness of female signals is greater in female-dominant species. Together, the findings from both comparative studies, coupled with case studies, suggest that signal richness is linked to some aspect of the focal species' socioecology. Lastly, (5) regardless of the scent source, strepsirrhine chemosignals evolve gradually over time, but at fast rates and homogeneously within different lineages. Comparative studies reveal patterns that cannot be detected from the single-species approach and are therefore critical for providing new insight into the function and evolution of olfactory signals