Why do helpers help? Molecular, Endocrine, and Phenotypic Expression of Allomaternal Care in Red-Bellied Lemurs (Eulemur rubriventer)

Photo credit: Jean Baptiste Velotsara

Dr. Andrea Baden (Hunter College / CUNY) describes her collaborative research with Dr. Stacey Tecot (University of Arizona) on allomaternal carrying in red-bellied lemurs.

Photo credit: Jean Pierre Lahitsara

The Cooperative Breeding Hypothesis proposes that the care and provisioning of infants by allomaternal helpers were profoundly important during early human evolution, as these prosocial behaviors (together termed ‘cooperative breeding’) conferred significant energetic benefits to mothers and their young, thereby enabling higher maternal fertility, protracted infant development, and less costly brain growth which ultimately led to more emotionally modern brains (Hrdy 2009; Isler & van Schaik 2012). When the cognitive abilities shared by apes and our earliest ancestors merged with the underlying prosocial motivations typical of many species with cooperative breeding, ‘shared intentionality’ -- a social disposition that has been identified as the source of many uniquely human traits, such as culture and language -- emerged (Burkart et al. 2009), and allowed our ancestors (and eventually modern humans) to forge deeper social relationships and to cooperate on an unparalleled level. In short, shared infant care paved the way for us becoming human. 

Allomaternal care, or infant care by individuals other than the genetic mother, is the presumed evolutionary antecedent to cooperative breeding, a specialized form of infant care shared by humans and callitrichines (Hrdy 2009). It is present, in some form, in all major primate taxa, and is abundant in primates relative to other mammalian orders (Hrdy 2010; Lukas & Clutton-Brock 2012; Tecot et al. 2013). The widespread presence of allomaternal care in the Order Primates suggests that there was strong selective pressure for this behavior early in primate evolution. Despite this, we know very little of the pressures leading to the evolution and expansion of allomaternal care throughout the Primate Order. Why care for another’s offspring? Or, why invest heavily in one offspring when one can mate with multiple partners? 

Together, Dr. Stacey Tecot (University of Arizona) and I are investigating these questions by focusing on a costly form of allomaternal care – infant carrying – in the red-bellied lemur, Eulemur rubriventer, a strepsirrhine with facultative allomaternal care. Our research is directed at identifying 1) the pressures that select for shared infant care behaviors, 2) the mechanisms promoting and maintaining such behaviors in paternal and alloparental helpers, and 3) the adaptive benefits of allomaternal care to mothers who allow others to help. Using a unique combination of molecular, endocrine, and observational methods in a natural physical, social, and physiological environment, our work will provide insight into how individuals are shaped into allomaternal helpers. Initiated in the summer of 2013 at the Vatoharanana research site in Ranomafana National Park, Madagascar, our project has thus far generated data from 13 study groups during two consecutive reproductive seasons. Research is ongoing.

This research has received financial support from the Leakey Foundation, the American Association of Physical Anthropologists, Rowe-Wright Primate Fund, Hunter College, and the University of Arizona.

References

Burkart, J. M., Hrdy, S. B., van Schaik, C. P. (2009). Cooperative breeding and human cognitive evolution. Evol. Anthropol.,18, 175–186.

Hrdy, S. B. (2009). Mothers and Others. Cambridge: Harvard University Press. 

Hrdy, S. B. (2010). Estimating the prevalence of shared care and cooperative breeding in the Order Primates, an appendix to mothers and others: the evolutionary origins of human understanding. Retrieved from www.citrona.com/hrdy/documents/AppendixI.pdf

Isler, K. & van Schaik, C. P. (2012). Allomaternal care, life history and brain size evolution in mammals. J. Hum. Evol., 63, 52–63. 

Lukas, D. & Clutton-Brock, T. (2012). Cooperative breeding and monogamy in mammalian societies. Proc. R. Soc. B., 279, 2151–6. 

Tecot, S. R., Baden, A. L., Romine, N., Kamilar, J. M. (2013). Reproductive strategies in Malagasy strepsirhines. In: K. B. H. Clancy, K. Hinde, J. N. Rutherford (Eds.), Building babies: Primate development in proximate and ultimate perspective (pp. 321-359). New York: Springer.