DETERMINANTS OF BI-PARENTAL CARE IN THE SPOTTED POISON FROG, DENDROBATES VANZOLINII 

A study of the spotted poison frog, Dendrobates vanzolinii carried out in Amazonian rain forest in Brazil, revealed that these frogs form pair bonds, using the definition of pair bonding as a social and copulatory, or mating, relationship between two individuals that share some aspect of offspring rearing.  Pairs of frogs co-operate to provide bi-parental care for their offspring.  

Observations of naturally marked pairs revealed that one to several eggs are attached above the waterline in tiny water-filled cavities.  These are typically in saplings or woody vines in the forest under story.  After an egg develops into a tadpole, the male transports it on his back to a different cavity where the tadpole undergoes further development in a small amount of water.  Tadpoles of D. vanzolinii, as well as those of other species of Dendrobates, are predatory and cannibalistic; eggs deposited above the waterline in a cavity are not allowed to drop in the water below where a larger, cannibalistic tadpole may be present.  

The male in this species chooses the tadpole deposition sites, and always transports them.  The holes in vines or saplings contain only a small amount of water and lack food for the tadpole.  Typically, unfertilised (nutritive) eggs deposited by the female parent are the only source of their food.  Both parents have a role in this form of bi-parental care: the male guides the female to the deposition site housing the tadpole where they undergo courtship behaviour, which appears to be necessary to induce ovulation in the female.  

Males are territorial, and no males were seen entering another male's territory.  Females remained in the territory of their mate and were not observed interacting with other frogs.  Large tree-holes and other types of potential tadpole deposition sites are scarce in this area of Amazon forest, but tiny vine and sapling holes are common.  Lack of food resources in these holes and the avoidance of tadpole cannibalism are potential determinants of bi-parental care in this species.  

Additional work on bi-parental care of this and closely related species should focus on the significance of size of deposition cavities, the role of tadpole deposition patterns, the extent of cannibalism, and other aspects of tadpole behaviour and ecology unique to these species.  

Caldwell, Janalee, P.de Oliveira, Veronica, R.L.  1999 COPEIA3 pp565-575