To avoid taking care of some other frog’s tadpoles by mistake, the female of a highly polygamous species remembers exactly where she laid her eggs (known as a clutch). The male, on the other hand, simply assumes that any tadpoles in his territory must be his. The findings are published in an upcoming issue of Animal Behaviour.
Brilliant-thighed poison frogs (Allobates femoralis) live along the tropical forest floors of South America. Males loudly defend their territories of about 150 square meters (1,615 square feet), while females occupy perches between the territories of different males. Courtship, mating, egg laying, and fertilization all occur in male territories. Afterwards, the female abandons its clutch and goes back to her perch. Three weeks later, the father transports the tadpoles on his back to the nearest body of water (pictured above). If the father disappears, the mother will take over the transportation duties.
Tadpole transport is an energy investment, and it’s risky. Not only are there predators all along the way, but the territory is left unguarded and the parent loses out on potential mating opportunities too. Because eggs are deposited within territories, males generally assume that all clutches inside their territory are their own. In contrast, females have clutches dispersed across multiple male territories, which also contain clutches of other females. In that way, the female faces a much higher risk of transporting someone else’s clutch and neglecting her own.
A team led by Eva Ringler from the University of Veterinary Medicine Vienna wanted to see if the different risks faced by the two sexes influence their strategies for discriminating between related and unrelated offspring. So they studied the tadpole transport behavior of male and female poison frogs – 19 wild-caught adults from French Guiana and 29 captive-bred adults – in glass terrariums furnished with half a coconut shell, a small plant, a branch, pebbles on the floor, and dried ferns on the walls.
The team conducted three experiments using eggs from other frogs. In the first, they added the unrelated clutch into a terrarium of a frog without a clutch of its own. In the second, they placed an unrelated clutch near the frog’s own clutch. And in the final test, they moved the frog’s clutch 20 centimeters (8 inches) and then placed an unrelated clutch in the original spot.
Males seem to follow a simple rule: “All clutches inside my territory are mine.” He’ll let any tadpoles present wiggle onto his back. Females, on the other hand, exhibit high spatial accuracy. They know and remember the exact position of their own clutch. Some females did, however, transport unrelated tadpoles when those clutches were placed in the spot where she laid her eggs; in those cases, she neglected her own clutch if it had been moved.
This sex-specific selectivity reflects the differences in the costs of confusing other tadpoles for their own – which is a result of differences in their spatial and reproductive behaviors. Exactly how females remember such specific locations in the dense leaf litter remains a mystery.