Variation in Dendrobates Species

Author not known

June 1997

Dendrobates pumilio is, of course, well known for its wide range of colour morphs. To try to find out how this variability arose, Kyle Summers and colleagues from the Smithsonian Tropical Research Institute in Panama compared the genetic variability among populations of D. pumilio from the Bocas del Toro archipelago with the variability among island populations of Phyllobates lugubris and Minyobates sp., neither of which shows much variation in colour. They looked at mitochondrial DNA: this is inherited solely from the mother and therefore passes from one generation to the next unchanged except for mutations.

Over many generations, different bloodlines accumulate their own set of mutations. Consequently, the number of differences between the mitochondrial DNA of two separate lines is an indication of the number of generations since they became separated. The comparison showed that the populations of D. pumilio were no more dissimilar from one another than island populations of P. lugubris or Minyobates spp. The authors concluded that the large differences in coloration between populations of D. pumilio probably could not be accounted for by a long period of neutral divergence while the populations were isolated from one another. Instead, they suggested that sexual selection might have been responsible. [Summers, K., Bermingham, E., Weight, L. & McCafferty, S. 1997. Phenotypic and genetic divergence in three species of dart-poison frogs with contrasting parental behavior. Journal of Heredity, 88: 8-13.]

In another study making use of genetic analysis, Kyle Summers and Bill Amos of Cambridge University compared the similarity of Dendrobates ventrimaculatus tadpoles within clutches, within pools and between well-separated pools. In the field, they found that more than one clutch was often deposited in a pool, and that cannibalism was common. On average, the tadpoles in a pool were intermediate in relatedness between members of a single clutch and tadpoles from separate pools (which were presumed to be unrelated). If pools contained tadpoles from various parents, as these results suggest, then adult frogs depositing food eggs would be feeding someone else's offspring - a phenomenon known as brood parasitism, which is now known to take place in many birds. [Summers, K. & Amos, W. 1997. Behavioral, ecological, and molecular genetic analyses of reproductive strategies in the Amazonian dart-poison frog, Dendrobates ventrimaculatus. Behavioral Ecology, 8: 260-267.]