Research topics

Evolution of parental care

Sexual selection

Reproductive ecology

Kin recognition and inclusive fitness

Mate choice

Aposematism and mimicry

Phylogenetics

Biogeography

Chytridiomycosis in Peru

 

 

 

 

 

The comparative method and the evolution of aposematism

Previous work on the behavior and ecology of a variety of species of poison frogs makes phylogenetic information obtained from analyses of mtDNA sequences useful for comparative analyses.  The evolutionary tree of relationships of the poison frogs is critically important for examining the evolution of behavioral, morphological and biochemical characters.  For example, the evolution of aposematic coloration, or warning coloration, has been a topic of considerable interest within evolutionary biology (e.g. Brodie, 1988).  If coloration acts as a warning of toxicity to predators (aposematism), then coloration should coevolve (evolve in tandem) with toxicity (Guilford, 1988).

This hypothesis can be tested by using recently developed statistical techniques that take into account information about the evolutionary relationships of the species involved in order to make phylogenetically independent comparisons of the association between two quantitative traits (in this case coloration and toxicity).  I have already carried out a preliminary analysis of this using the evolutionary framework from previous research (Clough and Summers, in press).  Data on the toxicity of different species was obtained from the work of John Daly at the National Institute of Health.  Dr. Daly has elucidated the chemical structure of most of the known poison frog toxins (e.g. Daly, et al., 1987).  Data on coloration was obtained by using photographs of the different species of frogs.  Photographs were rated by naive (unbiased) human raters for brightness and extensiveness of coloration relative to a brown (leaf litter-like) background.  Preliminary analysis indicates a statistically significant association between the evolution of toxicity and coloration, as predicted by the hypothesis that these colors serve as warning signals to predators.

 

Poison frog mimicry

Recently collected samples  from Peru present the opportunity to investigate what appears to be an example of mimicry in the poison frogs.  Mimicry among species of frogs is rare (Duellman and Trueb, 1986), although some researchers have suggested that certain non-toxic species (e.g. Lithodytes lineatus and Eleutherodactylus gagei) may be batesian mimics of certain poison frog species.  Schulte (1999) recently named a newly discovered species Dendrobates imitator based on its remarkable similarity in coloration to D. variablis, an apparently different species that is sympatric with some populations of D. imitator.  The two species can be distinguished by differences in the structure of the advertisement call, and in the color of the eggs.  Recently, other populations of a frog that has a similar call and egg color to the original D. imitator population have been discovered in the lowlands and in the Huallaga Canyon.  However, these populations have different color patterns that appear to be similar to the color patterns of other species of poison frogs that are sympatric with them (D. ventrimaculatus in the lowlands and D. fantasticus in the Huallaga Canyon).  This suggests the fascinating possibility that different populations of D. imitator have evolved to look like the members of the populations of other species that they are sympatric with.  In order to test this hypothesis, I have collected samples from the different populations of "D. imitator". I have also collected samples of the three other species that occur sympatrically with D. imitator in the different regions (D. variablis, D. ventrimaculatus and D. fantasticus).  If the different populations of D. imitator have in fact evolved from a common ancestral lineage to look like the species that they occur sympatrically with, then molecular phylogenetic analysis should reveal that they form an exclusive monophyletic clade, and the members of the other species should all fall outside of this clade.