MOLECULAR PHYLOGENY ANALYSIS OF FIDDLER-CRABS - TEST OF THE HYPOTHESIS OF INCREASING BEHAVIORAL COMPLEXITY IN EVOLUTION

The current phylogenetic hypothesis for the evolution and biogeography of fiddler crabs relies on the assumption that complex behavioral tra its are assumed to also be evolutionary derived, Indo-west Pacific fid dler crabs have simpler reproductive social behavior and are more mari ne and were thought to be ancestral to the more behaviorally complex a nd more terrestrial American species, It was also hypothesized that th e evolution of more complex social and reproductive behavior was assoc iated with the colonization of the higher intertidal zones, Our phylog enetic analysis, based upon a set of independent molecular characters, however, demonstrates how widely entrenched ideas about evolution and biogeography led to a reasonable, but apparently incorrect, conclusio n about the evolutionary trends within this pantropical group of crust aceans, Species bearing the set of ''derived traits'' are phylogenetic ally ancestral, suggesting an alternative evolutionary scenario: the e volution of reproductive behavioral complexity in fiddler crabs may ha ve arisen multiple times during their evolution, The evolution of beha vioral complexity may have arisen by coopting of a series of other ada ptations for high intertidal living and antipredator escape. A calibra tion of rates of molecular evolution from populations on either side o f the Isthmus of Panama suggest a sequence divergence rate for 16S rRN A of 0.9% per million years, The divergence between the ancestral clad e and derived forms is estimated to be approximate to 22 million years ago, whereas the divergence between the American and Indo-west Pacifi c is estimated to be approximate to 17 million years ago.