animal behavior - second lecture

animal behavior - second lecture - Proc. Natl. Acad. Sci....

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Proc. Natl. Acad. Sci. USA Vol. 93, pp. 10855–10857, October 1996 Evolution Molecular phylogeny analysis of fiddler crabs: Test of the hypothesis of increasing behavioral complexity in evolution C HRISTIAN S TURMBAUER *, J EFFREY S. L EVINTON ² , AND J OHN C HRISTY *Institute of Zoology, University of Innsbruck, A 6020 Innsbruck, Austria; ² Department of Ecology and Evolution, State University of New York, Stony Brook, NY 11794; and Smithsonian Tropical Research Institution, APO Miami 34002 Communicated by Robert R. Sokal, State University of New York, Stonybrook, NY, July 11, 1996 (received for review March 28, 1996) ABSTRACT The current phylogenetic hypothesis for the evolution and biogeography of fiddler crabs relies on the assumption that complex behavioral traits are assumed to also be evolutionary derived. Indo-west Pacific fiddler crabs have simpler reproductive social behavior and are more marine and were thought to be ancestral to the more behav- iorally complex and more terrestrial American species. It was also hypothesized that the evolution of more complex social and reproductive behavior was associated with the coloniza- tion of the higher intertidal zones. Our phylogenetic analysis, based upon a set of independent molecular characters, how- ever, demonstrates how widely entrenched ideas about evolu- tion and biogeography led to a reasonable, but apparently incorrect, conclusion about the evolutionary trends within this pantropical group of crustaceans. Species bearing the set of ‘‘derived traits’’ are phylogenetically ancestral, suggesting an alternative evolutionary scenario: the evolution of repro- ductive behavioral complexity in fiddler crabs may have arisen multiple times during their evolution. The evolution of behavioral complexity may have arisen by coopting of a series of other adaptations for high intertidal living and antipreda- tor escape. A calibration of rates of molecular evolution from populations on either side of the Isthmus of Panama suggest a sequence divergence rate for 16S rRNA of 0.9% per million years. The divergence between the ancestral clade and derived forms is estimated to be 22 million years ago, whereas the divergence between the American and Indo-west Pacific is estimated to be 17 million years ago. It is commonly supposed that species with complex traits evolve from ‘‘simpler’’ ancestors (1–4). Groups with complex behavior are thought to derive from antecedents with simpler systems (5). This sort of presumption is quite reasonable, given that a sequence of behaviors could have been constructed in evolution by accretion of individual behavioral modules. Such a temporal increase in complexity is not inevitable, though, and recent studies, for example, show strong conservation of social y behavioral traits within primate lineages (6). An im- portant question is whether the evolution of behavioral com- plexity is always a consequence of selection on behavior itself or whether it might evolve as a byproduct of natural selection,
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animal behavior - second lecture - Proc. Natl. Acad. Sci....

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