Abstract
We tested the contribution of the phylogenetic and specific components to the ecomorphological structure of stream fish from the upper Paraguai River and upper São Francisco River basins, and identified nodes in the phylogenetic tree at which major ecological shifts occurred. Fish were sampled between June and October of 2008 in 12 streams (six in each basin). In total, 22 species from the upper Paraguai River basin and 12 from the upper São Francisco River were analyzed. The ecomorphological patterns exhibited phylogenetic signal, indicating that the ecomorphological similarity among species is associated with the degree of relatedness. A strong habitat template is most likely to be the primary cause for a high phylogenetic signal. A significant contribution from the specific component was also detected, supporting the idea that the phylogenetic signal occurs in some clades for some traits, but not in others. The major ecological shifts were observed in the basal nodes, suggesting that ecological niche differences appear to accumulate early in the evolutionary history of major clades. This finding reinforces the role of key traits in the diversification of Neotropical fishes. Ecological shifts in recent groups could be related to morphological modifications associated with habitat use.
Highlights
Phenotypic traits provide useful information about the relationship between an organism and its environment (Ricklefs & Miles, 1994)
We found that the ecomorphological structure of stream fish of Paraguai and São Francisco River basins showed a high phylogenetic signal
This signal indicates that the ecomorphological similarity among stream fish species is associated with the degree of relatedness (Losos, 2008); closely related species are expected to have greater niche similarity (Darwin, 1859; Webb et al, 2002)
Summary
Phenotypic traits provide useful information about the relationship between an organism and its environment (Ricklefs & Miles, 1994). The similarity would be an indicator of shared ancestry instead of the result of a common relationship between the Phylogenetic signal and major ecological shifts in the ecomorphological structure of stream fish morphology and ecology (Ricklefs & Miles, 1994). Many studies assume that patterns revealed in ecomorphological analysis reflect adaptation to prevailing selective pressures. Such interpretations are problematic in the absence of phylogenetic information (Losos & Miles, 1994) and could generate potentially misleading conclusions (Harvey, 1996). Species cannot be viewed as independent points in statistical analyses due to common ancestry (Felsenstein, 1985; Losos & Miles, 1994) and in the absence of phylogenetic information, the evolutionary rate and trend cannot be deduced (Felsenstein, 1985)
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