Significance of This Research

Although reconstructing a phylogeny for a given taxon is exciting and significant in its own right, the reconstruction of a phylogeny for centrarchids will be of much greater significance than simply another tree for another group of organisms. The Systematics Agenda 2000 established as part of its goals the need for phylogenetic studies on species important to basic biological sciences. Centrarchids have figured prominently in numerous studies attempting to address many different and important questions relating to biological sciences. However, a robust phylogeny with appropriate outgroup taxa does not exist. This research aims to provide this much needed phylogeny and a stable classification for these fishes.

Recent years have been marked by a number of provocative ideas concerning

  • Phylogenetic inference of independent data sets
  • Evaluation of rates of evolution in groups of equal age and yet disproportionate diversity
  • Determination of modes of speciation and associated rates of divergence
  • Evaluation of zoogeographic patterns and estimation of geographic histories of single groups and communities
  • Partitioning of historically and non-historically constrained morphologies, behaviors and ecologies
  • Origins of communities.

Common to all of these studies and many more is the focus on a more complete understanding of the patterns and processes of evolution. All of these research programs are inherently historical and therefore dependent upon the genealogical histories of organisms being compared. It is impossible to partition out ecological and phylogenetic components of differentiation if reliable genealogical hypotheses are unavailable.

As addressed above, the extensive molecular data sets we are generating and our inclusion and re-evaluation of Branson & Moore’s (1962) and Mabee’s (1993) morphological data sets offer a rare opportunity for enhanced resolution and understanding of character evolution, as well as the evolution of corollary anatomical, behavioral, and ecological observations and patterns, all broad areas relating to character reliability and informativeness. The availability of a phylogeny generated independent of morphological data and combined analyses will provide a much more ideal situation to evaluate the efficacy of using ontogenetic transformations for assessing character homology and character polarity and order. Through the total evidence analysis we will be able to examine relationships and character congruence. Through separate analyses we can examine taxonomic congruence by evaluating tree lengths and character changes necessary to converge on identical (or consistent) phylogenies. With both the total evidence and separate analyses the identification of homology and homoplasy with the morphological and molecular data sets will be used to assess the following research questions/objectives.

  • Is there a quantitative difference in the level of homoplasy between the different data types?
  • What portion of homoplasious characters within each data type remain so in light of a phylogeny constructed from all data sets?
  • To what extent are characters of different types congruent with one another; that is do they converge on a single most parsimonious topology?
  • If so, how similar are they to that arrived at by a total evidence analysis?
  • What is the impact of alternative parsimony methods traditionally employed with sequence characters?
  • What are the effects of stem and loop characters or different regions of the genes on phylogeny reconstruction? A total evidence analysis offers a rare opportunity to compare multiple data sets (mitochondrial and nuclear DNA and morphology) and investigate their effects on the resolution of a phylogeny of the same organisms.

In addition, extensive investigation of the transformation of various character types can be undertaken; thus, providing new insights into the tempo and mode of the evolutionary process.

Centrarchids form a major component in warm-water ecosystems in North America and therefore it is important that we have a phyletic understanding of the group. A more reliable understanding of the relationships of these fishes will contribute greatly to developing the research programs listed above and provide a more stable classification for these fishes. For this reason, we feel that energies need to be invested into resolving the relationships of this fascinating and important group of fishes.

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Fish illustrations by Joseph R. Tomelleri and used with permission.