STELLWAG, Edmund/J; East Carolina University: Fish Genome Evolution, Organismal Complexity and Gene Value Optima

A growing body of evidence supports the hypothesis that genome expansion among chordates was fueled by a series of complete genome duplications. A corollary hypothesis proposes that genome level duplications provided the genetic basis for the continuous increase in organismal complexity observed during chordate evolution. The discovery of an additional genome duplication exclusive to the actinopterygian lineage, unparalleled by a similar duplication in sarcopterygians, has called into question the relationship between genome expansion and organismal complexity. Our laboratory is exploring a concept that we refer to as the Total Gene Value Optimum (TGVO). We hypothesize the existence of an optimum total gene value (G_t) required for the maintenance of a particular level of organismal complexity. Given that genome duplications sharply increase the total gene value, we argue that selection will favor reduction in the total gene value toward G_t, particularly in cases when genome duplications are unrelated to increases in organismal complexity. In a similar fashion, reductions in the total gene value below G_t may result in concomitant decreases in organismal complexity. The TGVO concept is useful in that it predicts that lineages exceeding G_t resulting from genome level duplication will undergo gene loss trending toward the value of G_t. Comparison of the genome values in actinopterygian and sarcopterygian lineages provides support for the TGVO concept, at least for the limited collection of trans-orthologous developmental regulatory genes we have examined to date. Moreover, comparative genomic analyses suggest that actinopterygians are undergoing a reduction in gene content relative to their inferred pre-genome duplication ancestors, which is consistent with the TGVO concept.