In a previous paper, Dingle (2003) considered the possibility of gene reactivation leading to the re-appearance of eyes in certain blind ostracod taxa after sightedness had been lost in lineages several million years earlier. These observations were based on two marine genera found at Marion Island in the Southern Ocean (Eocene–Recent Poseidonamicus Benson, and Campanian–Recent Dutoitella Dingle) that have evolved numerous deep-water species that were/are blind. The discovery of Recent, sighted, shallow-water forms led to the suggestion that adaptive pressure from the advantages of sightedness had resulted in the reactivation of genes that allowed an evolutionary advantage to be regained (Dingle, 2003).
While such transformations have not been enunciated in these terms by other micropalaeontologists, there have been tacit assumptions in the literature that similar processes do occur. Confrontation with the phylogenetic issues raised by these phenomena has so far been fudged by inconsistency, but, in this essay, further examples will be looked at to highlight the taxonomic swamp into which we are in danger of wading.
One of the issues is whether such processes violate Dollo’s Law (Dollo, 1893) at the phenotypic, if not genetic, level. Dollo’s Law has been expressed in modern terms by Marshall et al. (1994) as ‘degradation of genetic information … sufficiently fast that genes or developmental pathways released from selective pressure will rapidly become non-functional’. Gould (1970, p. 192) preferred to call this Dollo’s ‘notion of irreversibility’, while recent accounts stress its relevance only to ‘complex characters’ (e.g. Collin & Miglietta, 2008).
The author thanks A. R. Lord for comments that improved a draft of this contribution and I. D. Boomer for a helpful and perceptive review. Thanks also to Clive Jones (NHM) for encouragement.
- Received May 8, 2008.
- Accepted March 9, 2009.
- © 2009 The Micropalaeontological Society