Hypogean Fishes

Current Research

    Current research on the

         cave blind tetra

           Astyanax fasciatus

One of the most intriguing questions in evolutionary biology is the degree to which behavior can be viewed as a consequence of morphology. I explore this issue by examining behavior associated with the loss of phenotypic structure and its presence, using responses to light by characid blind cave fish, Astyanax fasciatus, that are eyed and eyeless. My experiments examine subjects that are epigean (eyed surface) and troglomorphic (blind cave) forms. I compare their photoresponsiveness with blind cave fish with restored eyes. These are produced transplanting the lens from an epigean fish into the optic cup of a blind cave form. The lens from the surface fish stimulates growth and development of the eye, restoring optic tissues lost during cave fish evolution. Fish are placed in an aquarium with one half illuminated with dim or bright white light or infrared light, the other half dark. Their photoresponsiveness is examined by scoring their presence in the illuminated or dark half. My results suggest that both the blind subjects and those with restored eyes are indifferent to the illumination whereas the surface forms are not.  The figure to the right shows the results of these experiments. They were published on December 2003 in the Journal of Experimental Zoology.

Romero, A., S. M. Green, Andrea Romero, M. M. Lelonek & K. C. Stropnick. 2003. One eye but no vision: troglomorphic Astyanax fasciatus (Pisces: Characidae) with induced eyes do not respond to light. Journal of Experimental Zoology (Molecular and Developmental Evolution) 300B(1):72-79.

      Current Research on  

   Convergent Evolution

Anecdotal evidence have suggested in the past that blindness, depigmentation, and simplification or loss of scales may be an example of parallel evolution among troglomorphic hypogean fishes. I investigate the level of blindness, depigmentation, and scalelessness among hypogean fishes. Our results suggest that levels of blindness, depigmentation, and scalelessness is different even among species of the same family (see figure to the right) and that simplification and/or loss of scales is a common feature among troglomorphic fishes but that the lack of scales in the family as a whole cannot be considered a preadaptive feature. Different phylogenetic histories, selective pressures, and genetic independence governing these features account for the explanation of these results.

Co-workers in this research: Kelly M. Paulson. Macalester College.

     Current research on

     Rhamdia quelen in

        Trinidad, W.I.

In 1926 the cave fish population in the Cumaca Cave of Trinidad, W.I., was described as a new troglomorphic genus and species, Caecorhamdia urichi, due to its reduction in eyes and pigmentation. Later studies indicated that this was just a cave population of the widely distributed epigean form of Rhamdia quelen. Beginning in the 1950's a number of specimens were collected in the cave showing variability in eye size and pigmentation. In 2000 and 2001 we conducted field studies that included direct observation of individuals using infrared equipment (video cameras and night-vision goggles), fish echo-sounders, and collecting. We also studied all available specimens of the cave population that have been deposited in museums. Our results strongly suggest that the troglomorphic population has been completely replaced by an epigean one in a period of time as little as 50 years (see figure to the right published in Romero et al., 2002). We hypothesize that some of the reasons for this replacement included, but are not limited to, a new and continuous gene flow from the surface population into the cave one and the preadaptations to nocturnal life among individuals of the cave population of R. quelen.

Romero, A., A. Singh, A. McKie, M. Manna, R. Baker,

    K. M. Paulson, & J. E. Creswell. 2002. Replacement

    of the Troglomorphic population of Rhamdia

    quelen (Pisces: Pimelodidae) by an Epigean

    population of the same species in the Cumaca Cave,

    Trinidad, West Indies Copeia 2002(4):938-942.

   Current research on the

  history of  hypogean fish

              research

The history of hypogean fish research has been strongly influenced by neo-Lamarckism (including orthogenesis) and typological thinking. Only in the last few decades neo-Darwinism has made any inroads in the research approach to this subject (see figure to the right published in Romero, 2001). The majority of the most distinguished and productive hypogean fish researchers have used their research subjects to confirm their own views on evolution rather than to use those subjects as a spring of knowledge to enrich mainstream biological thought. Of these views, I found that the most pervasive of all is the notion of evolutionary ‘progress’ that has led many researchers to envision hypogean fishes as prime examples of ‘regressive’ evolution. I propose that the utilization of hypogean fish for the study of convergent evolution should catapult these subjects of research into prime objects of evolutionary studies.

Romero, A. 2001. Scientists prefer them blind: The history of hypogean fish research. Environmental Biology of Fishes 62:43-71.