Unexpected ratio of allozyme expression in diploid and triploid individuals of the clonal hybrid fish Phoxinus eos-neogaeus

Phoxinus eos-neogaeus, a North American freshwater fish, was formed by hybr idization between P. Izeogaeus and P. eos. Individuals of P. eos-neogaeus e xpress one allozyme of P. eos and one allozyme of P. neogaeus for enzymes f or which the parental allozymes are distinctive. We performed densitometry on phosphoglucomutase (PGM) and one glucose-6-phosphate isomerase locus (GP I-A) separated by cellulose acetate electrophoresis to determine if the par ental species' allozymes are expressed in proportion to the number of genom es present in diploid and triploid individuals, and if these enzymes are re gulated separately in different tissues. In diploids, activity of the P. eo s allozyme was greater than the P. neogaeus allozyme in eye, liver, and mus cle but not in heart (one sample t-test, P = 0.05) for PGM. The activity of the P. eos GPI-A allozyme was significantly greater than the P. neogaeus a llozyme in heart, eye and muscle but not in liver (one sample t-test, P = 0 .05). The expected ratio of eos:neogaeus expression in triploid P. eos-neogaeus x eos individuals is 2:1. For PGM, the observed ratio of eos:neogaeus expres sion was not significantly different from 2:1 in all four tissues. The P. e os allozyme for GPI was expressed less than expected in all four tissues (o ne-sample t-test, P = 0.05). Thus, greater than expected expression of the P. eos allozyme was not observed in triploid individuals as it was in the d iploids. These data show that PGM and GPI are regulated separately, and tha t regulation differs by tissue, and in fish of distinct ploidy levels. J. E xp. Zool. 284:663-674, 1999. (C) 1999 Wiley-Liss, Inc.