The degree of polymorphism and heterozygosity in the striped hermit crab, Clibanarius vittatus (Bosc) (Decapoda: Anomura), from the Texas coast.




Killebrew, D.W.

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Texas A&M University.


Two populations of Libanarius vittatus (Bosc), the striped hermit crab, were sampled, one from Bolivar and the other from Port Isabel, Texas, in order to compare their degrees of polymorphism and heterozygosity with respect to the following enzymes: lactate dehydrogenase (LDG), glucose-6-phosphate (G6PDH), malate dehydrogenase (MDH), xanthine dehydrogenase (XDH), and tetrazolium oxidase (TO). The enzymes were separated by means of starch gel electrophoresis and identified by means of substrate-specific stains. An investigation was also made on LDH to determine tissue specificity and the isozyme patterns produced by various tissues. The fastest of the six bands of activity, designated LDH-3, was found only in extracts from gonad tissue and was inferred to be encoded by a single locus, Ldh-3. The slowest moving one (LDH-1) was considered to be a homotetramer composed of subunits encoded by the Ldh-1 locus, and the second fastest one (LDH-2) was considered to be a homotetramer composed of subunits encoded by the Ldh-2 locus. The three intermediate bands were concluded to be heterotetramers composed of different combinations of the two subunits. LDH-1 predominated in abdominal muscle, and LDH-2 predominated in claw and heart muscles. Of the 392 individuals assayed for LDH-1, only one had an electrophoretic variant; however, two phenotypes were consistently observed with respect to heat treatment (65 degrees C for 15 minutes), one heat-stable, the other heat-sensitive. A simple dominance model was postulated to explain the subunit's interaction, the sensitive subunit being dominant. In the sixty-six individuals assayed, twenty-seven had heat-stable LDH-1 and thirty-nine, heat-sensitive. Three phenotypes were visualized in gels stained for G6PDH, a slow, a fast, and a combination of these two, plus an additional intermediate band. Consequently this enzyme was assumed to be at least a dimer encoded by a diallelic locus (G6PDH), the alleles being codominant. Of the 160 individuals assayed, fifty were homozygous for slow, forty-four homozygous for fast, and sixty-six heterozygous. MDH had two zones of activity, MDH-1 being slow and MDH-2 fast. As neither zone, like XDH and TO, showed variation in mobility, these four enzymes were considered monomorphic. Thirty-three percent of the loci studied were polymorphic. The degree of heterozygosity for the two populations combined was 0.146. As none of the observed variability was significantly unique to either population, it was concluded that the individuals of C. vittatus taken from each location were from the same interbreeding population.


81 p., Dissertation


animal physiology, biological speciation, biopolymorphism, enzymes, Clibanarius vittatus