Allozyme Patterns in Two Unisexual Populations and One Bisexual Population of the Freshwater Crustacean, Triops Longicaudatus




Souther, Krista S.

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Three populations of Triops longicaudatus were studied using starch gel electrophoresis to study allozyme frequencies in the Triops populations. Two populations of Triops were unisexual or hermaphroditic while another well isolated population was bisexual or containing males and females. Both unisexual female populations shared a close Nei's genetic identity (I = 0.94) with one another which would suggest that the populations were conspecific. An average genetic identity of 0.71 was found when asexual and bisexual Triops were compared. This value would suggest that significant divergence has occurred between these two reproductive groups. Whether bisexual Triops belong within the same species as the unisexual Triops is unknown (mating behavior was not studied here). However, as genetic identity decreases below 0.8, the likelihood that speciation has occurred increases. Cyzacus mexicanus , clam shrimp, were used as an outgroup and showed a very low genetic identity with Triops at an average of less than 0.08. Genetic distance (D = -lnl) was used to create phylogenetic trees using the UPGMA (unweighted pairs group method using arithmetic averages) cluster analysis and Fitch Margoliash least squares method. Character data (presence or absence of an allozyme within the population) was used to derive hylogenetic trees using the maximum likelihood and maximum parsimony methods. All four trees shared similar topologies that placed the unisexual Triops as sharing a more recent ancestry and the bisexual Triops as being farther removed evolutionarily.



Triops, phylogeny, Triops longicaudatus, divergence


Souther, K.S. (1996). Allozyme patterns in two unisexual populations and one bisexual population of the freshwater crustacean, Triops longicaudatus (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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