Dissertation Defense: 
Molecular systematics and biogeography of 
sexual and asexual forms of
 Poeciliopsis|(Cyprinodontiformes: Poeciliidae)

Mariana Mateos
Monterey Bay Aquarium Research Institute

Friday, April 12, 2002
12:00 Noon–Pacific Forum

The fish genus Poeciliopsis is widely distributed from Arizona (US) to northern Colombia, and nearly half of its 21 named species have distributions that border on the geologically active Trans-Mexican Volcanic Belt (TMVB), a region that defines the uplifted plateau (Mesa Central) of México. To begin my work, I assessed the historical biogeography of freshwater topminnows in the genus by examining sequence variation in two mitochondrial genes, cytochrome b (1140 bp) and NADH subunit 2 (1047 bp). Using the parametric bootstrap method, I tested the hypothesis that a single vicariant event associated with the TMVB was responsible for divergence of taxa found to the north and south of this boundary.

Next I examined mtDNA and allozymes to infer whether a diploid clonal (hybridogenetic) fish of the Río Mocorito (Sinaloa, México) has an ancient or reticulate origin. Crossing experiments in a previous study revealed that this fish expresses morphological traits from three species. Its haploid maternal genome is inherited clonally (i.e., hemiclonally), and it expresses a mixture of morphological traits found in the closely related species P. monacha and P. viriosa. However, expression of mixed (monacha x viriosa) traits by this hemiclone is also consistent with retention of shared ancestral polymorphisms. If true, this hemiclonal lineage would be one of the few examples of an ancient asexual taxon.

Finally, I used mitochondrial DNA sequences and multilocus allozyme genotypes to examine possible modes of origin and clonal diversity of a triploid clonal (gynogenetic) fish of the genus Poeciliopsis, also from the Río Mocorito.

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