Variaciòn genetica del pejelagarto

Journal of Fish Biology (2008) 73, 1919–1936 doi:10.1111/j.1095-8649.2008.01993.x, available online at http://www.blackwell-synergy.com

Genetic variation and recent population history of the tropical gar Atractosteus tropicus Gill (Pisces: Lepisosteidae)
J. B ARRIENTOS -V ILLALOBOS *
AND

A. E SPINOSA DE LOS M ONTEROS

´ Laboratorio de Sistematica Filogentica, Departamento de Biolog´aEvolutiva, Instituto e ı de Ecolog´a A.C., Apartado Postal 63, Xalapa Veracruz 91070, Mxico ı e (Received 7 July 2007, Accepted 19 June 2008)
The tropical gar Atractosteus tropicus belongs to one of the few extant lineages of early bony fishes. The genetic variation detected both within and among 11 natural populations of A. tropicus in Mesoamerica along with the implications for their recenthistory are presented. Sequences from cytochrome b (307 bp) and cytochrome oxidase subunit II (607 bp) were used as data sources. Apparently, the populations of this fish have decreased in size because of anthropogenic pressures, such as habitat degradation and destruction. The observed values for nucleotide diversity (0Á0016 Æ 0Á0018) and haplotype diversity (0Á477 Æ 0Á302) suggest low levels ofgenetic variation. Nonetheless, most of the populations studied are currently in a period of genetic stasis. Recent isolation by distance, reduced gene flow and translocation were inferred as the processes maintaining this stasis. Phylogenetic analyses showed reciprocal monophyly between the haplotypes from Guatemala and the other populations. This, together with the observed genetic variation, suggeststhat the Guatemalan haplotypes might represent a new species. The haplotypes, other than those from Guatemala, exhibited a geographic pattern consistent with two main reproductive populations, one from the Pacific and the other from the Gulf of Mexico–Caribbean slope of Mesoamerica. Pleistocene glacial and interglacial periods might be responsible for moulding the heterogeneity in the genetic #2008 The Authors structure observed during this study.
Journal compilation # 2008 The Fisheries Society of the British Isles

Key words: gene flow; genetic variation; mtDNA; phylogeography; population structure; tropical gar.

INTRODUCTION The tropical gar Atractosteus tropicus Gill is one of the basal actinopterigian fishes in the family Lepisosteidae (Wiley, 1976). The palaeontological recordsuggests that current gar populations are relicts of an ancient worldwide clade. Fossils from this family are common within the marine deposits of the Niobrara formation in Kansas (Wiley & Stewart, 1977) and in deposits from the upper Cretaceous and early Palaeocene of India, Europe and Africa
*Author to whom correspondence should be addressed. Tel.: þ52 228 842 1800; fax: þ52 228 818 7809; email:barrientos.villalobos@posgrado.inecol.edu.mx

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2008 The Authors Journal compilation # 2008 The Fisheries Society of the British Isles

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J. BARRIENTOS-VILLALOBOS AND A. ESPINOSA DE LOS MONTEROS

(Woodward, 1908). In spite of the rapid decline of this clade, it is easy to find relict populations. This fish inhabits the backwaters and slow moving sections of rivers, lakes,swamps and shallow lagoons. It is often found in the warm stagnant waters of lowland areas, commonly visible on the surface and resembling a floating log. Juvenile gar feed mainly at night and exclusively on other fishes, but plants and fruit have been reported as part of the adult diet (Resndez & Salvadores, 1983). The presence of plant material in the stomach e of adult fish could, however, be anincidental consequence of their hunting techniques. This species has a rapid growth rate; reproductive size is reached after 2 years, and the estimated sex ratio is 1:1 (Velasco-Colin, 1976). Mature individuals enter shallow lakes at the beginning of the dry season to spawn. Some adults can also reproduce in June and July when rains are heaviest, and rivers flood their banks providing an ideal...