ISSN:
1573-5133
Schlagwort(e):
Polymorphism
;
Allozymes
;
Chromosomes
;
Geographic variation
;
Disruptive selection
;
Morphological systematics
;
Atheriniformes
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
Notizen:
Synopsis Some populations of one or more species of the goodeid fish genusIlyodon in certain tributaties of Coahuayana and Armeriá rivers (.Jalisco and Colima, Mexico) are dichotomous with respect to morphological features that are presumptive trophic adaptations. A narrow mouth ‘morph’ (described asI. furcidens in the Río Armería) is sympatric with a broad mouth morph (namedI. xantusi). The morphs are additionally divergent in tooth and gill raker numbers and in coloration of mature males. Other populations are essentially continuous (nondichotomous') in these features. An extensive allozyme survey of sympatric narrow and broad mouth morphs from four localities in the Río del Tule (a tributary of the Río Tuxpan in the Río Coahuayana basin) revealed striking geographic variation in gene frequencies between populations but no differences between morphs at any one locality. The data are consistent with the hypothesis that the morphs are components of the same gene pool, i.e. they are conspecific. This hypothesis receives additional support from analysis of the broods of field-impregnated females. A chromosomal polymorphism, probably involving pericentric inversions, exists at one or more sites in the Río del Tule system. Individuals have 0–4 metacentric chromosomes. The frequency distribution of metacentric chromosome phenotypes (homologs cannot be distinguished) at this site is divergent between the morphs. The chromosomal polymorphism of the Rio del TuleIlyodon appears to be part of a ‘step cline’ in the number of metacentrics among theIlyodon of the Rio Coahuayana basin. It is hypothesized that theIlyodon morphs in the Rio del Tule are in genetic contact, but that disruptive selection acts to eliminate individuals with intermediate trophic phenotypes. At one site, at least, the selection is sufficiently potent to foster chromosomal differentiation between the morphs. The biological basis of the natural selection is unknown, but availability of food resources is implicated by circumstantial evidence. The genetic basis of the morphological differentiation, including the possibility of an ecophenotypic component to the variation, is currently under investigation.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00690860
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