Coadaptation: lessons from
the brine shrimp Artemia, "the aquatic Drosophila" (Crustacea;
Anostraca)
G. Gajardo, J.A. Beardmore-2001
Revista Chilena de Historia Natural, 74 (1) : 65-72
(from Current Contents)
Abstract:
During the fifties Brncic and the Dobzhansky's
school, using the fruit fly Drosophila as a test organism, introduced the
term integration of the genotype. or genetic coadaptation, which has had
great impact on thinking in today's evolutionary biology. In this work we
use the brine shrimp Artemia - in many respects a sort of aquatic Drosophila
as a model organism to evaluate the relationship between population
structure, potential for divergence and the degree of morphological and/or
genetic change. These aspects, tightly linked with the organization of the
genotype, are important to understanding how recombination and adaptive
release of genetic and phenotypic variation affect the speciation process in
Artemia. Analysis of genetic (allozyme, diploid and chromocentre numbers),
morphological (Mahalanobis distances) and reproductive data (cross-fertility
tests) available for populations of the bisexual, endemic species of the
Americas, Artemia franciscana and A. persimilis, indicate that: (i) A.
franciscana and A. persimilis are morphologically distinct in correspondence
with observed genetic differences (D Nei > 1; 2n = 42 and 44; 12.5 and
1.5 mean chromocentre numbers, respectively); (ii) populations from Chile
and other South American localities (mainly A. franciscana) display high
levels of genetic variability and a trend to develop large genetic distances
between populations: (iii) the plasticity of Artemia gene pool is
associated, at least in part, with ecological heterogeneity. Hence an
adaptive divergence mode is thought to best define the speciation process in
Artemia; (iv) the succesful production of laboratory hybrids in the
allopatric Artemia populations studied in the Americas, a feature seen in
other anostracods. could be explained by the fact that formerly allopatric
populations have not achieved later sympatry, as required by the allopatric
speciation paradigm.
(Univ Los Lagos, Lab Genet & Acuicultura, Casilla
933, Osorno, Chile, e-mail: ggajardo@ulagos.cl)