Reproduction in the brine
shrimp Artemia: evolutionary relevance of laboratory
cross-fertility tests
G. Gajardo, M. Parraguéz, J.A. Beardmore,
P. Sorgeloos-2001
Journal of Zoology, 253: 25-32
Abstract:
The brine shrimp Artemia, a typical
inhabitant of hypersaline environments and characterized by a highly
subdivided population structure, was used as a model to evaluate, under
standardized laboratory conditions (at 65 ppt), primary reproductive traits
(offspring quality and quantity) along with levels of reproductive isolation
and degrees of divergence among populations. Intrapopulation experimental
crosses and cross-fertility tests were evaluated in five populations (mostly
A. franciscana) from coastal and inland environments in Chile, and
in reference samples of A. franciscana (San Francisco Bay, U.S.A.)
and A. persimilis (Buenos Aires, Argentina), which are the species
likely to be found in Chile. The populations compared displayed significant
variability in fecundity (total offspring, brood size) as well as in the
ratio encystment/oviviparity. Hybrid offspring, produced abundantly in
cross-fertility tests with reference populations, showed a pronounced switch
to the encystment mode, particularly in crosses with A. persimilis.
Exposure to a broad range of ecological conditions seems to have optimized a
generalist reproductive strategy in the Artemia populations studied
that combines variation in both the quantity and quality of zygotes.
Laboratory cross-fertility tests evaluated prime reproductive
characteristics in individual crosses with fair repeatability, as well as
testing barriers to laboratory reproductive isolation. The lack of efficient
mechanisms for reproductive isolation in the allopatric Artemia
populations studied follows a trend often seen in other anostracods.
Formerly allopatric populations have not achieved sympatry later as required
by the allopatric speciation paradigm, and this is a probable explanation
for production of the laboratory hybrids.
(Laboratory of Genetics and Aquaculture, Universidad
de Los Lagos, P.O. Box 933, Osorno, Chile, e-mail: ggajardo@ulagos.cl)