TEMPO OF HYBRID INVIABILITY IN CENTRARCHID FISHES
(TELEOSTEI: CENTRARCHIDAE)
DANIEL I. BOLNICK AND THOMAS J. NEAR
Centrarchid hybrids
show aberrant timing of allozyme gene expression during
early development, even when the parental species have
identical onset of gene expression (Phillip et al. 1983). These
results suggest that centrarchid species have diverged in their
gene regulation mechanisms even while expression location
and timing remained similar. In many cases, hybrids expressed
maternal alleles at the normal time, but paternally
derived alleles were delayed, premature, or failed to be expressed
at all (Phillip et al. 1983). Less viable hybrids in a
reciprocal cross are generally the ones with greater paternal
allele misexpression. Whitt et al. (1977) suggested that the
greater effect on paternal alleles is evidence for cytoplasmicnuclear
interactions, hypothesizing that maternally encoded
regulatory signals are misinterpreted by the paternal allele.
If one species’ gene expression is more sensitive to changes
in transcription factors, asymmetries will result.
the larger species tends to be
the more successful maternal parent (Table 3). Of the 18
species pairs with reciprocal cross data and nonzero viability,
one pair had equal body size and nearly symmetrical crossing
success. Focusing on the remaining 17 species pairs (admittedly
not phylogenetically independent; Table 3), the larger
parent was more successful in 13 crosses and less successful
in four crosses ( 5 4.765, P 5 0.029). We speculate that 2 x1
there is greater disruption of paternal allele expression when
the paternal allele is from a smaller species, placed in an egg
with cytoplasmic factors encoded by a larger maternal species.
However look at GSF X BG below where the better dam is not the larger species ( one of only a few).
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