The genetic basis of developmental abnormalities in interpopulation hybrids of the moss Ceratodon purpureus

Divergent populations are intrinsically reproductively isolated when hybrids between them either fail to develop properly or do not produce viable offpring. Intrinsic isolation may result from Dobzhansky-Muller (DM) incompatibilities, in which deleterious interactions among genes or gene products lead to developmental problems, or underdominant chromosome structure differences between the parents. These mechanisms can be tested by studying marker segregation patterns in a hybrid mapping population. Here we examine the genetic basis of abnormal development in hybrids between two geographically distant populations of the moss Ceratodon purpureus. Approximately half of the hybrid progeny to exhibited a severely reduced growth rate in early gametophyte development. We identified four unlinked quantitative trait loci (QTLs) that interacted asymmetrically to cause the abnormal-development phenotype. This pattern is consistent with DM interactions. We also found an excess of recombination between three marker pairs in the abnormally developing progeny, relative to that estimated in the normal progeny. This suggests that structural differences in these regions contribute to hybrid breakdown. Two QTLs coincided with inferred structural differences, consistent with recent theory suggesting that rearrangements may harbour population divergence alleles. These observations suggest that multiple complex genetic factors contribute to divergence among populations of C. purpureus.

Key Words: Chromosomal rearrangements, Dobzhansky-Muller interactions, epistasis, hybrid breakdown, speciation

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
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