Abstract
BackgroundGene duplications provide genetic material for the evolution of new morphological and physiological features. One copy can preserve the original gene functions while the second copy may evolve new functions (neofunctionalisation). Gene duplications may thus provide new genes involved in evolutionary novelties.ResultsWe have studied the duplicated homeobox gene homothorax (hth) in the spider species Parasteatoda tepidariorum and Pholcus phalangioides and have compared these data with previously published data from additional spider species. We show that the expression pattern of hth1 is highly conserved among spiders, consistent with the notion that this gene copy preserves the original hth functions. By contrast, hth2 has a markedly different expression profile especially in the prosomal appendages. The pattern in the pedipalps and legs consists of several segmental rings, suggesting a possible role of hth2 in limb joint development. Intriguingly, however, the hth2 pattern is much less conserved between the species than hth1 and shows a species specific pattern in each species investigated so far.ConclusionsWe hypothesise that the hth2 gene has gained a new patterning function after gene duplication, but has then undergone a second phase of diversification of its new role in the spider clade. The evolution of hth2 may thus provide an interesting example for a duplicated gene that has not only contributed to genetic diversity through neofunctionalisation, but beyond that has been able to escape evolutionary conservation after neofunctionalisation thus forming the basis for further genetic diversification.
Highlights
Gene duplications provide genetic material for the evolution of new morphological and physiological features
We hypothesise that the hth2 gene has gained a new patterning function after gene duplication, but has undergone a second phase of diversification of its new role
Duplicated hth genes in P. tepidariorum and Ph. phalangioides Previous studies in the entelegyne spider C. salei [23] and the bird spider A. geniculata [25] have shown that hth is duplicated in these species, and that the genes apparently form two separate phylogenetic groups, termed hth1 and hth2, that differ in spatio-temporal expression
Summary
Gene duplications provide genetic material for the evolution of new morphological and physiological features. Most genes have more than one function (pleiotropy), changes in their coding region and to a lesser extent in their regulatory regions will change a single feature of its function, but there is an increasing number of studies that provide evidence for a prominent role of gene duplication in the evolution of physiological or morphological novelty. In the classical model of gene duplication ([18], discussed in [19, 20]), the new copy evolves fast, because it is redundant and is not subject to selection It diverges quickly from the other copy which remains evolutionarily conserved, because of stabilizing selection on the old function. The typical outcome of this process is that duplicated genes within a species (paralogs) differ in their expression profile, but the expression pattern of each paralog is evolutionarily conserved between different species
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