Abstract
BackgroundBdelloid rotifers are microscopic animals that have apparently survived without sex for millions of years and are able to survive desiccation at all life stages through a process called anhydrobiosis. Both of these characteristics are believed to have played a role in shaping several unusual features of bdelloid genomes discovered in recent years. Studies into the impact of asexuality and anhydrobiosis on bdelloid genomes have focused on understanding gene copy number. Here we investigate copy number and sequence divergence in alpha tubulin. Alpha tubulin is conserved and normally present in low copy numbers in animals, but multiplication of alpha tubulin copies has occurred in animals adapted to extreme environments, such as cold-adapted Antarctic fish. Using cloning and sequencing we compared alpha tubulin copy variation in four species of bdelloid rotifers and four species of monogonont rotifers, which are facultatively sexual and cannot survive desiccation as adults. Results were verified using transcriptome data from one bdelloid species, Adineta ricciae.ResultsIn common with the typical pattern for animals, monogonont rotifers contain either one or two copies of alpha tubulin, but bdelloid species contain between 11 and 13 different copies, distributed across five classes. Approximately half of the copies form a highly conserved group that vary by only 1.1% amino acid pairwise divergence with each other and with the monogonont copies. The other copies have divergent amino acid sequences that evolved significantly faster between classes than within them, relative to synonymous changes, and vary in predicted biochemical properties. Copies of each class were expressed under the laboratory conditions used to construct the transcriptome.ConclusionsOur findings are consistent with recent evidence that bdelloids are degenerate tetraploids and that functional divergence of ancestral copies of genes has occurred, but show how further duplication events in the ancestor of bdelloids led to proliferation in both conserved and functionally divergent copies of this gene.
Highlights
Bdelloid rotifers are microscopic animals that have apparently survived without sex for millions of years and are able to survive desiccation at all life stages through a process called anhydrobiosis
Functional divergence of gene copies is not restricted to asexual lineages, it was argued that functional divergence of former alleles might have contributed towards adaptation to desiccating environments
Cloning and sequencing of bdelloid alpha tubulin yielded between 11 and 13 different copies in each species (Table 2). This is a conservative estimate because sequences were only considered unique when they varied by >1% to account for 99.5% PCR fidelity of the cloned copies
Summary
Bdelloid rotifers are microscopic animals that have apparently survived without sex for millions of years and are able to survive desiccation at all life stages through a process called anhydrobiosis. Both of these characteristics are believed to have played a role in shaping several unusual features of bdelloid genomes discovered in recent years. Bdelloid rotifers are microscopic aquatic invertebrates of particular interest for two features of their lifestyles They have persisted for tens of millions of years [1] and diversified into nearly 450 recognized species [2], despite the apparent absence of meiosis and sex [3]. Functional divergence of gene copies is not restricted to asexual lineages, it was argued that functional divergence of former alleles might have contributed towards adaptation to desiccating environments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
