NEW YORK (GenomeWeb) – An Auburn University-led team used genomic and transcriptomic clues to clarify phylogenetic relationships between members of the spider order Araneae.
As they reported today in PeerJ, the researchers used new and existing transcript and DNA sequences to put together a phylogeny with dozens of spider taxa based on as many as 3,400 genes. The resulting spider relationships suggested the ability to spin complex, spiral 'orb webs' — a feat once suspected of evolving more than once in spiders — was present in a single, early-diverging spider lineage that includes ancestors of non-orb web-making spiders.
"[W]hile orb-weaving taxa are not as closely related as previously thought, our data do support the notion that the orb web itself has evolved only once," senior author Jason Bond, a biological sciences researcher at the Auburn University Museum of Natural History, said in a statement.
More than 45,000 spider species have been identified so far, the team noted, though researchers suspect that there are far more to be discovered. And a number of notable features are found in Araneae — from their diverse lifestyles and mating habits to the production of web-making silk and venoms capable of incapacitating insect prey or potential spider predators.
Despite this complexity, many phylogenetic studies of spiders have focused on morphological features and/or sequences for just a handful of genes. To flesh out the molecular basis of spider relationships, Bond and his colleagues began by bringing together available genomic and/or transcriptomic data for 53 arachnid taxa.
To that, they added new transcriptome sequences generated for 22 more taxa with Illumina HiSeq 2500 instruments, bringing the tally up to 70 spider taxa and five outgroup arachnids.
From these data, the team analyzed eight subsets of sequence information, assessing up to 3,398 gene sequences and almost 700,000 amino acid coding sites at once.
In the process the researchers saw evidence of an ancient orb web lineage containing some spiders that lost the ability to make the complex aerial webs. In particular, they explained, a bout of spider speciation coinciding with non-flying insect diversification some 90 million to 125 million years ago seems to have produced several spider species more adept at hunting on the ground.
The study's authors hope to get an even clearer look at spider phylogeny and orb web origins in an upcoming study based on genome-wide data for hundreds of spiders.
"Our results clearly demonstrate that our understanding of spider phylogeny and evolution requires major reconsideration," Bond and co-authors wrote, "and that several long-held and contemporary morphologically-derived hypotheses are likely destined for falsification."