{"id":689878,"date":"2026-01-11T23:31:10","date_gmt":"2026-01-11T23:31:10","guid":{"rendered":"https:\/\/www.europesays.com\/uk\/689878\/"},"modified":"2026-01-11T23:31:10","modified_gmt":"2026-01-11T23:31:10","slug":"this-island-spider-that-deletes-half-its-dna-and-scientists-say-it-shouldnt-be-possible","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/uk\/689878\/","title":{"rendered":"This Island Spider That Deletes Half Its DNA, and Scientists Say It Shouldn\u2019t Be Possible"},"content":{"rendered":"

A spider species found only on the Canary Islands<\/strong> is forcing scientists to rethink long-held assumptions about how evolution works. Rather than expanding its genome like most island species, Dysdera tilosensis has reduced its DNA content by half<\/strong>, an unprecedented case of genome downsizing in an animal.<\/p>\n

The findings, recently published in Molecular Biology and Evolution<\/strong> describe how this island spider defies expectations by maintaining high genetic diversity<\/strong> while carrying a genome significantly smaller than that of its mainland relatives.<\/p>\n

The research was led by a team from the University of Barcelona<\/strong>, in collaboration with institutions including the Spanish National Research Council (CSIC)<\/strong> and the University of Neuch\u00e2tel<\/strong>. Using high-quality sequencing methods, the scientists compared two closely related spiders. D. tilosensis, which lives only on Gran Canaria, and Dysdera catalonica, a continental species found in Catalonia and southern France.<\/p>\n

Island Genome Half the Size of Its Mainland Cousin<\/p>\n

The most striking result from the study was the scale of the genome reduction<\/strong>. According to the study<\/strong><\/a>, D. catalonica has a genome of about 3.3 billion base pairs<\/strong>, while D. tilosensis carries just 1.7 billion<\/strong>, almost exactly half<\/strong>. Even more surprising, the smaller genome of D. tilosensis was not accompanied by reduced genetic diversity. As Professor Julio Rozas<\/a>, who led the project, explained:<\/p>\n

\n

\u201cDespite having a smaller genome, the species from the Canary Islands shows greater genetic diversity.\u201d This contradicts the usual assumption that small, isolated populations, like those found on islands, experience genetic bottlenecks<\/strong> and a drop in diversity due to limited founding individuals.<\/p>\n<\/blockquote>\n

This contradicts the usual assumption that small, isolated populations, like those found on islands, experience genetic bottlenecks<\/strong> and a drop in diversity due to limited founding individuals. The chromosome numbers also differed between the two species. D. catalonica has four autosomes and one X sex chromosome, while D. tilosensis has six autosomes plus the X. <\/p>\n

\"DysderaDysdera spiders from the mainland and Gran Canaria reveal an unexpected evolutionary twist. Credit: Molecular Biology and Evolution<\/p>\n

A Counterexample to Accepted Evolutionary Patterns<\/p>\n

The findings present a paradox in the field of evolutionary biology. Traditionally, it has been believed that island species, due to reduced selection pressure<\/strong>, accumulate non-functional DNA and expand their genomes<\/strong> over time. But the case of D. tilosensis shows the reverse.<\/p>\n

As explained by Professor Sara Guirao<\/a><\/strong>, one of the study\u2019s senior researchers, genome analysis and flow cytometry measurements indicate that the common ancestor<\/strong> of both spiders had a genome close to 3 billion base pairs<\/strong>. This confirms that D. tilosensis\u2019s smaller genome is a derived trait<\/strong>, the result of downsizing after the species arrived on the Canary Islands<\/a>.<\/p>\n

\"DysderaDysdera phylogeny and divergence timeline. Credit: Molecular Biology and Evolution<\/p>\n

In evolutionary theory, genome shrinkage is much less common than expansion, especially over a short timescale. What makes this case particularly unusual is that it occurred in an animal species and happened in a relatively recent evolutionary window<\/strong>. Doctoral researcher Vadim Pisarenco<\/a> added that the discovery challenges assumptions about the founder effect.<\/p>\n

\n

\u201cWe observed the opposite: island species have smaller, more compact genomes with greater genetic diversity,\u201d he said in the SciTechDaily article<\/a>.<\/p>\n<\/blockquote>\n

Streamlining, Not Adapting<\/p>\n

One of the key takeaways from the study is that natural selection<\/strong> may have remained strong in the island population. Rather than adapting by adding new DNA, the spider<\/a> may have undergone a process of genomic streamlining<\/strong>, eliminating repetitive sequences that had no clear function.<\/p>\n

According to the researchers, this points to non-adaptive mechanisms<\/strong>, that is, the genome became smaller not as a direct survival strategy but due to purifying selection<\/strong> that efficiently removed redundant or non-useful DNA. The team suggests that the D. tilosensis population may have remained large and stable<\/strong> for a long time after colonizing Gran Canaria.<\/p>\n","protected":false},"excerpt":{"rendered":"A spider species found only on the Canary Islands is forcing scientists to rethink long-held assumptions about how…\n","protected":false},"author":2,"featured_media":689879,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[70,16,15],"class_list":{"0":"post-689878","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-science","9":"tag-uk","10":"tag-united-kingdom"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@uk\/115879076548056744","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/689878","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/comments?post=689878"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/689878\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media\/689879"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media?parent=689878"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/categories?post=689878"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/tags?post=689878"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}