Their geological youth also makes the islands a natural laboratory for studying how species and their genomes evolve in isolation. Since the islands\u2019 formation, nearly 50 species of Dysdera\u00a0spider have emerged that are endemic, meaning they are found nowhere else in the world.<\/p>\n
One of those is Dysdera tilosensis, a species of red devil spiders found only on Gran Canaria, one of the most populated of the Canary Islands.\u00a0<\/p>\n
These spiders<\/a> are closely related to Dysdera catalonica, a continental species native to northern Catalonia and southern France. After a few adventurous ancestors somehow reached the islands, perhaps carried by wind or rafting on driftwood, they began to evolve along a separate path in the new environment, eventually becoming dozens of different species, including D. tilosensis.<\/p>\n However, something strange happened along this evolutionary path.\u00a0<\/p>\n Spot the difference: the mainland spider (Dysdera catalonica, left) and one from the Canary Islands (Dysdera tilosensis, right).<\/p>\n Image credit: Marc Dom\u00e8nech and Pedro Orom\u00ed, respectively<\/p>\n Led by scientists at the University of Barcelona, a team recently sequenced and compared the genomes of these two Dysdera\u00a0spiders. Remarkably, they found that mainland spider D. catalonica has 3.3 billion base pairs in its genome, while the Canary Island\u2019s D. tilosensis has just 1.7 billion.<\/p>\n In essence, this suggests the genome of the spider was almost halved in size after colonizing the Canary Islands. Furthermore, the genomic sequencing also reveals that D. catalonica has a haploid chromosome number of four autosomes and one X sex chromosome, while D. tilosensis has six autosomes plus the X chromosome.<\/p>\n \u201cThe genome downsizing of the spider\u00a0D. tilosensis, associated with the colonization process of the Canary Island, is one of the first documented cases of drastic genome downsizing using high-quality reference genomes,\u201d Professor Julio Rozas, director of the Evolutionary Genomics and Bioinformatics at the Faculty of Biology and the Biodiversity Research Institute of the University of Barcelona, said in a statement<\/a>.<\/p>\n \u201cThis phenomenon is now being described for the first time in detail for phylogenetically closely related animal species,\u201d he continued.<\/p>\n A smaller genome doesn\u2019t mean the organism is any less complex or less geared towards survival<\/a>. Much of the DNA lost during this downsizing likely consisted of repetitive or non-coding sequences rather than essential genes. The spiders\u2019 biological functions and adaptability remain intact, but their genomes have essentially been streamlined and repackaged into a more compact form.<\/p>\n Case in point, the species from the Canary Islands with the smaller genome actually has greater genetic diversity, hinting that a leaner genome doesn\u2019t necessarily limit evolutionary potential.<\/p>\n Nevertheless, the shrinking of the red devil spider genome is very unexpected. The genomes of living things are more inclined to increase over time<\/a>, rather than reduce in size.\u00a0<\/p>\n This trend is especially common in small populations that colonize new environments due to a phenomenon known as the Founder Effect.<\/a> When only a few individuals establish a new population, selective pressures are often reduced, allowing nonessential or repetitive DNA to accumulate and genomes to grow larger and more redundant.<\/p>\n It\u2019s unclear why the red devil spiders appear to buck this trend, although the researchers ponder whether it might have something to do with non-adaptive mechanisms, evolutionary forces that do not result from natural selection, but from random changes that don\u2019t impact an organism’s fitness.<\/p>\n \u201cPopulations in the Canary Islands would have remained relatively numerous and stable for a long time. This would have made it possible to maintain a strong selective pressure and, as a consequence, eliminate unnecessary DNA,\u201d explained Vadim Pisarenco, first study author, also from the University of Barcelona.<\/p>\n![\"Spot](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/10\/deciphering-the-mechan-6.jpg\" "\\"Spot")
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