The Sydney funnel-web spider (Atrax robustus) is a spider commonly encountered within Australia's most populous city and is regarded as one of the world's most venomous spiders. An international team of researchers recently published an article in the journal BMC Ecology and Evolution that makes the case for recognition of three Atrax species within the broader A. robustus species complex.
First described in 1877, A. robustus was originally described from a single female specimen. It took scientists decades to match the original female specimen with a male spider; an important discovery as male Atrax bites are almost always medically significant. Male funnel-web spiders are often encountered outside their burrows in search of females during summer and autumn and, to date, 13 spider bite deaths are associated with A. robustus. Despite this fearsome reputation, no spider bite deaths have occurred since the development of an effective antivenom in 1980.
An unexpected evolutionary history
Until now, A. robustus was thought to be a single widespread but morphologically variable species. Recently, Loira et al. applied genetic sequencing techniques and morphometric analyses to support the hypothesis that A. robustus comprises three genetically distinct species. Their study confirms that A. montanus, originally described in 1914 and later synonymized with A. robustus, is a valid species, while the northern A. robustus populations occurring near Newcastle are described as a new species. This novel funnel-web spider (A. christenseni) was named after Kane Christensen and likely diverged from A. robustus around 17 million years ago. Atrax christenseni is only known from a handful of locations and is likely threatened by urban expansion and the exotic pet trade.
Revised species boundaries and distributions
The three species recognised by Loira et al. are:
Sydney funnel-web spider (Atrax robustus) – This species is relatively widespread across the Sydney metropolitan region and surrounding areas.
Southern Sydney funnel-web spider (Atrax montanus) – Occurring primarily in the Blue Mountains and extending south and west beyond the distribution of A. robustus. The species distribution overlaps with the morphologically similar A. robustus and was previously considered the same species.
Newcastle funnel-web spider (Atrax christenseni) – The largest of the three species, nicknamed “Big Boy”, is restricted to a small region surrounding Newcastle in northern New South Wales. This species exhibits noticeable morphological differences, including a larger body size and distinct leg structure compared to its relatives.
Biomedical implications
The discovery of three distinct funnel-web species is an important discovery for venom research and antivenom production. While current antivenoms effectively treat bites from all three species, understanding the venom compositions of A. robustus, A. montanus and A. christenseni may lead to advancements in antivenom development. Additionally, the larger A. christenseni appears to produce significantly more venom than its near relatives, highlighting the importance of ongoing taxonomic work for medically significant species.
Full Article:
The world’s most venomous spider is a species complex: systematics of the Sydney funnel-web spider (Atracidae: Atrax robustus)
Stephanie F. Loria, Svea-Celina Frank, Nadine Dupérré, Helen M. Smith, Braxton Jones, Bruno A. Buzatto & Danilo Harms
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