Tag: Arachnids

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Tiny predator

Cambrian fossil,
your pincers – a coat of arms.
Ancient arachnid.

The Burgess Shale in the Canadian Rockies has some of the most complete and well preserved fossils found anywhere in the world, allowing researchers to gain huge insights into life millions of years ago during the middle Cambrian period.

Now a new species has been described that illuminates the early development of chelicerate – a group of over 115,000 species that contains spiders, scorpions and horseshoe crabs.

In their paper Aria & Caron (2019) describe the morphology of Mollisonia plenovenatrix, including robust but short chelicerae (pincers) that were located between the animal’s eyes, in front of its mouth. These are the predecessors of the pincers that spiders and scorpions use to kill, hold and cut their prey.

It’s likely that the species hunted close to the sea floor, using long walking legs and other sensory limbs to detect prey. The finding suggests that the origin of the chelicerate must be earlier in the Cambrian period and that the group must have rapidly expanded to fill an underutilised ecological niche.

A note about the sciku: For the sake of the poem I have simplified chelicerate to arachnids. Lead author Cédric Aria has described the pincers (chelicerae) as the ‘coat of arms’ of the chelicerate which felt suitably poetic.

Original research: http://dx.doi.org/10.1038/s41586-019-1525-4

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Astonishing carrier

Angolan spider –

astonishing carrier.

What is your horn for?

A new species of horned baboon spider has been described that has a soft horn on its back, unlike any spider previously found in the world. The species was found in Angola and Midgley and Engelbrecht (2019) have named it Ceratogyrus attonitifer – its name being a combination of the Latin for astonishment (attonit-) and carrier (-fer). The purpose of the large and soft horn on the spider’s back is currently completely unknown.

Original research: http://dx.doi.org/10.3897/afrinvertebr.60.32141

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Spider milk

Unexpected milk –

not a mammalian trait?

Lactating spider.

Caring mothers aren’t the first thing that spring to mind when you think about spiders. Yet plenty of evidence exists of female spiders providing food for their young and protecting their offspring. A recent and very surprising example of arachnid maternal care comes from a species of ant-mimicking jumping spider.

Chen et al (2018) observed female spiders secreting a nutritious milk-like substance, which the offspring first consume from the floor of the nest and once they are a bit older directly from the mother herself. Through a careful set of experiments the researchers found that the spiderlings are entirely dependent on this ‘milk’ for survival, and that there are still huge survival benefits to it even once they are old enough to forage independently.

Milk provision was once seen as an exclusively mammalian trait but this research adds to growing evidence that the practice is more widespread across animal taxa than previously thought.

Original research: http://dx.doi.org/10.1126/science.aat3692

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Ensnared

Poor social spider.

Ensnared, building its own tomb.

Parasitoid wasp.

 

Parasitoid wasps are known to lay eggs on their victims which are then consumed by the hatching larvae. Some species will even paralyse their victim and place them in a nest to be eaten alive by their offspring. Yet behaviour observed by Fernandez-Fournier et al (2018) has revealed a wasp species that behaves even more disturbingly.

Adult Zatypota sp. wasps were found to target a species of social spider that lives in a colony web and rarely leaves it. The wasps lay their eggs on the abdomen of the spider and when the larvae hatches it attaches to the spider. The larvae influences the spider to then leave its colony and spin a cocoon web in which the spider then waits until the larvae finally kills it. Its meal consumed, the larvae then spins a pupal cocoon within the protection of the outer cocoon web and a few days later emerges as an adult.

The results reveal that the spider is manipulated into performing unusual behaviours, since such social spiders rarely leave their colony and the cocoon web is a complete different form of web. The infected spider makes its own tomb before being eaten alive within it.

Original research: http://dx.doi.org/10.1111/een.12698

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Arachnid genome

Arachnid genome

duplicated long-ago.

Arachnid genome.

 

Sometimes having two of something is a good thing. Genes are occasionally duplicated and whilst duplications are often lost, they may be retained and may help aid the evolutionary diversification of organisms. Normally only a few genes are duplicated but occasionally duplication can occur on a greater scale.

Schwager et al (2017) sequenced the genome of the common house spider and found evidence that whole genome duplication occurred in the house spider’s distant past. In fact, comparison with the genome of bark scorpions suggests that the duplication event took place in the common ancestor of spiders and scorpions more than 450 million years ago.

Original research: https://doi.org/10.1186/s12915-017-0399-x

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Paternal spider

Paternal spider

to die at the ‘little death’,

worthy sacrifice.

 

Mating is a dangerous game for males of many species of spider, with females often winding up with a nutritional meal to help fuel egg production. Taking their paternal responsibilities to an extreme, male dark fishing spiders spontaneously die during copulation. Females that are allowed to eat their dead mates produce a greater number of offspring, of a greater size and with an increased survivorship compared to females prevented from eating their mate or females provided with an equivalently sized cricket. It seems cannibalism isn’t all bad. Schwartz et al, 2016.