Dating is hard and confusing for most… but especially for these guys.
A recent study on two native semi aquatic spiders, Dolomedes aquaticus and Dolomedes minor, revealed that spider dating is dramatic, but beneficial for their evolution. These spider species spend a lot of time diving for their prey in rivers and streams.
Male fishing spiders (Dolomedes species) perform complex courtship displays for their partners, which include vibratory, visual, and chemical signals, all just to avoid being killed by the female they are trying to impress, and just so he gets the opportunity to copulate.
Unfortunately for these eight-legged boys, their ladies are often aggressive, sexual cannibalism common, and dates often making up a significant portion of these feisty ladies diets.
These fishing spider species are found throughout New Zealand. In a particular area in the lower South Island, something interesting is going on… they are hybridising!… but only in one direction.
DNA analysis has revealed that mitochondrial introgression has occurred between D. aquaticus females and D. minor males. Introgression is when DNA moves from one species to another. But why, and why only one way? This study investigated the one way introgression between these two species, coauthored by one of New Zealand’s preeminent arachnologists, the one and only Cor Vink.
These species are closely related and have been observed to interbreed. This causes genes from one species to pass to the other; this process is called introgression. Introgression between these species has only been observed in one direction between female D. aquaticus and male D. minor. Introgression has also only been seen in one location, in the south of the South Island, the “introgression zone.”
Distribution of Dolomedes aquaticus and D. minor within New Zealand, with introgressed D. minor specimens shown. Data from Vink and Dupérré 2010 and Lattimore et al 2011. Also shows collection locations of spiders for laboratory experiments, and Waipara field monitoring site. The introgression zone is shown by the square box. (Content subject to copyright: please see the study image notes for details)
The purpose of this study was to investigate life history traits and mating behaviour that promoted and limited introgression that occurs only one way and is limited to one area.
Spiders were collected from within and outside the introgression zone and mating behaviour was tested in a lab.
From these experiments, it was found that males from outside the introgression zone were less willing to continue courtship once realising the female was of a different species from themselves, often ghosting halfway through, an experience familiar to those of us in the dating pool. On the other hand, D. minor males within the introgression zone were happy to flirt with any female. This unfussy selection seems familiar. Whether this is a spider phenomenon or a southern cultural trait remains unclear.
Another interesting find was that female D. minor were more short tempered when it comes to D. aquaticus males, having much higher attack and rejection rates towards D. aquaticus males than the opposite pairing. When a D. aquaticus male attempted courtship, the females often attacked and ate him. This suggests the differences in female behaviour between the two species may have just as much influence on gene flow as mate choice.
Female receptiveness to male courtship is key for introgression to occur, including female ability to recognise male courtship, female choice, and premating aggressive behaviour, these could all prevent interbreeding in ways that could vary throughout the species’ range.
Pairings were more successful if the pairings were similar in size. Females in both species are much larger than males, although D. aquaticus is larger overall. It was suggested that one way introgression could be because a female D. aquaticus assumes that a smaller male would be an easier snack, not a great mate!
Other potential factors could include that partners in the south could be less choosy in their mate selection as their breeding seasons may be shorter due to natural conditions. D. aquaticus females may think males of their species are rarer, or D. aquaticus male and D. minor female genitalia may not be compatible.
In summary, it is likely that mating behaviour has a strong influence on the dynamics of introgression gene transfer between these species within the introgression zone.
Male behaviour may limit introgression one way, preventing mating between D. minor females and D. aquaticus males. Also, female behaviour and choice may limit introgression because of a preference: mate or meal?
In the end, these spiders prove one thing: rejection is natural selection, and preference is important in evolution. So, next time you have a bad date, consider yourself grateful that your rejection did not end in sexual cannibalism. 🕷️
This article was prepared by Master of Bioprotection student Nicky Lowther as part of the ECOL608 Research Methods in Ecology course
Connolly, S. J., Hunt, J., Curtis, K. M., Painting, C. J., Cooney, C., & Vink, C. (2025). Mating behaviour influences the direction and geographic extent of introgression in New Zealand fishing spiders (Dolomedes). Journal of Evolutionary Biology, 38(3), 291–304. https://doi.org/10.1093/jeb/voae147
Leave a Reply