Masters of Deception: Part 2
RAHUL
My Journey into the World of Ant-Mimicking Spiders
In this two-part article series, Rahul introduces us to his fascinating research journey involving ant-mimicking spiders and the model ants that they mimic. In this second piece, he narrates an intriguing story of studying a class of black ant-mimicking spiders while in the first piece, he tells us about how he accidentally drifted into studying these fascinating arachnids. Make sure to read both the pieces!
While exploring the forests of Chotanagpur Plateau, one of the most ancient land masses of the world, I realized that Myrmarachne melanocephala is not the only ant-mimicking spider species present. There are many others too. One sunny afternoon, I encountered a huge night-shade jasmine tree, a tree known for its white fragrant flowers and called by various names in India such as Harsingar, Parijat, Prajakta, Shiuli flower, etc. near the Tiger-Trap of Hazaribagh Wildlife Sanctuary. On careful examination, I found a large population of completely black ant-mimicking spiders hovering around the trunk and branches of this tree. The ground beneath this tree was teeming with black ants of the species Camponotus compressus which is often found in our houses and in sweet shops. Since the ant and the mimic spider were found together, I concluded that these ants were the model that the spider species that I collected from this tree were mimicking.
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Myrmaplata plataleoides
Pavel Kirillov from St.Petersburg, Russia, CC BY-SA 2.0, via Wikimedia Commons
What are morpho-variants? Well, morpho-variants are individuals of the same species exhibiting different morphological features (such as, in this case, body color). The best textbook example of morphovariance that one can cite is that of the light and dark form of peppered moth (Biston betularia) from the famous work of Henry Bernard Davis Kettlewell on industrial melanism that demonstrates natural selection.
Red typical form of Myrmaplata plataleiodes male and female and its ant model Oecophylla smaragdina as spotted at NCBS campus, Bangalore.
Images by Rahul
Although the reproductive structures of the red spider variant and the black spider variant are identical, they mimic different ant models and their external morphology is also different.
Taxonomists generally ignore studying morphovariants as most taxonomists probably get better recognition when they discover and describe new species. Departing from this convention, I decided to study the black morpho-variant, focussing closely on its behaviour , which was later published in the journal Animal Biology. One of the images from this work was also featured as one of the journal issues’ cover photo. Prof. Renee Borges from IISc, Bangalore, who is well-known for her work on ecological studies of termites and wasps (and has also published a paper on mate recognition among sympatric ant-mimicking spiders in 2007), also appreciated this work. It gave me a deep sense of encouragement and motivation.
Although the courtship behaviour (behavior exhibited by animals to get potential mates) and foraging pattern (food searching behavior) were found to be similar in both the morpho-variants, the moulting (process by which insects shed their skin when they grow in size) behaviour exhibited significant differences. The most striking observation in black form was the sharp increase in body size (both length and breadth) with the final moult being bulkiest of all whereas the red form only increased its body length without gaining much in breadth throughout the process of moulting.
Night-blooming jasmine
Image credits to Nursery Live
Camponotus compressus
No machine-readable author provided. Shyamal assumed (based on copyright claims)., CC BY-SA 3.0, via Wikimedia Commons
I brought a few of these samples to my lab and studied them carefully. An important step towards identification of any spider species is to study their reproductive structures. After careful investigation, I was struck by the fact that the male and female reproductive structures of these black spiders were identical to that of another red ant-mimicking spider Myrmaplata plataleoides. So, I considered the black ones only to be the morpho-variants of Myrmaplata plataleoides.
Light and dark forms of the peppered moth
Siga, CC BY-SA 4.0, via Wikimedia Commons
To be sure, I also looked for the red variant, to compare it with the black spiders, everywhere in the Hazaribagh Wildlife Sanctuary. In vain, though. Even after extensive sampling, I could not find a single red variant anywhere. Therefore, I requested Dr. Divya Uma, Azim Premji University, Bengaluru for these specimens (as she works on these spiders too) and received an ethanol preserved female specimen from her for morphological studies. My friend Stuti had also sent me a pair of these spiders collected from Pondicherry. But I needed live spiders for comparative behavioural studies. Luckily, while visiting Dr. Deepa Agashe’s lab at NCBS, Bangalore for some work last year (2024), I spotted many red ant-mimicking spiders as well as the red ants (Oecophylla smaragdina) near the guesthouse that I was staying at inside the NCBS campus. I happily collected a few live specimens (males, females and juveniles) for my studies!
Mimics and model: A female (top) and a male (centre) Myrmaplata plataleiodes black morpho-variant and its ant model Camponotus compressus workers exhibiting different sub-castes (bottom).
Images by Rahul
What is really fascinating is that these differences in the spider-mimics are associated with the existence of multiple forms of ant models that they mimic! The worker ants of Oecophylla smaragdina (which the red spiders mimic) are slender and don’t have morphologically different sub-castes but the workers of Camponotus compressus (that the black spider that I study mimics) have morphologically different sub-castes namely minor, medium and major sub-castes, minor being the smallest in size and major being the biggest. Connecting the dots, I realised that the sixth moult the black ant mimicking spider seems to mimic minor ants, after the seventh, medium ants and after the eighth moult, major ants! Such kind of mimicry where different developmental stages (moults) of the spider mimic different subcastes of the workers of the same model ant species has been called temporal myrmecomorphy (the word temporal has to do with time).
Moulting in Myrmaplata plataleiodes: A female spider at moulting stage 3, 6, 7 and 8 respectively (from left to right, scale bars 2 mm).
Images by Rahul
When this work was published, it met with mixed reactions from various arachnologists (scientists who study the biology of spiders). I received some critical comments concerning the specific identity of the black morpho-variant I studied. Hill and Abhijith suggested that the morpho-variant I studied could be a different species altogether!
Therefore, I have also planned to study the molecular differences between the red and the black form of this ant-mimic. Some parts of this study are done, some are lined up to be worked upon in the near future. I have sequenced mtCO1 gene (mitochondrial cytochrome oxidase 1 gene) from the spiders for DNA barcoding and phylogenetic studies.
By comparing DNA sequences, I have found some degree of evolutionary divergence between the red and the black morpho-variants. In my study, I found 3.84% divergence based on mtCO1 sequence comparison between the red and the black morph. Among many insect taxa 3.5% rule is followed for species delimitation (note that spiders are not insects, they are arachnids). But there have been reports of 4.2% intraspecific genetic divergence among many spiders. Therefore, I have refrained from considering it a different species.
However, there are many significant morphological and behavioural differences between the morphovariants. Also, my molecular studies were considered preliminary in nature by various reviewers as comparison using just one gene in spiders is not considered much reliable in modern systematics. Studies involving both mitochondrial as well as nuclear genes in spiders would be considered more robust in modern molecular taxonomy.
I also need to figure out if there is the existence of assortative mating (a form of non-random mating where individuals of a species have mating preferences based on some observable traits) and if there exists any mechanism of reproductive isolation (mechanism preventing breeding among individuals) among these morpho-variants. So, many exciting discoveries are on the way. I feel nostalgic when I look back at how this journey began and what shape it is taking now.
Another morphovariant?
New species?
About Rahul
Dr. Rahul Kumar is a trained molecular biologist with special interest in ecology and evolution. During his Ph.D., he worked on the biology of mimicry using ant-mimicking spiders as model, recorded more than 150 mimic-model pairs from Chhotanagpur Plateau and also developed a nanotechnology-based quick insect species detection method. Along with teaching, he researches different aspects of arthropod behaviour (including mimicry), experimental evolution using flour beetles, chemical ecology of sessile hemipterans, arthropod diversity of Magadh region and survival strategies of different insects at his small "Evolution Lab" far from the noise of the cities. He is also associate editor of Indian Entomologist, a popular magazine published by Entomological Society of India. He is a published poet, avid storyteller and loves sketching in his free time.
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