Dynamics of salticid-ant mimicry systems

Ceccarelli, Fadia Sara (2006) Dynamics of salticid-ant mimicry systems. PhD thesis, James Cook University.

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Abstract

Mimicry in arthropods is seen as an example of evolution by natural selection through predation pressure. The aggressive nature of ants, and their possession of noxious chemicals, stings and strong mandibles make them unfavourable prey for many animals. The resemblance of a similar-sized arthropod to an ant can therefore also protect the mimic from predation. Myrmarachne is an ant-mimicking salticid spider genus, whose species associate closely with their model ant species. The behavioural reactions of Myrmarachne to ants were analysed, including instances when there was contact between the spider and the ant. In Townsville the salticid Cosmophasis bitaeniata and one Myrmarachne species associate with Oecophylla smaragdina workers. The Myrmarachne mimics the ant visually, and Cosmophasis bitaeniata mimics the cuticular hydrocarbons of the O. smaragdina worker ants. Cosmophasis and Myrmarachne also mimic ants through certain types of behaviour, such as the “antennal illusion” and bobbing the opisthosoma up and down. The behaviour of both salticids to O. smaragdina was compared. This Myrmarachne was also studied with a hemipteran mimic of O. smaragdina, Riptortus serripes, to see whether the salticid could discriminate between the potentially dangerous ant and its hemipteran mimic. The history of the evolutionary dynamics between Myrmarachne and the model ant species were studied by analysing molecular phylogenies of the two animal taxa.

In a confined space, Myrmarachne species displayed versatile reactions to sympatric ants that depended on factors such as the position of the ant and the distance between the Myrmarachne and the ant. Myrmarachne also show interspecific differences in their reactions to ants. All Myrmarachne species avoided contact with the ants whenever possible. Even when there was contact between the two, Myrmarachne managed to avoid being attacked by the ant. Cosmophasis bitaeniata also avoids contact with ants. C. bitaeniata and Myrmarachne had the same reaction types to ants, but actions occurred at different frequencies. Overall, there were more similarities than differences between the ways these two salticids interacted with O. smaragdina worker ants, even though Myrmarachne and C. bitaeniata have different methods of mimicking the ants. As for the types of behavioural mimicry, there was a significant difference between Myrmarachne species, as well as between the two salticid genera. When Myrmarachne was presented with another morphological ant mimic (the alydiid bug Riptortus serripes), the spiders’ reactions differed from those displayed towards the ants. These differences indicate that Myrmarachne can distinguish the ant and the bug using visual cues (perhaps through the structure of the mouthparts, or the way the two insects move around). So behaviourally, Myrmarachne is a versatile genus apparently under strong selection pressure and showing a high rate of differentiation and speciation. The phylogenetic study also reflects strong selection pressure, resulting in highly polymorphic species. Myrmarachne species have undergone adaptive radiation and speciation as they evolved towards resembling their different model ant species. Therefore the behavioural and evolutionary dynamics of these salticids and their model ants represents a case of plasticity and versatility by the salticids.

Item ID: 1311
Item Type: Thesis (PhD)
Keywords: Myrmarachne, Ant-mimicking salticid spider, Behavioural reactions to ants, Cosmophasis bitaeniata, Oecophylla smaragdina worker ants, Antennal illusion, Bobbing the opisthosoma, Molecular phylogenies, Behavioural mimicry, Polymorphic, Plasticity, Versatile reactions to sympatric ants, Riptortus serripes
Date Deposited: 04 Jan 2007
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 30%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 70%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 100%
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