Thermal Tolerance, Aggression Behaviour and Population Genetics of Meat Ant (Iridomyrmex purpureus)

Abstract

<p>Meat ant (<i>Iridomurmex purpureus</i>) is an Australian native ant very well distributed in the Eastern and Southern parts of the country. It is a comparatively large very numerous, and to some extent ecologically generalized species. These features have allowed them to be dominant members of ant communities. In this thesis, I assess the natural history, thermal performance, aggression behaviour and population genetics of meat ants inhabiting a temperate region.</p> <p>Meat ants construct nests can be found in different shapes and contain several entrance holes that provides an indication of the size of the nest population. After observing several meat ant nests in a small campus population in Armidale, NSW for three year period, I found that the shape of the meat ant nest is related to the level of disturbance it undergoes and size of the entrance holes changes with season, bigger entrance holes are seen in the summer period allowing ants to have frequent movements in and out the nest.</p> <p>Aggression behaviour is assessed in insects using different methodological approaches both in the field and in the lab. Although which method suits best for proper assessment of aggression behaviour is not very well known. I assessed critical methodological aspects regarding aggression behaviour of meat ants which would be of high importance irrespective of the species studied. Results suggest that using enclosures and colour marks can mask the true aggression behaviour of the ants during assays.</p> <p>Due to global climate change impacts most ectotherms are predicted to be under thermal stress and especially insects living in temperate regions are prone to temperature fluctuations in a daily and seasonal basis. Evaluation of critical thermal limits provide an understanding of the effect of increasing temperature on organisms. Meat ant was used as a model organism to carry out an in-depth investigation of thermal tolerance capacities. I found that the critical thermal maximum is affected by the ramping rate used in the thermolimit respirometry assays. According to the findings, thermal responses of meat ants inhabiting different populations did not vary in general except for western inland populations and no evidence was found of the climatic factors and elevation affecting thermal tolerance of meat ants in these different populations. </p> <p>Assessment of genetic structure of insect populations can reveal valuable information on gene diversity, relatedness and mating system. I used microsatellite markers to examine the genetic structure and mating system of two meat ant populations in New England, NSW. The two populations differ in the level of anthropogenic disturbances undergo. After analyzing several genetic parameters it was revealed that the genetic variation between these two populations was lower than expected. Strong genetic variation between the two populations was not supported by <i>F_st</i>, AMOVA or Shannon Informational Diversity. Low genetic variation between two populations might be an indication of meat ants’ intrinsic ability to recolonize and tolerate disturbance. After analyzing genetic relatedness and maternal and paternal families, each nest in both populations was found to harbor more than one queen and queens were found to be polyandry. </p>