Browsing by Subject "superkolonia"

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  • Huusari, Noora (Helsingin yliopisto, 2020)
    Social insects such as ants live in societies and have a strict division of labor between reproductive and worker castes. A colony can consist of even millions of individuals and the number of queens can vary a lot. Populations where each colony comprises just one or few queens are often called kin structured because the relatedness between nestmates is high. Colonies that have lots of queens and the society lives in many connected nests (polydomy) in are referred to as supercolonies. In these colonies relatedness between individuals is low and the workers represent many genetic lineages. Depending on species and the environment where the colony lives societies can behave aggressively towards individuals from other nests to protect their own nest. Ants must be able to recognize members of their own colony from the intruders to be able to protect the nest. Nestmate recognition is a key element in the interaction between nests and species and makes it possible for the workers in the colony to favour their own nestmates in form of care, defence or food acquisition to gain inclusive fitness benefits. To recognise nestmates ants must be able to sense chemical cues. Ants detect these chemical signals through the proteins expressed mainly in their antennas. In this thesis I studied gene expression of genes related to chemosensation in seven Formica species using the RT qPCR method. My study species were kin structured Formica exsecta, F. pratensis and F. fusca and supercolonial F. truncorum, F. pressilabris, F. cinerea and F. aquilonia. My study genes belong to gene families that code for odorant binding proteins (OBP), chemosensory proteins (CSP) and gustatory reseptors (GRT). I want to find out whether the expression of these genes differs between castes, and whether the caste difference varies between kin structured and supercolonial species. Workers have many tasks in the ant colony and to take care of them, they need to have a sophisticated sensory system. For that reason, I expect to find out that the study genes are expressed more in the worker than the queen caste. In addition, I expect the caste difference in gene expression to be higher in the kin structured species than in the supercolonial species. That is because kin structured species behave more aggressively towards intruders and possibly confront intruders more often than the individuals living in supercolonies. Furthermore, in the supercolonies low relatedness between individuals sometimes lead to conflicts inside the nest. For that reason, I suppose queens of the supercolonies express chemosensory genes more than the queens from the kin structured colonies. Overall expression level was the highest for the OBP and the lowest for GRT. The expression level of CSP was in between these extremes. In accordance with my hypothesis gene expression of OBP and CSP was higher in workers in all the study species. GRT expression was worker biased in six of the seven species. Caste difference in expression of chemosensory genes was similar in kin structured and supercolonial species. The expression level varied between species but did not show a pattern depending on the degree of the polygyny. The study revealed that the expression of OBP and CSP is correlated. My results revealed expected worker biased pattern in the expression. The result might be a consequence of better olfactory or taste abilities in the worker caste compared to queens or it may even be consequence of more sophisticated nestmate recognition skills of the workers. This study reveals valuable information about the gene expression of chemosensory genes related to the recognition system in the ants and awakes many new study questions. Chemical sensory system has been studied a lot in the ants, but in the field of expression studies there is still lot to reveal.
  • Lindgren, Rosanna (Helsingin yliopisto, 2019)
    Eusociality in ants is based on obligate differences of castes and fitness of workers is indirect following from helping relatives to reproduce. Superorganismality of ant colonies has required high within-colony relatedness to evolve. This has been made possible by one monogamous queen who is the mother of the whole colony. However, the most common wood ant in Finland, Formica aquilonia, forms supercolonies, where even hundreds of nests each containing even hundreds of egg-laying queens, form a network. This kind of social structure is very effective way to compete with other ant species and thrive in habitats where food is patchily distributed and new colony sites can be hard to find. Dispersal of queens is typically very limited likely due to poor success of independent colony founding. Queens stay and continue reproducing even in their natal nest, which increases queen number and makes the relative relatedness in the supercolony very low. According to kin selection theory this is threatening to the inclusive fitness of both workers and queens. Low relatedness can cause severe conflicts inside the supercolony. Some supercolonial ant species are known to kill their new queens and the aim of my study was to prove that killings are happening also in F. aquilonia. I also discuss some of the possible reasons to kill queens. I designed four different treatments and compared the survival of queens between them. Both young and old queens were together without workers, with only their workers, and in one treatment where all three parties were together. In this way, I could see who kills who and whether the absence or presence of some party affects the killings. I collected ants, old queens and pupae from the forest and waited for pupae to hatch to get young, unmated, winged queens. I put the ants together in experiment nests, followed their behavior for 7 days and counted the number of dead and alive old and young queens each day. According to my results young queens did best with old queens without workers. Workers killed young queens by biting and dragged them out of the nest chambers. Old queens seemed to suffer without workers which confirms that these queens were normally taken care of. Queens seemed not to be aggressive towards each other. Why young queens are executed? Maybe because they were unmated, so they could not lay new worker force or queens. It is also possible that there is dispersal conflict in the supercolony. Workers and old queens (the mother colony) want the young ones to fly away and start their own colonies, so that kin-competition would decrease, one queen could have more fitness and hence the fitness of workers would increase as well. It is also possible that workers don’t want extra queens when they have enough already, Old queens could possibly manipulate workers to kill young unrelated queens which could also explain why killing of young queens increased in their presence. Killing can also possibly increase worker relatedness in the supercolony, which could save their inclusive fitness and maintain this paradoxal social structure.