The role of factors promoting genetic diversity within social insect colonies
1University of Oulu, Faculty of Science, Department of Biology
|Online Access:||PDF Full Text (PDF, 0.6 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514262074
|Publish Date:|| 2010-06-01
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented with the assent of the Faculty of Science of the University of Oulu for public defence in Kuusamonsali (Auditorium YB210), Linnanmaa, on 11 June 2010, at 12 noon
Associate Professor Martin Hasselmann
Docent Heikki Helanterä
The evolution of sociality is often associated with close relatedness and genetic similarity of interacting individuals. However, colonies of advanced social insects (e.g. ants, bees and wasps) characterized by large colony size and division of tasks, are also shaped by acquisition of genetic diversity by polyandry, polygyny, recombination and even by hybridization. The balance between forces selecting for high relatedness on one hand and for improved colony performance though increased genetic diversity on the other hand forms an intriguing area of research.
My study has produced the first genetic linkage maps for ants (Acromyrmex echinatior and Pogonomyrmex rugosus) and social wasps (Vespula vulgaris). Together with the findings of earlier honeybee research, it is shown that advanced eusocial insects have higher recombination rates than any other insect (or animal) studied so far. The estimates obtained here were 14 cM/Mb for P. rugosus, 9.7 cM/Mb for V. vulgaris and 6.2 cM/Mb for A. echinatior.
Pogonomyrmex harvester ants have a genetic caste determination system in which workers arise from mating between two hybridizing lineages whereas sexuals are produced by within-lineage mating. I evaluated the origin of the lineages and the caste determination system by using 751 variable nuclear genetic markers. Fertile hybrids would lead to introgression, particularly in genomic regions characterized by a high recombination rate and lack of strongly selected loci. The hybridizing lineages (lineage pairs J1/J2 and H1/H2) showed many fixed differences. Nineteen of them were in the constructed linkage map, scattered in different linkage groups. The results suggest that there has been no recent introgression. As the hybrids are viable (as workers), caste differentiation can be affected by many loci scattered throughout the ant genome or by a small number of very strongly selected loci.
Genetic diversity in colonies of the ant Formica cinerea is affected by varying levels of polygyny. I tested the hypotheses that the prevalence of endosymbiotic bacteria can vary in polygynous colonies but be either very low or very high in monogynous colonies. However, I found no association between the level of polygyny and endosymbiont prevalence. In addition to Wolbachia, I found two other endosymbiotic bacteria Cardinium and Candidatus Serratia symbiotica which have not been earlier reported from ants.
Genetic diversity in insect colonies is affected by polyandry and polygyny. My results indicate that high a recombination rate is also an important factor influencing diversity. Genotypically diverse progenies can enhance colony success, e.g. through effects on division of labour or defence against pathogens. Recombination differs from the other factors in its effects on genetic relatedness among colony members.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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