Genetics of intersexual selection: conflict and coevolution
Zusammenfassung der Projektergebnisse
The project was focused on studying the behavioural ecology, quantitative and molecular genetics of grasshoppers. The main focal species, the club-legged grasshopper, shows a particularly spectacular two-stage mating behaviour. At the first stage, males sing and present their swollen front legs and at the second stage they use their legs to drum on their potential mating partners. Various experiments show that the development of clubs is dependent on past condition while performance during drumming is dependent on current conditions. Females do respond mostly to the frequency of drums. Drumming ceases when the pair engages in copulation. So far there is no evidence of female counter-adaptations, hence it does not seem that males manipulated females, but rather that females assess drumming as an honest signal of male conditions. We have studied the quantitative genetic architecture of various morphological and song traits in three species of grasshoppers. This allows the assessment of the stability of the genetic covariation among traits, a measure of genetic integration that determines how populations respond to selection. We find consistency among covariance structure among related species, but also relevant differences. Furthermore, we tested for the presence of male indirect genetic effects on female reproductive behaviour, but these effects appear to be low in our study system. Grasshoppers are intriguing for their very large genomes. In fact, their genomes are about 3-5 times the size of human genomes and represent the largest genomes among all insects and among the largest of all animals. While large genomes still represent an obstacle to genome assembly, the large interspecific and intraspecific variation in genome sizes also offers opportunities for studying the causes and consequences of genome size variation. We found that individuals with larger genomes sing less attractive songs, implying some cost of large genomes. Furthermore, we found that grasshopper genomes consist in large parts of satellite DNA, a class of repetitive motifs that may have some adaptive function during chromosome pairing. Since satellite DNA is particularly abundant in species with the largest genomes. However, the abundances of satellite DNA may not be the cause but rather the consequence of genome size expansion. Many grasshoppers are also characterized by the co-occurrence of green and brown individuals within the same population. There is currently no direct evidence that the green-brown polymorphism is of relevance in context of mate choice. Indirectly via thermoregulatory capacity, however, the polymorphisms may impact sexual selection. Interestingly, we find green and brown individuals in almost all populations across the alpine range of our study species, suggesting that the polymorphism is subject to balancing selection. Intriguingly, the pattern of inheritance suggests a very simple genetic architecture of the green-brown polymorphism.
Projektbezogene Publikationen (Auswahl)
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(2013). A general and simple method for obtaining R2 from generalized linear mixed-effects models. Methods in Ecology and Evolution 4: 133-142
Nakagawa, S. & Schielzeth, H.
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(2014). Challenges and prospects in genome-wide QTL mapping of standing genetic variation in natural populations. Annals of the New York Academy of Sciences 1320: 35-57
Schielzeth, H. & Husby, A.
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(2014). Genome size variation affects song attractiveness in grasshoppers: evidence for sexual selection against large genomes. Evolution 68: 3629-3635
Schielzeth, H., Streitner, C., Lampe, U., Franzke, A. & Reinhold, K.
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(2015). Choosiness, a neglected aspect of preference functions: a review of methods, challenges and statistical approaches. Journal of Comparative Physiology A 201: 171-182
Reinhold, K. & Schielzeth, H.
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(2015). Quantifying the predictability of behaviour: statistical approaches for the study of between-individual variation in the within-individual variance Methods in Ecology and Evolution 6: 27-37
Cleasby, I.R., Nakagawa, S. & Schielzeth, H.
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(2015). What triggers colour change? Background colour and temperature effects on the development of an alpine grasshopper. BMC Evolutionary Biology 15: 168
Valverde, J.P. & Schielzeth, H.
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(2016). High throughput sequencing and graph-based cluster analysis facilitate microsatellite development from a highly complex genome. Ecology and Evolution 6: 5718-5727
Shah, A.B., Schielzeth, H., Albersmeier, A., Kalinowski, J. & Hoffman, J.I.
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(2017). rptR: Repeatability estimation and variance decomposition by generalized linear mixed-effects models. Methods in Ecology and Evolution 8: 1639-1644
Stoffel, M.A., Nakagawa, S. & Schielzeth, H.
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(2018). Condition-dependence and sexual ornamentation: effects of immune challenges on a highly sexually dimorphic grasshopper. Insect Science 25: 617-630
Valverde, J.P., Eggert, H., Kurtz, J. & Schielzeth, H.
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(2018). Spatial analyses of two colour polymorphisms in an alpine grasshopper reveal a role of small-scale heterogeneity. Ecology and Evolution
Dieker, P., Beckmann, L., Teckentrup, J. & Schielzeth, H.
