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Dispersal of organisms occurs over many different time and space scales. Ultimately it is responsible both for the abundance, survival and extinction of populations, and for the genetic divergence between populations that might lead to speciation. Speciation requires isolation of populations, which can be caused by geographic, ecological and/or behavioral barriers. Principles I discovered in terrestrial animals show interesting similarities with marine processes, but –as result of sea water density and chemistry– the marine environment is also unique in its ability to float and sustain life. The long term goal of my research is to understand causes, consequences and limits of the spatial distribution of organisms in the marine environment.
In trying to understand the genetic structure of populations and dispersal patterns, we primarily use molecular approaches, namely the study of mitochondrial and nuclear DNA variation (microsatellites) in wild living populations. In addition, we perform behavioral studies under controlled conditions in the laboratory to answer specific questions on the mate choice, kin recognition, and olfactory communication. Zebrafish (Danio rerio) and different species of coral reef fish are used as model organisms.
Olfaction plays a major role in finding a suitable social and ecological environment. We perform behavioral studies on zebrafish to learn more about the link between genes, physiology and behavior. In order to understand and quantify behavioral deficiencies and changes caused by mutations it is instructive to know the variance in specific behavioral patterns of the wild type and compare this with specific mutants.
Major changes in the statistical analysis of population genetic structure
(Gerlach et al. 2010)
GST-values and its relatives (FST) belong to the most used parameters to define genetic differences between populations. Originally, they were developed for allozymes with very low number of alleles. Using highly polymorphic microsatellite markers it was often puzzling that GST-values were very low but statistically significant. In their papers, Jost (2008) and Hedrick (2005) explained that GST-values do not show genetic differentiation, and Jost suggested calculating D-values instead. Theoretical mathematical considerations are often difficult to follow; therefore, we chose an applied approach comparing two artificial populations with different number of alleles at equal frequencies and known genetic divergence. Our results show that even for more than one allele per population GST-values do not calculate population differentiation correctly; in contrast, D-values do reflect the genetic differentiation indicating that data based on GST-values need to be re-evaluated. In our approach, statistical evaluations remained similar. We provide information about the impact of different sample sizes on D-values in relation to number of alleles and genetic divergence.
The package "DEMEtics" to calculate D- and GST-values as well as confidence intervals and p values can be requested from the authors or downloaded (http://cran.rproject.org/web/packages/DEMEtics/index.html).
Gerlach G, Jüterbock A, Krämer P, Deppermann J, Harmand P (2010) Calculations of population differentiation based on GST and D: Forget GST but not the statistics! Molecular Ecology 19, 3845-3852.
Olfactory imprinting in zebrafish
(Gerlach et al. 2008)
Distinguishing kin from non-kin profoundly impacts the evolution of social behavior. Individuals able to assess the genetic relatedness of conspecifics can preferentially allocate resources towards related individuals and avoid inbreeding. We have addressed the question of how animals acquire the ability to recognize kin by studying the development of olfactory kin preference in zebrafish (Danio rerio). Previously, we showed that zebrafish use an olfactory template to recognize even unfamiliar kin through phenotype matching. Here, we show for the first time that this phenotype matching is based on a learned olfactory imprinting process in which exposure to kin individuals on day 6 post fertilization (pf ) is necessary and sufficient for imprinting. Larvae that were exposed to kin before or after but not on day 6 pf did not recognize kin. Larvae isolated from all contact with conspecifics did not imprint on their own chemical cues; therefore, we see no evidence for kin recognition through self-matching in this species. Surprisingly, exposure to non-kin odor during the sensitive phase of development did not result in imprinting on the odor cues of unrelated individuals, suggesting a genetic predisposition to kin odor. Urine-born peptides expressed by genes of the immune system (MHC) are important messengers carrying information about ‘self’ and ‘other’. We suggest that phenotype matching is acquired through a time-sensitive learning process that, in zebrafish, includes a genetic predisposition potentially involving MHC genes expressed in the olfactory receptor neurons.
Gerlach G, Hodgins-Davis A, Avolio C, Schunter C (2008) Kin recognition in zebrafish: A 24-hour window for olfactory imprinting. Proceedings of the Royal Society, London B 275 2165–2170.