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Abstract:
Background: Hybridization receives attention because of the potential role that it may play in
generating evolutionary novelty. An explanation for the emergence of novel phenotypes is given by
transgressive segregation, which, if frequent, would imply an important evolutionary role for
hybridization. This process is still rarely studied in natural populations as samples of recent hybrids
and their parental populations are needed. Further, the detection of transgressive segregation
requires phenotypes that can be easily quantified and analysed. We analyse variability in body shape
of divergent populations of European sculpins (Cottus gobio complex) as well as natural hybrids
among them.
Results: A distance-based method is developed to assign unknown specimens to known groups
based on morphometric data. Apparently, body shape represents a highly informative set of
characters that parallels the discriminatory power of microsatellite markers in our study system.
Populations of sculpins are distinct and "unknown" specimens can be correctly assigned to their
source population based on body shape. Recent hybrids are intermediate along the axes separating
their parental groups but display additional differentiation that is unique and coupled with the
hybrid genetic background.
Conclusion: There is a specific hybrid shape component in natural sculpin hybrids that can be best
explained by transgressive segregation. This inference of how hybrids differ from their ancestors
provides basic information for future evolutionary studies. Furthermore, our approach may serve
to assign candidate specimens to their source populations based on morphometric data and help
in the interpretation of population differentiation.
