| Summary: | Barriers to gene flow can be categorised as either prezygotic (e.g. spatial isolation) or postzygotic (e.g. reduced hybrid fitness) and can evolve among populations as a result of adaptation to different environments or resources. The Arctic charr in Thingvallavatn is a good system to study such barriers. It has recently diverged into four morphs (i.e. planktivorous (PL), piscivorous, small benthic (SB), large benthic). The morphs overlap partially in spawning timing and locations creating opportunities for interbreeding, but gene flow appears to be restricted among morphs. In this thesis I addressed questions regarding pre- and postzygotic barriers between Arctic charr morphs from the lake. In the first manuscript, I investigated whether there is spatial isolation in spawning among the morphs and whether hybrids can be detected. Embryos were collected from two known spawning sites and genotyped using a ddRADseq protocol. No spatial overlap among morphs, nor any hybrids were detected. This could be an indication of prezygotic barriers between morphs, or more likely this could due to low sample size. In the second manuscript I assessed if differences in head morphology could be detected before the onset of exogenous feeding in PL and SB progeny, and how hybridisation of these two morphs would affect early head morphology. Progeny of the two morphs and their hybrids were reared in a common garden experiment, stained for bone and cartilage, and analysed using geometric morphometrics. Significant differences between pure morphs were detected. Head shapes associated with the pure PL and SB morphs were similar to those of the adult head morphologies (i.e. rounded snout and subterminal jaw for the SB, pointed snout and terminal jaws for the PL). Hybrids had intermediate morphology, which may not be optimal for neither benthic nor limnetic diets.
|
|---|