Merels in de stad blijken te verschillen van soortgenoten in naburige bossen ten aanzien van lichaamsbouw, zang, en genetica. Nederlandse stadsmerels zijn zwaarder dan hun soortgenoten in het bos.... Show moreMerels in de stad blijken te verschillen van soortgenoten in naburige bossen ten aanzien van lichaamsbouw, zang, en genetica. Nederlandse stadsmerels zijn zwaarder dan hun soortgenoten in het bos. Daarnaast zingen stadsmerels met een hogere frequentie dan bosmerels wat de hoorbaarheid bij laagtonig verkeerslawaai ten goede komt. Merelmannen merken zelf daadwerkelijk de verschillen op tussen de zang van stads- en bosmerels, zo blijkt uit experimenten waarbij de zang werd afgespeeld in merelterritoria in stad en bos. Stadsmerels reageren namelijk sterker op hogere zang en bosmerels juist meer op lagere. Variatie in zang en reactie op zang kan mogelijk de onderlinge uitwisseling tussen stad- en bospopulaties be_nvloeden. Dit wordt ondersteund door de bevinding dat populaties uit steden en naburige bossen inderdaad genetisch anders zijn. De gevonden verschillen zijn opmerkelijk omdat de studiepopulaties in stad en bos slechts 5 _ 10 km uit elkaar liggen. Het onderzoek toont dus aan dat een stedelijke omgeving invloed kan hebben op belangrijke soortskenmerken waarbij het echter nog maar de vraag is of deze evolutie ooit zal leiden tot het ontstaan van twee gescheiden merelsoorten. Show less
Avian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate... Show moreAvian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate behavioural barriers are not always impermeable and provide a natural laboratory to examine the role of vocalizations in the causes and consequences of hybridization. This thesis examines a hybrid zone between two species of African doves: the vinaceous (Streptopelia vinacea) and ring-necked dove (S.capicola) by investigating its composition and history with molecular techniques, the mechanisms underlying the variation in dove coos and the response to hybrid signals within and outside the hybrid zone. The variation in hybrid signals and the possibility of learning which vocalizations to respond to can play an important role in facilitating further introgression between the two species. Show less
Mate choice by female cichlid fish from Lake Victoria plays an important role in speciation and the maintenance of species. Females are expected to select against males that are intermediate in... Show moreMate choice by female cichlid fish from Lake Victoria plays an important role in speciation and the maintenance of species. Females are expected to select against males that are intermediate in their phenotype during the process of speciation driven by sexual selection. To test this, we hybridized two species of cichlids that differ in male nuptial coloration. Male hybrids were intermediate in nuptial coloration compared to the parental species. Hybrids had a comparable fitness to the parental species and did not suffer from inviability, sterility, skewed sex ratios, reduced survival or reduced growth rates. Females preferred males of their own species over males of the other species. This implies that female mate preference can drive speciation. Females of one species were able to distinguish between males of their own species and hybrid males; females of the other species however, were not able to see this difference. When there is hybridization in nature, for instance when coloration becomes invisible by an increase in turbidity of the water, there would be asymmetrical selection against hybrids. An understanding of these processes is crucial in speciation research and for the maintenance of biodiversity. Show less
