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Pre- and post-zygotic isolation in hybrid zones

Leibowitz, Adam Herzl; (1993) Pre- and post-zygotic isolation in hybrid zones. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis considers three aspects of hybrid zones: modification through reinforcement; maintenance by assortative fertilization; and, the extent of morphometric variation across the Podisma pedestris zone. The theory of speciation by reinforcement postulates that, in areas of hybridization, selection will favour the evolution assortative mating since assortment prevents wastage of gametes in the production of partially sterile or inviable hybrids. A model is considered that extends this hypothesis to the evolution of hybrid inviability. Reduced viability of partially sterile hybrids may be favoured if they compete for resources, or parental care, with their non-hybrid sibs. The model is analysed for monogamous and polygamous species and for different degrees of sib-competition. Such reinforcement can only occur if hybrid fertility is very low, and is less likely, but not impossible, in monogamous species. A model is considered to determine the effect of assortative fertilization in the maintenance of clines between divergent populations. Assortment will produce frequency dependent selection, against the rare type, which will lead to stable clines if balanced by dispersal. When applied to the chromosomal dine in Podisma pedestris (in which assortment for karyotype has been observed), the model predicts a much narrower cline than is actually observed. An analysis of morphometric variation across the Podisma hybrid zone is also presented. No difference in morphology is detected between karyotypes within the zone. However, a significant correlation between size and the frequency of the XO karyotype is shown. Whether this is due to genetic or environmental variation cannot be determined with the available data.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Pre- and post-zygotic isolation in hybrid zones
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10102527
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