Selective forces in the evolution of gender dimorphism in Lycium (Solanaceae)

Persistent Link:
http://hdl.handle.net/10150/284266
Title:
Selective forces in the evolution of gender dimorphism in Lycium (Solanaceae)
Author:
Miller, Jill Suzanne
Issue Date:
2000
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Explanations for the transition from cosexuality to gender dimorphism have concentrated on overcoming the inherent 50% fitness loss of single-sexed nuclear gene mutants arising in cosexual populations. These mechanisms generally fall into two broad, non-exclusive categories: elimination of inbreeding depression by male-sterile mutants (i.e., selection for outcrossing) and compensatory resource reallocation following loss of one sexual function. This dissertation focuses on the relative importance of these mechanisms in the evolution of gender dimorphism in Lycium (Solanaceae) and then finds an emergent explanation. Plants of North American Lycium californicum, L. exsertum, and L. fremontii are either male-sterile or morphologically hermaphroditic, and populations are gynodioecious. Flowers on hermaphrodites are larger and have broader calyces and corollas than those on females. Phylogenetic relationships, using molecular and morphological data, indicate that gender dimorphism has evolved once in North America and have identified the cosexual relatives of the dimorphic taxa. Controlled pollinations and allozyme estimates of mating systems in cosexual relatives of dimorphic species indicate that gender dimorphism has evolved on a phylogenetic background of self-incompatibility. In contrast, studies of pollen tube growth indicate that hermaphrodites in the dimorphic species are self-compatible. To determine if females compensate for loss of male function, I estimated components of female reproduction for all three dimorphic and three cosexual species. I also investigated reallocation within flowers by quantifying the portion of total floral biomass allocated to each floral whorl. Despite substantial savings due to loss of male function, females do not produce increased numbers of seeds, fruits, or flowers, nor do they allocate additional biomass to gynoecia compared to cosexual relatives. Phylogenetic analysis suggests that the common ancestor of dimorphic Lycium in North America was self-compatible and polyploid. In contrast, relatives of the dimorphic clade are cosexual, self-incompatible diploids. This appears to have occurred independently in African Lycium. I describe a novel hypothesis for the evolution of separate sexes involving polyploidy. In this scenario, polyploidy disrupts self-incompatibility leading to inbreeding depression. Subsequently, male-sterile mutants invade and increase because they are fully outcrossed. Further evidence for this scenario is presented from 12 genera involving at least 20 independent evolutionary events.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Botany.; Biology, Ecology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Ecology and Evolutionary Biology
Degree Grantor:
University of Arizona
Advisor:
Venable, D. Lawrence

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleSelective forces in the evolution of gender dimorphism in Lycium (Solanaceae)en_US
dc.creatorMiller, Jill Suzanneen_US
dc.contributor.authorMiller, Jill Suzanneen_US
dc.date.issued2000en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractExplanations for the transition from cosexuality to gender dimorphism have concentrated on overcoming the inherent 50% fitness loss of single-sexed nuclear gene mutants arising in cosexual populations. These mechanisms generally fall into two broad, non-exclusive categories: elimination of inbreeding depression by male-sterile mutants (i.e., selection for outcrossing) and compensatory resource reallocation following loss of one sexual function. This dissertation focuses on the relative importance of these mechanisms in the evolution of gender dimorphism in Lycium (Solanaceae) and then finds an emergent explanation. Plants of North American Lycium californicum, L. exsertum, and L. fremontii are either male-sterile or morphologically hermaphroditic, and populations are gynodioecious. Flowers on hermaphrodites are larger and have broader calyces and corollas than those on females. Phylogenetic relationships, using molecular and morphological data, indicate that gender dimorphism has evolved once in North America and have identified the cosexual relatives of the dimorphic taxa. Controlled pollinations and allozyme estimates of mating systems in cosexual relatives of dimorphic species indicate that gender dimorphism has evolved on a phylogenetic background of self-incompatibility. In contrast, studies of pollen tube growth indicate that hermaphrodites in the dimorphic species are self-compatible. To determine if females compensate for loss of male function, I estimated components of female reproduction for all three dimorphic and three cosexual species. I also investigated reallocation within flowers by quantifying the portion of total floral biomass allocated to each floral whorl. Despite substantial savings due to loss of male function, females do not produce increased numbers of seeds, fruits, or flowers, nor do they allocate additional biomass to gynoecia compared to cosexual relatives. Phylogenetic analysis suggests that the common ancestor of dimorphic Lycium in North America was self-compatible and polyploid. In contrast, relatives of the dimorphic clade are cosexual, self-incompatible diploids. This appears to have occurred independently in African Lycium. I describe a novel hypothesis for the evolution of separate sexes involving polyploidy. In this scenario, polyploidy disrupts self-incompatibility leading to inbreeding depression. Subsequently, male-sterile mutants invade and increase because they are fully outcrossed. Further evidence for this scenario is presented from 12 genera involving at least 20 independent evolutionary events.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Botany.en_US
dc.subjectBiology, Ecology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineEcology and Evolutionary Biologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorVenable, D. Lawrenceen_US
dc.identifier.proquest9992085en_US
dc.identifier.bibrecord.b41167296en_US
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