Genetic variation and sexual reproduction in a moss with dwarf males, Homalothecium lutescens

Research output: ThesisDoctoral Thesis (compilation)


Dwarf males occur in many unrelated groups of organisms. Among land plants they are unique to mosses. Moss dwarf males originate from male spores that land and germinate on the female where their final size is restricted to a few mm. Fertilization in mosses occur over short distances with swimming spermatozoids. Having the males growing as tiny epiphytes on the females facilitates fertilization, as the male and female sexual organs are positioned more closely together. Many things are unknown about the moss dwarf males. In this thesis we investigate dispersal and establishment of dwarf males and female shoots within populations of a moss with dwarf males, Homalothecium lutescens. We also investigate regulation of spore germination on the female shoots. Finally, we investigate population genetic variation and structure as well as gene flow and levels of inbreeding in populations with high abundance of dwarf males. Our results confirm that the presence of dwarf males increase the level of fertilization. Dwarf males are often more closely related to their host shoot, which indicates that spores are mostly dispersed locally. In accordance, we showed that inbreeding levels were generally high. However, polyandry together with sporadic fertilization of dwarf males originating from non-host females appears to maintain the genetic variation on relatively high levels. We could not find any mechanisms that prevent or limit inbreeding, but as the significance of inbreeding depression in mosses is unclear, it is difficult to draw any conclusions regarding potential consequences. Dwarf males and females appear to follow two different recruitment models. Female shoots follow a repeated recruitment model where new females are rarely but continuously recruited from spores. Dwarf males on the other hand, follow a metapopulation or source-sink dynamics. Local dwarf male populations may occasionally go extinct (as a result of their individual short life span and drought sensitivity), but the high dispersal potential of spores and the ability of dwarf males to establish in high numbers in mature colonies, enables re-colonization when conditions improve. We also showed that spores from the moss Isothecium alopecuroides (another moss with dwarf males) could not develop into dwarf males on shoots of H. lutescens. Prevention of spore germination in mature colonies has been shown before and could be a mechanism to prevent hybridization or reduce competition. In contrast, spores from the sister species Homalothecium sericeum were able to develop into fertile dwarf males on shoots of H. lutescens. This result suggests a previously unexplored hybridization pathway between closely related species and could alter the way we view reproductive isolation in mosses.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Ecology


  • bryophytes, mosses, dwarf males, sexual reproduction, genetic variation, genetic structure, inbreeding, isozymes, allozymes, SNP, sporophytes, spore, fertilization, fertility
Original languageEnglish
Awarding Institution
Supervisors/Assistant supervisor
Award date2015 Apr 24
  • Department of Biology, Lund University
Print ISBNs978-91-7623-264-4
Publication statusPublished - 2015
Publication categoryResearch

Bibliographic note

Defence details Date: 2015-04-24 Time: 10:00 Place: Blå Hallen, Ekologihuset, Sölvegatan 37, Lund External reviewer(s) Name: Vanderpoorten, Alain Title: [unknown] Affiliation: Institute of Botany, University of Liège, Liège, Belgium ---

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