Abstract
BackgroundNannandry is a sexual system where males (”dwarf males”) are much smaller than the conspecific females. Dwarf males occur in a wide range of unrelated organisms but the evolutionary advantages of this condition are poorly understood. The dwarf male sexual system results in differences in the mode of dispersal and establishment as well as the life span between males and females. Such differences must have profound effects on the population dynamics and genetic structures. We have studied four populations of the nannandrous moss Homalothecium lutescens in southern Sweden. We genotyped dwarf males and female shoots with the aim of describing the genetic diversity and structure of the populations.ResultsDwarf males were most related to their host shoot, then their colony (within 0.5 m2) and then the rest of the population, which suggests restricted spore dispersal. However, a few dwarf males in each population appeared to originate from other colonies and sometimes even other populations. Genetic diversity of dwarf males was generally high but showed no tendency to be consistently higher or lower than female genetic diversity within the four populations.ConclusionsAlthough most dwarf males have local origin, sporadic dispersal events occur. The ability of the dwarf males to establish in high numbers in mature colonies facilitates gene flow between populations as well as increases the potential to accumulate genetic diversity within populations.
Highlights
Nannandry is a sexual system where males (”dwarf males”) are much smaller than the conspecific females
We present a study of moss genetic population structure and genetic diversity that includes both dwarf males and normal-sized female shoots
In our study we aim to answer the following questions: 1) What is the genetic structure of dwarf males and females, within and between populations? 2) How are the dwarf males related to their female host shoot? 3) Are the levels of genetic diversity similar in female shoots and dwarf males? By answering these questions we hope to get a better understanding of the potential evolutionary advantages of the dwarf male sexual system
Summary
Nannandry is a sexual system where males (”dwarf males”) are much smaller than the conspecific females. The dwarf male sexual system results in differences in the mode of dispersal and establishment as well as the life span between males and females. Such differences must have profound effects on the population dynamics and genetic structures. I.e. the presence of dwarf males, is a breeding system that has evolved in many different organism groups and environments [1, 2] For such a sexual system to evolve, small males need to have higher fitness relative to larger males. Despite the fact that dwarf males in several moss species represent the majority of male individuals in the population, they have to date not been taken into
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