Geographical range in liverworts: does sex really matter?

Abstract

Aim Why some species exhibit larger geographical ranges than others remains a fundamental, but largely unanswered, question in ecology and biogeography. In plants, a relationship between range size and mating system was proposed over a century ago and subsequently formalized in Baker's Law. Here, we take advantage of the extensive variation in sexual systems of liverworts to test the hypothesis that dioecious species compensate for limited fertilization by producing vegetative propagules more commonly than monoecious species. As spores are assumed to contribute to random long-distance dispersal, whereas vegetative propagules contribute to colony maintenance and frequent short-distance dispersal, we further test the hypothesis that monoecious species exhibit larger geographical ranges than dioecious ones.Location Worldwide.Methods We used comparative phylogenetic methods to assess the correlation between range size and life history traits related to dispersal, including mating systems, spore size and production of specialized vegetative propagules.Results No significant correlation was found between dioecy and production of vegetative propagules. However, production of vegetative propagules is correlated with the size of geographical ranges across the liverwort tree of life, whereas sexuality and spores size are not. Moreover, variation in sexual systems did not have an influence on the correlation between geographical range and production of asexual propagules. Main conclusionsOur results challenge the long-held notion that spores, and not vegetative propagules, are involved in long-distance dispersal. Asexual reproduction seems to play a major role in shaping the global distribution patterns of liverworts, so that monoecious species do not tend to display, on average, broader distribution ranges than dioecious ones. Our results call for further investigation on the spatial genetic structure of bryophyte populations at different geographical scales depending on their mating systems to assess the dispersal capacities of spores and asexual propagules and determine their contribution in shaping species distribution ranges.

Increased diversification rates follow shifts to bisexuality in liverworts

“…Even though this hypothesis has been recently challenged by some evidence that specialized asexual diaspores may also contribute to long-distance dispersal across liverworts (Laenen et al, 2015), Heilbuth's hypothesis remains consistent with the observation that bisexual bryophytes are proportionally more common on oceanic islands than on continents, not because of the in situ evolution of bisexuality, but because bisexual species produce a greater number of sporophytic capsules (Patiño et al, 2013). Hence, larger numbers of spores are potentially able to reach oceanic islands owing to random long-distance dispersal, which is precisely the main driver of speciation in organisms, such as bryophytes, that typically fail to radiate and slowly diversify by genetic drift in allopatry (Patiño et al, 2014;.…”

Biological traits explain bryophyte species distributions and responses to forest fragmentation and climatic variation

“…Löbel & Rydin, ; Pohjamo, Laaka‐Lindberg, Ovaskainen, & Korpelainen, ). So far, links between reproduction modes or other life‐history traits and ecological niches have not yet been established (see Laenen et al., ). In contrast, morphologies, that is, bryophyte life‐forms (Bates, ), have been traditionally assumed to be strongly correlated with moisture supply and light conditions.…”

Multiple transoceanic dispersals and geographical structure in the pantropical leafy liverwort Ceratolejeunea (Lejeuneaceae, Porellales)

“…In agreement with this is the occurrence of typical bryophyte island syndromes, which indicate that the ocean is a barrier to gene flow (Patiño et al ., ). Important traits influencing the intensity of dispersal and thus gene flow in bryophytes may be the size, quantity and durability of spores as well as the level of asexual reproduction through vegetative propagules capable of dispersal by wind (Van Zanten & Gradstein, ; Van der Velde & Bijlsma, , ; Laenen et al ., ). Although vegetative propagules are commonly implicated in short‐distance dispersal (Löbel et al ., ), they can also facilitate LDD (Pohjamo et al ., ).…”