Gemma output in the liverwortLophozia ventricosa(Dicks.) Dumort: spatial variation, density dependence, and relationships among production components

Abstract

Although gemma production is common among liverworts, and thought to play a key role in their population dynamics, quantitative data on numbers produced at shoot and colony levels, or on spatial variation in these numbers, are very sparse. Here we investigate gemma output of a boreal and arctic liverwort species, Lophozia ventricosa, at populations in Trøndelag, a boreal region of central Norway, and in arctic tundra on Svalbard. Production parameters investigated include colony size, shoot density, number of gemmae per shoot, proportion of shoots gemmiferous, and gemmiferous shoot density. Colony-level output was calculated as the product of the number of gemmae per shoot, colony size, and gemmiferous shoot density. Nested analysis of variance, used to spatially partition variance in these gemma-production components, reveals that the vast majority of the variation lies at the measurement level, i.e. among shoots within colonies or among colonies within plots. The only significant difference between the two geographic areas is that in boreal sites shoots tend to produce slightly more gemmae, and form larger, denser, colonies. This translates to somewhat higher colony-level output in boreal, compared to arctic, sites. Evaluation of a structural equations model reveals intricate patterns of relationship among the production components and provides strong evidence of negative density dependence of shoot-level production. We argue that explicit evaluation of size-number tradeoffs, allometric scaling of production with shoot size, and detailed studies of genetic versus phenotypic effects on production levels, are necessary to understand how asexual propagule production is shaped by selection on life histories.

Differences in species–area relationships among the major lineages of land plants: a macroecological perspective

“…In addition, liverworts produce more specialized asexual diaspores than mosses or pteridophytes (Mehltreter et al, 2010;Patiño et al, 2013a). In the British flora, for example, 46% of liverwort species but only 18% of moss species produce specialized asexual diaspores (Algar-Hedderson et al, 2013). Compared with spores, asexual diaspores allow for higher rates of successful establishment due to their lower sensitivity to habitat quality and, importantly, earlier and higher germination rates (Löbel & Rydin, 2010).…”

Geographical range in liverworts: does sex really matter?

“…In contrast, vegetative propagules are produced continuously and exhibit a larger size than spores (Schuster & Longton, , but see Pohjamo et al ., ) and do not have mechanisms that promote their release. They are, therefore, thought to contribute mainly to colony maintenance and short‐distance dispersal (Longton & Schuster, ; Kimmerer, , ; Longton, ; Löbel et al ., ; Algar‐Hedderson et al ., ). Consequently, if these assumptions are correct, geographical range should correlate with sexual condition and, given that long‐distance dispersal depends on spores, monoecious species should have larger ranges than dioecious species (see Longton & Schuster, for review).…”

Rainfall and gemmiferous shoots influence asexual reproduction in two tropical mosses

“…The production of specialized asexual propagules, such as gemmae, is crucial in bryophyte population dynamics because it contributes to the occupation of nearby areas with similar habitats. Gemma production may be influenced by environmental variables, like rainfall, and colony features such as colony size, number of shoots able to produce gemmae, i.e., gemmiferous shoots and the place of gemma formation on the leaf (Laaka-Lindberg 1999, Algar-Hedderson et al 2013. Reports on tropical Calymperaceous mosses indicate that gemma output responds to seasonal patterns where more gemmae are produced during constant rainfall (Odu & Owotomo 1982, Egunyomi & Olarinmoye 1983, Cerqueira et al 2016.…”

“…Shoot density, or the number of shoots per area, could be a good estimator of the gemma production. For temperate bryophytes, shoot density and gemma production could be negatively correlated (Kimmerer 1991b, Algar-Hedderson et al 2013, or they do not seem to have a significant effect (Laaka-Lindberg 1999). In contrast, the number of gemmiferous shoots a species can produce is variable and positively correlated with gemma output.…”

“…The gemma development could also be controlled by the occurrence of sexual structures (antheridia and archegonia) and sporophytes, suggesting a trade-off between sexual versus asexual reproduction modes. In some species, shoots developing gametangia and sporophytes produce fewer or no asexual propagules than sterile shoots (Kimmerer 1994, Laaka-Lindberg 2001, Manyanga et al 2011, Algar-Hedderson et al 2013, dos Santos et al 2022. In Camlyperaceous species of lowland Amazonia, the number of archegonia and perichaetia (male sexual branch) per shoot was lower when gemmae co-occurred (Pereira et al 2016), suggesting differential resource allocation for modes of reproduction.…”