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Animal dispersal influences the community structure and diversity of a wide variety of plant taxa, yet the potential effects of animal dispersal in bryophytes (hornworts, liverworts, and mosses) is poorly understood. In many communities, birds use bryophyte-abundant niche space for foraging and gathering nest material, suggesting that birds may play a role in bryophyte dispersal. As highly motile animals with long migratory routes, birds potentially provide a means for both local and long-distance bryophyte dispersal in a manner that differs greatly from passive, aerial spore dispersal. To examine this phenomenon, we collected and germinated bryophyte propagules from the legs, feet and tails of 224 birds from 34 species within a temperate forest community. In total we found 1512 spores, and were able to germinate 242 bryophyte propagules. In addition, we provide evidence that topical (externally-carried) spore load varies by bird species and behaviour. Tail feather spore abundance is highest in bark and foliage gleaning species and is positively correlated with tarsal length. Together, these data suggest that a variety of forest birds exhibit the potential to act as dispersal vectors for bryophyte propagules, including an abundance of spores, and that understanding the effects of animal behaviour on bryophyte dispersal will be key to further understanding this interaction.

Dioecy and sexual dimorphism occur in many terrestrial plant species but are especially widespread among the bryophytes. Despite the prevalence of dioecy in non-vascular plants, surprisingly little is known about how fine-scale sex-specific cell and leaf morphological traits are correlated with sex-specific physiology and population sex ratios. Such data are critical to understanding the inter-relationship between sex-specific morphological and physiological characters and how their relationship influences population structure. In this study, these data types were assessed to determine how they vary across three populations within one moss species and whether fine-scale morphological traits scale up to physiological and sex ratio characteristics. Twenty cell-, leaf- and canopy-level traits and two photochemical measurements were compared between sexes and populations of the dioecious moss Ceratodon purpureus . Field population-expressed sex ratios were obtained for the same populations. Male and female plants differed in cell, leaf and photochemical measures. These sexual dimorphisms were female biased, with females having larger and thicker leaves and greater values for chlorophyll fluorescence-based, leaf photochemistry measurements than males. Female traits were also more variable than male traits. Interestingly, field population sex ratios were significantly male biased in two study populations and female biased in the third study population. The results demonstrate that the larger morphology and the greater physiological output of female C. purpureus gametophytes compared with males occurs across populations and is likely to have significant effects on resource allocation and biotic interactions. However, this high level of dimorphism does not explain population sex ratio variation in the three study populations tested. This research lays the groundwork for future studies on how differential sex-specific variation in cell and leaf traits influences bryophyte plant fitness.

Volatile scents of moss Ceratodon purpureus show sex-specific differences and are similar in chemical diversity to those of plant–insect pollination mutualisms; and moss-dwelling microarthropods, whose presence increases C. purpureus fertilization rates, prefer scents of reproductive female C. purpureus to reproductive males, indicating a scent-based ‘plant–pollinator-like’ relationship between mosses and microarthropods. Mosses and springtails in long-term relationship The complex relationships between flowering plants and insect pollinators are well known, but what about non-flowering plants, such as humble mosses? Moss reproduction depends on motile sperm swimming from males to females through a continuous water layer. Primitive insect-like microarthropods called springtails are known to help to disperse sperm, but it has not been clear whether this dispersal relies on happenstance. Sarah Eppley and colleagues show that springtails respond in a sex-specific way to a complex cocktail of flower-like scents released by mosses, revealing a pollination-like syndrome between moss and springtails. This is particularly intriguing given that mosses and springtails belong to the same lineages that pioneered the conquest of the terrestrial environment. Sexual reproduction in non-vascular plants requires unicellular free-motile sperm to travel from male to female reproductive structures across the terrestrial landscape 1 . Recent data suggest that microarthropods can disperse sperm in mosses 2 . However, little is known about the chemical communication, if any, that is involved in this interaction or the relative importance of microarthropod dispersal compared to abiotic dispersal agents in mosses. Here we show that tissues of the cosmopolitan moss Ceratodon purpureus emit complex volatile scents, similar in chemical diversity to those described in pollination mutualisms between flowering plants and insects, that the chemical composition of C. purpureus volatiles are sex-specific, and that moss-dwelling microarthropods are differentially attracted to these sex-specific moss volatile cues. Furthermore, using experimental microcosms, we show that microarthropods significantly increase moss fertilization rates, even in the presence of water spray, highlighting the important role of microarthropod dispersal in contributing to moss mating success. Taken together, our results indicate the presence of a scent-based ‘plant–pollinator-like’ relationship that has evolved between two of Earth’s most ancient terrestrial lineages, mosses and microarthropods.

• Sexual reproduction in mosses requires that sperm be released freely into the environment before finding and fertilizing a receptive female. After release from the male plant, moss sperm may experience a range of abiotic stresses; however, few data are available examining stress tolerance of moss sperm and whether there is genetic variation for stress tolerance in this important life stage. • Here, we investigated the effects of environmental desiccation and recovery on the sperm cells of three moss species (Bryum argenteum, Campylopus introflexus, and Ceratodon purpureus). • We found that a fraction of sperm cells were tolerant to environmental desiccation for extended periods (d) and that tolerance did not vary among species. We found that this tolerance occurs irrespective of ambient dehydration conditions, and that the addition of sucrose during dry‐down improved cell recovery. Although we observed no interspecific variation, significant variation among individuals within species in sperm cell tolerance to environmental desiccation was observed, suggesting selection could potentially act on this basic reproductive trait. • The observation of desiccation‐tolerant sperm in multiple moss species has important implications for understanding bryophyte reproduction, suggesting the presence of a significant, uncharacterized complexity in the ecology of moss mating systems.

Life persists, even under extremely harsh conditions. While the existence of extremophiles is well known, the mechanisms by which these organisms evolve, perform basic metabolic functions, reproduce, and survive under extreme physical stress are often entirely unknown. Recent technological advances in terms of both sampling and studying extremophiles have yielded new insight into their evolution, physiology and behavior, from microbes and viruses to plants to eukaryotes. The goal of the “Life on the Edge—the Biology of Organisms Inhabiting Extreme Environments” symposium was to unite researchers from taxonomically and methodologically diverse backgrounds to highlight new advances in extremophile biology. Common themes and new insight that emerged from the symposium included the important role of symbiotic associations, the continued challenges associated with sampling and studying extremophiles and the important role these organisms play in terms of studying climate change. As we continue to explore our planet, especially in difficult to reach areas from the poles to the deep sea, we expect to continue to discover new and extreme circumstances under which life can persist.

Bryophyte population sex ratios are predominately female-biased, at least with respect to plants expressing sexual structures. One hypothesis to explain this bias is that males produce sexual structures less often than females, but occur at similar frequencies, a hypothesis termed the “shy male hypothesis.” Another nonexclusive possibility is that offspring sex ratios (as sporelings) are biased and populations retain this bias. To test these hypotheses, we examined sex ratios in expressing and nonexpressing shoots for the cosmopolitan moss Bryum argenteum collected in the field, and in shoots grown from spores in the lab. An examination of 154 collections of B. argenteum from native habitats and urban settings in the USA revealed that populations were significantly female-biased (>80% female). Male rarity was most pronounced in aridland regions of the Mojave Desert and California chaparral; males were significantly more common in altered urban habitats and in high elevation native habitats. When all shoots from clumps representing three mixed-sex, sporophytic populations were grown to sex expression, male nonexpressing shoots were not found to be significantly more abundant than expected based on the field expressing shoot sex ratio, lending little support to the “shy male hypothesis.” Offspring sex ratios derived from sporelings were not significantly different from 1∶1, thus not explaining the sharply female-biased population ratios observed in the field. We propose that factors between spore germination and adult maturation, including clonal dynamics, are causing the female-biased population and within-clump sex ratio imbalance of B. argenteum.

Mosses inhabit nearly all terrestrial ecosystems and engage in important interactions with nitrogen‐fixing microbes, sperm‐dispersing arthropods, and other plants. It is hypothesized that these interactions could be mediated by biogenic volatile organic compounds (BVOCs). Moss BVOCs may play fundamental roles in influencing local ecologies, such as biosphere–atmosphere–hydrosphere communications, physiological and evolutionary dynamics, plant–microbe interactions, and gametophyte stress physiology. Further progress in quantifying the composition, magnitude, and variability of moss BVOC emissions, and their response to environmental drivers and metabolic requirements, is limited by methodological and analytical challenges. We review several sampling techniques with various analytical approaches and describe best practices in generating moss gametophyte BVOC measures. We emphasize the importance of characterizing the composition and magnitude of moss BVOC emissions across a variety of species to better inform and stimulate important cross‐disciplinary studies. We conclude by highlighting how current methods could be employed, as well as best practices for choosing methodologies.

The evolution of sustained plant–animal interactions depends critically upon genetic variation in the fitness benefits from the interaction. Genetic analyses of such interactions are limited to a few model systems, in part because genetic variation may be absent or the interacting species may be experimentally intractable. Here, we examine the role of sperm-dispersing microarthropods in shaping reproduction and genetic variation in mosses. We established experimental mesocosms with known moss genotypes and inferred the parents of progeny from mesocosms with and without microarthropods, using a pooled sequencing approach. Moss reproductive rates increased five-fold in the presence of microarthropods, relative to control mesocosms. Furthermore, the presence of microarthropods increased the total number of reproducing moss genotypes, and changed the rank-order of fitness of male and female moss genotypes. Interestingly, the genotypes that reproduced most frequently did not produce sporophytes with the most spores, highlighting the challenge of defining fitness in mosses. These results demonstrate that microarthropods provide a fitness benefit for mosses, and highlight the potential for biotic dispersal agents to alter fitness among moss genotypes.

The need for reproductive assurance during dispersal, along with the pressure of local mate competition, means that the importance of frequent or repeated colonization is implicit in the sexual‐system evolution literature. However, to date there have been few empirical tests of the association between colonization and the sexual system in plants. Here we provide such a test by comparing occupancy and abundance of populations of the European plantMercurialis annuaacross regions characterized by different sexual systems. Specifically, we predicted that monomorphic, hermaphroditic populations, which are thought to have evolved under selection for reproductive assurance during repeated bouts of colonization, would be smaller and their suitable habitat less frequently occupied than dimorphic populations, where males co‐occur with either females or hermaphrodites. We show that both of these predictions are upheld. We evaluate our results against competing hypotheses for the occupancy‐abundance relationship and conclude that they are most consistent with the metapopulation model for sexual‐system variation inM. annua.