Long-lived sperm in the geothermal bryophyte Pohlia nutans

Abstract

Non-vascular plants rely on sperm to cross the distance between male and female reproductive organs for fertilization and sexual reproduction to occur. The majority of non-vascular plants have separate sexes, and thus, this distance may be a few millimetres to many metres. Because sperm need water for transport, it has been assumed that sperm lifespans are short and that this type of sexual reproduction limits the expansion of non-vascular plants in terrestrial environments. However, little data is available on the lifespan of sperm in non-vascular plants, and none is available for bryophytes, the group thought to have first colonized terrestrial habitats. Here, we documented the lifespan of sperm of Pohlia nutans, collected from a geothermal spring's area, and tested the effects of variation under environmental conditions on this lifespan. Surprisingly, 20 per cent of the sperm were still motile after 100 h, and sperm lifespan was not significantly affected by temperature variation between 22 and 608 8 8 8 8C. Lifespan was significantly affected by sperm dilution and temperatures above 758 8 8 8 8C. These results suggest the need to reconsider the importance of sperm motility in bryophyte fertilization.

Tolerance to environmental desiccation in moss sperm

“…As our measure of sperm tolerance to desiccation, we report sperm cell integrity rather than sperm motility, which we have used previously (Rosenstiel & Eppley, 2009), for two reasons: the ability of bryophytes to regain cellular integrity after desiccation has been well studied (Oliver et al, 2005); and, in further assessing moss spermatozoa systems, we have become aware of high variance in sperm motility; we have documented bimodal distributions within individuals for all three species in this study (E. E. Shortlidge, T. N. Rosenstiel & S. M. Eppley, unpublished). We believe that future studies should examine the relationship between sperm motility and viability in bryophytes.…”

“…Sperm extraction from all species began with the selection of three to 20 perigonia per plant as described in Rosenstiel & Eppley (2009). Briefly, all sperm extractions and rehydrations were performed using locally collected rainwater (average (± SEM) pH: 6.0 ± 0.09) that was frozen and filtered and supplemented with tetracycline (20 lg ml )1 ) to deter bacterial growth (Rosenstiel & Eppley, 2009).…”

“…Briefly, all sperm extractions and rehydrations were performed using locally collected rainwater (average (± SEM) pH: 6.0 ± 0.09) that was frozen and filtered and supplemented with tetracycline (20 lg ml )1 ) to deter bacterial growth (Rosenstiel & Eppley, 2009). Perigonia were placed in a small pool (c. 10 ll per perigonium) of rainwater on multiple glass microscope slides and gently agitated with curve-tipped forceps to encourage the sperm masses to release from the antheridial jackets.…”

“…Working forward from these studies in combination with what we know about the daily stresses of many mosses, it seems pertinent to investigate the effects of stress on the reproductive cycle of mosses. To our knowledge, only one previous study has examined the impacts of environmental stress on moss sperm (Rosenstiel & Eppley, 2009). This study found that sperm cells of the geothermal moss Pohlia nutans exhibit remarkable thermotolerance, with cells maintaining integrity at temperatures of 60°C.…”

Passive warming reduces stress and shifts reproductive effort in the Antarctic moss,Polytrichastrum alpinum

“…However, recent studies showed that dioicous mosses are more genetically diverse than would be expected with such dispersal limitation (Wyatt et al, 1989;Van der Velde et al, 2001;Wilson and Provan, 2003). Indeed several studies have since demonstrated greater sperm dispersal distances (for a review, see Glime, 2007), as well as stresstolerant sperm (Rosenstiel and Eppley, 2009;Shortlidge et al, 2012) and microarthropod-mediated sexual reproduction (Cronberg et al, 2006;Cronberg, 2012;Rosenstiel et al, 2012). Other factors can limit sexual reproduction in mosses, including: inadequate resources (Stark et al, 2000) growth trade-offs (Ehrlén et al, 2000) and investment in environmental stress defence (Convey and Smith, 1993;Stark et al, 2009;Eppley et al, 2011).…”