Fitness of an allopolyploid rupicolous fern compared with its diploid progenitors: from sporogenesis to sporophyte formation

Abstract

Premise When two populations of related cytotypes grow in sympatry, the rarer cytotype tends to be excluded due to a frequency‐dependent mating disadvantage. Evolutionary models predict that polyploids, which are typically the rarer cytotype upon first formation, should have higher relative fitness and/or higher selfing rates to establish and then coexist with diploid parents. Methods Performance during early recruitment was compared among three co‐occurring rupicolous fern species: the allotetraploid Cheilanthes tinaei and its diploid ancestors, C. hispanica and C. maderensis. In culture experiments, fresh spores and samples of soil spore banks were tested for variation among cytotypes in germination, survival, fecundity, and mating system of gametophytes. Results Compared with its diploid parents, C. tinaei fresh spores had higher abortion percentages, lower dispersal ability as a result of its larger spores, and similar vigor at germination. For gametophytes from soil spore banks, C. tinaei had high survival similar to C. maderensis, but its sex expression resembled that of C. hispanica, with a high proportion of males. Patterns of sporophyte formation by females and bisexuals indicate that the polyploid does not have an increased gametophytic selfing rate. Gametophytes were larger in C. tinaei, but its reproductive success (sporophyte formation) was intermediate relative to diploids. Conclusions Our results show no evidence of higher selfing or fitness advantage of the allopolyploid over both diploid parents at any stage of early recruitment. These two unexpected findings suggest that further factors, such as niche differentiation, play a more important role in cytotype coexistence.

Leaf structure and water relations of an allotetraploid Mediterranean fern and its diploid parents

“…shows cell enlargement due to genome doubling is not supported by these results. Consistent with this finding, the cell size of HHPP gametophytes is within the range of variation of HH and PP, while spores are larger in the allopolyploid (Pangua et al, 2019).…”

Ecophysiological Differentiation among Two Resurrection Ferns and Their Allopolyploid Derivative

“…HHPP exhibits substantial sympatry with both progenitors, which suggests that its niche is intermediate to those of its parents in terms of breadth and abiotic tolerances [ 17 ]. Indeed, in the localities where the three cytotypes coexist, there is some spatial segregation between them, which tend to form unmixed aggregates [ 40 ]. All three species inhabit siliceous rocks that are highly exposed to the sun, but PP grows on shallow soils, HH occupies crevices and concavities with hardly any soil, and HHPP is in intermediate microhabitats and sometimes grows in close proximity to one of the parents.…”

Apomictic fern fathers: an experimental approach to the reproductive characteristics of sexual, apomict, and hybrid fern gametophytes

“…Similarly, the percentage of meristic gametophytes (possessing lateral meristem; Figure 1A) was calculated using 50 gametophytes (ungerminated spores excluded) per dish every week for four weeks following the emergence of meristic gametophytes for a given species (week 3 or 4 of cultivation). Every two weeks, from week 6 to week 16, at least 10 gametophytes (rarely minimum 5 if too few were present) from each dish were stained with 1% acetocarmine for ≥30 min (similar to Pangua et al [2019] but without the heating) and subsequently observed for the presence of gametangia under a light microscope. The gametophytes were scored as either asexual, male, female, or hermaphroditic, based on the presence or absence of antheridia and archegonia (Figure 1B, C).…”