Platyzoma-A Queensland Fern with Incipient Heterospory

Tryon, Alice F.

doi:10.2307/2440244

Cited by 31 publications

(20 citation statements)

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“…This fossil history and the fact that Isoetes and the heterosporous water ferns are aquatic plants led Bateman & DiMichele () to suggest that heterospory is favoured in ‘aquatic–amphibious habitats’. More supporting evidence comes from Platyzoma microphyllum which appears in ephemeral water‐edge habitats in the wet season of northern Queensland (Tryon, ; DiMichele, Davis & Olmstead, ).…”

Section: Heterospory In Aquatic and Amphibious Environmentsmentioning

confidence: 99%

“…Spore size would likely have interacted with sexual expression in the gametophyte stage. Even today, the mechanisms by which gametophytes produce only antheridia or archegonia are not well understood (Banks, ), but experimental evidence going back to the 19th century has long indicated that environmental conditions affecting gametophytic growth and longevity can affect sexual expression in normally bisexual or unisexual gametophytes (Shattuck, ; Tryon, ). This finding accords with the Haig & Westoby () model, which starts from the assumption that only larger gametophytes would have the resources to sustain egg production and eventual provisioning of an embryo, while smaller gametophytes would produce only sperm.…”

Section: Nutrients and Spore Sizementioning

confidence: 99%

“…Although the universally heterosporous angiosperms are now the dominant lineage of land plants, they possess other features that contribute to their evolutionary success (Bodribb, Feild & Sack, ). A fourth instance of heterospory may be seen in the weakly developed heterospory of the leptosporangiate fern Platyzoma microphyllum – weak because size differentiation is not pronounced and unisexuality is inconsistent (‘megagametophytes’ that initially produce eggs can later produce sperm), and because gametophytes are free‐living, photosynthetic plants, unlike the endosporic gametophytes of the three major heterosporous groups (Tryon, ). Platyzoma , thought to be of recent origin, is monotypic (Tryon, ).…”

Section: Introductionmentioning

confidence: 99%

“…A fourth instance of heterospory may be seen in the weakly developed heterospory of the leptosporangiate fern Platyzoma microphyllum – weak because size differentiation is not pronounced and unisexuality is inconsistent (‘megagametophytes’ that initially produce eggs can later produce sperm), and because gametophytes are free‐living, photosynthetic plants, unlike the endosporic gametophytes of the three major heterosporous groups (Tryon, ). Platyzoma , thought to be of recent origin, is monotypic (Tryon, ). Although patterns of diversity in the geological past have differed greatly from current diversity, of course, it is clear from the species richness in these groups that heterospory has not, by itself, been an automatic key to evolutionary success (Duckett & Pang, ).…”

Section: Introductionmentioning

confidence: 99%

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Why did heterospory evolve?

Petersen

Burd

2016

Biological Reviews

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The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation-resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation - an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life-history patterns - suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm-producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency-dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re-invention of anisogamy within the context of a sporophyte-dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate-encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re-establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation.

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Section: Heterospory In Aquatic and Amphibious Environmentsmentioning

confidence: 99%

Section: Nutrients and Spore Sizementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Why did heterospory evolve?

Petersen

Burd

2016

Biological Reviews

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show abstract

“…The homosporous fern Platyzoma shows a bimodal distribution of spore size with the smaller spores developing into male gametophyte and the larger spores developing into female ganetophytes. It has been proposed that this species shows "incipient heterospory" (Tryon, 1964;Tryon and Vida, 1967).…”

Section: Gametophyte Sexualitymentioning

confidence: 99%