Isogamy in large and complex volvocine algae is consistent with the gamete competition theory of the evolution of anisogamy

Silva, Jack da; Drysdale, Victoria

doi:10.1098/rspb.2018.1954

Cited by 10 publications

(10 citation statements)

References 27 publications

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“…The PBS theory [ 1 ] is an explanation for one of the most consequential transitions in evolutionary history, shaping much of subsequent evolution and much of life as we now know it [ 2 ]. It is arguably the most widely accepted theory for this transition and for the evolutionary origin of the two sexes, with growing but as yet tentative empirical support [ 38 , 43 , 44 , 45 , 46 ]. The focus of this article has been not on the external empirical evidence, but on the internal robustness of the theory to various modifications of its assumptions.…”

Section: Discussionmentioning

confidence: 99%

The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness

Lehtonen

2021

Cells

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The evolution of anisogamy or gamete size dimorphism is a fundamental transition in evolutionary history, and it is the origin of the female and male sexes. Although mathematical models attempting to explain this transition have been published as early as 1932, the 1972 model of Parker, Baker, and Smith is considered to be the first explanation for the evolution of anisogamy that is consistent with modern evolutionary theory. The central idea of the model is ingenious in its simplicity: selection simultaneously favours large gametes for zygote provisioning, and small gametes for numerical competition, and under certain conditions the outcome is anisogamy. In this article, I derive novel analytical solutions to a 2002 game theoretical update of the 1972 anisogamy model, and use these solutions to examine its robustness to variation in its central assumptions. Combining new results with those from earlier papers, I find that the model is quite robust to variation in its central components. This kind of robustness is crucially important in a model for an early evolutionary transition where we may only have an approximate understanding of constraints that the different parts of the model must obey.

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Section: Discussionmentioning

confidence: 99%

The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness

Lehtonen

2021

Cells

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“…Both isogamy and anisogamy are found in small unicellular species and large multicellular species within a wide size range (see fig. 2 in [ 52 ]). The retention of isogamy in large multicellular species has been explained as a consequence of a low gamete encounter rate: gametes are constrained to be large because well-provisioned gametes are needed to survive for extended periods before sexual fusion [ 52 ].…”

Section: Discussionmentioning

confidence: 99%

“…2 in [ 52 ]). The retention of isogamy in large multicellular species has been explained as a consequence of a low gamete encounter rate: gametes are constrained to be large because well-provisioned gametes are needed to survive for extended periods before sexual fusion [ 52 ]. However, anisogamy in small unicellular species remains unexplained.…”

Section: Discussionmentioning

confidence: 99%

A comparative test of the gamete dynamics theory for the evolution of anisogamy in Bryopsidales green algae

2021

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Gamete dynamics theory proposes that anisogamy arises by disruptive selection for gamete numbers versus gamete size and predicts that female/male gamete size (anisogamy ratio) increases with adult size and complexity. Evidence has been that in volvocine green algae, the anisogamy ratio correlates positively with haploid colony size. However, green algae show notable exceptions. We focus on Bryopsidales green algae. While some taxa have a diplontic life cycle in which a diploid adult (=fully grown) stage arises directly from the zygote, many taxa have a haplodiplontic life cycle in which haploid adults develop indirectly: the zygote first develops into a diploid adult (sporophyte) which later undergoes meiosis and releases zoospores, each growing into a haploid adult gametophyte. Our comparative analyses suggest that, as theory predicts: (i) male gametes are minimized, (ii) female gamete sizes vary, probably optimized by number versus survival as zygotes, and (iii) the anisogamy ratio correlates positively with diploid (but not haploid) stage complexity. However, there was no correlation between the anisogamy ratio and diploid adult stage size. Increased environmental severity (water depth) appears to drive increased diploid adult stage complexity and anisogamy ratio: gamete dynamics theory correctly predicts that anisogamy evolves with the (diploid) stage directly provisioned by the zygote.

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“…Graham Bell’s wider surveys in 1978 and 1982 across algal and protozoan taxa offered broad support, though the predicted correlation between the degree of anisogamy and organismal complexity is less distinct across other groups of algae [ 96 , 114 ]. Some anomalies exist, and current efforts seek to explain why this is so [ 110 , 115 ].…”

Section: The Evolution Of Gamete Dimorphism and Two Sexes: “Pbs”mentioning

confidence: 99%

How Soon Hath Time… A History of Two “Seminal” Publications

Parker

2021

Cells

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This review documents the history of the two papers written half a century ago that relate to this special issue of Cells. The first, “Sperm competition and its evolutionary consequences in the insects” (Biological Reviews, 1970), stressed that sexual selection continues after ejaculation, resulting in many adaptations (e.g., postcopulatory guarding phases, copulatory plugs, seminal fluid components that modify female reproduction, and optimal ejaculation strategies), an aspect not considered by Darwin in his classic treatise of 1871. Sperm competition has subsequently been studied in many taxa, and post-copulatory sexual selection is now considered an important sequel to Darwinian pre-copulatory sexual selection. The second, “The origin and evolution of gamete dimorphism and the male-female phenomenon” (Journal of Theoretical Biology, 1972) showed how selection, based on gamete competition between individuals, can give rise to anisogamy in an isogamous broadcast spawning ancestor. This theory, which has subsequently been developed in various ways, is argued to form the most powerful explanation of why there are two sexes in most multicellular organisms. Together, the two papers have influenced our general understanding of the evolutionary differentiation of the two forms of gametic cells, and the divergence of sexual strategies between males and females under sexual selection.

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Isogamy in large and complex volvocine algae is consistent with the gamete competition theory of the evolution of anisogamy

Cited by 10 publications

References 27 publications

The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness

The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness

A comparative test of the gamete dynamics theory for the evolution of anisogamy in Bryopsidales green algae

How Soon Hath Time… A History of Two “Seminal” Publications

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