Environmental mutagenesis during the end-Permian ecological crisis

Abstract

During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism.

Aberrant Classopollis pollen reveals evidence for unreduced (2 n ) pollen in the conifer family Cheirolepidiaceae during the Triassic–Jurassic transition

“…WGD events may have lowered extinction risks during mass extinction events, such as at the Cretaceous-Paleogene boundary some 65 Ma [47]. We suggest that similar to aberrant lycophyte spores [48] and conifer pollen [49], during the end-Permian mass extinction aberrant Classopollis pollen may indicate environmental mutagenesis during the end-Triassic mass extinction. Extensive volcanism of the Central Atlantic magmatic province during the Triassic-Jurassic transition is generally viewed as a trigger mechanism of this global biotic crisis by extreme climate transitions [50].…”

The complexity of mass extinction

“…2b, they depended on water and represented vegetation that was certainly much less dense and had a lower biomass than the forests they replaced. Visscher et al (1) report that a significant percentage of microspores of these plants occurs as tetrads, which means that the four microspores that originate from one mother cell do not separate and are clumped together in the very place that opens during spore germination, indicating that they were not viable. It has been established in living plants that specific genetic changes are required to achieve this effect (3,4).…”

“…It is undisputed that the Permian-Triassic boundary extinction was not a single-step event and that the crisis lasted for 5-8 million years (9). Visscher et al (1) do not even consider an impact because they are describing a multiphase event that extended over a significant amount of time at the end of the Permian Period. Their explanation lies in the volcanism that occurred in a part of the globe that is opposite the impact but not antipodal.…”

“…One important insight has been the recognition that each event was different and very complex in itself. In this issue of PNAS, Visscher et al (1) add an astonishing insight into effects on the genetic material of plants during the most devastating of all mass extinctions 251 million years ago (2). The results of Visscher et al (1) document a complex chain of cause and effect relationships that occurred not as a single pulse but over a significant time span.…”

“…In this issue of PNAS, Visscher et al (1) add an astonishing insight into effects on the genetic material of plants during the most devastating of all mass extinctions 251 million years ago (2). The results of Visscher et al (1) document a complex chain of cause and effect relationships that occurred not as a single pulse but over a significant time span. The forests of gymnosperms that covered large areas of most climate zones of the late Permian Period disappeared and were replaced by herbaceous lycopsids (mostly relatives of quillworts) represented frequently only by the genus Pleuromeia covering the landscape with a rather monotonous vegetation (Fig.…”