Exploring the deep-time roots of plant diversity

The origin of vascular plants, more than 400 million years ago, changed the surface of our planet forever.

Beginning with small, simple, and grass-like ancestors, vascular plants (land plants that have lignified tissues for conducting water and minerals) evolved a huge variety of body plans. The conquest of land by early plants contributed to the establishment of the first terrestrial ecosystems and biogeochemical cycles.

Their astounding diversity – including 250,000 extant species ranging from clubmosses to sunflowers and from grass clumps to gigantic trees – is an example of a major adaptive radiation, where organisms diversify rapidly into a multitude of new forms.

A new study in the prestigious journal Earth-Science Reviews attempts to answer a number of questions relating to plant evolution.

Academics from Peking University, China, the University of Lincoln, UK, and the University of Bristol looked in detail at patterns of shape diversification in the leaves of early vascular plants, using a dataset of more than 300 fossil species from South China, ranging in age from 400 to 252 million years ago.

Key to the success of vascular plants is the origin of leaves, their primary light-harvesting organs. Leaves come in a huge variety of shapes and sizes, but how was this diversity attained? Did it reflect key environmental and climatic changes? And did modifications in leaf structure follow similar patterns around the world?

The team, led by Dr Jinzhuang Xue (Peking University), Dr Marcello Ruta (University of Lincoln), and Professor Mike Benton (University of Bristol), examined dozens of traits describing leaf shape and proportions, venation patterns (arrangement of leaf veins), and many others. The scientists were able to identify a stepwise increase in the complexity of leaves, marking two distinct phases in the evolution of early vascular plants.

Dr Xue explained: “During the first phase of plant evolution, from 400 to 320 million years ago, plants began to invade largely empty ecological spaces, and this process was presumably favoured by the lack of intense competition. In this phase, the complexity of simple and compound leaves increased gradually, in tune with an increase in species richness, an elaboration of plant body’s architecture, and the appearance of several floral types, such as shrubs, lianas, groundcovers, and trees of various sizes. During the second phase of plant evolution, from 320 to 252 million years ago, simple leaves increased again in complexity, while the complexity of compound leaves appeared to stabilize. New plant groups made their first appearance, particularly climbing and scrambling plants of humid habitats with leaves resembling those of several modern flowering plants in size, shape, and venation. Towards the end of this phase, we see a twofold increase in species richness, but no further expansion in the range of leaf types.”

Professor Benton said: “The study has revealed other unexpected findings. First, some groups of early vascular plants from South China developed large laminate leaves (leaves with a conspicuous blade) much earlier than their close relatives in Europe and North America. Second, despite a drop in species diversity some 320 to 300 million years ago, the complexity of leaves remained unaffected during that interval.”

Dr Ruta, from the University of Lincoln’s School of Life Sciences, added: “Overall, species richness and leaf complexity appeared decoupled during the 150 million years of evolution of early terrestrial plants from South China. Considerable experimentation drove initial stages of plant evolution in ecologically undersaturated and low-competition landscapes, with key changes occurring in plant anatomy and physiology including a remodelling of leaf architecture. Later stages of plant evolution witnessed massive changes in floristic composition, an explosion of plant types apparently matching the expansion of wetland communities, and increased specialisations in ecological roles of different plant groups.”

Experts meet to delve into the world of the early tetrapod

Paleontologist Dr Marcello Ruta is to give a talk at the latest meeting of a research project group which studies the early evolution and diversification of tetrapods.

The Tetrapod World: early evolution and diversification (TW:eed) Project is a scientific research project studying fossils and environments from the Early Carboniferous Tournaisian Stage, roughly 350 million years ago.

Teams of experts are collaborating to study some spectacular newly-discovered fossils which will fill in a significant gap (Romer’s Gap) in our understanding of how tetrapods moved from water onto land, the other animals and plants that existed at that time, and the environment in which these changes took place.

Dr Ruta, from the University of Lincoln’s School of Life Sciences, is a partner in the project. His scientific interests include the emergence and radiation of major animal groups, particularly early tetrapods, various aspects of morphological diversification, and patterns from the fossil record as a key to understanding crucial episodes in the history of life.

The TW:eed Project is studying not just the tetrapods, but also the fish, plants and invertebrates, the environments in which the organisms lived and the way they evolved from the survivors of the extinction event to the relatively modern-looking animals that we see later in the Carboniferous.

Dr Ruta will present Cladistic analysis of four Tournaisian tetrapods at the next TW:eed meeting at the Department of Zoology, University of Cambridge, on 7th and 8th May, 2015.

Image: Acanthostega – one of the earliest and most primitive tetrapods. Credit University Museum of Zoology, Cambridge.

How many ways are there to measure biological shape?

New research supports the use of cladistic data for quantifying the range of skull variation in a group of legless amphibians – the caecilians.

The rich and diverse array of biological shapes around us is astounding. Shape, however, may be an elusive concept. What do we actually measure, and how?

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, UK, was part of a team who conducted an exploratory study of morphological disparity (i.e. range of shape variation), employing both traits that are used for reconstructing evolutionary family trees and geometric morphometric approaches. For their study, they used caecilians, a group of superficially earthworm-like amphibians distributed in the tropical regions of the southern hemisphere.

Cladistics is a branch of systematics (the field of biological classification) that seeks to reconstruct evolutionary family trees using information on characters (traits) observed in organisms and grouping them together based on whether or not they share unique characteristics inherited from a common ancestor. However, those traits hold great promise in that they can also be employed to quantify morphological differences, and these differences are the basis for analyses of shape disparity.

Traditionally, morphometric analyses can be used for quantifying disparity, for instance via linear measurements or constellations of data points, or landmarks. However, cladistic data offer a bonus, in that they can be used when measurements or landmarks cannot be readily applied to vastly divergent organisms.

Dr Ruta said: “Analyses of disparity requires a scalable comparative framework. The difficulties of applying geometric morphometrics to disparity analyses of groups with vastly divergent body plans are overcome partly by the use of cladistic characters. In all instances, we found no statistically significant difference. This suggests that cladistic and geometric morphometric data appear to summarise morphological variation in comparable ways. Our results support the use of cladistic data for characterising organismal disparity.”

The paper ‘Do cladistic and morphometric data capture common patterns of morphological disparity?’ has been published in the journal Palaeontology.

Investigating the diversity of sea-urchins

Research into sea-urchin fossils collected from Portugal has revealed that diversity of the taxa seems to be linked with the evolution of the sea basin.

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, UK, was part of the team which investigated how echinoid (sea-urchin) diversity changed through the Mesozoic period – 252 to 66 million years ago.

They focussed on a comprehensive database of fossil specimens from the Lusitanian and Algarve basins in Portugal.

A long-standing debate in current paleobiological research concerns the significance of global diversity patterns retrieved from raw counts of fossils through time, and numerous quantitative studies of the quality of the fossil record have concluded that fossil diversity is biased by many factors.

In this study, researchers chose to focus on a regionally restricted, but well sampled series of echinoids from Portugal in order to control for certain biases.

The aim was to explore the nature of the Portuguese echinoid fossil record, by investigating the palaeodiversity signal and comparing it with the already documented echinoderm record from the same era from the UK.

The research revealed that the diversity pattern is far from having a defined trend, showing many fluctuations that appear to be linked with gaps in the geological record.

Dr Ruta concluded: “Echinoid diversity during the Mesozoic in the Lusitanian basin is far from having a general trend, differing from previous global studies in other taxonomic groups. Many of the variations in diversity seem to be linked to basinal discontinuities and, therefore, with the evolution of the basin. Furthermore, the temperature and sea level changes appear to have had very little influence on echinoid diversity.”

The study ‘Mesozoic echinoid diversity in Portugal: Investigating fossil record quality and environmental constraints on a regional scale’ is published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

The fossil sea-urchin Acrosalenia. Photo courtesy: Professor Andrew B. Smith, The Natural History Museum, London
The fossil sea-urchin Acrosalenia. Photo courtesy: Professor Andrew B. Smith, The Natural History Museum, London

Researchers go Back to Science thanks to new Fellowships

Two researchers have been awarded science Fellowships from the University of Lincoln, worth up to £21,000.

The University of Lincoln, UK, established the Back to Science Fellowships as part of its commitment to the Athena SWAN Charter, which supports women in science, technology, engineering, mathematics and medicine. Physicist Fiona Bissett and ecologist Dr Graziella Iossa have been selected to receive the first two awards and, as a result, they are now undertaking research projects alongside academic colleagues in Lincoln’s College of Science.

The Back to Science Fellowships have been designed to support researchers from science backgrounds who have taken extended career breaks, perhaps to start a family, who wish to resume their academic careers.

They consist of a £16,000 bursary with a further £5,000 available for consumable costs, such as travel or equipment. They can be taken over one or two years, to enable part-time work.

Fellows work with experienced academics in established research groups, enabling them to build confidence and develop contemporary research experience. Two scholarships are available each academic year until 2017.

Fiona obtained her undergraduate degree in Computational Physics from Heriot-Watt University in Edinburgh in 2001.

She will be working on a Computational Physics project with Dr Manuela Mura in Lincoln’s School of Mathematics and Physics. Her research will focus on the computer modelling of carbon-based molecules on surfaces.

Fiona said: “The Back to Science Fellowship is an amazing opportunity. This Fellowship allows me to return to scientific research, and provides me with training while I do it. The cherry on the cake is being able to work flexibly part-time so that my work and family life fit well together. I am really looking forward to the next couple of years and am thrilled to have been chosen.”

Dr Iossa, whose PhD at the University of Bristol focussed on the behavioural ecology of the red fox, went on to investigate animal welfare in wild mammals and co-ordinated a newly founded journal of the British Ecological Society.

Dr Iossa will be working on the reproductive biology of insect eggs, with evolutionary ecologist Dr Paul Eady and paleobiologist Dr Marcello Ruta, in the School of Life Sciences.

She said: “The Back to Science Fellowship has enabled me to return to research, supporting me with a training programme and allowing me to have a work-like balance by working part-time. It is a great opportunity and I am delighted to have been awarded one of the two Fellowships.”

Professor Belinda Colston, University of Lincoln’s Athena SWAN Coordinator, said: “The award of the first Fellowships is an important landmark in the University of Lincoln’s commitment to offer research opportunities to those who otherwise would have found it difficult to return to academia. Successful applicants can look forward to an extensive package of training and development, devised to develop the individuals as rounded researchers enabling them to realise their full potential.”