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Evolutionary biology – connections between environment and phenotype

One important way of preventing the extinction of species is to conserve and protect their habitats. In order to achieve this, some important questions need to be answered: how do new species develop and spread? How do they adapt to a new environment?

The individual organism is influenced by different factors. The sum of these factors leads to speciation. Helen Gunter and Julia Jones, fellows at the Zukunftskolleg (Future College) at the University of Constance, are investigating two of these factors. Helen Gunter is interested in the influence of the environment and Julia Jones is researching the level of gene flow between parent fish and their hybrid descendants.

Helen Gunter in the laboratory © University of Konstanz

The most common way for evolution to act is through the selection of organisms with advantageous genes. Under the right circumstances, this leads to speciation. Speciation also arises through the direct influence of the environment on the phenotype of an organism without any change in the genes. This process is referred to as “phenotypic plasticity” and is one of the issues Helen Gunter is investigating. “Fish that evolve in this way are very interesting for developmental biologists because of their quick and explosive speciation, which is partly due to their access to new food sources,” explains Helen Gunter. Her investigations focus particularly on the jaws of cichlid fish, found in East Africa’s Lake Victoria.

Phenotypic plasticity – many species rolled into one

The food sources of cichlids range from other fish to snails and algae as well as plants. Each specimen develops a different jaw morphology according to its own special requirements. While the fish that subsist on other animals have stronger jaws with fewer teeth, those that feed on a soft diet develop papilliform jaws. “If we manage to determine the genes that are used to form new jaw morphologies in cichlids, we may be able to understand the genes used in speciation,” says Helen Gunter. A particular characteristic of the cichlids is their pharyngeal or throat jaws, which are fused into a single unit. These special jaws are used for chewing so that their oral jaws can be used for capturing prey.

A male Xiphophorus clemenciae with scale © University of Konstanz

“A change in the size of the pharyngeal jaw also has implications for the adjacent structures in the head,” says Helen Gunter. For example, there is a direct connection between jaws and gills: the size of the jaw is directly influenced by the size of the gills. Thus, the accommodation of the fish to oxygen depends on the size of its jaws. Furthermore, the base of the skull needs to be more stable if the fish lives on a hard diet because greater jaw pressure is needed to chew this type of prey.

Dominance of the genes

A feeding trial was carried out by the scientists in Constance, during which the fish were separated into two groups. The groups were either fed a hard or a soft diet. The analysis of gene expression showed that the influence of the genes is greater than the influence of the environment. “Of course we are still interested in finding out how the environment can modify gene activity, as this remains an area that is not well understood,” comments Helen Gunter.

The role of natural hybridization in evolution and speciation

Julia Jones carries out measurements in natural environments © University of Konstanz

For Julia Jones, population genetics and evolutionary biology make an important contribution towards an understanding of why and how biological diversity is created and maintained in the natural world. Research on the interactions between and within species and the correlation with the environment should eventually lead to an understanding of these processes.

A small freshwater fish called Xiphophorus clemenciae is one of the rare species where evidence for natural hybridization is so strong that it is counted among the few examples of the role of hybridization in the process of speciation. Hybridization is the process of combining different species or varieties of plants and animals to create a hybrid. Julia Jones’ research addresses two very important issues in this field: does hybridization tend to consist of rare and isolated events or is it continuously happening over time? Which regions of the genome introgress and what proportion of the genome is involved?

Cases where hybridization occurred as a rare and isolated event are very difficult for scientists to detect. A possible solution to this problem is the more precise investigation of the phylogenetic datasets based on genetic markers. If any incongruity between these datasets is found, there is a strong indication of past hybridization. “When a signature of past hybridization is found in combination with current hybridization, it is likely that hybridization is ongoing,” remarks Julia Jones. She therefore concludes that there is no evidence for ongoing hybridization if current hybridization has not been detected.

The genetic consequences of hybridization (or the genetic structure resulting from hybridization) vary from case to case. The proportion of the genome that is involved in the hybridization depends largely on how hybridization occurs.

How hybridization works

Julia Jones during field work in a river © University of Konstanz

Two different kinds of speciation originate through hybridization. In polyploid speciation, a new species with a greater number of chromosomes emerges, while recombination speciation is defined as follows: “Hybridization between two species gives rise to a new lineage that is both fertile and true breeding but  is reproductively isolated from both parental species,” says Julia Jones. She also states that another important function of hybridization is the colonization of unexploited niches, i.e. habitats that the parental species could not use.

Julia Jones works with both genetic and non-genetic techniques. “To understand the nature and impact of hybridization, it is important to investigate a variety of different aspects of the system,” she explains. For this reason, one of the techniques she uses is next generation sequencing. This enables her to rapidly detect genetic variation in both model and non-model organisms. Environmental factors influencing the genetic structure of populations can be found by using landscape genetic tools. Through the use of these techniques she can help to build a complete picture of the processes which lead to hybridization and by extension, to biological diversity.

For further information:

Dr. Helen Gunter
E-mail: helen.gunter(at)uni-konstanz.de
Tel.: +49 (0)7531 / 88 - 4583
Fax: +49 (0)7531 / 88 - 3018

Dr. Julia Jones
E-mail: julia.jones(at)uni-konstanz.de
Tel.: +49 (0)7531 / 88 - 4583
Fax: +49 (0)7531 / 88 - 3018

Website address: https://www.biooekonomie-bw.de/en/articles/news/evolutionary-biology-connections-between-environment-and-phenotype