Senckenberg Research

Cryptic Biodiversity and Climate

Caddisfly catch from a light-trapping session.
Caddisfly catch from a light-trapping session.

  

 

We cannot detect the so-called cryptic biodiversity with our human senses, and yet it is of great importance for the survival of species. The term refers to the genetic variability within a given species. How does climate change affect this? As scientists from the Biodiversity and Climate Research Centre (BiK-F) have found out as a result of a recent overview study, the influence of climate change on the genetic variability is often negative.

Genetic diversity as a fundamental level of biodiversity

Cryptic biodiversity refers to biological units – e. g. species – that are not recognized as being distinct to the human observer. A very important component of cryptic diversity is genetic diversity. Genetic diversity is the most fundamental level of biodiversity, and comprises the sum of variations in the studied organisms’ DNA . It cannot be detected directly through the five human senses and is therefore referred to as ‘cryptic’ diversity.

Steffen Pauls light-trapping caddisflies in the Pyrenees Mountains in Spain.
Steffen Pauls light-trapping caddisflies in the Pyrenees Mountains
in Spain. On this expedition caddisflies were specifically collected
to assess their genetic diversity.

The importance of genetic diversity lies in the fact that it provides the basis for variability in all characteristics of individuals in a species or in a population. It is therefore also the basic precondition for natural selection, evolution, and adaptation to changing environmental conditions. Genetic diversity plays a decisive role in determining the fitness of individuals for survival and the resistance of populations to stress. For this reason, the United Nations declared molecular diversity one of the essential components of biodiversity alongside species and ecosystem diversity.

Nevertheless, until now, this level of diversity only plays a minor role in the research examining the relationships between biodiversity and climate. Scientists at BiK-F are conducting studies to establish the significance of genetic diversity for biodiversity forecasts, to anticipate the likely effects of changes in distribution ranges on the genetic variability of populations and species, and to assess how the loss of genetic diversity reduces the longterm viability of organisms.

Genetic diversity and sh ifts in dist ribution ranges

A temperature experiment with the model organism Chironomus riparius.
A temperature experiment with the model organism
Chironomus riparius. The animals are exposed to varying
temperature ranges, which simulate current or potential future
conditions under climate change..

Climate affects the genetic diversity of species and populations in different ways. Recently, Steffen Pauls and co-workers found that many of the processes triggered by climate change will reduce the genetic diversity of affected species. On the one hand, it is well-known that the distribution of species and populations is strongly influenced by changes in climate. Historical climatic changes, e. g. during the last Ice Age in the Pleistocene era, caused major shifts in species distribution ranges. Current climatic developments seem to be having the same effect. On the other hand, we know that genetic diversity is not uniformly distributed within species or populations, and that it can be strongly affected by changes in distribution ranges. For instance, populations at the leading edge of a spreading species are often genetically impoverished, as was shown for the freshwater snail Radix balthica. At the same time populations at the trailing edge of shifting distribution ranges are often genetically diverse and consist of old hereditary lineages that are strongly differentiated from one another. However, these lineages often contribute little to the new range that a strongly expanding species occupies. Thus, the overall genetic variability of populations colonizing new areas is greatly reduced.

Genetic diversity and the capacity to adapt

The genetic diversity of many species is under increasing pressure from anthropogenic stress factors, often resulting in its reduction. In many cases, the loss of genetic diversity is associated with a lower degree of evolutionary fitness and a reduced capacity to adapt to changing environmental conditions. The climate-mediated loss of genetic diversity may lead to a lower degree of adaptability of the affected species to environmental change. To date, however, the specific effects of environmental change on the genetic diversity of species remain largely unexplored. This is also true for the effects of changing climatic conditions, e. g. annual temperature profiles, temperature extremes and precipitation dynamics.

The montane caddisfly Drusus
The montane caddisfly Drusus discolor may lose large
parts of its range in central Europe as a consequence of
changing climate conditions. Consequently all the unique
genetic variants associated with this part of its range are
also threatened.(Copyright: Strid Schmidt-Kloiber,
Wolfram Graf)


Intensive research is being carried out at BiK-F in order to fill this gap. The indigenous species of midge Chironomus riparius has been selected as a prominent model species of this research. A recently completed experimental study at BiK-F investigated the extent to which genetic diversity influences the survival of populations under different climate change conditions. In this research, genetically diverse and impoverished midge populations were subjected to present-day and simulated future climatic change conditions in the laboratory. The results show that both the genetically diverse as well as the impoverished populations survive under present-day temperature conditions. When subjected to water temperatures that have been predicted for the end of this century, all the genetically impoverished lineages died during the maximum summer water temperatures. In contrast, some of the genetically diverse strains survived these conditions and successfully continued to reproduce. These findings highlight how important genetic diversity may be for the survival of populations and species in the future.

In another experiment, Sabrina Nemec and co-workers were able to show that populations of C. riparius are locally adapted to climatic conditions across Europe. Central European midges react more sensitively to increases in water temperatures than midges from populations in southern Europe. This shows that climate change will have regionally distinct effects on biodiversity not only because the actual changes in climate patterns will vary among regions, but also because of the different genetic ‘make-up’ of the local populations. To date little research has addressed the rate at which changes in environmental conditions affect genetic diversity. In a series of laboratory trials Carsten Nowak and co-workers found that pesticide pollution in concentration levels observed in natural environments can significantly reduce the genetic diversity of midge populations within a few generations. Ruth Müller and her coworkers obtained similar results through experiments that tested how populations of C. riparius react to pesticide pollution under climate change conditions: they also found a measurable reduction in diversity within a few generations.

 

Impact of climate change on the fitness of genetically impoverished populations.
Impact of climate change on the fitness of genetically impoverished populations. In the temperature experiment genetically impoverished midges (Gen-) produce significantly less progeny than diverse populations under future climate change conditions (Z). This effect only shows up under temperature maxima in summer (right), but not under current (H) or constant laboratory conditions (K).

 

 

Biodiversity projections and cryptic diversity

Most of the current studies and approaches that aim to assess the effects of climate change on living organisms concentrate on morphologically defined species, i. e. groups of organisms that can be clearly distinguished from each other on the basis of morphology. However, the high levels of genetic variation and genetic divergence within morphologically defined species, i. e. cryptic biodiversity, is generally not accounted for.

Freshly emerged mayflies (adults and subadults).
Freshly emerged mayflies (adults and subadults). Adults of many
different mayfly species are mophologically cryptic. The species are
often only distinguishable in the larval stages or with genetic analysis.

The potential effects of climate change on intraspecific diversity were demonstrated on aquatic insects in two pilot studies at BiK-F . Previous studies on the population genetics of mountain aquatic insects showed that the dispersal potential of these species is generally restricted. All the species investigated so far display a high degree of genetic differentiation from one mountain area to the next, and there is often even a significant genetic differentiation from one body of water to another within mountain areas. This means that these species will only have a limited capacity to populate new territories under conditions of rapid climate change. These species have particularly high extinction risks under climate change due to their limited dispersal capacity, small population sizes, and possible adaptation to cold habitats.

 

Ram Devi Tachamo Shah sammelt Insektenlarven für genetische Studien vor dem 7200 m hohen Berg Langtang (Nepal)
Ram Devi Tachamo Shah collecting aquatic insects in front of the
7200m high Langtang Mt, Nepal.

Both pilot studies computed forecasts to identify climatically suitable areas of mountain aquatic species for the year 2080. The results were unequivocal: the number of regions still climatically suitable for these cold-tolerant species decreases drastically. Numerous, currently suitable regions (e. g. the Massif Central in France or the low mountain ranges of Germany) will become climatically inadequate for these species by 2080. By then these species may only be present in high mountains (e. g. the Alps) and in the far north (Scandinavia). When a regional population ecomes extinct, all local genetic variants from that that region are also lost. Many of these variants constitute independent evolutionary lineages, i. e. populations that may be on a path towards forming new species. Thus the pilot studies were able to demonstrate that we seriously underestimate the potential loss of biodiversity if we focus exclusively on morphologically determined species and fail to consider genetic diversity.

In the meantime, the methods for projecting the effects of climate change on intraspecific genetic diversity have been further refined and statistically extended at BiK-F . A spezial feature of these methods is that they can be used for future studies, but also to exploit existing bodies of data. Using the methods developed at BiK-F it is now possible to estimate which species and populations may be particularly affected by a loss of genetic diversity mediated by climate change. Genetic diversity can thus be included in conservation planning, improving the efficiency of environmental and nature protection. This is particularly important considering the on-going debate about managing protected areas under climate change. If we consider both the required habitat and the genetic diversity of a conservation priority species, we can make better projections on which areas will best serve to protect that species. With the aid of the approaches outlined above, a recent BiK-F study identified Geranium sylvaticum populations in the Taunus Mountains that are particularly worthy of protection.

In conservation we have reached the point where biodiversity needs to be grasped not merely in terms of a given set of species, but as a multitude of evolutionary lineages that are subject to constant change. Regardless whether a lineage is considered to constitute a distinct ‘species’ or not, the loss of any such lineage will lead to a reduction of biodiversity. Modern nature protection strategies must therefore take genetic diversity into account when considering the impact of climate change on species or communities.

  

 Authors

 Dr. Carsten Nowak

Dr. Carsten Nowak studied and obtained his Ph. D. at the Goethe University, Frankfurt am Main. Following a period of postdoctoral research at the University of Notre Dame, Indiana, he took over as Head of the Senckenberg Conservation Genetics Section. There, he is conducting research on aquatic invertebrates to establish the significance of genetic diversity for the survival potential of populations. He is also researching the influence of environmental factors on genetic diversity. In addition to this, wildlife genetics as an interface between science and applied species conservation is playing an increasingly important role for his section.

 
  

Dr. Steffen Pauls

Dr. Steffen Pauls studied ecology at the University of Duisburg-Essen. He obtained his Ph. D. in 2004 in the Department of Hydrobiology of the University of Duisburg-Essen in cooperation with Senckenberg. The subject of his thesis was the phylogeography of high-altitude aquatic insects. Following postdoctoral research at the Field Museum in Chicago (funded by the German Academic Exchange Service DAAD, 2005-2006) and at the University of Minnesota (funded by Leopoldina, 2007-2010), he has been working as Head of the ‚Aquatic Evolutionary Ecology‘ Junior Research Group at BiK-F. He is investigating the population genetics, phylogeography and molecular systematics of aquatic insects in the context of historical and current climatic changes.


Dr. Miklos Bálint

Dr. Miklós Bálint studied in Cluj, Romania and also obtained his Ph. D. there. Since 2010 he works as a postdoctoral researcher at BiK-F. Initially he worked on the influence of climate change on the genetic diversity of aquatic insects. Currently he conducts research on the diversity and composition of microbial fungus communities under climate change with ‘next-generation‘ DNA sequencing.

 


 

Prof. Dr. Markus Pfenninger

Prof. Dr. Markus Pfenninger studied biology at the Goethe University. After postdoctoral work in France (funded by NATO, 1997/98), he worked as an assistant in the group of Professor Bruno Streit (Goethe University), where he obtained his habilitation in 2003. He held a post as laboratory supervisor at BiK-F, and was then called to the Chair of Molecular Ecology at the Goethe University. His research focuses on the ultimate and proximate basis for the distribution of species with special reference to climate, using a variety of methods spanning ecology, phylogeny, population genetics, and genomics.

 

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