UEF Joensuu
Molecular Ecology Group

       

Nyman Lab

The Joensuu Molecular Ecology Group (JMEG, a.k.a. Nyman Lab) is a small but persistent research team that tackles various ecological and evolutionary questions using a combination of traditional hands-on field ecology and modern molecular-genetic approaches. Depending on the question at hand, our 'indoors' toolbox consists of diverse population-genetic and phylogenetic markers and methods.

In particular, we focus on the evolutionary history of plant–herbivore interactions, and on connections between speciation, specialization, and niche shifts in complex food webs consisting of plants, insect herbivores, and parasitoids. Lately, our focus has expanded to include also the role of local adaptation in speciation of African Lithops plants (see below), as well as conservation genetics and the maintenance of genetic diversity in endangered animals. Our conservation-genetic studies mainly target the critically endangered Saimaa ringed seal, which is endemic to Lake Saimaa, a vast lake complex located right to the south of Joensuu.

Who eats whom and why I: plants and insects

Plants and plant-feeding insects form the starting point of practically all important terrestrial food webs. Many herbivorous insect groups are extremely species-rich, so research on plant–herbivore interactions can provide important insights into processes that generate diversity in nature. A particularly interesting possibility is that insect diversification is linked to evolutionary shifts among plant species and taxa: most insects are very specialized in their use of available host plants, yet related species often are associated with different, sometimes distantly related plant hosts. Such patterns require that feeding preferences change occasionally during the evolutionary history of herbivores.

Our research uses a two-tier approach:

(1) Population-genetic analyses of species and populations feeding on alternative plant species. These studies on the early stages of niche-driven divergence have mainly focused on Euurina sawflies that induce various types of galls on willows, because both willows and gallers are species-rich, ecologically diverse, and common across the Holarctic region. [Read more]

(2) Phylogenetic analyses of higher-level species-groups and taxa, with an aim to reconstruct past changes in resource use, and to infer possible connections between niche shifts and speciation events. Our phylogenetic analyses have mainly targeted heterarthrine and nematine sawflies, which are very diverse in their feeding niches. This line of research has recently been expanded to include order-level Hymenopteran phylogenetics; these new, macroevolutionary analyses especially focus on the relative effects of biotic interactions and abiotic factors (esp. long-term variation in the global climate) on insect diversification.

Who eats whom and why II: plants, herbivores, and parasitoids

Larvae of insect herbivores are attacked by diverse parasitic insects, such as parasitoid wasps and flies. Like their victims, many parasitoids are very specialized in their feeding preferences. The presence of parasitoids introduces substantial additional complexity to the ecology and evolution of plant–herbivore interactions, especially if the enemies use plants as cues for finding their host insects. In such cases, parasitoids can influence the perceived 'quality' of plants as a resource for the herbivores. Niche-specialist parasitoids could therefore speed up herbivore speciation by promoting evolutionary shifts to novel host plants providing 'enemy-free space' for the herbivore larvae. Hovever, subsequent evolutionary resource tracking in the parasitoids can trigger delayed diversification in the enemy communities as well.

Our studies on the phylogenetic, ecological, and physiological determinants of parasitoid-herbivore associations and on vertical 'top–down' and 'bottom–up' diversification effects in multitrophic food webs are mainly based on two study systems: willows, gall-inducing sawflies, and their natural enemies, and northern trees, leaf-mining sawflies, and parasitoids. In both cases, we have found evidence for a significant effect of herbivore niches on attack rates by different parasitoid species, supporting the existence of vertical diversification forces in complex trophic networks. [Read more]

The Lithops project

Plants belonging to the genus Lithops are arguably the strangest plants on our planet: there are 37 described species in the genus, and all of them resemble small pebbles (the photo on the left has five Lithops karasmontana plants in it!). These minute succulents inhabit deserts and semi-deserts in South Africa, Namibia, and Botswana.

In addition to being very charismatic, Lithops plants provide a highly promising model system for testing evolutionary hypotheses concerning the role of local adaptation in the generation of new species. The coloration of the soil varies markedly across the southern parts of Africa, and for small plants that rely on crypsis for avoiding herbivores, this creates a complex geographic mosaic of selective pressures. Locally optimized crypsis could therefore be a factor driving diversification within the genus Lithops.

Together with Professor Allan G. Ellis from the University of Stellenbosch in South Africa, we will conduct two one-month expeditions in April 2016 and 2017 to investigate the level of local adaptation in Lithops species and populations. These measurements will rely on hyperspectral imaging techniques, so that the extent of crypsis can be quantified objectively. We will also use experimental manipulations to test whether improved color matching enhances survival in Lithops species. In the future, we aim to expand the research focus to phylogeography, speciation patterns, and the genetic basis of color production in Lithops plants. [More information can be found at www.lithopsproject.org and www.blog.lithopsproject.org]

Our Lithops imaging expeditions are supported by National Geographic Society Science and Exploration Europe. Hyperspectral camera equipment is provided by the Surface Optics Corporation (San Diego, CA).

Saimaa ringed seal conservation genetics

The Saimaa ringed seal (Pusa hispida saimensis) is a landlocked endemic subspecies of the Holarctically distributed ringed seal (Pusa hispida). The ancestors of the Saimaa ringed seal population became trapped in Lake Saimaa in Southern Finland after the Pleistocene glaciations, when the bedrock slowly rebounded following the northward retreat of the continental ice sheet. During its isolation, the Saimaa ringed seal has diverged morphologically and genetically from its marine ancestors. The current population numbers barely over 300 individuals, so the subspecies is classified as critically endangered.

The JMEG has studied the genetic composition of the Saimaa ringed seal population since 2009. In comparison to its closest relatives in the Baltic Sea and the Russian Lake Ladoga, the Saimaa subspecies possesses very little genetic variability in mtDNA control-region sequences and nuclear microsatellite loci. We have also found that subpopulations inhabiting different parts of Lake Saimaa are partly genetically differentiated. Along with the UEF's Saimaa Ringed Seal Research Group, JMEG currently participates in the Saimaa Ringed Seal Genome Project, which is led by Prof. Jukka Jernvall at the University of Helsinki. The genome project aims at sequencing and publishing the whole genome of the Saimaa ringed seal by the end of 2016. [Read more]

 

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