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-genomic and phylogenomic markers and methods.

In particular, we focus on the macroevolutionary 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 community ecology of mushroom–fungivore–parasitoid networks, conservation genetics of endangered animals and their parasites, and the role of local adaptation in speciation of African Lithops plants.

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]

Conservation genetics of endangered host–parasite systems

Isolated and small animal populations will invevitably lose genetic diversity through inbreeding and genetic drift, and they are also vulnerable to extinction through adverse stochastic events. Low genetic diversity may also expose endangered animals to rapidly-evolving parasites and pathogens. Hovever, bottlenecks in host species may lead to parallel bottlenecks in their specialist parasites, and the parasite community may lose species through random extinctions.

We currently investigate the genetic makeup and community structure of seal lice (Echinophthirius horridus) and several species of acanthocephalan worms, cestodes, and nematodes in different-sized Fennoscandian seal populations. A particular focus is on the Saimaa ringed seal (Pusa hispida saimensis), which 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 last Ice Age. The current population numbers only about 360 individuals, so the subspecies is classified as endangered. In comparison to its more numerous relatives in the Baltic Sea and the Russian Lake Ladoga, the Saimaa subspecies possesses very little genetic variability. These three populations are therefore particularly well suited for testing hypotheses concerning parallel loss of genetic diversity in isolated host–parasite systems.

Comparative population-genomic and demographic analyses of seal parasites and their hosts will benefit from data produced by the Saimaa Ringed Seal Genome Project, which is led by Prof. Jukka Jernvall at the University of Helsinki. The project aims at sequencing and publishing the whole genome of the Saimaa ringed seal and its closest relatives in 2018. [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 two 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 in June 2018 to investigate the level of local adaptation in Lithops species and populations. These measurements will rely on multi- and 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 Specim Spectral Imaging Ltd. (Oulu, Finland) and the Surface Optics Corporation (San Diego, CA).


[Alternative CV]