torstai 7. syyskuuta 2017

Are changes in solar radiation and spectral composition reflected in leaf optical properties of forest understorey species?

Sunflecks and shaded areas on the forest floor in one of
our field sites at Lammi Biological Station
In the understorey, shade-loving plants live their whole life on the forest floor. Processes like leaf reflectance, transmittance and absorbance, determine the composition of radiation that reaches the understorey. We assist to the formation on the forest floor of micro-sites with different light conditions: shade and sunflecks, a brief increase of solar irradiance that occurs in the understorey when sunlight is able to directly reach the forest floor. As a result, understorey species are exposed to a very dynamic light environment during the day, meaning that they must develop mechanisms to quickly exploit the fluctuating PAR (Photosynthetic Active Radiation) in conditions where light is limiting to growth. The plants’ capacity to assimilate carbon under different species canopy cover determines the community structure and consequently alters nutrient cycling and the forest ecosystem  functioning. As my PhD focuses on the impact of spectral composition on ecosystem processes, we thought it would be interesting to understand how this function varies as a consequence of different lights conditions to which the understorey plants themselves are exposed every day. 

The aim of this study is to monitor the response of understorey plants to the transit of a sunfleck across the predominately-shaded forest environment and to assess how the season and structure of forest canopies, affecting the quantity and quality of irradiance, moderate the photosynthetic response of understorey plants to sunflecks. I focused on four early-spring ephemeral species (Anemone nemorosa L., Oxalis acetosella L., Fragaria vesca L., Hepatica nobilis Schreb.). Furthermore, I characterised the duration and intensity of several sunflecks in forest stands with different canopy species in Finland and Spain during spring and summer 2016 and 2017. Changes in leaf properties passing from shade through a sunfleck have been monitored through time-series of chlorophyll fluorescence (measured with a Walz mini-PAM) and leaf temperature (measured with an infrared thermometer).

My PhD supervisor Matt Robson with me
observing sunflecks in our field site
Preliminary results show a very fast response of the photosynthetic apparatus to sunfleck passage, on a timescale of seconds. The photosynthetic yield changed quickly when the leaves were exposed to different light conditions and recovered quickly from its sunfleck-depression on return to shade. Furthermore, in some of the studied species we observed an increase of the photosynthetic yield just before the leaves reached the edge of the sunfleck. This suggests that the plant is primed for the arrival of the sunfleck, probably by a spectral cue. The temperature of the leaves also changed during the transit of the sunfleck, just before the arrival of the sunfleck the temperature decreased, indicating that the plant can perceived the light changes as a cue to open the stomata and increase transpiration.

A coloured-film filter over beech seedling
during a sunfleck at our filed site in Spain
In order to detect the spectral cues that might be responsible of the priming of the plants we repeated the experiment in summer 2017, but now filters have been used to manipulate the solar spectrum. This meant that we could experimentally test the plant response to different light qualities in an attempt to identify the spectral cue that enables the plant to detect the sunfleck just before its arrival. This is only a small part of my PhD but it can have very important impact on the analysis and modelling of carbon cycle in the forest ecosystem. I am looking forward to go on with my project on this interesting topic and I wish to thank Lammi Biological Station for the opportunity to perform my research and the help that I received. 

Marta Pieriste of the University of Helsinki is a 2016 grant recipient

tiistai 13. kesäkuuta 2017

Morphological and Genetic Diversity of Harpacticoids (Copepoda, Crustacea)

The extraordinary diversity of forms and life strategies of copepods makes them very convenient subject for studies of variety of fundamental biological processes. They play a significant role in every ecosystem. As the dominant secondary producers, copepods are like the linchpin of aquatic food-webs. Also, they are sensitive indicators of local and global climate change. Copepods show a complex pattern of responses to variability in environmental conditions. Their abundance within a locality appears to be correlated with temporal and spatial conditions, especially food availability. Thus, they are present in various water bodies at a certain time of the year, when conditions are most favorable for them. The rest of the time, they are lying in cysts, a special resting stage, at the bottom. My PhD thesis focuses on the morphological and genetic diversity of Harpacticoida (Copepoda, Crustacea).
Harpacticoids are small copepods (1-2mm) which inhabit every water body in the world from hot springs and leaf base to deep seas and oceans. It is well known that almost all morphological structures, life-strategy and breeding system of harpacticoid copepods change within a certain range in connection with variations of geographical and environmental factors. When gene flow among populations is restricted, natural selection can result in adaptation to local environments. A good example of this is the unique Canthocamptus staphylinus population discovered in Lake Pääjärvi in 1979. The population changed its sexual way of breeding into parthenogenesis probably due to limited food availability and short growing season.
This fact served as the starting point for my investigation of harpacticoids intrapopulation diversity. I wanted to study how populations of several species of harpacticoids differ from each other and how their isolation can affect their morphology and genetics – I wanted to understand microevolutional processes which happen in populations of this crustaceans in different water bodies. During several weeks at Lammi Biological Station I was sampled hydrobiological material and looked for harpacticoid species, especially C. staphylinus, whose breeding transition was described by Jouko Sarvala (whom I had a pleasure to meet at the Station) in his paper “A Parthenogenetic life cycle in a population of Canthocamptus staphylinus (Copepoda, Harpacticoida)” (1979).
Populations of C. staphylinus sampled in Russia, Estonia, Finland, Sweden, Norway and Switzerland showed differences in morphology of body structures and characteristics. Based on the surveys of all the varying morphological characteristics, seven morphometrical indices of the length ratios were calculated. Only four indices out of seven were statistically valid for different populations. For example, population from the Komi Republic (Russia) — the northernmost point in this study — showed the smallest body and ratios of caudal rami and legs lengths in relation to other population (see picture below). 

Our genetic studies revealed a high level of intraspecific genetic variability of C. staphylinus. Nucleotide sequences of  CO1 gene mtDNA have divided into separate clades with the divergence of about 25%. Remarkable is that the clade from Pääjärvi showed the smallest numbers of haplotype and nucleotide diversity, thus revealing a homogeneous genetic structure of population consistent with the concept of transition to parthenogenesis. Furthermore, the high level of morphological and genetic variability of harpacticoids raised the question of taxonomic structure and existence of cryptic and sibling species. Having sequenced a more conservative nuclear gene (18S rDNA), we found out this was not a complex of sibling subspecies but still one species because divergence between populations tended to zero. Thus, it is a unique case of morphological and genetic diversity (in mitochondrial DNA) within harpacticoid species which could result from a high level of plasticity and high adaptive possibilities of this taxon. 

The research revealed some cases of intraspecific and intrapopulational morphological and genetic variability of harpacticoids. This is just a small step, but it could be important as a contribution to the wide investigation of copepods phylogenetic and populational structure and response to environment. Now I investigate variability of another harpacticoid species: Attheyella crassa and Paracamptus schmeili and I am excited to continue this study. Many many thanks to Lammi Biostation staff for help and kind support.

Elena Kochanova is a 2016 recipient of a LBAYS grant. She is a PhD student of Zoological Institute of Russian Academy of Sciences, Saint Petersburg, Russia

tiistai 4. huhtikuuta 2017

Response to Bacterial Infection in a Butterfly

Parasites and pathogens are ubiquitous and represent a major threat for every individual. A well-functioning immune system therefore is crucial for every species and is under strong selection pressure. Infection risk has shown to differ depending on the season, the climate, density in the population and other environmental conditions that the organism might experience during its development. However, the risk might further differ depending on the way pathogens enter the system. If a parasite breaks through the exoskeleton of insects, which is a protective barrier, it passes the haemocoel and faces the systemic immune response, a complex interaction of cellular and humoral components. Ingestion of pathogens or spores on the other hand do have the potential to infect a host, even though they first have to overcome the gut epithelium.

I wanted to investigate the importance of bacterial infection during the adult stage in the Glanville fritillary butterfly (Melitaea cinxia) via oral infection in comparison to haemocoelic exposure of the same strain. This species is in Finland only present in the Åland Islands where it occurs in a classical metapopulation. Adults disperse from habitat patches to recolonize new patches or fly for foraging and mating. During dispersal events, individuals might encounter a higher infection risk due to changes in quality or quantity of parasites. On the one hand individuals might encounter pathogens based on wounding that might occur due to predators such as ants, spiders and parasitoids. Such wounds allow pathogens to enter directly into the haemocoel. On the other hand, dispersal reflects a resource costly event and individuals might feed on more nectar after dispersal, potentially also increasing the amount of pathogens ingested.

In a series of experiments that I conducted in the Lammi Biological Station, I infected male and female adult butterflies with a bacterial strain to investigate how this species responds to bacterial infection in general, if the two sexes would differ in their immune response and if the responses would differ depending on the way the pathogens entered their system. I measured immune gene expression levels and encapsulation rate to measure immune response and further was interested in individuals’ lifespan.

Direct exposure to bacteria via injection as well as oral exposure both had an effect on the phenotype. Lifespan was reduced for both sexes and exposure to bacteria resulted in an increase in immune gene expression. However, more immune genes responded to haemocoelic bacterial infection compared to oral exposure. Moreover, females did show higher expression levels for some immune genes, indicating that females invested more in immunity than males supporting the commonly observed susceptible male hypothesis. One explanation for the observed sex difference in immune response might be due to different strategies for reproduction. Females of this species in general live longer and deposit their eggs in several clutches throughout their lifespan, whereas males are able to increase fitness via increased number of matings. Thus they do not need to live as long as females and therefore decreased survival due to bacterial infection does not necessarily reduce their fitness. 

Further studies are needed to investigate the effect of bacterial infection on reproductive success, to investigate why sexes respond differently to infections. Infections potentially play a crucial role in this system, as infected individuals could transfer pathogens to different habitat patches, spreading a disease and thus affecting population dynamics. It will be interesting to further look into effects of other pathogens, like fungi or viral infections, to better understand immunity in this butterfly and insects in general.

Luisa Woestmann is a PhD student at the University of Helsinki and a 2016 LBAYS grant recipient

maanantai 2. tammikuuta 2017


Kesän aloittaminen toukokuun lopulla Lammin biologisella asemalla  Pääjärven rannalla oli miellyttävä kokemus. Varsinkin kun olin lupautunut esittämään kaupungin tervehdyksen vuonna 2008 perustetun Ympäristötutkimuksen Säätiön järjestämällä Ympäristölounaalla. Kutsun tarkoitus oli jalo ja ylevä: Tukea erityisesti biologisella asemalla tehtävää ympäristötutkimusta. Hämeenlinnan kaupunki on ylpeä siitä, että sen alueella toimii maan suurin yliopistollinen kenttäasema. Jo 1950-luvun alkupuolella perustettu asema on tunnettu erityisesti vesiympäristöön liittyvistä tutkimuksistaan. Aivan aseman vieressä lainehtiva Pääjärvi taitaa olla yksi maailman tutkituimmista järvistä.

Tutkijat näytteenotossa Pääjärvellä
Tätä pohtiessani mieleeni palautuivat lapsuuteni kesät 1950- ja 1960-luvuilla isäni lapsuusmaisemissa Lammilla. Näihin kesänviettoihin liittyi tietysti paljon uimista ja kalastusta Pääjärvessä. Eipä silloin nuorella pojalla ollut käsitystä siitä, miten arvokasta tietoa ja taitoa järven rannalle perustettu tutkimusasema tuottaa aikanaan maailmalle. Toinen henkilökohtainen kokemus ja tutustuminen aseman toimintaan osui työelämääni radio Hämeen toimittajana. Tuolloin sain aina silloin tällöin käydä kertomassa tutkimustuloksista radiomme kuuntelijoille ja olipa meillä yhtenä talvena yhdessä kokonainen luentosarja, jonka välitimme kansalaisopiston myötävaikutuksella maailmalle.

Aihe tämänkertaisella Ympäristölounaalla oli hyvin aikaan ja paikkaan sopiva: Sinivihreä maisemamme - maa- ja vesiekosysteemien vuorovaikutus. Tilaisuuden armoitettuna juontajana toimi järjestävän säätiön varapuheenjohtaja Sirpa Pietikäinen, joka lupsakkaalla tyylillään nivoi esitykset hyvin yhteen. Varsinaista teemaa lähestyivät omilla havainnollisilla ja asiantuntevilla esityksillään pääjohtaja Lea Kauppi, professori Lauri Arvola sekä stipendiaatti Sari Uusheimo, jonka esitystä referoitiin alustajan sairastumisen vuoksi. Esitykset saivat arvostettua vastakaikua laajassa kuulijakunnassa.

Omalta kohdaltani eniten pohdittavaa ja ajatuksia herättävää oli kuulla vesiensuojelullisten kosteikkojen merkityksestä järvien tilan kohentumisessa. On kustannustehokkaampaa pysäyttää ravinteet pelloille kuin poistaa niitä vesistöistä. Meillä pitää olla taitoa, intoa ja rohkeutta vaikuttaa ympäristön parhaaksi.

Kotiin palatessani pohdin vielä Hämeenlinnan kaupungin tämänvuotista teemavuotta - Luonto ja vesi. Miten osuvasti biologisella asemalla vastattiin tähän huutoon. Toivottavasti saamme mahdollisimman monet huolehtimaan entistä puhtaammista vesistöistämme ja nauttimaan ainutlaatuisesta luonnostamme.

Aarne Kauranen