Browsing by master's degree program "Ekologian ja evoluutiobiologian maisteriohjelma"

Itämeri ja Suomenlahti ovat voimakkaan ihmisvaikutuksen alaisena, mikä on aiheuttanut suuria muutoksia monissa kalapopulaatioissa. Tästä huolimatta tieto rantavyöhykkeen kalaston tilasta näissä olosuhteissa on vähäistä ja paikoittaista: tietoa niiden pitkän ajan kehityksestä 2000-luvun Itämeressä ei ole. Tutkin touko-syyskuussa 2023 rantavyöhykkeen kalastoa poikasnuottaamalla Hangon Tvärminnessä, läntisellä Suomenlahdella. Selvitin kalojen runsauden alueella laskemalla sekä kalojen määrän pyyntiponnistusta kohti että kalaston yksilötiheyden. Kartoitin kalaston lajikoostumuksen laskemalla lajien suhteelliset runsaudet, sekä laskemalla ajallisia ja alueellisia diversiteetti-indeksejä. Vuodenaikaisvaihtelua selvitin vertailemalla kuukausittaisia saaliita, sekä arvioimalla poikasten määrän ajallista vaihtelua. Vertailemalla tuloksiani tietoihin vuodelta 1992 tutkin kalastossa tapahtuneita pitkän ajan muutoksia. Kalojen runsaus romahti yli 90 % vuodesta 1992 vuoteen 2023. Yksilömäärän lasku koski lähes kaikkia lajeja, ollen rajoittumatta sellaisiin, jotka suosivat tiettyjä ympäristön olosuhteita. Vuoden 2023 saaliissa oli kolme uutta lajia, kun taas kymmentä vuonna 1992 esiintynyttä taksonia ei havaittu. Runsaimmat lajit 2023 olivat kolmipiikki (Gasterosteus aculeatus L., 1758), salakka (Alburnus alburnus L., 1758), liejutokko (Pomatoschistus microps Krøyer, 1838) ja hietatokko (Pomatoschistus minutus Pallas, 1770), jotka muodostivat yli 90 % saaliista. Silakka (Clupea harengus membras L., 1761), kilohaili (Sprattus sprattus L., 1758) ja ahven (Perca fluviatilis L., 1758) olivat erittäin runsaita 1992 mutta erittäin harvassa 2023, kun salakan määrä taas kasvoi yli kaksikymmenkertaisesti. Poikasten ilmaantuminen runsaissa määrin tapahtui kuukautta myöhemmin vuonna 2023, todennäköisesti johtuen kylmemmistä alkukesän lämpötiloista. Kalamäärän romahdus on todennäköisesti seurausta sekä vuosittaisesta poikasmäärän vaihtelusta että kalojen vähenemisestä pitkällä aikavälillä. Silakan, kilohailin ja ahvenen vähäiset määrät johtuvat todennäköisesti poikasmäärän vuosittaisvaihtelusta, joskin tämän varmistaminen vaatii vuosittaisia mittauksia. Salakan määrän runsas kasvu viittaa rehevöitymisen ja vesien lämpenemisen vaikutukseen. Tulokseni korostavat tähän mennessä huonosti tunnettujen pitkän ajan muutosten laajuutta Itämeren rantavyöhykkeen kalastossa.

Artificial light at night (ALAN) is an emerging environmental problem, originating from e.g. street lightning and infrastructure. It has been found to alter the behavior of many organisms and thereby influence community composition and ecosystem functions. However, most studies on the impact of ALAN on wildlife and the environment have focused on terrestrial ecosystems, while aquatic ecosystems have received less attention, yet are increasingly exposed to artificial light. Gammarus species are amphipods commonly found in freshwater and estuarian ecosystems across Eurasia and North America. They are key components of ecosystems in recycling nutrients and serving as a food source for other species. They are night active and, hence, vulnerable to ALAN. Earlier studies show that ALAN increases their predation risk and induces physiological stress. However, no study has assessed the impact of ALAN on mating behavior, although mating success is a key fitness component that influences population dynamics. Gammarus pulex is a common freshwater detritivore where females are receptive for a short period and males compete for females and then guard them through amplexus, precopulatory guarding. The aim of this master’s thesis was to study if and how ALAN affects the mating behavior of the G. pulex, and if this depends on the presence of male-male competition for females. G. pulex, individuals were collected from a stream in Helsinki and exposed to control (natural light conditions) or ALAN in the absence or presence of male competition, eight treatment combinations in total, for one week under laboratory conditions. In each trial, one female and either one or two males were placed into a tank – in the absence or presence of ALAN – and their behavior recorded for ten minutes, including active time, contact between the sexes, and pair formation and separation. The results show that ALAN influences both night and day mating behaviour, but that the effect depends on the presence of male competition. ALAN had no impact on activity during the night, while male competition decreased it. During the day, ALAN decreased activity, but male competition counteracted and increased activity. Number of contacts between female and male(s) was only impacted by male competition during the night, but by both ALAN and male competition during the day; ALAN reduced contact time during the day in the absence of male competition, while male competition increased contact time. Pair formation was negatively affected by ALAN during the night, while male competition increased formation. Pair separation was higher under ALAN during the day, independent of male competition, but unaffected at night. These results indicate that ALAN causes a carry-over effect, with light conditions during the night influencing mating behaviour during the day. This is most likely through physiological changes incurred during the night because of the artificial light, such as increased stress levels. Further studies should assess how ALAN impacts mating behavior when many individuals are present, as G. pulex is more choosy in mate selection at higher population densities. Follow up studies are also needed to determine if the effect of ALAN depends on the colour of the light, as found for other organisms, as such information is needed in conservation work aiming to reduced negative effects of ALAN on ecosystems through the development of environment friendly lighting systems. Regarding the consequences of the change in mating behaviour when exposed to ALAN, this could alter population dynamics. Given the key ecological role of the species in ecosystems, this could lead to changes in nutrient recycling and the structure of food webs. Considering that the presence and intensity of ALAN is expected to increase in the future, it is of great importance to assess its effects on organisms, not only during the night but also during the day through carry-over effects, as indicated by the present study.

The taxonomy of the green macroalgal genus Monostroma is poorly known in the Baltic Sea region and worldwide.Two species of Monostroma are currently reported from the Baltic Sea: the cosmopolitan spring species Monostroma grevillei and a proposed endemic, free-floating summer species Monostroma balticum. However, previous work has highlighted the unclear taxonomic status of M. balticum, and some consider it a growth form of the cosmopolitan species M. grevillei or a monostromatic growth form of Ulva spp. No molecular data exists of M. balticum, and the morphological characteristics distinguishing this species from M. grevillei and similar species are unclear in the literature. The aim of this thesis is to explore the taxonomic status of M. balticum by firstly systematically reviewing the historical and contemporary literature, including the original description, to illuminate the current morphological circumscription of M. balticum and related species. Secondly, using DNA barcoding based on the tufA -marker, fresh collections of foliose monostromatic green algae from the Baltic Sea region are identified molecularly and put into an evolutionary context using phylogenetics. Thirdly, novel plastid genomes are produced from monostromatic green algae to explore the genomic features of these algae and to see if they aid in species delimitation or phylogenetic approaches. Based on the literature review, the morphological and ecological features used in specimen identification currently (micromorphology, free-floatingness and occurrence in summer) may not be enough for accurate identification, and especially the micromorphological features are quite vaguely described in contemporary literature making their use difficult in practise. All monostromatic specimens collected are identified using DNA barcoding as either M. grevillei, Kornmannia leptoderma or Ulva intestinalis, and those specimens mostly resembling the original description of M. balticum are recovered as U. intestinalis. Plastid genomes were produced from M. grevillei, K. leptoderma and U. intestinalis, from the latter species separate genomes were generated from a typical tubular-morphology specimen as well as a “M. balticum”-morphology specimen. M. grevillei and K. leptoderma plastids were unusual in being large, inflated by many introns and intrageneric regions and having many rearrangements. Produced U. intestinalis plastomes are similar and resemble previously published Ulva genomes. The accurate identification of M. balticum -like specimens is discussed, and for future work DNA barcoding is suggested to be the main tool for specimen identification. This thesis provides evidence towards a previous hypothesis that M. balticum is not a distinct species but a specific growth from of U. intestinalis. Investigating historical herbarium specimens, including original material, using molecular methods is proposed to verify if M. balticum should be synonymised formally with U. intestinalis. The potential drivers of the shift in growth form of U. intestinalis are discussed. Finally, the plastid genome landscape in these foliose green algae is discussed.

Nitrogen fixation by Sphagnum mosses in a boreal fen ecosystem Emmi Tuokko Master’s Programme in Ecology and Evolutionary Biology Faculty of Biological and Environmental Sciences University of Helsinki May 2022 Faculty: Faculty of Biological and Environmental Sciences Degree programme: Master’s Programme in Ecology and Evolutionary Biology Study track: Ecology and Evolutionary Biology Author: Emmi Tuokko Title: Nitrogen fixation by Sphagnum mosses in a boreal fen ecosystem Level: Master’s thesis Month and year: May 2022 Number of pages: 34 pages + 4 appendix pages Keywords: nitrogen fixation, Sphagnum, boreal fen, acetylene reduction, diazotroph Supervisor: Dr. Juha Mikola Where deposited: HELDA – Digital Repository of the University of Helsinki Abstract: Ecosystems in the North are heavily constrained by nitrogen (N) and the main pathway of N for plants is biological N2 fixation by Sphagnum mosses. Mosses fix N with either free-living, associated or symbiotic diazotrophs and convert it to a plant-accessible form. This way N2 fixation contributes significantly to the level of photosynthesis and carbon sequestration that these ecosystems can maintain. However, diazotrophs are exposed to large fluctuations in abiotic factors and earlier findings have suggested that to affect the rate of N2 fixed. Only a few studies have focused on boreal Sphagnum-dominated fens and thus, I wanted to figure out what environmental factors control N2 fixation activity in this habitat type. Most of the N2 fixing bacteria are heterotrophs but also methanotrophs have been shown to participate in N2 fixation. Therefore, I tested if methane (CH4) flux was connected to N2 fixation activity. As N is a necessary nutrient for plants, I also wanted to see whether the variation in N2 fixation can explain the variation in plant growth and productivity and on the other hand, if the productivity can explain the rate of N2 fixation by providing more energy. To test these interactions, we established the acetylene reduction assay (ARA) on a fen in Northern Finland to measure, how much N2 is fixed. We also recorded environmental factors (soil moisture, soil temperature, air temperature, relative humidity and radiation), measured CO2 and CH4 fluxes and calculated vascular plant coverage and Sphagnum growth from 20 study plots. I expected to find a correlation especially between soil moisture and N2 fixation because earlier studies have shown it to control the fixation activity the most. I found out that leaf area index (LAI) of vascular plants was explained by N2 fixation. This is a significant finding because it has not been proved before. It supports the earlier findings about the connection between N2 fixation and vascular plant photosynthesis. I also discovered that radiation (PAR) and potential gross primary production (GPP1200) explained the variation in N2 fixation in the first measurement. This shows the dependency of N2 fixation on the energy that photosynthesis provides. Contrary to my predictions, none of the other factors explained N2 fixation or were explained by N2 fixation. Further studies about moss-associated N2 fixation are needed especially in the light of future changes in climate and N deposition. Tiedekunta: Bio- ja ympäristötieteellinen tiedekunta Koulutusohjelma: Ekologian ja evoluutiobiologian maisteriohjelma Opintosuunta: Ekologia ja evoluutiobiologia Tekijä: Emmi Tuokko Työn nimi: Rahkasammalten typensidonta boreaalisessa suoekosysteemissä Työn laji: Maisterin tutkielma Kuukausi ja vuosi: 5/2022 Sivumäärä: 34 sivua + 4 sivua liitteitä Avainsanat: typensidonta, rahkasammal, boreaalinen, suo, ARA, diatsotrofi Ohjaaja: Dr. Juha Mikola Säilytyspaikka: HELDA - Helsingin yliopiston digitaalinen arkisto Tiivistelmä: Pohjoisen ekosysteemit ovat erittäin typpirajoitteisia, ja kasvit saavat suurimman osan typestä rahkasammalten biologisen typensidonnan kautta. Sammalet sitovat typpeä joko vapaana elävien tai symbionttisten diatsotrofien välityksellä ja muuttavat typen kasvien käytettävissä olevaan muotoon. Tätä kautta typensidonta vaikuttaa merkittävästi koko ekosysteemin fotosynteesin ja hiilensidonnan tasoon. Diatsotrofit ovat kuitenkin alttiita abioottisten tekijöiden suurelle vaihtelulle, ja aikaisemmat tutkimukset ovat todenneet sen vaikuttavan typensidonnan tasoon. Vain harvat näistä tutkimuksista ovat keskittyneet boreaalisiin minerotrofisiin soihin, joilla rahkasammalet dominoivat, joten halusin selvittää, mitkä ympäristötekijät kontrolloivat typensidonnan aktiivisuutta tällaisessa elinympäristössä. Suurin osa typpeä sitovista bakteereista on heterotrofeja, mutta myös metanotrofien on osoitettu osallistuvan typensidontaan. Sen vuoksi halusin tutkia, onko metaanivuo yhteydessä typensidonnan tasoon. Typen ollessa välttämätön ravinne kasveille halusin myös nähdä, voiko vaihtelu typensidonnan tasossa selittää kasvien kasvua ja tuottavuutta, ja toisaalta, voiko tuottavuus selittää typensidonnan vaihtelua tarjoamalla sille lisää energiaa. Testataksemme näitä yhteyksiä mittasimme typensidontaa asetyleenin pelkistysmenetelmällä Halssiaavalla Sodankylässä. Mittasimme myös ympäristötekijöitä (maan kosteus, maan lämpötila, ilman lämpötila, suhteellinen kosteus, säteily), hiilidioksidi- ja metaanivuota, putkilokasvien peittävyyttä ja rahkasammalten kasvua 20 tutkimusruudulta. Odotin löytäväni korrelaation erityisesti typensidonnan ja maan kosteuden väliltä, sillä aikaisemmat tutkimukset ovat todenneet kosteuden olevan merkittävin typensidontaa säätelevä tekijä. Sain selville, että typensidonta selitti ruutujen välistä vaihtelua putkilokasvien lehtipinta-alassa. Tämä on tärkeä löydös, sillä yhteyttä ei olla todistettu aiemmin. Tulos tukee aiempia löydöksiä typensidonnan ja putkilokasvien fotosynteesin yhteydestä toisiinsa. Ensimmäisten mittausten tulokset osoittivat, että säteily ja potentiaalinen bruttoperustuotanto selittivät typensidontaa. Tämä todistaa typensidonnan riippuvuuden fotosynteesin tarjoamaan energiaan. Vastoin odotuksiani muut tekijät eivät selittäneet typensidontaa, eikä typensidonta selittänyt niitä. Lisätutkimukset sammalten typensidonnasta ovat tarpeen erityisesti ilmastonmuutoksen ja lisääntyvän typpilaskeuman valossa.

Biogeography is a crucial aspect to ecological studies, as an ecosystem is comprised of the physical habitat, the organisms living there, and the interactions of these components. Community structure, and therefore functioning, are inherently of a spatial nature. Spatial structure of populations is often crucial basic knowledge for understanding the evolutionary history, dispersal patterns, and resilience of any given species. One aspect of spatial structure, and the topic covered in this study, is community distance decay, or the rate at which community similarity decreases with physical distance. More of the landscape is constantly being altered by humans on a large scale, so it is increasingly important to understand the effects that these anthroprogenic changes to the environment has on local populations. Studying community distance decay helps form understanding of dispersal and establishment limitations for different organisms, which is necessary for mitigating biodiversity loss. Many studies show that habitat fragmentation and loss has greatly impacted the structure of plant and animal communities, but there has been much less focus on fungal communities. There’s no certainty that fungi is impacted in the same ways, given the different lifestyles and dispersal methods, so the aim of this study is to contribute to the much needed research on fungal community structure at various scales. This aim is addressed by examining fungal community distance decay from small scale of a couple kilometers or less to a fairly large scale encompassing a landscape of primarily urban, forest, and agricultural areas. The five main localities of sampling were in middle and southern Finland: Helsinki, Lahti, Tampere, Jyväskylä, and Joensuu. Sampling locations and plot design were chosen to allow the comparison of communities separated by a mosaic, as well as along a short rural to urban gradient, to assess the effects of habitat type. From each location, six plots were decided, two in urban core, one in urban edge, two in natural core, and one in natural edge. The role of dispersal ability and functional traits in distance decay is also studied by comparing results from two different methods of fungi sampling, which were collecting spores from the air using cyclone samplers, and taking soil cores to gather fungal biomass. All samples were DNA analysed with high-throughput sequencing and the results from the DNA barcoding were used to create OTU clusters, by which the 30 plots could be compared through relative abundances of OTU’s. I determined the similarity of fungal communities using an analysis of similarity (ANOSIM) test in R, where all possible variables (site, habitat type, sample type) were used as a grouping in individual tests, thereby indicating which variable is associated with highest community difference. I also determined the differences in functional groups and major taxonomic levels among locations and sampling method using interactive taxanomic (KRONA) charts. Results showed that there are differences in fungal community structure among habitat type and sampling type. However there was greater difference at the level of plots than site locations, so clear patterns of strong community distance decay with physical distance was not measured in this study. The results suggest that fungal communities can be fairly impacted by human caused habitat change, and individual characteristics, such as dispersal methods or lifestyle, effect the rate of community distance-decay. This provides a valuable early insight into fungal community patterns, which need deeper study to understand the complexities and mechanisms behind them.

Ilmastonmuutos koettelee ankarimmin planeettamme pohjoisia alueita. Näiden alueiden eliöyhteisöt ovat ennestään erityisen herkkiä ympäristön muutoksille. Vaikka arktisen ympäristön fysikaaliset muutokset ovat jo monin paikoin nähtävillä, ovat tiedot näiden muutosten vaikutuksista alueen eliöyhteisöihin ja ekologisiin vuorovaikutussuhteisiin edelleen hyvin puutteelliset. Pohjoisten keväiden aikaistuminen altistaa yhteisöt fenologiselle irtautumiselle, jossa läheisessä ekologisessa vuorovaikutuksessa olevat lajit ajautuvat esiintymisaikojensa suhteen erilleen. Pölyttäjähyönteisen sekä pölytettävän kukkakasvin tapauksessa tästä voi olla seurauksena pölytystehon väheneminen. Tämän ja ilmastomuutoksen muiden seurausten ennustamiseksi käytetään usein nk. ajan ja tilan rinnastus –menetelmää. Menetelmän oletuksena on, että eliöt reagoivat ympäristötekijöihin samalla tavalla, tapahtuivatpa ne sitten ajallisesti tai paikallisesti. Selvittääkseni, onko arktisella alueella havaittavissa fenologista irtautumista, tarkastelen lapinvuokon sekä lajin pölyttäjäyhteisöön kuuluvan 14 hyönteisheimon fenologiaa Koillis-Grönlannissa. Tarkastellakseni, miten ilmaston vaihtelu vuosien välillä kuvastuu hyönteisaktiviteetin ajoittumiseen ja lajiryhmien väliseen vaihteluun, hyödynnän kahdenkymmenen vuoden aikasarjaa (jatkossa: aikasarja-aineisto). Selvittääkseni, miten ilmaston vaihtelu tilassa heijastuu paikallisiin eroihin pölyttäjäaktiviteetin fenologiaan, seuraan hyönteisaktiviteetin ajoittumisen yhden kasvukauden aikana maaston eri osissa (jatkossa: tila-aineisto). Molemmista aineistoista selvitän, mikä ympäristötekijä määrittää voimakkaimmin pölyttäjäyhteisön fenologiaa, keskittyen lumenlähtöpäivään ja lämpösummaan. Lopuksi arvioin, kuinka hyvin ajallinen ja paikallinen ulottuvuus vastaavat toisiaan. Näin pyrin selvittämään sitä, kuinka käyttökelpoinen ajan ja tilan rinnastus –menetelmä on pohjoisten pölyttäjäyhteisöjen tutkimuksessa. Totesin lumenlähtöpäivän selittävän lapinvuokon pölyttäjäyhteisön fenologiaa kokonaisuutena parhaiten. Tämä pätee sekä tila- että aikasarja-aineistossa. Lumenlähtöpäivän ja lämpösumman vaihdellessa eri lajiryhmien ajoitus muuttuu eri tavoin. Muutokset tilassa ja ajassa olivat lapinvuokon tärkeimpien pölyttäjäryhmien kohdalla suhteellisen yhteneväiset, mutta eräiden muiden ryhmien (esim. kukkakärpästen) kohdalla ja samalla koko yhteisön tasolla ennusteet olivat heikompia. Tulokseni osoittavat, että ilmaston vaihdellessa arktisissa yhteisöissä on nähtävissä fenologista irtautumista. Yhteisön sisällä eri lajiryhmät reagoivat sekä lumenlähtöpäivään että lämpösummaan eri tavoin. Tämä altistaa yhteisöjä fenologiselle irtautumiselle ympäristön edelleen muuttuessa. Pölyttäjäfenologiaa tutkittaessa ajan ja tilan rinnastus -menetelmä näyttää toimivan hyvin lapinvuokon ja tämän kasvilajin tärkeimpien pölyttäjäheimojen kohdalla. Koko yhteisön tasolla rinnastuksen ennusteet ovat kuitenkin puutteelliset, sillä joidenkin ryhmien ennusteet eroavat toisistaan merkittävästi sekä ajassa että tilassa. Tulevaisuudessa tulisikin selvittää tarkemmin sitä, kuinka nyt havaittu pölyttäjäyhteisön fenologinen epäyhtenäisyys heijastuu lajien välisiin vuorovaikutussuhteisiin eri trofiatasojen välillä.

Hybridization between species is widespread across the tree of life and plays a role in adaptation, speciation and evolution. A critical component of hybridization is the compatibility of the combining genomes. Mechanisms that create incompatibilities, such as transposable element (TE) activity, are thus central to understanding and predicting the evolutionary effects of hybridization. The genomic shock hypothesis posits a burst of TE activity in hybrid genomes due to the uncoupling of TEs and their silencers. While many studies on this topic have focused on laboratory hybrids, there is relatively little data for wild hybrid populations, especially in non-model species. Here, I take advantage of a recent (< 50 generations ago), natural, and replicated hybridization events between two wood ant species, Formica aquilonia and F. polyctena, to test for increased TE abundance in hybrids. Analyses of whole genomes (N total = 99) from both parental species and three hybrid populations revealed significantly more total TE copies in all hybrid populations compared to each parental species, and this partly remained after controlling for genome size, suggesting TE reactivation in the hybrids. LINE, DNA, and LTR elements, as well as multiple new and unclassified repeats, contributed most to the observed increase. However, I also found concurrent increases in satellite DNA copies in hybrids, suggesting heterochromatin expansion after hybridization. So while the observed TE-copy number increase I have detected is consistent with the genomic shock hypothesis, additional work is required to demonstrate and fully characterize TE reactivation in hybrids. Overall my work contributes to our understanding of the effects of hybridization on TE reactivation, satellite DNA abundance, and genome size evolution in natural populations.

Norway rats are common commensal species across the world. Despite their long history with humans, the ecology of urban rats is still relatively unknown. Which is why in my thesis, I model the population dynamics of wild urban rats of Helsinki using trap data from a professional pest management company. To protect the privacy of the company’s customers, the data are on the scale of postal code areas. Using a generalized linear mixed model, I investigate several different factors that might affect rat populations. As the data come from a pest management company, trapping factors need to be considered. Other factors include environmental, such as the proportion of parks or the type of sewer present in the postal code area. But as urban rats live in cities, anthropogenic factors such as human density and income matter too. In the span on seven and half years, 8 415 rats were trapped all across Helsinki, in some places more than others. Of all the factors only the trapping factors along with household median income were significant. Median income was negatively associated with trapped rats, so more rats were trapped in areas with lower income. Future studies should try to uncover for what unknown factor income acts as a proxy for.

Driven by the growing world population and increased food demand, the conversion of natural habitats into agricultural lands is occurring at an unprecedented rate. This is in turn the leading driver of the current biodiversity crisis, particularly in tropical forest areas characterised by prominent species diversity. Due to an accelerating cash-crop expansion, the once forest-savannah landscape of Northern Guinea-Bissau is now notably occupied by cashew orchards, in addition to scattered forest patches and floodable rice paddies. So far, it remains unknown how these kinds of human-modified landscapes can sustain mammal species over contrasting seasons, and how the habitat use varies across feeding guilds. To address this gap, this study aimed to understand how medium-sized mammals make use of mosaic-like landscapes in Northern Guinea-Bissau by considering the interactive effects of (1) habitat type: forest patch, cashew orchard and rice paddy and (2) season: before (June-July 2022) and after (October-November 2022) the peak of the rainy season. To do so, in each of the two seasons we conducted a 30-day consecutive camera-trap survey across seven landscapes, each of which comprised the three habitat types, amounting to 21 sampling sites. I evaluated mammal species richness, abundance (number of records) and composition across habitat types and seasons at the assemblage-level and discussed the species-specific habitat dependency. I further analysed species abundance across four feeding guilds: carnivores, insectivores, herbivores and omnivores. Based on a sampling effort of 1200 camera-trap days and 940 records, I identified 21 mammal species from 10 families and five orders. At the assemblage-level, species richness and abundance were similar between habitat types, but higher after the peak of the rainy season, except for rice paddies. Forest and cashew habitats shared similar species composition, which differed from rice paddies. Habitat-dependent species were found in each of the habitat types. At the feeding guild-level, in both seasonally periods carnivores and insectivores were less abundant in cashew orchards, while omnivores were more abundant. The results demonstrate that habitat conversion is likely to disrupt the functional structure of mammal assemblages. Maintaining heterogeneous landscapes, including both forested and open-area habitats, is crucial to maximize the integrity of mammal assemblages in Northern Guinea-Bissau. These findings can be used as baseline information in effective conservation measures in Guinea-Bissau and other tropical regions undergoing rapid conversion for cashew cultivation.

Many maternally inherited bacterial infections in insect species can have negative or positive effects on their hosts. One of the diverse phenotypes these bacteria can induce in their hosts is the selective death of the male offspring at early development stages. Male-killing (MK) symbiotic bacteria have been reported in diverse insect species, and these symbionts have been shown to play important roles in shaping the ecology and evolution of diverse host species. One such species is the African Monarch butterfly: Danaus chrysippus, the target species of my study. There are four subspecies of D. chrysippus, which are geographically loosely isolated in different parts of Africa. However, they do interbreed in a hybrid zone located in central Africa. The MK phenotype in D. chrysippus is caused by a Spiroplasma bacterium, which is highly prevalent in the host hybrid zone, where the MK phenotype is so strong that females can only reproduce thanks to a few males that migrate from the surrounding subspecies. Other studies have found a correlation between the size of the female (wingspan) and infection rate. In my thesis the main objective is to study parts of the internal female structures, aiming to investigate if the size of the female reproductive organs correlates with infection as well. My hypothesis is that the female reproductive organs are smaller in highly infected areas because the rare males produce small and resource-depleted spermatophores. This study considered if D. chrysippus females collected from different populations (with different infection rates and sex-ratios) showed a difference in the size of their reproductive organs (corpus bursae and signa). Some females were also dissected to count the amount of spermatophores, and to measure their size. My study includes photographs of these particular organs (corpus bursae and signum) because those have not been published before. The results showed that (A) Danaus chrysippus has two signa, one on the ventral- and one on the dorsal side of the corpus bursa, and they are covered with spike-like structures; (B) spermatophores varied in size between females, but that population, female infection status and population sex-ratio did not significantly affect spermatophore count nor spermatophore size, and (C) in Rwanda, where the sex-ratio is slightly female-biased, the signa covered a significantly smaller portion of the females’ corpus bursa than observed in females from other populations showing either no or a strong female sex-ratio bias.