Mattila, A. | Search bioRxiv

bioRxiv2026

Interactive effects of land use change and climate drive the decline of a threatened boreal forest orchid in Finland

Land use and climate change are two of the greatest threats to biodiversity globally. However, their interactive effects remain poorly understood. In the boreal forest biome, where species are experiencing increasing pressures from forest management and climate change, improved understanding of these effects is urgently needed. Here, we assess the impacts of forest loss and both baseline and changing late spring climatic conditions on the extinction probability of a threatened boreal forest orchid, Calypso bulbosa. We use a unique dataset consisting of 1,006 C. bulbosa occurrence sites located in Finland, historical aerial images, and climatic data spanning the last 60 years. Our results reveal that forest loss, at the local rather than landscape-scale, and both the site-specific baseline climatic conditions and their change over time influence the extinction probability of C. bulbosa. These effects were mainly interactive with greater temporal increase in rainfall ameliorating and greater baseline rainfall exacerbating the negative effect of forest loss on the species persistence. Furthermore, greater baseline snow depth ameliorated this negative effect. We also found some statistical support for independent effects of baseline thermal sum and its change over time, but their ecological relevance was interpreted as minor. Overall, our results align with the expectation that forest loss can modify the exposure of forest-dependent species to climatic conditions, thus altering their vulnerability to climate change.

ecology↗

bioRxiv2023

Pollen-feeding delays reproductive senescence and maintains toxicity of Heliconius butterflies

Dietary shifts may act to ease energetic constraints and allow organisms to optimise life-history traits. Heliconius butterflies differ from other nectar-feeders due to their unique ability to digest pollen, which provides a reliable source of amino acids to adults. Pollen-feeding has been associated with prolonged adult lifespan and increased fertility, yet there is a lack of empirical data demonstrating how pollen consumption influences key fitness traits, including chemical defences and adult body weight, as well as fertility over their elongated lifespan. Here, we investigated the effect of pollen-feeding on fertility, weight and chemical defences, as well as offspring defences, controlling for butterfly age and sex. Recently emerged Heliconius erato butterflies of similar size were fed for 14 or 45 days on one of three diets: sugar solution only, or sugar solution replenished with either amino acid supplement or pollen. At the end of the experiment, oviposition assays were performed to evaluate fertility, and afterwards all butterflies and eggs were weighed and used for quantification of cyanogenic glucosides (CG). We found that there is an age-specific and sex-specific effect of pollen-feeding on butterfly weight, with both the sugar-only and amino-acid supplement diets reducing the weight of old females (45d), but not young females (14d) or males of any age. Females fed only sugar significantly reduced their egg-laying through adulthood, whereas females that had access to pollen maintained their fertility. Diet had a significant effect on the maintenance of the chemical defence of females, but not males. Curiously, even though females that have access to pollen were heavier, more toxic and laid more eggs, this did not translate into improvements in offspring defences, as eggs from butterflies of all ages and diet treatments had similar CG content. Our results emphasise the importance of controlling for age-specific and sex-specific effects in studies of life-history evolution and demonstrate that dietary novelty can relax energetic constraints.

evolutionary biology↗