The unicellular freshwater cyanobacterium Synechococcus and mixotrophic flagellates: evidence for a functional association in an oligotrophic, subalpine lake

1. We applied Reynolds's approach to the study of phytoplankton ecology through functional associations of species to identify possible algal species, which associate with the freshwater cyanobacterium Synechococcus. Previously an association among Synechococcus spp. and small‐celled chlorophytes (association Z) has been recognised by evaluating phytoplankton associations according to functional criteria. 2. Biomass data for phytoplankton and picocyanobacteria from Lago Maggiore spanning more years were organised in a matrix and a cluster analysis was performed. The results showed four groups separated at a linkage distance of 0.20. Mixotrophic species which clustered with Synechococcus spp. were Ceratium hirundinella, Chrysochromulina parva, Cryptomonas erosa, Cryptomonas ovata, Dinobryon bavaricum, Dinobryon sociale, Rhodomonas minuta and Uroglena americana. The redundancy analysis (RDA) consolidated the association of Synechococcus with C. hirundinella and R. minuta showing greater probability of occurrence than random aggregates of species. 3. The association Synechococcus spp. –C. hirundinella also appeared from temporal variation of their biomass. In early summer both these species increased at the same time; later, the peak of C. hirundinella (potential predator) coincided with a minimum of Synechococcus spp. suggesting a possible predator‐prey interaction. This implied that phytoplankton assemblages which form a functional group cannot only have similar adaptations and requirements but can also exhibit trophic interactions. 4. We propose to enlarge the association Z and create an association Z_MX (where _MX stands for mixotrophs) which would include Synechococcus spp. and C. hirundinella as the most representative of the mixotrophic species found in the oligotrophic Lago Maggiore.     

Direct and indirect effects of weather variability in a specialist butterfly

1. Climate change poses serious threats to the long‐term persistence of many animal and plant populations. Species having specific niche requirements, or characterised by highly co‐evolved interactions, will face the greatest challenges. An example is represented by Maculinea alcon (Denis & Schiffermüller), a monophagous and univoltine butterfly species, which lays eggs only on larval host plants which occur inparticular phenological conditions. 2. The present 2‐year study focused on two M. alcon populations, both located at the southern boundaries of the species, but facing different climatic conditions (360 m, low altitude versus 860 m, high altitude). Population vulnerability with respect to direct and indirect effects of climate change was analysed, focusing on two important aspects of butterfly biology, i.e. the flight activity of adults and the degree of synchrony in the larval plant–insect interactions. 3. It was observed that, when positive temperature anomalies are reached, the temperature can exert detrimental effects on adults' activity. At a low altitude, in a hotter than usual year, a temperature threshold was recorded (around 32 °C), above which the activity of butterflies is inhibited. In contrast, at a high altitude, temperature increases maintain the opportunity to enhance butterfly activity. Altitudinal differences were also observed in the phenology of the two interacting species, which generate stronger asynchrony at low altitudes. 4. High‐ and low‐altitude populations represent different conservation units: a global increase in temperature would pose a serious threat to the lowland populations, whereas high‐altitude populations would gain a greater role in assuring the persistence of M. alcon at its southern boundaries.     

Environmental perception avenues: the interaction of cytokinin and environmental response pathways

Cytokinins were discovered in the 1950s by their ability to promote cell division in cultured plant cells. Recently, there have been significant breakthroughs in our understanding of the biosynthesis, metabolism, perception and signal transduction of this phytohormone. These advances, coupled with physiological and other approaches, have enabled remarkable progress to be made in our understanding of the interactions between cytokinin function and environmental inputs. In this review, we first highlight the most recent advances in our understanding of cytokinin biosynthesis, metabolism and signalling. We then discuss how various environmental signals interact with these pathways to modulate plant growth, development and physiology.