Safety out of control: dopamine and defence

We enjoy a sophisticated understanding of how animals learn to predict appetitive outcomes and direct their behaviour accordingly. This encompasses well-defined learning algorithms and details of how these might be implemented in the brain. Dopamine has played an important part in this unfolding story, appearing to embody a learning signal for predicting rewards and stamping in useful actions, while also being a modulator of behavioural vigour. By contrast, although choosing correct actions and executing them vigorously in the face of adversity is at least as important, our understanding of learning and behaviour in aversive settings is less well developed. We examine aversive processing through the medium of the role of dopamine and targets such as D2 receptors in the striatum. We consider critical factors such as the degree of control that an animal believes it exerts over key aspects of its environment, the distinction between 'better' and 'good' actual or predicted future states, and the potential requirement for a particular form of opponent to dopamine to ensure proper calibration of state values

Silver Ferns of Bangladesh and the exclusion of reported Aleuritopteris grisea (Blanf.) Panigrahi (Pteridophyta, Pteridaceae)

The three species of Aleuritopteris ("Silver Ferns") present in Bangladesh are discussed, A. bicolor (Roxb.) Fraser-Jenk, A. anceps (Blanf.) Panigrahi and A. subdimorpha (C.B.Clarke &amp; Baker) Fraser-Jenk., correcting some previous erroneous reports. Aleuritopteris grisea (Blanf.) Panigrahi has recently been reported from the Chittagong Hills, S.E. Bangladesh. But that species is well known to be a high Himalayan Sino-Himalayan species of the Tibetan subtype, confined to the main Himalayan ranges and occurring from c. 2900 - 4000 m altitude. The specimen misreported as it from Bangladesh belongs to the low-altitude species, A. anceps (Blanf.) Panigrahi, which occurs from c. 300-750 m altitude and is a S.E. Asian (Malesian) element in the flora of the Indian subcontinent. This species was first knowingly collected in Bangladesh in the same District in 2003 by the present author, but unfortunately Bangladesh was then inadvertently omitted from its range in his monographic summary of Indian subcontinental cheilanthoid ferns. DOI: http://dx.doi.org/10.3329/bjb.v42i2.18020 Bangladesh J. Bot. 42(2): 195-206, 2013 (December)</jats:p

Natural hybridization between genera that diverged from each other approximately 60 million years ago.

A fern from the French Pyrenees-×Cystocarpium roskamianum-is a recently formed intergeneric hybrid between parental lineages that diverged from each other approximately 60 million years ago (mya; 95% highest posterior density: 40.2-76.2 mya). This is an extraordinarily deep hybridization event, roughly akin to an elephant hybridizing with a manatee or a human with a lemur. In the context of other reported deep hybrids, this finding suggests that populations of ferns, and other plants with abiotically mediated fertilization, may evolve reproductive incompatibilities more slowly, perhaps because they lack many of the premating isolation mechanisms that characterize most other groups of organisms. This conclusion implies that major features of Earth's biodiversity-such as the relatively small number of species of ferns compared to those of angiosperms-may be, in part, an indirect by-product of this slower "speciation clock" rather than a direct consequence of adaptive innovations by the more diverse lineages