37 research outputs found
The same frequency of planets inside and outside open clusters of stars
Most stars and their planets form in open clusters. Over 95 per cent of such
clusters have stellar densities too low (less than a hundred stars per cubic
parsec) to withstand internal and external dynamical stresses and fall apart
within a few hundred million years. Older open clusters have survived by virtue
of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when
they formed. Such clusters represent a stellar environment very different from
the birthplace of the Sun and other planet-hosting field stars. So far more
than 800 planets have been found around Sun-like stars in the field. The field
planets are usually the size of Neptune or smaller. In contrast, only four
planets have been found orbiting stars in open clusters, all with masses
similar to or greater than that of Jupiter. Here we report observations of the
transits of two Sun-like stars by planets smaller than Neptune in the
billion-year-old open cluster NGC6811. This demonstrates that small planets can
form and survive in a dense cluster environment, and implies that the frequency
and properties of planets in open clusters are consistent with those of planets
around field stars in the Galaxy.Comment: 18 pages, 6 figures, 1 table (main text + supplementary information
Sole coloration as an unusual aposematic signal in a Neotropical toad
Many animals have evolved remarkable strategies to avoid predation. In diurnal, toxic harlequin toads (Atelopus) from the Amazon basin, we find a unique colour signal. Some Atelopus populations have striking red soles of the hands and feet, visible only when walking. When stationary, the toads are hard to detect despite their yellow-black dorsal coloration. Consequently, they switch between high and low conspicuousness. Interestingly, some populations lack the extra colour display of the soles. We found comprehensive support that the red coloration can act as an aposematic signal directed towards potential predators: red soles are significantly more conspicuous than soles lacking red coloration to avian predators and the presence of the red signal significantly increases detection. Further, toads with red soles show bolder behaviour by using higher sites in the vegetation than those lacking this signal. Field experiments hint at a lower attack risk for clay models with red soles than for those lacking the signal, in a population where the red soles naturally occur. We suggest that the absence of the signal may be explained by a higher overall attack risk or potential differences of predator community structure between populations. © 2019, The Author(s)