A new cold sub-Saturnian candidate planet orbiting GJ 221

Mikko Tuomi, 'A new cold sub-Saturnian candidate planet orbiting GJ 22', Monthly Notices of the Royal Astronomical Society, Letters, Vol 440: L1-L5, advanced access publication 11 February 2014. The version of record is available at doi: 10.1093/mnrasl/slu014 © 2014 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.We re-analyse the recently published HARPS and PFS velocities of the nearby K dwarf GJ 221 that have been reported to contain the signatures of two planets orbiting the star. Our goal is to see whether the earlier studies discussing the system fell victims of false negative detections. We perform the analyses by using an independent statistical method based on posterior samplings and model comparisons in the Bayesian framework that is known to be more sensitive to weak signals of low-mass planets. According to our analyses, we find strong evidence in favour of a third candidate planet in the system corresponding to a cold sub-Saturnian planet with an orbital period of 500 days and a minimum mass of 29 $M_{\oplus}$. Application of sub-optimal signal detection methods can leave low-amplitude signals undetected in radial velocity time-series. Our results suggest that the estimated statistical properties of low-mass planets can thus be biased because several signals corresponding to low-mass candidate planets may have gone unnoticed. This also suggests that the occurrence rates of such planets based on radial velocity surveys might be underestimated.Peer reviewe

Ornamental evolution in Trinidadian guppies (Poecilia reticulata): insights from sensory processing-based analyses of entire colour patterns

The evolution of exaggerated sexual ornamentation is classically thought to proceed as a compromise between opposing vectors of sexual and natural selection. In colour-based ornamentation, as exhibited by guppies (Poecilia reticulata), heightened trait expression may be beneficial in promoting attractiveness, but costly in terms of predation. Opportunities to reconcile this compromise will exist if there are differences between conspecifics and predators in their sensory systems; in such situations guppies should evolve to exploit the ways in which their ornamentation would appear maximally conspicuous to conspecifics. In the present study, we addressed this hypothesis via a study of geographic variation employing the most sophisticated colour analysis yet attempted for Trinidadian guppies. We made two paired contrasts, one between two Aripo populations that vary in the presence of the potential predator Aequidens pulcher, and another between Quare and Marianne populations that vary in exposure to a predatory prawn, Macrobrachium crenulatum. We predicted that, if ornamentation is constrained by the presence of either predator, then guppy conspicuousness should change most markedly across each of the two paired populations as viewed by that predator. Although disparity analysis of entire colour patterns indicated significant differences in both contrasts, this prediction was most clearly supported for the Marianne/Quare contrast. Marianne fish, which co-exist with prawns, exhibited larger black spots coupled with less extensive, less bright flank iridescence. The brightness reductions are notable because, as the only potential guppy predator with a dedicated ultraviolet (UV) photoreceptor, prawns may detect passing male guppies via their UV-bright blues, violets and 'UV/oranges'. We discuss our findings in light of the additional insights that might be obtained by combining spectral assessments and visual modeling with more traditional methods of colour pattern appraisal