• Brief Communications Arising |

    • Martin A. Nowak
    • , Corina E. Tarnita
    •  & Edward O. Wilson
  • Letter |

    The annelids, or ringed worms, comprise one of the largest and most diverse animal phyla, and are found everywhere from garden soil to the deep sea. Their precise phylogeny has always been sketchy, but now, a new phylogenomic analysis unravels annelid evolution. Notable features include a division of most annelids into the Errantia and Sedentaria — a restitution for two groups based on classical morphology — showing how many details of anatomy and life history bear on the evolution of this important animal group.

    • Torsten H. Struck
    • , Christiane Paul
    •  & Christoph Bleidorn
  • Letter |

    The 'Cambrian explosion', just over 500 million years ago, was a burst of evolution during which most kinds of animals we see today first appeared in the fossil record. They were, however, accompanied by a large number of creatures whose lineages were destined to disappear. Among these were the lobopodians, creatures vaguely related to modern arthropods and the velvet worms of tropical forests, and which — like velvet worms — looked more like worms with legs. Lobopodians came in a variety of bizarre forms, and the discovery of a lobopodian from the Cambrian of China adds to this group. It looked like a thin, flexible worm with oddly inappropriate, chunky, armoured legs. It is claimed that this creature was, however, the closest known fossil relative of modern arthropods, suggesting that the process of acquiring the robust external skeleton characteristic of the group started with the legs, and worked upwards from there.

    • Jianni Liu
    • , Michael Steiner
    •  & Xingliang Zhang
  • Letter |

    It has recently been shown that neurons in the lateral habenula (LHb), a nucleus that projects to midbrain reward areas, can signal aversive outcomes and may be disrupted in depressive disorders. This study now shows that in rats exhibiting learned helplessness (a model of major depression) excitatory synapses onto LHb neurons are potentiated, and that this correlates with helplessness behaviour. Furthermore, depleting transmitter release by repeated electrical stimulation of LHb using a protocol similar to deep brain stimulation rescues both synaptic changes and learned helplessness behaviour.

    • Bo Li
    • , Joaquin Piriz
    •  & Roberto Malinow
  • Article |

    Certain regions of the hypothalamus are important in aggression, but until recently, it has been difficult to specifically stimulate specific cell types within a mixed population of cells. Here, optogenetics is used to solve this specificity problem, finding that optogenetic stimulation of a subdivision within the ventromedial hypothalamus can elicit inappropriate attack behaviours in mice, but electrical stimulation does not produce the same result. Additional analysis of genetic and electrophysiological activity revealed overlapping neuronal subpopulations involved in fighting and mating, with potential competition between these behaviours, as neurons activated during aggression are inhibited during mating.

    • Dayu Lin
    • , Maureen P. Boyle
    •  & David J. Anderson
  • Letter |

    Jawless fish were recently shown to possess T- and B-like lymphocytes expressing diverse assembled antigen receptors. This study identifies and characterizes lympho-epithelial thymus-like structures at the tips of gill filaments of lamprey larvae, thus providing evidence that the similarities underlying the adaptive immune systems of both types of vertebrate appear to extend to primary lymphoid organs.

    • Baubak Bajoghli
    • , Peng Guo
    •  & Thomas Boehm
  • Letter |

    Müllerian mimics have convergently evolved similar warning colouration because of the advantage of strength in numbers. However, it is not clear if this effect is sufficient to maintain coexistence when competitive exclusion would be expected to favour one mimic at the expense of the others. Here, Müllerian mimicry in catfish is characterized, and it is shown through morphometric and stable isotope analysis that mimics do not occupy identical niches, so are not in direct competition, thus explaining their coexistence.

    • Markos A. Alexandrou
    • , Claudio Oliveira
    •  & Martin I. Taylor
  • Article |

    Humans and animals readily learn to associate neutral cues paired with rewards, but the exact role that dopamine release has in this learning is controversial. Using previously established rat strains selectively bred for many generations to have greater or lesser propensity to assign value to learned cues, this study uses cyclic voltammetry to measure dopamine signals in the different strains and also examines the effect of blocking dopamine. It is concluded that dopamine selectively mediates motivational, rather than predictive, aspects of the cues.

    • Shelly B. Flagel
    • , Jeremy J. Clark
    •  & Huda Akil
  • Letter |

    Acid sensing has so far been demonstrated in the gustatory system only. Now, fruitfly olfactory sensory neurons selectively activated by acidic compounds have been identified. Acid sensing also requires the transmembrane protein IR64a, expressed in those neurons as well as neurons involved in the detection of non acidic odorants. Although the IR64a protein isn't sufficient by itself to determine acid recognition, the requirement for IR64a in acid recognition is the first function for a member of this recently discovered family of putative odorant receptors — the ionotropic receptor family.

    • Minrong Ai
    • , Soohong Min
    •  & Greg S. B. Suh
  • Article |

    Light sensing outside the eyes is common in many animals but is usually confined to specialized organs. Here, the entire body wall of the fruitfly larva is found to be tiled with blue- and ultraviolet-light sensing neuronal dendrites, which are essential for the larva's innate light-avoidance behaviour. The phototransduction machinery used by these neurons is distinct from other Drosophila photoreceptor molecules but similar to a system recently identified in nematode neurons.

    • Yang Xiang
    • , Quan Yuan
    •  & Yuh Nung Jan
  • Article |

    Mutations in the methyl-CpG-binding protein 2 (MeCP2) gene cause Rett syndrome, a neurodevelopmental disorder with features of autism. Multiple mouse models of MeCP2 have been generated, but show only a subset of the symptoms of Rett syndrome. These authors find that mice with selective deletion of MeCP2 in GABA-mediated neurons show not only impaired GABA-mediated function, but capitulate multiple key features of Rett, further suggesting a role of inhibitory function in neuropsychiatric disease.

    • Hsiao-Tuan Chao
    • , Hongmei Chen
    •  & Huda Y. Zoghbi
  • Article |

    The central amygdala relies on inhibitory circuitry to encode fear memories, but how this information is acquired and expressed in these connections is unknown. Two new papers use a combination of cutting-edge technologies to reveal two distinct microcircuits within the central amygdala, one required for fear acquisition and the other critical for conditioned fear responses. Understanding this architecture provides a strong link between activity in a specific circuit and particular behavioural consequences.

    • Stephane Ciocchi
    • , Cyril Herry
    •  & Andreas Lüthi
  • Letter |

    In vertebrates, sex can be determined either genetically or by temperature, but the evolutionary causes of this variation remain unknown. These authors show how live-bearing lizards at different climatic extremes of their range differ in their sex-determining mechanisms, with temperature-dependent sex determination in the lowlands and genotypic sex determination at higher altitudes. Their results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection.

    • Ido Pen
    • , Tobias Uller
    •  & Erik Wapstra
  • Brief Communications Arising |

    • Nina Veselka
    • , David D. McErlain
    •  & M. Brock Fenton
  • Brief Communications Arising |

    • Nina Veselka
    • , David D. McErlain
    •  & M. Brock Fenton
  • Letter |

    A phylogenetic analysis of breeding behaviour in birds shows that cooperation is more likely when promiscuity is low — a circumstance in which helpers can be more certain that they are offering aid to relatives. Intermediate levels of promiscuity favour the ability to distinguish relatives from non-relatives. At high levels of promiscuity, no form of cooperation is favoured. Levels of promiscuity therefore provide an explanation for differences between species in levels of cooperation.

    • Charlie K. Cornwallis
    • , Stuart A. West
    •  & Ashleigh S. Griffin
  • Letter |

    A spectacular adaptive radiation among notosuchian crocodyliforms in the southern continents of Gondwana led to all manner of strange forms; in particular, their teeth, rather than being undifferentiated conical fangs, were often differentiated into biting and crushing types, as seen in mammals. These authors describe a new form from the Cretaceous period of Tanzania in which upper and lower dentitions were capable of occlusion, a feature otherwise known only from mammals.

    • Patrick M. O’Connor
    • , Joseph J. W. Sertich
    •  & Jesuit Temba
  • Letter |

    The fossil record of primates is sparse, and many gaps remain in our knowledge. One gap relates to the divergence within the catarrhines — the ancestors of hominoids (apes and humans) and Old World monkeys. The discovery of a previously unknown catarrhine in Saudi Arabia, dated to 29–28 million years ago, helps to fill in some details. This specimen shows very few catarrhine specializations, suggesting that the divergence between Old World monkeys and hominoids must have occurred after this date.

    • Iyad S. Zalmout
    • , William J. Sanders
    •  & Philip D. Gingerich
  • Article |

    Extended cocaine taking triggers several structural and functional changes in the brain that may lead to compulsive drug seeking, but the mechanisms that regulate the process are unclear. Here, a microRNA — miR-212 — is identified that is upregulated in the striatum of rats with a history of extended access to cocaine. The authors suggest that miR-212 protects against the development of compulsive drug taking, and that it may act through the CREB protein, a known regulator of the rewarding effects of cocaine.

    • Jonathan A. Hollander
    • , Heh-In Im
    •  & Paul J. Kenny