Encoding of female mating dynamics by a hypothalamic line attractor.

Females exhibit complex, dynamic behaviours during mating with variable sexual receptivity depending on hormonal status1-4. However, how their brains encode the dynamics of mating and receptivity remains largely unknown. The ventromedial hypothalamus, ventrolateral subdivision contains oestrogen receptor type 1-positive neurons that control mating receptivity in female mice5,6. Here, unsupervised dynamical system analysis of calcium imaging data from these neurons during mating uncovered a dimension with slow ramping activity, generating a line attractor in neural state space. Neural perturbations in behaving females demonstrated relaxation of population activity back into the attractor. During mating, population activity integrated male cues to ramp up along this attractor, peaking just before ejaculation. Activity in the attractor dimension was positively correlated with the degree of receptivity. Longitudinal imaging revealed that attractor dynamics appear and disappear across the oestrus cycle and are hormone dependent. These observations suggest that a hypothalamic line attractor encodes a persistent, escalating state of female sexual arousal or drive during mating. They also demonstrate that attractors can be reversibly modulated by hormonal status, on a timescale of days.

Facultative hypothermia as a survival strategy during snowstorm induced food shortages in Antarctic storm-petrel chicks.

Wilson's storm-petrels (Oceanites oceanicus) are the smallest marine birds breeding in Antarctica, where events like snowstorms often prevent parents from providing food daily for their offspring. To minimize energy expenses, Wilson's storm-petrel chicks can reduce their metabolism and body temperature by entering hypothermia. Hypothermia is reported to impact development, hence we hypothesized that hypothermia will be majorly used after long fasting periods. Chick development in a breeding colony of Wilson's storm-petrels on the South Shetland Islands was monitored daily during three consecutive summers by recording chicks' body mass and temperature, as well as environmental parameters. Provisioning, and body conditions were highest in 2017, and chicks became hypothermic most frequently in 2016. Body temperature was influenced by age, mass, body condition, and minimal nocturnal temperatures. While most chicks were able to maintain stable body temperatures when not fed for one day, some chicks' body temperatures decreased by up to 21 °C. Age did not differ between those two groups, but chicks maintaining their active body temperatures had higher body conditions. Snowstorms were typically followed by several days of unreliable food provisioning and continuous days of fasting. Most chicks were hypothermic during this time, and were hence able to survive periods of food shortages, reverse their low body temperatures after the next feeding event, and regain body mass. We conclude that hypothermia is a strong survival strategy to endure times of fasting, which might be necessary for Antarctic storm-petrel chicks to reach adulthood. However, in future scenarios, which may include more frequent snowstorms due to climate change, malnourishment could lead to more frequent use of hypothermia, which could affect chicks' development.

Gastrointestinal helminths of Gentoo penguins (Pygoscelis papua) from Stranger Point, 25 de Mayo/King George Island, Antarctica.

The aim of this work is to contribute to the knowledge of gastrointestinal parasites of the Gentoo penguin (Pygoscelis papua) from 25 de Mayo/King George Island (South Shetlands, Antarctica). Gastrointestinal tracts of 37 fresh dead individuals (21 chicks, 10 juveniles, and 6 adults) were collected from December 2006 to February 2012 and examined for macroparasites. Four adult parasite species were found: one Cestoda species (Parorchites zederi), two Nematoda species (Stegophorus macronectes and Tetrameres wetzeli), and one Acanthocephalan (Corynosoma shackletoni). Two species of immature acanthocephalans, Corynosoma hamanni and Corynosoma bullosum, were found in a single host. This is the first record of Tetrameres wetzeli in Gentoo penguins. The low parasite richness observed could be related to the stenophagic and pelagic diet of this host species which feeds almost exclusively on krill.

Reproductive effort affects oxidative status and stress in an Antarctic penguin species: An experimental study.

The oxidative cost of reproduction has been a matter of debate in recent years presumably because of the lack of proper experimental studies. Based on the hypothesis that different brood sizes produce differential reproductive costs, an experimental manipulation during breeding of Adélie penguins was conducted at Hope Bay, Antarctica, to study oxidative status and stress. We predict that a lower reproductive effort should be positively related to low oxidative and physiological stress. We randomly assigned nests with two chicks to a control reproductive effort group (CRE), and by removing one chick from some nests with two chicks, formed a second, low reproductive effort group (LRE). We examined how oxidative status in blood plasma (reactive oxygen metabolites, ROMs, and total antioxidant capacity, OXY) and stress (heterophil/lymphocyte ratio, H/L) responded to a lower production of offspring total biomass. Our nest manipulation showed significant differences in offspring total biomass, which was lower in the LRE group. As predicted, the LRE group had higher antioxidant capacity than individuals in the CRE group. We have also found, although marginally significant, interactions between sex and treatment in the three variables analysed. Females had higher OXY, lower ROMs and lower H/L ratio when rearing one chick, whereas males did so when rearing two except for OXY which was high regardless of treatment. Moreover, there was a significant negative correlation between the H/L ratio and OXY in females. Finally, we have found a negative and significant relationship between the duration of the experiment and OXY and ROMs and positive with H/L ratio which suggests that indeed breeding penguins are paying an effort in physiological terms in relation to the duration of the chick rearing. In conclusion, a reduction of the reproductive effort decreased oxidative stress in this long-lived bird meaning that a link exists between breeding effort and oxidative stress. However, our findings suggest different sex strategies which results in opposite physiological responses presumably depending on different life-history strategies in males and females.

Multiple sex chromosome system in penguins (Pygoscelis, Spheniscidae).

Penguins are classified in the order Sphenisciformes into a single family, Spheniscidae. The genus Pygoscelis Wagler, 1832, is composed of three species, Pygoscelis antarcticus Forster, 1781, P. papua Forster, 1781 and P. adeliae Hombron & Jacquinot, 1841. In this work, the objective was to describe and to compare the karyotypes of Pygoscelis penguins contributing genetic information to Sphenisciformes. The metaphases were obtained by lymphocyte culture, and the diploid number and the C-banding pattern were determined. P. antarcticus has 2n = 92, P. papua 2n = 94 and P. adeliae exhibited 2n = 96 in males and 2n = 95 in females. The difference of diploid number in P. adeliae was identified as a multiple sex chromosome system where males have Z1Z1Z2Z2 and females Z1Z2W. The C-banding showed the presence of a heterochromatic block in the long arm of W chromosome and Z2 was almost entirely heterochromatic. The probable origin of a multiple system in P. adeliae was a translocation involving the W chromosome and the chromosome ancestral to Z2. The comparison made possible the identification of a high karyotype homology in Sphenisciformes which can be seen in the conservation of macrochromosomes and in the Z chromosome. The karyotypic divergences in Pygoscelis are restricted to the number of microchromosomes and W, which proved to be highly variable in size and morphology. The data presented in this work corroborate molecular phylogenetic proposals, supporting the monophyletic origin of penguins and intraspecific relations.