Individual contributions to group behaviour in the cooperatively breeding southern ground-hornbill Bucorvus leadbeateri

Cooperative breeding, in which individuals other than breeders contribute to raising offspring, has been the focus of much scientific research over the past decades. Why do some individuals help to raise offspring that are not their own? In birds, cooperative breeding is found mainly in harsh regions with greater environmental variability, such that individuals might do better to help relatives than attempt to breed themselves. However, in some bird families cooperative breeding is instead associated with stable and benign environments, suggesting that species may form cooperative groups for different reasons. Most studies have focused on the benefits that additional group members bring to offspring, by increasing provisioning rates, nestling survival, and overall reproductive output. These benefits have been suggested to mitigate the effects of harsh climatic conditions and to be particularly important in the face of anthropogenic climate change, during which increases in temperature extremes and interannual rainfall variability are expected to push species' tolerance to the limit. However, other advantages of group living have been less often considered; for example, collective territory defence is common in cooperative breeders and ensures exclusive access to crucial resources such as food, nesting sites, and mates. A better understanding of the diverse factors favouring cooperative behaviour can offer insights as to why, and in what environmental conditions, social behaviour has evolved, and whether and how it might help animal populations to cope with environmental change. Therefore, the aims of this thesis were to investigate how individuals within cooperative groups contribute to reproduction and territory defence in an atypical cooperative breeder, the southern ground-hornbill Bucorvus leadbeateri. The large body size and exceptionally long lifespan of ground-hornbills leads to a “slow” life-history strategy, providing a striking contrast to most wellstudied avian cooperative breeders, which tend to be small, relatively short-lived passerines. Furthermore, while the hornbill family is usually associated with mesic, stable environments, groundhornbills inhabit semi-arid, fluctuating environments. Studying them thus may shed light on why cooperative breeding might be favoured in both harsh, fluctuating environments, as well as benign, stable environments. I use a combination of my own data collected over five years (2017‒2022) and long-term data collected from the APNR Southern Ground-Hornbill Project (2000‒2022) to test the effects of environmental and social factors (climatic conditions, group size and composition, and age structure of group members) on reproductive and territorial cooperative behaviour. The first two data chapters focus on how group members influence provisioning efforts and reproductive outcomes, and whether group members of different ages can mitigate the effects of harsh climatic conditions. My results showed that high temperatures and low rainfall had generally negative effects on reproduction, and that cooperative breeding provided some reproductive benefits, but did not act as a buffer to provisioning rates or reproductive outputs. Specifically, we showed that adult males had the highest provisioning rates and provisioned larger items, but the additive care they provided did not buffer the effects of high temperatures. Additionally, we showed that hot and dry conditions were associated with decreased breeding probability, later laying dates, and decreased nestling body mass, and that group composition did not significantly mitigate these negative effects. Instead, our results suggested that group or territory quality may be a more important factor in determining reproductive success. The second two data chapters focus on territory defence. Specifically, I asked how different group members contributed to the species' characteristic deep booming chorus vocalisations used to advertise territories, and how responses to territorial intrusions were mediated by caller identity and group size. I showed that calls were significantly different between the sexes, and that females produced sequences of calls that formed unique melodies that could be automatically assigned to the correct individual with a 94% success rate. Melodies are an effective way of signalling individual identity in long distance communication, as this acoustic information travels well when composed of low-pitched sounds. Therefore, since each group generally contains only one adult female, groups can be identified by the female's signature. Next, I showed that there were no clear effects of intruder group identity on the responses of territory holders, but found that group size was positively associated with aggressive responses, indicating that group living may provide resource defence benefits. Overall, the findings in this thesis indicated that group living provided benefits for territory defence and to a lesser extent, reproduction, and that individual contributions of different group members varied between different cooperative behaviours. Despite ground-hornbills inhabiting semiarid regions with harsh climatic conditions, the presence of additional group members of different ages during reproduction were insufficient to mitigate the negative effects of high temperature and low rainfall. However, the likely benefits provided by additional helpers to territory defence suggest that the ecology, longevity, and slow-development of ground-hornbills may render the presence of additional helpers less critical for reproduction, but more important for resource defence. Further research into other group behaviours such as predator vigilance, foraging and hunting, and energy conservation would provide additional insights into other benefits that cooperative breeding might provide. This study implies that a species' life-history strategy may be an important mechanism determining the benefits individuals receive from breeding cooperatively, and so help to explain the ecological correlates and diversity of forms taken by cooperative breeding, including the remarkable biology of the southern ground-hornbill

Causal inference in medical records and complementary systems pharmacology for metformin drug repurposing towards dementia.

Metformin, a diabetes drug with anti-aging cellular responses, has complex actions that may alter dementia onset. Mixed results are emerging from prior observational studies. To address this complexity, we deploy a causal inference approach accounting for the competing risk of death in emulated clinical trials using two distinct electronic health record systems. In intention-to-treat analyses, metformin use associates with lower hazard of all-cause mortality and lower cause-specific hazard of dementia onset, after accounting for prolonged survival, relative to sulfonylureas. In parallel systems pharmacology studies, the expression of two AD-related proteins, APOE and SPP1, was suppressed by pharmacologic concentrations of metformin in differentiated human neural cells, relative to a sulfonylurea. Together, our findings suggest that metformin might reduce the risk of dementia in diabetes patients through mechanisms beyond glycemic control, and that SPP1 is a candidate biomarker for metformin's action in the brain

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements