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About 50 y ago, Crow and Kimura [An Introduction to Population Genetics Theory (1970)] and Ohta and Kimura [Genet. Res. 22, 201–204 (1973)] laid the foundations of conservation genetics by predicting the relationship between population size and genetic marker diversity. This work sparked an enormous research effort investigating the importance of population dynamics, in particular small population size, for population mean performance, population viability, and evolutionary potential. In light of a recent perspective [J. C. Teixeira, C. D. Huber, Proc. Natl. Acad. Sci. U.S.A. 118, 10 (2021)] that challenges some fundamental assumptions in conservation genetics, it is timely to summarize what the field has achieved, what robust patterns have emerged, and worthwhile future research directions. We consider theory and methodological breakthroughs that have helped management, and we outline some fundamental and applied challenges for conservation genetics.

Animal and plant species around the world are being challenged by the deleterious effects of inbreeding, loss of genetic diversity, and maladaptation due to widespread habitat destruction and rapid climate change. In many cases, interventions will likely be needed to safeguard populations and species and to maintain functioning ecosystems. Strategies aimed at initiating, reinstating, or enhancing patterns of gene flow via the deliberate movement of genotypes around the environment are generating growing interest with broad applications in conservation and environmental management. These diverse strategies go by various names ranging from genetic or evolutionary rescue to provenancing and genetic resurrection. Our aim here is to provide some clarification around terminology and to how these strategies are connected and linked to underlying genetic processes. We draw on case studies from the literature and outline mechanisms that underlie how the various strategies aim to increase species fitness and impact the wider community. We argue that understanding mechanisms leading to species decline and community impact is a key to successful implementation of these strategies. We emphasize the need to consider the nature of source and recipient populations, as well as associated risks and trade‐offs for the various strategies. This overview highlights where strategies are likely to have potential at population, species, and ecosystem scales, but also where they should probably not be attempted depending on the overall aims of the intervention. We advocate an approach where short‐ and long‐term strategies are integrated into a decision framework that also considers nongenetic aspects of management.

Post‐mortem investigations indicate that the locus coeruleus (LC) is the initial site of hyperphosphorylated pretangle tau, a precursor to neurofibrillary tangles (NFTs) found in Alzheimer's disease (AD). The presence of pretangle tau and NFTs correlates with AD progression and symptomatology. LC neuron integrity and quantity are linked to cognitive performance, with degeneration strongly associated with AD. Despite their importance, the mechanisms of pretangle tau‐induced LC degeneration are unclear. This study examined the transcriptomic and mitochondrial profiles of LC noradrenergic neurons after transduction with pseudophosphorylated human tau. Tau hyperphosphorylation increased the somatic expression of the L‐type calcium channel (LTCC), impaired mitochondrial health, and led to deficits in spatial and olfactory learning. Sex‐dependent alterations in gene expression were observed in rats transduced with pretangle tau. Chronic LTCC blockade prevented behavioral deficits and altered mitochondrial mRNA expression, suggesting a potential link between LTCC hyperactivity and mitochondrial dysfunction. Our research provides insights into the consequences of tau pathology in the originating structure of AD. Hyperphosphorylated tau (ptau) leads to calcium overload via LTCC Cav1.2 channels (1), mitochondrial complex I deficit (2), increased mitochondrial fusion (3), which can be associated with reactive oxygen species (ROS) production. Ptau also impedes anterograde transport of distinct cargoes including mitochondria. (4) Together, these pathological changes lead to synaptic and axonal degeneration in the locus coeruleus neurons.

The maternally inherited intracellular bacteria Wolbachia can manipulate host reproduction in various ways that foster frequency increases within and among host populations. Manipulations involving cytoplasmic incompatibility (CI), where matings between infected males and uninfected females produce non-viable embryos, are common in arthropods and produce a reproductive advantage for infected females. CI was associated with the spread of Wolbachia variant wRi in Californian populations of Drosophila simulans, which was interpreted as a bistable wave, in which local infection frequencies tend to increase only once the infection becomes sufficiently common to offset imperfect maternal transmission and infection costs. However, maternally inherited Wolbachia are expected to evolve towards mutualism, and they are known to increase host fitness by protecting against infectious microbes or increasing fecundity. We describe the sequential spread over approximately 20 years in natural populations of D. simulans on the east coast of Australia of two Wolbachia variants (wAu and wRi), only one of which causes significant CI, with wRi displacing wAu since 2004. Wolbachia and mtDNA frequency data and analyses suggest that these dynamics, as well as the earlier spread in California, are best understood as Fisherian waves of favourable variants, in which local spread tends to occur from arbitrarily low frequencies. We discuss implications for Wolbachia-host dynamics and coevolution and for applications of Wolbachia to disease control.

The arbovirus vectors Aedes aegypti (yellow fever mosquito) and Ae. albopictus (Asian tiger mosquito) are both common throughout the Indo-Pacific region, where 70% of global dengue transmission occurs. For Ae. aegypti all Indo-Pacific populations are invasive, having spread from an initial native range of Africa, while for Ae. albopictus the Indo-Pacific includes invasive populations and those from the native range: putatively, India to Japan to Southeast Asia. This study analyses the population genomics of 480 of these mosquitoes sampled from 27 locations in the Indo-Pacific. We investigated patterns of genome-wide genetic differentiation to compare pathways of invasion and ongoing gene flow in both species, and to compare invasive and native-range populations of Ae. albopictus. We also tested landscape genomic hypotheses that genetic differentiation would increase with geographical distance and be lower between locations with high connectivity to human transportation routes, the primary means of dispersal at these scales. We found that genetic distances were generally higher in Ae. aegypti, with Pacific populations the most highly differentiated. The most differentiated Ae. albopictus populations were in Vanuatu, Indonesia and Sri Lanka, the latter two representing potential native-range populations and potential cryptic subspeciation respectively. Genetic distances in Ae. aegypti increased with geographical distance, while in Ae. albopictus they decreased with higher connectivity to human transportation routes. Contrary to the situation in Ae. aegypti, we found evidence of long-distance Ae. albopictus colonisation events, including colonisation of Mauritius from East Asia and of Fiji from Southeast Asia. These direct genomic comparisons indicate likely differences in dispersal ecology in these species, despite their broadly sympatric distributions and similar use of human transport to disperse. Our findings will assist biosecurity operations to trace the source of invasive material and for biocontrol operations that benefit from matching genetic backgrounds of released and local populations.

Genetic rescue has now been attempted in several threatened species, but the contribution of genetics per se to any increase in population health can be hard to identify. Rescue is expected to be particularly useful when individuals are introduced into small isolated populations with low levels of genetic variation. Here we consider such a situation by documenting genetic rescue in the mountain pygmy possum, Burramys parvus . Rapid population recovery occurred in the target population after the introduction of a small number of males from a large genetically diverged population. Initial hybrid fitness was more than two-fold higher than non-hybrids; hybrid animals had a larger body size, and female hybrids produced more pouch young and lived longer. Genetic rescue likely contributed to the largest population size ever being recorded at this site. These data point to genetic rescue as being a potentially useful option for the recovery of small threatened populations. Genetic rescue can be valuable for the conservation of small populations threatened by low genetic diversity, but it carries the perceived risk of outbreeding depression. Here, Weeks et al. report increased hybrid fitness in a rescued population of the mountain pygmy possum, which likely contributed to population growth following genetic rescue.

Women are advised to optimise weight before pregnancy. However, many are either already living with overweight or obesity prior to becoming pregnant, increasing the risks for adverse outcomes. Health care professionals (HCP) are responsible for advising women of risks throughout and following pregnancy. However, midwives often find broaching the conversation around maternal obesity difficult. This study explored the experiences of pregnant women living with obesity in accessing antenatal care. Seventeen women completed a semi-structured interview. Transcripts were analysed thematically. Four themes were developed: 1) antenatal care is inconsistent, 2) additional support is needed, 3) women feel judged about their weight, and 4) weight cycling is highly prevalent. Findings suggest that pregnant women living with obesity often experience weight bias from HCPs, feel judged because of their weight and are left feeling confused and overlooked. Women reported inconsistencies in advice and care offered and acknowledged a lack of continuity of care throughout pregnancy. We call for an urgent need for further multidisciplinary training to address the concerns, experiences and needs of pregnant women living with obesity.

In sub-Saharan Africa, stillbirth rates remain high. To design effective interventions to reduce stillbirths, accurate determination of their aetiology is important. Conventional autopsy for accurate confirmation of cause is not acceptable or feasible in several societies in sub-Saharan Africa; minimal invasive tissue sampling (MITS), is a recently developed, less invasive alternative. In this study, we explored the acceptability of MITS in the community and among healthcare workers in Uganda to guide the future implementation. A qualitative study was done among community members and healthcare workers in Mbale in Eastern Uganda. We undertook in-depth interviews and focus group discussions in English or local languages. Interviews were audio-recorded, transcribed as necessary prior to formal content analysis. The themes were organised using NVivo software and presented according to Sekhon's theoretical framework. Overall, participants preferred the idea of MITS to conventional autopsy because of the perception that it was fast, maintained the facial appearance and kept the body intact. It was thought that the procedure would improve the detection of the cause of stillbirths, which in turn would help to prevent future stillbirths. It would also resolve conflicts in the community between community members or the women and the healthcare workers about the cause of a stillbirth. It was suggested that some community members may not approve of MITS because of their religious beliefs; the fear that the body parts may be extracted and stolen for witchcraft or organ donation; and a lack of trust in the healthcare system. To implement the procedure, it was suggested that extensive community sensitization should be done, space limitations in healthcare facilities overcome, healthcare workers should be trained and limited human resource should be addressed. The implementation of MITS in Mbale, Eastern Uganda, is likely to be acceptable given sufficient training and sensitisation.