Biology subjects

Kruger, L.

Publications and source records attributed to Kruger, L..

8 recordsLinked to original sources

bioRxiv2026

A Bayesian hierarchical analysis of trends and risk to identify regional conservation priorities of Chinstrap Penguins

Chinstrap penguins (Pygoscelis antarcticus) in the Antarctic Peninsula and Scotia Arc regions (CCAMLR subareas 48.1 and 48.2) have experienced substantial declines, yet uncertainty remains about regional variation and conservation priorities. We applied a Bayesian hierarchical model to 1,072 nest counts from 194 colonies (1970 to 2024) to quantify population trends, estimate probabilities of exceeding IUCN Red List thresholds, and assess compensation potential across four locations. The regional population declined by 41.9% over three generations, with 91.4% probability of exceeding the 30% Vulnerable threshold but only 9.2% probability of exceeding the 50% Endangered threshold. Declines were spatially heterogeneous: South Shetland Islands (40.2% of regional population) declined by 74.7% with near-certainty of exceeding both thresholds, while South Orkney Islands showed stability with high uncertainty (median -5%, 95% CI: -31.5% to +36.8%). The probability of increasing colonies compensating for regional losses was only 7%. These results support a three-zone conservation strategy for CCAMLRs proposed Marine Protected Area: urgent protection for the South Shetland Islands, enhanced monitoring for South Orkney and Elephant Islands, and adaptive management for the Antarctic Peninsula. Our uncertainty-quantified framework provides evidence-based guidance for balancing krill fishery access with predator protection in a rapidly changing Southern Ocean.

ecology↗

bioRxiv2026

Lessening the bottleneck: reduced spatiotemporal overlap between krill fishing vessels and post-fledging chinstrap penguins led to increased apparent survival

Fledging is a critical period of a seabird life cycle. Using satellite telemetry, we compared movements and survival proxies (transmission duration) of chinstrap penguin fledglings tracked in 2017 (n=8) and 2025 (n=17) relative to krill fishing vessel activity. In 2017, fishing vessels operated intensively near colonies during summer, resulting in early, frequent encounters (median 1.3 days post-fledging) and short transmission durations (median 9.2 days). In 2025, reduced fishing delayed encounters (median 10.0 days) and tripled tracking duration (median 24.0 days). Hidden Markov Models revealed that vessel encounters reduced the probability of transitioning from foraging to transit behavior ({beta} = -0.76), an effect stronger than the productivity ({beta} = -0.11). While 87.5% of 2017 fledglings ceased transmission prematurely within weeks (half of those right after entering areas intensively used by fishing vessels), 65% of 2025 fledglings survived beyond March, with half of those five transmitting until May after dispersing eastward to the South Orkney Islands. These findings suggest that spatiotemporal overlap with krill fisheries during the critical post-fledging window affected foraging behavior and was associated with shorter transmission durations. Our results support further research of post-fledging penguin ecology to better understand the potential impact of fishery, and, following the precautionary principle, support fishing seasonal protection of important areas during critical periods of krill predators life cycle.

ecology↗

bioRxiv2025

Drone Survey Reveals a Severe Chinstrap Penguin Decline and a Novel Gentoo Colony in an Antarctic Specially Protected Area

Seabird populations in Antarctica are sensitive indicators of environmental change and understanding their dynamics is crucial for assessing the health and future of the Antarctic ecosystems. This study provides an updated population assessment for three key seabird species - the Antarctic Shag (Leucocarbo bransfieldensis), Gentoo Penguin (Pygoscelis papua), and Chinstrap Penguin (P. antarcticus) - within the Antarctic Specially Protected Area (ASPA) 133 on Nelson Island. Using drone-based imagery and photogrammetric analysis, we conducted comprehensive nest counts to evaluate current population size in comparison with historical data. Our results reveal a pronounced 57% decline in the Chinstrap Penguin population at Harmony Point since the 1990s, with 38,080 nests counted compared to historical estimates of nearly 90,000. In contrast, Gentoo Penguin numbers at Harmony Point (3,659 nests) appear stable following a previously documented increase. We also provide the first population estimate for a large Gentoo Penguin colony located on a small peninsula south of Harmony Point, known as the Toe, where 4,641 nests were recorded. Additionally, we report an 84% increase in Antarctic Shags, with 127 nests recorded at Harmony Point. These findings are consistent with regional species-level trends and provide critical baseline data for monitoring the impacts of rapid environmental change on Antarctic seabird communities.

ecology↗

bioRxiv2025

Skuas mortalities linked to positives HPAIV A/H5 beyond Polar Antarctic Circle

The ongoing extinction crisis, driven by human activity, poses a significant threat to seabirds and its especially relevant in highly valuable environments such as Antarctica. Among these threats, seabirds face the risk of local extinctions due to emerging infectious diseases like the Highly Pathogenic Avian Influenza Virus (HPAIV).Progressive spread of HPAIV A/H5N1 outbreaks across South America and the sub-Antarctic islands have been detected, reaching the northern regions of the West Antarctic Peninsula (WAP) during the 2023-2024 season. Here we conducted a comprehensive epidemiological survey conducted on sixteen seabird nesting localities along the WAP from November 2024 to January 2025 to assess the health status of the Antarctic seabirds and detect the presence of HPAIV. We observed unusual mortalities among nesting populations of skuas, with a total of 35 deaths skuas recorded along the WAP and beyond the Antarctic Polar Circle, including Important bird breeding areas around Margarita Bay. HPAIV A/H5 was confirmed in all dead skuas sampled (n=11), from six different locations. This finding represents the southernmost record of seabird mortality in Antarctica related to HPAIV to date. The expansion of HPAIV observed here raises concerns about further spread of avian flu out the Antarctic Peninsula, potentially leading to increased mortality rates in the Antarctic bird populations. These findings are relevant for the assessment of the general health status of Antarctic seabird populations and provide a baseline for the continuous monitoring of the HPAIV spread in avian species during the next breeding seasons.

ecology↗

bioRxiv2024

Confirmation of Highly Pathogenic Avian Influenza (HPAI) H5N1 Associated with an Unexpected Mortality Event in South Polar Skuas (Stercorarius maccormicki) during 2023-2024 Surveillance Activities in Antarctica

From December 2023 to March 2024, a surveillance program to detect HPAI H5N1 was performed on Antarctica Territory, at Fildes Peninsula (King George Island, Maritime Antarctic), and James Ross Island. At Fildes Peninsula, samples from marine birds and mammals from four sampling locations were collected, based on their accessibility and the presence of animal colonies: Ardley Island, which presents a high concentration of Gentoo penguins (Pygoscelis papua); Ardley Cove were small groups of likely non-reproductive Chinstrap penguins (Pygoscelis antarcticus); Southern elephant (Mirounga leonina) and Weddell (Leptonycotes wedellii) seals haul-out sites; and, a nesting site of Southern giant petrels (Macronectes giganteus). On February 28th the surveillance group received a request for sample collection, due to the observation of deceased seabirds at James Ross Island in the area neighboring the Lachman lakes (63.7989 S, 57.8105 W). Six samples from five dead South polar skuas (Stercorarius maccormicki) were collected on March 3rd, 2024. All samples were collected adhering to the Antarctic Treaty guidelines. After collecting a total of 943 samples from Fildes Peninsula all results tested negative, and no individuals had clinical signs or behaviors compatible with HPAI. However, all samples from South polar skuas from James Ross Island were confirmed positive for HPAI H5N1 clade 2.3.4.4 by specific real-time RT-PCR reactions. These results confirmed the first mortality event registered in Antarctica (south of 60{degrees}S) caused by HPAI H5N1, in this case on South polar skuas. Further studies are needed to genetically characterize the virus and to better understand the role of skuas in the dynamics of viral dissemination in Antarctica.

microbiology↗

bioRxiv2023

A tipping point in West Antarctica in 2023's circumpolar 5-sigma event? a glimpse from the emperor penguin's perspective

Emperor penguins are one of the seabird species most vulnerable to climate change in Antarctica, as they depend on stable sea ice for breeding and molting. Recent extremes of warming have taken to the lowest records of sea ice in West Antarctica in 2022 and 2023, raising concerns to the extent that emperor penguins have been affected. We evaluated historical satellite data (1985-2022) of sea ice around the 10 emperor penguin breeding colonies, identified so far along the coast of the Amundsen and Bellingshausen Seas, and compared them to recent sea ice cover (2022-2023) to identify where and when critical thresholds of sea ice cover have been crossed. We found that the sea ice retreated below the critical thresholds in 2022-2023 during the chick-rearing and in some cases failed to return at the start of the following breeding season, hence likely affecting 9 of the 10 emperor penguin colonies in the region. This is an unprecedented climatic phenomena affecting breeding habitat of emperor penguin colonies over a large area, potentially affecting numerically important colonies in West Antarctica.

ecology↗

bioRxiv2023

Reversible conjugation of a CBASS nucleotide cyclase regulates immune response to phage infection

Antiviral defence systems build the prokaryotic immune system and their proper regulation is vital for survival and fitness. While it is important that they are readily available in case of infection, they need to be tightly controlled to prevent activation of an unnecessary cellular response. Here we describe how the bacterial cyclic oligonucleotide-based antiphage signalling system (CBASS) uses its intrinsic protein modification system to regulate the nucleotide cyclase. By integrating a Type II CBASS system from Bacillus cereus into the cognate host Bacillus subtilis, we show that the Cap2 protein conjugates the cyclase exclusively to the conserved phage shock protein A (PspA) in the absence of phage. This cyclase-PspA conjugation is reversed after infection by the isopeptidase Cap3. Finally, we propose a model in which the cyclase is held in an inactive state by conjugation to PspA in the absence of phage and that this conjugation is released upon infection, priming the cyclase for activation.

microbiology↗

bioRxiv2020

Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human induced pluripotent stem cells, neural stem cells and neurons

The coupling of the endoplasmic reticulum (ER) with mitochondria modulates neuronal calcium signaling. Whether this link changes with neuronal development is unknown. The current study first determined whether ER calcium stores are similar during development of human neurons, and then tested if the ER/mitochondrial coupling varied with development. The release of ER calcium to the cytosol by the IP3 agonist bradykinin was determined in human induced-pluripotent stem cells (iPSC), neural stem cells (NSC) and neurons. The concentration dependence for the release of ER calcium was similar at different stages of development. Metabolism changes dramatically with development. Glycolysis is the main energy source in iPSC and NSC whereas mitochondrial metabolism is more prominent in neurons. To test whether the coupling of mitochondria and ER changed with development, bombesin or bradykinin releasable calcium stores (BRCS) were monitored after inhibiting either of two key mitochondrial enzyme complexes: the alpha-ketoglutarate dehydrogenase complex (KGDHC) or the pyruvate dehydrogenase complex (PDHC). Inhibition of KGDHC did not alter BRCS in either iPSC or NSC. Inhibition of PDHC in neurons diminished BRCS whereas decreased KGDHC activity exaggerated BRCS. The latter finding may help understand the pathology of Alzheimers disease (AD). BRCS is exaggerated in cells from AD patients and KGDHC is reduced in brains of patients with AD. In summary, a prominent ER/mitochondrial link in neurons is associated with selective mitochondrial enzymes. The ER/mitochondrial link changes with human neuronal development and plausibly links ER calcium changes to AD.

neuroscience↗