Biology subjects

Larsen, E.

Publications and source records attributed to Larsen, E..

5 recordsLinked to original sources

bioRxiv2026

Large-scale atmospheric circulation cells regulate migratory dynamics of the iconic monarch butterfly

Understanding the impacts of climate on migratory dynamics is a priority for global change research, especially as phenological mismatches have been identified as a primary concern for long-distance migration. The eastern monarch (Danaus plexippus) is a flagship species for insect migration, but there has been surprisingly little research on their spring and summer migratory timing and mismatches with their key breeding resources. We show that spring, but not summer, phenological mismatch with their milkweed host plants has the potential to be a limiting factor in the eastern monarchs yearly population growth. To better understand arrival at their breeding grounds, we developed models specifically to tease apart the factors that push (from departure grounds), pull (towards arrival grounds), or facilitate flow (in the flight corridor) during migration. We found wind (flow) dynamics to be the most important factor associated with arrival timing, especially in spring. Further, we show how spring and summer migratory flyways coincide with the large-scale Hadley and Ferrel atmospheric cells respectively, and how their dynamics appear to be essential for understanding monarch migratory timing.

ecology↗

bioRxiv2025

Spore morphology and evolution in Isoetes (Isoetales)

Isoetes (Isoetaceae, Isoetales) is a cosmopolitan genus with an ancient and diverse evolutionary history that presumably peaked in the Paleozoic. The age of the living clade has never been satisfactorily clarified. With little morphological (and molecular) divergence among species, megaspore morphology may provide valuable information on relationships in the group, not least among extant and extinct forms. We study megaspore ornamentation and surface texture/structure in 74 phylogenetically placed samples representing 59 species of Isoetes using SEM, and we discuss evolutionary implications of the results. Ornamentation (classified into 12 categories) and surface structure/texture (10 categories) were mapped onto a phylogeny constructed based on molecular data from the same samples whenever possible. All megaspores of the family are trilete with an outermost siliceous coating. There is ample micromorphological variation, of which some appears clade specific. The megaspores of Isoetes reticulata, discovered from the late Oligocene to early Miocene of Tasmania, share remarkable similarities with those of extant species in the Australasian clade, in particular Isoetes neoguineensis and partly also Isoetes japonica. We argue that this fossil could be used to calibrate the age of the Australasian crown group (clade D) to absolute time (c. 20-25 Ma) in analyses of divergence times of clades based on molecular data.

evolutionary biology↗

bioRxiv2024

The wake and sleep-modulating neurons of the lateral hypothalamic area demonstrate a differential pattern of degeneration in Alzheimers disease

BackgroundSleep-wake dysfunction is an early and common event in Alzheimers disease (AD). The lateral hypothalamic area (LHA) regulates the sleep and wake cycle through wake-promoting orexinergic neurons (OrxN) and sleep-promoting melanin-concentrating hormone or MCHergic neurons (MCHN). These neurons share close anatomical proximity with functional reciprocity. This study investigated LHA OrxN and MCHN loss patterns in AD individuals. Understanding the degeneration pattern of these neurons will be instrumental in designing potential therapeutics to slow down the disease progression and remediate the sleep-wake dysfunction in AD. MethodsPostmortem human brain tissue from donors with AD (across progressive stages) and controls were examined using unbiased stereology. Formalin-fixed, celloidin-embedded hypothalamic sections were stained with Orx-A/MCH, p-tau (CP13), and counterstained with gallocyanin. Orx or MCH-positive neurons with or without CP13 inclusions and gallocyanin-stained neurons were considered for stereology counting. Additionally, we extracted RNA from the LHA using conventional techniques. We used customized Neuropathology and Glia nCounter(R) (Nanostring) panels to study gene expression. Wald statistical test was used to compare the groups, and the genes were considered differentially expressed when the p-value was <.05. ResultsWe observed a progressive decline in OrxN alongside a relative preservation of MCHN. OrxN decreased by 58% (p=.03) by Braak stages (BB) 1-2 and further declined to 81% (p=.03) by BB 5-6. Conversely, MCHN demonstrated a non-statistical significant decline (27%, p=.1088) by BB 6. We observed a progressive increase in differentially expressed genes (DEGs), starting with glial profile changes in BB2. While OrxN loss was observed, Orx-related genes showed upregulation in BB 3-4 compared to BB 0-1. GO and KEGG terms related to neuroinflammatory pathways were mainly enriched. ConclusionsTo date, OrxN loss in the LHA represents the first neuronal population to die preceding the loss of LC neurons. Conversely, MCHN shows resilience to AD p-tau accumulation across Braak stages. The initial loss of OrxN correlates with specific neuroinflammation, glial profile changes, and overexpression of HCRT, possibly due to hyperexcitation following compensation mechanisms. Interventions preventing OrxN loss and inhibiting p-tau accumulation in the LHA could prevent neuronal loss in AD and, perhaps, the progression of the disease.

neuroscience↗

bioRxiv2020

Reframing Fouquieria splendens in its larger environmental and ecological context: Effect of topography and interspecific neighbors on ocotillo morphology and distribution

Fouquieria splendens is a stem-succulent native to the Chihuahuan, Mojave, and Sonoran Deserts that spans Mexico and the American Southwest. It is well-known for its variable morphology, the underlying reason for which remains incompletely understood. Here, we attempt to quantify the effect of topographic and interspecific factors on F. splendens morphology and distribution. To this end, we measured 27 ocotillos located in the Organ Pipe Cactus National Monument within the Sonoran Desert during June of 2019. We also quantified the spatial distribution of interspecific neighbors relative to F. splendens within two topographically different sites: a bajada gradient and a plain. Using ocotillo morphology, the distances to the nearest neighbors of ocotillos, and hydrographic data extracted from the National Hydrography Dataset, we demonstrate 1) the effect of major interspecific neighbors, i.e. shrubs and cacti, on ocotillo morphology; 2) the effect of elevation on intraspecific spacing as individuals compete for limited space; and 3) a trade-off between height and number of branches. This places F. splendens morphology in its larger environmental and ecological context, highlighting the importance of individual traits and associated trade-offs among traits affected by topography and interspecific neighbors. By examining the ocotillo in a multi-species community and diverse landscape, this study provides empirical insight into a wider range of factors contributing to the variation in F. splendens morphology and spacing.

ecology↗

bioRxiv2020

Sampling bias exaggerates a textbook example of a trophic cascade

Understanding how ecosystems respond to the loss and recovery of large predators is a major challenge because these free-living systems are difficult to sample properly. We show how an accepted practice of nonrandom sampling has confounded this understanding in a textbook system (Yellowstone National Park) where carnivore [Canis lupus (wolf)] recovery is often associated with a trophic cascade involving changes in herbivore [Cervus canadensis (elk)] behavior and density that promote plant regeneration. Long-term data indicate that a customary practice of sampling only the tallest young plants overestimated regeneration of overstory aspen (Populus tremuloides) by a factor of 3-8 compared to random sampling. Sampling only the tallest young plants favored plants taller than the preferred browsing height of elk and overlooked non-regenerating aspen stands. Our results demonstrate how seemingly minor departures from principled sampling can generate substantial misunderstandings about the strength of trophic cascades in response to large predator recovery.

ecology↗