Biology subjects

Contreras, E. B.

Publications and source records attributed to Contreras, E. B..

3 recordsLinked to original sources

bioRxiv2026

Functionally convergent anti-predator morphologies arise through divergent cellular strategies in Daphnia

Phenotypic plasticity exemplifies how environmental signals can shape organismal development, yet the cellular mechanisms translating ecological cues into adaptive morphologies remain incompletely characterized. Many species of Daphnia (freshwater crustaceans) develop a diverse array of inducible defenses in response to predator chemical cues (kairomones), providing a tractable system for examining how ecological pressures are transduced through developmental mechanisms. Daphnia lumholtzi produce elongated head and tailspines in response to kairomones. How this occurs at the cellular level, through changes in cell size, proliferation, or both, is currently unknown. To address this question, we quantified the temporal dynamics of cell proliferation in D. lumholtzi across 72 hours following kairomone exposure using EdU incorporation (marking proliferating cells) and DAPI staining (to quantify total nuclei). Predator cue exposure induced a three-phase proliferative response: initiation within 24 hours (slightly increased proliferation and total cells), a transitional plateau at 48 hours (minimal effects in both treatments), and commitment by 72 hours (strong increases in both proliferation and cell accumulation). Headspines exhibited higher proliferation than tailspines, suggesting anterior- posterior developmental prioritization. Treated animals maintained smaller average cell sizes throughout the response, consistent with continuous addition of newly divided cells rather than cell enlargement. Unlike the delayed-division strategy in D. longicephala or bilayer formation in D. pulex, D. lumholtzi employs sustained hyperplasia, demonstrating that the same selective pressure produces similar ecological outcomes through mechanistically distinct developmental programs. Our findings bridge ecological signals with cellular responses, exemplifying eco-evo- devo integration whereby environmental pressures (predation) are transduced through developmental processes (cell proliferation dynamics) to generate adaptive and heritable morphological diversity across ecological and evolutionary timescales.

cell biology↗

bioRxiv2025

Predator induced phenotypes are inherited over four generations in genetically identical Daphnia lumholtzi

Teaser TextCan the ghosts of environments past shape organismal phenotypes of future generations? In an experiment with clonal Daphnia lumholtzi, we reveal that predator-induced changes in body shape in one generation can persist across several unexposed generations, even when the predator signal is long gone. Exposing only the first generation to predator cues, we tracked morphological shifts through five generations of genetically identical individuals. We found that these induced plastic phenotypes persisted to the F4 generation before fading in F5. This discovery supports the importance of non-genetic inheritance and underscores the powerful interplay between ancestral and current environments in shaping organismal form and function. Environmental variation can induce phenotypic changes through adaptation of populations and acclimation of individuals. While genetic adaptation creates persistent change within a population via allele frequency shifts, reversible plastic phenotypes can be inherited through non-genetic mechanisms. However, most transgenerational plasticity studies examine generations where direct embryonic or germline exposure to environmental cues cannot be excluded. Empirical evidence for persistence definitively beyond the critical threshold for distinguishing true transgenerational plasticity from in utero exposure remains scarce, particularly for vertebrate predator-induced defenses. We measured phenotypic effects of vertebrate predator exposure in the clonally reproducing water flea, Daphnia lumholtzi, isolating environmental effects from genetic variation. We exposed the F0 generation to fish conditioned media, then measured morphological defenses in definitively unexposed F3, F4, and F5 generations characterizing the temporal dynamics of non-genetic inheritance. Predator-induced morphologies persisted through F4 before receding in F5, demonstrating that non-genetic effects extend well beyond the embryonically exposed F1 and germ cell exposed F2 generations. This provides rare empirical evidence for transgenerational plasticity lasting through F4, without confounding genetic variation. We also examined ontogenetic patterns of somatic and defensive trait development, revealing trait-specific temporal dynamics in transgenerational effect expression and decay. These results highlight how current and ancestral environments interact to determine phenotypic variation across generations and underscores the ecological significance of non-genetic inheritance in natural populations, particularly for understanding population responses to environmental change and predator reintroduction. Characterizing molecular mechanisms underlying transgenerational phenotypic plasticity remains critical for predicting persistence and ecological consequences of non-genetic inheritance.

evolutionary biology↗

bioRxiv2022

Regional variation in cholinergic terminal activity determines the non-uniform occurrence of cortical slow-wave activity during REM sleep

Sleep consists of two basic stages: non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. NREM sleep is characterized by slow high-amplitude cortical EEG signals, while REM sleep is characterized desynchronized cortical rhythms. While, until recently, it has been widely believed that cortical activity during REM sleep is globally desynchronized, recent electrophysiological studies showed slow waves (SW) in some cortical areas during REM sleep. Electrophysiological techniques, however, have been unable to resolve the regional structure of these activities, due to relatively sparse sampling. We mapped functional gradients in cortical activity during REM sleep using mesoscale imaging in mice, and observed local SW patterns occurring mainly in somatomotor and auditory cortical regions, with minimum presence within the default mode network. The role of the cholinergic system in local desynchronization during REM sleep was also explored by calcium imaging of cholinergic terminal activity within the mouse cortex. Terminal activity was weaker in regions exhibiting SW activity more frequently during REM sleep. We also analyzed Allen Mouse Brain Connectivity dataset and found that these regions have weaker cholinergic projections from the basal forebrain.

neuroscience↗