Biology subjects

Willems, E. P.

Publications and source records attributed to Willems, E. P..

3 recordsLinked to original sources

bioRxiv2026

Prey diversity revealed by environmental DNA elucidates ecological specialisation and social structure in bottlenose dolphins

Human disturbance drives rapid biodiversity loss, yet how prey diversity shapes individual niche differentiation and scales up to structure social organisation remains poorly understood, particularly in marine systems where prey are largely invisible to observation. Here we mapped prey community structure ( prey fields) using environmental DNA metabarcoding, integrating these maps with stable isotope data and >20 years of behavioural observations on bottlenose dolphins. We show that dolphins specialised on specific prey fields to varying degrees, and that none of 471 tracked individuals changed their predominant prey field -- even through climate-driven habitat reorganisation. Isotope profiles confirmed dietary differentiation scaling with specialisation strength. Across four independent sex-subpopulation networks, prey field overlap predicted social affinity in non-foraging contexts, revealing that prey community structure organises social ties beyond foraging. These results expose a socio-ecological link between prey diversity, trophic ecology, and social organisation, providing a transferable eDNA framework for predators with elusive prey.

ecology↗

bioRxiv2026

A phylogenetically informed comparative analysis of sexual testosterone dimorphism across mammals in relation to paternal care and sexual size dimorphism

Within species, male testosterone is often linked to mating competition and paternal care, suggesting that sex differences in endogenous testosterone values across mammals may covary with broader reproductive strategies. Using a structured literature search, we compiled 63 studies, spanning 31 non-human species and 9 human populations, reporting endogenous, non-experimentally manipulated testosterone values for both adult males and females within the same population and context. From these studies, we calculated male-to-female testosterone ratios, and analysed these data using Bayesian phylogenetic multilevel models. We tested whether testosterone dimorphism was associated with paternal care and sexual size dimorphism while accounting for sampling matrix, assay method, breeding context, and wild versus captive setting. Across non-human mammals, neither paternal care nor sexual size dimorphism (indexing competition) showed a clear association with testosterone ratios, and the same pattern emerged in the primate-only subset. By contrast, sampling matrix was consistently associated with testosterone dimorphism across all analyses, with lower male-to-female ratios in non-blood than in blood-based measures. In primates, testosterone ratios were also lower in captive than in wild populations, although this pattern was not clearly supported in the broader non-human dataset. In the human-only analysis, testosterone ratios did not clearly differ between industrialized and small-scale societies, whereas the matrix effect remained evident. Overall, our results suggest that sampling matrix is a major source of variation even for ratio-based measures, highlighting the need for caution when inferring between-species endocrine differences from studies using different substrates. More broadly, directly comparable, non-experimentally manipulated testosterone data for both sexes remain rare across mammals, limiting comparative inference.

evolutionary biology↗

bioRxiv2025

Common marmosets (Callithrix jacchus) excel in a one-trial spatial memory test, yet perform poorly in a classical memory task

When quantifying animal cognition, memory represents one of the most tested domains and is key to understanding cognitive evolution. Memory tests thus play an important role in comparative cognitive research, yet slight variations in the experimental settings can substantially change the outcome, questioning whether different memory tests tap into different memory systems or whether they test memory at all. Here, we first assessed memory performance of 16 common marmosets (Callithrix jacchus) in two distinct paradigms varying in their format and delay. First, we examined marmoset memory in a 24-hour delay memory test (24h-DMT) in which they could freely explore an environment with three novel objects of which one contained food. We examined their retention the day after, and the procedure was iterated cumulatively with previous objects remaining in the enclosure until the marmosets had to choose the correct out of 30 objects. Second, we administered a classical delayed response test (DRT) in the same animals with three objects and a maximum delay of 30 seconds. In the DRT, marmoset performance was poor and not better than chance after 15 seconds already. However, individuals excelled in the 24h-DMT, performing above chance level after 24h even with tenfold the number of objects to choose from compared to the DRT. Moreover, individual performances in the two tests were not correlated, and typical age effects on memory could not be detected in both experiments. Together, these results suggest that the two tests explore different domains, and that the 24h-DMT examines long-term memory. The outcome of the DRT is more difficult to assign to memory since individuals performed only moderately even in the 0-second delay condition. This puts into question whether this task design indeed tests memory or other cognitive processes.

animal behavior and cognition↗