The influence of substrate size upon pulling and gripping forces in parrots (Psittaciformes: Agapornis roseicollis)

"Are You Stronger Than a Lemur?" An effective, interactive STEM outreach program for increasing anatomical and biomechanical knowledge across diverse populations

Access to high-quality outreach programs is crucial for preparing students for STEM careers, yet traditional classrooms often lack diverse, hands-on learning opportunities, particularly in anatomy and evolutionary biology. We present "Are You Stronger Than a Lemur?"-an interactive STEM activity that introduces K-12 students to fundamental concepts in anatomy, evolution, physics, and data analysis through real-world applications. Participants formulate hypotheses, collect and analyze data, and engage with age-tailored educational materials that support differentiated learning. We assessed the program's effectiveness through pre- and post-program knowledge assessments across 1670 participants (1045 eligible responses) from the United States and Mongolia. Results showed a significant increase in knowledge acquisition in anatomy, evolution, physics, statistics, and zoology. After controlling for confounding variables, we also observed a significant increase in interest in STEM careers. "Are You Stronger Than a Lemur?" bridges gaps in STEM education, particularly in underrepresented fields like anatomy and evolutionary biology, by providing an adaptable program suited to different age groups, genders, and countries. Its success lies in connecting theoretical concepts to tangible data, fostering critical thinking, problem-solving, and data interpretation skills. The program not only reinforces core STEM concepts but also offers students a unique, engaging experience that deepens their understanding and enhances their potential for future STEM careers.

Ecomorphological correlates of grasping forces in strepsirrhine primates

Powerful digital grasping is essential for primates navigating arboreal environments and is often regarded as a defining characteristic of the order. However, in vivo data on primate grip strength are limited. In this study, we collected grasping data from the hands and feet of eleven strepsirrhine species to assess how ecomorphological variables-such as autopodial shape, laterality, body mass and locomotor mode-influence grasping performance. Additionally, we derived anatomical estimates of grip force from cadaveric material to determine whether in vivo and ex vivo grip strength measurements follow similar scaling relationships and how they correlate. Results show that both in vivo and anatomical grip strength scale positively with body mass, though anatomical measures may overestimate in vivo performance. Species with wider autopodia tend to exhibit higher grip forces, and forelimb grip forces exceed those of the hindlimbs. No lateralization in grip strength was observed. While strepsirrhine grip forces relative to their body weight are comparable to those of other primates and slightly exceed those of humans, they are not exceptional compared to other arboreal mammals or birds, suggesting that claims of extraordinary primate grasping abilities require further investigation.

Quantitative assessment of grasping strength in platyrrhine monkeys

OBJECTIVES

Despite the longstanding importance of grasping adaptations in theories of primate evolution, quantitative data on primate grasping strength remain rare. We present the results of two studies testing the prediction that callitrichines-given their comparative retreat from a small-branch environment and specialization for movement and foraging on tree trunks and large boughs-should be characterized by weaker grasping forces and underdeveloped digital flexor muscles relative to other platyrrhines.

METHODS

First, we directly measured manual grasping strength in marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri boliviensis), using a custom-constructed force transducer. Second, we reanalyzed existing datasets on the fiber architecture of forearm and leg muscles in 12 platyrrhine species, quantifying digital flexor muscle physiological cross-sectional area (i.e., PCSA, a morphometric proxy of muscle strength) relative to the summed PCSA across all forearm or leg muscles.

RESULTS

Callithrix was characterized by lower mean and maximum grasping forces than Saimiri, and callitrichines as a clade were found to have relatively underdeveloped manual digital flexor muscle PCSA. However, relative pedal digital flexor PCSA did not significantly differ between callitrichines and other platyrrhines.

CONCLUSIONS

We found partial support for the hypothesis that variation in predominant substrate usage explains variation in empirical measurements of and morphological correlates of grasping strength in platyrrhines. Future research should extend the work presented here by (1) collecting morphological and empirical metrics of grasping strength in additional primate taxa and (2) extending performance testing to include empirical measures of primate pedal grasping forces as well.

A functional framework for interpreting phalangeal form

Across tetrapods, the proportional lengths of the manual and pedal phalanges are highly constrained, following a generalized blueprint of shortening in a proximodistal gradient. Despite this, several lineages of both mammals (e.g. sloths, bats and colugos) and birds (e.g. raptors, parrots and woodpeckers) have broken this pattern, shortening the proximal phalanx while elongating more distal elements. As yet, no unifying explanation for this convergence has been empirically evaluated. This study combines a comparative phylogenetic assessment of phalangeal morphology across mammals and birds with a novel bioinspired robotics approach to explicitly test functional hypotheses relating to these morphotypes. We demonstrate that shortening the proximal phalanx allows taxa to maximize forces produced at the proximal interphalangeal joint, while elongation of subsequent elements maintains total ray length-ensuring arboreal species can still enclose large-diameter supports. Within suspensory and vertically clinging mammals, we additionally observe a secondary adaptation towards maximizing grip strength: namely increasing the height of the trochleae to increase the moment arm of digital flexor muscles that cross the joint. Together, our analyses highlight that numerous tetrapod lineages independently converged upon this morphotype to maximize proximal gripping strength, an adaptation to support specialized hunting and locomotor behaviours.