**Author(s):** Albuquerque, R; Codogno, B; dos Santos, B; Izar, P In primates, touching is fundamental for the social development of infants. We hypothesized that the frequency of touching the face of other individuals by Sapajus libidinosus infants, assuming an active role within their social network, is correlated to the number of social interactions they establish. We analyzed 41 hours of videos of a wild capuchin group at Piauí, Brazil, recorded using focal animal sampling, from the digital data collection from the Laboratory of Ethology, Development and Social Interactions, corresponding to the 1st, 2nd and 3rd months of life of 6 infants (3 males and 3 females). All social interactions and facial touches involving the infant under analysis were coded. A total of 485 interactions and 45 touches were registered. We conducted a GLMM, considering individual and month as fixed effects and sex as a random variable. We found no correlation between the number of interactions of the infant and the number of touches on the face of other individuals. Future studies should investigate other factors, such as infant temperament, that might explain variation in frequency of touching.

Is the touch of capuchin monkeys infants (Sapajus libidinosus) on other individuals influenced by their popularity?

**Author(s):** Vale, G; McGuigan, N; Whiten, A Humans are distinctive in their propensity for cumulative cultural evolution, yet few studies directly compare human and non-human abilities to solve and socially learn the same increasingly complex tasks. Here we explore chimpanzees’ and children’s solving of an extractive foraging and tool use task, designed to offer opportunities for the emergence of cumulative culture. Groups of 3-4-year-old children and adult chimpanzees were each presented with a large puzzlebox incorporating four increasingly difficult levels of solution. Some required tool use, or building on this, tool modification, to retrieve increasingly preferred rewards. Overall, children, but not chimpanzees, showed some indication of cumulative progress, with group-tested children’s solution complexity surpassing what individuals invented when tested alone. However, after controlling for test time, such that asocial controls and groups received the same exposure to the task, this species difference disappeared. Direct species comparisons further suggest there were no significant differences in the highest task level reached by chimpanzees and children, nor in the number of individuals that solved each task level. Our results suggest that young children may not outperform adult chimpanzees on a cumulatively evolving tool use task.

Testing the scope of cumulative culture in groups of young children and chimpanzees

**Author(s):** Hersh, T; De Gregorio, C; Kwong, A; Whitehead, H; Gero, S; Rendell, L; Muldoon, M; Lewis, R; Soma, M; Anichini, M; de Reus, K; Berry, C; Ravignani, A Introduction: Small integer ratio (SIR) categorical rhythms—where intervals separating sounds are distributed around SIRs—dominate human music and some birdsong, and are thought to emerge from or foster cultural transmission of learned vocalizations. Other species with culturally transmitted, socially learned vocalizations should thus also have rhythm categories.
 Methods: We looked for categorical rhythms in sperm whale codas, Java sparrow songs, and harbour seal pup calls. All three species learn vocalizations, but only the first two show extensive evidence of culture. We calculated ratios of adjacent sound intervals and quantified whether there were significant distribution peaks at SIRs.
 Results: Sperm whale codas and Java sparrow songs exhibit SIR categorical rhythms. As in humans, exact ratio preferences vary by whale cultural group. In Java sparrows, sons mirror the rhythms of their social, but not genetic, father. Harbour seal pup calls show no evidence of categorical rhythms.
 Conclusions: These human/animal parallels emphasize that culture can drive rhythmic similarities in communication systems even when underlying sound production anatomies and acoustic environments differ.

Does culture spur rhythmic categories in animal communication? Evidence from sperm whales, Java sparrows, and harbour seals

**Author(s):** Schulze, J N; Denkinger, J; Oña, J; Poole, M M; Garland, E C Cultural transmission of behaviour is an important aspect of many animal communities ranging from humans to birds. Male humpback whales (Megaptera novaeangliae) sing a repetitive, stereotyped, socially learnt, and culturally transmitted song display that slowly evolves each year. Most males within a population sing the same, slow-evolving song type; but in the South Pacific, song ‘revolutions’ have led to rapid and complete replacement of one song type by another introduced from a neighbouring population. Songs spread eastwards, from eastern Australia to French Polynesia, but the easterly extent of this transmission was unknown. Here, we investigated whether song revolutions continue to spread from the central (French Polynesia) into the eastern (Ecuador) South Pacific region. Similarity analyses using three consecutive years of song data (2016-2018) revealed that song themes recorded in 2016-18 French Polynesian song matched song themes sung in 2018 Ecuadorian song, suggesting continued easterly transmission of song to Ecuador, and vocal connectivity across the entire South Pacific Ocean basin. This study demonstrates songs first identified in western populations can be transmitted across the entire South Pacific, supporting the potential for a circumpolar Southern Hemisphere cultural transmission of song and a vocal culture rivalled in its extent only by our own.

Humpback whale song revolutions continue to spread from the central into the eastern South Pacific

**Author(s):** Borofsky, T; Feldman, MW; Ram, Y Introduction:
Despite being widespread, the benefit of cooperative hunting (CH) is unclear. When rare, CH may allow predators to escape competition and access "big prey" (BP). However, a lonely CH predator cannot catch food. Cultural transmission may allow CH to spread fast enough so cooperators can find hunting partners, but there is a catch: competition for BP will rise. 
 Methods: We model a one-predator, two-prey model in which the predators either learn to hunt "small prey" (SP) alone, or learn CH to target BP. The predators first learn vertically and then choose partners from whom they learn horizontally at rate $H$. CH predators only catch the BP if their partner is cooperative. 
 Results: Without horizontal learning, CH cannot spread from rarity. High rates of horizontal learning, combined with competition for the SP, allow CH to evolve. However, the CH can only fix in the predator population if the BP is very abundant.
 Discussion:
Competition for prey is not enough to explain the initial evolution of CH. We found that the addition of horizontal learning allows CH to spread, but future models should explore other factors that can select for CH, such as territorial defense.

Cultural transmission, competition for prey, and the evolution of cooperative hunting

**Author(s):** Snyder, K; Sellers, M; Creanza, N Introduction 
Environmental stress, especially during development, can cause impaired learning in individuals. Thus, learned behaviors, such as birdsong, may exhibit unique evolutionary dynamics after severe weather events relative to other traits. We predict that ecosystem-level stressors may cause population-level changes to birdsong as cohorts experience early-life stress, learn songs imperfectly, and tutor future generations. 
Approach
In 2016, an unprecedented drought affected western New York. We analyzed publicly available and our own birdsong recordings from 2010-2020, comparing two species in the drought-affected area and a nearby unaffected area. We also developed an agent-based model of song evolution after environmental stress. 
Results and Conclusions
We found drought-associated song changes in the species with more complex songs but not in the species with a simple song, implying that stress-induced deficits may disproportionately affect traits that are more difficult to learn. With our model, we found important factors for enduring cultural evolution after stress: population isolation and stressor duration. Together, these results demonstrate that climatic events can induce population-level trait evolution due to disruption in learning.

Cultural evolution after environmental stress: a case study of songbird populations affected by the 2016 New York drought

**Author(s):** Leon, X; Creanza, N Introduction 
Since songbirds use their songs for species recognition, we investigated whether two newly formed species could be distinguished by their songs. Differences in the songs of the Spotted Towhee (Pipilo maculatus) and Eastern Towhee (Pipilo erythrophthalmus) are evident; however, intermediate songs have been reported, particularly in the Great Plains where their breeding ranges overlap. 
Approach
We obtained recordings from Xeno-canto and performed syllable segmentation and song analysis using our recently published software, Chipper. Using log-transformed syllable features, we analyzed song variation across the geographic range of the two species and used a Random Forest Model to predict species classification. 
Results 
Our data showed several patterns, including a positive correlation between the longitude coordinates and the bout duration (rho = 0.612, p < 2.2e-16). Additionally, our model had an accuracy of 89.4% using the log-transformed syllable features. 
Conclusions
Our results indicate that the songs of the Spotted and Eastern Towhees exhibit geographic patterns, and these closely related species can be distinguished by their songs with high accuracy using our model.

Role of learned song in the evolution and speciation of Eastern and Spotted Towhees

Animal bite force is an ecologically relevant performance trait, crucial for individual fitness through its impact on food ingestion and intraspecific agonistic interactions. Despite its popularity in vertebrates, bite force has only recently begun to be measured across the huge diversity of insects. Bite force studies generally use either in vivo measurements or forces modelled based on muscle physiological cross-sectional area (PCSA), and very rarely compare both. PCSA can be measured in a variety of ways, in particular in insects, which have never been thoroughly compared. Here we compare several digitally computed estimates of PCSA (and its components muscle volume and fiber length) in the major mandibular adductor muscle of Schistocerca gregaria, together with an experimental baseline estimate. This experimental estimate relies on dissecting out the muscles, weighing them, dissolving fiber bundles in acid and measuring fibre length. The digital estimates are based on CT scans of the heads, in which it is possible to measure muscle volume, fibre length, and muscle attachment area. After scanning the heads of the specimens and segmenting their mandibular apparatus, we used manual and automated approaches to measure the above mentioned values, to assess the comparability of the various PCSA methods and proxies, as well as the reliability of the automatization process. In addition, using the different PCSA estimates and muscle stress values from the literature, we model bite forces, which we compare to in vivo measurements from the same individuals.

Modelling bite force in insects: comparison of different PCSA approaches with in vivo measurements

Bipeds provide a unique study system to address hindlimb allometry both across and within archosaurs and mammals — having size ranges spanning five orders of magnitude yet overlapping near 1 kg body mass for most major clades. Previous work on non-avian and avian theropods shows that hindlimb proportions cluster within 1/9th of available morphospace, centered around a 60:40 tibia:femur isoline. Here we expand on previous work by including bipedal hopping mammals and examining potential drivers of divergence. We investigate 1) within group scaling, 2) phylogenetic signal, and 3) differences between hopping and striding bipeds. Our avian analysis includes 374 species, spanning 74 families and 17 orders. Our mammalian analysis is restricted to habitual bipedal hoppers and includes 47 species distributed across 5 families and 2 orders. Prior to phylogenetic correction, significant hindlimb positive allometry is seen in Anseriformes, Gruiformes, and Palaeognathae, while significant allometry of some individual segments is found in nearly all avian clades. For mammals, significant positive allometry is seen in Macropodiformes but not Rodentia. After phylogenetic correction using PGLS, significant positive allometry persists in the metatarsal segment of Galliformes, Gruiformes, Palaeognathae, and Diprotodontia. (Macropodiformes exhibited positive allometry of the hindlimb, tibia, and metatarsals after PGLS.) Examining segment proportions revealed negative allometry of the femur with respect to total hindlimb length in these same groups. Hence, whether striding or hopping — avian or mammalian, significant positive allometry of the distal segment is a hallmark of both birds and mammals.

Variable scaling of limb segment proportions in bipeds: Does allometry drive divergence?

Sea lamprey (Petromyzon marinus) invaded the Laurentian Great Lakes in the early 20th century and remain a threat to fisheries in the largest freshwater ecosystem of the world. Nowadays, population growth is restrained by a highly successful control program that mainly relies on the application of the lampricide 3-trifluoromethyl-4’-nitrophenol (TFM) to streams infested with larval sea lamprey. Recent work shows that the effectiveness of TFM is affected by temperature, with the toxicity to larval sea lamprey decreasing with increasing temperature. As such, we set out to unveil the thermal breadth of larval sea lamprey using intermittent-flow respirometry. To do so, we calculated thermal performance curves for this life stage using two approaches: First, we acclimated larvae to 7, 13, 18, 21, 25 and 28°C and tested their aerobic scope at the respective acclimation temperature. Second, we acclimated larvae to 6, 13 and 21°C and subsequently performed acute exposure tests (6, 10, 13, 15, 18, 21, 25, 28 and 31°C), with a temperature increase/decrease rate of approx. 0.1°C/min. Our results show a wide thermal tolerance, consistent with the plasticity required to become a successful invasive species. Further, sea lamprey larvae show a thermal optimum nearing 28°C, indicating that their tolerance to TFM will likely continue to increase as water temperatures in the Great Lakes continue to rise due to climate change.

Effects of temperature acclimation on thermal performance for sea lamprey larvae

The progression of climate warming will expose ectotherms to transient heatwave events and temperatures above their tolerance range at increased frequencies. It is therefore pivotal that we understand species’ physiological limits and the capacity for various controls to plastically alter these thresholds. Exercise training could have beneficial impacts on organismal heat tolerance through improvements in cardio-respiratory capacity, but this remains unexplored. Using juvenile Chinook salmon (Oncorhynchus tshawytscha), we tested the hypothesis that exercise training improves heat tolerance through enhancements in oxygen-carrying capacity. Fish were trained once daily at 60% of their maximum sustainable swim speed for 60 min. Tolerance to acute warming was assessed following three weeks of exercise training, measured as the critical thermal maximum (CTMax). CTMax measurements were coupled with examinations of the oxygen carrying capacity (haematocrit, haemoglobin concentration, relative ventricle size, and relative splenic mass) as critical components of the oxygen transport cascade in fish. Contrary to our hypothesis, we found that exercise training did not raise the CTMax of juvenile Chinook salmon with a mean CTMax increase of just 0.35°C compared to unexercised control fish. Training also failed to improve the oxygen carrying capacity of fish. Exercise training remains a novel strategy against acute warming that requires substantial fine-tuning before it can be applied to the management of commercial and wild fishes. 

Does exercise training improve heat tolerance in Chinook salmon (Oncorhynchus tshawytscha)?

Boxfish (Ostraciidae) have peculiar body shapes, with conspicuous keels formed by their bony carapaces. Previous studies have proposed various hydrodynamic roles for these keels, including reducing drag during swimming, contributing to passive stabilisation of the swimming course, or providing resistance against roll rotations. We tested these hypotheses using computational fluid dynamics simulations of five species of Ostraciidae with a range of carapace shapes. The hydrodynamic performance of the original carapace surface models, obtained from laser scanning of museum specimens, was compared with models where the keels had been digitally reduced. The original carapaces showed no reduced drag or increased passive stability against pitch and yaw compared to the reduced-keel carapaces. However, consistently for all studied species, a strong increase in roll drag and roll added mass was observed for the original carapaces compared to the reduced-keel carapaces, despite the relatively small differences in keel height. In particular, the damping of roll movement by resistive drag torques increased considerably by the presence of keels. Our results suggest that the shape of the boxfish carapace is important in enabling the observed roll-free forward swimming of boxfish and may facilitate the control of manoeuvres.

Underline digital video library

Is the touch of capuchin monkeys infants (Sapajus libidinosus) on other individuals influenced by their popularity?

Testing the scope of cumulative culture in groups of young children and chimpanzees

Does culture spur rhythmic categories in animal communication? Evidence from sperm whales, Java sparrows, and harbour seals

Humpback whale song revolutions continue to spread from the central into the eastern South Pacific

Cultural transmission, competition for prey, and the evolution of cooperative hunting

Cultural evolution after environmental stress: a case study of songbird populations affected by the 2016 New York drought

Role of learned song in the evolution and speciation of Eastern and Spotted Towhees

Modelling bite force in insects: comparison of different PCSA approaches with in vivo measurements

Variable scaling of limb segment proportions in bipeds: Does allometry drive divergence?

Effects of temperature acclimation on thermal performance for sea lamprey larvae

Does exercise training improve heat tolerance in Chinook salmon (Oncorhynchus tshawytscha)?

The hydrodynamic function of keels in boxfish

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES