Biology subjects

Schradin, C.

Publications and source records attributed to Schradin, C..

10 recordsLinked to original sources

bioRxiv2025

Thermal Refuges as Extended Phenotypes: Lodge Construction by Bush Karoo Rats

Animal architecture has received considerable attention as an extended phenotype that buffers organisms against environmental harshness. However, few studies have described animal architecture in a representative sample, assessed and then tested its function experimentally. We adopted such an approach for stick lodges built by the bush Karoo rat (Otomys unisulcatus), a solitary rodent inhabiting semi-arid regions of southern Africa. These lodges are among the largest animal-built structures by solitary mammals, yet their structural variation and ecological function remain poorly quantified. We conducted the first population-level survey of all lodges in our 4.5 ha field site to assess external and internal lodge structure, assess their effects on microclimate, and tested experimentally whether lodge size affects microclimate. Lodges were several hundred times larger than their builders and featured complex structure, including basking platforms, nesting, food and latrine chambers. Inside lodges, temperatures were closer to the bush Karoo rats thermoneutral zone and exhibited higher humidity than ambient conditions, which could reduce costs of thermoregulation and reduce water loss. These benefits correlated with initial lodge size and decreased when lodge size was experimentally reduced. Tunnels were often blocked off with thorny branches, possibly to deter snakes. Platforms typically faced eastwards and were regularly used for basking, likely enhancing passive heat gain. We conclude that bush Karoo rat lodges are complex, and costly to build and maintain. They improve thermoregulation and provide predator protection and food storage. Bush Karoo rat lodges (1) are external structures, adding to the builders body (2) are functional, (3) probably increasing fitness, (4) result from behavioural activity, and (5) are likely genetically encoded. We therefore consider them an extended phenotype shaped by ecological pressures and evolutionary history.

animal behavior and cognition↗

bioRxiv2025

Pair-Living Emerged Early in Placental Mammals

It is widely assumed that the first placental mammals were solitary. This assumption has been used as the default in previous comparative studies, but has never been tested independently. Here, we compiled a comprehensive database by reviewing over 14,000 primary peer-reviewed publications on the social organization of the 5,386 extant placental mammal species. We found empirical data for 738 species across 1,478 populations: 354 populations were primarily solitary, 241 populations pair-living and 878 populations group-living. Notably, 383 species (52%) and 580 populations (39%) exhibited intra-specific variation in social organization. Using a Bayesian phylogenetic framework that incorporates intra-specific variation, we show that the ancestral placental mammal - living approximately 160 to 100 million years ago - was not exclusively solitary, but likely displayed intraspecific variation. Pair-living was predicted to account for approximately 26% of ancestral social organisation. Our analysis found that ecology and life history of extant solitary and pair-living mammals was very similar and different from those of group-living mammals. Our results revise prevailing theories of mammalian social evolution, revealing that pair-living emerged early, shifting the focus of mammalian social evolution from the origins of pair-living to the origins of group-living.

evolutionary biology↗

bioRxiv2024

Shared foraging grounds in a solitary rodent: indication for cooperation by kin selection and mutualism?

O_LIKinship is important for understanding the evolution of social behaviour in group living species. However, even solitary living individuals differentiate between kin and non-kin neighbours, which could lead to some form of cooperation, defined as both partners benefitting from each other. A simple form of cooperation is mutualism, where both partners benefit simultaneously. C_LIO_LIHere we tested whether there is mutual tolerance by sharing foraging grounds between kin in a solitary species. This would indicate the possibility of kin selection and mutual cooperation. C_LIO_LIWe used mini-GPS data loggers to investigate range overlap in the solitary bush Karoo rat (Otomys unisulcatus) between kin- and non-kin neighbours. Next, we quantified the extent to which individuals shared foraging grounds containing food plants within their overlapping ranges. Lastly, using step selection functions applied to GPS fixes collected every five minutes, we analysed how individuals moved relative to each other. C_LIO_LIKin-neighbours had larger home range overlap than non-kin neighbours (70.4% vs 29.6%) and shared more of their foraging grounds (63% vs 37%). C_LIO_LITemporal analysis of spatial data found no indication that neighbours avoided each other, independent of kinship. Instead, activity was synchronised. C_LIO_LIIn sum, we found mutual tolerance between neighbours with regards to sharing foraging grounds, and kin shared nearly double as much of their foraging grounds than non-kin. C_LIO_LIThese data can be interpreted as a simple way of mutual cooperation between kin in a solitary species, where both members benefit from sharing a considerable part of their foraging grounds. C_LI

animal behavior and cognition↗

bioRxiv2024

Tolerant mothers: aggression does not explain solitary living in the bush Karoo rat

Many mammal species are thought to adopt solitary living due to mothers becoming intolerant of their adult offspring as well as social intolerance between adults. However, field studies on how solitary mammals interact are rare. Here we show that solitary living can occur without social intolerance. Over three years, we recorded interactions between free living bush Karoo rats (Otomys unisulcatus ) and conducted dyadic encounter experiments between kin and non-kin female neighbours, both in a neutral test arena and in field intruder experiments. Social interactions were rare (N=230 in N=2062 observations), and, when observed, were aggressive in only 34% of the cases. In dyadic encounters, mothers interacted amicably with young offspring. Aggression between mothers and offspring was almost absent. This mother-offspring relationship remained amicable even after the offspring had dispersed. Aggression between neighbouring adult females was low in neutral arena tests, independent of kinship and season. However, in the field, females reacted more aggressively towards non-kin than kin intruders, especially during the breeding season. Tolerance between mothers and adult offspring indicates that aggression is not the mechanism leading to natal dispersal and solitary living. We found a solitary social system characterised by social tolerance, suggesting that dispersal in combination with a lack of social attraction rather than aggression can lead to solitary living.

animal behavior and cognition↗

bioRxiv2024

A cooperatively breeding mouse shows flexible use of its vocal repertoire according to social context

Mice exchange information using chemical, visual and acoustic signals. Long ignored, mouse ultrasonic communication is now considered to be an important aspect of their social life, transferring information such as individual identity or stress levels. However, whether and how mice modulate their acoustic communications is largely unknown. Here we show that a wild mouse species with a complex social system controls its vocal production both qualitatively and quantitatively, depending on social context. We found that the African striped mouse Rhabdomys pumilio, a cooperatively breeding species, has a vocal repertoire consisting of seven call types, which it uses differently depending on whether the individuals encounter another mouse that is familiar, unfamiliar, of the same or different sex. Familiar individuals, whether of the same or different sex, vocalize more than two unfamiliar same-sex individuals. The greatest diversity of vocalisations is recorded when a female and a male first encounter, suggesting that certain calls are reserved for courtship. Our results highlight that familiar mice alternate their vocalisations (turn-taking) while unfamiliar individuals tend to overlap one another. These observations suggest that African striped mice control the production and temporal dynamics of their vocalisations, addressing targeted information to specific receivers via the acoustic channel.

animal behavior and cognition↗

bioRxiv2024

Advancing cooperative breeding research with a peer-reviewed and "live" Cooperative-Breeding Database (Co-BreeD)

Research on cooperative breeding (a system with the core characteristic of individuals providing care for the offspring of others) is important for understanding sociality and cooperation. However, large-scale comparative analyses on the drivers and consequences of cooperation frequently use considerably inaccurate datasets (e.g. due to inconsistent definitions and outdated information). To advance comparative research on cooperative breeding, we introduce the Cooperative-Breeding Database (Co-BreeD), a growing database of key socio-biological parameters of birds and mammals. First, we describe Co-BreeDs structure as a (i) sample-based (i.e. multiple samples per species linked to an exact sampling location and period), (ii) peer-reviewed and (iii) updatable resource. Respectively, these curating principles allow for (i) investigating intra- and inter-species variation and linking between fine-scale social and environmental parameters, (ii) accuracy and (iii) continuous correction and expansion with the publication of new data. Second, we present the first Co-BreeD dataset, which estimates the prevalence of breeding events with potential alloparents in 265 samples from 233 populations of 150 species, including 2 human societies (N = 26,366 breeding events). We conclude by demonstrating (i) how Co-BreeD facilitates more accurate comparative research (e.g. increased explanatory power by enabling the study of cooperative breeding as a continuous trait, and statistically accounting for the sampling error probabilities), and (ii) that cooperative breeding in birds and mammals is more prevalent than currently estimated.

animal behavior and cognition↗

bioRxiv2022

Primate Social Organization Evolved from a Flexible Pair-Living Ancestor

Explaining the evolution of primate social organization has been fundamental to understand human sociality and social evolution more broadly. It has often been suggested that the ancestor of all primates was solitary and that other forms of social organization evolved later. However, previous research included the assumption that many understudied primate species were solitary, then finding transitions to more complex social systems being driven by various life history traits and ecological factors. Here we show that when intra-specific variation is accounted for, the ancestral social organization of primates was variable, with the most common social organization being pair-living but with approximatively 15-20% of social units of the ancestral population deviating from this pattern by being solitary living. We built a detailed database from primary field studies quantifying the number of individuals (social units) expressing different social organizations in each population. We used Bayesian phylogenetic models to infer the probability of each social organization, conditional on several socio-ecological predictors, in ancestral populations. Body size and activity patterns had large effects on transitions between types of social organizations. Our results challenge the assumption that ancestral primates were solitary and that pair-living evolved afterwards. Moreover, our results emphasize the importance of focusing on field data and accounting for intra-specific variation. Pair-living is evolutionary ancient, likely caused by reproductive benefits such as access to partners and reduced intra-sexual competition, with more complex social structure (pair-bonding) and care systems (biparental and allo-parental care) evolving later. Significance StatementWas the ancestor of all primates a solitary-living species? Did more social forms of primate societies evolve from this basic and simple society? The dogma has been that the answer is yes. We used a modern statistical analysis, including variations within species, to show that the ancestral primate social organization was most likely variable. Most lived in pairs, and only 15-20% of individuals were solitary. Living in pairs was likely ancient and caused by reproductive benefits, like access to partners and reduced competition with the sexes. More complex social elaborations like pair-bonds, and biparental and allo-parental care, probably evolved later.

evolutionary biology↗

bioRxiv2022

An information sign changes the way the public perceives exotic pond sliders Trachemys scripta in the Altrhein of Kehl (Germany)

Invasive pond sliders (Trachemys scripta) have been released in thousands of freshwaters within Europe and reproduce in the southern states and even in warm areas of Germany. All member states of the European Union must have an action plan how to fight this invasive species. The German action plan focusses on informing the public, but to date no study investigated the impact of such actions. Instead, NGOs setting up information signs report that this does not stop the release of exotic pond turtles, but without any quantitative measure. In 2019, we put up an information sign at the Althrein of Kehl, an oxbow lake where for the first time it had been shown that T. scripta is breeding in Germany. I performed interviews with people walking along the oxbow lake before the sign was pit up in 2019, and again in 2022. Counts of exotic pond turtles still increased, but this was mainly due to an increased number of small pond turtles, while numbers of very large ones did not further increase. This indicates that the increase in peak counts might be rather due to local reproduction than additional release. After the information sign was set up, more people responded that the presence of exotic pond turtles is problematic for nature conservation and animal welfare, that its illegal to release them, and that they should be removed. This response was especially strong in people who had read the information sign. Independent of the information sign, most interviewed people stated that one should not release pond turtles into the wild, but bring them to animal shelters. While the data here only represent one single case study that might not be representative, its the first study showing that putting up information signs is effective in changing the attitude of people who had read it. This indicates that investment into informing the public is worthwhile, but also that at the same time evaluations of the impact of the measures are important. National action plans should focus on a combination of informing the public and removing the exotic pond turtles, but also on providing keepers of these animals the option to leave the animals at an animal shelter instead of releasing them into the wild.

ecology↗

bioRxiv2020

Successful reproduction of Trachemys scripta in the Altrhein of Kehl (Germany) and simultaneous increase of estimated population size

The European Union categorised pond sliders (Trachemys scripta) as an invasive species for which all member countries have to develop an action plan. While T. scripta has been released illegally in thousands of freshwaters in Europe, monitoring programs in Germany are missing. Based on short term surveys, anecdotal data, and assumptions, the action plan in Germany proposes that T. scripta does not represent a problem as the cold weather causes high mortality and does not allow for successful reproduction. Here I present data of five years of monitoring at the Altrhein of Kehl, at the border between Germany and France showing: 1. Apart from T. scripta, five additional species have been released (Pseudemys nelson, Pseudemys concinna, Graptemys pseudogeographica, Mauremys spec., Chrysemys picta.). 2. Population size seemed to increase over the years, with 116 individuals being counted in 2020 compared to 33 individuals in 2016. 3. Successful reproduction of. T. scripta was indicated by the observation of very small individuals and proved by the collection of hatchlings in two years. While the data presented here would benefit from more years of more intensive monitoring, they are sufficient to draw the conclusion that the German action plan is insufficient because individuals survive for long periods and do reproduce successfully. Similar results have been reported from other central European countries. Thus, T. scripta might become invasive not only in south but also in central Europe. In sum, national action plans of how to deal with the invasive T. scripta should to be revised in Germany and many other European countries.

ecology↗

bioRxiv2019

Intraspecific variation in Artiodactyla social organisation: A Bayesian phylogenetic multilevel analysis of detailed population-level data

Understanding inter-specific variation in social systems is a major goal of behavioural ecology. Previous comparative studies of mammalian social organisation produced inconsistent results, possibly because they ignored intra-specific variation in social organisation (IVSO). The Artiodactyla have been the focus of many comparative studies as they occupy a wide diversity of habitats and exhibit large variation in life history patterns as well as other potential correlates of social organisation. Here we present the first systematic data on IVSO among Artiodactyla, infer their ancestral social organisation, and test whether habitat, sexual dimorphism, seasonal breeding, and body size predict inter- and intraspecific variation in social organisation. We found data on social organisation for 110 of 226 artiodactyl species, of which 74.5% showed IVSO. Using Bayesian phylogenetic multilevel models, the ancestral artiodactyl population was predicted to have a variable social organisation with significantly higher probability (0.77, 95% CI 0.29-1.00) than any non-variable form (i.e. solitary, pair-living, group-living). Greater sexual dimorphism and smaller body size both predicted more IVSO; smaller body size also predicted a higher likelihood of pair-living. Our results challenge the long-held assumption that ancestral Artiodactyla were pair-living and strongly imply that taking IVSO into account is crucial for understanding mammalian social evolution.

animal behavior and cognition↗