Biology subjects

Walker, R. S.

Publications and source records attributed to Walker, R. S..

4 recordsLinked to original sources

bioRxiv2025

The Role of Pace of Life in Animal Social Networks

The fast-slow continuum is a key axis of variation in life history strategies that captures the evolutionary trade-off between allocating in lifespan versus reproduction. It has been suggested that social behaviour, and therefore network structure, may vary across the fast-slow continuum, but formal theory remains scarce. We develop a novel mathematical model to examine how the rate of demographic replacement may influence emergent social network structures in natural populations. We additionally consider variation in social preferences and modes of social inheritance. Our key finding is that more rapid demographic replacement can substantially constrain the structure of dynamic social networks. For species with longer generation times, network structures are primarily determined by social preferences, while for shorter generation times they are primarily determined by mechanisms of social inheritance. By considering how demographic replacement can constrain social network organisation, our work provides important insights into social evolutionary ecology.

ecology↗

bioRxiv2022

Regulation of Klebsiella pneumoniae mucoidy by the bacterial tyrosine kinase Wzc

Klebsiella pneumoniae is a frequent nosocomial pathogen associated with urinary tract infections (UTI), pneumonia, and septicemia. Two lineages of K. pneumoniae have emerged that challenge the treatment of these infections. One lineage includes hypervirulent strains, causing invasive community-acquired infections, and the other encompasses carbapenem-resistant isolates. Non-mucoid, carbapenem-resistant isolates are most frequently isolated from UTI. Therefore, we hypothesized that environmental conditions may drive K. pneumoniae adaptation to the urinary tract. We found that two rmp-positive, hypervirulent strains and two rmp-negative clinical UTI isolates all suppressed mucoidy when cultured in urine compared to rich LB medium without altering capsular polysaccharide (CPS) abundance. We then performed a transposon screen to identify genetic factors through which urine suppresses mucoidy. Due to variations within transposon hits, we performed whole genome sequencing on our hits and found 100% association between secondary mutations in Wzc and increased mucoidy. Wzc is an inner membrane tyrosine kinase that regulates CPS assembly. When Wzc mutations are encoded chromosomally we observed both increased mucoidy and increased cell-free extracellular polysaccharide (EPS). However, when Wzc mutations are expressed in trans we observed increased mucoidy without impacting CPS or cell-free EPS abundance. Functionally, one periplasmic mutation increased Wzc autophosphorylation, while four active site mutations reduced Wzc autophosphorylation. These four active site mutations are also sufficient to increase mucoidy in one of the rmp-negative clinical UTI isolates without affecting EPS abundance. Combined, these data implicate mutation-driven modulation of Wzc activity as a global, rmp-independent mechanism for increasing K. pneumoniae mucoidy, without altering EPS uronic acid content. Wzc activity may represent the lynchpin that coordinates both capsule biosynthesis and mucoidy, explaining why these two phenotypes have been historically intertwined.

microbiology↗

bioRxiv2021

Reconstructing hunter-gatherer planet Earthusing machine-learning

Estimating the total human population size (i.e., abundance) of the preagricultural planet is important for setting the baseline expectations for human-environment interactions if all energy and material requirements to support growth, maintenance, and well-being were foraged from local environments. However, demographic parameters and biogeographic distributions do not preserve directly in the archaeological record. Rather than attempting to estimate human abundance at some specific time in the past, a principled approach to making inferences at this scale is to ask what the human demography and biogeography of a hypothetical planet Earth would look like if populated by ethnographic hunter-gatherer societies. Given ethnographic hunter-gatherer societies likely include the largest, densest, and most complex foraging societies to have existed, we suggest population inferences drawn from this sample provide an upper bound to demographic estimates in prehistory. Our goal in this paper is to produce principled estimates of hunter-gatherer abundance, diversity, and biogeography. To do this we trained an extreme gradient boosting algorithm (XGBoost) to learn ethnographic hunter-gatherer population densities from a large matrix of climatic, environmental, and geographic data. We used the predictions generated by this model to reconstruct the hunter-gatherer biogeography of the rest of the planet. We find the human abundance of this world to be 6.1{+/-}2 million with an ethnolinguistic diversity of 8,330{+/-}2,770 populations, most of whom would have lived near coasts and in the tropics. Significance StatementUnderstanding the abundance of humans on planet Earth prior to the development of agriculture and the industrialized world is essential to understanding human population growth. However, the problem is that these features of human populations in the past are unknown and so must be estimated from data. We developed a machine learning approach that uses ethnographic and environmental data to reconstruct the demography and biogeography of planet Earth if populated by hunter-gatherers. Such a world would house about 6 million people divided into about 8,330 populations with a particular concentration in the tropics and along coasts.

ecology↗

bioRxiv2019

Nonlinear diversification rates of linguistic phylogenies over the Holocene

The expansion of the human species out of Africa in the Pleistocene, and the subsequent development of agriculture in the Holocene resulted in waves of linguistic diversification and replacement across the planet. Analogous to the growth of populations or the speciation of biological organisms, languages diversify over time to form phylogenies of language families. However, the dynamics of this diversification process are unclear. Bayesian methods applied to lexical and phonetic data have created dated linguistic phylogenies for 18 language families encompassing [~]3,000 of the worlds [~]7,000 extant languages. In this paper we use these phylogenies to quantify how fast languages expand and diversify through time both within and across language families. The overall diversification rate of languages in our sample is [~]0.001 yr-1 (or a doubling time of [~]700 yr) over the last 6,000 years with evidence for nonlinear dynamics in language diversification rates over time, where both within and across language families, diversity initially increases rapidly and then slows. The large-scale replacement of the worlds hunter-gatherer languages by agricultural languages over the Holocene was a non-constant process.

evolutionary biology↗