Biology subjects

Rosenbaum, S.

Publications and source records attributed to Rosenbaum, S..

8 recordsLinked to original sources

bioRxiv2026

Accounting for the life history structure of fitness in tests for adaptive reproductive acceleration

A prominent developmental plasticity theory proposes that early life adversity accelerates life history trajectories so organisms can maximize fitness in challenging environments. Standard tests of this hypothesis rely on empirical predictions about observable life history variables (e.g., age at first birth), because the proposed internal processes cannot be directly measured. However, the observable proxies are themselves mechanically linked, and regressions that ignore this may conflate causal effects with mechanical relationships among proxies. Here, we develop theory that explicitly justifies some existing empirical tests but rejects others. We integrate an accounting model that incorporates age at first birth, interbirth intervals, and lifespan with an optimization model, to derive the mathematical form that tests of the hypothesis should take. We apply these tests to data from wild female baboons, using early life rainfall as an exogenous proxy for early adversity so that estimates can plausibly be interpreted causally. The accounting model explains >98% of the variation in lifetime reproductive success among females that reproduced. However, our theory-derived tests find no evidence for the reproductive acceleration hypothesis. Our study illustrates the value of formal theory for causal inference in developmental plasticity research, where intertwined measurable variables may be obscured by strictly verbal hypotheses.

evolutionary biology↗

bioRxiv2026

Distribution of genetic paternity in primate groups

Understanding the distribution of paternity within social groups is critical for testing hypotheses about the evolution of behavior and morphology in primates, but assembling the requisite comparative data is a challenging task. We compiled genetic paternity data from 52 species of wild nonhuman primates along with information about socioecological, morphological, and life history traits that are relevant to understanding what proportion of offspring are sired by primary males (i.e., alpha males in multi-male groups and resident males in single male groups). Our dataset, which currently contains information about 11 primate families and >3,000 individual paternities, is presented as a publicly accessible, living database designed to be updated as new data become available. Using Bayesian regression models, we investigated the role that phylogeny, group composition, and seasonality play in determining primary males paternity share, and assessed the relative share of paternities obtained by non-primary residents versus extra-group males. First, we found that phylogeny has a detectable but relatively modest influence on primary males paternity share. Species-level differences explained roughly 35-40% of variation in primary males paternity share, and of that interspecific variation, [~]50-70% was attributable to shared phylogenetic history. Second, group composition strongly predicted paternity share outcomes. Primary males in single-male/multi-female groups obtained the highest share of paternity ([~]80%), while those in multi-male groups had the lowest ([~]60%), though there was substantial variation within each category. Pair-living animals showed a striking split: males in cohesive pairs sired [~]90% of offspring, while those in dispersed pairs sired only [~]55%. Contrary to expectations, reproductive seasonality did not predict primary males paternity share in any group type. Finally, when primary males in multi-male groups lost paternities, [~]75% of losses were to other resident males. Overall, [~]5-15% of offspring in these groups were sired by extra-group males. Our results largely confirm earlier findings based on smaller datasets, but also show that the relationship between social organization and paternity is more complicated than simple categorical predictions suggest. We discuss the gap between the data that would ideally be available for testing these hypotheses versus what currently exists, with hopes that our living database can help close this gap over time.

evolutionary biology↗

bioRxiv2026

The effect of chronic, latent Toxoplasma gondii infection on human behavior: Testing the parasite manipulation hypothesis in humans

Parasitism is one of the key, structural, interspecific interactions in ecology. One remarkable parasitic strategy that has been documented in multiple systems is the behavioral manipulation of hosts to increase parasite fitness. While not yet documented in humans, we propose that a ubiquitous zoonotic parasite - Toxoplasma gondii - may change human behavior to favor the parasite by increasing the fitness of the parasites definitive host - cats. Specifically, we assess the possibility that human behavioral changes resulting from chronic, latent T. gondii infection lead to measurable changes in attitudes, actions and dopaminergic responses towards cats that function to increase domestic cat fitness. We assessed the potential role of humans in the T. gondii lifecycle by identifying and testing behavioral changes in humans that benefit the parasite; specifically, human affection for cats. We assessed T. gondii infection status in 68 participants using T. gondii serum antibody testing, and assessed their attitudes towards cats in three ways: i) surveys, ii) participant behavior in the presence of domestic cats, and iii) participant oxytocin levels before and after interactions with cats to assess dopaminergic changes. Only 2 of 68 participants were positive for T. gondii antibodies, limiting statistical power. However, our results indicated that T. gondii-positive participants both reported a greater affection for cats in surveys, and spent more time engaged with cats during behavioral trials than T. gondii-negative participants (87% of study time engaging with cats vs 75%). Oxytocin results were inconclusive.

evolutionary biology↗

bioRxiv2026

Allonursing (Co-BreeD): Its prevalence, functions and hypotheses across mammals and human cultures

Allonursing, where dependent young are nursed by females other than their mothers, has been observed across diverse mammalian species and human cultures. Yet, the proximate functions underlying this seemingly altruistic behaviour, and its benefits for the offspring, the mother, and the nursing allomother, remain poorly understood. To facilitate testing hypotheses concerning these questions, we compiled the to date largest allonursing dataset from wild populations (N = 101 species, including 133 populations and 5 human cultures). Using this dataset, we (i) map the taxonomic distribution of allonursing, thereby expanding the list of mammal species qualified as cooperative breeders by 17 additional species, (ii) differentiate cases of non-voluntary from voluntary allonursing and consequently reject the hypothesis that milk stealing explains regular allonursing in most species, (iii) quantify the within-population extent of allonursing to assess its significance across species and evaluate the energy/time saved for mothers, (iv) use phylogenetically controlled analyses to revisit the association between allonursing and polytocy (i.e., litter size >1), and provide an alternative explanation for this association. We conclude by proposing that allonursing has multiple functions, with the most empirically supported ones being provisioning and insurance against maternal loss. Finally, the presented AlloNursing dataset complements the Cooperative-Breeding Database (Co-BreeD) to further expand this integrative resource for cooperative breeding research.

animal behavior and cognition↗

bioRxiv2024

Testing frameworks for early life effects: the developmental constraints and adaptive responsehypotheses do not explain key fertility outcomes in wild female baboons

In evolutionary ecology, two classes of explanations are frequently invoked to explain "early life effects" on adult outcomes. Developmental constraints (DC) explanations contend that costs of early adversity arise from limitations adversity places on optimal development. Adaptive response (AR) hypotheses propose that later life outcomes will be worse when early and adult environments are poorly "matched." Here, we use recently proposed mathematical definitions for these hypotheses and a quadratic-regression based approach to test the long-term consequences of variation in developmental environments on fertility in wild baboons. We evaluate whether low rainfall and/or dominance rank during development predict three female fertility measures in adulthood, and whether any observed relationships are consistent with DC and/or AR. Neither rainfall during development nor the difference between rainfall in development and adulthood predicted any fertility measures. Females who were low-ranking during development had an elevated risk of losing infants later in life, and greater change in rank between development and adulthood predicted greater risk of infant loss. However, both effects were statistically marginal and consistent with alternative explanations, including adult environmental quality effects. Consequently, our data do not provide compelling support for either of these common explanations for the evolution of early life effects.

evolutionary biology↗

bioRxiv2022

Neither kin selection nor familiarity explain affiliative biases towards maternal siblings in wild mountain gorillas

Evolutionary theories predict that sibling relationships will reflect a complex balance of cooperative and competitive dynamics. In most mammals, dispersal and death patterns mean that sibling relationships occur in a relatively narrow window during development, and/or only with same-sex individuals. Besides humans, one notable exception are mountain gorillas, in which non-sex biased dispersal, relatively stable group composition, and the long reproductive tenures of alpha males mean that animals routinely reside with both same and opposite-sex, and full and half siblings, throughout their lives. Using nearly 40,000 hours of observation data collected over 14 years on 699 sibling and 1258 non-sibling pairs of wild mountain gorillas, we demonstrate that individuals have strong affiliative preferences for full and maternal siblings over paternal siblings or unrelated animals, consistent with an inability to discriminate paternal kin. Intriguingly, however, aggression data imply the opposite. Aggression rates were statistically indistinguishable among all types of dyads except one: in mixed-sex dyads, non-siblings engaged in substantially more aggression than siblings of any type. This pattern suggests mountain gorillas may be capable of distinguishing paternal kin, but nonetheless choose not to affiliate with them over non-kin. A preference for maternal kin occurs despite gorillas not possessing low male reproductive skew, the key characteristic believed to underlie such biases. These results call into question reasons for strong maternal kin biases when paternal kin are identifiable, familiar, and similarly likely to be long-term social partners, and suggest behavioral mismatches at play during a transitional period in mountain gorilla society.

animal behavior and cognition↗

bioRxiv2022

Seeing the future: a better way to model and test for adaptive developmental plasticity

In many species, individuals who experience harsh conditions during development often have poor health and fitness outcomes in adulthood relative to peers who do not. There are two classes of evolutionary hypotheses for the origins of these early life contributors to inequality in adulthood: developmental constraints (DC) models, which focus on the deleterious effects of low-quality early-life environments, and predictive adaptive response (PAR) hypotheses, which emphasize the cost of mismatches between early and adult environments. Distinguishing DC and PAR models empirically is difficult for both conceptual and analytical reasons. Here, we resolve this difficulty by providing explicit mathematical definitions for DC, PARs, and related concepts, and propose a novel, quadratic regression-based statistical test derived from these definitions. Simulations show that this approach improves the ability to discriminate between DC and PAR hypotheses relative to a common alternative based on testing for interaction effects between developmental and adult environments. Simulated data indicate that the interaction effects approach often conflates PARs with DC, while the quadratic regression approach yields high sensitivity and specificity for detecting PARs. Our results highlight the value of linking verbal and visual models to a formal mathematical treatment for understanding the developmental origins of inequitable adult outcomes.

evolutionary biology↗

bioRxiv2021

The role of ventromedial prefrontal cortex in reward valuation and future thinking during intertemporal choice

Intertemporal choices require trade-offs between short-term and long-term outcomes. Ventromedial prefrontal cortex (vmPFC) damage causes steep discounting of future rewards (delay discounting; DD) and impoverished episodic future thinking (EFT). The role of vmPFC in reward valuation, EFT, and their interaction during intertemporal choice is still unclear. Here, twelve patients with lesions to vmPFC and forty-one healthy controls chose between smaller-immediate and larger-delayed hypothetical monetary rewards while we manipulated reward magnitude and the availability of EFT cues. In the EFT condition, participants imagined personal events to occur at the delays associated with the larger-delayed rewards. We found that DD was steeper in vmPFC patients compared to controls, and not modulated by reward magnitude. However, EFT cues downregulated DD in vmPFC patients as well as controls. These findings indicate that vmPFC integrity is critical for the valuation of (future) rewards, but not to instill EFT in intertemporal choice.

neuroscience↗