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Biology subjects

Kramer, B. H.

Publications and source records attributed to Kramer, B. H..

3 recordsLinked to original sources

Resource sharing leads to the emergence of division of labour

Division of labour occurs in a broad range of organisms. Yet, how division of labour can emerge in the absence of pre-existing interindividual differences is poorly understood. Using a simple but realistic model, we show that in a group of initially identical individuals, division of labour emerges spontaneously if returning foragers share part of their resources with other group members. In the absence of resource sharing, individuals follow an activity schedule of alternating between foraging and other tasks. If non-foraging individuals are fed by other individuals, their alternating activity schedule becomes interrupted, leading to task specialisation and the emergence of division of labour. Furthermore, nutritional differences between individuals reinforce division of labour. Such differences can be caused by increased metabolic rates during foraging or by dominance interactions during resource sharing. Our model proposes a plausible mechanism for the self-organised emergence of division of labour in animal groups of initially identical individuals. This mechanism could also play a role for the emergence of division of labour during the major evolutionary transitions to eusociality and multicellularity.

evolutionary biology↗

The evolution of ageing in cooperative breeders

Cooperatively breeding animals live longer than their solitary counterparts. The traditional explanation for this is that cooperative breeding evolves more readily in long-lived species. Here, we reverse this argument and show that long lifespans are an evolutionary consequence of cooperative breeding. Natural selection favours a delayed onset of senescence in cooperative breeders, relative to solitary breeders, because cooperative breeders have a delayed age of first reproduction due to reproductive queueing. Especially long lifespans evolve in cooperative breeders with age-dependent reproductive queueing. Finally, we show that lower genetic relatedness among group members leads to the evolution of longer lifespans. This is because selection against higher mortality is weaker when mortality reduces competition between relatives. Our results link the evolutionary theory of ageing with kin selection theory, demonstrating that the evolution of ageing in cooperative breeders is driven by the timing of reproduction and kin structure within breeding territories.

evolutionary biology↗

Eusociality and the evolution of aging in superorganisms

Eusocial insects - ants, bees, wasps and termites - are being recognized as model organisms to unravel the evolutionary paradox of aging for two reasons: (1) queens (and kings, in termites) of social insects outlive similar sized solitary insects by up to several orders of magnitude; (2) all eusocial taxa show a divergence of long queen and shorter worker lifespans, despite their shared genomes and even under risk-free laboratory environments. Traditionally, these observations have been explained by invoking classical evolutionary aging theory: well-protected inside their nests, queens are much less exposed to external hazards than foraging workers, and this provides natural selection the opportunity to favor queens that perform well at advanced ages. Although quite plausible, these verbal arguments have not been backed up by mathematical analysis. Here, for the first time, we provide quantitative models for the evolution of caste-specific aging patterns. We show that caste-specific mortality risks are in general neither sufficient nor necessary to explain the evolutionary divergence in lifespan between queens and workers and the extraordinary queen lifespans. Reproductive monopolization and the delayed production of sexual offspring in highly social colonies lead natural selection to inherently favor queens that live much longer than workers, even when exposed to the same external hazards. Factors that reduce a colonys reproductive skew, such as polygyny and worker reproduction, tend to reduce the evolutionary divergence in lifespan between queens and workers. Caste-specific extrinsic hazards also affect lifespan divergence but to a much smaller extent than reproductive monopolization.

evolutionary biology↗