Biologie | Umwelt
Seraina Hänggi, 2007 | Dornach, SO
In the shorebird species of wattled jacanas, females are behaviourally dominant, not responsible for chick care, and have harems of up to four males, marking a mating system of simultaneous polyandry. To find an evolutionary explanation for this unusual mating-role reversal, this work hypothesized that energy strain on females due to egg laying was associated with polyandry and tested the mechanism’s plausibility using an agent-based computational model of the jacana’s presumed ancestral state and habitat. Across two versions of the model, the second being a revised and more functional version of the first, the sex that cared less tended to have more mates. A higher energy cost of laying eggs tended to decrease female incubation and increase the frequency of polyandry. Males incubated much more than females under energy strain, indicating that the female energy household is important for the occurrence and degree of polyandry. In general, the results mostly supported the hypothesis, but the model is based on assumptions and simplifications and could exhibit a bias toward expected outcomes in its programming, which reduces its empirical value. Nonetheless, the results seem plausible and mostly align with predictions based on the hypothesis.
Introduction
The hypothesis was that a high energy cost of laying eggs shifts care responsibility toward the males to ease the energy strain on the females. This might enable the females to be completely freed from care and become polyandrous. Conditions of low offspring care need and high food availability potentially favour this shift. The goal was to employ evolutionary modelling to determine whether this proposed mechanism can plausibly work in principle on the basis of the underlying assumptions about interaction dynamics and tradeoffs.
Methods
The agent-based model was coded using Python and consisted of individual birds and nests with state attributes, such as reproductive phase and energy, as well as varying heritable traits, such as size and behavioural tendencies. Individuals could interact and attempt reproduction every month under simplified environmental conditions. The offspring inherited the parents‘ traits with random mutations applied to them to allow for evolutionary changes. The model handled males and females equally, except that females were required to lay eggs, which cost energy. This represents an initial state of equal mating roles and ensures that any emerging changes originate from the initial difference. The energy cost of eggs and the offspring’s care need was varied across 50’000 runs.
Results
Only 10% of populations survived. Lower egg cost and care need coincided with greater survival. Males provided most of incubation (0.16 vs. 72) and more than half of chick care (0.59 vs. 0.43) for surviving runs. A higher egg cost was associated with males caring more and females losing care behaviours, often even population-wide. Generally, the sex that cared less had more mates, which occurred more frequently for females, especially when egg cost was high. Therefore, higher egg cost correlated with a greater degree of polyandry (r = 0.28, p >> 0.01).
Discussion
In general, the results mostly supported the hypothesis, though there were some unexpected relations among the countless possible analyses on the extensive data. A reason might be that the occurrence of simultaneous polyandry is multifaceted and cannot be attributed to a single cause. Furthermore, it is important to consider that a model is based on assumptions and simplifications and could exhibit a bias toward expected outcomes in its programming, which reduces its empirical value. It is very plausible that inconsistencies in the code distorted the outcomes. More thorough testing and revision could probably improve the model’s reliability. Nevertheless, the model produced plausible results that are in line with predictions.
Conclusions
Across both models, the energy strain on females because of egg laying had significant effects, indicating that the female energy household is important for the occurrence and degree of polyandry. A lower offspring care need likely favours this transition. Overall, the model seems sound and can generate vast amounts of potentially meaningful data, which opens possibilities for countless further runs and analyses.
Würdigung durch den Experten
Dr. Xavier Richard
In her research, Seraina Hänggi focuses on the black jacana, in which the reversal of sexual roles—dominant females, polyandry, and males involved in incubation—challenges our assumptions about gender roles. Using complex stochastic simulations that reproduce thousands of possible evolutionary scenarios, she explores the mechanisms underlying this phenomenon to understand how it emerged. Throughout her work, she has demonstrated her ability to master and integrate fields as diverse as evolutionary biology, mathematical modelling, and statistics.
Prädikat:
Gold
Sonderpreis «Exporecerca Jove – Barcelona Science Fair» gestiftet von der SJf-Trägerschaft
Gymnasium Münchenstein, Münchenstein
Lehrer: Dr. Dominic Eicher