Reproductive Skew Theory

Barbora Trubenová, University of Manchester, Manchester, UK
Reinmar Hager, University of Manchester, Manchester, UK

Published online: July 2012

DOI: 10.1002/9780470015902.a0023661

An almost universal characteristic of cooperatively breeding animal groups is the unequal sharing of reproduction within the group, referred to as reproductive skew. Reproductive skew theory has been developed to investigate the adaptive causes underlying the variation in reproduction between and within species seen in nature. From its inception in the late 1970s, skew theory has expanded over the years both conceptually and in its application. Three main types of models are distinguished: Transactional models assume that reproductive shares are offered as a reward for cooperative behaviour, tug‐of‐war; TOW (or compromise) models assume that reproductive shares are determined by competitive abilities of individuals. Both assumptions are reconciled in the third type of models, most recently developed synthetic models.

Reproductive skew theory makes predictions about the range of skew using a set of key parameters such as relatedness and competitive abilities of group members. Skew theory has been applied to a wide variety of topics in evolutionary biology such as parent–offspring conflict, sex ratio conflict or the evolution of cooperation. Key to skew theory is the question under what conditions groups remain stable and it has thus been advanced as a framework to understand the evolution of sociality.

Key Concepts:

  • Social animals living in groups must often resolve a conflict over the allocation of reproduction.
  • Unequal partitioning of reproduction is termed reproductive skew. Reproductive skew is a degree of reproductive bias in favour of one or a few breeders.
  • Skew theory provides a possible explanation for conflict resolution and adaptive causes of sociality.
  • Several indices of skew exist, suitable for different types of studies and questions.
  • There are three main types of models: transactional, tug‐of‐war (TOW) (also referred to as compromise) and synthetic models, based on different assumptions and yielding different predictions.
  • Transactional models are subdivided into two categories: concession and restraint models. Concession models assume full control of dominants over reproduction in the group, and reproductive share is offered as a reward for cooperation. Restraint models assume subordinates are free to claim reproduction and are only limited by the threat of eviction.
  • TOW models are based on the assumption that both subordinates and dominants have only a limited control over the reproduction and reproductive share is determined by the mutual competitive abilities.
  • Synthetic models combine features of transactional and TOW models. The maximal and minimal reproductive share of the subordinate for a group to remain stable is determined as in transactional models, while, within the range given by the maximal and minimal share, the exact reproductive share is determined by the competitive abilities of both subordinate and dominant in a TOW scenario.

Keywords: reproductive skew; conflict resolution; transactional models; tug‐of‐war models; compromise models; sociality; cooperative behaviour

Figure 1. Division of reproductive skew models.
Figure 2. Illustration of the minimal and maximal subordinate's reproductive share as a function of relatedness r and group productivity k in transactional models. Both pmin (solid line) and pmax (dotted line) are shown for different values of k, the productivity of the association: 6 (green lines), 7 (blue lines) and 8 (red lines). Productivity of lone subordinate and dominant are xs=1 and xd=4, respectively.
Figure 3. Dominant's (a) and subordinate's (b) reproductive share as a function of relatedness r and their relative competitive abilities b, according to TOW models.
Figure 4. Synthetic model. Maximal and minimal subordinate's reproductive shares required for a group to remain stable depend on relatedness between individuals. Restraint models give the maximum share that subordinates can gain, while its minimal share is given by concession models. Inside this range, the exact reproductive share is determined by competitive abilities of both subordinate and dominant (TOW model).
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Related Sub-Topics:

Evolution: Theories and Ideas | Population Structure and Genetics | Evolutionary Ecology | Life History and Reproduction | Competition | Behavioural Ecology
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Article Title: Reproductive Skew Theory
 
How to Cite close
Trubenová, Barbora, and Hager, Reinmar(Jul 2012) Reproductive Skew Theory. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023661]