This article examines some of the important hypotheses relating to sexual dimorphism and brain size in bats.
Social Brain Hypothesis
What is the ‘Social Brain Hypothesis’ and what does it predict with regard to sexual dimorphism in brain size?
The social brain hypothesis suggests that an increase in social difficulty improves cognitive arms races. The suggestion that individuals with relatively large brains are superior in influencing the behavior of others to favor the manipulator’s own desires has been contended.
However, the social brain hypothesis has been supported and predicts that there is a positive relationship between brain size and social group size (Pitnick et.al, 2006).
Sexual Conflict Hypothesis
What is the ‘Sexual Conflict Hypothesis’ and what does it predict with regard to sexual dimorphism in brain size?
More recent hypothetical and experimental studies in sexual selection theory put forward the sexual conflict hypothesis (Pitnick et.al, 2006). This hypothesis implies an existence of sexually opposed coevolution for cognition; whereby females and males are mutually under selection to challenge the reproductive investment and resist being undermined by their sexual partners. It predicts that species reproducing promiscuously will have moderately larger brains than species with genetic monogamy (Pitnick et.al, 2006).
Expensive Tissue Hypothesis
What is the ‘Expensive Tissue Hypothesis’ and what does it predict with regard to sexual dimorphism in brain size?
An additional hypothesis in sexual selection theory, is the expensive tissue hypothesis.Pitnick et.al (2006) entails that changes in brain size may accompany compensatory changes in other expensive tissue for the reason that moderately large brains are metabolically expensive to sustain and develop. This hypothesis has not been measured in any taxon considering ornaments, weapons or sexual organs performing in reproductive antagonism (Pitnick et.al 2006).
Expensive Sexual Tissue Hypothesis
How does the ‘Expensive Sexual Tissue Hypothesis’ differ from the ‘Expensive Tissue Hypothesis’?
Noting that sexually selected traits can also be expensive, the expensive sexual tissue hypothesis differs from the expensive tissue hypothesis. The latter is condition–dependent and predicts that more concentrated sexual selection will restrict the evolution of improved brain size as a result of vigorous compromise with costly sexual organs, ornaments or armaments (Pitnick et.al 2006).
What kinds of data do the authors use in this study and what specific hypotheses do they propose to test with regard to brain evolution in bats?
The researchers, Pitnick et.al (2006), analyze comparative data on overall brain and neocortex dimension, testis mass, and social and mating systems for 334 Chiroptera species to assess predictions of the social brain, sexual conflict and expensive sexual tissue hypothesis for brain evolution in bats.
Reference
Pitnick, S., Jones, K.E., Wilkinson, G.S. (2006). Mating system and brain size in bats. Proc. R. Soc 273:719-724.
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