Brain Evolution in Bats
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.
Comparative Data
Do the authors generate the data needed to adequately address all of the proposed hypotheses?
Yes, the authors, Pitnick et.al (2006) use data on both brain mass and volume of the neocortex to decide if brain size has been influenced by social complexity or sexual conflict by investigating the association between both the social system and mating system and brain size evolution in bats.
After calculating for allometric disparity related with body size, they found highly significant relationships between both brain traits and female promiscuity and mating system (sexual conflict hypothesis) and marginally non-significant relationships with roosting association (social brain hypothesis).
With regards to expensive tissue hypothesis, the data of the distributed residual brain mass reflected that of residual testis mass, noting that the bat species bearing relatively largest testes, for which brain dimension data was also available.
Finally the authors addressed the expensive sexual tissue hypothesis by comparatively probing the connection between relative dimension of brain and testis; taking into account phylogeny, allometry and ecological grades associated with diet and echolocation.
A considerably negative relationship was observed between independent contrasts in residual brain mass and independent contrasts in residual testis mass of all species (Pitnick et.al 2006).
Ornamentation or Testes Investment
Based on the introduction to this paper, is ornamentation or testes investment a more reasonable response of male bats to sexual selection?
Testicular tissue can represent a substantive energetic investment and is regarded as a more reasonable response of male bats to sexual selection (Pitnick et.al 2006).
Testing Expensive Sexual Tissue Hypothesis
What is a critical assumption of testing of the Expensive Sexual Tissue Hypothesis by comparatively examining the relationship between relative dimension of brains and testes?
The researchers (Pitnick et.al 2006) identify that both brain dimension and breeding structure may display phylogenetic inertia and that the breeding system is predicted to covary with foraging ecology, which is non-randomly distributed across bat clade and known to select on relative brain size 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.
