Trends of Brain Size in Bats
The Relationship between Sexual Selection and Brain/Testes Size
Mar 2, 2008
Comparing Social Structure and Brain Size in Bat Species
Why do the authors have to control for body size allometry before comparing the relationships between social structure and brain/testes sizes among bat species?
To control for allometry in the species-level analyses, analysis of covariate (ANCOVA) was used with body size treated as a covariate (Pitnick et.al 2006).
Mean Residual Brain Mass and Testes Mass for Bat Species
Explain completely the meaning and interpretation of the mean residual in brain mass and testis mass for bat species relative to the occurrence fo female promiscuity and their mating system?
The main purpose is to produce residuals from regression of 1n brain mass or 1n testis mass on 1n body mass, with regressions executed discretely by family as partial phylogenetic control (Pitnick et.al 2006). .
The residuals are used to illustrate trait differences among treatment groups.Figures (1a-c) show mean residual in brain mass whereas figures (d-f) show mean residual in testis mass. Findings show that there was no evolutionary influence on relative brain dimension by comparing monogamy and polygyny in male promiscuity figure (1b).
Figure (1c) opposes the social brain hypothesis with findings of an apparent trend towards brain size decreasing as intricacy in roosting group organization increases. However when we take into account that brain evolution may be more important than composition or colony size, we observe a rejection of the sexual conflict hypothesis as seen in figure (1a) since findings show that females inseminated by a single male within a breeding cycle have moderately large brains (Pitnick et.al2006).
Nonetheless, all relationships taken into account show a strong association between sexual selection and brain dimension between bat species. Similarly, it is important to note that the allocation of residual brain mass with treatment groups (figure 1a-c) reflects that of residual testis mass (figure1d-f), with regard to the expensive tissue hypothesis. In addition, figure (1d, f) illustrates that female promiscuity (not male prospect to inseminate multiple females) is linked with the rise in relative testis mass.
Echo-locating Bats and Brain/Testes Size
Given that echo-locating bats must be very good/efficient fliers relative to fruit-eating bats, can you think of an alternative hypothesis that explains why there would be a trade-off between brain and testes size in echo-locating vs. non- echo-locating bats?
One alternative hypothesis demonstrated in (Pitnick et.al 2006) is genetic constraint (e.g antagonistic pleitropy) as a potential clarification for converse evolutionary brain-testes association. A functionally varied display of genes show evidence of co expression in brain and testis. Another alternative, in my opinion, could be the influence of stress during predation in echo-location bats.
Reference
Pitnick, S., Jones, K.E., Wilkinson, G.S. (2006). Mating system and brain size in bats. Proc. R. Soc 273:719-724
