Effects of change in altitude on the auditory bulla of midday gerbil,Meriones meridianus

The size of body parts in animals is influenced by environmental factors. relative to other rodents,those of the subfamily gerbillinae (gerbils) are characterized by greatly enlarged auditory (tympanic) bullae. to understand the effects of altitude on the size of auditory bullae in the midday gerbil (meriones meridianus pallas,1773),339 adults were collected from areas in inner mongolia and northwest china,from -103 m to 3205 m above sea level,and relevant body and skull measurements were taken. through partial correlation analysis,we found that the relative size of auditory bullae (rsab) was significantly and positively correlated with increasing altitude. we also looked for correlations between the rsab and each of 6 environmental factors that change with increasing altitude (mean annual temperature,frost-free period,relative humidity,precipitation,annual sunshine hours,and annual average wind speed). of these,the results of multiple linear regression analysis indicated that the rsab was associated with only the frost-free period and annual average wind speed. we believe that the harsh conditions at higher elevations that include lower oxygen concentration,shorter growing season,and constant strong wind work against auditory acuity,and the increase in the size of auditory bullae of m meridianus with altitude is a compensatory adaptation.