The macroevolutionary pattern of Rensch’s Rule, i.e., positive allometry of sexual size dimorphism, has had mixed support in turtles. Using the largest carapace length dataset and the only large-scale body mass dataset heretofore assembled for this group, we determine (a) whether turtles conform to Rensch’s Rule at the order, suborder, and family levels, and (b) whether inferences regarding allometry of sexual size dimorphism differ based on choice of body size metric used for analyses. We compiled large databases of mean body mass and carapace length for males and females of as many populations and species as possible using mostly primary literature. We then determined scaling relationships between males and females for average body mass and straight carapace length across species of turtles using traditional and phylogenetic comparative methods. We also used linear regression analyses to evaluate sex-specific differences in the variance explained by carapace length on body mass.
In non-phylogenetic analyses, body mass supports Rensch’s Rule, whereas straight carapace length supports isometry. Using phylogenetic independent contrasts, both body mass and straight carapace length support Rensch’s Rule with strong congruence between body size metrics. More variance is explained by mass than carapace length. At the family level, support for Rensch’s Rule is more frequent when mass is used as a body size metric and in phylogenetic comparative analyses. Turtles do not differ in their mass-to-length regressions by sex. Turtles display Rensch’s Rule overall and within some families of Cryptodires, but not in Pleurodire families. At broad scales, mass and length are strongly congruent with respect to Rensch’s Rule in turtles, and discrepancies are observed mostly at the family level (which is the level where Rensch’s Rule is most often evaluated). At macroevolutionary scales, the purported advantages of length measurements over weight measurements are not supported in these ectothermic vertebrates.
|Advisor:||Meik, Jesse M.|
|Commitee:||Herrmann, Kristin K., Sudman, Philip D.|
|School:||Tarleton State University|
|School Location:||United States -- Texas|
|Source:||MAI 55/05M(E), Masters Abstracts International|
|Keywords:||Body mass, Body size, Carapace length, Rensch's rule, Sexual size dimorphism, Turtles|
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