BODY ELONGATION AND DECREASED REPRODUCTIVE OUTPUT WITHIN A RESTRICTEDCLADE OF LIZARDS (REPTILIA, SCINCIDAE)

Relationships between body shape and relative abdominal size were comp ared among differentially elongate species within the scincid lizard g enus Brachymeles, to investigate how morphological evolution affects t he proportion of body volume available to hold eggs and offspring. Rel ative abdominal size is inversely related to elongation, suggesting th at relative clutch mass decreases with addition of abdominal body segm ents. Shape-volume relationships contradict trends seen in comparisons among distantly related limbed and limbless squamates (lizards and sn akes), in which snakes have relatively more abdominal volume. Comparis on within a phylogenetically restricted group allows the identificatio n of functional and ontogenetic factors potentially limiting reproduct ive output. In Brachymeles, constraining factors include retention of anterior body segments bearing parasternal ribs, which prevents extens ion of the clutch anteriorly within the body, and reduction of allomet ry of abdominal segments, which provides extended series of uniformly- sized vertebrae for limbless locomotion, but reduces the relative size of the abdomen. The latter trait is associated with overall size redu ction, which affects relative egg-size and packing. Factors constraini ng abdominal volume in this genus are probably common to other elongat e lizards, a morphological group that has been rarely represented in c omparative studies of life history.