Aplysia behavioral biology: I. A multivariate analysis of burrowing in A. brasiliana

Abstract

This study describes burrowing for the first time in the marine gastropod mollusc Aplysia brasiliana. The animals were collected along the southern coast of Texas in the Gulf of Mexico during the late summer. Ten burrowing parameters were operationally defined from burrowing observations on 32 subjects. In an effort to determine the relationship among the heterogeneous subjects to underlying pure-types along distinct dimensions of variation, the data were subjected to Linear Typal Analysis and Q-type orthogonal powered-vector Factor Analysis with a cluster-oriented solution. Three independent subject-related factors were extracted which clustered the subjects according to behavioral profiles on the burrowing parameters. Intercorrelations among the 10 burrowing parameters revealed two general behavior-related groups descriptive of burrowing; burrowing speed and burrowing responsiveness. Factor I contained nine subjects considered “Inefficient Burrowers” on the basis of scores indicating slower burrowing speed and lowered burrowing responsiveness. Factor II contained 15 subjects considered “Efficient Burrowers” due to scores indicating faster burrowing speed and greater burrowing responsiveness. Factor III contained eight subjects considered “Intermediate Burrowers” on the basis of low- to middle-range scores on the 10 burrowing parameters. Since these analytical techniques reliably identified and characterized three clusters of subjects from a naturally selected heterogeneous sample on the basis of their burrowing behaviors, testable hypotheses can now be generated to study the adaptive mechanism and functional significance of burrowing. Preliminary evidence suggests that Efficient Burrowers were probably young and/or healthy animals for whom burrowing might represent a preparatory state for subsequent reproductive activities. Inefficient Burrowers were probably old and/or unhealthy animals for whom burrowing represented an energyconserving response to deteriorating health or lowered tolerance to unfavorable environmental conditions. Intermediate Burrowers seemed to represent transitional animals, those older and less vigorous than Efficient Burrowers, but considerably younger and more vigorous than Inefficient Burrowers.