Larval orientation mechanisms: The power of controlled experiments

Abstract

Recent reports of field-based experimental research on ecology of marine invertebrate larvae has renewed debate on the applicability of laboratory-based research. This paper addresses the context in which the laboratory approach to larval ecology is appropriate, using research on larval orientation mechanisms as examples. The basic premise is that application of laboratory-derived results requires acceptance ofthe principal underlying assumptions; namely, that application of naturally-occurring conditions provides a rigorous description of species-specific traits that are the results of adaptation and that contribute to larval success. Larval orientation contributes to vertical distribution by regulating direction of locomotion, thus compensating for, or complementing, the effects of gravity. Special care must be taken in designing orientation experiments that determine taxis response by use of larval movement and of groups of organisms. Such approaches can confound responses related to activity level of experimental subjects for an orientation response, particularly when activity level varies among individuals, through time, or as a function of the stimulus. Laboratory investigation of behavioral adaptations requires a careful assessment of the response components and an experimental design that permits unequivocal interpretation, an approach that many may consider to be very reductionist.