Doctoral Dissertations

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Life Sciences

Major Professor

Gordon Burghardt

Committee Members

A. Echternacht, R. Etheridge, J. Gittleman, R. Saudargas

Abstract

Sand burying behavior has been reported in many species of lizards spanning several taxonomic families. Burying behavior has been linked to possible functions such as predator escape, avoidance of extreme temperatures, or as an effective means of spending the inactive part of the daily or seasonal cycle. Rarely is the behavior itself described or, even more unusually, referred to in a historical context. This is understandable in light of a resistance to consider behavioral patterns stable enough within a species to be meaningful in an evolutionary setting. Nevertheless, many authors have verified the conclusion of early ethologists that behavioral characters are species-characteristic and are as useful in phylogenetic reconstructions as are morphological characters. In the present study, sand burying behavior was investigated in a group of species belonging to the genus Liolaemus, Tropiduridae. The main objectives were to describe the behavior, determine the amount of variation within species, and to use the obtained information to construct a phylogenetic hypothesis of the relationship among the species under study. The genus Liolaemus contains more than 150 species that occupy a wide variety of habitats over a range that extends from Peru and Bolivia in the North to Tierra del Fuego in the South, within this large genus, certain groups of species have been identified, among them the monophyletic boulengeri group which is diagnosed on the basis of morphological evidence. Of the 26 known species belonging to this group, many have been reported to bury in sand. The relationships among these species are largely unresolved. Sand burying behavior was considered a potential, even critical, phylogenetic tool in helping clarify these relationships. This behavior appeared to be species specific and variation among species was suspected. Furthermore, sand burying arose in conjunction with living into more extreme type habitats characterized by the presence of a loose sandy substrate and little vegetation available for cover. This situation triggered a series of adaptive changes in the organism, among them behavioral changes such as sand burying. Nineteen species of the boulengeri group formed the ingroup. Another four species of Liolaemus. which did not belong to the boulengeri group, constituted the functional outgroup. Lizards were tested at least twice on two types of loose sand, one somewhat coarser than the other. Their behavior was videotaped and later analyzed. Descriptions of burying behavior were based on movements prior to entering the sand, movements of the head upon entering the sand, movements of the tail, location on body where the lizard first stopped, whether a lizard ended up totally covered or only partially covered, total number of stops made by the lizard before settling down for the night, and time recordings of the burying. These formed 7 character subsets, each containing various behavioral characters, totalling 26. In an attempt to establish the stability and stereotypy of sand burying within species, 5 character subsets were compared in different situations: intra-individual variability; context variability; variability between males and females; variability among populations within a species; and variability between adults and neonates. Most of the results of the various statistical tests were non-significant indicating that the behavioral characters involved in sand burying were species-specific and, thus, appropriate for use in a phylogenetic analysis. The four species of the functional outgroup and one of the 19 species of the boulengeri group, L. ornatus. did not bury. Within the remaining 18 species, 3 burying modes were observed:

1. Species that dug or burrowed their way into sand, keeping their head straight as they entered and keeping their tail straight throughout. They often were not completely covered.

2. Species that entered loose sand by generally using a lateral movement of the head and by retrieving or pulling in their tail to get completely covered.

3. Species that dove or plunged into sand, often back stepping prior to entering sand, thrusting their head forward into sand, and lashing their tail to get completely covered. A cladistic analysis of 26 behavioral characters supported the observed burying modes within the boulengeri group. The consensus tree gave three main branches, each branch representing a different type of sand burying behavior. In addition, the results generally agreed with what is known for this group based on morphological evidence and they further discriminated among species. This study indicates how behavior can clarify the phylogenetic relationships among species while suggesting a hypothesis that may later be confirmed or refuted by additional behavioral, morphological, ecological, or molecular data. Different burying styles do not seem to reflect different mechanical problems that lizards may encounter. In fact, the sand in which lizards bury is very similar across geographical regions. Instead, these different burying modes seem to reflect the history of lizard species in the form of lineage constraints which may limit or expand available options when confronted with a specific situation.

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