Intraspecific Variation in Reproductive Behavior and Morphology in the Male Green Anole Lizard

1. Intraspecific Variation in Reproductive Behavior and Morphology in the Male Green Anole Lizard (Anolis carolinensis)Joseph R. Vandecar1, Michele A. Johnson2, Rachel E. Cohen2, Juli Wade1,2Departments of 1Psychology and 2Zoology, Michigan State University Purpose Discussion Copulation Courtship To determine relationships between courtship behavior and morphology of reproductive structures in adult male green anole lizards. (1) The reproductive structures, together, influenced a large proportion (60%) of display behavior. However, the lack of significant relationships between the morphology of individual components and level of function might suggest that displays require their collective influences. This idea contrasts with data from green anoles in the lab, in which ceratohyoid fiber size is positively correlated with dewlap extension (Neal and Wade, 2007). (2) Negative relationships between seminiferous tubule size and both display time and muscle fiber size could be due to either: (a) a “trade-off” such that resources are selectively allocated; or (b) increased testis size might result in enhanced reproductive capacity independent of courtship behavior. (3) The positive correlations between overall size of the dewlap (cartilage length) and display of behavior parallels previous findings from this and other anole species (Vanhooydonck, 2005), and is consistent with the idea that increased benefits are provided by use of larger dewlaps. Introduction Why Anoles? Green anoles are an ideal animal model for the study of reproductive behavior and morphology. Unlike many bird and mammalian models, this lizard species exhibits both courtship and copulatory behaviors that are easily observable by researchers. Courtship consists of three displays: head-bobs, push-ups, and extensions of a throat fan (dewlap). While these display behaviors are stereotyped, display rates vary within each species. Dewlap Results Table 1. A multiple regression indicated that, overall, reproductive morphology predicted display rate. However, individual components did not show significant relationships with behavior. Prediction Larger reproductive structures exist in males with increased levels of behavior. Methods • Focal behavioral observations of 12 adult males were conducted in the Jean Lafitte National Park and Preserve in southern Louisiana during the breeding season (May 2008). • Animals were collected and rapidly decapitated after 90-180 min behavioral observations. Tissues were frozen on dry ice and returned to MSU where they were stored at -80oC. • Tissues were cut at 20µm, stained with hematoxylin and eosin, and measured using Scion Image software. • Cross-sectional areas were measured from the following structures : • -Testes – semeniferous tubules • -Kidneys – renal sex segment • - Ceratohyoid muscle fibers (Fig.1) Figure 2. Negative relationships exist between testis morphology and both courtship behavior and size of the muscle fibers that control it Future Directions • Measure the muscles that control copulatory behaviors (use of the two penises, hemipenes). • Add six more adult males into our sample size. • Examine the motoneurons that innervate the muscle that controls the movement of the hemipenes. • Investigate courtship and copulatory structures and behaviors in females. Acknowledgements Funded by Ronald E. McNair Post-Baccalaureate Achievement Program/Summer Opportunity Research Program, Michigan State University, East Lansing, MI and the National Science Foundation Acknowledgements : Nancy Walters, Jean Lafitte National Park and Preserve, National Park Service; Louisiana Department of Fish & Wildlife; Danny Horton, Michelle Tomaszycki, Kenneth Sands, Parth Tikiwala Correspondence: Joseph Vandecar, jrvandecar@yahoo.com Overall dewlap size (cartilage length) was positively correlated with dewlap use (R= 0.75, p = 0.005). No relationships were found between ceratohyoid fiber size and the display time or length of the associated ceratobranchial cartilage. Body size was not correlated with any measure of reproductive morphology. Figure 1: The ceratohyoid muscle controls dewlap extension. From Wade, 2005.