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Unformatted text preview: 8-1 Laboratory 8Agonistic Behavior in Betta splendensThe star of today's show is Betta splendens, sometimes known as the Siamese Fighting Fish. Although it is important for you to know this species' phylogeny, the focus of today's exercise will be your own experimental manipulation of external stimuli that affect the courtship and/or aggressive physical displays of this interesting animal. I. Phylogeny and Evolutionary RelationshipsFish, like all vertebrates, are deuterostome chordates that share several synapomorphies with other deuterostome taxa. Like protostomes (e.g., Annelida, Mollusca, Arthropoda), deuterostomes are bilaterally symmetrical, triploblastic coelomates. But unlike the protostomes, in deuterostomes: 1. The blastopore becomes the anus (a secondary opening becomes the mouth) 2. The coelom is derived via enterocoely 3. Cleavage is radial and indeterminate 4. The nervous system is primitively dorsal 5. The circulatory system is primitively ventral The deuterostome phyla with which you are probably most familiar are Echinodermata(e.g., starfish, sea urchins, sea cucumbers) and Chordata. Chordata, includes three subphyla, Urochordata(tunicates), Cephalochordata(lancelets) and Vertebrata(vertebrates). Chordate synapomorphies include: 1. pharyngeal gill slits present during some stage of development 2. dorsal, cartilaginous notochord at some stage of development 3. dorsal, hollow nerve cord 4. having an endostyle (Urochordata, Cephalochordata) or homologous thyroid gland (Vertebrata) at some stage of the life cycle 5. tail posterior to the anus (primitively muscular and used for locomotion) 6. segmentally arranged muscle bundles (sarcomeres) Synapomorphies that set vertebrates apart from all other Chordates include: 1. skeleton constructed of bone (at least primitively) 2. a bony cranium encasing the brain 3. articulated vertebral column The vertebrates may be the most recognizable of all animals, including such familiar forms as fish (a vast and diverse assemblage), frogs, lizards, snakes, birds, and mammals. Vertebrates, with nervous systems and brains far more complex than other animals, often exhibit complex behaviors related to foraging, territorial defense, and reproduction. In today's lab, you will examine reproduction-related behaviors of a representative vertebrate, Betta splendens(Osteichthyes). Wild Betta splendensare colorful and sexually dimorphic, with males being more brightly colored than females (Figure 8-1). Because of their attractive colors and interesting behaviors, this species has been subject to many years of artificial selection (particularly the males) for mutant color morphs and very long fins and tails. Despite the 8-2 domestic variety's showier appearance (Figure 8-2), courtship and other intraspecific displays have remained relatively unchanged. Both wild and domestic Betta splendenswill react strongly and aggressively to the appearance of another fish of the same species....
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- Spring '08