Lecture 25

1 Diversity of Fish Behavior and Life History Fishes are as diverse in their behavior and life history as they are in their taxonomy, anatomy, and ecology. Behavior usually involves learning to respond to changeable conditions • Food capture • Predator avoidance, schooling, hiding • Choosing habitat; migration, • Mate choice, parental care All fish accomplish difficult location and capture mechanisms. (Selection? Learning?) Archer fish accurately spit to knock insects from vegetation into the water. (Nature? Nurture?) 2 African electric catfish can electrocute prey with 200-volt shocks (and discourage would-be predators) Which came first? Behavior or morphology ? Elephant fishes, Mormyridae make electric currents; locate food in electric field. communicate with electric signals to maintain territories and attract mates Deep-sea predators hang in the dark of ocean depths and wait for food to drop by. How are habitat, behavior, morphology integrated? 3 Deeps-sea Angler attracts prey with fishing lures. Food capture is by suction. Which came first, the lure or the sit-and- wait feeding behavior? Mouth opens in a few thousandths of a second “Cleaning” (removing parasites) is a complex cooperative behavior in which the cleaner and the cleaned (different species) both benefit: one in survival, the other in growth. How might genetics and learning interact? Protection from predators takes many forms-- selected for by the effectiveness of predators Porcupine fish puff themselves up behind bony spines 4 One-third of fishes show schooling behavior, which can serve several functions: A= save energy; B= feed; C & D = avoid predation 2) Reproduction: Egg-laying fishes • Most fish species are egg-layers • Most fish species have external fertilization • Is egg-laying necessarily a primitive trait? – All male Sharks fertilize females internally, – females of some species bear live young; but other shark species lay fertilized eggs – What are the advantages of laying eggs, rather than giving birth to live young, after internal fertilization? Some egg-layers, like this jawfish, show parental care Mouth-brooding fertilized eggs and young is common among fishes. There is a tradeoff between many small eggs and few large eggs. There is also a tradeoff between parental care and more offspring-- without parental care. 5 Mouthbrooding contributes to fitness by protecting the young. It may also contribute to the speciation process by imprinting the young on the odor and colors of the mother. So that breeding adults are attracted to the right mates by odor. A new species could get started by evolution of a new, attractive odor. Especially in a new habitat or new season. Cichlid mating behavior is based on mouth brooding. yellow"egg dummies" on the anal fins of the males connect fertilization and parental care behaviors. Males and females swim in circles: The female lays her eggs and circles around to pick them up in her mouth. How are they fertilized? FM F F F F FF F 6 DIVERSITY IN PARENTAL CARE discus (Cichlidae) of South America Young feed on a milky secretion from the skin of the parents, enhancing survival and growth of the young Seahorse reproduction: males care for the young, which the females lay in the male's pouch when they mate. Males give birth to the young. DIVERSITY IN PARENTAL CARE Female mate choice often results in extreme male secondary sexual characters, like large fins. Apparently taken by females to be evidence of fitness, or maturity 7 Live-bearers (guppy family). Males have modified anal fins for transmitting sperm to females, coordinated with behavior for increasing fertilizations. Live-bearing fishes: Poeciliidae (guppies and others); Goodeidae, etc. • What is the advantage of bearing live young? Think about the tradeoffs. • What are the costs and risks of bearing live young? female, Goodeidae male The young are nourished by placenta-like structures inside the mother. These young advance far beyond the egg stage. 8 California surf-perch giving birth These young males are born mature and ready to fertilize mates immediately! Live birth and protection of the growing young enables surprising novelties in life history evolution Anemone Fish Immunity to Anemone stings allows them to avoid predators. Anemone fish change sex during life history What might be the advantages of sex change in fishes? How might it be related to body size? Sex reversal allows individuals to increase their fitness by breeding as both sexes • Sex reversal – Protandry-first, a male – Protogyny-first, a female • Socially controlled--some protogenous groups have one large male and many females. If a predator takes the male, the largest female changes sex, makes sperm, and changes behavior. Bluehead wrasse 9 Most life history traits are coordinated among growth, maturation, and reproduction; e.g. salmon Each step requires complex behaviors Behavior and life history in pacific salmon • Females dig nests, choose males, defend nest to the death. (All adults die after spawning.) • Young hatch, emerge from gravel, swim downstream to the ocean, grow on rich food for 2-5 years. • Mature individuals migrate back to where they were born, using chemical, magnetic, visual cues. • Why do they go back to where they were born? • Why do they all die after spawning? Adaptations to increase survival, growth, and reproduction take many complex forms. • Behavior integrates many adaptations – Feeding, schooling, predator avoidance,mate choice, parental care, are just a few examples • Behaviors in today’s examples are partly learned and partly facilitated by structural adaptations, hormones, and unlearned reward systems that reinforce learning. 10 Summary • All life history adaptations are tuned to increase survival and reproduction in the environment in which their ancestors lived. • Varying environments select for responses that can be changed on the spot, like learned behaviors for feeding or avoiding predators. • All complex adaptations are directly or indirectly the products of natural selection. Philip Myers fish behavior 3/17/06.ppt