CHAPTER 18 Interactions Among Species

1. CHAPTER 18 Interactions Among Species

2. Coevolution • Two species that interact affecting the genetic structure of one another. Each one acts as a selective force on the other (lineages change in parallel) • Co-speciation – Do 2 lineages speciate in the same pattern? Perhaps like a lichinous fungi and its algae symbiont.

3. Concepts of Coevolution • Coevolution as a process of reciprocal adaptive response • Specific coevolution: Coevolution of two (or few) species • Guild Coevolution (diffuse, or multispecific): Coevolution among sets of ecologically similar species • Escape-and-radiate coevolution • Cospeciation (introduced by interaction) • Coevolution as a pattern, detected by phylogenetic analysis • Cospecieation (coincident speciation) • Parallel cladogenesis

4. Co-evolution VS. Co-adaptation • Co-evolution is when genetic composition of both species changes, each affecting the other. • We assume co-evolution leads to co-adaptation. • But you can have co-adaptation without co-evolution (birds on same island with different bill shapes may have evolved in allopatry before sympatric overlap) • So, co-evolution should lead to co-adaptation but co-adaptation is not necessarily the result of co-evolution

5. Using Phylogenies to Answer Questions • Coevolution • Leaf-cutting ants and fungi they farm • Leaf cutters grow fungus on leaves that they cut for food • 200 ant species of tribe Attini each farm a different fungus species • Did the two groups cospeciate? • Phylogenies should be congruent • Hinkle found congruence on all branches but one • Fungi were domesticated more than once

6. Leaf Cutting Ants

8. Evolution of Mimicry • Complex interaction among multiple species believed to arise from co-evolution, though it has not been proven so. For sure, at least, this is co-adaptation. • Major Types of Mimicry: • Mullerian Mimicry • Batesian Mimicry • Mertensian Mimicry

9. Mullerian Mimicry • When a group of species that are distasteful, poisonous, or otherwise noxious, resemble each other in morphology or behavior • Often brightly colored and have some kind of warning system  Aposematic Trait • They call attention to themselves and warn of danger. This warning is assumed to ward off potential predators or increase fitness in some way. • The more these species look alike, the easier it is for a predator to remember that one warning pattern (eg. coral snakes bands)

10. Examples of Mullerian Mimicry • Coral snakes all coral snakes are venomous. There are around 70 species in the new world. Over 90% of them look extremely similar, especially with respect to color and pattern • We assume that their similarity in appearance allows predators to evolve the ability to identify them as poisonous and leave them along • Thus, there is an advantage that all share from looking similar

11. Batesian Mimicry • A non-noxious or non-poisonous mimic looks like a noxious model • For our coral snake example, the venomous coral snakes would be the model and non-venomous snakes looking like coral snakes are the mimics

12. Examples of Batesian Mimicry In each picture, the snake to the right is the Venomous Coral Snake, while those to the left are the mimics (harmless)

13. Mertensian Mimicry • We have seen some examples of deadly poisonous snakes such as Micrurus (Elapidae) and non-poisonous snakes such as Lampropeltus and Pliocercus (Colubridae). • But there are other snakes that are moderately poisonous, such as members of the genera Rhinobothryum, Erthrolammprus and Pseudoboa. • Mertens suggests that the moderately poisonous snakes could be the model, not the poisonous snakes.

14. Mertensian Mimicry • If the moderately poisonous snakes bite a predator, it would get sick and therefore would learn to avoid those and similar snakes in the future. • But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. • So, Mertens proposes that the moderately poisonous snakes are the model and both the poisonous and non-poisonous snakes are the mimics. This situation is termed Mertensian mimicry

15. Ecomorphs • What is an ecomorph? • We can loosely define an ‘ecomorph’ as a particular set or characters that define a body plan commonly associated with living in a particular habitat • Eg. snakes that live in trees are typically Green, slender, elongate...

16. Parallel Evolution of Anolis lizard ecomorphs on Caribbean islands # species per island shown There are 138 species in the Caribbean and about 340 species of anoline lizards overall.

17. Parallel Evolution of Anolis lizard ecomorphs on Caribbean islands Anolis lizards occupy many different ecological niches on Caribbean Islands

18. Ecomorphs are not closely related!! Each Island has independently evolved ecomorphs!!! Trunk-dweller Trunk-dweller Twig-dweller Twig-dweller tree-top tree-top Island 1 Island 2 Common Ancestor

19. CHAPTER 19 Evolution of Life History Characters

20. Reproduction Strategies • Mice mature early and reproduce quickly whereas bears mature late and reproduce late • Some plants live and flower for only one season, others live and flower for centuries • Some bivalves produce millions of tiny eggs at once, others less than 100 large eggs at a time

21. Life History Analysis • The branch of evolutionary biology that tries to sort our reproductive strategies • A “perfect” organism would mature at birth and produce many high quality offspring throughout life • No organism can do this because there are tradeoffs in time, size of offspring, and parental investment

22. Life History Analysis • Life history extremes • Thrip egg mites are born already inseminated by mating with brothers inside mother’s body • Adults have short lives • The offspring eat there way out of their mother when she is four days old • Brown kiwis lay eggs 1/6 of their body weight • Chicks are self-reliant within a week • Takes one month for female to produce each egg

24. Life History Analysis • Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring • For organisms that wait, chance of dying before reproducing is high • Environmental variation creates life history variation

25. Life History Analysis • Questions to Consider • Why do organisms age and die? • How many offspring should an individual produce in a year? • How big should each offspring be? • Must balance among fitness aspects • Conflicts arise between male and female parents

26. Life History Analysis • Female Virginia opossum • Nursed for three months and then weaned • Continued to grow for several months until reaching sexual maturity • Had first litter of 8 offspring • Months later had second litter of 7 offspring • At 20 months was killed by a predator • Energy allocation changed through life

28. Life History Analysis • Differences among life history concern differences in energy allocation • Other female opossums could mature earlier and reproduce earlier • Or devote less energy to reproduction and more to maintenance • Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction

29. Why Do Organisms Age and Die? • Senescence = late life decline of fertility and probability of survival • Aging reduces an individual’s fitness and should be opposed by natural selection • Two theories on why aging persists

31. Why Do Organisms Age and Die? • Rate-of-Living Theory • Senescence is caused by accumulation of irreparable damage to cells and tissues • Damage caused by errors during replication, transcription, and translation, and by accumulation of poisonous metabolic by products • All organisms have been selected to resist and repair damage as much as physiologically possible • Have reached limit of possible repair

32. Why Do Organisms Age and Die? • Rate-of-Living Theory • Populations lack genetic variation needed to enable more effective repair mechanisms • Two predictions of theory: • Because damage is partially caused by metabolic by products, aging rate should be correlated to metabolic rate • Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans

33. Why Do Organisms Age and Die? • Rate-of-Living Theory • Austad and Fischer tested first prediction • Calculated amount of energy expended per gram of tissue per lifetime for 164 mammal species • Should expend same amount regardless of length of life • Found great variation in energy expenditure • Found that bats expend three times the energy of other mammals their size

35. Why Do Organisms Age and Die? • Rate-of-Living Theory • Luckinbill tested second prediction • Artificially selected for longevity in fruit flies • Increased life span from 35 days to 60 days • These long-lived fruit flies had lower metabolic rates during first 15 days of life

37. Why Do Organisms Age and Die? • Rate-of-Living Theory • Both of the predictions of the theory have been falsified • Examine energy expenditure on cells and chromosomes, not whole organism • Normal animal cells are capable of a finite number of divisions before death • All cells except cancer cells, germ line cells, and stem cells • Senescence may result from chromosome damage

38. Why Do Organisms Age and Die? • Rate-of-Living Theory • Telomeres of chromosomes consist of tandem repeats • Added by enzyme telomerase • Overactive in cancer cells • During each replication pieces are lost • Progressive telomere loss is associated with senescence and death • Cells die because chromosomes are too damaged to function

39. Why Do Organisms Age and Die? • Rate-of-Living Theory • Life spans of mammals are correlated with life spans of skin and blood cells • These results consistent with rate-of-living • Why doesn’t natural selection activate telomerase to add more telomeres? • Could be tradeoff between extending cell life and proliferating cancer

41. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • If genetic variation for extending life spans does exist, why hasn’t natural selection produced this result in all species? • Aging is not caused by damage itself but the failure to repair the damage • Damage is not repaired because of deleterious mutations or tradeoffs between repair and reproduction

42. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Hypothetical life history of individual with wild-type genotype • Mature at age 3 • Die at age 16 • Probability of survival from one year to the next is 0.8 • Expected lifetime reproductive success = 2.419 • Will consider two mutations that alter life history strategy

44. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Mutation Accumulation Hypothesis • Mutation cause death at age 14 • Deleterious mutation, but how deleterious? • Expected lifetime reproductive success reduced to 2.340 • Still 96% of original • Weakly selected against • May persist in mutation-selection balance

46. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Deleterious mutations that affect individuals late in life can accumulate in populations and be the cause of aging • Cancers that usually occur late in life only slightly affect fitness of the individual • Not strongly selected against and can accumulate rapidly • Can cause senescence and death with few fitness consequences

47. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Mutation of two different life history characters with pleiotropic action • Matures at 2 years • Dies at 10 years • Tradeoff between early reproduction and survival late in life • Antagonistic pleiotropic effects • Expected lifetime reproductive success is 2.66 • Mutation is beneficial

49. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Reproduce so much early that early death is not selected against • Mutation devotes less to repair and more to reproduction • Heat-shock protein hsp70 • Prevents damage due to denaturation • Heat-shock binding interferes with normal cellular functions • Heat-shock genes only expressed during environmental stress • Proteins removed after stress passes

50. Why Do Organisms Age and Die? • Evolutionary Theory of Aging • Expression of hsp70 in Drosophila causes longer life span but lower reproduction early in life • Tradeoff between early fecundity and late survival is mediated by hsp70 • Heat-shock proteins may mediate this tradeoff in many organisms