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Evolutionary success is unevenly distributed Ecological success is measured as population growth rate how fast does one population grow, compared to others? Microevolutionary success is measured as fitness – how many of your offspring survive to reproductive age? Macroevolutionary success equals clade biodiversity, or number of surviving species in a clade - typical animal phyla have ~5,000 species (=spp.) - lineages below the phylum level with >5,000 spp. are thus unusually successful Identifying characteristics that make one lineage especially successful is a major goal of evolutionary biology How do _____ evolve? microevolution populations allele frequencies - genetic drift - natural selection - migration macroevolution species reproductive isolation adaptation lineages (clades of species) diversification why do some groups have more species than related groups? one common ancestor clade of 3 extant species (surviving today) 1 surviving species 2 daughter lineages, of equal age Evolutionary success = number of living species Why does one lineage diversify into many more species than its less-successful sister lineage? Evolutionary success is unevenly distributed Major goal of macroevolutionary studies: explain why some groups are more species-rich than others 3 spp. Can we identify the traits that explain why biodiversity is unevenly distributed among sister clades? 60 spp. what led this group to out-radiate its sister group by 20 to 1? - change in habitat, feeding method, traits involved in competition or reproduction...? Evolutionary success is unevenly distributed Major goal of macroevolutionary studies: explain why some groups are more species-rich than others Woo-hoo! **Winners** colonizing dry land led to explosive radiations in many groups beetles: 350,000 spp. named (probably >1 million) Pulmonata: land / freshwater snails + slugs ~60,000 spp. (including marine members) vertebrates: ~45,000 spp. Evolutionary success is unevenly distributed other lineages can hover at low species numbers despite being ecologically abundant and important - may survive unchanged for hundreds of millions of years and be very well adapted to their niche, yet never diversify Losers – the “200 club” sharks + rays: top marine predators cephalopods: pinnacle of invertebrate vision & intelligence Some lineages undergo adaptive radiations, filling all available ecological niches and diversifying into many species 1) opportunity: ancestor colonized an empty habitat with many unoccupied niches... - went from marine into terrestrial + freshwater habitats - got onto an empty continent, early - survived mass extinction of dominant competitors 2) specialization: when related species exploit different ecological niches (i.e., food or host), many related species can co-exist in one place without competing 3) key innovation: evolution of a trait that allows exploitation of new niches, or greater competitive ability Some lineages undergo adaptive radiations, filling all available ecological niches and diversifying into many species 4) evolved a trait that promotes rapid speciation: - sexual signaling or mating system - strong host or habitat association - tendency to get allopatrically isolated (dispersal) - fast-evolving gamete recognition proteins 5) being biogeographically widespread – meaning, some member species are distributed across different regions and biomes across the globe - lineage is more likely to survive local wipe-outs, and global mass extinction events Evolutionary success is unevenly distributed Diversification rate of a lineage (r) is the net difference between speciation (new spp. born) and extinction (existing spp. vanish) - thus, either of two things can lead to a lineage diversifying more: 1) increase in speciation rate (l) shift in rate of diversification (speciation extinction) Rabosky 2014 2) decrease in extinction rate (m) r=l-m Evolutionary success is unevenly distributed Diversification rate of a lineage (r) is the net difference between speciation (new spp. born) and extinction (existing spp. vanish) - thus, either of two things can lead to a lineage diversifying more: 1) increase in speciation rate (l) shift in rate of diversification (speciation extinction) Rabosky 2014 2) decrease in extinction rate (m) r=l-m Evolutionary success is unevenly distributed Diversification rate of a lineage is the net difference between speciation (new spp. born) and extinction (existing spp. vanish) 1) key innovation may lead to an adaptive radiation into many new ecological niches key innovation evolves, sets off burst of diversification Rabosky 2014 problem: typically a one-time event, not naturally replicated 2 living species of Bosellia - flat sea slugs - eat one algal genus - tropical only 134 species in sister clade Plakobranchidae - parapodia: sides rolled up - eat >20 algal genera - tropics to poles Why only 2 Bosellia but 134 plakos? - flat sea slugs - eat one algal genus - tropical only 134 species in clade Plakobranchidae... - parapodia (sides of body rolled up) may protect stored chloroplasts from too much sun (possible key innovation?) - each species feeds on just one of >20 kinds of algae (specialized) - species live and mate on their host (host choice may promote speciation) Candidate key innovation: antifreeze proteins One group of fish diversified in the Antarctic after evolving anti-freeze glycoproteins, allowing them to survive water temperatures below freezing 9 species, non-Antarctic (no anti-freeze) 123 species, Antarctic - anti-freeze glycoproteins - within Antarctic, species also diversified into benthic (bottom) and pelagic (open water) forms - again, however, only happened once so hard to test hypothesis Identifying trait-dependent diversification Easier to test hypotheses if diversification rate is character state-dependent, and character state changes often ancestral state derived state 3x higher rate of diversification repeated, independent shifts between states naturally replicated experiment Rabosky & McCune 2010 Comparative methods can identify such traits Identifying trait-dependent diversification Easier to test hypotheses if diversification rate is character state-dependent, and character state changes often derived state 3x higher rate of diversification Traits that cause greater diversification result in species selection - form of selection acting on trait(s) shared by all members of a species, or that are a species property (e.g., range) Rabosky & McCune 2010 - unrelated to fitness within species Identifying trait-dependent diversification l = speciation rate From a model-fitting perspective, the question is: Does a model with two different speciation rates (one for state “blue”, one for “red”) fit the data better than a default model with the same speciation rate for both states? Species selection in plants Flowering plants repeatedly evolved self-compatible pollen, allowing selffertilization, from selfincompatible pollen (cannot self-fertilize) Selfing Non-selfing Goldberg et al. 2008, Science Species selection in plants In non-selfing plants, estimated speciation rate is higher than extinction rate – thus, lineages diversify (r > 0) - however, some non-selfers are always gradually evolving into self-fertilizers by character change.. selfing non-selfing diversification rate (r) Goldberg et al. 2008, Science Species selection in plants In selfing plants, rates of both speciation and extinction increase... however, extinction increased more than speciation - selfing plants have decreased diversification rates (r < 0) - this explains why non-selfing plants persist, even though some keep turning into selfers: the remaining non-selfers outcompete the species that undergo character change and become selfers selfing non-selfing diversification rate (r) Marine larval type and dispersal marine invertebrates produce microscopic larvae that swim for short periods (0 - 5 days) or long periods (>30 days) Planktotrophy lecithotrophy long-distance dispersal short-distance dispersal Consequences of long-distance dispersal planktotrophy lecithotrophy population connectivity gene flow local adaptation speciation rate extinction risk planktotrophic populations remain connected over evolutionary timescales Evolutionary consequences of larval type planktotrophy population connectivity gene flow local adaptation speciation rate extinction risk ancestral lecithotroph lecithotrophy Evolutionary consequences of larval type planktotrophy demographic connectivity gene flow local adaptation speciation rate extinction risk populations diverge... lecithotrophy Evolutionary consequences of larval type planktotrophy lecithotrophy demographic connectivity gene flow local adaptation speciation rate extinction risk theory and genetic data suggest lecithotrophic populations will split and diverge into new species... Evolutionary consequences of larval type planktotrophy lecithotrophy demographic connectivity gene flow local adaptation speciation rate extinction risk theory and pop-gen data suggest lecithotrophic populations will split and divergence into new species... Evolutionary consequences of larval type planktotrophy lecithotrophy demographic connectivity gene flow local adaptation speciation rate extinction risk ...but may also go extinct more often Evolutionary consequences of larval type For 40 years, paleontological studies of snail fossils have inferred larval type from the shape of the larval shell, at the tip of adult shell lecithotrophic shape Shuto 1974 Shuto 1974, Hansen 1978, 1980, 1982, Jablonski & Lutz 1983, Jablonski 1986 Six studies, cited >1,400 times, concluded lecithotrophs diversify more than planktotrophs, so benefit from species selection - that’s 1/12th the number of citations of the discovery of PCR! Paleontological Perspectives short-distance long-distance each vertical line is a species, showing where it 1st appeared in the fossil record, and when it disappeared (went extinct) 65 million years ago Hansen 1978, Science Paleontological Perspectives lecithotrophic plankto. 1. short-distance dispersers speciate more often, but survive for short periods 2. long-distance dispersers survive for longer, but speciate less However, these studies never calculated diversification rate: r = speciation - extinction Hansen 1978, Science short-distance may increase speciation and extinction rates, but the net difference between the two is what matters Paleontological Perspectives long-distance (n = 50) % short-distance (n = 50) Jablonski (1982, 1986) confirmed for several groups of snails that lecithotrophs have higher rates of both speciation and extinction inferred that species selection favors lecithotrophs, because: i) they speciate faster ii) they accumulate in fossil record over time % duration (m. y.) Has been cited >450 times, and become a textbook example of species selection Paleontological Problems Studies also did not address the fact that short-distance migration arises in two ways: 1) when a short-distance ancestor speciates, or 2) when a long-distance species undergoes character change ‘species-selection’ hypothesis short-distance dispersal evolves once, triggers rapid diversification ‘character-change’ hypothesis – accumulation w/out diversification short-distance evolves 4 times from different long-distance ancestors; short-distance species don’t diversify Paleontological Problems i) studies did not factor in rates of character change ii) paleontological studies never calculated diversification rate short-distance may increase both speciation and extinction rates, but it is the net difference between the two that matters speciation rate (l) diversification rate (r), the rate at which a lineage accumulates species (the measure of evolutionary success) extinction rate (m) r = net gain in species over time Paleontological Problems i) studies did not factor in rates of character change ii) paleontological studies never calculated diversification rate short-distance may increase both speciation and extinction rates, but it is the net difference between the two that matters speciation rate (l) long-distance short-distance r=1 r=2 extinction rate (m) both l and m go up, yet r decreases Paleontological Problems long-distance (n = 50) % speciation rate (l) = 0.23 extinction rate (m) = 0.17 diversification rate: (r) = l - m = 0.06 short-distance (n = 50) speciation rate (l) = 0.43 extinction rate (m) = 0.34 diversification rate: (r) = l - m = 0.09 % 1) minimal difference (if any...) duration (m. y.) Jablonski 1986 2) assumes all “appearances” of shortdistance dispersers reflect speciation, but some must result from character change (long turns into short) Using sea slugs to study macroevolution Objective: identify traits that promote diversification, using herbivorous slugs in clade Sacoglossa as a model Oxynoacea - 6 genera, 74 spp. shelled Limapontiodea - 18 genera, 152 spp. cerata-bearing Plakobranchoidea - 4 genera, 137 spp. (103 in Elysia) photosynthetic short-distance long-distance Ancestral devel. mode Limapontioideainferred using evolutionary quantitative probability genetics that an model ancestor had given type of larval dispersal a short-distance long-distance Plakobranchoidea - more lecithotrophs in Plakobranchoidea, but only two pairs of lecithotrophic sister species species-selection hypothesis predicts (a) clades of short-distance dispersers, which (b) should contain more species NOT the case! 1. Testing for shifts in diversification rate Software ‘Medusa’ used to model diversification across 32 genus-level clades, using total # of known spp. 1 Medusa identifies shifts in the overall rate of diversification, not taking into considerating character state 2 two branches where rate of diversification accelerated: 1) after loss of shell 2) after photosynthesis evolved Alfaro et al. 2008 We then modeled rates of speciation, extinction, and change between longand short-distance larvae Tested whether data better fit a model in which rates depended on larval dispersal, or if ignoring larval type fit the data just as well Considered the three superfamilies of Sacoglossa as distinct, since they diversify at different background rates Speciation rate depends on larval type a) unrestricted BiSSE l (1), m (1), q (1) l (1), m (2), q (1) l (2), m (1), q (1) l (2), m (2), q (1) df ln(L) AIC χ2 P 9 12 12 15 -68.73 -66.06 -61.90 -61.20 155.46 156.12 147.79 152.40 n/a 5.33 13.67 15.06 n/a 0.149 0.003 0.020 best-fit model b) restricted BiSSE l- (1), m (1),which q (1) allowed 9 -70.33 158.66 n/a vary n/a model speciation rate to with larval type l (1), m (2), q (1) preferred 12 -66.87 157.75 which 6.91 ignored 0.075 larval type was highly over model l (2), m (1), q (1) 12 -63.78 151.55 13.10 0.004 l (2), m (2), q (1) 15 -63.29 156.58 14.08 0.029 - letting extinction rate covary with larval type did not improve fit l = speciation rate m = extinction rate q = rate of character change Maddison et al. 2007, FitzJohn 2012 Species selection favors planktotrophy longdistance rP Oxynoacea Limapontioidea Plakobranchoidea 3.2 10.4 26.1 shortdistance rL 1.8 <0 10.1 q1 4.3 1.1 9.8 diversification rate (speciation – extinction) was always higher for long-distance (rP) than short-distance (rL) dispersers most short-distance dispersers arose recently by character change, when a long-distance species evolved into a shortdistance species Are sacoglossans just weird, though? “This is not a group that appears to have speciation rates driven by lecithotrophy: lecithotrophy is the much rarer state in this group. Presumably this is not the case for many other clades.” “You are characterizing patterns in a single somewhat odd clade of mollusks, with relatively poor fossilization.” - anonymous reviewer comments about this work Are sacoglossans just weird, though? Heterobranchia Anaspidea Cephalaspidea Notaspidea Nudibranchia Sacoglossa #P 17 47 7 171 108 #L 2 13 3 60 35 %P 89.5 78.3 70.0 74.0 75.5 Caenogastropoda Calyptraeidae Conidae Fasciolariidae Littorininae Muricidae Volutidae 39 56 9 139 36 0 39 35 25 13 46 9 50.0 61.5 26.5 91.4 43.9 0.0 % of known species with planktotrophic development outliers are some clades in Neogastropoda that have few surviving planktotrophs ...but guess who paleontological studies focused on? Are sacoglossans just weird, though? “This is not a group that appears to have speciation rates driven by lecithotrophy: lecithotrophy is the much rarer state in this group. Presumably this is not the case for many other clades.” “You are characterizing patterns in a single somewhat odd clade of mollusks, with relatively poor fossilization.” As a function of changes per branch, larval type changed about as often in Sacoglossa (0.067) as in cone snails (0.067), and less often than in slipper shells (0.176) Thus, Sacoglossa is typical in its % of planktotrophs, and in its rate of developmental evolution Short-term solutions to a long-term problem Species selection favors long-distance dispersal in Sacoglossa, and perhaps (probably?) in most invertebrate groups Loss of dispersive larvae is.. i) favored at ecological timescales, so change is frequent ii) a dead-end at macro-evolutionary timescales Most short-distance dispersers are the Walking Dead: short-lived lineages that go extinct before they can diversify into daughter species Short-term solutions to a long-term problem Species selection favors: 1) self-incompatible pollen in plants 2) long-distance larval dispersal in molluscs in both cases, the derived state (selfing in plants, short-distance larvae in sea slugs) evolves frequently, but increases extinction more than speciation, so dooms that lineage thus, what’s favored by selection in the short-term or within a species may not be an evolutionarily “winning strategy” in the long term >1,400 citations support a hypothesis that our results indicate is wrong. Don’t believe everything you read!