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TWO BASIC PREMISES: Rapid evolution and speciation in a marginal environment 1. Natural selection can drive adaptive divergence on ecological time-scales "CONTEMPORARY" OR "RAPID" EVOLUTION (<100 GENERATIONS) 2. Adaptive divergence can lead to reproductive isolation PREDICTION: Adaptation to new environments can cause the contemporary evolution of reproductive isolation Via 2009 Butlin et al. 2011 Nosil et al. 2008 Anthoxanthum odoratum Euhrychiopsis lecontei Oncorhynchus nerka Via 2009 Hybrid speciation: Hybrids may sometimes land on new adaptive peaks exploiting new environments that parental species cannot. Antonovics & Bradshaw 1970 Sheldon & Jones 2001 Hendry et al. 2000 1 Lycaeides spp. Gompert et al. 2006 The low saline Baltic: an extreme environment for marine species The low saline Baltic: an extreme environment for marine species Peripheral pop Species distribution Central population Marginal pop Different environmental conditions Reduced connectivity Different selection pressures Reduced sexual reproduction Reduced gene flow Increased genetic drift 1. Loss of genetic variation 2. Genetically divergent from central populations Baltic populations more diverse than North Sea populations Divergent Baltic populations Baltic populations less diverse than North Sea populations 0.6 Genetic distance to reference population A. No differentiation 1.0 Allozyme Microsatellite 0.8 mtDNA RAPD X=Y 0.6 0.4 B. Isolation-by-distance 1 C. Peripheral perturbation 4 D. Atlantic-Baltic genetic shift 4 0.5 Genetic distance 0.5 Genetic diversity of species X in Baltic pops 0 11 0.4 Cod Eelpout Blue mussel Macoma baltica 0.3 ltic Ba 0.2 rt No 0.1 ea hS 0 Geographic distance to Baltic entrance (dashed line) 0.2 20 species 0.0 0.0 0.2 0.4 0.6 0.8 -2000 -1000 0 1000 2000 3000 Distance from Öresund (km) 1.0 Genetic diversity of species X in North Sea pops From Johannesson & André 2006 From Johannesson & André 2006 2 CASE STUDY: Fucus vesiculosus & F. radicans in the Baltic Sea LIFE IN THE BALTIC SEA FOR Fucus SPECIES •F. radicans smaller (dwarf) with NORTH SEA TIDAL EXPOSED TO DESICCATION narrow thalli and bushy appearance. •F. radicans distributed in the Baltic; F. vesiculosus Arctic & temperate regions •Produce important complex structure & feeding habitat for other species •MtDNA and ITS sequences unable to discriminate both species LIFE IN THE BALTIC SEA FOR Fucus SPECIES BALTIC CONSTANTLY SUBMERGED Serrao, 1996 •F. radicans AND BALTIC F. vesiculosus SPERMS SWIM FASTER THAN SWEDISH WEST-COAST AND ICELANDIC F. vesiculosus SPERMS AT LOW SALINITIES COVERED BY ICE AT LOW TIDE LOW LIGHT CONDITIONS •F. radicans AND BALTIC F. vesiculosus PERFORM BETTER AT 10 AND 5 PSU POTENTIAL MECHANISMS OF FUCUS DISPERSAL IN THE BALTIC SEA Modified from Tatarenkov, 2005 INTERSPECIFIC DIFFERENCES BY LOCALITY PCA MORPHOLOGY PuuliPanki Fradicans PuuliPanki Fvesiculosus Trigii Fradicans Kõiguste Fvesiculosus Djursten Fradicans Djursten Fvesiculosus Bönhamn Fradicans Bönhamn Fvesiculosus ESTONIA White Sea 2 Norwegian Sea F. radicans F. vesiculosus 1 13.4% SWEDEN 3 0 -4 -3 -2 -1 0 1 2 3 4 Gulf of Bothnia 5 lan f Fin lf o Gu -1 -2 42.92% -3 ag Sk d ak err North Sea Baltic Proper 100 km Pereyra et al. in prep 3 PROPORTION OF SEXUAL vs ASEXUAL REPRODUCTION (CLONALITY DISTRIBUTION) Individuals with identical genetic identity (Clones) F. vesiculosus SWEDEN F. ves FIN F. radicans F. radicans SWE-FIN ESTONIA F. ves ESTONIA F. vesiculosus FINLAND F. radicans SWEDEN 97 Fr ad SW E (SW DEN E) Fv FINLAND (FIN) F. radicans FINLAND 64 F. vesiculosus SWEDEN Fv F. radicans ESTONIA 82 Frad Fv F. vesiculosus ESTONIA 0.1 F. radicans F. vesiculosus Johannesson et al. 2011 ...BUT,WHERE DID ALL START FOR Fucus radicans?? III OB F. radicans J Järnäs NW Gulf of Bothnia III Fv White Sea (Russia) I WHITE SEA IN SU L PE N ARCTIC ORIGIN? AN AV I IN I F. radicans II Öregrund SW Gulf of Bothnia II F. vesiculosus Öregrund IV SW Gulf of Bothnia Fv Öland Baltic proper D LAN IN ak err BALTIC PROPER 2 SPECIES PREVIOUSLY DIVERGED -POSTGLACIAL COLONIZATION FROM NORTH SEA? 100 km ... OR RECENT ORIGIN WITHIN THE BALTIC SEA?!!! 0.12 0.1 POSTERIOR PROBABILITY SC AN D ag IV 0.1 GULF OF BOTHNIA FF Sk 99 Fv Norway Fv Lysekil Skagerrak O LF GU NORTH SEA 91 72 A NORWEGIAN SEA 0.08 0.06 0.04 0.02 0 0 1500 3000 4500 6000 7500 9000 10500 TIME OF SPECIES DIVERGENCE (YEARS) Pereyra et al. 2009 APPROACHES THAT MIGHT REVEAL SIGNATURES OF RAPID EVOLUTION •Test whether individuals in new environments 'prefer' those new environments, a tendency that will reduce dispersal between new and ancestral environments •Use reciprocal transplants among similar and different environments and look at survival and reproductive success of transplanted individuals. •Examine the mate preferences of reproductively active males and females from similar and different environments. •Consider the effect of multiple reproductive barriers by testing whether gene flow is lower between populations in different environments than between populations in similar environment 4