Which set of elements is arranged in order of increasing electronegativity?
Hybridization, Speciation, and Extinction Why the ability to disperse is ^That ever existed How many species are there on Earth Estimates range from 9—100million species total Of about 1.9 million described species on Earth… Three Species ‘Concepts’ • Morphological— classification based on similar physical characteristics (with some allowable variation within a ‘species’ (morphospecies) • Phylogenetic— group of organisms that share a common ancestor (divergence must be sufficiently clear) • Biological— a group of interbreeding or potentially interbreeding organisms that can produce viable offspring. (Ernst Mayr, 1942) Species are the smallest evolutionarily independent units isolated because of a lack of gene flow Figure 16-1 Ageneralized Phylogenetic or Evolutionary tree. TESTABLE, Verifiable, not Monophyletic magically group thought up in a scientist’s head Common ancestor What about bacteria within the definition of a species Some scientists say, gene transfer helps bacteria diverge & become new species Is every individual bacterium a species Bacterial species best-defined in an ecological context Figure 16-3 The power of using more than one species concept to ‘discover’or delineate a species Important to understand biodiversity (Endangered SpeciesAct) and further practical significance directly relevant to ecosystem function and human health (these species important in algal blooms) Figure 16-4 Why understanding a ‘species’can have critical implications for conservation Figure 16-5 Figure 16-6 How do species form Isolation: a reduction in gene flow TIME!!!!!!!!!!!!!!!! Hawai’i Figure 16-7b Islands (especially Hawai’i) represent a natural experiment of adaptive radiation through dispersal Tell a historical narrative of speciation and dispersal over millions of years Figure 16-7a Two hypotheses of ‘dispersal and colonization’ hypothesis: 1) closely related species on spatially adjacent islands 2) sequence of island formation should match branching pattern of divergence in fruit flies (molecular analysis) One of the most diverse locales on Earth for fruit flies: >1,000 species occupy MANY habitats (niches) many species are endemic to particular islands (very Figure 16-7 Figure 16-7c Okay, sure, this phylogenetic tree was generated but where’s the evidence -used 2 mitochondrial genes (maternally inherited) -4 nuclear genes -excellent data collection and statistical analysis! Oldest taxon predates oldest Hawai’ian island, however… One way to check the data… Figure 16-7c Do more ancient species exhibit more changes in DNA sequences compared to more recent divergent species YES! Figure 16-8 Please read the Snapping Shrimp speciation description in the text! What are the mechanisms of divergence • 1) Adaptation to different habitats – May still be very close spatially • Again, TIME! • Different habitats may incorporate: – Biotic and abiotic factors (competition, predation, disease, nutrient availability, etc.) – Slight differences over long time periods lead to speciation Carl Sagan’s Cosmic Calendar Reviewed by Neil deGrasse Tyson; Episode 1, 2014 Figure 16-14 2)Assortative Mating Choosing mates with very similar phenotypic traits In this case male song pulse rates Females attracted to particular songs Deep genetic basis Sexually selected phenotype Figure 16-16 3) Environmental factors and mating preferences can act together (interaction effect) Phenotypes vary greatly depending on where fish are located, the clarity of the water, and Cichlids in Lake Victoria inAfrica possibly other factors—So, attractiveness varies Figure 16-17 Color in these cichlids is genetically controlled Some females will be attracted to males of their species BUT….there’s variation We can consider this a hotspot of evolution or even rapid evolution Figure 16-18a What happened here Figure 16-18b Figure 16-18c Figure 16-18d When do we know if a new species has been formed • Secondary contact occurs (not entirely common) – And the closely related species cannot hybridize or interbreed – Outcomes of contact with 2 two sister or closely related species: • Pre-Zygotic isolation • Post-Zygotic isolation What Drives Diversification on Earth • Reproductive isolation is VERY important • Environmental heterogeneity – Drives diversification into new niches • How do we explain changes in diversification rates over time – Relatively stable/low rates of speciation – Rapid diversification in some/all groups Figure 16-27 Rate of species formation slows over time but depends on the ecology of each island—size matters Number of Anolis spp. Represented throughout the Caribbean The ability of individuals of a species to disperse is insurance • Against extinction • And assurance in getting genes (DNA) to the next generation • But dispersal ability is not a guarantee against extinction – Ability to become established in a new habitat/niche with slightly different resource