Evolution - Intro, Claudius Kratochwil, 2025-10-13

Initial example

• Lake Ladago, 18,000 km² largest lake in Europe, 40 fish species
• Lake Malawi, 29,600 km², >500 fish species
• Why?

Diversity explosions

Adaptive Radiations

• This still puzzles biologists. Is it because
  • Ecological opportunity?
  • Why do some families diversify?
  • What are the role of certain processes (Sexual Selection)

Darwin's Finches

• Concluded that speciation occurs between animals with a common ancestor

Morphology

Is not always easy to tell species based on morphology, color morphs and subspecies can be very different within a species, even more so than between species

Species definition

There are around 30 concepts about what a species is - differs between disciplines a lot, taxa, study system...

Morphological species concept

• Early taxonomists, still used today
  • Problems, polymorphism, convergent forms

Biological species concept

• Group of actually or potentially interbreeding populations reproductively isolated from other groups
  • Problems: Hybrids, allopatric species, asexual animals, fossils

Phylogenetic Species Concept

• Emphasizes species as the outcome of evolution
• Phylogenetic species is an irreducible basal cluster of organisms, which have a parental pattern of ancestry and decent
• Species is the smallest exclusive monophyletic group of common ancestry

Sympatry and allopatry

• Allopatric populations - geographically separated populations
  • Makes it harder to tell if they would interbreed if they had overlapping range
• Sympatric populations - in the same location

Example - pygmy and brown-headed nuthatch

• They are allopatric populations but are probably the same species
• Difficult to tell

Cryptic Species

Mosquito example - some species transmit malaria and some don't, but they appear very similar

Sibling Species

Two morphologically similar species, not necessarily closely related

Sister species

The two most closely related species

Example - Toads

• Separating Bufo bombina and Bufo variegata is difficult
• They have partial inbreeding in a very small region, where gene flow is happening. The populations on the other ends of the range are stable (no gene flow)
  • This is called parapatry

Example - butterflies

• Introgression occurs where species somewhat distantly related will transfer genes
• If a gene producing an advantageous phenotype emerges it can spread between species
• Example in some south american butterflies:
  !Speciation_Kratochwil_24, p.16

Assigning Species

• All phenotypic (or genetic) markers should be in Hardy-Weinberg Equilibrium
  • These indicate reduced gene flow among sympatric populations
  • If there are few heterozygoes, (differs strongly from Hardy-Weinberg) that means they might be different species (or at least that they have population structure)

Reproductive Isolation

Types of speciation

Allopatric speciation

• Often starts with a geographic barrier
  • Can be caused by vicariance (barrier appears)
  • Or dispersal (colonization of new region)

Sympatric speciation

• Can also occur with no geographic barrier (sympatric speciation)
  • This is less common, rare and difficult to show
  • SPecies in sympatry rarely originate from sympatric speciation, usually secondary contact
• Example: Kentia palm and curly pallm from Lord Howe island
  • Flowering times barely overlap
  • This causes temporal Reproductive Isolation

Parapatric speciation

• is when neighboring populations diverge into two species
• Example given with lizards that live in light and dark soil habitats- genotypes differ between habitats strongly in one species and less so in another

Causes of speciation

Speciation Continuum

• When do you define when a species splits?
• After a certain number of genetic combinations?
• Recombination makes this more confusing

"Magic Traits"

• A trait that causes both ecological divergence and reprductive isolation between species
• Example - hawthorn flies began moving to apples in the 19th century
• In these, one or a few genes create new species. Otherwise, the coupled effects of many genes cause speciation.
• Some hawthorn flies began specializing in apples
  • This led to flies diverging both ecologically and temporally, since the fruiting season diverges. Since flies mate where they eat, this also effected their mate preference
  • Theoretically this could have been a single gene

Cichlid example

• Geonomic islands of speciation causes divergence between species
• In crater lakes in Nicaragua, they are usually fairly young but some species have spread between a few of them

Field experiment:

• Using some kind of aquatic drone, observe the behaviour of cichlids at different depths
  • Do the different pheontypes differ in feeding other behaviour?
• Next use nets to survey different depths and regions of the lakes and record the numbers of cichlids, measurements and weights at different depths
  • Also see what other fish are at the same depth (potential prey)
• Next take some back to the lab in different phenotypes and try to see if they will mate with each other
  • If they don't, this might be sympatric speciation, if they do, if the offspring are not very fit this is maybe allopatric, or if they produce viable offpsring they might be the same species
• Genetic analysis? Still in budget?

Determine if they are different species

• PCA of geonomes (or cluster analysis)
  • Matrix of 600,000 SNIPS (columns) - PCA will collect these on to two axes and try to find trends between them
• Differences in diet (stomach component analysis)
• Plot all their morphological differences (coloration, jaws, lips, body shape)