Speciation & macroevolutionary change

Allopatric Speciation Most common form of speciation Due to geographically isolation - Gene flow between them stops between populations - Genetic differences emerge - Small populations = FOUNDER EFFECT (different allelic frequencies when populations separated)

Sympatric Speciation Populations in same habitat become reproductively isolated from each other Related to polyploidy (offspring born with twice the normal number of chromosomes!) These individuals can’t mate with original population Super rare! Mostly seen in plants as it’s easier for them to self-fertilize

Comparing Allopatric & Sympatric Speciation

1. Heterochrony Developmental change in the timing of events leading to changes in size and shape Timing of when genes are expressed Two main components: (i) the onset and offset of a particular process (ii) the rate at which the process operates *Allometric growth and Paedomorphism are examples of heterochrony! Let’s take a look…

2. Allometric Growth Varied rates of growth in certain organisms Ex. the claw of fiddler crab grows much larger and faster than the rest of the crab

3. Paedomorphism Organism becomes reproductive sooner than an ancestral species (due to mutation) Body is still in its juvenile form when the animal becomes sexually mature; body development then STOPS Ex. Mud puppy (salamander) retains juvenile gills externally

Ex. Many domestic dog breeds (Canis lupus familiaris), derived from wolves (Canis lupus), exhibit paedomorphy with respect to adult wolves

4. Homeotic Genes Genes which regulate the development of anatomical structures Regulation is done via the programming of various transcription factors by the homeotic genes These affect genes through regulatory genetic pathways

Imagine what can happen if a mutation occurs to one of these… Example: Hox Genes Group of related genes that control body plan of an embryo along head to tail axis  Hox proteins determine type of segment (ex. Legs, wings, antennae, etc) Initiate identity of a segment but not the actual segment, itself Imagine what can happen if a mutation occurs to one of these…