Mechanisms of Species Diversity

Which of the following provides evidence that vertebrates evolved from a common ancestor? A) homologous structures B) the common development of pharyngeal pouches in an embryonic stage C) the presence of similar genes D) similarities in protein structure E) All of the choices are correct.

What is genetic drift? A) chance changes in the gene pool of a small population   B) the entry of alleles into a population due to immigration   C) changes in the gene pool of a population that are due to differential reproductive success   D) a change in allelic frequencies due to mutation   E) the loss of alleles from a population due to emigration  

All life is organized into 3 domains 2 Domains of prokaryotes, 1 of all eukaryotes Bacteria & Archaea- prokaryotic Eukaryota- Includes all 4 eukaryotic kingdoms: protista, animalia, plantae, fungi All domains have a common ancestor

Taxonomy is the science of classification Categories move from the general to the specific Species are named according to the genus and species to which they belong (Binomial nomenclature) e. g. Homo sapiens

Millions of species have been named However, the definition of species remains vague and flexible Yet there are unquestionably a wide variety of living things on earth

Change in allele frequencies alone cannot generate diversity

Evolution happens at the level of species

The Biological Species Concept is based on reproductive isolation

The Biological Species Concept “Two organisms that are able to reproduce naturally to produce fertile offspring. Organisms that can reproduce but almost always make infertile hybrids, such as a mule or hinny, are not considered to be the same species.”

Other Species concepts Ecological Species concept- species are define by the ecological niche which they fill Morphological Species concept- Species are defined and categorized by the physical structures they share

Reproductive Barriers cause reproductive isolation

Reproductive Barriers cause reproductive isolation

Behavioral Isolation can cause speciation Courtship rituals are a prime example of behavioral isolation Temporal behavior can also isolate a species

Mechanical Barriers can lead to Speciation

Postzygotic barriers

When populations are isolated from each other, genetic drift and selection ensue, causing allopatric speciation

In plants, polyploidy is a cause of sympatric speciation

Ecological pressures and opportunities fuel adaptive radiation Of course the answer to that one is yes. The way is by adaptive radiation. The primary feature of adaptive radiation is the rapid formation of multiple species from a single ancestor, as we see in this picture. Adaptive radiation- one species becomes many, rapidly to fill vacant ecological niches

Natural selection is a driver of speciation Selection occurs against traits, and thus the genes that determine them. Many traits, in fact many of those most important to evolution and to speciation, are what we all continuous traits- like these, we have a distribution curve. Well, as it is, perhaps some of these trait forms are better suited to an environment than others? Imagine a case where the extremes of a trait are selected against. This appears to be the case with human fetal birth wieght. Since humans have move to a fully bipedal existence, childbirth has become a complicated and difficult affair. Babies tend to be smaller and more undeveloped, yet to deliver a baby before it is fully developed is to jeopardize its life. On the other hand, if a baby is overly developed, the delivery could be fatal to both motther and child. Thus, child birth weight is subject to what we call stabilizing selection. The spectrum of trait phenotypes selects only those phenotypes closest to the middle of the distribution of the trait. Likewise, we can imagine the old classic, giraffe neck length. Recall that one of the most ancient exmaples of speciation is thatof the giraffe. W eecided that the blah blah blah, and that’s how we got a giraffe with a longer neck than members of that community had befre. Lastly, we can imagine a little critter sitting in the bushes. A predator is nearby. Should our little frightened rodent run, or wait? Well, that’s certainly dependent on the proximity of the predator. It might be that if the predator gets close at all, Directional and disruptive pressures cause species to change

Artificial selection shows the pliancy of species morphology From these pictures we can see the vast diversity of phenotypes available to a species from a single genome. All the different doggies, from the largest to the smallest, from the ordinary to the postitively freakish, are desended from the wolf. Why is this relevant? This shows us the potential of a single species to be genetically manipulateable. Even though they have had only about 100,000 years to evolve, we can see an unbelievable range of phenotypes that the doggie can enjoy. How many

Can natural selection create the same diversity? So here is another example of the power of a genome to generate variety, as facilitated by the power of artificial selection, one which I just couldn’t let go of. Can natural selection create the same diversity?

Hallmarks of Adaptive Radiation Common ancestry of radiants Rapid speciation Phenotypes show adaptation suited to new niche Where can we find evidence of adaptive radiation? Here are some basic tenets of Adaptive radiation- Everything involved in a radiation must have a common ancestor. All these species of African cichlid can be found in lake Malawi and lake Tanganyika along the great rift valley in Eastern Sub-saharan africa. There must be rapid radiation. The adaptations, the changes in traits that the individual experience, must be relevant to the new niche

Adaptive Radiation is easily seen in island ecosystems

New islands contain vacant ecological niches Species which arrive are often in reproductive isolation Novel competition conditions Many available resources Great opportunity One place we can see adaptive radiation is with new environments.

The Hawaiian islands are geographically isolated from continents The most isolated landmass in the world Colonization events are rare When they do occur, they are momentous

Hawaiian islands are geographically isolated from each other Distance from Maui  Big Island: ~40 miles Islands are isolated from each other But less isolated than all are from continents Islands appeared in sequence (temporal isolation) So each of these islands is, to a lesser extent, isolated from the others. Furthermore, the islands appeared in sequence. As the crust of the earth travelled over a magma hotspot beneath, volcanoes would erupt above on the surface of the earth’s crust, the bottom of the ocean. From there, lava would eventually build up into an island size. As the hotspot traveled underneath the crust, or the crust from the hotspot, new islands were formed. Afterward, the ocean would begin to erode islands that had been formed. In The hawaiian islands, this trend has progressed from NW SE. The oldest of the Hawaiian islands is Kauai, which is about five million years old, wheras the big island of Hawaii is a little less than a million years old. Therefore, the species populating the islands are to some degree in temporal isolation from each other.

Hawaiian islands exhibit a wide diversity of habitats Sea level 13,000 ft. Rainforest  desert Fertile soil barren rock Warm  snowy Tremendous ecological opportunity

800 Species of Drosophila are endemic to Hawaii Evidence points to a single colonization event, 5 million years ago We can see tremendous numbers of colonization events within the drosophila of the Hawaiian islands.

The “Silversword Alliance” shows adaptive radiation These radically different species have all evolved from a single common ancestor. We can see that they were all descended from a single tarweed species, perhaps akin to the one we see at the upper left of the picture. Without a doubt, we can see that these silversword alliance members are not only drastically different in terms of their shape and form, but also that the tremendous differences betweeen the different species are adaptations to the various environments on the islands which they inhabit. For example the silversword at the bottom is a different color from regular green plants- it grows in barren, rocky soil that is often dry. Certainly for such a creature, uptaking sufficient sunlight is not the most important issue- there is no comptetition at all for light- in fact,the shape of the leaves- pointing at the sun rather than sitting perpendicular to it, indicates that these plants are in no shortage of light, but are rather adapted to lose water as slowly as possible. Likewise, the big tree at the lower left, has certainly found a much more acceptable niche, and an acceptable adaptaition to it- it sits among other trees, and we can see it here standing tall, like other trees, in order to compete for sunlight- it’s a rainforest that this tree sits in, so obviously 28 species of Hawaiian plants Traced to a single Californian tarweed

Extinction events create vacant niches Cretaceous-Tertiary (K-T) extinction allowed radiation of mammal species K-T one of the five important global extinction events Extinction events certainly create vacant ecological niches. They also therefore allow for the adaptive radiation of those species that do survive the extinction event to survive and reproducece, and adapt into the niche vacancies.

Adaptive radiation in the lab In variable environments, varying strains of P. fluorescens are generated Strains are genetically distinct When environments are homogeneous, no such variants are generated So one of the problems that evolutionary principles faces is the fact that they can, by and large never be seen. This creates problems with people who have a vested incentive to suggest that there is no such thing. It stands to reason that evolutionay events are difficult to observe in action- they ordinarily take millions of years to occur. However, bacteria like E. coli have generation times of twenty minutes. P. fluorescens, as we see in this set of experiments, has a generation time somewhat longer, but still measured in minutes rather than years. So cultures, such as the ones in the flasks on the bottom of the figure, can be left for a few weeks, and these few weeks can constitute a thousand of generations a week. During this amount of time, a single clonal colony of a single species sis’This technique has helped show the effects of different kinds of conditions on adaptive radiation– conditions such as competition for resources, a favorite predictor of adaptive radiation, as well as predation, which, since species being preyed upon are less likely to run out of resources, tends to reduce the amount of competition for resources that would otherwise occur.

Speciation can occur by gradualism or by puncuated equlibrium

Exaptation is the shift in functionality of a structure

Exaptation is the shift in functionality of a structure

Evolution is not a directed process Evolution perfects, but never creates perfection Living things adapt to ever-changing environments