Question 1
1. For species to have a high heritability for traits that are under selection, they need to be
genetically based. In cases of high heritability, there is less environmental variation.
This can be seen in the equation H2 = VG/VG+VE. Either high genetic variance or low
environmental variance will cause high heritability. High heritability be also be
illustrated graphically (graph shown). The slope of the line will be greater (close to 1)
when the heritability is high. If the heritability is high and the trait is under selection
(related to fitness), then there will be a big response to selection. This can be seen in
the equation R = H2*S. This equation shows that if there is high heritability for choice in
host plant, then selection cause specialization.
2. Looking at the same equation. Heritability will be low if there is low genetic
variation or high environmental variation. Low heritability can be shown
graphically (graph shown). If the slope is low and there is a lot of scatter in the
points, the heritability is low. If the heritability is low, there can be little response
to selection (evolutionary change), even if selection if very strong. If there is
strong selection for host plant but there is little or no heritability, there will not be
any possibility for specialization.
3. Heritability can affect the likelihood of sympatric speciation by divergence in a
habitat. For example, in an insect species, some individuals may prefer one host
plant over a different host plant. If “preference for host plant” is a heritable trait,
then selection can drive these two groups of insects toward separate host plant use
(divergent selection). If mechanisms of reproductive isolation arise, then
sympatric speciation can occur. However, if the heritability is low, then even is
selection is strong, there will be no response to divergent selection and it will not
be possible for sympatric speciation to occur.
(Note from Dr. Etterson – The relationship between fitness and a trait does not determine
heritability. Many people said that because a trait was related to fitness it had high heritability.
This is a false statement. Heritability is determine by how much variation there is among
genotypes and how sensitive a trait is to the environment. Traits that are tightly related to
fitness can have either high or low heritability. If it is high, then there will be a response to
selection which will reduce the genetic variation and reduce the heritability each generation. If
heritability is low, there will be no evolutionary change even if selection would strongly favor it.)
Question 2
1. The Biological Species concept (BSC) focuses n the process of evolution. A species is
defined in terms of reproductive isolation between organisms that co-occur. The
phylogenetic species concept (PSC) defines species in terms of the products of
evolution. Species are defined in terms of sequence divergence and some people
consider one fixed DNA base pair change to be indicative of a new species. The four
mechanisms of speciation are: allopatric, peripatric, parapatric, and sympatric. All of
these forms of speciation involve a barrier that causes divergence, be it geographic or
behavioral. When moving from BSC t5o PSC, molecular analysis can be used in all forms
of speciation to determine sequence similarities and areas of difference. The problem
with BSC is that it is often difficult to tell whether organisms can interbreed. The reason
for this may be a land barrier that separates two populations that would otherwise
interbreed. Also, even in cases of sympatric speciation where some other barrier is
occurring, species that tend not to interbreed may still be able to interbreed, and by BSC
they wouldn’t be distinct species
2. As stated above regarding PSC, one base pair change in a DNA sequence can be
used as evidence to define a new species. With this definition, even organisms
that can interbreed and are morphologically similar could be defined as separate
species by PSC. Estimates of species worldwide would increase dramatically.
Geographical barriers would not have to be taken into account here either. Also,
PSC can account for speciation in asexual organisms which is a limitation for
BSC.
3. In terms of conservation, there are laws established to determine the
endangerment level of a species. Typically lower numbers of individuals in a
population and reduced range of habitat are indicative of endangered species.
Using PSC, a population that is lumped into one species by BSC can be divided
into multiple species by PSC, with the population split into multiple species, there
will be a low number of individuals in the species and their range will also be
smaller than that of the original populations. This will lead to conservations being
able to put way more species on an endangered species list. While more
organisms have the potential to be better protected with human interventions, this
enormously raises the costs of conservation in the U.S. Much more money will
be need to be put into rehabilitation and increasing number of species. Also the
costs would go up in trying to determine all of these species. Samples would have
to be take and DAN sequence analysis performed and compared. Current laws
would have to be altered to account for an unmanageable number of new
“endangered” species. In conclusion, while conservationists may initially support
his idea to help more organisms and get increased funding, they would quickly
deplete time and money resources.