Biology Assignment: Darwin's Finches, Sticklebacks, and Speciation

This biology assignment presents an analysis of Darwin's Finches and sticklebacks, focusing on evolutionary adaptations and speciation. The assignment begins with an examination of the Grants' research on Daphne Major, detailing changes in finch beak depth in response to a drought and the resulting natural selection. It then delves into the classification of birds, exploring the biological species concept and the factors contributing to reproductive isolation. The assignment concludes with a study of sticklebacks in Paxton Lake, comparing benthic, limnetic, and hybrid populations. This includes an examination of their physical characteristics, feeding behaviors, and the impact of hybridization on their survival and evolution. The experimental design, controls, and measurements are also discussed, highlighting the interplay of natural selection and environmental factors in shaping these species.

Running head: BIOLOGY 1
Biology
Name
Institution

BIOLOGY 2
Darwin’s Finches
Question 2.01: Bar graph
Question 2.02: The x-axis shows depth of beak measured in millimeters
Question 2.03: The y-axis is a representation of the finches
Question 2.04: 8.8 mm
Question 2.05: 7.3 mm to 10.8 mm
Question 2.06: Just above 8.8 mm
Question 2.07: 10.3 mm
Question 2.08: 7.8 mm to 10.8 mm
Question 2.09: Just below 9.8 mm
Question 2.10: 9.8−8.8=1mm
Question 2.11: The medium population has changed from beak depth of 9.3mm to 8.8 mm
Question 2.12: Beak depth is a suitable character for investigation because of the relationship
between beak size and diet. Due to drought, small seeds became scarce and the finch birds had to
evolve and eat larger fruits.
Question 2.13: The graph indicates that the number of survivors was smaller than the initial
population of the birds. Additionally, the survivors had averagely greater depth of beak as
compared to the initial population. The difference in the mean population of the initial
population of finch birds and the survivors is a measurement of the changes in evolution between
the two generations.
Classification of Birds
Question 2.14.0: The 10 birds belong to 6 different species.

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Question 2.14.1-21.14.8
Species Bird Characteristic
Bullock’s oriole A and B They both reside in deciduous
woodlands and shade trees.
They spend their winters in
the tropics. They also feed on
insects and lays between 4
and 6 greyish eggs.
Baltimore oriole C and F These two birds both reside in
deciduous woodlands or
shade trees. Additionally,
they both feed on insects and
fruits. The two birds also
spend their winters in Florida
and Southern Atlantic coast.
They lay 4-6 grey eggs.
Hooded oriole D and J There habitat is similar. They
both have a length of 18-20
cm and feed on insects and
fruits. They lay between 3
and five eggs that have dark
brown and purple spots.
Spot-breasted oriole H Habitat is open country where
trees are scattered. This bird
lays 4 white eggs that have
black streaks. The bird feeds
on insects and fruits.
Altamira oriole E Habitat is forests and trees
that are near water. This bird
lays between 2 and 4 white
eggs that have purple streaks.

BIOLOGY 4
The bird feeds on insects and
fruits.
Scott’s oriole G and I They share a similar habitat
and lay between 3 and 5
bluish white eggs. They build
their nests on pines, yucca
fronds, and live oaks. Both
feed on insects and fruits.
Question 2.14.1.1-2.14.8.1
Species Bird Characteristic
Bullock’s oriole A and B They lay between 4 and 6
grey eggs. Bird A cannot
mate with any other bird but
can only mate with bird B.
Bird B can also only mate
with bird A.
Baltimore oriole C and F They lay between 4 and 6
grey eggs. Bird C cannot
mate with any other bird but
can only mate with bird F.
Bird F can also only mate
with bird C.
Hooded oriole D and J They lay between 3 and five
eggs that have dark brown
and purple spots. Bird D
cannot mate with any other
bird but can only mate with
bird J. Bird J can also only
mate with bird D.

BIOLOGY 5
Spot-breasted oriole H This bird lays 4 white eggs
that have black streaks. It
does not mate with any of the
other 9 birds.
Altamira oriole E This bird lays between 2 and
4 white eggs that have purple
streaks. It does not mate with
any of the other 9 birds.
Scott’s oriole G and I They lay between 3 and five
eggs that are bluish white in
color. Bird G cannot mate
with any other bird but can
only mate with bird I. Bird I
can also only mate with bird
G.
Question 2.14.10
The biological concept that helped in the above classification is the concept of taxonomy that
helps in identifying, naming, and classifying living organisms according to common
characteristics. The biological species concept then helped in classifying the birds in groups of
populations that can interbreed and are reproductively isolated from the other living organisms.
Question 2.14.11
A Species is a population group that contains members who can naturally interbreed with one
another to reproduce fertile and viable offspring but cannot effectively reproduce with a member
of a different species. Members of one species are reproductively isolated from members of other
species (Rabosky, 2016). The classification of the 10 birds, therefore, followed the biological

BIOLOGY 6
species concept to group birds that share similar characteristics and that can viably reproduce
fertile offspring together. The other two birds (E and H) that were classified to belong to Spot-
breasted oriole and Altamira oriole shared some characteristics with the other birds. However,
table 2.01 has established that the two birds cannot naturally reproduce with any of the other
birds. This is an indication that they are reproductively isolated and thus have their classification
of species. It is important to note that birds from one species, for example, Baltimore orioles
cannot interbreed with those from Bullock’s oriole due to prezygotic and postzygotic barriers.
Prezygotic barriers prevent birds from different species from mating. In case they mate, the
prezygotic barriers prevent fertilization (Monteiro, Serrão & Pearson, 2012). Prezygotic barriers
include habitat isolation, geographical isolation, mechanical isolation, and temporal isolation.
Mechanical isolation is when anatomical differences cannot allow copulation. Geographical
isolation is when the birds live in separate regions. Habitat isolation is when the geographical
isolation is similar but habitats are different (Harrison, 2012). For example, bird B and bird C
can be found in Texas, Minnesota, Arizona, and South Dakota. However, due to mechanical
barriers, these two birds cannot mate or produce fertile and viable offspring. Postzygotic barriers,
on the other hand, do not allow the zygote to develop into a viable offspring after the sperm of
the male bird has fused with the egg of the female bird (Johnson, Price, Price & Stacy, 2015).
Speciation in Sticklebacks
Question 2.15
Table 2.02 shows that the population of benthic is the highest in Paxton Lake followed by
Limnetic. Hybrid has the lowest population. Additionally, benthic have the highest body depth
followed by hybrid and the limnetic. It is also notable that limnetic rarely has 2 dorsal spines and
therefore limnetic has the lowest population with two dorsal spines. Benthic has the highest

BIOLOGY 7
population with 2 dorsal spines followed by hybrid. Benthic rarely has a pelvic girdle and
therefore the population that lacks a pelvic girdle is dominated by benthic. Limnetic, on the other
hand, normally has pelvic girdle and thus the population that lacks pelvic girdle is lowest for
limnetic. The population of hybrid is between the other two species. Limnetic has the highest
number of gill rakers with the longest length of gill rakers followed by hybrid and finally
benthic. The table also shows that benthic has the largest jaw width followed by hybrid and
finally limnetic. Limnetic has the highest number of lateral plates followed by hybrid. Benthic
has the least number of lateral plates.
Question 2.16
When compared to the parental benthic and limnetic sticklebacks, hybrid sticklebacks have a
poor feeding performance. It is also worth noting that limnetic and benthic sticklebacks
specialize on different feeds (Taylor, Gerlinsky, Farrell & Gow, 2012). For example, limnetic
sticklebacks feed on zooplanktons while benthic sticklebacks normally feed on bottom-dwelling
organisms like anthropods. These two species of fish are each suited appropriately to exploit
their distinct trophic niches. This feeding relationship, therefore, shows that limnetic and benthic
sticklebacks can coexist almost comfortably in Paxton Lake. Hybrid sticklebacks, on the other
hand, will feed on both zooplanktons and anthropods. Given that hybrids are poorly adapted to
feeding, they will not get enough food in Paxton Lake thus affecting their reproduction (Taylor et
al., 2014). Additionally, given that limnetic sticklebacks and benthic sticklebacks are adapted to
different environments, the hybrid may not be adapted to the different environments as good as
the parent sticklebacks. As a result, the hybrids become less fit as compared to the parent
sticklebacks and natural selection therefore only favors offspring from the same species (Roesti

BIOLOGY 8
& Salzburger, 2014). Additionally, a study of the mating behaviors shows that hybrids are highly
likely to mate with limnetic sticklebacks. However, due to behavioral barriers that describe
differences in courtship, most limnetic sticklebacks will mate with fellow limnetic sticklebacks
instead of hybrids. As a result, the number of hybrids does not grow as first as those of the parent
sticklebacks.
Question 2.17-2.21
Experimental controls Open water and benthic zone
Treatments 3 species of Sticklebacks
Separation Paxton Lake
Replication 21 days
Measurements Growth in milligrams per day
Question 22.2
In the benthic zone, the rate of growth of benthic sticklebacks is higher than limnetic and hybrid
sticklebacks. This difference in growth rate is because benthic sticklebacks are better adapted to
the benthic zone. The limnetic sticklebacks with the least adaptation have the lowest rate of
growth. Hybrids have an intermediate growth rate. In open water, on the other hand, limnetic
sticklebacks had the highest growth rate because limnetic is better adapted to the environment of
open water. Benthic sticklebacks had the second-best growth rate while hybrids had the slowest
growth rate in open water. The data do not support the hypothesis because hybrids should have
an intermediate growth rate in both environments.

BIOLOGY 9
References
Harrison, R. G. (2012). The language of speciation. Evolution: International Journal of Organic
Evolution, 66(12), 3643-3657.
Johnson, M. A., Price, D. K., Price, J. P., & Stacy, E. A. (2015). Postzygotic barriers isolate
sympatric species of Cyrtandra (Gesneriaceae) in Hawaiian montane forest
understories. American Journal of Botany, 102(11), 1870-1882.
Monteiro, C. A., Serrão, E. A., & Pearson, G. A. (2012). Prezygotic barriers to hybridization in
marine broadcast spawners: reproductive timing and mating system variation. PLoS
One, 7(4).
Rabosky, D. L. (2016). Reproductive isolation and the causes of speciation rate variation in
nature. Biological Journal of the Linnean Society, 118(1), 13-25.
Roesti, M., & Salzburger, W. (2014). Natural selection: it’sa many-small world after all. Current
biology, 24(19), R959-R962.
Taylor, E. B., Gerlinsky, C., Farrell, N., & Gow, J. L. (2012). A test of hybrid growth
disadvantage in wild, free‐ranging species pairs of threespine stickleback (Gasterosteus
aculeatus) and its implications for ecological speciation. Evolution: International Journal
of Organic Evolution, 66(1), 240-251.