7.4: Size and Shape - Biology

7.4: Size and Shape - Biology

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The final type of developmental patterning that evolution can act on is the size and shape of tissues or organs. These are generally considered "morphometric" scaling issues and are classified as "allometric" changes. Morphometrics is the study of how a continuous geometry (like the outer surface of a body) can be warped. Allometry studies this in the context of evolution and development. One of the people who defined the field, D'arcy Wentworth Thompson, came up with morphometric changes that allow one known species of fish to be warped into another known species (Figure 7).

While the extent of the role that allometry plays in evolution isn't totally clear, we know from examples that it does play some role. It's easy to see this if we look around at related species. For example, hominid skulls are very alike and often differ in ways that are easily explained by small variations in developmental growth patterns. Extra or earlier cell proliferation here, less or later cell proliferation there. While we know many genetic markers of cell proliferation (for example cell-cycle regulator Cyclin D1) increase cell-proliferation, there are many different upstream activators of proliferation depending on tissue/cell-type and developmental stage. To begin to understand the role of allometry in evolution, researchers compare tissue growth and the regulators of that growth between fairly closely related species.

Two places where both the development and evolution of size and shape changes are fairly well understood are beak shapes in birds and elytra in beetles. One of the most famous examples of evolution is Darwin's Finches. This group of finches underwent an adaptive radiation on the Galapagos Islands beginning about 2.3 million years ago12. Since then, the finches have adapted to different island niches into 14 different species. Comparing beak morphology between these species uncovered two conserved allometric programs for changing cell proliferation patterns. In early development, beak width is regulated by levels of BMP4 - higher BMP4 means a deeper and wider beak. For example, ground finches have high BMP4 expression in a region that signals to the predominate skeletogenic region of the early beak - the pre-nasal cartilage (pnc)13. Likewise, high levels of calmodulin next to the pnc are associated with longer beaks, like the beaks of cactus finches (Figure 8).

Slightly later in development, an upper beak structure called the pre-maxillary bone (pmx) begins to grow. This will eventually form the parts of the upper beak that structurally and functionally differ between many bird species. This part of the beak also expresses different sets of genes in different beak shapes. TGFβ receptor type II (TGFβIIr), β-catenin, and Dickkopf-3 (Dkk3) are all signal transduction cascade genes that are expressed at much higher levels in the large ground finch beaks compared to smaller beaked finches. These three genes were expressed in broader domains in larger beaks than in smaller beaks when looking at all five species in the figure above (Figure 9)14.

These findings buoyed the idea that allometric growth can fuel rapid evolution by changing the scale of a particular feature. Changing the scale just refers to scaling something up or down, making it larger or smaller in one or all dimensions. For example a large square is simply a scaled-up version of a small square. A rectangle would be a square that has been scaled larger in one dimension but not the other. Researchers noticed right away that simply changing scaling of the upper beak could explain a lot of the variation in Geospiza and this could be explained by the coordinate system of genetics above (or even a simpler genetic system). However, scaling wasn't enough to explain the variation in other related finch species. To explain that variation, researchers found that both scaling and shearing had to be considered. Shearing refers to a geometric transformation like that seen in the fish example from Thompson et al. above. In a shear transformation, each point moves along x at a distance proportional to its y coordinate (or vice versa) giving a diagonal line from a straight line. Shearing plus scaling was enough to explain at least the length and depth axes of the finch beaks studied (Figure 10)

The next question to answer is how broadly applicable is this coordinate system for beak shape transformation? Increasing or decreasing the expression levels of these genes does change chick beak shape in the ways predicted by Mallarino et al.14. This information might lead us to predict that evolution would use this coordinate system to make the wide variety of beaks that we see in living and fossil birds. However, studies of non-Geospiza finches show that evolution is more variable than we might imagine. If we have time, we will discuss the paper: "Closely related bird species demonstrate flexibility between beak morphology and underlying developmental programs".

10 - Body Size and Shape: Climatic and Nutritional Influences on Human Body Morphology

Since the initial spread of Homo erectus from Africa some 1.8 million years ago, the human lineage has colonized every major ecosystem on the planet, adapting to a wide range of environmental stressors (Antón et al.,2002). As with other mammalian species, human variation in both body size and morphology appears to be strongly shaped by climatic factors. The most widely studied relationships between body morphology and climate in mammalian species are those described by “Bergmann's” and “Allen's” ecological rules. Bergmann's rule addresses the relationship between body weight (mass) and environmental temperature, noting that within a widely distributed species, body mass increases with decreasing average temperature (Bergmann, 1847). In contrast, Allen's rule considers the relationship between body proportionality and temperature (Allen, 1877). It finds that individuals of a species that are living in warmer climes have relatively longer limbs, whereas those residing in colder environments have relatively shorter extremities.

Biology Of E. Coli

E. coli (Escherichia coli) are a small, Gram-negative species of bacteria. Most strains of E. coli are rod-shaped and measure about 2.0 μm long and 0.2-1.0 μm in diameter. They typically have a cell volume of 0.6-0.7 μm, most of which is filled by the cytoplasm. Since it is a prokaryote, E. coli don’t have nuclei instead, their genetic material floats uncovered, localized to a region called the nucleoid.

E. coli are Gram-negative bacteria, meaning that they do not retain the crystal violet stain commonly used to differentiate bacteria. Their status as Gram-negative bacteria is due to their thin cell walls. E. coli has cell walls made out of two thing peptidoglycan layers, an inner and outer membrane. The Gram-negative outer membrane explains why many strains of E. coli are resistant to penicillin the mechanism of action is disrupted by the thin cell walls. Many serotypes also have an external, flagella extending from the cell wall that is used to motility. In the mammalian gut, E. coli use their flagella to cling to the microvilli of the intestines.

E. coli are small rod-shaped bacteria. Credit: Public Domain

E. coli is a facultative anaerobe meaning that it primarily breathes oxygen, but can anaerobically respirate when oxygen is not available. Specifically, when oxygen is not present, E. coli derives its nutrients from the process of fermentation. During fermentation, E. coli breaks down carbohydrates into pyruvate in the absence of oxygen. This process produces ethanol and carbon dioxide.

Like all bacteria, E. coli reproduces through binary fission, in which one cell splits into a genetically identical copy. E. coli’s cell cycle is divided into three periods that roughly mirror the phases of eukaryotic mitosis. The B period occurs directly after cell division. The B period is the “normal” period in the life cycle in which the cell is functioning normally, similar to interphase in mitosis. Once DNA begins to replicate, the cell enters the C period which lasts until chromosomal replication is complete. The D period takes place after chromosomal replication and is the point when the cell splits in two. Once the D period is finished, the new cell proceeds into the B period, starting the cycle over again.

The exact length of the B period depends upon the available nutrients. The more food, the quicker E. coli goes through its normal phase and the quicker it begins copying chromosomes. However, the lengths of the C and D periods remain constant. When food sources are very high, cells will begin replicating before the previous round of replication is complete, resulting in a very fast growth rate. This fast growth rate is one reason why E. coli are often used as a model organism in laboratory research. In ideal conditions, E. coli can achieve a duplication rate of 22 minutes.

E. coli are known to engage in horizontal gene transfer, a process in which one bacterium inserts a section of its genetic code directly into the DNA of another. Horizontal gene transfer in bacteria serves an analogous function to sexual reproduction in eukaryotes in that it provides a source of genetic diversity. Some strains of E. coli inherit their pathogenic features from having their DNA altered by other bacteria.

The growth of an E. coli colony over time. Credit: WikiCommons CC-BY SA 4.0

2. How Big Is a Protein Molecule?

Assuming this partial specific volume (v2 = 0.73 cm 3 /g), we can calculate the volume occupied by a protein of mass M in Dalton as follows.

The inverse relationship is also frequently useful: M (Da) = 825 V (nm 3 ).

What we really want is a physically intuitive parameter for the size of the protein. If we assume the protein has the simplest shape, a sphere, we can calculate its radius. We will refer to this as Rmin, because it is the minimal radius of a sphere that could contain the given mass of protein

Some useful examples for proteins from 5,000 to 500,000 Da are given in Table ​ Table1 1 .

Table 1

Rmin for proteins of different mass

It is important to emphasize that this is the minimum radius of a smooth sphere that could contain the given mass of protein. Since proteins have an irregular surface, even ones that are approximately spherical will have an average radius larger than the minimum.

Additional information


• Size and shape-dependent MnFe2O4 NPs were prepared via a facile method.

• Ligand-exchange chemistry was used to prepare the hydrophilic MnFe2O4 NPs.

• The catalytic properties of MnFe2O4 NPs toward dye degradation were fully studied.

• The catalytic activities of MnFe2O4 NPs followed Michaelis — Menten behavior.

• All the MnFe2O4 NPs exhibit selective degradation to different dyes.

Inside Birding: Size & Shape

How closely and carefully do you need to look at a bird to identify it? Having a live bird in hand would be ideal, but you can learn a lot even from a distance. Is the bird about the size of a crow, or closer to the size of a sparrow? How large is the bill in relation to the rest of the head? These characteristics can often distinguish one bird species from another. Join Chris Wood and Jessie Barry as they put their knowledge of external avian anatomy into practice in the field.

This video is part of our 4-part Inside Birding series. Each roughly 10-minute video guides you through the 4 basic keys to bird identification with clear instruction and examples. The four videos in the series are:

Would you like to learn more about using size and shape to identify more birds in your area? Bird Academy’s online courses let enthusiasts of all levels learn at their own pace. You can browse our course catalog to find the perfect online learning resource for yourself. Be a better birder today: View course catalog

Watch the video: Cell. Variety in Cell Number, Size and Shape. videos for kids (January 2023).