Explain The Three Hypotheses Concerning The Evolution Of Segmentation

Embryological Evidence – similarities in early embryos can indicate they came from a common ancestor.

Most treehoppers have an expansion of the T1 (1st thoracic segment; prothorax) dorsal sclerite which has led to a number of hypothesis for it’s evolutionary novelty (Stegmann,1998). The origin of novelty is one of the major issues in biology due to its inherent definitional variability (Brigandt & Love, 2012). According to Wagner & Lynch (2010) most definitions of evolutionary novelty can be summarized into two categories based on functional and structural novelty consisting of the genetic origin of such traits. The treehopper helmet may be considered functionally novel due to its unique adaptations to the environment. Although its morphological and genetic basis of novelty remain a controversy (Heffer & Pick, 2013).

Knowledge of relationships between animals may allow us to deduce the answer: the two main branches of the animal tree are protostomes and deuterostomes, while the trunk of the tree includes sponges and cnidarians. The first appearance of these protostome and deuterostome groups is arguably in the Cambrian period – while arguments have been made for an earlier bilaterian, for instance the 555 million year old Kimberella, they are not persuasive – for reasons discussed later in this essay. We can assert that whatever was shared by two or more groups was likely to have been present in their last common ancestor. In this case, all members have bilateral organization in their life stages. Thus, the theory of the common ancestor of bilaterians – Urbilateria – arose (De Robertis & Sasai,

A possible explanation for the appearance of these additional “tails” is naturally occurring fission as Planaria are able to regenerate after both amputation and after natural occurring fission (Newmark & Sánchez Alvarado, 2002, p. 127). The organisms may have naturally divided as a way to conserve energy in the absence of food while in the process of regenerating a head. Because it possible that the lack of a food source effected the size of the Planaria, it would be interesting to repeat this experiment in the presence of food and compare the sizes of the “heads” and “tails” after fourteen days in order to the determine the importance of a food source during regeneration. After this experiment, if both the “heads” and “tails” were the same size, it could be confirmed that regenerating a head is costlier than regenerating a tail in terms of

Among the innumerable abundance of incredibly diverse organisms that roam this uniquely life-sustaining planet, Deuterostomes hold a value that truly reflects the how organisms may have changed over our long period of time on Earth. Deuterostomes are unique in their embryonic development when compared to Protostomes and it is suggested that these two groups split at the time of the Cambrian explosion, a brief time in history that blossomed into the vast array of organisms found today. Eventually, the phylum Echinodermata developed and under it, a set of classes arose. Archinidea was one of these classes, and later became commonly known as the starfish. They are radially symmetrical and contain some of the characteristics that set Echinodermata apart.

Believe it or not, there are morphological (phenotypic) similarities as well as dietary and behavioral similarities between all of these taxa. BEFORE molecular data was available, scientists already suspected that these groups were

Phylum Echinodermata consists of organisms that are invertebrate, thus they lack a backbone and have a simplistic circulatory system, but their respiratory system is versatile with the variety of organs, such as gills (as seen the sea star), tracheas, skin, and book lungs (Hsia 2013). Since Phylum Chordata is more complex than Echinodermata, Chordata has a variety of organs in their organ systems, such as the skin and muscles in the circulatory and respiratory systems (Shu 2003). In order to completely analyze the circulatory and respiratory systems in the phylums Echinodermata and Chordata, organism from each phylum can be thoroughly dissected to expose entire organs and to allow manipulation of the organs. To execute this experiment, several

Independent evaluation of similar features new species of different lineages Is called convergent evolution. analogous structures with similar form or function that were not present in the last common ancestor of these groups are created by convergent evolution. delete current evaluation of flight is a good example of convergent evolution. flying insects, birds, and bats have evolved the capacity of flight independently. in other words, that have converged on these useful traits. Analogous are functionally Similar features that arise through convergent evolution. a homologous structure of the traits have

The ostracoderms once were considered the oldest and most primitive of the known chordates (Gregory, 1935).

Cambrian explosion is one of the great evolutionary events of animals. Before this event (635 to 541 Mya), most animals called Ediacaran fauna were almost flat and soft bodies (ref). However, in early Cambrian (around 550 Mya), most of modern phyla of animals have evolved with skeletal tissues were remain as fossils (ref). This direct evidence suggested that the mechanisms of skeletogenesis have evolved in the near base of Bilateria in the earliest Cambrian period, and the Cambrian explosion might have been due, partly, to the acquisition of this novel body plan. The common ancestors of Ecdysozoa or Lophotrochozoa have evolved the external hard tissues, exoskeleton, and became diversified morphological and mineral structures in each phylum

In the single origin of neurons, comb jellies are said to the oldest in the clade coming before Porifera, Placozoa, jelly and bilateria (Bucher 2015). In the process of evolution the sponges and Placozoa lost their ability to send rapid signals and their neurons. The loss of their nervous system is still uncertain, however there could be an environmental role that could have played a role in the evolutionary process. The phylum Placozoa only has one species called Trichoplax adhaerens. This particular species have been identification with six somatic cell types containing proteins that are normally in neurosecretory cells. Which includes FMRFamid-like peptide, opening the door to the possibility of neuronal like cell existence in the phylum (Bucher 2015). Only Hexactinellida also recognized as the glass sponges practice electrical impulses that send brisk signals to the current. Primary cilia are present in the cell of vertebrate, invertebrate and also in sponges. Primary cilia’s function is similar to one another. Similarly, the cilium are involved in sensing chemical activity, sending signals through calcium wave. By removing the cilia or the osculum, sponges lose their ability to ‘sneeze”, which is used by freshwater sponges to unload their waste. Cilia is present in the osculum of all sponges that have been examined, displays the common sensory organ in Porifera (Leys 2015). The nervous system did evolve once through the common ancestry, however sponges and Placozoa lost their nervous system in their development

Even though every class has some common attributes such as segmented vertebrae, specialization of the structure occurs in each class according to their function and the surviving environment. As such, organisms in class reptilian have got distinctive features that of aves, chondrichthyes, mamalia, and so on (Campbell et al. 2008).

Variations in parts of the developmental pathways responsible for segmentation and appendage patterning explain the differences in body plan across the phylum. However, certain portions of the pathway must be conserved, resulting in body segments with paired appendages in all arthropods. Research on the developmental pathways that control segmentation in arthropods has shown that gene expression is more highly conserved across the

In the Cnidarians, some organisms possess only a medusa form, some organisms possess on a polyp form, while others possess both a medusa and a poly form in their life cycle. Propose a hypothesis, either medusa first, or polyp first that could explain the evolution of cnidarian life cycles. From this, hypothesis identify which taxonomic class in cnidarian would be ancestral and explain why you think

Echinoderms having larvae with bilateral symmetry and adults with pentaradial symmetry is an example of metamorphosis