Introduction to Animals Flashcards
Nutritional Mode
Animals are heterotrophs that ingest their food
- Need to consume organic substrates in order to grow
- Typically have some sort of orifice through which food enters
Cell Structure
- Animals are multicellular eukaryotes
- Animal cells lack cell walls
- Tissues are held together by structural proteins such as collagen
What kind of cells are unique to animals?
Specialized neural cells and muscle cells
- Nervous system allows perception of noxious or favorable environmental conditions, predators, prey
- Muscle tissue allows the animal to respond to environment or stimuli
Cleavage
Mitotic cell divisions which lead to the formation of the blastula
- In most species, a small flagellated haploid sperm fertilizes a larger, haploid, non-motile, polarized egg
- In protostome development, cleavage is spiral and determinate
- In deuterostome development, cleavage is radial and indeterminate
- With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo
Larva
The sexually immature & morphologically and ecologically distinct from the adult
- They eventually undergo metamorphosis, transforming into an adult
What kind of genes are unique to animals?
Most animals have homeobox-containing family of genes called Homeotic or Hox genes
- Transcription factors that regulate the genes that control development of body form
- May have arisen in the eukaryotic lineage that gave rise to animals
Who won the nobel prize for medicine in 1995 and why?
Edward B. Lewis, Christiane Nusslein-Volhard and Eric Wieschaus for discoveries concerning “ the genetic control of early embryonic development
What did Lewis find from his experiment on flies?
He found a cluster of homeotic (Hox) genes in the chromosome and colinearity in time and space
- The gene order in the cluster mimics the order of expression of genes and their function along the anterior-posterior (A-P) body axis
- Exhibit temporal colinearity - anterior genes expressed first during development and posterior later
Duplication of Hox genes
- First duplication ~520 MYA
- Duplication of cluster provided ‘extra’ regulatory control to direct new body plans, eg. vertebrae
- Second duplication ~425 MYA
- Further duplication of cluster provided even greater regulatory control allowing greater structural complexity
What was most likely the first common ancestor of living animals?
Probably a colonial flagellated protist related to choanoflagellates, a group that arose about a billion years ago, may have lived between 675 and 875 mya
What is the main evidence that choanoflagellates are related to animals?
- Sequence data indicates that Choanoflagellates and animals are sister groups
- Collar cells only found in animals and not in protists
- Choanoflagellate cells resemble sponge collar cells
What do colonies rapidly invert their curvature in response to?
Changing light levels
- Inversion may be a primitive form of contraction
- These findings may inform reconstructions of hypothesized animal ancestors that existed before the evolution of specialized sensory and contractile cells
Snowball Earth
- Geologic evidence for a “snowball Earth” from 750 to 570 MYA
- May have limited diversity & distribution of higher eukaryotes until very late Precambrian
- Diversification of higher eukaryotes appears with thawing snowball Earth thawed 565 MYA`
Neoproterozoic Era
1 Billion - 542 MYA
- Recent chemical evidence (steroids) of presence of sponges i S. Oman >635 mya (represents oldest evidence for animals in the fossil record)
- Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 mya
Precambrian fossil animals of the Ediacara Hills
In 1946, mining geologist R.C. Sprigg discovers these fossils - dated as 560 MY old
Early embryos found in China
Recent fossils finds from the Doushantou Formation in China have produced a diversity of algae and animals from 570 mya, including supposedly beautifully preserved embryos
Paleozoic Era
542-251 million years ago
- Vertebrates made the transition to land around 360 mya
- Animals began to make an impact on land by 460 mya
- The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals
The Burgess Shale
THe Burgess Shale in the Canadian Rockies holds the remains of an ancient sea from 530 mya
- Was discovered by Charles Walcott in 1909
Causes of Animal Diversification
- Ecological Causes: Emergence of predator-prey relationships led to diversity of evolutionary adaptations, such as variations kinds of protective shells and diverse modes of locomotion
- Geological Causes: Atmospheric oxygen may have finally reached high enough concentrations to support more active metabolism
- Genetic causes: Diversity in body form is associated with duplication and variation in the spatial and temporal expression of Hox genes
What was interesting about the body plans observed in the fauna in the Burgess shale?
Many of the body plans are not present today
- Gould argued that given a change to “rewind the tape of life” and play it again that we might se quite different animal forms today
What do many Cambrian animals represent?
- Now extinct “experiments” in animal form
- In last half-billion years, animal evolution has mainly generated new variations of “old designs” - one of the main themes of evolution
What is one way that Zoologists sometimes categorize animals according to?
By body plan, a set of morphological and developmental traits
What is a grade?
- A group whose members share key biological features
- A grade is not necessarily a clade (a monophyletic group that includes an ancestral species and all of its descendants)
Symmetry
- Animals can be categorized according to the symmetry of the bodies, or lack of it
- In general, symmetry firs lifestyle
- Animals either have radial symmetry or bilateral symmetry - both present in fossil record for 550 million years
