Armour Flashcards
what is armour
a protective barrier between external threats (e.g. a predator) and animal in question and usually refer to strong mechanical barriers which resist penetration
outline the evolutionary convergence of animal armour
it has evolved at least once in most major animal lineages, including tetrapods, which helps to refelct the success of such adaptations
outline the structural diversity of animal armour
made of lots of different materials, typically made of hard materials which are already prodcued or readily available such as bone or caclium
e.g.
osteoderms (additional boney elements outside of the skeleton) in the skin of lizards or crocodiles
caclium carbonate shells of snails etc
give an example of armour structural diversity when the armour is made up of different materials
Armodillo
formation of strong triangles made up of a thick and thin layer
1) thick = collogen layer which forms triple helix collogens = thick and tough
lays ontop of
2) thin = hexagon layer of alpha keratin
= provides flexibility, hardness and toughness
outline the structural divrsity of armour in terms of body coverage and behaviour = provide examples
may be present over most of only a little bit of the body and may or may not be enhanced by behaviours shown in the presence of a threat
e.g.
1) Alagator snapping turtle = full coverage spikes with thickened skin
2) box turtle = less body coverage but can retract head (behaviour) to be full covered
3) leatherback turtle= armour reduced
what are the problems with protection
1) energetic costs
2) locomotor costs
3) thermoregulatory costs
4) constraints on escape
5) constraints on body plan
outline the problems of protection in terms of energetic costs
most armour is heavy so is energetically costly to carry around
= might explain why birds dont have any
Doake et al 2010= as armour weight increases lactate levels which show energetic use also increase
= possible that such costs could be partly offset by reduced energy needed to fight or run away from predators
outline the problems with protection in terms of locomotor costs
the added weight also reduced ability to move, potentially limiting alternative defensive stratergies such as running away
= losos et al 2002 = as spine (armour) length increases the speed decreases
outline problems with protection in terms of thermoregulatory costs
thick and highly effective armour doesnt just create barrier against predators but also against rest of environment= issues with thermoregulation in ectotherms as armour could interfere with transfer of heat from enviro to body
e.g. smaug giganetus has thick osteoderms vs armadillo lizard and holy armour so more blood vessels= able to thermoregulate more
outline problems with protection in terms of constraints on escape
it creates big and bulky animals it can reduce ability to escape options which can put them out of reach e.g. climbing or disappearing in burrows
losos et al 2002= spine length increases indivudals using vertical surfaces decreases
outline problems with protection in terms of constrains on body plan
the need to have effective armour that is strong enough and with enough coverage to protect often limits further evolution of body plan
e.g. turtle body plan = constrained by the major shift in the relative positions of limb girdles and ribs
or
as relative weight increases weight of armour as proportion of body weight as animal gets smaller restricts evolution of small body size
outline the evolution of the turtle shell
. Firstly, the ribs became much broader (assisted by elongated vertebrate to incorporate wider ribs), then the intercostal muscles were lost (these typically connect ribs to each other) which necessitated the evolution of a different way of breathing. Additional bone growth increased the coverage of the shell and incorporation of the scapula inside the ribcage enabled the vast majority of the body to be protected under the shell.
what type of animal has armour favoured
in spp unable to effecltivley hide or aggressivley defend themselves to reduce predation pressure
larger spp might also struggle to bear the costs of armour
stankowich and campbell 2016 = found armour mostly in mid size spp in open habitats
outlien metabolic rate in armoured animals
relatively lower compared to other mammals
Probably as a consequence of the increased energetic demands imposed, mammals which bear armour typically have lower metabolic rates. A low metabolic rate may help to reduce the overall energy required by the animal and hence reduce the energetic cost of being armoured, but it may convey other costs such as reduced ability to engage in other energetically expensive activities
